pushbike sizes

[redtrummy]

Right Bibio! The chain width is determined by how many sprockets are on the rear. Its explained here. https://bike.bikegremlin.com/3555/bi...ion-standards/
Chainrings are usually determined by its BCD measurement.

explained here https://www.wolftoothcomponents.com/...e-diameter-bcd.


Shim hollowfit is a high end chainset, the hollowtech is outside my knowledge apart from its not a solid axle.
You may find this useful https://www.youtube.com/watch?v=zIfOIjPH_bU. I am assuming that its hollow tech 1. They have now upgraded the design to a mk 2. version.
If the rings are worn, look at the back sprockets and check the wear on the teeth - its often worth changing the lot as worn sprockets will prematurely ruin the chain. If you are unsure about what will be compatible SPA cycles of Harrogate are pretty good. Hope this helps - its a minefield.
Loads of different b/b designs about but so many cause problems that there seems to be a shift back to the BSA bottom bracket design that was probably fitted to your bike when you were a lad.


Good luck

[Bibio]

fantastic links there redtrummy thanks.

well the bike has 9 rear sprockets and the crank BCD is 104. i'll get the veryneers out later.

i have looked about the net but i still cant find out if hollowtech mk2 fit in hollowtech mk1 crank bearings..

[redtrummy]

I found this Bibio
https://www.bikeforums.net/bicycle-m...ompatible.html
I am pretty sure the mk1 spindle was larger than the mk2 which is 24 mill. If you can be certain its a mk1 then the spindle may be about 32 mill (I think.) You may find that its as cheap to buy a complete chainset that's compatible. It really is a mine field, not only may it have internal bearings but a lot of later ones have external, the axle length needs to be the right size to, and there are two standards if its a tapered/square fit fit it could be ISO or JIS. When I did my renovation I fell foul of this. Older bikes had ISO, new ones JIS but since its shimano then maybe they always used JIS. The taper is compatible but one or the other pulls the crank too close to the frame spoiling the chain alignment which is crucial for good gear changes.
A little light reading!
https://www.bikeforums.net/bicycle-m...ompatible.html


and if you want to really understand bottom brackets these ytube vids will make you think that life is too complicated, just ytube Hambini who is an aircraft engineer or (from 3 min on) https://www.youtube.com/watch?v=-uK7FSZ6OFM. Not relevant for your problem but gives an insight of an industry creating its own problems.

[johnnyrod]

Are they that badly worn? Some cycle teeth look a bit weird, like they're worn, helps the shifting. Can you post a pic to be sure? Also TBH for a kid's bike unless they are serious, I'd wait until the chain/sprockets are giving actual problems.

[redtrummy]

I forgot about that JR. Yes Bibio. As you look at the chainwheel it looks like the top of the teeth have been worn away at 3 or 4 places around the chain wheel.This is how they are made its to aid smooth gear changes. I think JR advice is pretty sound. Wait until any problems manifest themselves

[Bibio]

i've been told to give the bike to the big brother to sort as "he knows what he is doing" and "has all the tools". well i can guess whats going to happen there.. mum, that'll be £500 for fixing the bike. coz he's a chancer and always skint.

[redtrummy]

Well if no progress is forthcoming then come back to us - and welcome to the intricacies into the world of bottom brackets. (And you thought m/bikes were complicated)
JR I am sure hit the nail on the head re the way forward