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Discussion Starter · #1 ·
The Demo requires a crankset with a 57mm chainline, but I have a spare XT M760 crankset with a 50mm chainline I'd like to put on there to reduce some wieght on my bike (I'm 140 lbs. wet). I currently have a Truvativ Hollzfeller/Gigapipe DH setup on there. The BB width is 73mm.

Is it safe to install the crankset with all the spacers on the drive side to get a 55mm chainline? If so, would it be ok to add a fourth spacer to get a 57.5 chainline? I'm concerned about not threading the drive side cup into the BB enough for load bearing purposes. Also, the length of the plastic tube that covers the axle might be too short.

TIA
Duc
 

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I would suggest setting up the bottom bracket normally and living with the bad chainline. I've heard mixed things about playing with the spacers.

Are you really saving enough weight to make it worth it? I have the same setup, using '04 Holtzfellers. They're not that heavy.
 

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Monte Su Bici Maldita
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I wouldn't suggest it. First, your Holzfellers are the lightest DH/FR worthy cranks that you are going to find. Second, the XT's won't hold up, and they will bend. Plus, I wouldn't suggest messing w/ your chainline that much w/ spacers. Like you said, it won't be threaded enough to tolerate the load of the rider and stress that bottom brackets go through.
 

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mtnbykr06 said:
I wouldn't suggest it. First, your Holzfellers are the lightest DH/FR worthy cranks that you are going to find. Second, the XT's won't hold up, and they will bend. Plus, I wouldn't suggest messing w/ your chainline that much w/ spacers. Like you said, it won't be threaded enough to tolerate the load of the rider and stress that bottom brackets go through.
I do not know your experience, but there are lots of guys running XTs on their DH rigs with NO problems at all, I am one. Go to ridemonkey and do a search..lots of success with a couple bent via solid, high speed rock impacts, not riding.

As far as the cranks on that frame, what I have seen have always been single ring DH set-ups, and with this, you can just move the ring to the outer (big ring position) and go with a E-13 LG1. In your set up, I would start by measureing the actual chainline on your bike, to see what you need to get (56mm I think).
A stock XT with only two rings will actually be a 52mm chainline (chainline is measured to the middle of your front gears, however many you have)
The XTs have spacers between the bb cup and frame but also (IIRC..not at home to check right now) a thin spacer between the bb cups and crank arm for fine tuning. These can be moved, but you need to make sure that some measurements are not changed. For example, the non-drive side arm NEEDS to have a certain amount of spindle insertion to prevent the arm splines from stripping out.

The shimano stock cups are quit shallow. It seems to me that there is little room for moving the cups further out via spacers...I think you will quickly experience either the frame or bb cup stripping out, or at the very least, loosening often...

There is a simple and fairly cheap solution though..
a race face diabolus bottom bracket..the threaded insertion is about 50% (maybe 8mm) longer than the XT unit, allowing the drive side cup to be shimmed out without worry (most likely have more threads even with 5mm of extra shim). You might look into getting some thinner bb shims as well (they come in 1mm vs the standard provided 2.5mm ones) to be able to fine tune.

Without the RF bb, I think that you could get 53mm chainline without harm. If you feel like you need to go further (if you ride in the smaller ring often) then get a RF diabolus and swap both shims to the drive side and you should have a 56 -57mm chainline..

good luck.
 

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Discussion Starter · #5 ·
Dave,

Thanks for the info. Some follow up questions though. Will the plastic sleeve on the BB cups be long enough if? Is it even necessary? Will the spindle on an XT crankset be long enough to accomodate the added spacers on the drive side when the BB is already 73mm?

BG and mtbykr06,

I'll be saving over a pound of weight switching over to the XT cranks. These are actual measured wieghts on a digital scale. :)

Thanks to everyone for all your suggestions so far.

Duc
 

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duc135 said:
Dave,

Thanks for the info. Some follow up questions though. Will the plastic sleeve on the BB cups be long enough if? Is it even necessary? Will the spindle on an XT crankset be long enough to accomodate the added spacers on the drive side when the BB is already 73mm?

BG and mtbykr06,

I'll be saving over a pound of weight switching over to the XT cranks. These are actual measured wieghts on a digital scale. :)

Thanks to everyone for all your suggestions so far.

