[dr13zehn]

I am having some trouble with the installation of a GXP BB into my 2009 Fuel EX 8.

In the instructions it tells me to put one spacer for each cup, but if I only use one on the drive side, the granny gear teeth touch the frame.
The Shimano Hollowtech II I had on there before had 2 on the drive side and one on the other, but the GXP only came with 2 spacers total and not with 3.

The GXP cups themselves are wider than the Holowtechs, but still not wide enough to use only one ring on the drive side like instructed.

If I reuse one of the spacers I had from the Holowtech, I fear that the cups are too wide apart from where they should be. Also, if I use 2 on the drive side of the GXP the crank sticks out further than it did with the Shimano setup. Like I said, the GXPs have wider cups.

Does anyone have any advice?


Thanks,

D

 

[Beemer2]

better idea

Dump the Truvativ and get another Shimano, LX's on sale everywhere for $99.00, much better and easier to install than what you have. If you must use the GXP then put the spacers back like they were on the Shiimano, two on the drive side, one on the non drive side. I have used both in my 2009 EX 9.

 

[dr13zehn]

Sorry, not going to ditch the Noir for an LX crank. :eekster:

Maybe I will just try one on the non drive and 2 on the drive side. See what happens...

 

[reptilezs]

try 2 on the drive and non on the non drive. i believe the chainline for truvativ gxp cranks is 51mm opposed to shimano's 50mm

 

[mtnbiker72]

i believe the chainline for truvativ gxp cranks is 51mm opposed to shimano's 50mm

They're actually exactly the same...Shimano measures from the inside of the middle chain ring, Truvativ measures from the center of the middle chain ring...chain rings are 2mm wide so measuring from the center accounts for the 1mm difference.

 

[dr13zehn]

Hey mtnbiker72,

I see you are using a Truvativ part. If it's a crank, how do you have it installed? Assuming your shell is 68mm if I'm lucky.

 

[davep]

If you push the crank out further, you are going to have a pretty messed up chainline. The correct chainline for a frame with a 135 rear hub is 47.5mm. With a single spacer (stock set-up) the Noir are already at 51mm. Another spacer will put you at 53.5mm..

Are you running the stock 22 tooth granny? If so, it sounds like the frame has some sort of non-standard crank clearance issues (although they came with standard cranks as a complete..).

Ring to ring spacing is standard with all cranks, so although a different brand might have a (much) better chainline stock, they will still contact the frame if set-up with the same chainline.

Regardless.. I have to agree with beemer in general. Just because they are pretty, and a company considers them top end....does not make a crank 'high end' when compared to other brands. The truvativ cranks are pretty so-so across the board for many reasons (interface, bb design, compatability, price for weight).

 

[mtnbiker72]

If you push the crank out further, you are going to have a pretty messed up chainline. The correct chainline for a frame with a 135 rear hub is 47.5mm. With a single spacer (stock set-up) the Noir are already at 51mm. Another spacer will put you at 53.5mm..

47.5mm is no longer the standard chainl ine, with the advent of external bearing cranksets...50mm (same as Truvativ's 51mm measurement) is the "new" standard. That said, you are correct in that putting two spacers on the driveside will result in a 52.5mm (53.5mm by Truvativ's measurement) chain line.

 

[mtnbiker72]

Mine is installed with a spacer on each side...no issue. I would caution against using two spacers on the driveside...it will result in a bad chainline.

Something is fishy as Truvativ and Shimano use the same chainline and the same chainring spacing, so it shouldn't hit the chainstay. Are you using the 22t granny or is it something bigger.

 

[davep]

47.5mm is no longer the standard chainl ine, with the advent of external bearing cranksets...50mm (same as Truvativ's 51mm measurement) is the "new" standard. That said, you are correct in that putting two spacers on the driveside will result in a 52.5mm (53.5mm by Truvativ's measurement) chain line.

Standard or not, the chainline of a 135 mtb hub IS 47.5. I am well aware of why most cranks are wider than this, but it does not change what the chainline of the frame/hub actually IS. My point is that the majority of cranks are already wider than they should be, and to add more spacers is just going to make things worse.
If these cranks were somehow 45 or 47mm chainline, then the spacer swaping might help the interferance issue...and not make the chainline all the more wrong.

I think we are on the same page here. There is no reason that one crank would fit and another would not, given they have the same chainline. I would guess a larger granny ring is the issue (it is the only thing that makes any sense, other than some kind of mis-instalation).........

 

[dr13zehn]

Guys,

Thanks for the replies! I am sad to admit that I figured it out and I'm dumb as a dry piece of bread.

I will elaborate with an edit.


Edit:
I have never installed cranks before. Now that I established that excuse, I will tell you how I am stupid.

I installed the drive side cup and wanted to see what the crank will look like on the bike like a little child. So I pushed it in all the way and since there was no other cup installed to stop the crank, it slid in further than it should have. With both installed, one spacer on each, it works perfectly now.


There, I'm simple... You may laugh at me now... I would.

 

[mtnbiker72]

Standard or not, the chainline of a 135 mtb hub IS 47.5.

That is not always true...a chain line can vary according to frame, crankset, and gearing. The ideal chainline for a mountain bike triple is 47.5mm. A singlespeed mountain bike with a 135 hub is not ideally a 47.5mm chainline at all. Freewheel singlespeed hubs are a 51.5mm chainline in most cases.

