BBs, chainstays and tire clearence

[Yonas]

I’d really like to see this one finished. Track frame?

[Swood]

Swood's Goods: A Build Log

Avast ye landlubbers! I’ll post some build photos here while I drink coffee in the mornings, starting with ‘Chingona’! In collaboration with Wren Sports (and a number of other industry contributors), this frame was built and donated for an athlete who was a member of last year’s Ride for Racial Justice cohort. Ride for racial justice is a 503c non profit which exists to ensure access to resources, education, and community for Black, Indigenous and People of Color cyclists. The cohort would go …

[Daniel_Y]

@Yonas

This is amazing! Thanks for helping a novice out like this, much appreciated.

The T47 upgrade could do the trick it seems and I can get the Zona CSs.

No problem. Just be careful, the chainstays or dropouts might not match up to the published specs. The CAD can get you 90% there, but you will still want to make sure things make sense IRL.

[Alex]

Another option if you want shorter stays is to run 650B wheels. This also will reduce TCO, which can be a problem with many geometries that will fit 45-622 wheels. The first bike that I built fits 55-584 tires with 435mm chainstays and an eccentric bottom bracket. I used single bend chainstays.

I built a second similar frame that is S&S coupled and that bike has 26/559 wheels. It fits 65mm tires with 435 chainstays.

[jimg]

I am trying to figure out if the chainstays I’ve selected will work for my frame design. My “client” (er, my friend) wants the following:

• 473.5mm chainstays
• 68mm BB shell
• Clearance for a 40/30/22T MTB triple crank like a Shimano Deore
• Clearance for a 29x2.35in tire
• 135mm OLD rear QR axle

The chainstays I sourced are Nova’s “CrMo Cyclo-X S-Bend Chain Stay 24mm - 8/6 - 425mm” mainly because they were the only thing I could find that were long enough. Laying things out on my drawing, I’m not confident the parts will fit together and give me the clearance I need – can anyone offer a sanity check and/or advice?

Thanks!!!
-Jim G

[Flav-CCW]

IMO it depends on what tire clearance you’re confortable with. I always use the worst case scenario on my drawing ( biggest tire I’d like to fit measured on the rim+ a couple mm) chainline is consistent.

Here it looks like you have a good tire clearance, maybe add a light dimple on the stay for the inner chainring and you’re good to go.

[jimg]

Thanks for that confirmation – that’s what I was thinking as well.

-Jim G

[Daniel_Y]

Unless I am missing something, it looks pretty straightforward to clear with a single bend. You are in the bay, right? Nick and I would be happy to bend you a set.

These were the parameters I punched in:

• 40-30-22 Shimano MT500-3 crankset (50mm chainline)
• 29x2.4 tire (750mm diameter)
• If you dimple the stay, you can get a bit more tire clearance for oopsies and mud

Do you mean 73mm BB? That makes more sense with your MTB crank, unless you are trying to do something different with the crankset.

[jimg]

OK I think I just realized my mistake. The chainstays I ordered are “S-Bend” and there is a difference between S-bend and Triple-bend. To wit, these are S-bend chainstays:

And these are Triple-bend chainstays:

Note how in the first photo, the left end of the chain stay (e.g. the BB end) curves UP, while in the second photo, the left end of the chain stay curves DOWN. This is because (as is probably obvious by now) Triple-bend stays have a third bend, whereas S-bend stays only have two bends. I think I really need Triple-bend stays, not S-bend. Duh/Oops.

Thanks!
-Jim G

[jimg]

Ok I got some triple bend chainstays in - these look better to me…

-Jim G

[Frederiksoelver]

Hi @Daniel_Y,
This might be a stupid question, but where do you find information for the crank arms “inside” Q-factor and the chain line for both chainrings on a 2x crankset?

[Duanedr]

Sram is very friendly and puts theirs frame fit documents out on their site. Shimano is a little less free with their docs. They are floating around but are harder to get directly from Shimano.

Manuals & Documents | Service | SRAM

[Daniel_Y]

not a dumb question! Most people don’t check…

@Duanedr posted the SRAM specs.

More specifically, Page 34 on the Road Frame Specs:

2023-road-frame-fit-specifications.pdf

Here are another frame component manufacturer’s road specifications. Their specs are more conservative, so I usually design around that:

Crank_ROAD.pdf (2.2 MB)

Let me know if you need the MTB doccumentations

[Frederiksoelver]

Thanks for showing me the documents. Really appreciate it!

[Frederiksoelver]

Hi Daniel,
I got another question for your Fusion360 chainstay clearance sketch: Is the sketch around the tire (Ø45mm x R356mm) meant for illustrating tire knobs or mudguards?

[Daniel_Y]

The tire body I draw is the tire with knobs + 6mm of clearance. 6mm min clearance is recommended for offroad bikes. 4mm for road bikes.

I don’t design for mudguards (un)fortunately!

Tire clearance is very difficult. People focus on width, but I have found the variance in diameter and knob location can easily be +/-5mm. Throw in different rim widths, pressure, hookless, hooked, etc… and tires are all over the place

Some manufacturers give drawings, but they are typically +/-5mm:

[Spencermon]

and maybe a little out of date. That’s a 23mm internal rim and I don’t even have gravel rims that narrow anymore.