Behind the Numbers: The Grim Donut

Mar 12, 2020
by Dan Roberts  


bigquotesLet me beat you to it: when will the next Grim Donut video come out?

We're in the thick of filming riding impressions and testing right now, so part two isn't that far off, but these things take way more time than the movie magic suggests. In other words, don't expect one of those "first ride reviews" tomorrow, but maybe check just in case.

In the meantime, here's Dan Roberts to reveal the "intricacies" of the Grim Donut's rear-suspension.
Mike Levy


This special edition of Behind the Numbers is made possible by Tim Hortons, bubble tea, and painfully out of the box thinking.


In a world where bike brands are slowly and incrementally evolving one tiny half-degree at a time, the Pinkbike editorial team wanted all the length right now and a head angle that not only looked into the future but actually put the front wheel in it.

Using quantum-ish physics, they looked back ten years to extrapolate what we’ll be riding ten years in the future. Either that or Levy spilled his bubble tea all over the 2D drawings before handing them to the factory.
Grim Donut Analysis Details

Travel Rear: 169.8mm
Travel Front: 180mm
Wheel Size: Mullet (29" F & 27.5" R)
Frame Size: "Small"
COM Height: 1,150mm
Chainring Size: 32T
Cassette Cog Sizes: 50T, 24T and 10T





Maybe a peg or two were descended when proposing the original idea to manufacturers in Taiwan and current industry members and brands. But he stuck with it, and with the help of Genio bikes in Taiwan and some open-mold options, the initial ideas of futuristic geometry were realized in this aluminum steed.

The Grim Donut

The Grim Donut uses a single pivot system with a pull-style linkage to actuate the shock. In an age of high-pivot bikes with modified chain lines to account for all that rearward bump gobbling axle path, the Grim Donut follows Levy’s ideas of being so futuristic that it hurts. The main pivot has literally gone full circle and come back up through the ground to find itself pretty damn close to the bottom bracket, which results in it driving quite a few of the suspension characteristics. It’s probably good that the main pivot is so low otherwise it would have needed two chains to encompass the barge-like chainstays.


The Grim Donut
The original Grim Donut envisagement saw the use of many more pivots, an idler pulley, and more water bottles than a feed zone at a World Cup XC race.


Mike originally envisaged the Grim Donut as a dual short-link bike, similar to an older Santa Cruz, but with a high pivot and idler. Yes, it broke the laws of nature, but it let him call it High Pivot Virtual™ suspension. That said, the single pivot system might actually be a godsend. With that many pivots all dictating a virtual pivot point flying around in space there would have been many, many eventualities for Mike to have landed on suspension characteristics that would add to the already tall order that is riding a bike with this radical geometry. The single pivot system with the linkage driving the shock does result in somewhat fewer rollercoaster curves that probably would have ensued given his hand/eye coordination with crayons.

It’s also a mullet bike. Mullet due to the business in the front and party in the rear philosophy of the big 29” wheel up front and the smaller 27.5” wheel out back.




With the Grim Donut being a single pivot, the main pivot is the instant center, and is tucked neatly close to the BB, as shown by the Feline Instant Centre Locator.



Leverage Ratio

GD Leverage Ratio

The Grim Donut has options for running 60mm or 65mm stroke shocks resulting in 158mm and 169mm of travel respectively.

Using a 65mm stroke shock to get the most travel, it has a 16.3% progression and an average ratio of 2.62.

The leverage ratio is overall fairly linear but there is a more pronounced region of progression in the first third of travel. Looking a bit closer at the curve there are some subtle deviations from a straight line that could reveal themselves as quirks in getting the suspension setup truly bang on. Although I’m not sure bang on shock setup is going to be high on the list of priorities when trying to weight the front wheel enough to stop understeer. Perhaps more donuts are in order to up the load on the tires.

The end linearity in conjunction with the 2.44 leverage ratio would benefit from some help from the shock, either in air volume tokens or hydraulic bottom-out resistance. I’d genuinely love to see the scenario where this thing gets bottomed. To have got up to that speed on the trail or confidence level to hit a feature to use all the travel will be the confirmation that the Grim Donut is the future and that Mike was wrong, sorry, right all along.

The Grim Donut was built with a coil shock because it looks awesome, but I predict a choice between having good traction or good bottom-out resistance, so we have a Super Deluxe air shock on standby.





Anti-Squat

GD Anti-Squat

Oh, the irony of someone slating climb switches with such hatred yet designing a bike that would definitely benefit from one. That Low Pivot Technology drags the anti-squat values right down to well under 100%. The chains influence in the anti-squat equation isn’t good either, with some of the chain force going towards a pro-squat effect.

The sheer wheelbase of the Grim Donut is actually the reason the anti-squat figures aren’t lower. The front-wheel being so far from the rear wheel gives the anti-squat force line time to creep up to the center of gravity height. Maybe the original idea of three water bottles would have actually dragged the center of gravity of the system down enough for the anti-squat values to edge over 100% and give some countering to the squatting from load transfer.

With a seat angle that steep it’s not only the load transfer that is going to try and compress the suspension. More of the force from Mike’s legs is going to go vertically into the bike and provide a downwards force trying to compress the suspension.

Combined with possibly a quite active suspension feel from the leverage ratio and coil shock likely setup for maximum traction, it’s going to result in not the most efficient pedaling of bikes. Maybe fire road climbs might be the best bet. Like, really damn wide and gently sweeping fire roads. Otherwise, it’s three-point turns.





Anti-Rise

GD Anti-Rise

Again, the low main pivot would cause lower levels of anti-rise on a more conventional bike. But thankfully Mike had that covered and made it a barge to bring back some suspension performance.

The anti-rise curve starts quite close to 100%, resulting in the anti-rise forces canceling out most of the rise forces created from the braking induced load transfer. As Mike ventures deeper into the travel, the anti-rise drops somewhat, which will lead to an overall effect of a bit of suspension extension when braking deeper in the travel. But the bit of rise that will come about will likely be well dealt with by the muscular disposition Mike possesses and forced riding attack position from the forward-thinking geometry.





Axle Path

GD Axle Path

Trend shattering ideas flow all the way through the Grim Donut and even percolate as far as the axle path. While most brands are concentrating on allowing the rear wheel to move out of the way of oncoming impacts, the Grim Donut forcibly resists that idea and the oncoming bumps.

