I have a 10t bmx driver unit with a knackered bearing (it uses 2 15/24/5 single row bearings). The chain line is over the outer bearing and that’s the worn bearing. If you were going to replace the bearing would you use regular single row bearings, a dual row angular contact, or two single row angular contact bearings face to face.

the outsider option is needle roller bearing, but I don’t really fancy running it against an axle of unknown hardness.

your thought appreciated

I don't see any advantage to using anything other than regular deep groove radial bearings in that application - the bearing isn't loaded when it's turning, and it doesn't see much axial load. 61802 is a standard size bearing, but do you buy a box of cheap ones and change them often, or buy a single high quality bearing that costs more than the box of cheap ones? IDK, this seems to be an atypical application, where it's more about resisting shock loads than turning reliably.

First thing I think of is too much chain tension. I've seen so many single speed chains that are way too tight. One can sometimes feel each link engage each tooth when on the repair stand. This will accelerate bearing wear big time. The right chain tension is no tension, as measured at the tightest point of the chain's rotations. Andy

Forgot to mention the type of bearing- Use the OEM design/spec if at all possible. Angular contact bearings are very dependent on the ability to preload them axially. Think of the cup and cone bearings that are used on inexpensive rolling things (baby strollers and joggers as example), without any axial preloading these wheels have a lot of slop and rattle about on the axle as the bearings wear. I strongly suspect your (brand yet unknown) driver has zero ability to address this preloading need. Additionally double row and/or angular contact cartridge bearings are often wider than a single row radial contact design on the same OD and ID.

Last bit I'll add is that of the dozen+ freehub bearings I have replaced (cartridge radial contact) almost every one has been a royal pain to remove, heating the FH body in the oven to 200+ F helps Andy

Good point - some BMXers seem to like the chain to be completely rigid, I guess it's an engagement issue where any amount of free play is considered too much when you're doing tricks, but if you don't set the chain at the tight spot that's going to put a big load on the bearings.

just get a new freewheel assy(assuming that is what you're calling a "driver")... other parts will also be worn out by now.

and i agree completely with Andy on the "Too Tight Chain" explanation... i see that all too often here.... the 9 tooth hubs are FAR worse, and excessive chain tension kills them quickly.... add some runout in the drivetrain components, and you end up with a cam operated bearing shredder that also wears the chainring in a big hurry.

chain tension could have been an issue (I bought the bike s/h and my preference is for a looser chain), but i doubt it contributes much to the wear issues compared to pedalling forces, which could be as high 3.5-4k newtons according to this dude https://odysseybmx.com/2003/12/67-super-small-gearing/ (i have no idea how to calc forces at driver - 250 over 20 x ????)


i've tried making sense of the tech but unfortunately i'm too thick. i might be able to go up to an 11t driver at rear without messing up the chainline too much, and i'm hoping that with the right bearing choices (including perhaps shims), i might get a drive train that is reasonably reliable (i've already blown up one chain)

you need to add the pedalling force to the tight chain loading... and the excess chain load is way beyond the pedal force load....
if you have a need for doing stunts that include handrail riding and sliding your bike along angle iron bowl lips, then the tiny drive train is justified, and expect high maintenance frequency and costs..
if there is no need for those stupid-small gears, GET RID OF THEM, FRONT AND REAR, and go with a more reasonably sized setup. 42/16, and the much more substantial freewheel possible.

i regularly replace hubs and entire rear wheels with 9-10t freehubs in them..... i swear the things are built to break.... internal bearing failures and broke ratchets... the last one i did was lubed with WD-40 until NO Grease remained, and the guy left the Jam Nuts loose on the axle too... A Cone finally Shattered.... the beginning of the problem was traced back to An Over-Tightened CHAIN... and the chain was then Over-Tightened AGAIN... i tried to get the dad to bring the entire bike here, but he assured me he knew what he was doing... The repaired hub lasted about 20 minutes.
49 new balls, a new cone, a half hour of labor.. all for naught.
and then, there's the rapid tooth and chain wear on them too... and the neglective habits of the owners, regarding lubing a chain... YIKES!

i'll spare others from reading the entirety of that mess of an "article"...
here's a sample passage...
"Now rather bizarrely you have a big elephant specific swimming pool round the back of your house, (of course if you lived in Sheffield you would have at least one world class elephant highdiving training centre which you have to pay an enormous amount of council tax towards and never gets used, and the council would be planning a second) but for some reason your diving board is broken and just hangs limply over the pool. Just a hunch but it might be something to do with the frigging great elephant that keeps using it!

