BB Spacing Question
 

I have a 2018 Kestrel Talon X Ultegra with a PF 30 BB shell and currently a Praxis Works PF30 to GXP BB with Oval 300 cranks (in GXP obviously). The Praxis BB has around 10mm of threaded space outside the BB shell (i.e. the inside of the crank arm at the bolt is 10-11 mm away from the carbon shell of the bike). I'm asking because I'm looking to get a Quarq PM and I would like to ditch the conversion BB and get an actual PF30 BB and a DZero in BB30, not GXP. Or, alternatively, a Wheels Mfg PF30 to Shimano BB with R8000 cranks (PM location TBD if I do that).

Do PF30 / BB30 BB run flush with the carbon shell or do they press out as well, like my Praxis?https://cimg2.ibsrv.net/gimg/bikefor...5423354b29.jpg

Praxis BB pushes 10 mm or so out from the shell, roughly 7 mm of clearance between brake and crank arm

In answer to last question...unlike your Praxis shown, they run flush which is design intent. This is because the bearings are within the 68mm shell and not outside the shell as you show in your picture. The GXP crank is a long spindle crank which can take advantage of an outboard bearing BB which btw promotes the 'purchase' of a spanner wrench on each side to 'thread together' respective cups for a rock solid unified sleeve that won't creak. Praxis was really born out of the inherit design weakness of PF/BB30.

If you pick the crank you want for this bike, the decision relative to which BB maybe best will be clear.

Let us know what you decide for a crankset and I can try and help with your BB decision.

Will tell you what I prefer and why however if interested. Also I am not a fan of GXP with wacky dissimilar bearings ID which is merely a proprietary kluge...actually not much of a fan of Sram or their cranks. Nor am I a fan per se of native BB/PF30 albeit typically BB30 with alloy bores can be tamed more easily compared to PF30 provided Loctite is used. I prefer your aftermarket BB setup aka an outboard bearing design if you don't need the more narrow Q-factor of PF30. Reason is pretty simple. Not only is running bearings more outboard a more solid support of the crank spindle but this allows threading together respective halves of the each side of the BB cups that capture the bearings which ensures the most solid BB aka no creaking. PF30 in its native form is more problematic because respective cups can not be mechanically fastened together. Having the BB flush to the shell does not afford any purchase for a spanner wrench to thread cups together as you show in your pic.

So my preference is R8000 crank with single or dual arm PM with outboard bearing BB taking advantage of the long Shimano spindle originally designed for BSA with outboard bearings. To me Shimano cranks from 105 to DA are the best in the industry and have them on a couple of bikes.

Thanks for the reply. So, basically I either get Quarq in GXP to keep everything the same and known compatibility, but accept that the spindle isn't quite as good as 30/Shimano, or I get a Wheels Mfg 30 to shimano conversion and add a couple spacers to get that spacing between the brake and the Stages (or Pioneer or 4iiii) unit. To your knowledge, is the Shimano spindle long enough to accommodate for 2-3 mm of spacers on the non-drive side? I spoke to the LBS about it and he kinda shrugged saying he doesn't know until he sees it, but obviously if the spindle won't allow for 2-3 mm of spacing I don't want to drop $1,000 in to a R8000 PM just to find out I can't mount it on my bike.

People have their preferences all said. No doubt a pretty big following for Quarq
on this forum in different spindle formats.
Really comes down to what you prefer all said. How do you feel about Sram crank designs?

Here is a good technical critique of GXP which to me exposes the design weakness. Forgive my cynicism as to why Sram uses 24mm on one side and 22mm on the other...to 'equalize lateral bearing forces'. To me the design does anything but. To me, the crank is a horrid design, not only the crank retention but also BB execution. I wouldn't own one but you have a converted one with a Praxis sleeve that may work ok.


To me, the Shimano crank has few peers. The only crank that rivals it I believe is Campy UltraTorque, but Campy UT has more limited applications.
What to look for in a crank design is simplicity. Both Shimano and Campy are very simple designs that are least tolerance sensitive. I own both.