There’s a whopping 0.56mm of rearward axle path that's dished out early on in the travel before the wheel then moves a mere 23mm forwards until the end of travel. This does, however, result in very low levels of the dreaded (by some) pedal kickback. Not having the chain tug on the cranks quite so aggressively might help in reducing the number of stimuli to deal with when piloting the Grim Donut swiftly down the trail.





Analysis Assumptions

Centre of Gravity (CoG) height is 1,150mm above the ground.

Anti-squat and anti-rise always assume a static CoG. In the real world this is rarely the case, but might actually be the case here with sheer fear rendering Mike’s body rigid. But this needs to be done for analysis’ sake to allow it to be calculated and compared to other designs and bikes.

Fork is at full travel. There’s no industry standard for the fork in anti-squat and anti-rise analysis. Changing the fork travel to be at sag throughout the analysis does result in some change to the curves. Having the fork compress at the same rate as the rear suspension could be a more realistic way of analyzing, but adds complication to the analysis and makes comparisons harder. As long as these assumptions about AS and AR are known and understood, it’s easier to analyze and compare bikes.





Final Thoughts

bigquotesThe wonder that is the Grim Donut might not be as the team first envisioned it but, thankfully, its radically forward-thinking geometry made it through to the final product. While the geometry is going to be one thing to consider while riding, it’s good that the suspension shouldn’t throw any horrendous surprises into the mix while piloting it down the trail. It will likely pose itself as a handful on the climbs, but perhaps the overall active ride of the bike is going to help out in taming those next-generation angles and lengths on the descents. Or maybe it all gets too much and he simply admits defeat. Only time will tell. We all wait with bated breath to know exactly how he gets on with his creation.






Previous Behind the Numbers Articles:
Santa Cruz Megatower Suspension Analysis
GT Force Suspension Analysis
Orange Stage Six Suspension Analysis
Marin Mount Vision Suspension Analysis
Specialized Stumpjumper EVO Suspension Analysis
Introducing Behind the Numbers - A New Suspension Analysis Series


275 Comments

  • 494 9
 WHEN IS PART 2 COMING OUT?????

Soon, I swear Smile
  • 137 1
 So you didn’t die then???
  • 13 0
 ...soonish
  • 130 6
 part 2 will probably be delayed by COVID-19 now
  • 30 0
 SOON™
  • 37 0
 all the sport events I care about is cancelled. I NEED THIS!
  • 61 14
 FRT™

Full Review Tomorrow
  • 18 0
 How do you fit the Donut in your mini?
  • 8 1
 That's what you said on the 7th of March and it still hasn't arrived, haha.
  • 50 0
 @PhillipJ: He didn't fit the Donut in the mini. He jammed the mini in the three bottle cages.
  • 9 0
 @PhillipJ: Also, how do you fit in your mini after donuts?
  • 8 0
 Home, Refresh Refresh Refresh Refresh Refresh
  • 5 0
 Hope you're having a cracking good time with it.
  • 1 1
 soon...? prove it!! post part 2 now... Wink
  • 1 0
 @philip9175: I am still trying to figure out why it was we oppressed the media coverage of 1-18......I think I need to go to Dunkin Donuts and ponder this issue with some sugar on my chin.
  • 1 2
 @PhillipJ: Yeah, dozen of them.
  • 4 1
 @PhillipJ: the Donut can fit a full size mini in the front triangle
  • 2 1
 @Dav82: Yet. He didn't die yet.
  • 10 2
 @WAKIdesigns: Since we're on acronyms... High Pivot Virtual™ suspension. HPV? Who is going to want that?
  • 2 8
flag RoadStain (Mar 12, 2020 at 5:35) (Below Threshold)
 @ijskiak: Magic Johnson?
  • 4 9
flag WAKIdesigns (Mar 12, 2020 at 5:53) (Below Threshold)
 @ijskiak: I have a few different ones...
  • 7 0
 @RoadStain: magic had HIV.... and beat it, like a grim donut
  • 1 2
 @Dav82: its a garage queen, too dangerous to ride, so they just analyze it for the number because hey, even I aint stupid enough to ride a bike THAT slack lol
  • 45 0
 GIVE US A HUCK TO FLAT!!!!!!!!!!!!!!!!!!!!!!!!!!!
  • 27 4
 HUCK TO FLAT!!!!!!!!!!!!!!!!!!!!!!
  • 24 5
 HUCK TO FLAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  • 25 6
 HUCK TO FLAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  • 16 1
 @WAKIdesigns: I'm pretty sure you wanted to write FART™

Full Anticipated Review Tomorrow
  • 7 2
 You guys have been milking the grim donut thing for like 3 months.
  • 3 2
 @WAKIdesigns: which hopefully evolves into “fart tomorrow?”
  • 4 6
 @samdeatley: that's like Taco Bell with slow fuse
  • 2 0
 @PhillipJ: been my question from the getgo.
  • 3 0
 @hollowing2000: I see what you did there. :-)
  • 2 0
 @lightsgetdimmer: I think you need to switch the lights back on.
  • 1 0
 The chopper! What a waste of time!
  • 10 0
 Need a Part 3 with a Shout Trust on it.
  • 1 1
 Soon?

I'm expecting the setbacks to be due to the sheer amount of volume of info you want to share, and you're trying to compress it all the geeky tech stuff into graphics, and compressing all the opinionated stuff into superlatives, to make it all digestible.

