Video: Vorsprung on Understanding Advanced Bike Geometry

Dec 18, 2018 at 13:05
by Vorsprung Suspension  

Steve from Vorsprung is back to nerd out about bikes. In Part 1 of this episode we deviate a little bit from suspension-specific tech talk, and get stuck into some limit-case aspects of geometry that are not frequently discussed. Part 2 of this episode will cover some other aspects of bike geometry and handling.


MENTIONS: @VorsprungSuspension



62 Comments

  • + 85
 I can't believe VORSPRUNG didn't get a nod for PB Product or Value of the year 2018! They've been consistently producing good quality product at value price!
  • + 48
 That's high praise, thank you! Glad we seem to be doing the right things Smile
  • + 3
 @drivereight I feel like these guys need to be designing bikes o.O . And shocks. And forks.

I'll definitely be sending my Pike to Vorsprung the next time I need a full service so they can fix the danged thing.
  • + 2
 I agree, bought the luftkappe, set aside 5 hours for install (because I'm not a bike mechanic) took no time and brought my pike to life, Great people making great stuff.
  • + 1
 @rad3144: Did you notice an immediate improvement? I tend not to use all my fork travel because with less PSI it's not supportive enough. If I sent to Vorsprung I'd probably also get a custom tune.
  • + 1
 @rezrov: YES. Luftkappe transforms the Pikes (at least the 2017 and older without Debonair air spring, I have not tried one of those).
  • + 32
 Tuesday Tune is back!
  • + 25
 spreadsheets next week...I'll be back.
  • + 3
 Me too!
  • + 9
 Hahah we'll try to make it more interesting than it initially sounds!
  • + 1
 @VorsprungSuspension: Have you devised an optimal geometry calculation in those spreadsheets for given parameters?
  • + 2
 @jollyXroger: Not as such. I don't believe such a thing is currently possible - everything is currently comparative and up for personal interpretation.
  • + 11
 Not a fan of really long front centres.there comes a point where it’s really hard to get your weight over the front of the wheel for flatter corners,then the rear will slide and it’s much harder to balance the drift.

Unless it’s a steep track,then it’s awesome.
  • + 9
 You're going to enjoy Part 2 then Smile
  • + 2
 @VorsprungSuspension: I think what a lot of people is experience is a bike being the right size (long front centre) but this means the chainstay is too short to provide adequate front wheel grip. TLDR: Short chainstays suck
  • + 12
 Now that's a nice Christmas present ! Thanks Steve!
  • + 5
 Steve - but wouldn't you say the reality is you have different center of masses standing (descending) vs seated (climbing). Seems that would indicate you have Alpha (Descend), Alpha (Climb) and Beta (Descend) and Beta (Climb). Seemed like the premise of the new geo was to optimize both climbing and descending at the expense static flat ground optimization. The steep STA and slack HA (longer wheelbase) sorta killed two birds with one stone.

MTB's in general are getting close and closer to Dirtbikes every year, which has always made sense (to me), those things have decades of R&D. Dirtbike HA's are right around 64 degrees, they have ~800mm bars and direct mount minimal offset stems. I'd be interested to see what the fork offset figures are along with reach, stack and "spread" of current motos.

Well laid out thoughts, not an easy subject to get across!
  • + 3
 You would, but the looping angle is irrelevant when descending and the endo angle is irrelevant when climbing. So yes, the CoM location is dynamic, but you still only have two limit cases.