So what for you to decide?

You have my assurance that a Shimano crank will bolt to your a PF30 bottom bracket...what you have. Don't know where you get the 2-3mm reference. Can you explain this concern?

I just measured the driveside clearance and it seems that I have 8-9 mm of clearance between the chainstay and the inner ring with the outboard bearings of my current BB. If I remove that and go flush with a PF30, would I have clearance issues with my inner ring? I can't imagine a bike manufacturer didn't take this into account so I have to believe it would work but I don't want to spend the money and find out later that it won't. I'm not as worried about Shimano because from what I can tell the Wheels Mfg also has the outboard bearings so clearance shouldn't be an issue. I refer to the 2-3mm of spacers because if I get an R8000 crank, I'd most likely get a Stages/4iiii/Pioneer PM, either in L/R or just L form, but I need 2-3 mm of space for it to clear my brake as I only have 7 mm of clearance instead of the required 10.

https://cimg4.ibsrv.net/gimg/bikefor...5e62005b1c.jpg

I believe you are making a false assumption unless I am misunderstanding you. You would be buying a new Shimano crank and new bottom bracket correct?
This has no relevance to any flushness you reference. A good bottom bracket to mount a Shimano crank to your PF30 bike would look very similar to what you have. The bearings would be outboard of the shell.

Can you show me a picture of your brake issue?

Correct, I believe a Shimano crank would go on there just fine because of those outboard bearings. I'm wondering if I were to go with another crank, like Rotor 3D+ or FSA, in PF30, whether I'd run into clearance issues.

I have attached two more photos of the brake clearance issues - one photo shows a comparison with a 10 mm allen key. For reference, the typical clearance required for the Stages/4iiii/Pioneer PMs is 10 mm, hence I need to be able to fit that 10mm key https://cimg5.ibsrv.net/gimg/bikefor...157e5f0566.jpg
https://cimg6.ibsrv.net/gimg/bikefor...0032d78018.jpg

A bb30/pf30 specific crank will have crank arms that flair out more so you don't have to worry about the BB spacing, for sram red I think there is a 1mm difference in q-factor.

This is not quite accurate.

In some cases, the crank arm will be flush to the frame. In some cases there will be a spacer. Some Sram BB30 cranks and some Hollowgram cranks, for example, will require a spacer. It depends on which model you get.

You made a real generic claim tfp. For veracity, you will have to be quite specific. Quite possible we aren't even talking about the same thing and speaking right past one another. All PF/BB30 bottom brackets are flush by design. Spacing the crank away from the frame may vary. Depends on the crank. Some 30mm long spindle cranks will be spaced well away from the frame like Rotor with a regular PF30 BB with bearings within the shell.

This thread could get very messy with different points of view. BB's are so complex as they relate to specific cranks that people are going to misunderstand what is being said. Its like what the guy in the video said about GXP. 90% of the people who install them have no concept of how GXP controls preload.

OP, you are bringing many different cranks now into the mix. We talked about GXP and Shimano and now you are adding more. Each is a bit different that may require different spacing and BB selection..

I hope what I wrote made some sense and if not, perhaps others can help.

Good luck.

Speaking of space---what about spacers? I had an issue with my left heel hitting the chain stay on one of the three bikes I have equipped with Wheels thread-together BBs. I added a couple spacers. Problem solved.

Again, your statement that ALL BB30 cranks are flush by design is inaccurate. Some are. Some aren't. It depends on the crank.

Cannondale, at some point, switched from a 104mm spindle to a 109mm spindle to accommodate the BB30A system. If you put one of those BB30A spindles on a BB30 frame, you will need a spacer to fill the gap between the NDS crank arm and the frame.