I'm sure you've more than tripled your ideas and theories after trying this, as I've experienced making experimental stuff. Off to find the prediction thread where all the armchair engineers are...
  • 12 0
 @pinhead907: "milking the grim donut" probably belongs on a NSFW site.
  • 6 0
 Did you guys miss the "head angle that not only looked into the future but actually put the front wheel in it" part? The 2nd part is coming out so far into the future it actually came out in the past www.pinkbike.com/photo/13635027 (credit to waki, the alcoholic time traveller)
  • 2 4
 @hamncheez: I don’t like alcohol... beer and whiskey in particular... long live fungae!
  • 1 0
 @PhillipJ: Is that a euphemism?
  • 3 1
 @philip9175: I heard the Grim Donut actually caused COVID-19.
  • 4 16
flag RoadStain (Mar 12, 2020 at 15:05) (Below Threshold)
 @mike-gamble: Shit...that explains it. Unfortunately some black women already looted all of the Clorox bleach from our Lowes....now I am screwed to prevent certain death.....(seriously, a gang of black women went into Lowes and was looting....for bleach).
  • 5 7
 @RoadStain: what do you reckon: are they trying to get white? I know where the door is...
  • 10 0
 @RoadStain: was the color of their skin relevant?
  • 1 0
 Soon in the mtn bike industry mean anywhere from 3 weeks to 8 months. (hate that F*kn word)
  • 2 2
 @darrenf410: please... transcend!
  • 1 0
 This is the greatest thing to happen in our community since Shitbike!!!!!!
  • 2 1
 @WAKIdesigns: Don't lie to me, you're Polish. Therefore, alcoholic.
  • 3 0
 Can the water bottle mounts be retrofitted to hold toilet paper? Because, with the stockpiles of TP that people must have at their homes, they must have somewhere to put it.
  • 1 0
 @eric-knowles: everything is being postponed or delayed by coronavirus (COVID-19) hence my comment
  • 4 0
 I don't care how many bottle mounts it has anymore, how many toilet paper rolls can it hold !!??
  • 1 0
 The real question is has mike got Coronavirus yet
  • 1 0
 @Willybennett171: True! We need someone at Pinkbike to test ride it!
  • 3 0
 @RoadStain: (clicks on username) ohh hes a florida man. Now this makes sense. @Austink
  • 3 0
 @pargolf8: yes, the quintessential Florida man!
  • 1 7
flag RoadStain (Mar 13, 2020 at 9:33) (Below Threshold)
 @xy9ine: Yes, with out a description it is harder to identify a person who is now a known criminal. Their color is very germane to the situation at hand. Oh, brown hair and brown eyes too. While they did not have money for bleach, as it would seem....well, they did have money for the fancy over sized wheels on the car they fled in.
  • 6 0
 @RoadStain: What is the point your trying to make? People stole bleach. So what? Aren't you trying to mobilize the international mountainbike community trying to catch these bandits? Sorry, no one gives a shit here. If you care so much about that bleach then pay your local police a visit and tell them all you've seen. Oh boy, maybe they catch them, retrieve the bleach and you'll get a reward! Oh yes, that would be soo nice. So keep your crap to yourself, shut the f*ck up and bugger off.
  • 2 11
flag RoadStain (Mar 13, 2020 at 11:37) (Below Threshold)
 @vinay: Oddly, maybe if stereotypical people would not behave so stereotypically...there would not be a stereotype (common here in the US as facts do not lie).

Certain segments of the population are far more excited and panicked than others. Those who are on the public dole (generations deep now) are in general the ones who are at the facilities demanding free care for something they do not even have. What is funny, I know of five PCP's who closed their offices because it is not worth the drama. Now, thanks to some insurance companies waving deductibles people think somehow that care is "free". No deductible simply means the facility does not get paid for a visit with a PT. So, a simple solution. Do not provide a service for non-paying customers. It seems to work for gas stations (pre-pay only).Well, and most facilities do not take any of the exchange plans to begin with.

This is only made worse by the NY Governor saying that this is going to go on for a long long time and those in public housing will be affected the most. Sure, the people who again contribute the least will take a majority of the resources at hand. Simply, not worth my time nor concern. The big question is what will they do all day if Maury Povich goes off the air? Not only will there be nothing to watch, no one will figure out who the "father" is (same demographic).
  • 10 0
 @vinay: In an effort to stop losing brain cells after reading the incoherent ramblings of a delusional Florida man, I recommend just blocking roadstain. Nothing he posts is ever worth reading and only perpetuates misinformation.
  • 1 0
 @xy9ine: No, but what about there gender? He's obviously gender shaming with a comment like that...
  • 2 0
 @Austink: RoadStain, the WAKI of America.
  • 3 0
 @RoadStain: racism ain't cool... and f@ck your facts....
  • 2 5
 @scottlink: I suppose the facts of the criminal justice system are racist? I suppose the facts about terrorism is anti-Muslim? Then again, in society these days men win womens races.....oddly, seemingly proudly.
  • 6 1
 @RoadStain: so simple isn't it when you can't be bothered to think past the first dimension, 99% of terror attacks in the US have been by white supremacists and people with mental issues (and guns). 9/11 was pretty much the exception.
  • 1 0
 @BenPea: Not to mention that bast majority of US born terrorists were either on antidepressants or on speed and it was long before Obama care that Trump now managed to accuse of starting Corona. After causing 9/11 Barrack Obama just became the biggest super villain in the world. So effectively, according to Donald Trump no other president has changed the world as much as Obama.
  • 3 1
 @WAKIdesigns:
Obama: Kenyan father
Nairobi US Embassy bombing: in Kenya

You do the math.

The places Trump fans have been taken since getting on the orange mobster's batshit bandwagon... Not dissimilar to the re-education scene in Clockwork Orange coincidentally. Nothing clockwork about this horrific parody of a leader unfortunately.
  • 3 1
 @BenPea: I love how Danish and Swedes are throwing crap at each other now over corona. Sadly, I must admit it, Swedes are slowly bending over to the stupidity. There’s no toilet paper in the local shops, Not even the harsh one that immigrants used to buy! Big Grin Oh what a show. Swedes: let’s keep it cool and see what happens, wash your hands, Danes: Step 1 Quarantine, Step 2 ?, Step 3 No Corona. Also all journalist douche canoes left the harbor and are shitting all over the place, particularly those with non Swedish names. These people are so full of sht, that They should know that they are as useless as Bob on Facebook, I may as well listen to advices of Bob and Ellen on Facebook...

