150mm rear, 73mm bb, chainline, questions

zdubyadubya · Feb 6, 2009

I have the same question. I want to order a new rear triangle for one of my big bikes, but the manufacturer only makes them in 150 rear ends now. And I have a 73mm bb.

I have a question that goes along with this too. I currently have an internal fsa bb. If I get a bb with external cups and a longer spindle, does this fix the problem?

Dogboy · Feb 6, 2009

I think Dave sums it up best here:

davep said:
Within the same bb shell width catagory, yes to an extent. SO lets say a set of XT cranks (only avail for 68/73 mm bb) or 68/73mm saints have a nominal 50mm chainline when set up as suggested by shimano (it should also be noted that 50 is NOT the correct chainline for a frame with a 135mm rear end....47.5 is. The extra width came about with external bbs). If desired, you can move spacers from drive to non-drive side (or vice versa) to change the chainline by the spacer thickness (2.5 mm as supplied).

Now look at a set of 83mm bb cranks like Saints or G-lights (they have a longer spindle than the 73mm bb versions). The nominal chainline is around 57mm (new saints are pushed out to 59mm) again due to external bearing spacing (unfortunately the correct chainline for a 150mm rear frame is 55 mm). Just like the smaller (narrower) external cranks, these are recomende to use a spacer (or two) on each side of the bb shell, so again, you can adjust the chainline a little bit by re-arranging spacers.

gemini2k · Feb 6, 2009

My vp free has a 73mm bb and a 150mm rear wheel. I'm runnin 83mm saints with 2 bb spacers on the drive side, and 2 bb spacers on the non drive side, and 1 5mm crank spacer on the non-drive side. Chainline is perfect. Matches with the mrp guide without any washers needed. I dunno if any of this helps though...

davep · Feb 6, 2009

gemini2k said:
My vp free has a 73mm bb and a 150mm rear wheel. I'm runnin 83mm saints with 2 bb spacers on the drive side, and 2 bb spacers on the non drive side, and 1 5mm crank spacer on the non-drive side. Chainline is perfect. Matches with the mrp guide without any washers needed. I dunno if any of this helps though...

A home made 83-73 converter. RF makes the exact item for this application thta includes a longer 'inner seal tube' if that matters on your bike. My only hesitation with this set-up with saints would be the cup insertion. Taking away an additional 5 mm of threads could be an issue with the narrower shimano cups. The RF cups are significantly longer/more threads.

davep · Feb 6, 2009

bdamschen said:
Nice. So with a couple spacers on the drive size of the 73 mm bb, I should be good to go for a 150 rear...... right? If I was running saints like Dave's example, it'd be two 2.5mm and I'd be good to go?

How do you figure out what the chainline for your cranks is? Where to do you measure out from?

Chainline is defined as the distance from the centerline of your bike to the centerline of your gears..ie middle ring on a three ring crank...middle cog in the cassette, etc.
Generally the rear end determines the chainline and there are essentially two MTB standards.
135 rear = 47.5mm
150 rear = 55mm
Now there are the odd frames like all the demos (and others) that have 135 rear ends with 150 chainline and you IH that had a 150 rear with 135 chainline (because of floating brake).

You cannot space an external bb out that much because of the fixxed spindle length. Check out the instal instructions for shimano cranks. On a 73mm bb, you need a single 2.5mm spacer (or equivalent) on the drive side. No spacers on the non-drive side. This provides a 50mm chainline. TO get to 55mm, you would need a total of 7.5mm of spacers on the drive side. Two things would happen (both bad). One, the drive side cup would only have a very few threads left in the frame. Two, the spindle would be shifted 5mm to the drive side..out of the non drive arm. The non-drive arm interface would only overlap about 1/2 of what it is supposed to. I dont think it would take long (maybe one run) to rip the ND arm right off the spindle.

There are a couple ways to make this work correctly.
1 83mm external cranks with an 83 - 73mm adapter from RF (or make you own).
2 Isis cranks with 128mm bb.
3 73mm external cranks with a single ring on the outer mount. This requires removing granny tabs and an LG-1 type guide.

gemini2k · Feb 6, 2009

davep said:
A home made 83-73 converter. RF makes the exact item for this application thta includes a longer 'inner seal tube' if that matters on your bike. My only hesitation with this set-up with saints would be the cup insertion. Taking away an additional 5 mm of threads could be an issue with the narrower shimano cups. The RF cups are significantly longer/more threads.

Well that was why we (I didn't machine the new part) went with a crank spacer instead of just more BB spacers (Just an aluminum spacer) 2 spacers on the BB cups isn't anything out of the ordinary. I remain unconcerned about it.

Iridemtb · Feb 6, 2009

I am pretty sure I had to get a 55mm chainline, and most 83mm cranks have a 56mm chainline I believe. So I used 73mm x type bottom bracket and spacers.

