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2 sizing questions: chainrings and seat post bolts

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2 sizing questions: chainrings and seat post bolts

Old 03-24-23, 02:10 PM
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tiger1964 
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2 sizing questions: chainrings and seat post bolts

Two questions:

(A) 50.4mm chainrings: I'm putting a TA ring on a Nervar crank. Should work fine, right? Well, I noticed where there's a "shoulder" on the DS crank arm, where the chainring has a corresponding hole -- there's a little clearance. Is this normal? Maybe 1mm, maybe 0.5mm -- but it's not zero. This implies that there's going to be more load on the mounting bolts, not (as they would say on automobile wheels) "hub centric". I also have a Velo Orange 50.4mm chainring; same results. I've never had TA cranks, perhaps it's the same. I do have a TA ring on Stronglight 49 arms, don't really want to dismantle that just to check.

(B) Seat post bolts: I think I asked this before but suspect it might have been buried in someone else's topic. When looking for a seat post bolt (let's presume the Allen-key type for now) and a size is lists, say "19mm" for example, is that the minimum size it will grip before the two halves of the bolt touch and thus no longer tighten, or is the the maximum it will grip? In either case, one would think there's a "range" of seat lugs it would work with.
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Old 03-24-23, 05:33 PM
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For the crank, all the load is on the mounting bolts even if the hole for the crank does not touch the shoulder of the crank at all.

The load will be some combination of shear at the joint-line between the crank and the spider, and tension from the nut.
The tension (if the nut is done up proper) should be sufficient to make the two pieces stick together under almost any cycling situation, so the shear load is zero or close to it.

In sum, don't worry.
Make sure you have a decent spanner for the bolts; if using a box-spanner or socket, grind the face flat so it grips the whole of the tiny flats on the nuts and bolts.
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Old 03-24-23, 05:39 PM
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While they aren't cheap, the mounting bolts from velo orange are quite a bit better if you feel the need.

https://velo-orange.com/products/cha...0-4-bcd-cranks
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Old 03-24-23, 05:53 PM
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Originally Posted by tiger1964
Two questions:

(A) 50.4mm chainrings: I'm putting a TA ring on a Nervar crank. Should work fine, right? Well, I noticed where there's a "shoulder" on the DS crank arm, where the chainring has a corresponding hole -- there's a little clearance. Is this normal? Maybe 1mm, maybe 0.5mm -- but it's not zero. This implies that there's going to be more load on the mounting bolts, not (as they would say on automobile wheels) "hub centric". I also have a Velo Orange 50.4mm chainring; same results. I've never had TA cranks, perhaps it's the same. I do have a TA ring on Stronglight 49 arms, don't really want to dismantle that just to check.

(B) Seat post bolts: I think I asked this before but suspect it might have been buried in someone else's topic. When looking for a seat post bolt (let's presume the Allen-key type for now) and a size is lists, say "19mm" for example, is that the minimum size it will grip before the two halves of the bolt touch and thus no longer tighten, or is the the maximum it will grip? In either case, one would think there's a "range" of seat lugs it would work with.
SP binder = age old conundrum = you can always grind a bit off the female side if its close for more clearance if need be.

This is why so many Campy ones have suffered, they were too close to minimum tolerance and couldn't tighten the clamp without bottoming out after it stretched, wore in or had a smaller SP used.

All the Campy's should be ground down a bit IMO.

And I would loosen the chainring bolts a tad, load the crank a bit and then tighten to eliminate the slack that may loosen if not preloaded.

I also think it is a non issue but......

Last edited by merziac; 03-24-23 at 05:57 PM.
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Old 03-25-23, 06:16 AM
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Originally Posted by oneclick
For the crank, all the load is on the mounting bolts even if the hole for the crank does not touch the shoulder of the crank at all. The load will be some combination of shear at the joint-line between the crank and the spider, and tension from the nut. The tension (if the nut is done up proper) should be sufficient to make the two pieces stick together under almost any cycling situation, so the shear load is zero or close to it. In sum, don't worry. Make sure you have a decent spanner for the bolts; if using a box-spanner or socket, grind the face flat so it grips the whole of the tiny flats on the nuts and bolts.
Thanks -- end of problem. These cranks really don't have a spider (or, you could say it does but each spider arm is 3/8" long ), but I get your point.

Originally Posted by 52telecaster
While they aren't cheap, the mounting bolts from velo orange are quite a bit better if you feel the need https://velo-orange.com/products/cha...0-4-bcd-cranks
Absolutely! I have those on my Gitane, which has the Stronglight/TA combo. A nice bit of "bike jewelry". I just need to put together a list of things to pick up to justify driving over (freight $$$ for a small package going 25 miles drives me nuts. Or, nuts and bolts in this case).

Originally Posted by merziac
SP binder = age old conundrum = you can always grind a bit off the female side if its close for more clearance if need be. This is why so many Campy ones have suffered, they were too close to minimum tolerance and couldn't tighten the clamp without bottoming out after it stretched, wore in or had a smaller SP used. All the Campy's should be ground down a bit IMO.
Good point, I did not think about that. That said, I am still hoping someone knows the answer to question B.
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Old 03-25-23, 10:54 AM
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I recently purchased one of those titanium SP bolt, and the dimension (eg19mm) was the minimum clamping distance (two parts fully screwed together till it bottoms out).
For my application, I ordered 15mm version.
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