My solution is simple: Edibles. Edibles will keep people calm at home.
  • 1 0
 @WAKIdesigns: I didn't know what to make of that until your last paragraph. Unfortunately I have to agree.
  • 1 1
 @BenPea: it was an update on current situation in Sweden. We’ll see next week. Right now Danes and Poles are virtue signalling.
  • 2 0
 @WAKIdesigns: So Sweden is doing a UK? Thought I hadn't heard about them. This is the Russian roulette world championships.
  • 1 0
 What is doing a UK? @BenPea:
  • 3 2
 @WAKIdesigns: Denial, delay, contrarianship, opportunism? In France, the teachers are looking after the kids of nurses.
  • 2 2
 @WAKIdesigns: what the right path is seems to be a matter for debate. Someone's lying.
  • 2 1
 @BenPea: what’s the f*cking point then?! Here’s an idea! We will close schools, we will send kids to teachers homes. We both know that the biggest terror in this world is trucks stopping arriving to shops - why wouldn’t farmers, Growers, food factories not stay home? Imagine many people queueing in to buy food and then trying to pay and the card doesn’t work? Running to ATM and it’s empty. Three days like this baby, three days. Network down?

We are risking hell of a lot more than 5% of population, far more. Quarantine makes sense when big portion of society is infected. But when you have so few cases it’s pure stupidity. What will we do in 2 weeks? What? Prolong it to 4? Fine! What’s next? This spreads so quickly no amount of quarantine
can help until everyone got it or vaccine is ready and that’s march next year earliest they say ATM.

I don’t think anyone is lying, I think we have no fkng clue what to do, but given how few people get even remotely worrying symptoms, this is a f*cking gamble with economy. Jobless people are not healthy man... not even close.
  • 2 1
 @WAKIdesigns: I hear you. But kids are little biological weapons. It's the economy or the infirm... Glad I'm not running this thing.
  • 3 1
 @BenPea: whole thing would look differently if kids were in the high risk group. That would be The real shit storm. That would be the real panic. Nobody wants to save grandma as much as they want to save their kid. Not even close. We don’t know, we just don’t know, we are doing something that we have never done before. But I won’t take shit from a Dane Big Grin
  • 3 0
 @WAKIdesigns: I don't think anyone is trying to stop the virus. It doesn't make sense, it is never going to work. Lots of people are going to be infected anyway. What they're trying to do is to flatten the curve. The health system can deal with ill people, just not that many in such a short period of time. The situation they have now in Italy is that the medics need to choose who to help and who to leave to die. No one wants that and it obviously sucks for medics having to make decisions like that. If this same number of people (most of which obviously never even needs to seek medical care) becomes infected but over a longer timeframe, they can help them no probs. And just like with the regular flu, they probably have something available up front for the vulnerable people. It just isn't available at the moment. So yeah, they're just trying to get more time. Not by any means trying to avoid people from ever catching this virus. It isn't worth trying.

I guess the small bright point for us mountainbikers is that we don't necessarily have to stop riding trails. In fact it would probably be better to dump your snot trailside than spray it around at home. Volleyball players (who don't happen to be into beach volleyball) have it much worse. They can't play their game anymore. And until the end of March at least we're supposed to work from home. So I'll definitely will put in an hour or so mid-day of mtb or bmx riding every day "to compensate for my commute". Obviously this still dwarfs in comparison by all the bad stuff the virus has brought, but just meant to say it is always good too look for opportunities too.
  • 2 0
 @WAKIdesigns: this is morality tearing itself to bits
@vinay: luck is everything
  • 2 1
 @BenPea: I guess you know that morality is strongly related to conditions. It’s moving the problem.

@vinay - I know it’s about flattening the curve, that’s why WHO said early quarantine makes no sense because it will create more spikes. It’s a true grim picture to imagine nurses and doctors work 18/7 for 6 months. Italians messed up on several levels, they ignored the quarantine, they stopped coming to work but kept partying, going to church, restaurants. Over here, half of my office already works from home, gyms are empty, virtually all events were cancelled. Folks with symptoms of cold are staying home. The only big issue I an seeing is that people are still using public transport a lot. Time to get a bicycle for many. But we are trying to keep this rolling. Danes And Poles put it to halt. We’ll see how long they can hold the breath, it’s just that it’s not just about them. Decisions have been political as hell rather than rational.
  • 27 4
 On a more serious note.

Have you considered using a 37mm (27.5 reduced offset fork) to help pull the front wheel back a bit farther into the realm of "actually weightable"? Its only 5mm less offset than a 29in reduced offset fork, but every little bit should help

Plus, they say reducing the fork offset has a somewhat similar effect as slackening the bike out a bit. So that could help overcome the somewhat steep 57 degree HTA...

With some luck, and some speed, you might be able to turn the thing Big Grin .
  • 36 19
 How’s that serious?
  • 6 0
 @mikelevy In all seriousness this could be an intetesting long term tester.

It would be interesting to see how different riders would change the bike to make it better.

Or just use it instead of the 8 Ball.
  • 39 1
 You could just turn the fork around completely. That may help. I would also spec a 70 mm lay back post.
  • 6 1
 Hell no! In the spirit of this project, it should be a zero or negative offset fork. Might as well run the freakin' fork backwards!
  • 46 0
 @dldewar: Run a Manitou backwards, that way the arch is correct for once!
  • 4 9
flag WAKIdesigns (Mar 12, 2020 at 7:27) (Below Threshold)
 @jfcarrier: no. It has to be a tiny number always. Like 5mm. 47 head angle head angle or 87 seat angle will still make some couch engineers go “maybe worth trying”, but 44HA or 90SA will turn them away. So 5mm offset would still turn some gears in the heads of dweebs.
  • 4 0
 @WAKIdesigns: *more serious
  • 2 0
 @WAKIdesigns: For a "normal" bike, stable steering is nice. However this concept is : "numbers so futuristics it hurts". I feel zero offset is very close to "hurt".
  • 1 11
flag WAKIdesigns (Mar 12, 2020 at 8:32) (Below Threshold)
 @jfcarrier: exactly... but 7mm offset or 86 seat angle?... man for an "average kind of engineer himself"? That's like bike version hypersonic VTOL Tesla passenger jet capable of flying you from Vancouver to Wuhan in 15 minutes.
  • 4 0
 I really want to see the steep technical climb test video. I don't think they can keep the front wheel on the ground.
  • 7 8
 @tacklingdummy: why? Very long rear end improving the BB to rear axle relation, super steep seat angle with saddle to axle relation, even more ridicuous front end adding weight to the front and putting your body weight towards the front - It's easier to flip Ninos Scott than this thing
  • 3 1
 @WAKIdesigns: You are right. It does have a long chainstay length. I didn't look at that spec. It may climb ok.
  • 3 0
 @tacklingdummy: it's long but not long enough for the length of the front centre. I have 445mm on my bike and the wheelbase is 100mm shorter that this beast. It will climb fine but it is going to be hard work to weight the front around corners.
  • 2 5
 @WAKIdesigns:

The 37mm offset was an actual serious suggestion in my mind.

