Too much emphasis on anti-squat for DH bikes, and not enough emphasis on front and rear suspension axle path balance, stability,

PB Forum :: Downhill
Too much emphasis on anti-squat for DH bikes, and not enough emphasis on front and rear suspension axle path balance, stability,
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flag mr-bishi
Posted: Sep 19, 2014 at 5:09 Quote
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Of course there is an advantage, the less leverage you have on your damper the more precise it is and less stresses on internal parts they also run cooler. Hence why they are on a cantilever to increase the throw also i hardly think a kurb at 200mph isn't a hard impact
flag johan90
Posted: Sep 19, 2014 at 7:31 Quote
mr-bishi wrote:
photo
Of course there is an advantage, the less leverage you have on your damper the more precise it is and less stresses on internal parts they also run cooler. Hence why they are on a cantilever to increase the throw also i hardly think a kurb at 200mph isn't a hard impact

Sure that would be a hard impact but I was thinking more in relative terms to the chassi weight, a V10 carbon frame weighs quite little compared to the chassi of any motor vehicle. So I still think a hard hit on a bike can cause more realtive stress on a bike frame.

About the leverage, with bikes the problem is springrates for lighter riders. A small girl for example will on a Morewood or Gambler for instance have a hard time finding a low enough spring. But that is more of no problem if bikes started overall come with lower leverage ratios it would force spring manufacturers to produce lower spring rates.


Overall I would say it is hard to relate anything from a 4 wheeled sport to dh, and even relating moto is stressing it a bit. The dynamics of a bike compared to anything motorized is way different. On a bike the human provides most of the suspension travel and the rider is relatively heavy in the overall weight. In a car it is only the dampers that provide suspension and the terrain a dh bike see is quite diverse and at which speeds it sees it is also very changing.

Imo the biggest problem in mtb is not the mechanical layout of linkages etc, it is crappy plastic internals, bad seals and a unhealty obssesion with lowering weight. An open bath fork is far more reliable than a cartridge and needs way less maintenece while it is still more than easy to make it perform better.
flag mr-bishi
Posted: Sep 19, 2014 at 7:52 Quote
i completley agree with you on the conponents hence one of the reasons i choose dorados, everything inside is anodised with a superb damping system, but what i would like to see and the point im trying to make is. a bike company could still use a similar design as to what they have now but instead of a 3" stroke damper on a 8" travel bike they could have a spring like they do now and external damper on a linkage which would be easy enough to do, and an 8" stroke on the damper. Its alot more effective whether its on 2 or 4 wheels its the same principals just the design thats different.

https://www.4x4review.com/everything-you-wanted-to-know-about-shock-absorbers/

This will explain the theories of matching your dampers to suspension travel etc.
im not saying the bike companies are wrong but i haven't seen any of them attempt it and it could be such a good thing if other more technical sport are using this idea.
flag mr-bishi
Posted: Sep 19, 2014 at 8:01 Quote
i also think alot of bike companies are trading off effecient suspension for attractive suspension, lets face nobody like to ride anything ugly!
flag johan90
Posted: Sep 19, 2014 at 10:18 Quote
Although this is were theory meets practice. A damper with 8 travel would be alot heavier and the frame would also become a lot heavier with two linkages. In other words the bike will feel more sluggish. The syndicate actually found that even shorther dampers were enough on the old v10's and for next years V10 it looks like they are going 8 something travel with a shorter shock again. And personally I wont argue agains Peaty, Ratboy and Minnaar, its ony an inconvenience when I cant swap shocks around the frames I own.

Look at Foes for instance, they used to run 2:1 leverage shocks and even at that ratio the shock is hard to fit without making a true frankenbike. Again I would dread to make a xs frame to fit a damper with 8" of travel.

No as far as I am concerned suspension design is good today, most frame brands have got it pretty dialed. I dont see running bigger dampers and lower leverage rates as a major benefit. Sure the bike has 8" travel but your arms and legs give maybe 2feet of the absolute best travel so the 8" from the frame is relatively small.

Gearboxes on the other hand, that is something that they could start stealing now! Ive had it with clapping chains, lubing chains, rear mechs flying left and right and what not.......next bike will be an Ion 20 with belt drive!
flag mr-bishi
Posted: Sep 19, 2014 at 14:30 Quote
No this where theory has been proven through practice, downhill dikes are no exception, this industry is ripe for gimmicks and hype. As far as extra weight of linkages, how big do you think dampers have to be.

And yes the foes does use a closer ratio of 2.1, for good reason, all the reasons ive explained because brent foes came from a background of designing and building off road vehicles.
flag johan90
Posted: Sep 20, 2014 at 2:57 Quote
Well if a 3" stroke require 9.5" e2e an 8" stroke would require at least 20" which is not to far off the top tubes of small dh bikes. And it would be extremly heavy compared to the frame. So yes in theory it might be better but in all practical manners ratios lower than 2:1 is not really viable. Again dh bikes dont rely as much on the dampers for shaving time of the clock as motorizied vehicles. So the slight advantage of a better performing damper is not higher than the practical problems it would generate in frame building.


Not to say damper tech cant be improved but slapping on a giant shock wont solve any real problem (like putting on a fork on the back end). Heating is not an issue these days on dh, maybe on air shock equiped enduro bikes but not really.

