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Appreciate the response back! As i feared, all would be smaller sizes. It is a struggle for myself with the preferences I have and being 6'2" on XLs.
Very challenging to find much even close to 1.8.
So I just picked up a xl transition spire, with a ratio of 1.9 or so. It corners great, and I couldn’t quite figure out why until I thought about skiing- having that longer reach and fairly long rear end gave me a larger sweet spot to maneuver around in. On flat corners and steep sharp corners it felt easier to move around and get my body weight to the spot where I could hit the most traction.
I'm also 6'2" on a Spire with Large front triangle, XL chainstay (452mm). I thought I had a pretty good balance with it, but nowhere close to 1.7! 1.86.
Also anecdotal, but adding the 6mm from the Large CS to the XL was a major noticeable improvement for all the reasons stated above. I can ride more neutral from the middle of the bike and it's much more intuitive and safer feeling and makes it so I feel more confident cornering aggressively because I trust the front wheel. I also have an XL Spur (1.88 ratio) and have a blast riding it, but I notice I have to consciously be more forward and active and it's a bit scarier trusting the front wheel. Also interesting point about clips. I switched from flats a couple summers ago and it was a huge benefit from a body position perspective (could get forward more), especially on the Spur.
Wild! I’m 6’0.5” and the reach and effective top tube just felt great to me (coming from a 2018 sentinel with a 475 reach). I do love the long chainstays, but a 485 reach feels too cramped for me. I do have a positive ape index, so maybe that changes things.
With the caveat that this is all dynamic and everyone is different, one element I (think) I noticed, was that the longer rear end let's me ride more upright/middle/neutral, so the shorter reach doesn't feel as "short".
Ha, that's funny, that was my previous bike too. Then I was on the stock Spire large before going with the XL chainstay.
I can see that. It’s counterintuitive to me, but I think the longer rear end is helping me jump higher too. Maybe just a new bike placebo effect though.
What does bother me is the inconsistency between manufacturers sizing recommendations. I found this between the specialized enduro and the spire- very very similar geometry, but different size range recommendations
more than just rear centre effects weight bias, especially suspension and things like stem length(and Growing rear centres based on suspension platform)
I agree with that. Excluding growing rear centres from higher pivots though would you agree all of those other factors will also pull your torso forward? I think that’s what distinguishes the long RC from the short RC crowd it’s the willingness to have a forward lowered torso compared to being more upright and on the feet.
The mix match is rad! Glad you were able to dial in your ride a bit further!
My trail bike I believe is 1.84 and DH 1.85. I do agree that they are enjoyable to ride but it does leave me wondering after these awesome changes from Bronson and V10.6... that stretching the rear more is a better ride at least for me. That makes me really want to try something even closer to 1.8 even into the 1.7s if possible. It's an exciting thought! Ive been considering mating a XL rear to L front Raaw Madonna V3 for a 1.82 ratio.
Bringing stack into it is also good to think about like you mentioned in a different post. I agree. The more neutral and upright position makes it feel not as cramped. A major win. It's all a tough balance to strike because I don't want an absurd wheelbase trail bike either. Lots of these XLs are freaking bigger than my XL 29 V10 which is insane! So its fun/frustrating/exciting/etc to think about!
I would like to try clips. Never had the balls to stick with and go for the change yet as Ive spent my whole life, racing, and everything on flats. Maybe I will give it a go..
Its awesome you have two bikes similarishhhhh enough to put numbers to the feelings and draw some thoughts about it.
well, lets say you and a friend have the same bike an height, weigh the same aswell.(these numbers are a bit out there but example)
he has 90psi in his fork and 240 psi in shock - he has more LSC
you have 80psi in your fork and 260 in the shock - you have less LSC
the weight bias of your friends bike will be more rearward and its not just by a little bit, that makes a massive difference to how much the bike squats and holds the front up. - what about deep travel with valume spacers? you may see 90% travel with 1 spacer and he may bottom it out.
This is why dynamic ride height is so important (where the BB and CG is under correctly working conditions)
Downhill bikes are naturally made with downhill descent angle in mind ie standing up more when the bike is pointed down.
vs a trail bike/enduro bike that you want to be able to achieve both, if you watch enduro racers they get right over the front and whip the rear end around corners.
