Due to using a frame that’ll only take 40mm bearings (lollipops) I have tried to find solutions for a while for me to use ISIS. Kris came out with his ‘40mm’ shimmed bearings but it seems these are quite a pain for a lot of riders, most notably Tholub.
I found the measurements for the ‘Mid’ bottom bracket bearings that are used for BMX frames…:
External Diameter of bearings- 40.5mm
Code for Mid 19mm Bearing- R12 2RS
Code for Mid 22mm Bearing- R12RS - 22
In short, the dimensions are: 40.5 x 22 x 11.
Now this looks like the ideal bearing for me, except it’s 11mm fat rather than unicyles’ standard 12mm. I also do wonder, would it not have been cheaper/easier to just get these very standard off-the-shelf bearings to use for 42mm bearing’d frames? Just bung unicycle.com’s 40->42 shim on there? And then we have a 42x22x11 bearing.
I know we now have a proper 42x22x12 bearing thanks for Kris/Nimbus custom ordering them through bearing manufacturers; and they are always better than a shimmed option… but I do wonder why the BMX Mid bearing idea wasn’t used?
If my calculations are correct, could the 22mm ID Mid bearing be the ideal ISIS bearing for us 40mm frame users? I just want confirmation from the brains of this forum because this idea of using BMX mid bbs seems farrr too ideal?
I would love to see an isis conversion for 40mm bearing unis that use square taper to ISIS! This would allow the use of crank spacers to squeeze the bearings into the inside of the frame and not slide around that 1mm gap in the bearing holder. The crank spacers would make a bolt on bearing cap caliper mount work for a disk brake more consistently on frames intended for square taper. will these bearings only work in lollypop holders?
Being 11mm wide, if you add an extra 1mm spacer on the outside of either bearing, and tighten the whole wheelset down, and put the frame on after the whole wheel is set up with cranks installed tight… then it’ll work.
^This is for normal bearing holder frames. For my lollipops I have to do something like the reverse, but all in all this’ll work I believe.
Luckily, Mid 22mm bearing kits are so easy to get off any BMX webstore or even at your local bike shop… Most bearing kits come with thin spacers so make sure the pack has at least 2x 1mm spacers!
I’m glad I really don’t need to use KH shimmed bearings anymore pheewww
Do you reckon 40.5mm bearings will fit in your 40mm lollipops? I would have thought there wouldn’t be enough give in the (cast?) lollipop to make up the extra half mm - or else they’d be extremely baggy with 40mm bearings. Or are you planning on machining a bit out of the lollipop?
It would probably work well in normal pressed bearing holder frames though - I’ve got 42mm bearings in my 40mm coker frame and it’s not that bad, so 40.5mm would be be a pretty good fit I reckon.
To be fair, I probably shouldn’t have mentioned 40.5mm and just put 40mm instead. Why? It’s because the people who measured the bearings for me did it in imperial inches first and then roughly converted it to metric. That being said, I looked at 0.5 mm on a ruler and it’s next to nothing. Even so, I bet the usual 40mm bearings aren’t even properly 40mm. There’s always a bit of give, especially when imperial measurements are first used.
They’ll fit in my pops no problem. Even if it’s a tight squeeze, popping my 'pops in the oven for 10 minutes expands the steel temporarily.
You are also right that 40mm bearings are not exactly 40mm’s, but the to be off by half a millimeter is huge. The tolerances for machine parts is usually within the hundredths of a milliimeter range.
I did a quick search on the bearing number that you posted and it came back as 40.5 or 41mm O.D. I think you will have to machine your lollipops to get it to fit, but that being said it may be the best solution for the long term. The machining would be fast and easy for anyone with a metal turning lathe. The best part is that you could bring a mid bearing and have them fit the bearing to the holder so that it fits exactly like the original bearing did.