Custom gravel bike - chainstay length, opinions wanted!

[sparky33]

Originally Posted by dmitrik4

Agreed; 425 vs 430 doesn’t seem worth worrying about, but the 50mm tire clearance vs 45 presents a lot more options.

Get the chain stay length that offers good clearance.

I’ve owned several Firefly’s with varying cs length (420-440). They all had great power transfer and handling. The only regret I ever had was cheating chainstay length a bit short and finding that the largest tire was tight at the seattube.

Their yoke and 1” cstays are all business at any reasonable length.

[KonaSS]

Put me in the camp of get the tire clearance you need, and ask Firefly to do their job in making sure the bike rides how you want.

[wallymann]

IME 42.5 is more allroad/cross biased...43.0 and up is more gravely/adventury.

my gravel riding is more road-biased:
- gravel bike #1 had 42.5 stays, which i loved
- gravel bike #2 has 43.5 stays and its OK
- would rather the shorter #1 stay length for the snappier handling for my riding

+10mm CS there is a difference in handling. +5mm maybe less noticeable.

Originally Posted by solographik

Hey - looking for some collective wisdom from the PL folks.

My turn in the firefly queue is coming up soon, and we're finalizing the geometry. The bike is meant to be a nimble gravel/adventure bike -- something that won't feel out of place at a cross race but still comfortable enough to take on longer multi-day off road adventures.

The default spec is a 425mm chainstay w/ 45mm of measured tire clearance (700c). I have the option of a 430mm chainstay to increase the measured tire clearance to 50mm.

Will the rear end be noticeably more sluggish with a 5mm longer chainstay? My initial thought was that the increased tire clearance would open up a lot more options for tires (in the 47-48mm range) that would help keeps more plush on longer rides, though I don't expect to run things bigger than a 42-45mm normally.

I know that I'm really splitting hairs at this point but just wanted a bit of help putting my mind at ease. Thank you!

[vespasianus]

Originally Posted by mstateglfr

I have 430mm chainstays on my gravel bike and have yet to come upon a time where I raised my fist in the air and cursed the gods for not giving me 425mm chainstays.

72.5deg hta, 50mm fork offset, 44mm actual width tires = 60mm trail. <--- just other geometry that might allow that 'mutumbo-esque' 430mm chainstay design to still make the bike feel fun.

Agree 100%. My belief is that the feeling of a lively and agile bike comes from the head angle and overall wheelbase - as opposed to just the CS length.

[Pinned]

Have you asked Firefly their thoughts on this from a handling perspective? It's not hard to make a bike with 430mm chainstays feel snappy - they'll be able to build what you want.

Personally, I have no interest in bikes with super short rear ends - but there is also someone here looking to do things like offset seat tubes and such to shorten the chainstays. These are all opinions but none of them are truly valuable to your pursuit. Firefly will surely alter things to suit - such as the BB drop, front center length, STA, etc so your weight balance and the bike's handling are aligned for your riding regardless of the CS length you're choosing. 5mm is not a huge difference in CS length considering it is unlikely to be altered without other considerations.

[boomforeal]

I can’t imagine buying a production bike without knowing what geometry I wanted. Going into a custom Ti build with such questions unanswered seems unwise. No amount of hmming or online advice will answer this question effectively. You’re just as likely to get lucky as you are to be unsatisfied with your choice. Or suffer from fomo on the path not taken: “it rides great, but I can’t help but wonder if I’d like it even more with…”. You might consider dropping back in the queue a few spots and demoing some bikes to get a better sense of what you want.

[lavistaa]

Originally Posted by vespasianus

I have 437 mm chain stays and love it. Long stays, but with road bike angles is a great setup in my mind and gets you that nimble gravel/adventure bike you want.

I think the same, even 10mm of chainstay is unlikely to be a big deal when you have over 400mm already. Chainstay changes impact handling over obstacles (a bit) and cornering when you're walking but not so much on the road unless we're talking large (like 20mm) amounts and even then....

