Shimano pressfit 86 to Sram pressfit GXP

Discuss light weight issues concerning road bikes & parts.
itguy
Posts: 131
Joined: Tue Jan 20, 2015 3:43 pm

by itguy

Recently I got a bike frame that runs Shimano pressfit 86 BB.

I got a SRAM Red GXP crank.

I tried to fit this crank into the BB and it seems to be loose, as the spline at the end doesnt fit the BB's diameter.

Looked up Chris King and they got this Pressfit 24 with a conversion kit that has a ring that fit onto the spline to make it fits the BB's diameter. Seems like this is a solution.

How about SRAM pressfit GXP BB? Would it fit into the frame and not requires a ring for my crank?


Cheers

Fiery
Posts: 420
Joined: Sat Mar 16, 2013 9:21 am

by Fiery

Yes, the PressFit GXP is the bottom bracket for use with Sram GXP cranks in BB86 frames.

by Weenie


itguy
Posts: 131
Joined: Tue Jan 20, 2015 3:43 pm

by itguy

Here's a really old post and there was something highlighted about SRAM GXP BB having problems.

viewtopic.php?t=102151

Is this issue still happening on SRAM's BB?

Mr.Gib
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Joined: Fri Mar 18, 2005 4:12 pm
Location: eh?

by Mr.Gib

No problems. I ran GXP bottom brackets from Sram in my Giant BB86 for years. The Sram product was also smoother, had less drag than the Shimano BB86.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

itguy
Posts: 131
Joined: Tue Jan 20, 2015 3:43 pm

by itguy

Mr.Gib wrote:No problems. I ran GXP bottom brackets from Sram in my Giant BB86 for years. The Sram product was also smoother, had less drag than the Shimano BB86.


Awesome, good to know. Guess there's no point going for Chris King (very expensive).

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DMF
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by DMF

The problem that CAN potentially occur is that there is literally nothing holding the BB-cups to the frame other than the force of the tight tolerances squeezing them there, which in some frames can be pretty low tolerances to be honest. With the Shimano and similar the crank arms push against the hearings, which keeps the cups in place. With GXP, when pedalling it's actually the opposite and the NDS crank/axle assembly is actually wiggling the entire BB-cup assembly, which with poor tolerances can come loose. The BB-cup can be glued to the frame to solve this, or at the very least use some sort of locking compound. I've seen fhis happen to customers bikes in my workshop and Pressfit + GXP is IMHO technically speaking a less than ideal solution for pretty obvious reasons. GXP belongs in NDS cups where the bearing is tightly secured to the cup and the cup is tightly secured with something more than just Pressfit to the frame.

Mr.Gib
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by Mr.Gib

DMF wrote:The problem that CAN potentially occur is that there is literally nothing holding the BB-cups to the frame other than the force of the tight tolerances squeezing them there...


DMF I am not sure that I agree with your position. The side load to hold SRAM BB86 cups comes from compression of the wave washer. In previous threads on this topic, a number of forum members with engineering degrees have described the wave washer system as very good for this type of application. The system does grab the NDS cup but also holds drive side in place just fine.

The anecdotal experience is pretty good. There doesn't seem to be any more outcry from GXP users with creaky bottom brackets compared to other systems, in fact it seems less then some others. The sample size is pretty big also. SRAM GXP is on a lot of different bikes. Personally, I have used it on four different types of bb standards over 7 different bikes and they all work just fine. Carbon shells, alloy shells, BB86, BB90, and also BSA, PF30 (without wave washer) - all good.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

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DMF
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by DMF

Where do you have a wavy washer on a BB86 GXP? BB86 with other axle systems yes, but with BB86 GXP there is a pretty big gap between DS crank arm and DS bearing, and NDS bearing of course having the bearing inner race cradled between the axle and NDS crank arm. Basically nothing of the crankset touching anything other than the NDS bearing inner race?

I could be wrong, but I've never seen a wavy washer with GXP. Are you perhaps thinking of a 30mm crank axle in BB86?

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HakeemT
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Joined: Thu Mar 18, 2004 7:39 pm

by HakeemT

No, the SRAM BB86 PF BB comes with a wavy washer, to be installed on the drive side.
See page 29: https://www.sram.com/sites/default/file ... -rev-a.pdf

Interestingly, I have not found a need to use it in my install (on a Fondriest with a BB86 bottom bracket). There is no play even without the washer installed; I've been running it like this for almost a year now without any issues. BB is still smooth.

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DMF
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by DMF

Ahh thank you. We've had some issues at my shop where people have bought bikes online, used or tried to install it by themselves, without a wavy washer then, with creaks coming from the NDS side cup wiggling loose. Wasn't actually aware there was a wavy washer for this. Will order in some spare ones of those today ;) live and learn :)

wingguy
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by wingguy

DMF wrote:We've had some issues at my shop where people have bought bikes online, used or tried to install it by themselves, without a wavy washer then, with creaks coming from the NDS side cup wiggling loose.

And you/they never checked the product manual while trying to fix it? :noidea:

I feel pretty strongly that a big part of what makes a good mechanic good is finding out the details of the parts they work on. There is no level of innate technical skill that can compensate for learning how each specific component is supposed to work.

topflightpro
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Joined: Tue Jan 13, 2009 2:35 am

by topflightpro

OP, I've used the regular Sram GXP PF86 BB and the Wheels Manufacturing Angular Contact PF86 BBs. Both worked perfectly fine for me.

goodboyr
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Location: Canada

by goodboyr

wingguy wrote:
DMF wrote:We've had some issues at my shop where people have bought bikes online, used or tried to install it by themselves, without a wavy washer then, with creaks coming from the NDS side cup wiggling loose.

And you/they never checked the product manual while trying to fix it? :noidea:

I feel pretty strongly that a big part of what makes a good mechanic good is finding out the details of the parts they work on. There is no level of innate technical skill that can compensate for learning how each specific component is supposed to work.


Lol. This is not a unique situation with LBS's....but at least give him credit for being honest. Typical lbs approach is to bs and blame everything but their skill and knowledge. How many times have you heard, "that's the way it is"....?

grover
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Joined: Mon Jul 26, 2004 1:06 pm

by grover

Hakeem, the wavy washer isn't there to take out play. It's there to ensure the cups don't creep out of the frame. So all will seem fine on initial install. And with good tolerance frame and a good install you'll probably never have a problem. Without it either cup can creep out of the frame though. This will likely result in some noise, and if it's the non-drive cup that creeps out it also means the whole crankset is moving with that cup towards the non-drive side...which means impaired chainline, chaindrops off the outside, chain noise on derailleur etc.

by Weenie


grover
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Joined: Mon Jul 26, 2004 1:06 pm

by grover

double post

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