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Sort of related to the topic, is how I agree with the OP, but will theorize what the ratio is to keep proportions right, so taller riders don't need to make an effort to weight the front tire, and short riders don't need to make an effort to weight the rear tire. I theorize that 430 is the ideal CS length for a 1200 wheelbase. +/- 5mm for +/- 25mm of wheelbase (435 for 1225, 450 for 1300, 420 for 1150). Of course, anything that changes the wheelbase affects this ratio, such as brands making a full complement of sizes by adding an inch here and there, and how telescopic forks, in combination with slack HTA, shorten the front upon compression.
Always nice to talk to someone who understands the potential of front linkages!
Yes, most of the front-centre length is retained, and it does a lot more:
1. The head angle slackens as it compresses. Compared to a telescoping fork, the head angle gets about 7° - 8° slacker through the travel. This causes trail to increase, rather than decrease.
2. Brake dive is reduced by about 40% and is adjustable. I didn't go for 100% anti-dive because I find 100% AD is detrimental to traction.
3. Pivoting on bearings, rather than linear bushings, reduces friction by over 90% at maximum braking.
4. Front and rear leverage curves are precisely matched for truly balanced suspension performance.
5. The linkage is integrated into strong and stiff heart of the chassis, rather than being perched all the way out at the head tube, for a strong and stiff chassis.
6. The rear end has some innovative features, too! For example, this is the only bike that tunes the location of every pivot for each size, resulting in the same anti-squat, anti-rise, and leverage curve for every rider.
Check it out at www.structure.bike and let me know if you have any questions.
Thought I saw a glimpse with the Tantrum Missing Link, but this answers my wish for outside-the-box holistic bike design.
If you're not quite bold enough to place a pre-order (we do have money-back guarantee), then please ask your favourite shop to contact us about acquiring a demo.
Short chainstays DO suck. I decided to count the brands that make trail bikes where the rear wheel isn't sucked as far into the frame as humanly possible. I came up with:
Nukeproof
Norco
Niner
GT
And those aren't even long chainstays. Those are just not 425mm chainstays on a fucking 29er. Meanwhile we're in the midst of a goddamn arms race to see who can make the longest front-center possible on their bike, because MOAR PLOUGH.
I'm as guilty as anyone for supporting this nonsense. I have 2 Transitions hanging up in my garage right now.
Either downsize, deal with it or make something custom to fix the problem. Seems bike companies don't want to address this one.
i ride a 445 reach bike so IDK
Number of all-mountain / enduro bikes since 2016 with normalized reach equal to or great than 490 mm: 197
- This includes multiple sizes of the same model, when applicable
- "Normalized reach" is the reach measured at a standardized stack (the average stack of all bikes in the category)
- Sample size is well over 1000 bikes
Among these bikes:
- Average chainstay length: 437 mm
- Number of chainstay lengths equal to or greater than 445 mm: 44
- Number of chainstay lengths equal to or greater than 450 mm: 24
-- Nicolai: 10
-- Nukeproof: 2
-- Orange: 1
-- Pole: 9
-- Raaw: 1
-- Vitus: 1
If the cause for concern is weight distribution, then let's look at chainstay length relative to front-centre. This incorporates head angle, which has a larger effect than a few millimetres of chainstay length.
Among the previously filtered bikes, average chainstay length as a percentage of front-centre: 53%
- Average value for Pole: 52%
- Average value for Pole Machine: 50%
Despite the long chainstays, Pole uses such slack head tube angles that the weight distribution is no better than average.
Highest CS/FC value: 56%
- Banshee Phantom
- Devinci Django 29
- Propain Hugene
- Transition Smuggler
Average CS/FC value for bikes with reach between 460 mm and 490 mm (a more conventional fit for the size of customer who may currently be buying 490+ mm bikes): 55%
Conclusion: Long reach does not inherently lead to an unusually high rearward weight bias.
- If we want a steep seat tube angle a short stem (don't know about you, but I can't go back to slack / long), then we need long reach.
- We can have long reach without rearward weight bias with a steep (compared to on-trend numbers) head tube angle.
- Stability, via mechanical trail, can be maintained with a steep head tube angle through reduced offset (which also helps weight distribution, if you're concerned about that).
The best ratios I've found were:
- Stumpjumper ST (not enough bike for what I want)
- Yeti SB5.5 (discontinued)
- Yeti SB6 (too much bike for what I want)
- Nukeproof Mega 290 (too much bike for what I want)
The next crop of bikes I've identified, which are closer to the Smuggler's numbers:
- Nukeproof 275
- Intense Carbine
- The new YT Jeffsy
- Smuggler
I agree, I want to keep the new school front end design. I like a long aggressive bike that can ride steeps. Also agree we can keep the front-center number under control by using steeper HA and upping the trail with reduced offset (also shrinking the FC).