With a super slack 57mm hta, even with long chainstays, it seems like weighting the front properly would be tough. So was wondering if that would help.

Then I realized that the super slack hta and super short offset of 37mm may make it... difficult to handle and basically couldn’t Keep a “straight face” anymore. So... “more serious”, but not entirely “100% serious “ I guess.

I actually wondered though.

Can you install a CSU backwards into fork lowers, and get negative offset? Assuming of course that just installing a fork backwards is bad (seems like braking forces would be a bad idea with backwards lowers).
  • 7 1
 @Karpiel073: Put a trust linkage fork on it, but backwards. That'd be truly grotesque!
  • 7 7
 @tacklingdummy: not just that. seat angle, reach and head angle too play a role. Even Cesar Rojo said it that not so long ago Enduro bikes provided better uphill handling and position than XC bikes of the same time. Seat angle has dramatic impact on geometry. If you are making it very steep, the ETT gets stupid short, even if reach would allow you to handle the bike well when you are standing on pedals. So the long reach is in a way byproduct of steep seat angle (goes back and forth off course). Then you add head angle which has a lot to do with how bike transfers terrain to your bars an BB, massive influence on handling, and suddenly your front/rear balance gets challenged and you need to increase the chainstay length. I came from seat angle, but you can pick almost any number and kind of go from there like I went from STA - It's all interconnected.
  • 1 1
 @WAKIdesigns: Of course, that is a given that STA and HTA play a role.
  • 22 0
 I tried to flip the crown around to get a ~10mm offset, but there was a tiny little bit of interference between the crown and the arch. I also briefly tried to get the guys on board with running a Manitou backwards.

We think it's the right amount of stupid as it stands... we'll see!
  • 1 0
 @ocnlogan: just put an angleset in it backwards to increase the HA to 59. It will also slacken the ST and lift the BB. 29 rear wouldn't hurt either. Then it maybe just rideable.
  • 1 0
 @brianpark:

Glad that I’m not the only one thinking about this as a way to make this thing rideable Smile .

Validated!

Loved “It’s the right amount of stupid” comment Big Grin .
  • 1 0
 @ocnlogan: Hence my comment about it being a long term project. I think it is possible but is too progressive atm.
  • 2 0
 @brianpark: Yeah, review it as is. It is perfect with the stock setup. Lol. Everyone wants to see the ride review in it's raw wild wild west setup.
  • 1 0
 @ocnlogan: Serious? Suggesting to increase the slack steering feel, that Mike noticed so massively the moment he got on the bike?

This should be a learning experience, not an expensive joke.
  • 2 0
 @Varaxis:

The wheelbase on this thing is at least 100mm longer than any other bike with the same reach measurement has today. The suggestion was actually a serious question trying to find a way to weight the front end, similar to what manufacturers may try to do if we "evolved" our way to producing bikes like this in the industry.

The less serious part was when I started to consider what having crazy short/no fork offset would do when combined with its crazy head angle, and realize it may not actually turn, then yes, I resorted to humor, as I realized my suggestion may not be the "best" method for solving the problem.

The alternative is to run a normal offset and ~100mm stem, and stretch out on it TRONcycle style? Assuming that "X" lbs of weight need to be on the front tire to make the bike turn of course.

In the name of science though, I'd actually legitimately like to see both of these done, and see which one works better.
  • 3 0
 @ocnlogan: geometronbikes.co.uk/bikes/g1 an XL G1 is close but still ~40mm shorter thank the Donut. I would consider the G1 the limit as Chris Porter has gone beyond this come back.
  • 3 7
flag WAKIdesigns (Mar 12, 2020 at 10:56) (Below Threshold)
 @fartymarty: I am nut sure if being close to Grim Donut is a pro...
  • 1 0
 @ocnlogan: yes, but it’s still not negative due to the axle location. Chris Porter has tried this.
  • 3 0
 @ocnlogan: it's literally what I wrote at the top of my notes during the kickoff meeting.
  • 1 0
 @WAKIdesigns: bring it on
  • 1 0
 @jfcarrier: Hmmm... I believe White Industries had a dual crown with zero offset back in the day.. or was it a Hannebrink?
  • 19 0
 I appreciate the cat monocle chainguide assembly/overlay.

Very classy.

Will that be standard on the production models, or at least available as an optional accessory?
  • 5 12
flag WAKIdesigns (Mar 12, 2020 at 2:12) (Below Threshold)
 That thumbnail... like a rainbow in the dark
  • 2 1
 Cat Monocle? I think you're onto something there. Now what to call it...
  • 15 0
 @AirBud: Meownocle
  • 1 0
 @mtbikemccoy: I need one of those right meow!
  • 14 0
 With no weight encumbering the front end--ever--do you really need a stout enduro fork? I would think something light and poppy would suffice. Maybe Cannondale could Jerry rig an Ocho Carbon Lefty into 180mm? Do those things stretch? Maybe you could tie one between a tree and the Mini and tug it out to sufficient travel? Now, before I get downvoted for suggesting that you make the front end so light that only a trials rider could climb on it due to the hovering nature of the front end how's this for a solution? A front mounted picnic basket to hold your water bottles while climbing?

Disclaimer: I'm not an engineer, just spitballing here.
  • 2 0
 Being so slack, vertical loads on the fork from drops/jumps are going to have more of that load trying to "bend" the fork, and less of that load travelling axially into the spring/damper. So my take would be you want the strongest fork possible to handle that. Stiffer crown/lowers/stanchions to support the bending loads, larger stanchion bushings to support the loads, etc.