I really don't know if this will help, as I don't remember exactly what I did, but... I have a 2004 specialized demo 9 that I pimped out with new parts (I will get it up on ridemonkey once I get my new rear shock from elka). I got a race face diabolus crankset, and used this to achieve the correct chainline:

http://www.shopwiki.com/detail/?q=RACE+FACE+83MM+TO+73MM+SHELL+RETRO+KIT&s=719098&o=189099245&d=RaceFace+Retro+Kit+for+68-73bb+to+83mm+bb

ciszewski · Feb 6, 2009

Ok, I have a question on the same subject.

For the demo, using SLX or XT's (all slx vs. xt debates aside), would it be better to get the SLX and just run the ring in the outer mounts or to get the XT 771's and treat them like on an 83mm just with the converter (or is this even possible).

The one thing that puzzles me about the first one is that if I ever upgrade from them, they will probably make their way onto my xc bike where I would like to have the granny posts.

Thanks for your help in advance.

davep · Feb 6, 2009

I dont think the 771s will be of any benefit as they have a 50mm chainline (per shimano..). This seems odd (maybe this is w/o the 6mm spacer), and I have not seen anyone actually measure the chainline of these cranks on any instal to be sure. The original arcticle by Nathan Riddle does not mention the actual measurements, nor if he bolted the ring to the middle or outer mount....He does mention needing to have to remove the granny bosses though for clearance.

The 771s are supposed to be wider for chainring clearance. If they are actually wider (shimano says they are not, but that makes no sense) then you could just mount then as they come. ??..????

PhilipW · Feb 6, 2009

Hey guys,
I thought I would chime in...

I agree with DaveP's three solutions for bikes with 73mm BB shells and 150mm rear ends. I've found several cranks work.
1. Truvativ Howitzer 56mm chainline BB with your choice of arms (I like my Holzfellers).
2. Raceface 83mm cranks (Diabolus) with the reducer kit mentioned above.

Shimano cranks can be made to "technically" work...but long term bearing life could be reduced (and they don't recommend it).

If you feel particularly DIY, the ID of the spindle spacers is 24mm...

As for the XT 771s...it might work, it might not. I'm with DaveP again in that I would like to measure the setup before approving it.

Have a good weekend guys!
-philip @ e*thirteen

ciszewski · Feb 6, 2009

Thanks Davep and Phil

Well i'm a fan of the shimano cranks, so i'll end up with either the SLX or XT's. And if I get the 771's I'll be sure to measure them on the bike (it won't be for a while b/c it is mighty cold here and my bike just got ordered) and take a picture with measurements.

gemini2k · Feb 6, 2009

bdamschen said:
? I know where a bb spacer goes. What is a crank spacer? Does it sit on the spindle?

Between the left side crank and BB cup, on the spindle, yes.

Over-x · Mar 5, 2009

davep said:
Chainline is defined as the distance from the
You cannot space an external bb out that much because of the fixxed spindle length. Check out the instal instructions for shimano cranks. On a 73mm bb, you need a single 2.5mm spacer (or equivalent) on the drive side. No spacers on the non-drive side. This provides a 50mm chainline. TO get to 55mm, you would need a total of 7.5mm of spacers on the drive side. Two things would happen (both bad). One, the drive side cup would only have a very few threads left in the frame. Two, the spindle would be shifted 5mm to the drive side..out of the non drive arm. The non-drive arm interface would only overlap about 1/2 of what it is supposed to. I dont think it would take long (maybe one run) to rip the ND arm right off the spindle.

There are a couple ways to make this work correctly.
1 83mm external cranks with an 83 - 73mm adapter from RF (or make you own).
2 Isis cranks with 128mm bb.
3 73mm external cranks with a single ring on the outer mount. This requires removing granny tabs and an LG-1 type guide.

Hi,

I have the same issue. I'm trying to fit a Saint 2009 crankset 83mm in a 73mm shell.

I already have the 83-73mm adapter from RF. I'm a little confused. How many 2.5mm spacers should I place in the drive side and non drive side (to avoid the two problems you referred)?

I'm planing to get a diabolus cups or a 2009 saint cups, to mount with the adapter...

Many thanks.

Regards from Portugal
NS

davep · Mar 5, 2009

Did the race face kit not come with instructions??

Either way, you should be able to measure the spacers and figure out what you need. One 2.5mm bb cup spacer is typical on the older shimano bb cup thread depth. You should have no problem putting one bb spacer on each side and then using the spindle spacers to make up the difference.

THe new saint uses 'longer' bb cups. I have not measured them, so I do not know how much longer they are. It might be possible to use two (a total of 5mm of bb spacers) on each side....and then using spindle spacers from there to fine tune.

Supa8 · Mar 5, 2009

Look at the instruction sheet and although it does not say "set this way" it is correct how the spacer layout is set up. After figuring it out in my head what was what it matched up to the instruction sheet... they should say "typical setup" which would be a helpful note on the setup sheet.

Over-x said:
Hi,

I have the same issue. I'm trying to fit a Saint 2009 crankset 83mm in a 73mm shell.

I already have the 83-73mm adapter from RF. I'm a little confused. How many 2.5mm spacers should I place in the drive side and non drive side (to avoid the two problems you referred?

I'm planing to get a diabolus cups or a 2009 saint cups, to mount with the adapter...

Many thanks.