So whenever your elephant wants to go diving you have to hang upside-down from a helicopter and support the diving board. Now this wouldn’t be so bad if you could hold it at the end but obviously you would be completely in the way of the elephant diving off, so instead you have to hold it down near the attachment pivot."

the "article" boils down to this :The Chain is over-stressed by tiny tooth counts, so get away from tiny tooth counts, unless you think you need them to grind your bike better."

the wheel i mentioned in my previous reply was destroyed by a 10 year old kid that let his dad tighten the chain., "fix the wheel", then over-tighten the chain again, and again after i repaired the damaged hub's guts... several of the "Driver's" 1/8" balls were literally split in half.

maddog's experience mimics mine. I saw a lot of BMX and messenger service work back in the day and we rarely saw really busted up bearings. But back then the balls were larger (in so many ways...), remember the load capacity of a ball increases in a geometric way WRT diameter and only linearly WRT ball number. Do the math and you'll understand why the "classic" eras had bigger balls in their bearings. Then break apart those cartridge bearings so many swear by these days and see how tiny in diameter the balls and how few they are.

To the OP- I suggest figuring out the chain tension when the chain has some loose points and the chain is tightened at its loosest point really tight and then pedaled past that now super taught point. I suspect you would be surprised at how much tension can be produced by poor set up alone. And remember this tension is all the time, even when no riding is going on. I could see fretting being an added path to bearing degradation.

I try to be a student of history when it comes to bike problems. When a type of "failure" (how I dislike that term...) happens over and over and is reported by many in other places it seems to make sense that a shared experience and understanding might result. Andy

AIUI driver is the BMX-specific term for the little freehub bodies they use that allow low tooth counts so they can use small chainrings to improve clearance as they slide around on steps and railings and whatever else lends an edge. All clever stuff but totally alien to me, although trials riding is similar and I follow a couple of guys who do that.

i can see how a too tight chain might contribute to wear, but i still think the fundamental issue is the pedalling forces involved. bmxers have been running tight chains for decades and i don't think it's as much of an issue if you're running 44/16-36/13.
yes bearing size is a concern, hence trying to find out if there's a way to get two small cartridge bearings to work together to share the forces better. i think maybe a top hat bearing (with apropriate spacers) might be the way to go, that way the chainline is roughly half way between the two bearings. it is at least a relatively simple solution. another alternative is bushings

i'll suggest that you should think less, and learn more.
the balls in the hub i recently repaired were shattered in half... a skinny ten year old kid isn't capable of that sort of force.
i've seen this many times.. at least five such ruined hubs since the new year began.
all had extremely tight chains before breaking down.

that’s great and all but I’m not a skinny kid running a too tight chain on loose ball hub I’m a fat **** who breaks chains with a sealed bearing cassette hub. If the given load ratings for 6802 bearings are correct sorting the chain line by using 2 7mm bearings will help.

my point was that the chain tension was breaking 1/8" balls in half.
it is not a high dollar BMX, so parts quality is questionable, eh?
i put decent bearings in... they too failed, i think... his dad parked the bike, for now.
it's the third one that boy's had in 2 years.
"sealed" doesn't make any difference to the bearing until weather comes into the equation.

the angular design of cup/cone can make a difference though...they handle axial and moment loading better, but handle radial loads less well.

I’ve seen people talking about old cup and cone bearings being bigger therefore stronger, which I guess makes sense crept for the fact it’s the inner race deterioration that causes the problems. Is it easier to crack one large bearing or several smaller ones? I also have no idea what wear characteristics are like for one large ball vs n/smaller balls distributing the load. But none of that really matters because I’m stuck with trying to find the best configuration with the parts I have, and I reckon bearing spacing and correcting chainline relative to those bearings is the best shot I have

Re big ass cupbcone bearings, isn’t it feasible that by tightening the chain you’re effectively creating a ramp/wedge hence the bearing cracking/ something that might not happen with the forcibly spaced bearings in a cartridge?

I don't get this. You've been told repeatedly by knowledgeable people here that running a too-tight chain in a single-speed setup kills freewheel bearings. (And hub bearings.) We've seen it many times. That's all you need to know.

Is it just that running a tight chain is considered cool by BMXers?

I didn’t ask for chain advice, I was looking for advice on how best to get two off centre bearings to best distribute load, but I think I’ve figured it out now

fwiw freewheels cope with tight chains pretty well.

So you go to the doctor for your hurting arm and don't want to listen to him give advise how to not injure your arm again? All you want him to do is stop the hurting now? Some might consider this attitude a bit short sighted. Andy (who is use to customers not heeding advise too)

Actually it was snapping the chain that hurt my arm, not the driver bearings wearing. I was looking for advice on how to get two bearings to wear evenly, but thanks for telling me to loosen off an already loose chain, I’m sure that would have helped

that's as bad as calling tires with the tubes sewn into them "tubulars" and calling fork offset "rake".