I assume a bunch of you on here have disc braked commuters, I’m spec-ing up a bike at the moment, it will have hydraulic discs (probably XTR), but I’m debating what rotor size I’d need.

The bike is going to be running 25mm (max 28mm) rubber Conti GP 4Seasons or the like, and I’m concerned that 160 rotors front and rear will be too much brake for such a small contact patch, basically do you think I’d be fine with 140’s or can you never have too much brake?

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"We live in an age when unnecessary things are our only necessities." Oscar Wilde

Pegoretti Responsorium
Parlee Z5i
Donhou Commuter

I run XTR hydraulics on my commuter, with 160 non-floating discs. The tyres are 28mm Conti GP4Seasons.

Performance wise - and I'm not bragging here - it really is head and shoulders above any rim-brake setup, wet and dry. Better feel, modulation, control, everything. There's no way any rim-brakers can get close on any type of descent, especially on tight hairpins.

The quicker the bike world embraces discs on road bikes the better.

One day we'll look back on rim brakes the same way we look back on side-pull brakes, toeclips, quill stems, friction gear changers, steel forks, etc.

I'm running xtr disc brakes as well as conti 4seasons 28mm (they measure only about 26.5mm at 5-6bar) and find it great! Front rotor is 160 and the rear 140mm, mostly to reduce weight. These brakes modulate so well you never feel like having too much brake. I recommend this combination highly.

Thanks guys, 160/140 rotors it is. I’m having Tom Donhou build me up the bike later in the year. Will post some picks when it finally comes to fruition.

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"We live in an age when unnecessary things are our only necessities." Oscar Wilde

Pegoretti Responsorium
Parlee Z5i
Donhou Commuter

I have 160/160 mechanical discs on my commuter. Even mechanical discs blow away the best rim brakes from Shimano, Campy, and SRAM. I can't wait to get a converter so I can get hydraulics and improve it even further.

If you do a lot of braking on long descents, I would definitely get 160mm rotors which will get real hot and be susceptible to disc fade.

Dont go with XTR brakes. They are inconsistently bled from the factory and they almost always need rebled, right out of the box. I would have throw in a vote for the XT option instead. Yeah they are a bit heavier, but they are bled much more consistently (which makes no sense at all) and they are quieter.
Regarding the rotor size, I would just run 160 fr/rr. Unless your commuting in San Francisco, then that should do you just fine.

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http://www.zencyclery.com

http://www.wheelbuilder.org

Thanks for the tip Zen, I need silver caliper levers thoug so maybe XO would be an option.

It's a London bike, so no hills to mention.

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"We live in an age when unnecessary things are our only necessities." Oscar Wilde

Pegoretti Responsorium
Parlee Z5i
Donhou Commuter

whoever said the sooner the road world goes to disks the better is 100% spot on!!!!!

who cares if they need to be bled out of the box? You'll be cutting the lines to length anyway, and any halfway competent person can bleed a shimano brake in about 2 minutes. You get an olive and barb in the packaging.

Get the XTR, because they are pimp.

I'd probably just go for bb7s on a commuter. Then again, I commute on a hard rubbish bike.

160 front, and either 140 or 160 rear will be fine.

[quote="Tokyo Drifter"
Get the XTR, because they are pimp.
[/quote]

Out of every Shimano rep I have chatted with (which was really only 2 or 3), not one has recommended XTR as a good purchase. If pimp factor is your only concern, sure, XTR is great. However, if you value practicality and durability, then XT is a much better choice.
Those guys deal with hundreds (if not thousands) of brake sets every year. And they consistently say that the XTs are much more low maintenance than the XTRs.

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http://www.zencyclery.com

http://www.wheelbuilder.org