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Are these caliper mounting bolts too long?

3714 Views 16 Replies 8 Participants Last post by Harold, Jan 10, 2022

CMinSC

Discussion Starter · Jan 8, 2022

Bicycle Bicycles--Equipment and supplies Wheel Bicycle tire Crankset

I decided to replace my 180mm rotors with 203mm. I ordered the F203P/P adapter which came with bolts to mount to the fork. This adapter has separate holes for the caliper and I reused the original bolts but they are really long for this adapter. They seem like they might work because there is around 12mm of thread engagement but I’m wondering if this is going to cause the problem. I’ve looked to see what length bolts should be used with this adapter but can’t find the answer anywhere. Anyone know what length bolts I should be using?
Thanks

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Joe Handlebar

· #2 · Jan 8, 2022

If you've got over a centimeter of engagement, I would suspect you'd be fine. If you're worried about it, full thread M6 bolts (w/metric allen heads) are less than a $1 pretty much any hardware store.

Harold

· #3 · Jan 8, 2022

I mean, yeah, they're too long...but as long as the extra length isn't interfering anything, it shouldn't be a problem that they're too long.

The bolts you're "supposed" to use are probably the standard ones that usually come with the caliper to begin with (if you buy your brakes aftermarket, anyway). I usually have some extras of these sitting around because I've changed adapters at some point, and there's been a few times where I'm happy that I've had spares.

Reactions: 5

Cleared2land

· #4 · Jan 8, 2022

^^^^^
What he said

hkmeup

· #5 · Jan 9, 2022

SRAM recommends 9-13mm of bolt thread engagement for their post mount brakes. Should be the same for a Shimano setup. From the picture your lower bolt looks a bit short. See page 7 of the included link for details. https://www.servicearchive.sram.com...2_disc_brake_caliper_specs_road_mtb_rev_e.pdf

CMinSC

Discussion Starter · #6 · Jan 9, 2022

hkmeup said:
SRAM recommends 9-13mm of bolt thread engagement for their post mount brakes. Should be the same for a Shimano setup. From the picture your lower bolt looks a bit short. See page 7 of the included link for details. https://www.servicearchive.sram.com...2_disc_brake_caliper_specs_road_mtb_rev_e.pdf

Thanks, I'm surprised they recommend that much overhang. I don't even see how the amount that protrudes makes a difference. It seems like if all of the internal threads are engaged that should maximize the strength.

hkmeup

· #7 · Jan 9, 2022

For what it's worth, I have run bolts similar in length to your lower bolt with no issues. Also, I have used bolts with the recommended 9-13mm of thread engagement on my MRP and X-Fusion forks with no "bottoming out" or any other issues.

Sparticus

· #8 · Jan 9, 2022

Unquestionably those bolts are longer than they need to be.
Too long?
That comes down to personal opinion.
For me, yes. Too long. I'd replace them with bolts that end where the threads extend beyond the mount.
For others? Maybe not.
The bolts in the photo aren't hurting anything beyond some folks' sensibilities.
The extended threads aren't visually appealing to some of us anal retentive types.
Plus you're carrying around all that extra weight -- OMG!

=sParty

Reactions: 3

Loll

· #9 · Jan 9, 2022

Those are some funny 200 adaptor. It looks like flat mount adaptors? My shimano 203 looks like an arch with the long bolt going directly into the post. Was your fork originally using 160 disc?

My bike is on the stand and brakes taken out, otherwise I will snap a pic for you.

Christopher Robin

· #10 · Jan 9, 2022

I think SRAM is referring to having the 9-13mm engagement when the bolts go into the fork mounts or the adapter stacked underneath.

In this case, you could cut the bolts so the ends are flush with the bottom of the adapter.

Reactions: 1

Harold

· #11 · Jan 9, 2022

Christopher Robin said:
I think SRAM is referring to having the 9-13mm engagement when the bolts go into the fork mounts or the adapter stacked underneath.

In this case, you could cut the bolts so the ends are flush with the bottom of the adapter.

yeah, thread engagement has nothing to do with how much bolt is hanging out the back side of the threaded hole doing nothing.

thread engagement is the amount of threaded bolt that's engaged with the threads of the mount.

Reactions: 1

Joe Handlebar

· #12 · Jan 9, 2022

I may not be interpreting the OP correctly then. By "engagement", I think of the total length of threaded bolt in contact with the internal threads. Some brake mount bolts are not threaded their entire length, which I presumed was the premise for the concern. Certainly whatever extra length isn't "doing anything".

Harold

· #13 · Jan 10, 2022

also, I note that the hemispherical washers aren't necessary in this case, so this means that there's definitely extra bolt length. though looking at how much bolt passes through the adapter here, they're at least keeping the bolt from hitting the fork.

the hemispherical washers are only used for these brakes (on top of the caliper, not like SRAM's use between the caliper and adapter) for helping to allow the bolt head to seat flush when you have the sort of adapter that's not threaded and a single bolt attaches the caliper and adapter to the post mount on the fork/frame. Like the old mount that was replaced, in this case.

if you wanted to follow "best practice" for this, you'd use shorter, standard caliper mounting bolts without the washers. this setup works, though, so if you don't want to fuss with hunting down the correct hardware, you can leave it. if you want to be anal and detail-oriented, then you can go for the "best practice" application.

CMinSC

Discussion Starter · #14 · Jan 10, 2022

Loll said:
Those are some funny 200 adaptor. It looks like flat mount adaptors? My shimano 203 looks like an arch with the long bolt going directly into the post. Was your fork originally using 160 disc?

My bike is on the stand and brakes taken out, otherwise I will snap a pic for you.

Thanks, yes I have a Pike that has 160 mounts

CMinSC

Discussion Starter · #15 · Jan 10, 2022

Christopher Robin said:
I think SRAM is referring to having the 9-13mm engagement when the bolts go into the fork mounts or the adapter stacked underneath.

In this case, you could cut the bolts so the ends are flush with the bottom of the adapter.

Yeah, I think you’re correct but the document he referenced shows the 9-13mm of overhang but I realized those threads would be engaged in the fork mount for a normal direct mount adapter. It doesn’t apply to an adapter with offset holes like the one I’m using.

CMinSC

Discussion Starter · #16 · Jan 10, 2022

Harold said:
also, I note that the hemispherical washers aren't necessary in this case, so this means that there's definitely extra bolt length. though looking at how much bolt passes through the adapter here, they're at least keeping the bolt from hitting the fork.

the hemispherical washers are only used for these brakes (on top of the caliper, not like SRAM's use between the caliper and adapter) for helping to allow the bolt head to seat flush when you have the sort of adapter that's not threaded and a single bolt attaches the caliper and adapter to the post mount on the fork/frame. Like the old mount that was replaced, in this case.

if you wanted to follow "best practice" for this, you'd use shorter, standard caliper mounting bolts without the washers. this setup works, though, so if you don't want to fuss with hunting down the correct hardware, you can leave it. if you want to be anal and detail-oriented, then you can go for the "best practice" application.

I thought the hemispherical washers were to get better alignment with the rotor by allowing a small amount of angular tilt. The Shimano documentation for this adapter is not very helpful.

Harold

· #17 · Jan 10, 2022

CMinSC said:
I thought the hemispherical washers were to get better alignment with the rotor by allowing a small amount of angular tilt. The Shimano documentation for this adapter is not very helpful.

yes, and the kind of angular tilt where that's important occurs when the bolts pass completely through the adapter to thread into the fork. not this kind of adapter that has separate bolts for the adapter to the fork and for the caliper to the adapter.

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