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SRAM Crank Drag?

7 posts from 4 voices

Started 2 years ago by AggieMike
Latest reply from Doc Moots

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AggieMike
Member

I have a SRAM Force Crank with Chris King BB on my Moots Vamoots. It feels to me to have quit a bit of drag when spinning. For example, when I spin it with the chain off it barely makes it two times around in contrast to a Shimano DA I have on another bike which spins freely. I don't think it's the BB b/c I experience the same problem with the GXP BB. Also, I have it torqued less than recommended. In fact I tighten the crank just to the point of no side-to-side play. Have you all experienced this same problem with SRAM Cranks? What, if anything, have you done about it? Does it impact efficiency when pedalling? It certainly appears to mentally, but I can't really tell when riding. I appreciate hearing from you.

Thanks,
Mike

Posted 2 years ago #
arm017
Member

I think that it could be a couple of different issues. King bearings have a higher amount of drag in just about all of their components to the the amount of grease they put in from the factory. This is part of their secret to their stuff lasting for decades. Also it can also be due to the inherent design of a GXP. It is a stepped spindle. That being said, it should spin a bit more freely than 2 revolutions with minimal torque.

First off, I would take everything apart back to the frame and start from scratch. You should be using NO BB cup spacers (the black 2.5 mm spacers) since it is a 68 mm BB shell. The BB cups should be torqued down to around 40 nm. There should also be no spindle spacers with the use of any road double crankset. Make sure you put that compression washer (spring ring looking thing) on the drive side of the GXP spindle before you put it through the BB; a little lube won't hurt it too. Grease up the contact points of the spindle, put it through the BB, and put the other metal ring that fits on the GXP tip in place. Lastly, (I think this is the part that could be affecting your drag) make sure to put that silver adaptor washer on the spindle before you put the crank arm on. It would give you a false torque reading without this washer. It could also be due to any BB cup spacers. But definitely, definitely, torque it down the the correct settings. (45 nm). The whole GXP system is particularly contingent upon correct torque. Also king makes two different types of road bottom brackets: one for GXP with a stepped spindle and the other for shimano. Make sure you have the stepped one. King makes very precise stuff, but it can be complicated with all of their different designs to put it together.

Now once everything is in their perfectly, and you spin it freely, it will still have a bit more drag than that of a shimano DA (Both broken in). That is definitely negligible, and if anything, take comfort in the fact that that bottom bracket will likely last much longer than the shimano dura ace (King makes a grease injector tool too shoot fresh grease in too).

Once you know for sure that everything is in there correctly and torqued down to the correct spec, I would just ride the hell out of it and shoot some grease in their on a biannual basis. You could always put some lighter, less viscous grease through that can help to reduce drag.

I don't know if you were in town for aggie muster yesterday, but I work at BCS bikes if you had your bike in town today. I hope this helps.

Austin
FTA C/O 2011

Posted 2 years ago #
AggieMike
Member

Thank you very much for your comments. I appreciate it. I've done everything you've mentioned with the exception of using the silver washer between the non-drive arm and BB. I'll give that a try and see how it works. Also, I do go to Austin from time-to-time. I'll have to stop by you shop. Thanks again.

Posted 2 years ago #
JonC
Administrator

AggieMike,
Let us know, I'd like to hear the end of this. I'm running a King bb on my mountain bike and it spins the longest of any bb I've had. I also have not greased it ...ever. Which is probably not good.

Jon@Moots

Posted 2 years ago #
AggieMike
Member

I put the metal washer back on the non-drive side and that made a world of difference. The crank still doesn't spin like some of my others, but I don't think it will. In any event, it does spin much more freely than it did before - 100 times better actually. Also, I did regrease the BB which I think may have contributed to some of the drag. I suspect that will loosen up over time too. It has been difficult to find grease cartridges for the gun I use with the injector tool. The bike shops around the OKC area don't carry grease cartridges. The auto stores do, but I don't know if there are better greases for bikes - I suspect there are. Does anyone have any recommendations? Arm017, thank you for you for your recommendations.

Posted 2 years ago #
arm017
Member

That is good to hear Mike. Philwood makes some pretty good grease cartridges. Its not going to be super swav racing grease, but it will be a solid all around grease that is cycling specific. Its not unreasonably priced either. Im not a car guy, but I would imagine the automotive grease to be a bit more viscous.

Posted 2 years ago #
Doc Moots
Member

MIke,
Last season I rebuilt my YBB with a SRAM XX Groupo and King hubs. My CK head set was still going strong after ten years of zero maintenance. Chris King engineering said I should have cleaned the sand off the top of the head set seal every two years and added ring lube to the bearing per the instructions. This is why CK makes the seals so tight. I also learned they don't use the Ring lube grease in MTB hub bearings. The grease they use is like Phil Wood grease, very thick but holds up to water well.

I next learn that water is greases biggest nemesis. I went through many SRAM GPX BB last year! The old design was garbage. Actually, it's worse than that but this is a family blog so I'll keep it clean. However, SRAM was great about warranting the BB. The new SRAM ceramic gutter seal BB is a completely new design, one that looks a whole lot like a Chris King BB. Because I went through so many BB's last year, (it was a really muddy riding year for me) I tried many different greases.

The best grease I found is DuPont Krytox which does not break down in water. However, this grease is super expensive $$$$ and requires a complete bearing disassembly and cleaning as it's not compatible with hydrocarbon base greases. Next I would use Finish line ceramic grease, and after that I would use Phil Wood. Motorex makes a nice grease too. Lastly, Finish Line makes a grease pump you might be able to rig with a zerk fitting to feed the CK BB grease injector tool. Though, I have not tried this yet?

Happy trails, and remember to keep the rubber side down!
Doc

Posted 2 years ago #

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