Bottom bracket question

Discuss light weight issues concerning road bikes & parts.
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parajba
Posts: 613
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

Hi All,

Can somebody explain if the below powermeter is compatible (without adapters) with the following bikes:

https://www.sigmasports.com/item/Quarq/ ... Meter/ENWU

Canyon Aeroad/Ultimate CF SLX 2019
Cervelo S5D or S3D 2019 or R5D 2019
BMC Teammachine 2019
S Works SL6/Venge 2019 (I think ideally I need the BB30 version of the Quarq for these 2 bikes, as explained by a user on this forum).

I simply don’t understand how BB and framesets work. :-/

There must be something online which explains all this stuff...somewhere.

Thanks for reading.

Is there a guide or something to read?

by Weenie


TobinHatesYou
Posts: 4198
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

A GXP DZero can be fitted to any of those bikes (it can in fact be fitted to any road bike you can think of.)

However you will need specific bottom bracket conversions for all of them.

Cervelos use BBRight
Specialized use OSBB aka BB30
Canyon and BMC use BB86 (I think?)

parajba
Posts: 613
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

TobinHatesYou wrote:
Sun Dec 16, 2018 5:40 pm
A GXP DZero can be fitted to any of those bikes (it can in fact be fitted to any road bike you can think of.)

However you will need specific bottom bracket conversions for all of them.

Cervelos use BBRight
Specialized use OSBB aka BB30
Canyon and BMC use BB86 (I think?)
Thanks a lot. How does an adapter work? For example, the SL6/Venge S Works have ceramic bearings. Is using the DZero GXP + adapter + ceramic speed making any sense or will I be loosing the efficiency of the ceramic bearings? Again, this is down to my lack of knowledge on the subject...Additinal friction? Weight? Less optimal power transfer as “there is an adapter” in between? I am having a bike fit so I might have to seek the powermeter anyway (I might need different crank arms) but I would like to understand the differences between the various options...

Jugi
Posts: 543
Joined: Sun Jun 24, 2018 8:10 am

by Jugi


parajba wrote:
Thanks a lot. How does an adapter work?
1. Frame has a bottom bracket shell, which dictates the compatible bottom brackets.

2. Bottom brackets are made to fit different bottom bracket shells and different crank axles. Therefore you, in basic mechanical principle, you can think of different BBs as "adapters". On top of that, actual BB adapters exist as well. Those are meant to be used when there is a discrepancy between the BB and the crank axle.

3. Crank axles are made in different diameters and lengths. Like Tobin mentioned, in your situation the GXP is universally adaptable because the crank axle's diameter is nominally 24mm. All frames you mentioned are designed to fit cranks which have a 30mm diameter axle. So basically you need to shrink the BB bearing's inner diameter from 30mm to 24mm (or actually 24mm and 22mm in GXP's case because of it's construction) to make a GXP crank fit the frame.

4. For example for the Tarmac SL6 there are different options for a BB if a GXP crank is to be used. BBs which are specifically designed for a BB30 BB shell and a GXP axle are available. Also, a typical BB30 BB can be adapted to a GXP axle with a separate adapter.

5. For mechanical durability, I'd choose a WheelsMFG BB30 to GXP thread-together BB, which mitigates the most common mechanical issues of a pressfit (BB30) BB and it does so by using the smallest amount of components. For lightweight construction, I'd choose the BB30 axle and fit that crank into a BB30 BB, as that will most likely produce the lightest BB + crank combination. However, at the same time it retains the basic mechanical issues of a pressfit BB.

Ceramic bearings are only a nice addition to a bike. Not necessary by any means.

parajba
Posts: 613
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

Thanks Jugi. Very comprehensive.

The SL6 comes with ceramic bearings (I think it does, am planning to buy the frameset only). If I buy the adapter you mentioned, will I undo the ‘benefits’ of the ceramic bearings? Or they are two different (and separate) things so the ceramic bearings are not affected and will function as intended? Apart from the weight penalty (80-100 grams I think), will there be any other penalty compared to the BB30 version of my power meter? I need to decide if I sell the GXP version and buy the BB30 version, or if it doesn’t matter and I can just use the adapter.

Jugi
Posts: 543
Joined: Sun Jun 24, 2018 8:10 am

by Jugi

As long as you have ceramic bearings in the BB, you will reap the tremendous benefits they offer. Installing adapters which make the BB (and the bearings) compatible with a GXP axle just introduce more components into the equation. A higher number of components means just more possibilities of something to fail, or start to creak. The ceramic bearings will work just as intended.

parajba
Posts: 613
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

Thanks again, found this useful diagram in case anyone has the same question.

https://wheelsmfg.com/tech/PDF/BB30-SRAM_ASSEM.pdf

Last question: will the adapter change the Q Factor?

Karvalo
Posts: 737
Joined: Fri Aug 10, 2018 6:40 pm

by Karvalo

parajba wrote:
Sun Dec 16, 2018 9:21 pm
Last question: will the adapter change the Q Factor?
No.

alcatraz
Posts: 2222
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Unless you are very rich it's usually a good thing to keep pwms compatible with future frames. For 700 euro I'd certainly choose that route.

I buy my power meters used so I can afford to get a proprietary frame standard that maybe saves a few grams.

A 2nd hand bb30 power meter usually comes at a discount and can be installed on osbb/pf30/bb30 sometimes pf/bb30a framesets. That means cannondale, felt, sworks, specialized etc and some chinese frames.

I don't recommend bb30 frames if you are a heavy rider. They usually remain flawless for light+medium riders assuming they were installed using the proper tolerances and retaining compounds.

parajba
Posts: 613
Joined: Tue Oct 28, 2008 9:00 pm
Location: London, United Kingdom

by parajba

I got my new Venge delivered with the Wheels Manufacturing adapter.

A few questions:
1) I noticed that the adapter turn with the crankarms. Is this normal?
2) I noticed a certain friction / resistance when turning the pedals, particularly obvious when spinning backwards with the hands. I noticed this while cleaning the bike. Noticeably more resistance than any of my other bikes. Is this the effect of the adapters, or the rear mech (Di2 DA), or the Ceramic Bearings in the BB, or the Ceramic Bearings in the hub, or should it be super smooth and free? Tbh I wasn’t expecting this at all, curious to hear opinions before I conctact my LBS.

by Weenie


1415chris
Posts: 1285
Joined: Sat Apr 18, 2009 8:59 am
Location: Surrey UK

by 1415chris

If by saying adapter you mean adapter converting 30mm bearing bore to 24mm, yes it will spin with the crank as it plays spindel width extention role "filling the gap "between the spindle and bearing inner race.
In terms of resistance when spining the crank backwards, assuming no cross chaining, I would say with the vigorous hand spin the crank should make a turn at least. If not, take the wheel off and check where the resistance is coming from, freehub or from the bottom bracket.

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