Dirt bikes have a much lower CoM to start with (due to the weight of the bike and its location) so their looping/endo angles tend to be shallower to begin with. Trail figures (affected by fork offset) matter a ton on a dirtbike (or any motorised vehicle) simply because as speeds pick up, so do steering correction forces, and wobble stability becomes critical. Those things aren't as relevant to MTBs - nobody gets a tankslapper on a bicycle for example, although the feel of the steering is somewhat important.
  • + 1
 @VorsprungSuspension: Well, outdated 26" MTB bicycle with some 66° head-angle has similiar trail values to current BMW R 1200GS.
R1200GS has 64° steering angle and front wheel diameter 698mm, with 190mm of front suspension travel. This bike seems to have NO axle offset from steering axis. Despite having longer ground trail values, it is fitted with steering damper!
"Ancient" 26" bicycle with 66° steering angle and 680mm wheel diameter has cca 110mm of ground trail.
  • + 1
 @VorsprungSuspension: Incorrect estimate. BMW R 1200GS has 170mm of ground trail and 150mm of normal trail. POLE Machine has 156mm ground trail and 140mm normal trail. While oldish 26" wheel with 66° HA and 40mm offset has 134mm ground trail and 120mm normal trail.
  • + 1
 @VorsprungSuspension: except for a jump bike/bmx, shows why a lower bb bmx bike is harder to pull up than a higher bb one. What I always found interesting is how a low bb with higher bars would feel different than a high bb with lower bars despite both being pretty easy to get off the ground..
  • + 5
 Thanks for breaking it down @VorsprungSuspension !

The more informed we are as consumers the easier it will be to select suitable bikes on more than the marketing and how sick the release edit was.
Most current bike reviews all read the same (climbs like an XC bike, descends like a DH bike blah blah blah) and the consumers end up not knowing why a bike is better/worse than another bike and not being able to work out if the subtle differences in geometry will work for them and their riding style/terrain. Sure, we can't all be engineering majors but knowing that a steep seat angle and longer stays will generally provide a better climbing bike is a large step in the right direction.
  • + 4
 Nice work Steve... I like the way you break things down, using the more familiar geometry numbers to explain front and rear centres and how this impacts the handling of a bike. Looking forward to part 2.
  • + 5
 Thanks for taking the time to speak with me today Steve! Looking forward to a Luftkappe sprung Pike.
  • + 4
 You're welcome, hope you enjoy it.
  • + 4
 Luftkappe are amazing, you're going to love it.
  • + 2
 Once I get my wheelset sorted, I'll be getting one for my Pike also..
  • + 2
 Well done Steve! Looking forward to the next instalment. My previous bike, a Tallboy LTC, had a Corset and Tuning Valve on my Fox 34. That was a rad combo back then! Hope to run into you in the spring of 2019! Merry Christmas S
  • + 2
 Thank you Steve @VorsprungSuspension for highlighting this topic!

If only people will demand perfect weight bias distro, like they demand perfect anti-squat levels, I can maybe then enjoy bikes that aren't so forward-biased in smaller sizes! I'd prefer if they balanced the weight distro based on a CoG 175mm forward of the BB, for a neutral out-of-saddle position (and also move the seated position's CoG forward to match with a steeper SA). Good thing there's many that at least have the out-of-saddle perfect weight bias: med SB150, med Process 153 29, L in many other bikes like the Spartan 29, Sentinel, Rallon. Right now, since I'm a shorty, I'm on a '18 Jekyll 27.5.

On my old short travel bikes, I was so tired of people saying that I shouldn't need to have my ass so far back, when the damn designers force me to by having such front heavy geo, and making optimizing weight balance around the seated position. Inconvenient to have to hover over the saddle when it's so far back, to get maintain traction levels on both wheels. Seriously, if I weren't so back, my front will dive on drops and I wouldn't be even able to get any significant air off rollers. I accepted that this was sound advice for taller riders, or people on long travel bikes, but it's suicidal for shorties on short travel steep HTA 29ers.