 

[davep]

That is not always true...a chain line can vary according to frame, crankset, and gearing. The ideal chainline for a mountain bike triple is 47.5mm. A singlespeed mountain bike with a 135 hub is not ideally a 47.5mm chainline at all. Freewheel singlespeed hubs are a 51.5mm chainline in most cases.

and a threaded freewheel single speed hub is no where near a standard 135mm hub, in fact you would hard pressed to actually find one for purchase. Be pedantic if you must, tell me about asymetric frames, home made hubs, partial cassettes that are shifted inboard or outboard, single speed freehubs with 1, 2, 3, 4, 5 speeds spaced to any chainline you make up in your mind, and find every exception that makes the rule, but a standard 135mm mtb hub DICTATES a 47.5 mm chainline plain and simple...

BTW, Crankset has NOTHING to do with the correct chainline of a particular frame, or hub, or gearing, or anything else. It is the slave. All of the other parameters dictate the chainline (hub, gearing, frame)....the crank either matches the dictated chainline (with correction for number of rings) or it does not.

and for the standard (8 or 9 or 10 speed cassette (or any other gear ratio or combo centered on the cassette carrier)) 135mm mtb hub in a symetric frame (99%+ of MTBers) that chainline is 47.5mm

 

[davep]

Guys,

Thanks for the replies! I am sad to admit that I figured it out and I'm dumb as a dry piece of bread.

I will elaborate with an edit.

Edit:
I have never installed cranks before. Now that I established that excuse, I will tell you how I am stupid.

I installed the drive side cup and wanted to see what the crank will look like on the bike like a little child. So I pushed it in all the way and since there was no other cup installed to stop the crank, it slid in further than it should have. With both installed, one spacer on each, it works perfectly now.

There, I'm simple... You may laugh at me now... I would.

Cheers, glad you got it fugured out, and good for you installing cranks on you own. FIrst time is always a bit of a chore (especially with mediocre documentation) but it will soon become second nature (and save you much $$).

 

[SPEEDMONKEY]

worth mentioning

The GXP BB design does not allow for you to simply "add" spacers to it as you see fit. The spindle bottoms on the ND-side bearing - so - if you add in MORE spacers than you called for you will end up crushing your bearings when you tighten down the non-drive arm.

If you've got a 68m shell you *could* put both on the drive side or both on the non-drive side, but you obviously be affecting your chainline and reducing the thread engagement on said cup.

(68mm shell = 1 spacer Drive, 1 spacer non-drive, 73mm shell = NO SPACERS)

I like Shimano because you have more flexibility to add or remove spacers to a degree, since the non-drive arm "floats" on the spindle.

 

[davep]

Exactly ^^^^ and one of the big reasons that the system is poorly designed..I did not say engineered for a reason! (and I brought up the shortcommings of the interface earlier).

BB shell width tollerance is fairly large (up to 1mm +/- is not uncommon). The GPX system is designed for an EXACT bb width...a number that SRAM does not even provide. 1/4 mm to much preload is enough to prevent free spinning and significantly shorten bearing life. Of course you can back off the crank arm fixing bolt....and have the press fit interface destroy itself (no surprise that this is such a common complaint with these cranks)....

From the RF crank instructions per the same issue (that RF deals with via 0.5mm shims)

c) Critical!!! BB shell width tolerance after face milling must be:
- 68mm shell = 67.25mm - 68.25mm*
- 73mm shell = 72.25mm - 73.25mm*
Note: BB shell widths outside this specification may result in unacceptable function and life of the BB assembly (too loose or too tight). Out of
tolerance BB shells can be compensated for with use of optional preload elastomer and/or spacer(s) (see TROUBLE SHOOTING section).

 

[reptilezs]

gxp system has no preload system designed into it. the left side spline is basically and isis spline. the left crank bottoms out on the bearing and spindle. this is why the left side bearing has a spacer in it. the drive side bearing just "floats" on the spindle. the crank relies on the left cup for setting the chainline/proper spacing. if you want a system that is really deigned for an exact width and no preload look at the campy ultra torque cranks. bb shell to narrow and the crank slides back and forth. too wide and it binds

 

[mvi]

The GXP floating driveside bearing is how an engineer would build it. From a bearing design point it rules IMO. It lasts too, as I rode a GXP mountain triple crank on the mountainbike as a 1x9 for years on the original cups.

 

[nitropowered]

If you can look at the DS cup to crank interface, you'll see a few mm of gap because of the floating bearing. Unless you have a shell that is extremely out of tolerance (2+mm wider) I don't think you will have a binding issue.

The main binding issues I've come across is non-faced shells. This affects all external bottom bracket bikes.

And Campy Ultra-Torque is even more picky on shell tolerance. If your shell is too narrow, you can actually push the DS arm in and have play. But you can obviously shim the cups to get rid of it.

 

[Mr.P]

It lasts too, as I rode a GXP mountain triple crank on the mountainbike as a 1x9 for years on the original cups.

I've had a similar experience.

2 Shimano BBs, XT & XTR were done in 6 months
1 Race Face done in 3 months

This in lovely sunny California...!

I put over a year on a Truvativ BB, and decided on an overdue service of them (easily done and part of the design) and the bearings were clean, still greased and smooth. So I repacked anyway and am still running. Over a year on this set. About 2 years on the previous set with no service (it's still good but just relegated to back-up)

P