I'm not sure about this, but I suspect we wouldn't need crazy vertical seat tubes to climb well *IF* we're using longer chainstays, as they achieve the same effect in terms of positioning the riders' CG far enough from the rear wheel. The shitty thing about climbing on slack STAs is hunching over, which I think is only necessary to achieve enough forward bias due to short rear ends.
In reality I haven't found a bike that incorporates this approach better than the SB5.5, by the numbers.
[EDIT] Yeah, Pole is a big no. They have long chainstays, but they have ridiculously long front-centers. The most imbalanced bike you can buy, next to maybe an Enduro.
There is a lot in your analysis that is being missed. Years after I posted this thing Vorsprung put this together, which articulated a lot of what I was saying in more objective terms. https://www.youtube.com/watch?time_continue=72&v=i5R60JHJbxI
To start, I just threw Pole out there as a bike that is at least getting semi close. There are a lot of different Pole models. I remember running the math on a bike "another mountain bike website" featured (race bike, not the one in the video above), and noted it to be close.
Second, I frankly don't care what other companies are doing or how many are doing what. Length by itself means nothing (that's what she said). Balance is what I'm after. This is hard to quantify without looking at other attributes such as stem length, offset and your own "biomechanics". End of the day, the only way to *really* test it is on scales or with some data acquisition stuff (not likely).
Hence, for us commoners, you need to put the bike on a scale both front and rear, and stand up in your most comfortable riding position. This will give you a fore/aft balanche that is usable when setting up your bike. I'm aiming for a very specific number here.
My cocktail napkin math coupled with the data I've got from my own garage experiments suggest if I had 465mm chainstays on my 500mm reach Sentinel I'd be a lot more balanced on the bike (40mm stem, 37 or 42mm offset).
EDIT for math revision.
If you dislike having this rearward bias, then seek something that has a longer CS for that specific front center. The FC is the WB minus the CS length. Since geo tables don't list FC, you can conveniently use WB instead. So if you have a 420 CS and a 1150 WB, it might be perfectly fine, and a 5' 4" bike tester might find the bike to be 5/5 stars, amaze-balls. In size XL, adding on 3" on the WB, you got a 420 CS and 1225 WB... super rearward biased now. Nice if you ride like 50:01 and love backwheel, but not everyone likes to fall over in high speed corners when their dirt ain't soft.
Enter modern AM 29ers. That 1225 WB is now accompanied with a 435mm CS. That size large SB130 is 5/5 stars, amaze-balls! Better than the 1250 WB and 435 CS on the SB150 L, according to the fine testers at pinkbike... hmm, interesting, right? Is there a sweet spot? There is!
If you liked that L SB130 over a L SB150, then you can probably extrapolate your sweet spot:
415 CS to 1125-1165 wheelbase
420 CS to 1150-1190 wheelbase
425 CS to 1170-1220 wheelbase
430 CS to 1190-1240 wheelbase
435 CS to 1210-1260 wheelbase
440 CS to 1230-1285 wheelbase
445 CS to 1250-1310 wheelbase
450 CS to 1270-1340 wheelbase
Oh look, the Pole fits right in at the 450 mark in Large. Coincidence? Maybe. Maybe not. If you follow this, you may determine that mfgers are doing things all wrong by not adjusting their CS length to the WB/size. Well, if buyers don't know better, they'll keep buying their stuff, and that's the feedback the mfgers are looking for... maybe Norco and YT were onto something? The Pole Taival does this too.
Can't only judge by this CS-WB relationship. Transition tunes their bikes for size L, but with giddyup 2.0, they lengthened the reach and steepened the STA, essentially shifting the rider forward, so it offsets the more rearward bias. Still dialed, even though their old size XL CS-to-WB proportions are now the same as Ls, shifting the geo down 1 size. Have to consider how suspension compression and axle path lengthens CS and shortens the WB too, so slack long travel high pivot bikes should have a bit longer WB or shorter CS.
Some people have their sweet spot bit closer to 55:45, since they have a habit of riding defensively. Nothing wrong with that, just different preference. Get too close to 50:50, and the you get a cruiser bike though, which is what most emtbs are currently (except maybe the Shuttle, eZesty, Altitude Powerplay, Canyon Spectral On).
I'd love to convince some mfger of this, but some prefer to just follow trends and conserve brand image. It's engineering incest, when employees only ride their own brand's bikes, or are only looking within the industry for ideas. I got a job application for Intense... wonder if they would even interview me. xD
I wish so badly that I could have a balanced Sentinel, it would be an incredible bike. As it is, it's only truly better at monster trucking down steep rocky shit. It's really dodgy when I'm carving high speed, flat or off camber stuff.
@ninjichor yeah you're right about this. It's sort of a crapshoot when designers just pick a CS length and run it through the sizes. A small or medium might be perfect while an XL is a wheelie machine.
