Totally. Climbing is probably my favourite part of cycling. I’m doing a tour in Sept 2023 through the lower Austrian Alps and the Julian Alps. Three Everest’s worth of climbing. I’m making two gravel bikes with 68HTA / 75STA almost specifically for these 3+ hour climbs, and 1+ hour descents. My local climbs max out at about 1h30min of sustained climbing time, so I think they’ll be happy locally as well. The mountains and climbs around me are old Volcanoes.
I find on these long climbs the steep STA and a broken in Brooks saddle to be just perfect.
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As someone who currently rides a 90s mtb and is really interested in trying modern geometry i’m really curious what adjectives you’d use to describe bikes with a long front center. PVD stresses the benefits of a long FC in pretty much any aplication, and i’m wondering how the logic of low and long applies to smooth roads or if it is a compromise for perfomance in the dirt?
I have a new theory on long front center/slack bikes. I switch between two 790 and 760mm front-center mountain bikes. I think long front-center bikes require more rider input to keep the bike tracking (even on smooth roads) because they have less weight on their front wheel and less precise steering response. I find that I have to have my arms and core engaged at all times, which leads to more fatigue.
This is fine on short rides or on local trails where I’ve memorized every root and rock location. However, I notice the fatigue most riding new trails bind. I don’t know the best line and make mistakes, so I have to constantly adjust and react. It’s a lot of physical and mental fatigue that adds up.
Contrast that to my road or track bike, I can turn the bars a fraction of a degree and the bike will follow. IMO, front center really only helps with technical descending. So for road and gravel bikes, energy conservation and efficiency matters more.
I think the energy and mental cost of long front centers is hard to quantify, varies from person to person, and is impossible to measure. Anecdotally I think there is a difference, but I am curious to hear other people’s experiences who have tried both.
I know @wzrd rides both styles and has some pretty gnarly terrain. Maybe they can comment?
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What you are describing there is 100% a bike with a high FC:RC ratio. That is how my 3rd bike rides exactly. Its got a 390mm rear centre and 859mm front centre so its pretty extreme. If you are tired its a pig of a thing because you are likely to lose the front wheel.
If you extend the chainstay length you make it much easier to weight the front wheel, even with a long front centre.
I would describe a bike with a long front centre and short rear centre as having a strong rear traction bias, you need to work to maintain front end grip. Some people like to call it playful, but I would disagree. It depends on how you like to play. If you are into manuals and whips the short rear centre helps, so that might be considered playful. But if you like to slide the rear end around it doesn’t really work, way too much rear end traction. Try to force it and you will end up taco’ing wheels! It is great for hooking the rear into tight corners. Its not for me, but I can see the appeal in it.
With a long front centre and long rear center things become a lot more drifty at the limits which is what I like. Going “fast”* feels easier to me, less effort to manage front traction. Wheelbase starts getting pretty long. My long hardtail has 1314mm wheelbase. The upshot is that when the bike starts sliding you have longer to do something about it. The downside of the bike getting very long is that it gets hard to wheelie/manual/whip. I can get it up on the rear wheel but its a struggle.
For reference the 2 bikes I am describing have 1:2.2 and 1:1.75 front centre to rear centre ratios. I would describe 1:1.75 as neutral front to rear ratio for me. I have a few bikes on my ride diary near that ratio and they all feel pretty neutral. I have a couple of bikes around 1:1.66 in my diary and they have a front traction bias meaning they tend to slide in the rear before the front.
*my version of fast, probably not very fast. Also subjective fast, I don’t time so I don’t know if one type of bike is faster than the other. I don’t care about that! I just want to make bikes handle how I want.
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The FC difference on my two mtbs is quite stark - 735 on the xc bike and 880 on the enduro. The chainstays are also scaled to the difference - 435 xc, 450 enduro.
The enduro bike feels amazing on steep trails. You can ride the ever loving shit out of the fork over everything and pretty much never have that ‘going over the bars’ feeling. The only thing holding you back is the strength of the rear wheel. The wheelbase also means you can (slowly) climb walls, I am always surprised what it can monster truck up. That being said - it sucks on low angle and flat trails. It’s almost hard to ride on pavement- like @Daniel_Y said it takes a lot of input on flat stuff.
This bike is on the extreme side with a 61° hta, 505 reach, 50mm stem, 140mm travel and the previously mentioned 450 chainstays. I call it the NAAR - Not An All Rounder.
Most of the bikes I build for customers sit between my xc bike and enduro bike.
For a ‘large’ customer bike I’d aim for a 810ish front center, and a 64°ish hta, with a 120mm. I spec them with short forks to keep the FC in control while still having the confidence of a slack head tube angle. Thoroughly modern, but can be ridden more comfortably on more terrain.
Most of my mtbs end up within BC, which is worth mentioning since even a 810 FC bike would feel long in a flatter area.
Elevation profile of a recent NAAR ride -
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For reference, and to be pedantic, to get your ratio math you’re just doing:
FC / RC = num : 1 ?
Now that I look at it its probably rc:fc hahaha. Its FC/RC= I think I have just been writing it backwards
*fixed now!
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Thanks! Just wanted to clarify in case anyone was feeling tired and having trouble with maths… it’s not me… I promise…
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This comment is insanely interesting to me. A 610mm FC on a hardtail with a 64 degree head tube angle and 120mm fork? I’m sorry Em, but I may build something like that in the near future just so I can know what that feels like.
610 was a typo haha, 810 is what I aim for.
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I don’t yet have my design process nailed down into a fixed protocol where I could point to driving dimensions. I’m tall (6’4.5" / 194cm) and focused on geo for taller riders, so my initial designing focused on righting obvious wrongs like too short chainstays, stack, reach and cranks.
