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Discussion Starter · #1 ·
20 year old bike, and the one thing that still confuses the heck out of me are the BB standards.

Anyway, should be BSA threads, and I know the width is standard too, it's my Cannondale.

My current crank PLUS bottom bracket PLUS chainring is 853 grams.

Is it possible to get that trio down to the 650 gram range for a dollar a gram or less? I assume used, but I can't find any option that gets me there for the dollar. The crank arms basically have to be 575g-ish for the total weight to be in the 650-ish range. I'm on 175mm now, seems good for me.

The chainring will be reused if possible. If not, it will be a 30 or 28 tooth oval. Probably 30 tooth absolute black oval. If I have to replace it, I am NOT counting that cost in the dollar per gram. Just the crank arms and BB combined to be in the $200 range.

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Biggest issue is I often don't know what I'm looking at when I look at these more modern cranks, the concept is just so foreign compared to the old style.
 

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Discussion Starter · #4 ·
hrm. I guess I need non-boost.

My C-dale does not use boost hubs. Today, I'm using 18 year old crank arms and a 104 BCD chainring. I've tried two, one that mounts on the middle ring flange, and one that has 3mm spacers so it is closer to the frame. Both ride just great, but I wouldn't want to push any more out of this boundary.

With the old spiders, I have made and experimented with making and using 1-3mm spacers (I have a lathe and turned some from brass), but anything new would be direct mount I assume. So I also assume I have to nail the chainline out of the box and end up with no adjustability.
 

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Discussion Starter · #6 ·
Spindle comes in different lengths too, or should I be good there? Says BB30, I assume I need a BSA BB with 30mm inside diameter and it works with a BB30 SRAM crank?

(quite old frame, it's threaded I am sure BSA, but it's the width that has me not 100% sure)
 

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ilmfat
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I had issues with 2 BB30 labeled cranks. They were designed for BB92 and had spindles too short for my 73mm. So I'm gun shy on cranks now. I like 104 BCD so usually by generations old cranks.

As far as using a boost spindled crank, it might work with a 4 bolt spider running the ring in the middle. Other people would know about that better than I do.
 

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ilmfat
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20 year old bike, and the one thing that still confuses the heck out of me are the BB standards.

Anyway, should be BSA threads, and I know the width is standard too, it's my Cannondale.

My current crank PLUS bottom bracket PLUS chainring is 853 grams.

Is it possible to get that trio down to the 650 gram range for a dollar a gram or less? I assume used, but I can't find any option that gets me there for the dollar. The crank arms basically have to be 575g-ish for the total weight to be in the 650-ish range. I'm on 175mm now, seems good for me.

The chainring will be reused if possible. If not, it will be a 30 or 28 tooth oval. Probably 30 tooth absolute black oval. If I have to replace it, I am NOT counting that cost in the dollar per gram. Just the crank arms and BB combined to be in the $200 range.

-----------

Biggest issue is I often don't know what I'm looking at when I look at these more modern cranks, the concept is just so foreign compared to the old style.
I bought a single ring 36 oval square bottom bracket for an outstanding $39 for my city bike on e-bay and it works perfectly 104bcd MTB Crankset 170mm Bike Chainring 30-42T Narrow Wide Single Chain Ring AL | eBay. Weight without chainring is a very competitive 510 grams, all together clearly lighter than the triple set Race Face Prodigy it takes the place of. That old Race Face set sold for $59 on e-bay so I came out ahead!

Note that there are now again a lot of good square bottom bracket choices on e-bay, so no need to switch to anything else.
 

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Discussion Starter · #10 · (Edited)
Well, the first thing I’d have to do is switch to a square BB!

the weight advantage of the new stuff is all in the BB. 510g is not saving weight when the square BB is 300g.

I have a truvativ ISIS BB, weighs 240g. So for me its a total package.

All that is baked into the first post
 

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Well, the first thing I'd have to do is switch to a square BB!

the weight advantage of the new stuff is all in the BB. 510g is not saving weight when the square BB is 300g.

I have a truvativ ISIS BB, weighs 240g. So for me its a total package.

All that is baked into the first post
Oh, I thought you had a square bottom bracket. I use a Race Face NEXT SL on my Ibis HD3. But a square BB works fine. Weigh wise it is not bad at all and you can do better only by spending 10 times as much. Plenty square BB are in the 100-150 grams, never used a BB square that was 300 grams, heaviest was XT at around 220.
 

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There were some great deals two years ago when Universal Cycles was discounting XTR 9000 cranksets for $200. I bought a bunch of the 2x then sold the chainring sets for $100 and put a Oneup or Wolftooth ring on them. Total was about $150/set. Those were the days boys.
 

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I just happen to have two sets of xtr m970 175mm cranks on my bench that I can weigh (doing some changes from xc to cx, - I'll spare you the explanation). XTR M970 with a single aluminum 'snail' 30t ring and the outer 3rd ring spider points ground off is 558g, the inner bolt points are ground off too. Triple ring xtr m970 with an aluminum 24t, steel 32t, and aluminum raceface 'rockring' outer ring is 686g. You need the tl-fc35 removal tool with that crank. I've been using those for almost ten years with no issues, good crank imo. My spare shimano bb in a bag is 93g. Avoid the M960, it uses a non-standard bolt width for the chainring, 102bcd or something like that.
 

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Discussion Starter · #15 ·
For the shimano 970, what BB is needed for an older bike? I think the bike is 68mm BSA, existing BB has a spacer on it. I assume I need BSA 68/73 (or just 73 and reuse the spacer), but not sure about that spindle.

Shimano SM-BB93 is what is needed for the XTR 970? or any BB that says it fits Shimano Hollowtech?
 

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The bb with this bike is a sm-bb70, which I believe is 'english' threads that would fit most of the threaded bbs from the past 30 years. It looks like the bb93 and xt-bb-mt800 are updated (improved?), but I have not verified replacement fit (I think it's just standard hollowtech), I just clean the bb70 bearings and repack periodically. There's some big washers that go between the bb cups and the frame, they're used to space/widen the outer bearing races to better match the crank inner width. Then there's a lockable adjustment ring on the non-drive side crank to sort of set bearing 'preload' (keep the axle from moving side to side) after the big aluminum bolt that holds everything together is tight (I forgot to weigh the big aluminum bolt earlier (10g). I would check carefully to make sure your bottom bracket width is compatible. The bb on this bike is 68mm wide, and I use one spacer washer on the non-drive side, - you would choose which side to use the spacer(s) on to adjust chainline.
 
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