Prob with the Jekyll is the seated position is behind the ideal CoG point. While it saves me energy out-of-the-saddle, it wastes me energy on the steep seated climbs, with me needing to shift weight forward. Props to all the brands, Norco, Pole, Cannondale, Spec, etc. for making a big effort for standardizing new size-specific features (size-specific CS, suspension kinematics, and tube stiffness). Now to make this all mainstream! Tweaking geo is relatively low cost, right? I can hold off on new bike shopping until they figure this out.
  • + 1
 Again you'll like part 2 of this. I don't think you actually want your CoM 175mm forward of the BB though, you'll see why Smile
  • + 1
 Hi Steve, already looking forward to the 2nd part, this one was a bit introductory for me. But I wish you could make this miniseries covering bike geometry in regards of the 3rd chapter, 4th chapter and A1 Experiment of Tony Foale's book Motorcycle Chasis and Handling Design, nowadays geometron buses and the Trust Message linkage fork or STRUCTURE bike. I'm sure you could tell the story in comprehensible manner, but it really might require more than two parts miniseries.
  • + 2
 If you have Tony Foale's book then I don't think you need me to replicate his excellent explanations on those Smile
  • + 1
 It only took 40 years of mountain bikes to property understand geometry. The industry evolved geometry pathetically slow. Glad we're here now. Most bikes in the buy and sell I won't touch b/c the geo is garbage! Once you ride a proper geo bike you can go back. Anything else feels like a tinker toy!
  • + 2
 Beng a light rider (65kg), I find on bikes with a lonnnnng front centre when I weight the front wheel the back end gets kicked all over the place. If I move my weight further back the front drifts.
  • + 1
 For transient condition, in acceleration mode, would it not be more meaningful to form the looping angle by considering the rear wheel centre instead of the rear tyre contact patch? This is because the acceleration force is reacted by the frame at the rear hub. Just wondering, can't wait for part 2. Excellent stuff as always @VorsprungSuspension
  • + 1
 In non-limit conditions the looping/endo angles are not as relevant (though not entirely irrelevant, but not a big deal IMO) as the rates of weight shift on a bike are pretty slow and so damping forces generated by CoM shift (relative to wheelbase) alone have little effect on wheel normal forces. When accelerating (braking or pedaling) at/near limit conditions however, you have to look at the contact patch not the axle.
  • + 3
 Thanks for mentioning Spread (i.e. Hypotenuse), a meaningful yet rarely used metric in bike geo.
  • + 1
 I didn’t even know that was a thing. This video blew my mind and I can’t wait for the next one!
  • + 9
 @ridebikesyall: in my best Chong voice... "bikes are just triangles and circles man"
  • + 2
 @yzedf: I think this is my new favorite comment on the internet.
  • + 4
 YESS!! maybe even better than wyn tv...
  • + 2
 The tuesday tune is the best thing that appened to mountainbiking in the last 3 years. I was really looking forward for another episode.
  • + 3
 Glad you like it Smile
  • + 2
 Cool. Please apply your thoughts also on the very extreme bikes like a Pole. Will be interesting to hear why these bikes are as fast as people say Wink thx
  • + 3
 Best video series on bike suspensions around. Glad your back. Love my vorsprung luftkappe.
  • + 2
 Great Vid!! I am predicting for next vid that what really makes you faster is centered wheight... and not wheel diameter... look at Brook Mackdonald...
  • + 3
 Awsome - deep geek on bike sus and geo - RAD!
  • + 1
 Yeah never really thought about this. Bicycles have the worst center of gravity ever. Pretty much a triple scoop ice cream cone on wheels.
  • + 2
 Best christmasgift ever @VorsprungSuspension Smile
Thanks for coming back with TT!
  • + 2
 Tuesdays are worth looking forward to again!
  • + 2
 Great info as always from the guys at vorsprung!
  • + 1
 At least one german word that is positive :-) Like your video´s - always learning...
  • + 1
 While this is all well and good, this video does nothing to explain why Randy's spleen volume dictates his handlebar width.
  • + 2
 Looking forward to next week!
  • + 2
 YES!!!! Steve is back. You bloody legend!
  • + 2
 Woohoo best mtb tech series on youtube is back!!
  • + 2
 Number crunching is all I need to hear
  • + 1
 "Uhhh.. yeah, gimme a sec… I’m coming up with thirty-two point three three uh, repeating of course, percentage, of survival."
  • + 2
 science!!!
  • + 2
 I like this. Thanks
  • + 2
 Absolute gold.
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