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PostPosted: Thu Nov 03, 2011 10:41 am 
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I've searched and searched, and no one else seems to have this problem, or atleast think of it as a potentional problem.

So I've just got some Sram RED cranks and a Hope (Ceramic) Road BB, with the Hope GXP conversion-set. Now what the GXP-conversion set does, is that it changes the way the crankset mounts to the BB. There are two "rings" that pressfit mount on either side of the non-drive side BB bearing. A: Making the ID of the bearing smaller to fit the Sram crankset axle, and B: Taking all the pressure of the non-drive side bearing when installing the non-drive side crankarm as it presses only against the outer "ring", which in turn presses against the inner "ring", which in turn presses against the ridge on the Sram crankset axle. There by in theory putting all of the preload pressure on the ridge of the axle, not on the BB bearing. This way the drive-side crankarm doesn't even touch the drive-side bearing.

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That's fine in theory, but I have two potential problems that I just can't figure out. For one the GXP-conversion "rings" are about 4mm wide together, in the parts that sit outside of the bearing, leaving me very little visible crankset axle to engage the non-drive side crankarm on. With a normal Sram GXP BB the crankarm will sit about 16mm in on the crankarm, I've got 12mm showing... It's tight, for now, but I haven't ridden it yet and I fear there will develop some play, and ruin the axle splines and non-drive side crankarms splines.

Second problem, and the main one. As I fully tighten the non-drive side crank, there really is some serious drag from the BB (I get about 2 full revolutions from a hard spin on the crank). If I loosen the crank even slightly the drag is gone (5-6 revolutions from a hard spin on the crank). In theory, with the BB/Crankset interface of the Hope BB, this should not be possible????

The frame has been used with a Shimano setup earlier, which worked fine and very little drag on the BB, and the frame was faced by a good mechanic with the proper tools prior to mouting the Hope BB / Sram RED cranks. Everything has been mounted to the proper instructions and I've watched the Hope Tech YouTube video which explains the procedure in the same way...

Has anyone else had issues like this? Is the shortage of visible axle gonna be a problem, is the (hopefully initial) drag normal with a ceramic BB? And why does tightening the crankarm give more drag when in theory it shouldn't even be pushing on the bearing?

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Posted: Thu Nov 03, 2011 10:41 am 


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PostPosted: Thu Nov 03, 2011 1:03 pm 
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are you running any spacers on your BB cups? If so, I'd say remove them, so the NDS crank arm isn't squashing the system together as much, thereby causing drag.

All you say is correct and true :D The NDS bearing is indeed made wider by fitting the Hope adaptors, but then the NDS GXP bearing is wider than an equivalent NDS Shimano bearing, so you should still have enough axle sticking out to mount the NDS crank arm... In other words the GXP crankset/BB system is designed for a fairly wide NDS bearing.

ps. you may have already fitted the Hope adaptors but if not then file a notch in one of them, on the inside edge, to enable them to be tapped out in future should you need to replace the bearing itself. Without the notch they are a pig to get out.


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PostPosted: Thu Nov 03, 2011 2:29 pm 
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Sounds reassuring that I can run the crankarms with what seemed like a bit of short axle. Had read everywhere how difficult a time people had installing Sram RED on original GXP bearings because they had to mash hard on the crankbolt to get the NDS crank arm far enough in on the axle, and this went too easy. But it's a different system so maybe that's okey then...

I'm running the two 1mm spacers, one in either cup, which seems pretty useless as the drive-side crank arm isn't anywhere near the drive-side BB bearing. But I don't see how the system would be squashed together as there is nothing pressing on any part of the drive-side bearing or cup. It seems everything is held together only by the ridge on the axle pressing the NDS bearing outwards and the NDS crank arm pressing the NDS bearing inwards, with the DS bearing totally free of preload, the axle just sort of "floats thru" it...

So how would there be less drag, or drag caused, by having or not having the BB spacers (between the cups and the frame)?

Unfortunatly I've already installed the adaptors, without filing a notch, guess I'll have to get new ones if I don't get them out next time :)

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PostPosted: Thu Nov 03, 2011 3:59 pm 
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How about doing an experiment where you take the BB & crank off the bike and assemble the crank "in the air" with the non drive-side BB cup over the axle. That way you'll be able to see if you can reproduce the drag against the non-DS bearing, and also to confirm that the bearing spacer is correctly pressing up against the axle shoulder (and not getting hung up on something).

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PostPosted: Thu Nov 03, 2011 4:10 pm 
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Quote:
the drive-side crank arm isn't anywhere near the drive-side BB bearing


ah okay. The drag isn't caused by 'being squashed' then. Sometimes you can get drag because there is lateral pressure on the driveside bearing but given you have some space between the driveside crank and the bearing then this can't be the case.

You are correct that the driveside axle 'floats' inside the bearing and has no direct pressure on it.