It's the trade-off to slack head angle, the take head on hits better and the expense of vertical hit capability.
  • 2 1
 You sure about that? You sound like an engineer. A really good engineer.
  • 4 0
 @srstudent: He's definitely not an engineer. He didn't start his comment with "I'm an engineer and...".
  • 15 1
 I personally think that a 29/34 Mullet would be the better option AND the future......think forward.
And Hey - we could invert the stem length!
  • 10 0
 Terrifyingly, someone on the Pivot Owners FB group has already done the reversed stem thing, on a Firebird 29, because it's too long for trail riding, apparently! Unsurprisingly there is Zero support for it within the group.
  • 10 0
 I tried to get a 32" front wheel made, and the rim would have been pretty easy, but getting tires proved a lot harder.
  • 1 0
 @brianpark: it's a shame, I'm sure it would look awesome on a Fox 32 fork.
  • 14 0
 Rear travel, 169.8mm, should climb more efficiently than a 170mm jalopy.
  • 14 0
 SRAM approves this rear travel.
  • 3 1
 I wish it "looked like a Session", then this bike would be full PB meme.
  • 9 0
 Late to this discussion but what people need to realize is that this bike is so fast that it actually experiences relativistic length compression in the frame of reference of a spectator. As seen by a viewer at rest, Length(Bike)= L(v=0) *sqrt(1-v^2/c^2) where v is the rider's speed and c is the velocity of light. This effectively shortens the wheelbase at relativistic speeds so the bike appears normal.
  • 12 0
 I think this bike would look a lot more balanced with 700mm chainstays.
  • 2 0
 I kind of agree.
  • 2 0
 Should be put in a crusher. Piece o shite
  • 7 1
 Timing of this project is quite noticeable. You guys were waiting for RC to retire to go bonkers. When you wake up after going off the trail and hitting your head ( because it doesn’t corner) , you will realize his timeless balanced wisdom. Maybe should’ve done a unicycle shootout instead.
  • 7 0
 RC helped me loads with this one behind the scenes.
  • 10 2
 The fact that E13 tyres are out of alinement with the Rim is setting off my OCD...
  • 1 1
 Rookie mistake.
  • 7 1
 I predict... It rides like shit on flats, rides less like shit on the downs and the fork barely functions and when pulled apart will have stanchion shavings in the oil lol
  • 11 0
 They probably should have fitted a Lefty, to get some of that roller bearing action instead of bushings.... but maybe backed up the strength with a second Lefty on the Righty side too.
  • 2 0
 @MeloBikeCO: Just throw a Trust on there and call it a day.
  • 1 0
 @mammal:
Wasn't it the Trust fork that is reported to feel super stiff if you landed heavy on the rear wheel? Or was it a different linkage fork? That wouldn't work out to good in this situation, though.
  • 8 1
 That bike is going to understeer like a 1982 Mustang.
  • 3 0
 "It's not a motorcycle, baby it's a chopper". Now it seems everyone is in a race to make bikes with the most outrageous reach and headtube angle numbers. How come we don't see these clown bikes on podiums?
  • 2 0
 So, real question here. What will happen to the bike when you're done with it?

I submit that after testing* you loan it out to other industry publications/etc.

I'd love to see Blake from GMBN give this a go, like his tiny handlebar video he did a bit ago. This seems to fit the same sort of idea. But also just to get more perspectives on it from others in the industry.

*assuming it doesn't break in half, or is proven to be exceptionally dangerous to ride.
  • 5 1
 are you worried about the head tube snapping off? would a linkage fork reduce the stresses?
  • 7 1
 This'll be like racing the Dakar in a clown car. I reckon it'll make it til about half way through the first turn or compression. Wear a full face, Levy.
  • 12 0
 If you were to put a Trust linkage fork on that bike it would look like your fork is pretty much horizontal that'd freaky !
  • 6 0
 Why should a linkage fork reduce the stresses? If anything, i would think stress would increase if the wheelpath isnt in line with with the head tube.
  • 3 1
 @Ttimer: exactly
  • 4 0
 The bushing bind on the fork at that angle is gonna be horrible, a linkage fork might just be a better option.
  • 1 0
 I'm late to the party, but my question was exactly this -- what's the over-under on that head tube just snapping right off?
  • 3 1
 Wonderful how the numbers highlight the major oversight a few manufacturers make: the reach is way out there progressive but the top tube is shorter than on an early 90's XC bike. Must be hell to climb on.
  • 9 1
 It’s a small!
  • 2 0
 @makkelijk: I was also amazed at how small the reach was in combination with the STA. Also the stem will be a bit closer with a HTA like this. I think my 470 reach/76 STA/64.5 HTA will feel bigger. They should have gone for a 550mm reach!
  • 3 2
 This is all for entertainment value of course, but I would have preferred if they used their know how and bike experience to attempt to combine all the best characteristics of their favorite bikes, all in to one bike. An attempt to see the real future. Oh well.
  • 2 0
 One of the geometry numbers is incorrect. Chainstay length, stack, reach and head angle do not match the wheelbase.

Check this drawing:
www.bike-stats.de/en/compare_geometry?Bike1=Grim_Donut_2020_S
  • 1 0
 "With a seat angle that steep it’s not only the load transfer that is going to try and compress the suspension. More of the force from Mike’s legs is going to go vertically into the bike and provide a downwards force trying to compress the suspension."

