Investing in BB30 PM a bad idea?

Discuss light weight issues concerning road bikes & parts.
AW84
Posts: 79
Joined: Fri Aug 15, 2014 7:04 am

by AW84

dudemanppl wrote:https://www.lightningbikes.com/cranks/bottom-bracket-cups.html

For Trek. Scroll down to BB90/95. 4130 bearings wouldn't fit.

AW84, please find all the correct information before you make another post. Don't spread the wrong info.


You may want to re-read the post...I've only asked questions.

Hexsense
Posts: 370
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

AW84 wrote:
dudemanppl wrote:Oh my god LOL we just outlined this. A BB30 Quarq fits in everything that isn't BB90. In fact it will still fit BB90. So yeah it fits everything.


Without buying new arms/spindle, how does it fit everything but BB90?

Okay i'll start slowly.
On the crank:
GXP spindle are 24mm diameter, long enough for 86.5mm wide bb.
BB30 spindle are 30mm diameter, long enough for 68mm wide bb.

Their corresponding BB:
Threaded BB: 41mm diameter, 68mm wide then the cup expand outside the frame make it 86.5mm wide bb
BB86: 41mm diameter, 86.5mm wide bearing inward.

BB30: 42mm diameter, fit Bearing in directly. 68mm wide.
PF30: 46mm diameter, bearing inside plastic cup then the module fit inside the frame.

There is enough space for the bearing for 30mm diameter axle to fit in 41mm diameter frame bb hole. but the problem is the axle is not long enough.

now BB386 enter the picture:
BB386 frame: same as pf30 but 86.5mm wide rather than 68mm. So normal length BB30 axle is not long enough. 24mm axle all fit fine with a correct bearing size.

BB386 crank spindle: 30mm wide, spindle long enough for 86.5mm bb.
it fit in BB30,PF30 frame on their own BB (no adapter needed) by using spacer on the side to make up the extra width 68->86.5 (included in the box of Quarq BB386).
fit in BB386 frame natively with no spacer.
fit in BSA/ITA easily just use bigger outboard bearing.
fit in BB86 but not optimal, 30mm axle in 41mm hole. it's diameter so each side has 5.5mm of space for cup and bearings. we start to see double row bearing on each side because of how small the bearing is.

BB90 has 37mm inner diameter, that's a big no. too little space for bearing system that is decently reliable.
====================================================================
Interestingly i got quoted for the weight of Quarq BB386 and GXP which is not really different at all. Spider and bolts weight the same so we focus on the part that is different.
Quarq GXP arm 416g. optional: extra weight of pf30 to gxp adapter.
Quarq BB386 arm 404g. optional: spacer to fit in bb30,pf30 which is 17.8g

It weight so similar that i suspect that both are steel axle unlike their real BB30 non power meter counter part which weight near 100g different between GXP and BB30.
Last edited by Hexsense on Mon Aug 21, 2017 8:33 pm, edited 1 time in total.

by Weenie


dudemanppl
Posts: 716
Joined: Fri Feb 22, 2013 5:09 am

by dudemanppl

Beautiful post, Hexsense. I didn't have the patience to explain it all over text... I can gladly talk about it all day though!

bm0p700f
in the industry
Posts: 3553
Joined: Sat May 12, 2012 7:25 pm
Location: Glermsford, Suffolk U.K
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by bm0p700f

I am confused byt the term investing. that normally means an appriciating assett but the moment you buy anything bike the value falls away.

Get a 24mm spindle and use adapters so it works in a BB30 frame. shimano are not going away from hollowtechII and frame most manufacturers wont make a bike that wont take a shimano chainset.

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