Regards from Portugal
NS

Over-x · Mar 5, 2009

Unfortunatelly, the adapter didn't come with the instructions. I've searched the web and didn't find it too.

Thanks for your explanation. I'll try to fit it as you recommended.

NS

Supa8 · Mar 5, 2009

OK here it goes. RF 83mm to 73mm BB adapter to spacers.

Drive side.

From BB out. Black 1mm spacer seal to BB, 2X 1mm white spacers, 1x 5mm spacer

Non drive side

From BB out. Black 1mm spacer seal to BB, 2x 5mm spacers, 2 x 1mm white spacers, crank face end seal.

TKCastle · Mar 5, 2009

I have a "wacky" chainline bike and almost all instructions for installations are always off. I use the trial and error method now. Yeah sure I have to assemble /re-assemble, but it's better than going crazy thinking the specific component isn't going to work. As for figuring out spacing and chainline's I would just use a Micrometer, find the center of your bottom bracket, install cranks with a spacer and measure center of BB to the center of the two chainrings or from the one ring if your running a single up front. Manufacturer specified CL is still off add or subtract a spacer re-install cranks, measure, Etc,Etc...

TWeerts · Mar 5, 2009

the shell width has less to do with it than the chainline measurement.

generally,though you can fine tune it with spacers,

50mm chainline is for 135mm hub and
56mm is for 150mm hub

davep · Mar 5, 2009

Just to confirm that I am a little retentive....

for a non-offset frame....
135 hub is exactly 47.5mm chainline
150 hub is exactly 55mm chainline

The currently used but 'incorrect' 50mm used for 135 hubs, and 56,57,58mm, etc used for 150 hubs are to allow for external bb bearing clearance.

Supa8 · Mar 5, 2009

The setup I listed above with the adapter kit gave a 55mm chain line. I ended up with a 56mm chainline ( swapped one 1mm white spacer ) which matched the Truvativ Howitzer setup on my Demo 7. I used the ISCG BB mount and only had to use one 1mm spacer to mount up an LG1 to the ISCG BB mount. Would have been flush at 55mm.

I have Race Face Atlas FR cranks so I did not feel like removing them at this point to shift over. Not fun pre-loading the BB on a RF setup.

davep said:
Just to confirm that I am a little retentive....

for a non-offset frame....
135 hub is exactly 47.5mm chainline
150 hub is exactly 55mm chainline

The currently used but 'incorrect' 50mm used for 135 hubs, and 56,57,58mm, etc used for 150 hubs are to allow for external bb bearing clearance.

Huck Banzai · Mar 5, 2009

gemini2k said:
My vp free has a 73mm bb and a 150mm rear wheel. I'm runnin 83mm saints with 2 bb spacers on the drive side, and 2 bb spacers on the non drive side, and 1 5mm crank spacer on the non-drive side. Chainline is perfect. Matches with the mrp guide without any washers needed. I dunno if any of this helps though...

Same here - Im using a raceface 'kit' for the Diabolous, but on my 83mm saints, which includes alu 5mm spacers and a wider BB 'tube' (the plastic tube that connects the bearing cups internally.)

Works perfect with my SRS (with flipped ISCG adapter)

bigjimmy · Oct 3, 2009

so to confirm that i have this right???

the following will work with spacers ? my new frame is 73/150

gravity light cranks off a 2008 sunday team. (from a 83mm mega exo BB)
new 73mm mega exo BB
space them out to get the right chainline.... ? ?

or do i need to go and buy cranks for the 73mm BB ? ? ?

sorry if this is a pain, i just have so many conflicting opinions with some people saying it will work, and others saying it won't.

i just need to know if i need to go buy new cranks.

DirtyMike · Oct 3, 2009

bigjimmy said:
so to confirm that i have this right???

the following will work with spacers ? my new frame is 73/150

gravity light cranks off a 2008 sunday team. (from a 83mm mega exo BB)
new 73mm mega exo BB
space them out to get the right chainline.... ? ?

or do i need to go and buy cranks for the 73mm BB ? ? ?

sorry if this is a pain, i just have so many conflicting opinions with some people saying it will work, and others saying it won't.

i just need to know if i need to go buy new cranks.

Ok first off, this is all about external bearing BB systems.

Ok its really simple..... 150 rear<or offset 135 demo> you buy the 83MM crankset, unless your running a howitzer<will come back to that>

If said bike with the 150/135 offset bike has a 73MM shell, the easiest way to set it up is with the RF spacer kit. You can also make some spacers if your mechanically inclined at all. It doesnt move the BB itself, they go between the cranks and the BB bearings. Its really easy

If you have a bike with a standard 135 rear, and a 73MM shell..... you just run the 73MM cranks.

If your running a Truvativ Howitzer system its even easier to set up a bike that has a 73mm shell with a 150m rear end<IE Socom with 150 drop outs>......... You order the 73/68MM BB, but in the 56MM chainline Model.

JCL · Oct 4, 2009

IMO chainline is the most overrated recommendation spec on bikes. Anything other than 83mm BB with 135mm rear axle works fine.

150mm rear, 73mm bb, chainline, questions

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