I do agree there is a lot of hype and extreme marketing going on, brands making ridiculous claims left, right and center but most big brands has got their kinematics within reason as to what can be tuned to by normal shocks.

Drivetrain and puncture reliability are areas that are far more limiting these days to how fast dh bikes can go than suspension design.
flag mtbman1980
O+ FL
Posted: Sep 20, 2014 at 8:31 Quote
Look at most of foes bikes they try and keep the compression ratio as close to 2:1 as possibleUnsecure image, only https images allowed: http://www.singletracks.com/blog/wp-content/uploads/2008/09/foes-fxr.jpg
flag johan90
Posted: Sep 21, 2014 at 2:10 Quote
And look at this "solution", the extra damper is to create more supple negative travel. Going to make popping of rocks to double stuff a lot harder. So in theory more supple negative travel might sound good but in practice not really. Its going to make the bike feel sluggish in a lot of normal situations but the added negative travel will only really help in super ruff chunder.

This is what happens when a designer dont have/understand what it takes to go wc speed down a dh course


Foes Racing FFR Prototype 2014
flag mr-bishi
Posted: Sep 22, 2014 at 13:13 Quote
have you rode one?
and why do you keep assuming these dampers have to be so heavy?
flag mtbman1980
O+ FL
Posted: Sep 22, 2014 at 13:49 Quote
do you know what it takes to go wc speed downhill?
flag gabriel-mission9
Posted: Sep 22, 2014 at 14:40 Quote
mr-bishi wrote:
have you rode one?
and why do you keep assuming these dampers have to be so heavy?
cos a damper with 8" of travel would be heavy. It would basically be one side of a dh fork. Perhaps a little shorter but not much. And it seems a bit pointless when you see 8" travel bikes with 222mm shocks performing on a similar level to 8" travel bikes with 267mm shocks. The lower leverage rate clearly doesn't give a huge advantage. The weight difference however is quite noticeable. Although you do have to account for the extra weight of the longer spring which your idea of separating the two would counter.
flag johan90
Posted: Sep 22, 2014 at 14:48 Quote
Nope I havent and it hasnt blown the doors of at WC's either but I've ridden my V10 which has a few, plus a few others before that of various suspension design which also have a few more titles. Not saying I wouldnt take the chance to try one if the oppertunity arose. But to the point, a V10 will have somewhat of a similar feature, meaning that the initial ratio makes it really easy to compress the suspension a fair bit into the travel. Same shock and same spring on my Scalp frame (ignoring the slight change in overall leverage) takes a whole lot more force to compress the same initial ammount, think one finger on the V10 and a good push with the palm on the Scalp.

This is quite noticealble out on the trail, the Scalp is alot easier to get of the ground than the V10 even though I've compromised the V10 a little to get more pop and less dead couch feeling. If I were to add an inch or two extra to the V10's soft initial travel I wouldnt want to ride it.

I think this were the difference in total system weight is why you cant use the same approach to bikes. A trophy truck or MX bike you cant really pop to gap stuff on the track/trail but a bike you can and want to quite often. A fast bike rider relies on him/her self for most smoothing out the trail not the suspension, a fast trophy truck driver relies on the truck to keep the tires glued. And MX is somewhere in the middle, like 50/50 rider suspension and vehicle suspension doing the work.



Not saying that it isnt good that conventional thoughts are challenged but there is usually a fair few good reason why conventional is just that.


Well not just the dampers per say but the overall package to add a 8" damper on a separate linkage from the spring is going to add significant weight/cost/increased ease of damage in a crash etc which we dont want.

I would be curious too see a rough sketch of something on how you would try to accomlish your thoughts? Like a concept drawing



In the end all I am saying is that in theory you some valid points but then there is all the unaccounted for variables that arise in practice which seem to render those theories quite impractical and useless for getting down dh trails faster. I for one know many parts on trails I could huck straight into at twice the speed if I knew I wouldnt 100% get a puncture etc which would save time instantly. But I doubt I would get an overall faster time just because I had more negative travel or longer dampers. So for this time I will follow the herd and trust that all major brands combined R&D departments know and have more resources than Brent Foes.


A full carbon split pivot of this and I would say we are pretty close to the best compomise in my eyes plus some of those Schwalbe Procores. But in full black ano of courseBatman

Nicolai Ion 20 Effigear
flag gabriel-mission9
Posted: Sep 22, 2014 at 14:55 Quote
johan90. you just described a f*cking sick bike. And then you threw in that little split pivot detail just to make me even happier about my trek. Props to you sir. Gearboxes are the future...
flag mr-bishi
Posted: Sep 22, 2014 at 17:29 Quote
Well it wont blow the doors off the wc curcuit as its not in it yet.
And why do you asume foes dont know what their talking about? Because they might be the only ones to push the boundries.
And as for weight it could be alot lighter than you think, its not like 1 side of a fork as it wont have to be, it doesnt have to take loads from from all directions unlike a fork which has to support alot of weight plus braking and turning forces, and as a damper mainly works when its being pulled on you can make this lighter and take more stress from pulling than you can pushing as pulling always pulls straight. Grab a spoke and try it.
And yes i think gearboxes are the future, but how heavy is a reliable 1 of them going to be? Abit more than a cassette and derailier i bet

 


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