Are all brake mounts (disc to be clear), post and IS, in the same position relative to the axle? i.e. the same caliper would fit the same size disc on the same end of any bike?
And is there a standard default (i.e. no adapter) rotor size? I know with the BB7s I have on a couple of bikes now that they're 160 front or 140 rear IS without adapters, but is that standard with all (or most) recent brakes?
And what's the situation with post mount?
Ta.
I have wondered this as I have a surprising number of washers between the fork and the calliper when using a 180 mount on a 180 disc
The frame design is what dictates rotor size and caliper position - on some frames maximum rotor size may be deliberately limited because of the bigger stresses placed on the frame. 160F/140R is becoming common for road disc / CX whereas whereas most MTBs will go bigger as you can apply more braking force due to better tyre traction
Theoretically yes. All should be swappable and can be swapped front and rear too but will be 20mm out. The reality is there are small differences, some sit the calliper higher or lower, some are just bigger or smaller. A washer or two usually fixes it.
I have wondered this as I have a surprising number of washers between the fork and the calliper when using a 180 mount on a 180 disc
Are they dished/cup-and-cone washers though? They can look like quite a stack.
The frame design is what dictates rotor size and caliper position - on some frames maximum rotor size may be deliberately limited because of the bigger stresses placed on the frame.
To be clear, I mean where the caliper will locate without adapters, rather than what size rotor could theoretically be accommodated with adapters.
Theoretically yes. All should be swappable and can be swapped front and rear too but will be 20mm out. The reality is there are small differences, some sit the calliper higher or lower, some are just bigger or smaller. A washer or two usually fixes it.
Sounds like a yes then. There's always going to be minor differences both radially and probably axially, with different pad sizes and shapes, rotor braking surfaces, etc. but basically...
...all calipers are designed to fit a 160mm rotor at the front or a 140mm rotor at the back without adapters? Both post and IS?
Most frames are designed for a nominal 160mm front and 140mm rear setup, but as noted by others, they're sometimes a little out either the frames out of tolerance or some brake calipers or disks just seem to be the a different size.
Some frames and forks have deliberately bigger mounts to allow normal sized disks to fit without adapters (e.g. 180 front and 160 rear post mounts).
The max rotor size has little to do with the mount's, it's as you say to do with the frame's strength.The frame design is what dictates rotor size and caliper position - on some frames maximum rotor size may be deliberately limited because of the bigger stresses placed on the frame. 160F/140R is becoming common for road disc / CX whereas whereas most MTBs will go bigger as you can apply more braking force due to better tyre traction
But I'd point out you can generate a LOT more friction with a 23C slick on the road than you can with a nobly tyre on dirt. Disk size is more to do with effort and cooling (you don't tend to get arm pump braking in CX, and cooling is rarely an issue!).
...all calipers are designed to fit a 160mm rotor at the front or a 140mm rotor at the back without adapters? Both post and IS?
ish.
Some more expensive (XTR, Hope) IS calipers came in different sizes to avoid the need for adapters, so you could run a nominally rear XTR caliper on the front with a 180mm rotor, or a front caliper on the back with a 140. Hope had a letter/number system for calipers (or half calipers back when they were split) , so you bought brakes with the right sizes for your frame.
thenorthwind - Are they dished/cup-and-cone washers though? They can look like quite a stack.
They are the cup and cone ones, and some others I think
Most frames are designed for a nominal 160mm front and 140mm rear setup
That's what I thought, but I did wonder about this:
Some frames and forks have deliberately bigger mounts to allow normal sized disks to fit without adapters (e.g. 180 front and 160 rear post mounts).
I guess that information for a given frame or fork isn't necessarily obvious when buying. One of the many frustrating things that need to match but are rarely listed in a spec.
Edit: I'm concluding that at least calipers are consistent in that they position the pads at a certain distance from the mount - it's the frame that can vary. Right?
Hope had a letter/number system for calipers (or half calipers back when they were split) , so you bought brakes with the right sizes for your frame.
I remember my first disc brake - 150mm Hope XC4. I don't remember it being as poorly performing as many people would have you believe!
Post mount, broadly yes. They're intended to work with their own brand rotors and in avids case the conical washers. But 95% of the time a 180mm rotor works with a caliper and a 180mm adapter.Edit: I'm concluding that at least calipers are consistent in that they position the pads at a certain distance from the mount - it's the frame that can vary. Right?
IS could and were any size they wanted to be. But generally worked in the same increments.
What's the actual problem? If you've not bought them yet, just stick within a brand, there's not really much point mixing and matching calipers/rotors/adapters as they're all +/- a few £ and grames.
Cheers, really appreciate the help.
What's the actual problem? If you've not bought them yet, just stick within a brand, there's not really much point mixing and matching calipers/rotors/adapters as they're all +/- a few £ and grames.
Nothing as such. Just something I'm working on 8)