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In my ideal dream process, it would all begin with an evaluation of how your body moves. I spent a number of years doing crossfit (yeah yeah) and by far the best takeaway was how to properly engage my posterior chain while doing compound movements like squating, cleaning, and snatching. ‘use your legs to lift’ while keeping your back upright turns out to be wrong. I think crank length, seat tube angle, and torso angle can either lead you to having good engagement of the hamstrings while pedaling and appropriate use of range of motion, or being quad dominant, getting knee pain and using too little range of motion. Aside from building an elaborate fitting machine, one idea is to check a person’s movement of their knees, arse, and torso as they do a proper unloaded squat with hamstrings engaged to a depth that simulates pedaling. Their hands will be held out in front of them at handlebar-ish width to counter balance and their weight will be kept even between the ball and heel of the feet. Because they don’t fall forward of backward while doing this, their weight is balanced and some conclusions can be drawn about how to fit them.
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I like @Daniel_Y 's ratio, but first I need the rear length. How is the person going to use the bike? Do they want to ride all day in comfort, or compromise on comfort for marginal performance gains? I lean towards comfort so that to me means a more upright riding position. I’d say right now, after settling on the crank length, STA and horizontal arse-to-hand distance, I turn my attention to the rear of the bike, i.e. how does the bike feel to wheelie? It should have a nice balanced sweet spot and also not get all unweighted and wild when climbing.
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After figuring out the chainstay length, I want the front and rear wheel weight distribution to feel right, which means having a decently long front center, but not so long as to unweight the front tire while seated and maneuvering on loose stuff. I think looking at the above mentioned ratio could help as a rule of thumb for that, but I’d also need to take into account intuition about how the bike will be used a well.
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I feel like having a rigid vs suspension fork is another important consideration in the design, given that changing the HTA changes the ratio of horizontal to vertical movement of the wheel. My sense is that a slacker HTA and longer front center is needed on hardtails vs the equivalent rigid design.
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The secret is not long, low and slack. It’s long, moderate and moderate. For example, I’m 5’10" and use a 485 reach with a 66 (trail) or 65 (enduro) deg HA and bars at about same height as saddle. Any less HA than that and wheel flop becomes an issue especially on flatter terrain or climbing steep trails. Where as with a longer FC and moderate HA you get the benefits of a more stable wheel base without the draw backs of a slack head angle and your center of gravity is further behind the steering axis, which in very steep terrain makes for a more confident bike. In my opinion.
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We finally made it to roughly the same head angles as dirtbikes (ie, 62-64 or so)! They do run less fork offset, though.
They run their hands a bit behind the steering axis but we’ve been moving that direction as well.
It’ll be interesting to see if we stop around where we’re at (bikes haven’t been getting longer or slacker for a few years now) or not. Dirtbikes have been pretty stable for a while, they’re not much different in terms of geometry than they were when I was racing/riding them 20 years ago. My clapped out KDX200 from the mid 90s was a 63.5 head angle, for example.
I would not be too surprised (and would like) to see lower offset forks become a thing, but I’ve been wrong too many times about where the bike industry is headed to believe myself.
-Walt
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I think having set offsets from the fork manufacturers kind of limits the experimenst we can do. I’m fairly settled on my recipe but it also suits the way I ride and the local terrain. It’s seems to gel with riders better than me than go a hell of a lot faster. Like road bikes, there is a little sweet spot that mtbs operate well in and I think most of us are getting it fairly right for what they are building.
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That’s all well and good but it’s what everyone was telling themselves in the 90s, too, when everything was 71/73. I was one of the fastest people back then in both XC and gravity stuff and I certainly had no particular inkling that longer/slacker was better. As a framebuilder at the end of my racing career I was thinking harder about that stuff but what I (and everyone else) ended up doing was 72 HTA 29ers for quite a while.
Point being I’m not so sure we’ve “arrived” just because things have stabilized for a short while.
-Walt
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I do purely because a lot of the designers are pulling back from the 64/63 HA for trail bikes as an example and most DH bikes are parked at 63 degrees. I think its also discipline specific. A DH bike is not going to be anywhere near what an XC bike is, which is nothing like a road bike. When I ride my old xc bike from mid 90s (actually don’t have it anymore as about a year ago) it was nowhere near as capable or as fast over a xc loop than my 130mm trail bike.
Funnily though, I rode much more technical trails back then than what is available now ( the glow teail and modern mtb riding in Australia has killed tech riding) on my okd 26" full rigid DB Axis Pro without a dropper super narrow bars and cantis. Lol
This is purely my experience though and having dabbled with a few different setups now, there is a point where too long, too low and too slack is a thing. 
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Just off the top of my head, stuff that imo should happen:
-Much shorter cranks and bikes designed around them.
-Longer chainstays for almost everything and more relaxed seat angles to go with, or at least some actual logic behind picking seat angles for good biomechanics.
-32” wheels for a lot of riders for xc and road/gravel.
There’s still a lot of experimenting to do.
-Walt
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I agree with the cranks and chsinstays. Im a forward position advocate. Even the road bokes Im building have steeper seat tubes bevause the riders are positioned differently now. Im struggling to see real world benefits of 32" wheels otger than better roll over. Road bikes don’t need it, gravel and xc could but it only would suit the taller half of riders. But thats the great thing about all this. We can all bring different things to the table to appeal to different riders and none of it is wrong when people are smiling while riding their bikes.
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Interesting, why much shorter cranks? Is this from a bicycle geometry perspective, or a biomechanics perspective? How long would you personally use?
Are we talking proportional, or just all cranks should be much shorter for everyone?
Personally, I’ve got long legs and had 170s on two new bikes in a row and greatly disliked them. Went with 180s and they feel much better regarding utilizing adequate range of motion. But I’m well above normal height, so I could certainly see wanting significantly shorter cranks than what’s commonly available for short people.
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