Chainstay Spec

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9/14/2021 3:28 PM

I have an S&M Whammo V2 that I ride @~13” chainstay with a half link chain and a 9t driver. I say “~13” because if I’m riding a 25t it’s a hair shorter, a hair longer with a 28t sprocket.

The published (online) spec of the chainstay is 12.9-13.5; however, when I play around with the 28t dimensions, I can easily slam my rear wheel with 70 half links, which is ~12.75”. On the flip side, if I were to extend my chain by three links technically I would be at ~13.5, but the rear axle would literally be hanging off the drops...not something that I would feel comfortable with from a safety standpoint.

Is this an urgent issue? No, as mentioned before I am pretty comfortable with 13” and don’t plan on changing. But it’s interesting that a spec can have this much variation...anyone else see this kind of spec variation with their geo?

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9/14/2021 4:56 PM
Edited Date/Time: 9/14/2021 4:56 PM

Half chain and adjust . I never even worry about my chainstay length to that miniscule degree you just adjust to a new frame and geometry .

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9/14/2021 5:00 PM

eskimojay wrote:

Half chain and adjust . I never even worry about my chainstay length to that miniscule degree you just adjust to a new frame ...more

TBH, I have been riding this frame for about a year and haven’t even thought about it considering that I hover around 13” anyway. It’s not an issue for me (love this frame) but think that it is odd considering that some buyers make decisions on chainstay length...just seems weird to claim a spec and then have variation that falls out of spec.

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9/14/2021 8:36 PM

Have you actually measured it from spindle to hub or are you just calculating teeth combos? Does 70links at 28/9t actually measure 12.75"?

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I get big airs off small things

9/14/2021 9:35 PM
Edited Date/Time: 9/14/2021 9:39 PM

crispyoldcraig wrote:

Have you actually measured it from spindle to hub or are you just calculating teeth combos? Does 70links at 28/9t actually ...more

I measured from the center of the spindle to the center of the rear axle when slammed...12.75. At this point the chain still had slack at 70 halflinks. When I pulled the wheel back to tighten the chain I measured again and it was just shy of 12.8”.

I thought that I was definitely measuring wrong (but in retrospect I don’t see how) which is why I counted the half links again and calculated...the configuration confirmed the initial/secondary measurements.

EDIT: sorry, didn’t answer your last question. At 28/9, 70 half-links comes to a calculated stay of 12.785, which makes sense considering there was still chain slack at the slammed position.

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9/14/2021 10:50 PM

Deflection could make your measurements a little out. And any wear to the parts could make the calculation out. I don't think there should be that much variation. Depends on the law in your country but there's a +/- legal tolerance of about 3mm generally iirc. If you're correct, it literally means they've measured things wrong, but still managed to make it fit in a jig?

Personally, it would bug me. But if it feels nice to you I wouldn't worry about it.

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9/15/2021 10:39 AM

.pegless. wrote:

Deflection could make your measurements a little out. And any wear to the parts could make the calculation out. I don't think ...more

I thought it was weird as well. It doesn’t bother me, as my axle is at 13” in the middle of the drops, but really just wanted to know if this kind of variation was common.

My other frame is a Tallboy. It is listed at 13” and slammed it is dead-on. I’m in meetings now, but I’ll update with pics and measurements of the Whammo CS length. My knowledge of metal working practices is really lacking (I focus more on fabric and electronic specs), so am generally unfamiliar with acceptable tolerances for frames. I k ow that if I sold a commercial tower where the fabric did not meet the tight technical spec, I would open myself up for a lawsuit.

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9/15/2021 11:16 AM
Edited Date/Time: 9/15/2021 11:18 AM

My new volume is longer than advertised OR the Fit Wifi i had previously was shorter than advertised.

same parts, But on the "longer" CS i could remove the wheel without breaking the chain. On the "shorter" one, I can not. Now I have to file down a drop out.

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9/15/2021 1:23 PM

So here is what it looks like. Note: I realize that the sprocket in the picture is 25t, not 28t. I’m working on my cranks and grabbed this sprocket just to install my cranks because it is the closest thing to me.

1. This pic shows my measurement points. It was taken over my shoulder by my wife so is kind of difficult to see exactly the tape measure between the centers of the spindle bolt and axle.
2. The second pic is a close-up of the actual slammed CS length.
3. The slammed axle with no bolt

Photo
Photo
Photo

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9/15/2021 2:04 PM

Yeah I'd say that's clearly 12.75. unless 12.9 is nearly slammed with enough room to take your wheel out without having to break the chain? Seems odd they're not using that extra shortness to aid marketing

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9/15/2021 2:22 PM

.pegless. wrote:

Yeah I'd say that's clearly 12.75. unless 12.9 is nearly slammed with enough room to take your wheel out without having to ...more

That’s kind of what I thought. Kind of expands the options for anyone who wants a mid length (13-13.25) chainstay but may want to experiment with a shorter chainstay without committing to buying one of the super short CS frames.

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9/15/2021 5:07 PM

Thats the problem. There seems to be no industry standard for chainstay measurements. I bought 5/6 different frames within the last 2 years and every company measures their own way. Some brands will even vary within their own lineup.
A frame details a single measurement like 13 inch. One brand will mean slammed 13 and another will mean its optimized for 13 and actually slams at 12.8 or 12.9

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