Afternoon all,

I’ve currently got Formular disk brakes on my MTB. I’ve noticed the rear is a bit warped. I’ve just checked out the price of a new one and it’s about 90 CHF. Being as the bike is just over a year old and disks are warped, I’m not really keen on spending that amount of money on a disk that’s likely to do the same. I was thinking, is it possible to fit a Shimmano disk? Quick look at the price and it’s nearly half and it can’t be any worse.

Is it possible as long as I get the same diameter ?

Cheers,

GL.

Yes.

At worst, a re-bleed or adjustment to cater for a marginally different thickness, but crack on and you’ll be fine!

Cheers for that.

Actually after I’d posted I thought a bit more about it and thought I’d try something with the disk from my cross bike which is shimano, but the same size. Put the cross disk on my MTB wheel and worked like a treat.

It can’t be any worse than the last one!
Cheers,
GL

straighten it, small adjustable spanner and push it onto disc, snug like, and tweak a bit at a time.

When you say ‘warped’ do you mean bent out plane? If discs on a car do that, it’s a fault, and they are too thick to bend back easily. Discs on an mtb get bent for all kinds of reasons, and can usually be straightened with nothing more than fingers. Spin the wheel and look how it runs through the pads to see which way it needs to be bent, then thumbs on the hub, fingers on the edge and pull – or vice versa and push if necessary – wear gloves to avoid contaminating the disc. I usually find each pull makes it a bit straighter, re-check, about 6 – 10 pulls gets it straight.

The formula rotors with all the holes are crap, mind- it’s a bit of “you get what you deserve”, they released them as an option for the R1 with a “race only” recommendation but they’re like 20g lighter so all of a sudden, everyone stopped buying their older, stronger ones and started fitting the lightweight version. So they kind of folded to customer demand and made them standard even though they’re a poor option for most.

hmmm, okay, I’ll give it a whirl. I had assumed they had bent and that was that….worth a try to straighten them.

I’ll say they stop okay, but I’m surprised they have bent/warped. I wonder if a lot of it is getting very hot on the descents and then cooling quickly (I’ve been riding all winter and quite a few times in snow)…..that’s my uneducated guess.

Must admit, they came with the bike, I’m a boring ol fart and would normally stick with Shimano given the choice!….I’m just that crazy!!! 😉

Cheers for the advice.

my formula extreme fr rear brake uses a 180mm magura rotor

The answer is usually yes. There are some exceptions or combinations that might not work perfectly (eg pad depth is wider than braking surface depth).

Also, some floating rotors will foul certain rotors (but the OP doesn’t have floating rotors by the sounds of it).

I wouldn’t risk it!!!! oh look what I’ve just found 😉

http://singletrackworld.com/forum/topic/formula-180-solid-rotors

It depends on the brand and the size.

For example Shimano callipers won’t work with Avid 185mm rotors, because shimano made them for 180mm rotors. Even with the same (shimano 180mm or avid 185mm) addapters. But they do work with the 160mm rotors (and no addapter on the front and the same addapter on the rear).

As long as the outside diameter matches it should work (otherwise it’ll wear out the pad leaving a lip at the top where it doesn’t touch it), the inside diameter isn’t critical as the arms will sweep the pad and wear them, plenty of designs do this deliberately to clear dirt).

If the rotor is larger than nececary then you can make it work by adding IS calliper shims to the post mount bolts to move the calliper out by 1-3mm untill it just clears the disk. If the rotor is a few mm too small there’s not much you can do.