I didn't claim my analysis was exhaustive, nor did I make any statements about varying stem length between bikes. My point was just to explore the topic and correct one statement you made, not to write my thesis on the topic.
Off course "there is a lot in your analysis that is being missed". There's a lot in every analysis being missed. You didn't mention:
- The quality of analogy between the rider's position while measuring weight distribution in the lab and the actual riding position on the trail
- The steepness of terrain for which we're trying to optimize handling
- Changes in rear-centre and front-centre through the travel
- Upper body strength of the rider
- Physical build and dimensions of the rider
- Shoe size and position on the pedals
- Tire balance (ex. narrower, faster rolling, and/or more durable compound on the rear)
- etc.
I hope you'll experiment with the dimensions you feel are optimal and let us know your findings.
First, I think one of the big lacking data points in all of this is "what weight distribution are we aiming for". 50/50? 45/55? 47/53? Only way to really know this is to start using scales on flat ground to document this, then go ride. Record your lap times. Pay attention to fatigue. Test in a variety of different situations. Etc etc. Lots of testing among a sample size will establish this. My $0.02 is I want something closer to 50/50 than I do 45/55. Where exactly? I'm not sure. Honestly, its hard for me to get something close to 50/50 in neutral "attack" position at this point being I'm into 475-500+ reach bikes.
Second, what is a neutral riding position? Personally, I don't really care about seated weight distribution that much. We figured out steep STAs fix any issues there awhile back. We can debate this further, sure, but that's really not my hope in this post. I want better weight distribution ***while standing***. I don't want to have to move my whole body forward, loading my hands, while just standing there. Anyway, point here is anyone who has thrown their bike on scales will attest its really picky based off how you stand. The best way to measure this would be sensors on your wheels while riding, but this side of Jeff winning the lottery, that's not happening.
Third, how effected is this weight distribution by a little movement front or back? Does a small shift of your hips overly weight the front or back? The amount of change based on a small movement will be based on your overall weight, where you carry that weight and the size of the bike in proportion to these things. EG, a longer bike will be less impacted by a rider's shift in weight and/or you'll have to move further to get things to change.
Okay, so those are the three variables we're really looking at here. We could add angles to this, namely head angle, along with offset and stack to really start to dial this thing in (see also: Vorsprung) but for the most part I think we are learning 63-65 deg headtube angles work best. I think we're also learning 35-45mm offset works best. I post that here because those two variables are "working variables" in that they can be changed after buying the bike. Angleset, different CSUs etc. My hope is we can get bikes to a point where the weight distribution is damn near nailed, and stem height, offset, HTA etc is all at the "bike tuner's" digression to get the ultimate bike fit for a rider. Unfortunately, at the moment, those "fit tools" are a knife in a gun fight when getting a lot of taller riders to properly fit their bike, which is where all this ranting and raving started from in the first place.
I'm to the point where I've drawn up some seat stays that'll work on a sentinel. They'll increase the CSs to 465mm while keeping BB, HTA, STA all constant. It will increase my travel to ~150mm and increase overall leverage ratio to around ~2.6 (from ~2.4). Obviously would be aluminium. See if it works!
Yet again, I go back to moto. There is adjustment for the rider (offset and obviously where the wheel is in the swingarm), but motos come in one size, for a big reason. They don't want to upset the balance of the motorcycle.
This balance is what I'm asking mountain bike companies to pay more attention to.
I think one thing I keep aiming for that may not "apply to all" is I'm looking for outright speed. Cornering, straight line, all of it.
Just like certain skiers center mount their skis to be more fun in the park, so too will mountain bikers go to super short CSs to be more cutty-friendly in situations where speed is less the game and fun more the game.
How are you going about this project?
Another way to say it maybe is that the neutral zone is so small on an unbalanced bike so when reacting to terrain at speed it's really easy for that balance to get upset and then the rider has to react super quickly or lay on the brakes. As has been said that's fine if jibbing around but for a enduro race bike that is antithetical to the purpose.
Specialized Stumpjumper Evo is another candidate I think too. In S3 size, 475mm reach, 1252 WB, 443CS, 63.5 HA.
Was thinking of the L or XL Scott Ransom or L SB150 but both do not have the geo balance as nailed.
I rode a XL Spec Enduro 29 last year with 44mm offset fork and 50 mm stem and although it felt good at speed it did not have a big neutral zone and for sure my race results suffered as compared to two years ago on a short L SB5.5c. Trying to avoid investing a season on a bike that is compromised for racing.
@Jeff/JFL: I'll tell you ahead of time that 50:50 is cruiser bike territory. Current examples of it include entry level 29er HTs in smaller sizes, on the compact end of the spectrum, and emtbs on the scaled up end of the spectrum. Enduro bikes are closer to 60:40 (more weight on the rear).
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