Why the hell would anyone be sitting down while riding this bike?
  • 1 0
 What a waste of time and money and people. Is it April 1st yet? Once again the rear end gets more attention than the front, just a standard fork gets thrown on like an afterthought. This chasing of a mystical holy grail of geometry based only on rake and reach is pointless, made even more pointless because no attention whatsoever has been made to the relationship between rake and trail. Why do we see so much variability and innovation at the rear but almost no effort at all at the front? There are dozens of questions about bike suspension but apart from a few noteable exceptions no-one is asking them. For example, perhaps the simplest of all: Why are the handle bars always mounted in front of the steering axis?
  • 1 0
 Almost forgot to say: This article annoubces itself as thinking outside the box, but the reality is this is an article about chasing one dimension, the fork rake angle reduction. Nothing new in that and the results are fairly predictable. Thinking outside the box would be something like asking how to increase the fork and angle, or perhaps asking what is the ideal trajectory for the front wheel for the type of riding intended, or even, dare I say it, how can I increase front wheel grip using suspension? After all is said and done, grip translates to time. I am going to tear my hair out the next time I read words like "progression" and "support" in an article about suspension. Get the stop watch out please.
  • 1 0
 Wow, I think you'd actually have to try pretty hard to design something with worse rear suspension kinematics. Weird to give a bike so little anti-squat when you're known for hating climbing switches and bad suspension design with a passion. Also material fatigue is a very much a thing on parts that are overstressed due to ridiculous design choices and I wouldn't want to ride the bike at that point when the head tube inevitably snaps clean off the down tube.
  • 1 0
 Looking at the angles I feel like this bike just wants to fold in half. Maybe it should have been more forward-thinking to move back to a SINGLE shock - located somewhere in the middle of the bike. Good for traveling too, just remove the shock and the bike folds in half!
  • 2 0
 Pretty good on the slacker bit but I feel like they could have gone lower too. Custom 100mm cranks and a bottom bracket 4 inches off the ground. Maybe next year's model
  • 3 0
 This is almost art. It's something that interests most of us and shouldn't be rushed. Take your time. Excited to see it.
  • 4 0
 I hope the simpsons movie wont sue for the use of their doughnut Wink
  • 6 1
 Looks like a POLE!
  • 1 1
 ...looks like a hot mess.
  • 4 1
 The feline instant centre locator needs to be used on all field tests please.
  • 5 0
 And it should be an acronym. FICL (pronounced "fecal") as in FICL matter.
  • 1 0
 @robmurray12: Yes. Yes please.
  • 2 0
 This junk science fake news article has no place on the Grim Donut, it'll climb like a goat and decend like a session- guaranteed.
  • 3 0
 PB went for the Harley geometry. Climbs like a choppa and descends like a choppa.
  • 1 0
 I'm sure it has already been said in countless other places, but that head angle and fork travel is just begging to snap the top tube at the first flat landing it encounters...
  • 2 0
 @mikelevy "Oh, the irony of someone slating climb switches with such hatred yet designing a bike that would definitely benefit from one" Wink
  • 1 0
 A corona is a ‘gaseous envelope of the sun‘, kinda like a donut around the sun.
Grim like the reaper... bringing death... or at least, flu like symptoms...
Fear the donut?
  • 4 1
 I clicked thought that this is the part 2 already.
  • 1 1
 same here.. can't wait to see levy trying to ride that thing down a trail.. gonna be a shocker for sure....
  • 3 1
 I clicked to see the bike in 2 parts all ready
  • 4 1
 I can’t tell if this thing is a joke or not
  • 6 0
 The answer is yes
  • 1 1
 I dont think they actually had the option to pick anything other than geometry....and this is the result of figuring out if they chose a good open mold design afterwards---or in the future?....that's future thinking!
  • 2 0
 We looked at several open model designs and chose the one we thought would work best for our angles. I asked Dan Roberts to do the original suspension analysis on this 2D frame drawing before he was officially part of the Pinkbike team.
  • 1 0
 @brianpark: nice, that's cool. I need to spend more time trying to learn that stuff...I wish I had more time.
  • 3 2
 Dear Pinkbike, please fill this thing with sensors, shred it and report us about all the crazy telemetry readings. More sensors around the head tube, please.
  • 4 0
 Probably shouldn't waste money on sensors since the headtube is gonna snap off within minutes.
  • 2 1
 Funny that this got built & will it ride like tandem for one?
Could ride better with the fork CSU turned the other way round if it had clearance?
  • 8 8
 @mikelevy I feel like you missed a huge opportunity here to make the bike electric, since in the future _all_ bikes will be electric Smile

Then its crap climbing performance wouldn't matter.
  • 1 3
 It's still doable. Bafang mid drive conversion. They've done at embn on an old Cannondale and they loved it. I'm sereously thinking of doing just that on my only top fuel 8 2011 with 140mm fork.
  • 3 1
 Oustanding refunds from Sick should be transferred to the production of GD's.
  • 3 1
 It takes the coronavirus to get them to feature more about the grim donut...
  • 1 0
 Before you release de next video,someone would introduce a new bike that made the GD look old&slack as an XC bike...3 month for a video????cmon....
  • 2 1
 uuuuhhhh. What happens when you rip the head tube off? #hucktoflat. #bushingbind. Seriously though I'm concerned for the test pilot's safety.
  • 1 1
 Yo, its literally the biggest meme ever. I dont think anybody is taking this seriously, we're all just having a bit of fun. Im pretty sure even PB is expecting the fork to snap or something of that caliber.......
  • 3 0
 Tester 1: Huck to flat.

Tester 2: No, you go first.

Tester 1: No, be my guest.

Tester 2: No, you.
  • 3 0
 what happens when you get to a corner and need to turn the bike?
  • 1 0
 Grimm news but Donut worry, unless its you are the one who drew the short straw and has to Huck to flat or rip Dirt Merchant on this"beast". Insert Unicorn.

Leaving now
  • 1 0
 What's with the odd texture by the BB, a short ways up the downtube? Is that where they welded a 2nd downtube to extend it, since they didn't have one long enough?
  • 1 0
 You need adjustable geometry with an adjustable fork, like the old Fox 36 Talas but this time with 100-140-180mm travel.
  • 4 2
 Pinkbike's obsession with water bottles...2003 flashback.
  • 3 0
 Next out of Levi's mind: packduro, where you strap your camping tent, cooler and BBQ grill to the frame of your 180mm rig. Must sport at least 5 water bottle mounts.
  • 3 1
 @southoftheborder: I think you mean to say a Salsa?
  • 1 1
 BikeRadar designed, built, and tested a MTB in one go, and here we are; still waiting for part two of The Grim Donut.
  • 2 2
 Did the Grim Donut clone the Privateer 161, or the Privateer 161 clone the Grim Donut. They both look equally kind of ridiculous.
  • 1 1
 How many clicks on this one today Smile

In all seriousness, looking forward to ride impressions!

If it's good please make a production batch Smile
  • 1 0
 The one thing it is missing: the price. I want to know how much money I will have to spend to get this beautiful bike!
  • 1 0
 I’m surprised mike @MikeLevy didn’t make it an XC bike with full enduro angles...
  • 1 0
 "In other words, don't expect one of those "first ride reviews" tomorrow, but maybe check just in case." -ML

Haha funny AF
  • 2 1
 Lol, this will bend the Rockshock Fork, what a stupid design, those fork aren't engineered to take that bending.
  • 2 0
 Why not just design it to be better?
  • 2 0
 Grim means ugly in danish
  • 1 0
 Engineering brought to you by the same fantastic math as the following: youtu.be/Ac7G7xOG2Ag
  • 4 4
 One thing for sure: your knees will scream out after first meters of pedaling!
  • 4 1
 For what reason?