SAG does not tell you much since you set sag with no compression etc AND everyone tends to sit/stand differently its purely a starting point.
stem length doesn't affect weight bias, only the ability to weight your hands, which isn't the weight bias everyone is talking about, were discussing the distribution of weight from the feet through the BB to front and rear wheels.
Same, I'd love to be able to experiment more and find the limit for me on the ratio and wheelbase! If TR made a 460, 465, 470 rear end I could bolt on I would 100% try them.
It sure does effect it, not static but dynamically it does. CG. Weighting feet is moving CG.
We are here arguing about rear centre and Weight bias but theres to many other factors to just limit it to a static rear centre lol.
Brands use computer that run simulations on all this for a reason, they dont just slap long or short rear centres on and say "DONE, SELL IT".
It's all a piece of the puzzle and why MTB geo and suspension changes so much.
"Weighting feet is moving centre of gravity"
Huh?
Even dynamically stem length doesn't affect how your feet distribute weight through the tyres, yes you can take weight off your feet, but that doesn't change the split of F/R distribution from your feet, just the total loading at the F/R tyres.
Everyone is discussing static weight bias on flat ground, for obvious simplification purposes, its too complex to break down multiple different bikes, at sag, with different stack heights etc etc.
Yeah the weight bias will be more forward with a softer fork and stiffer rear but wouldn’t that be because the stiffer rear pushes you up and forward and the softer fork pulls you back down and forwards? Personally I’m not a fan of tuning suspension to achieve a certain weight bias and I’d rather have it setup for the terrain and pitch as the former seems to lead to an unbalanced feel.
If we aint discussing this seriously why even bother?🤷♂️
Banshee Titan frames are going for cheap right now, a large gets you to a 1.77 ratio with the long dropouts. Maybe worth trying for someone really wanting to experiment. Seatpost insertion isn't great, but that's my only complaint with mine
I think this is a pretty interesting point, although dynamic ride height is very challenging to discuss/compare without some numbers from a DAQ system, because like you said SAG doesn’t give the full picture.
I remember discussing this to some extent with Craig at Avalanche Suspension when working through my fork tune. He commented on the fact that he would be aiming for 25% static sag, but dynamically it would ride higher than I was use to, and recommended against bumping up my fork travel an extra 10mm (as I wanted to) until I’d tried the setup first, for fear that the extra 10mm on top of the higher dynamic ride height may cause me to push the front wheel in corners. Having previously run forks on the firmer end of things, I was a little skeptical, but after being on the fork for a year, I can confirm he was right.
People will come on here debating f/r ratios and best cs lengths, reach etc without talking at all about cleat / foot position.
The preference that a rider has for a particular foot position hugely affects f/r weighting. And two riders on the same bike with the same proportions will have very different experiences if they run 5mm different cleat positions.
Exactly, Theres so much that effects balance on a MTB - I mentioned clips vs flats on anther post explaining that often Clip riders(this is heavily mentioned by Pro's) Will ride more ontop of the pedal or even and inturn will weight the front more - purely because flat pedals you have to remind yourself and/or naturally drop the heels.
I believe Dak mentioned this in a video at sea otter when discussing high bars.....
for the sake of serious discussion: just Whacking on a long rear centre isnt the answer or cure to balance without understanding everything that plays a dynamic role in Balance.
we all know that bike-body system dynamics are complicated and heavily coupled in a myriad of ways, and that there are major simplifications that need to be made to compare geometry meaningfully (flat ground, static or at sag, rider in attack position, etc). sure, foot position and suspension design & setup affect F/R bias. but if we don't take an "all else equal" approach to talking about geometry, why even bother?
I generally don't think these assumptions invalidate the discussion, and I'm happy to live with the reality that the conclusions I might draw from reading people's thoughts on this stuff are heavily nuanced. what you and Linc bring up are helpful to keep in mind so we don't give those conclusions too much weight in the grand scheme of things, but nobody is claiming rear center length is the "answer or cure" to anything. I do however think it's an important aspect of modern mountain bike geometry, which is the point of this thread, right?