See here: https://www.cannondaleexperts.com/Ca...83_p_5630.html

And here: https://www.cannondale.com/~/media/F...nstr_1012.ashx

Also, Sram requires spacers and pre-load adjusters on some BB30 cranks (those with carbon arms and removable spiders), which space the arm from the frame: https://www.sram.com/sites/default/f...brackets_0.pdf

The full carbon Sram BB30 cranks, like Sram Red, are flush with the frames.

This is our second time around on this...lol.
For you to extrapolate your comments from what I wrote suggests no amount of words will create agreement. Of course what you wrote is true but it isn't what I wrote. I wrote all BB30/PF30 'BB's' are flush...not cranks. Of course spindle lengths vary on 30mm dia spindle cranks which requires different spacing...or not.
That is my last attempt.
I admit surprise we are talking past one another so profoundly because I generally agree with you on the forum. If you care to, re-read what I wrote that you quoted. I said 'bottom brackets flush' not cranks. Spacing of cranks may vary. As plain as day. Come on tfp.

Ahh. Yes, we are talking about different things. I stand corrected.

Hey folks ...

I saw where this was going and really hoped it wouldn't ... let's stop it before it gets there.

Campag did his best to help the OP ... remember the OP? Sure, he didn't mention every single aspect of every single crankset and BB on the market ... but he did say, Can we possibly have ONE FREAKING THREAD where we don’t devolve into a bunch of toddlers in a kiddie pool urinating at one another?

If the idea is to Help the OP—Awesome. If the idea is to bicker over minutiae with another poster for e-peen points,… aren’t there enough other threads where people can do that?

Can we Once forget our egos and actually care about a person trying to get advice?

Even the info offered by [MENTION=92828]topflightpro[/MENTION] could be helpful … if it was stated and expressed in a helpful way.

But really, what is need here is more information, not more bickering. And really, as [MENTION=88222]Campag4life[/MENTION] notes, once the OP picks a crankset, there will be some real opportunities to choose the best BB.

I think both parties here are well-meaning and very well-informed. Ths may be a classic—“What we have here … is Failure to Communicate” situation, or it may be nit-pickery … there may be one exception or two to some otherwise useful generalization, and those exceptions can be noted without any sort of value judgments.

So far everything has been civil … and I am pleased. But … I think if the posters focus on what ther OP needs, and not on each other, the civil mood could prevail. The other trend would be normal, which in his case is not good.

As far as it goes … Most press-fit BBs seem to slide in flush with the frame, while thread-ins need a flange for a wrench. Spindle lengths and spacers are a completely different issue.

I think the OP is confused about spindle length, which is independent of BB. I know I have Hollowtech BBs on a couple bikes and they protrude quite far … and Wheels Mfg on a few bikes and they protrude about 1 mm. I use whatever Shimano cranks I have on hand (or in one case FSA---and that ignorant SRAM 24/22 expletive deleted) with no issues at all. I use spacers on the left-non-drive side to balance Q-factor.

There are spacers available for both sides if the OP feels he needs extra clearance, but I think the Shimano cranks will work just fine as they stand.

To the OP: As [MENTION=88222]Campag4life[/MENTION] suggested—pick the rank you like (and make it Shimano ;) ) and someone here can help you with your then more specific needs.

Hey - SRAM has their frame fitment standards posted and available online to the public. You can simply look and measure.

In general BB30/PF30 (same standard BTW just with cup or without) will clear the frame. Stupid to make a frame with a 30 BB shell if it won't. Same with the brakes. That's an OEM brake spec - believe it or not they do actually check this stuff when they spec it.

Quarq has replaceable arms/spindle standards now. Better than the 3 bolt ones from before.

Honestly the easiest is to get the GXP knowing that no matter what frame you move to you will be able to get a conversion to GXP as it is the longest and narrowest spindle option. You most likely won't go wrong with the BB30 version anyway. If you do then call Quarq. They will have you ship it to them and they will swap the spindle to the other standard. If it's new they most likely won't charge you. If they do it's only like $150 or so....about retail on a new praxis conversion BB with ceramic bearings.

Here: https://www.sram.com/service/sram/437
Took a couple of seconds with Google.