Pairing disc rotor sizes

ishaw

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I've usually gone bigger front, smaller rear.

Contemplating same size at both ends.

Does it really matter?
 

rwm1962

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Got 165 both ends on the 2002 P7 in my signature. Don't use it for anything crazy. Relatively easy trails & bike packing. For my more trail park orientated 2011 P7 got 180 front 160 rear.
 

ishaw

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I was considering 180 at both ends. Not for any particular reason other than I have a pair if rotors. Not checked rear clearance yet, may just get a 160 for the rear, just wondering if there will be any issues. Assume a larger rotor could stress the frame more?
 

mattr

Old School Grand Master
Theoretically more risk of glazing pads as you'll never get them hot enough, though 180/180 are unlikely to be more of an issue than 180/160 anyway. Unless you are a hardcore brake dragger.
I've done 180/160, 160/160 and 160/140 and none of them make a huge difference until you're really going for it. Costs you virtually nothing in weight either.
 

ishaw

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Interesting you mention glazing. Ive had an issue with a set of brakes which I think this keeps happening too. 180/160 rotors, tried everything from new pads, sanding pads, sanding rotors, cleaning everything with brake cleaner and they always seem to glaze and squeal. Never had this with any other brake.

It is why I'm asking this question actually, as thinking about simply swapping them out for some hopes and have some 180 rotors on the way.
 

coomber

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203 and 180 on my hardtail

Going 180 and 180 on my nearly finished rigid ramin

I like 180 front, don't use rear so much.
 

captaincowelly

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Theoretically more risk of glazing pads as you'll never get them hot enough, though 180/180 are unlikely to be more of an issue than 180/160 anyway. Unless you are a hardcore brake dragger.
I've done 180/160, 160/160 and 160/140 and none of them make a huge difference until you're really going for it. Costs you virtually nothing in weight either.
Only have one bike with discs so I'm certainly no expert in this area but from experience of other applications (road vehicles/motorbikes) glazing occurs when the pads are overheated,not from under-use.Don't know the exact science but I'm assuming the higher temperatures 'draw out' something from the compound (possibly resin?) which leaves a hard,glass like coating on the surface.
My theory on size is this (assuming we're talking XC not DH) F+R 180's have awesome stopping power on an XC bike but if they're 'too much' and only get used gently,more chance of calipers sticking over time.Sometimes better to go less powerful but use them more.
180 Front/160 Rear I can imagine being a great combo but I can't help but lean towards having them both the same.
But that's just me.
 

mattr

Old School Grand Master
Only have one bike with discs so I'm certainly no expert in this area but from experience of other applications (road vehicles/motorbikes) glazing occurs when the pads are overheated,not from under-use.Don't know the exact science but I'm assuming the higher temperatures 'draw out' something from the compound (possibly resin?) which leaves a hard,glass like coating on the surface.
Yes, sorry, sloppy use of language and a lazy post!
You're right though, glazing or polishing is usually from maintaining them at the same, high, temp for ages, under pressure, without either stopping or releasing the brake.

Dragging on overly large discs *seems* to be a fairly common cause of this. Possibly as those who get overly large discs tend to do it because they aren't particularly good descenders!

Using the brakes hard (and getting them hot) then stopping doesn't have the same issue as getting them hot, then baking them under pressure for ages!
 

jimo746

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Does size matter? 😁
I don’t think it matters all that much, 160/160 was pretty standard on my Xc bikes, should be enough braking for most situations. Actual brakes and pads make more of a difference,
I use 180/160 now on my full-sus bike, makes sense to have the larger disc at the front and not the other way around!
if you have 180 rotors just use those, assuming you have the adapters needed.
 
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