Long RC is nice for climbing as well. Less prone to wheelies. You can relax your back and sit upright. Better traction and balance going up steep chunk.
Absolutely agree. Fine to note other things, but at the end of the day a change of cs/rear center is impactful. I was able to do this exact thing (change nothing on my bike except cs length) and it had many/all of the impacts people are talking about in the thread.
To people saying that a bike would come too long with your prefered reach if you went with balanced front to rear ratio, you are in my opinion looking at it from wrong angle.
Reach is like the fifth most (least?) important geometry number.
One should always firstly look at wheelbase, followed by f/r center ratio, headangle, bb drop and then stack and reach because they are kinda intertwined (higher stack shorter reach for given wheelbase and vice versa).
Also balanced front to rear ratio is not the same for different sizes and different riding styles as some have already mentioned. Find a ratio you like and then when looking for a new bike just pick one that has simmiliar wheelbase and ratio and it will most likely ride very simmilarly.
Basically for me I started with V3 Meta (1200 wheelbase, 440 stays), went to stumpy evo (1260 wheelbase, 440 stays), after few years of riding that bike I figured I want something that does not require me to ride so much off the front of the bike and something a bit longer than the Meta, and went with Banshee Prime (1225 wheelbase, 450 stays) and damn it feels good. All the wheelbase for stability, with good balance for corners.
bernard doesn't know if he's on a 40 or 45mm stem and he's pretty quick i guess 🤣
I wish more bikes came with reach adj headsets.
I know some brands have launched bikes with ZS56/56 headsets touting reach and angle adjust compatability, but unless you're running a straight steerer, you'd have to run an external lower cup to adjust reach, which negates a lot of the effects. I think one workaround is to intentionally design the bike and geo around extrernal cup to compensate for this but as far as I'm aware, I don't currently know of anyone doing this. Probably a niche use case.
Could it help if instead we start from riding posture? For example, start instead by refining our model of posture like the upright Jackson & Asa stance, the attack Amaury Pierron stance, Finn Iles crouching tiger, etc.
If we thought about our own stance as the starting point then bikes could be properly fit to our measurements and center of mass, including optimizing weight distribution across the wheelbase, FC/RC ratio, stack/reach (including spacers, bar height, etc.) to maximize fore/aft stability and cornering grip? I think WC riders already do it, with custom stack heights, eccentric BBs (Bruni), mm perfect stems, custom chainstays, etc... all fit to the riders' preferred positioning and improve resulting grip and cornering performance.
Otherwise just give us decent standard geo (few sizes fit most approach) and lower prices. In the absence of clear, consolidated geo and sizing my only answer is to demo and see what rides well.
I wonder if limb length correlates in any way to how a bike feels at the different FC/RC ratios.
Someone with long limbs might feel great at a 1.9 ratio because they have space to move around the area that useful body positions often find themselves while someone with short limbs on a bike with a 1.9 ratio might feel uncomfortable as they approach the ends of the useful body position area.
Completely just shit runnin' through my brain rather than any real experiments. My two bikes have been (not on purpose) 1.72 and 1.73 so I don't have any experience in how the different FC/RC ratios feel.
Id be happy to see the return of Straight steerer's assuming we can control the flex/issues with pressfit steerers.
zs56 or even bigger is excellent for adjusting without having a brand having to invest in its own cups.(trek, F U, Making people pay for mullet & adjusting headset pieces)
I disagree, Reach, stack, and effective seat angle are primary for determining how you fit on the bike and the body position you are in. A strong and comfortable body position unlocks your riding. No matter how good the fore aft balance of a bike is, you can't ride to the best of your ability if you are stretched out or cramped. Right now I'm wishing my current bike has about 20mm extra reach, and 15-20 mm extra stack to get me in a comfortable strong riding position while maintaining the same stem length and bar width for steering feel. I could ride my current bike (over forked, over stroked 2023 Norco Sight) better if I had that fit, even without changing the 440mm stay length.
Post a reply to: Modern Geo Talk: Chainstays, Stack, Reach, and Bitching About It