Duc
its best to use a crankset designed for a 57.5mm chainline. Truvativ makes a 56mm version for a 73mm shell and the raceface 57mm crankset for the 83mm shell can be converted with a reducing kit comprised of a shorter tube and some 1mm spacers for the non drive side.

OR, just keep the 50mm crankset w/ BBmount-I-OLD DRS and do alot of climbing.

if you go with the 57.5mm crankset option keep in mind that you should use the I-05 DRS with the concave side of the adapter facing away from the shell. the larger diameter of the I-05 plate will allow space for the external type BB cups, which would otherwise hit on the I-OLD DRS backplate.
 

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duc135 said:
Dave,

Thanks for the info. Some follow up questions though. Will the plastic sleeve on the BB cups be long enough if? Is it even necessary? Will the spindle on an XT crankset be long enough to accomodate the added spacers on the drive side when the BB is already 73mm?

Duc
You are right, for some reason I was thinking that there was a 2.5 mm spacer on the non-drive side as well that you would just move to the drive side...not the case with a 73mm bb...sorry my bad. Is there any way that you can get a hold of a set of these cranks to play with (a buddies or something)? There are several places that parts could vary in tollerance that might make it 'kind of' work. For example, a 73mm bb is NOT exactly 73mm. Race face lists the acceptable range as 72.25 - 73.25. Nor are bb shells exactly centered in the frame. So some of these variables could help you, they could also hurt what you are trying to do, depending in which direction the tollerances are..

as a final thought, you could have the frame faced/tapped down to 68mm by a reputable shop, this would allow the adjustment you would need.

Oh.. one more question..do you really need two rings in front? An 11 - 34 rear cluster and a 34 front will give a LOT of gear range and plenty of speed (the world cup DH champ runs either a 36 or 34). There are definately climbs here that require a granny (although sometimes I think it is esaier and just as fast to walk at that point), so I understand if you need it....but that is a big bike to be doing a lot of seated pedaling :D

I dont think the plastic sleeve actually does anything. The back side of the bearings are sealed just like the front (exposed sides), so the sleeve is redundant. Maybe if you do a lot or rain/wet weather riding, it may help. I have seen older bikes that have collected enough water down the seat tube that it actually poured out the bb when it was removed.

I will check out/pull apart my XT set up on my DHR and get back if I think of anything else,
 

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Discussion Starter · #8 ·
Dave,

Thanks for the input. I'll try a dry fit of the crankset tonight without the DRS to see how it all fits and if the spindle is long enough.

Yea, I do a fair amount of uphill riding on that thing so I'll need my granny ring. I, unfortunately, have to earn my downhills 95% of the time.

Duc
 

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Discussion Starter · #9 ·
To all you nay sayers out there. You were correct. The spindle was much too short. So my follow up question is what is the lightest crankset out there with a 57mm chainline and 165mm - 170 mm arms?

Duc
 

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Monte Su Bici Maldita
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I would go w/ the Truvativ Holzfeller OCT. Currently the lightest DH/FR crankset out there by far.
 

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Discussion Starter · #11 ·
mtnbykr06 said:
I would go w/ the Truvativ Holzfeller OCT. Currently the lightest DH/FR crankset out there by far.
Are they even available yet? How much do they weigh? I don't think I need DH specific cranks as I am only 145 lbs. with gear and am not doing huge crazy stuff yet. I think I should be able to get away with XT level cranks.

Duc
 

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Monte Su Bici Maldita
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Well they should be perfect then. They aren't quite the strongest, but will stand up to a lot of Dh abuse. I don't know the exact weight but I am guessing about 880 grams comparing it to the others. And they should be available seeing as we are in the year 2007, but then again I am not sure.

And I wouldn't try and figure out what parts you want at your current skill level, because everyone progresses and you need the parts for when you do.
 

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Discussion Starter · #13 ·
d-rod said:
its best to use a crankset designed for a 57.5mm chainline. Truvativ makes a 56mm version for a 73mm shell and the raceface 57mm crankset for the 83mm shell can be converted with a reducing kit comprised of a shorter tube and some 1mm spacers for the non drive side.

if you go with the 57.5mm crankset option keep in mind that you should use the I-05 DRS with the concave side of the adapter facing away from the shell. the larger diameter of the I-05 plate will allow space for the external type BB cups, which would otherwise hit on the I-OLD DRS backplate.
Derek,

Can you tell me the model cranksets you are referring to?

Duc
 
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