Head angle though- I've seen references to a few bikes in this thread with HTA of 70 and 71 degrees. Unless they are very small bikes with relatively narrow tires bikes like this will have trails in mid to high 70s so definitely not feeling like a road bike with that much flop, esp on wider tires. It would be felt mostly on the initial bits of a turn, when riding uphill (esp slowly) and standing. If you want road bike feel you gotta aim for trail in the high 50s to mid 60s if you are running 30mm or wider tyres.

[Pastashop]

First: Terrain, weight, power. Tire second. Then balance (including location of extra load). The frame dimensions flow from there.

[weisan]

Originally Posted by Pastashop

First: Terrain, weight, power. Tire second. Then balance (including location of extra load). The frame dimensions flow from there.

- Pai Mei's five point palm exploding heart technique

[benisfroms]

The difference of 5mm in chainstay length is subtle and whether it will be “noticeably more sluggish” can depend on several factors, including the type of terrain you’re riding on and your personal riding style. Civil 3D 2023 subscription discount. For most riders, the difference in handling is minimal, but the increased tire clearance could indeed offer more versatility for tire choices and potentially more comfort for long rides.

[kingpin75s]

When it comes to CS length, I only have strong opinions and a limited range of what is acceptable, when it comes to mountain bikes and tight single track. Since that is not generally a consideration for gravel, it comes down to personal preference.

Get what you need to clear the tire you want to run and from there its whether you want more stability/cush or more agility/snap in the rear. There is no right answer, only the right answer for your own preferences.

[kanjielee123]

Originally Posted by polyhistoric

I have a Seven Evergreen with modified CX/gravel geo - pretty old, 2014. ai face anonymizer Clearance is limited to 40 in the back, but runs 442 cs with a 7cm drop. Front end is pretty traditional with a 71.5 headtube angle and 47mm rake fork. Kobilabs I don't notice the cs as any limitation on any road or flat gravel. In a CX race or tight, twisty singletrack it definitely slows down the handling with the extra wheelbade - it doesn't want to pivot. On a rocky, rutted loose and fast downhill, it bombs and is so stable (overconfidence).

I would say it depend on your riding needs and desired trait. Ask Kevin at FF, I bet he has some right answers on the question.

Your Seven Evergreen setup sounds like it's tailored for versatility!

[litcrazy]

I'm considering a Waltly option for a ATB leaning, custom gravel bike with a shorter reach, higher stack and massive tire clearance.

I just rode the White Rim in a day, and took my rigid Chumba, since my BMC Road+ only fits a 48-52mm tire in back if I want any clearance. I live in Albuquerque and so for much of the gravel I ride, 27.5"/2.25-2.35 would be ideal with an option for 2.6."

As I shorten the front, I'm inclined to lengthen the back in order to keep more balance and keep more weight on the front wheel. I'm 6'2", so I'm going the other direction of many and looking at 455mm chainstays. It feels proportional to my frame size, and with a 72 seat angle, 70 head angle and 590 top tube, longer stays would work to keep the same front/rear proportion many builders like.

I'll ride my cross bike that fits 38mm tires when I want to feel frisky and ride this for chunky gravel rides. I find the pneumatic trail of a big tire (57mm in front) already, renders the front rather lethargic on pavement, even with the low trail of my Road+...

I have long femurs and like about a 10cm setback saddle nose to bottom bracket, so short chainstays means I don't feel in the bike as folks like to say. I borrowed son's Kona Big Honzo with 415mm chainstays and a 3" rear tire for some out of character for my steep mountain trail this weekend. It felt great on downhills with it's long, slackish front but my weight was clearly too far back for climbing. That tucked back would work better, I imagine, if I went all in on adapting to a very steeping seat/seatpost angle, but I don't prefer that for long rides (and long rides are what I prefer).

Even on road, I have a 1981 Trek 710 with 440mm chainstays and 32mm tires, and I'm always surprised how well it rides. It's not as quick as my Seven with 415mm chainstays and .5 steeper head angle, but it's no slouch. But I don't race or ride in packs, so my baseline agility preferences might be different (though I've ridden many a road bike with a 74 degree head angle).

Besides losing agility, is there something else I'm missing in this geometry equation? Riding the Kona felt like it only confirmed my inclinations (as kind of a limit case in the other direction).