Changing 160mm rotor to 180mm

tomb57

Think I need a new rotor for my rear brakes it’s 160mm front is 180mm
Do I gain any braking efficiency by changing to 180mm on the rear .
Many thanks for your always good advice
Tom B

mully79

There will be more power with a bigger disc. Whether that means more control or digital brakes depends on your brakes.

You will need an adapter to position the calliper further out but beware a bigger disc may touch the chain stay so check clearances first.

vanamees

oxoman said:

You'd have to put some sort of adaptor in to make up the extra diameter. Personally can't see it making much difference. The pads are the same size regardless.

Braking power = friction constant x power applied, contact area is irrelevant.

tomb57

Bike has Shimano SLX brakes was going to buy Shimano bracket and rotor
Had a quick look at bike (Giant Fathom 1 2019 ) think bracket would
Fit along chain stay ok and calliper would fit but will check with LBS I think 180 on front and rearWould balance braking more
Thanks for all your answers all
Let you know how it goes
Tom B

steve_sordy

Bigger discs work even with the same size of pads because the braking torque is increased. There is also a bigger area of disc to cool the heat generated by friction.

Bigger discs will increase your braking power, but as @mully79 implied, too big if you are a light rider could mean that the discs are a bit on/off.

Quite a few years ago now, I went to the French Alps for a weeks riding with a bunch of mates. I put 200mm discs on front and rear and boy did I need them! Those hills are STEEP! But when I got back I had to swap out the rear disc for a 180 because the braking was not "balanced" (note to @tomb57), the rear wheel kept locking up because it wasn't riding non-slip granite any more.

According to the experts (not me), 70% of braking comes from the front wheel. This is because when you brake, your weight transfers to the front wheel and lifts off the rear wheel. This is why most bikes have a smaller disc on the back, to ensure "balance".

@tomb57 what I would do if you want much improved braking, I'd put a 200 on the front and transfer your 180 to the back. It's either that or a whole new braking system.

reaperactual

I had 180 rotors fitted as stock front and rear which was fine. I left the 180 to the rear and fitted a 203 on the front along with some SLX 2 pot brakes from a previous bike.

On any mtb with 160 front and/or rear I'd always swap out for a 180 minimum size increase for riding trails that have steep decents.

As mentioned impoved braking, cooling with the front size increase.

I'll add you'll still have ample modulation and the more on/off feeling on the rear (if you even notice) isn't a bad thing for locking up on purpose to negotiate tight switchbacks as one example.

tomb57

Thanks everyone on reading your answers I have reassessed my rides
And needs think I’m going to stick to 160 on rear and put money saved
Towards some other parts most of my riding is flat with small
Hillls (great for my arthritic knees )
Many thanks
Tom B