Custom gravel bike - chainstay length, opinions wanted!

[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!

[truth]

I don't think I'd notice 5 mm on a chainstay, but I'd definitely notice it in a tire. Go for it!

[dmitrik4]

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

[EB]

I would definitely go longer, but I'm clearly pretty biased as my gravel rig has 452mm chainstays.

[Hilltopperny]

Longer stays help smooth the ride out and give stability down hill. They may feel a touch less snappy, but not drastically so.

[prototoast]

I personally have a strong preference for short chainstays on gravel bikes for all-around handling, and would go with that option. But if you need 50mm tires, that can be an overriding concern, and 5mm is not the end of the world.

[jdp211]

My gravel bike has 450 chainstays and its mega stable, but I definitely struggle getting it turned in tight spaces. Were I to have it made all over again, I'd probably have specced something shorter like 435 or 430, especially knowing I could keep the same clearances.

I guess its important to note, my bike is 650b

[NHAero]

If I wanted 50mm tires I'd spec the bike with 650B. That's what I did on my Bingham, which will accept 650Bx48. My Habanero has 440mm stays, the Bingham 425mm. I prefer the Bingham's handling but that's a result more of the front end geo than the chainstay length IMO.

[tellyho]

I could go either way on longer stays - they definitely make a difference in overall comfort and especially downhill, but they definitely make it harder to get the front wheel up and over things. I suspect many don't treat their gravel bikes as rigid 29ers like I do, but "gravel" in the suburban Boston region = singletrack + busy roads

[solographik]

Originally Posted by NHAero

If I wanted 50mm tires I'd spec the bike with 650B. That's what I did on my Bingham, which will accept 650Bx48. My Habanero has 440mm stays, the Bingham 425mm. I prefer the Bingham's handling but that's a result more of the front end geo than the chainstay length IMO.

Funnily enough, the clearance w/ 650bs does not change w/ chainstay length (i think due to how the rest of the rear triangle is set up. It'll clear 650x53mm with either a 425mm or 430mm stay.

I do have a set of nice 650bs but i think i see myself using the 700s more...I guess the other way to think about it is if i do need the extra clearance, to just run the 650s...argh!

[Wunder]

Originally Posted by solographik

Funnily enough, the clearance w/ 650bs does not change w/ chainstay length (i think due to how the rest of the rear triangle is set up. It'll clear 650x53mm with either a 425mm or 430mm stay.

I do have a set of nice 650bs but i think i see myself using the 700s more...I guess the other way to think about it is if i do need the extra clearance, to just run the 650s...argh!

The 650 clearance doesn't change with chainstay length because it is determined by the width of the stays which doesn't change. The Cervelo Aspero for example will do a 650x47 or so and 700x40 with only 420mm stays. I'd er shorter and tighter personally. In theory a 650 wheel should also be more nimble and handle correclty if using monster tires (total inflated wheel diameter about the same).

[pwgoode]

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.

I would second this. Plus the additional tire clearance in addition to giving you more tire options would also provide some additional clearance in a muddy cross or gravel race.

[Alistair]

I have two "gravel" bikes, a Trek Checkpoint SL7 and an All-City Nature Boy ACE.

https://geometrygeeks.bike/compare/t...c-e-2020-49cm/

The Trek has a 10mm longer CS and 20mm longer WB. It's noticeable less "snappy" on pavement (most noticeable on fast group rides). But also more stable on chunky descents.

Would I notice a 10mm longer CS on its own? Probably not. But, if the reach/front center are also lengthened, it could be noticeable. I use the Nature Boy as my primary road bike, but if I didn't have it, the Trek would be fine for road rides.

And, if I were having a gravel bike built today, 50mm tires would be a must-have (neither of mine are rated that wide, the Trek will probably clear them ok, the Naure Boy absolutely will NOT clear a 50).

[rothwem]

Man, personally, I'd be trying to figure out how they could get it down to 420 or less, maybe with a seat tube bend? For drop bars, shorter is better since so much weight is forward already. My previous gen Crux is 425 and it handles well on gravel, but every now and then I wonder if it would be better if the rear end were just a smidge shorter. It still feels a little long in certain circumstances like road group rides (yeah, not really what its made for) and weirdly, tight cyclocross chicanes (which it is kinda made for).

As for clearance, this is really personal, but I think 45 is all I think I'd really need. My current frame only has room for 40's and its fine, but I'd like to be able to fit 42s because it seems like a lot of good gravel tires are made in that size and I love having access to a big selection of tires.

[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.