The GXP design is that the NDS crank tightens up on the axle and squeezes the inner race of the NDS bearing up against the lip on the crank axle, thereby removing any side-to-side play. There is no preloading of the bearings laterally like on Shimano's system.

If you have drag then either of the bearings is draggy, or .... I'm not sure what else it could be. If the BB shell is faced then the bearings should be parallel so that's okay.


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PostPosted: Thu Nov 03, 2011 4:42 pm 
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dwaharvey wrote:
How about doing an experiment where you take the BB & crank off the bike and assemble the crank "in the air" with the non drive-side BB cup over the axle. That way you'll be able to see if you can reproduce the drag against the non-DS bearing, and also to confirm that the bearing spacer is correctly pressing up against the axle shoulder (and not getting hung up on something).


Unfortunatly I don't have the BB removal tool at home, and getting it back to a mechanic is sort of a time consuming drag that's a last resort... But if I can't find out what it is, I suppose it has to come apart to figure it out...

Maddog 2, yeah that's what bothers me... if any of the bearings were draggy, I figure it should be about as draggy without tensioning the NDS crank arm that last quarter of a turn, which almost triples the drag. Total conundrum...

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PostPosted: Thu Nov 03, 2011 5:07 pm 
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Defect of the shoulder edge on the axle that means when its tightened down hard there's a distorting effect on the bearing? Seems its getting hard to think of a way that the bearing drag could be dependent on the bolt tension...

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PostPosted: Thu Nov 03, 2011 5:12 pm 
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when we installed those rings on my friends Hope bottom bracket, for using it with sram red crankset, the instruction clearly said that this spacers should be inserted from the backside of the bearings. so you have to unmount the bearingscups from the frame, so that you can insert the spacers from behind.

but thats many wrong? and maby it wash´t your problem


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PostPosted: Thu Nov 03, 2011 5:16 pm 
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JensW, the spacers/adaptors where fitted accordingly with the Hope Tech YouTube video and the paper instructions they came with, i.e pressfitted in from both sides on the NDS bearing before the cup was installed in the frame. I suppose that's what you mean too?

I might have found the solution though, or sort of... I gave both crank arms a couple of firm punches from each side with the rubberized gripping end of a large screwdriver (had no rubber/plastic mallet) and then spun the cranks by hand like a thousand revolutions or so (couple of minutes...)

And it seems to have eased up the problem quite a bit. There is still some drag, and the BB makes a noise like "Hssschhhh...." when spun, but it's a continous sound so I'll write that down to (hopefully) being the seals and not the ceramic balls.

With pedals mounted it will now turn some 10-15 revs with a semi-hard spin but there is still some detectable drag when giving it a lighter touch, which I hope will fade away while breaking it in on the road.

Although I was contemplating breaking the seals/bearings in "manually" under controlled circumstanses, ie putting a 10mm hex bit in i drill and running it at, say 100-150 rpm for half an hour or so. Is that crazy? Not that I'm too lazy to break the BB in the old fashioned way, but it's winter here so the bike is out of comission for the months to come anyhow.

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PostPosted: Thu Nov 03, 2011 10:38 pm 
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I've used this setup for a couple of years, with the only difference being that I have the stainless steel bearings and not the ceramic version (the cranks have been a SRAM Red compact crank or a Truvativ Rouleur triple crank, with frequent changes depending on the ride/time of year).

As for bearing smoothness, this is one of the smoothest setups I've experienced, with the cranks spinning almost effortlessly when on the repair stand (and I work in a bike shop, so I've had plenty of chances to spin a lot of different cranks in various BBs) - even better than some setups that I've seen with ceramic bearings. This has been the case right from the start, no break-in period was needed.

As I said, I've swapped between cranks many times (and also removed the cranks several times to switch chainrings). Removal and re-installation was always a breeze - torque the bolt to the recommended range and the cranks spin super-smooth. I appreciate having only one bolt to mess with, it really speeds up the process compared to Shimano cranks.

The GXP adaptors pressed in easily, and I recently needed to remove them after a couple of years and they came out without much hassle at all.

Overall, I'd rate the Hope bearings as some of the best I've used, and the GXP adaptor sleeves worked great for me. The anodized color options of the Hope BB was what made me choose it in the first place, but in the end I loved all aspects of the BB.


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PostPosted: Fri Nov 04, 2011 10:29 am 
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Quote:
With pedals mounted it will now turn some 10-15 revs with a semi-hard spin


That's fine. Just ride it! :wink:


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PostPosted: Fri Nov 04, 2011 11:15 am 
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Yeah, I suppose it's good enough. Even if I really was hoping for a very low friction setup, especielly considering the premium price tag... But maybe it will get better. My CK rear hub was a huge dissapointment regarding bearing drag when new, but after some 60-70 initial hours of riding it's just fine.

The thought struck me that maybe the bearings/seals require a little side loading, ie force on the pedals, to properly break in. So I'll leave the drill in the tool box ;-)

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Posted: Fri Nov 04, 2011 11:15 am 


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