I could see the arms hating all the weight on them on everything but the super steep climbs. But why would a person's knees hurt, what would be the force that causes knee pain?
  • 1 1
 @MeloBikeCO: have a look on the common "correct" position on a bike. On the grim donut the knee is far beyond the pedal's axle... it's all but anatomic. In the video you can see Levy trying to put his shoe on the pedal: he land his heel first...
Regarding the teeth, I was talking of the possibility the fork breaks because of its mad angle!
  • 3 1
 @Zarma:
I agree that head angle will play havoc with the front suspension either wanting to break off, or just seize up due to bushing bind.

On the knee pain front, I have never understood this idea that your knees could be damaged by being away from what is refered to as KOPS. There is only one force that changes at all due to being in front of the pedal spindle. The angle of gravity in relation to your leg and therefore knee. I have never understood how a few degrees difference in the gravitational force will damage my knees, or even make them hurt for just a moment.

If I was way behind the pedal spindle would you also anticipate knee problems? Like say a recumbent.

Do all people that pedal with a 90° seatangle have totally destroyed knees? Like the guy I see commuting to work everyday for the last 14 years on his jumbo sized wheel unicycle.(BTW that guy is an animal, I don't know him, but his commute seems to be neither short nor flat, seen him at the top of a 800 ft elevation climb on one side of his commute and 5-6 miles away up another couple hundred foot climb up near the university, which I assume is the other end.)
  • 3 0
 Found the roadie
  • 7 0
 "Knee Over Pedal Spindle" aka KOPS was a rule of thumb (aka an unscientific generalization) made by someone looking at road bike pro riders in the 90s and saying "Hey, it looks like most of their knees are above their pedal spindles so that must be the best position for everyone on every bike for all of eternity!" Seriously, I'm not making that up. It's been proven wrong time after time and has no place being mentioned for MTB fitting.
  • 2 0
 @pnwpedal:
It started well before the 90's, but the rest is generally right.

It is a good starting point for a road bike. For a fairly fit rider, that is average or lower in weight, KOPS will be roughly correct fore/aft position . For people with low fitness and/or heavier weight you will likely find that a saddle position rear of KOPS will likely feel a lot better. For road bikes, or bikes that are generally ridden on nearly flat ground.
  • 1 0
 @MeloBikeCO: thanks for the clarification, it's been a while since I dove deeply into fitting. I'm eager to get on a new bike with really progressive geometry and see what that can do to my riding.
  • 1 0
 @MeloBikeCO: seeing as all the modern geometry throws traditional fitting ideas out the window.
  • 3 0
 Steep seat angle + steep climb = KOPS.
  • 1 1
 Fearfully following Mike Levy's Insta page for evidence of hospital visits.
  • 3 1
 8008135... Hahahah
  • 1 1
 sooooo funny!!!!!
  • 1 1
 I am so looking forward to video of Levy's Grim Donut three point turns whilst climbing...
  • 2 1
 Ironic. The Pink Donut has no space for a bottle.
  • 2 1
 That's why it's so grim
  • 2 1
 To be truly futuristic flip the front fork around to run negative offset
  • 2 1
 Waiting to see it on A-Line
  • 2 1
 We the SLOW MO HUCK TO FLAT TEST
  • 1 1
 Could have at least lined up laser cat eyes with the sta and hta angles, Maybe from above, I mean come on!
  • 1 1
 Is there a price for the first person who busts the fork out of the headtube?
  • 1 0
 I bet the price may be paid at the endodontist office.
  • 1 0
 Grim EBike Donut, can’t wait!
  • 1 0
 Less chat, lets see it on Dirt Merchant.
  • 1 0
 I feel like a chocolate donut now????
  • 1 0
 So, is it considered to be a medium sized frame. Serious question. Lol.
  • 3 0
 Small
  • 2 0
 8008135 he he
  • 1 0
 @mikelevy is dead after the last shot of ep1. Convince me I’m wrong.
  • 7 1
 Sup dawg?
  • 1 1
 @mikelevy: I'm gonna need a picture of you holding a recent newspaper. For all we know, the PB admins gave your credentials to Mike Kaz, who is now complicit in the cover up of your death.
  • 1 0
 Anyone else think the cat was a gearbox?
  • 1 0
 That thing looks like it goes scary fast at 10mph.
  • 1 0
 I was expecting 30" wheels. Shame on you
  • 1 0
 Next time on Pikebike tells everyone 'making bikes is hard!'
  • 1 0
 Basically it's a Privateer 161 with some Levy craziness. Big Grin
  • 1 0
 What's with the 1x3 drivetrain? Don't see it in the above photo.
  • 1 0
 CAN SOMEBODY EXPLAIN WHAT THE f*ck IS THIS?
  • 1 1
 ... well... and maybe also your teeths after the first jump!
  • 2 2
 I still think this bike looks mental ha
  • 1 1
 What happens if it’s great though...??
  • 2 1
 So much WHY?!
  • 3 3
 Because they could. At no point did they ask themselves if they should. It's glorious.
  • 1 1
 @lowgear: Next thing we know....records will be broken and everything as we know it changes......
  • 1 1
 "Travel Rear: 169.8mm"
You've been working closely with Sram, eh?
  • 1 1
 Now if it only had a Bosch motor tuned to above 25kph...
  • 2 2
 Huck to flat, a big one. I wanna see the forks snap off!!
  • 1 1
 Press fit, ffs does he not even read the comments
  • 1 1
 The rake looks bad for the fork
  • 1 1
 Grim Donut is pure entertainment. Fun, fun.
  • 1 1
 Hm...
  • 3 3
 GRIM DONUT!
  • 3 4
 I think I’d sooner ride an eTurd...
  • 1 2
 @constantly-broken correct post this time... GRIM DONUT UPDATES
  • 3 3
 NICE rear travel
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