Brake rotor size

[Gluteus Maximus]

Hey guys!

 

I currently ride 160mm rotors. Will I feel a big difference if I change to 180mm? I ride a 26" at speeds between 35 and 60kmh on downhill sections.

 

Will 180 front and 160 rear be a suitable combo?

 

Thanks!

[kosmonooit]

I changed to a 180 front, cant say I feel a rad difference. Hope X4 brakes always worked well, but I was thinking larger front disc might run a bit cooler on those long steep descents.Use Hope Floaters, no problems ever.

 

Might be more critical with the dowhhillers though, they even go to 200mm.

[Mojoman]

I run a 160 rear and 180 front. I am a bit heavy though so would rather have a bit more stopping power. I changed from the stock standard 160 Tektro rotor to a 180 Shimano, changed the pads and the breaking is pretty good. I used to have a 180 Windcutter on the front but it seemed every other day I was having to straighten the disc so I opted to try a Shimano and so far no warping.

[Smolly]

160 180 combo is fine. (running shimano xt)

I weigh in at about 85 and so far, so good.

[patches]

I run

 

203 front & back on my DH bike

203 front, 180 back on my AM bike

180 front, 160 back on my 4X bike.

 

The rotor size will make a difference, it's simple mechanics.

 

Torque = Force x Distance.

 

Torque in this case is your stopping power

Force is what the brake calipers are applying.

Distance is how far away the force is being applied from the rotational axis (ie. your rotor size)

 

So therefore to get more stopping power one can do 4 things

1. Increase Force - ie. buy better brakes... costly
   
2. Increse Distance - ie. buy bigger rotors... cheaper, but don't forget to consider the cost of the adapters too
   
3. Increase both - self explanatory
   
4. Jam foot in wheels - works for brakeless BMXers... sounds like cheapest option but consider potential medical bills
   

Oh, also remember that your front brake is the most effective when stopping (unless you're rolling backwards), so running 2 different size rotors is a good idea... a 180F/160R (as you mentioned), or 203F/180R combo. Having a 203R rotor is all fine and well, but you may find yourself locking the back wheel up a lot, and when it's locked it is less effective. A smaller rotor is less likely to do this. Take cars and motobikes for example. Nearly all of them run bigger discs, and more powerful calipers at the front.

 

Bottom line... if you want more stopping power, upgrade brakes. upgrade rotors. or upgrade both

Edited April 15, 2012 by patches

[Cruz Addict]

I run shimano ice 203 front and 160 rear, honestly can't say I have ever had such stopping power, am looking at changing to 180 rear purely as i want them to run cooler. As for the mechanics and physics, it's all as patches says.

[Capricorn]

On my XC bike, i have 180 up front and 160 rear, with 203mm (f) and 185mm ® on my DH bike. The 180+160 does the job pretty well despite reaching speeds over 70kph on sufficiently steep descents, and that's using Elixir 5s. The big difference is, the 203+185 + Codes on my DH bike , brings me to a standstill in an often discomfortingly short space of time.

 

It's how you use em, and how well your brakes are setup that defines how efficient they will be. On some course, even DHers will drop to 160mm all round to lighten the bike up (Mount Stromlo track in Aus). Just make ensure the brakes are well bled, especially on pre-2012 Avids, and you will have the best starting point for efficient braking. But if you want more stopping force, then it's as Patches outlined above.

[Palaeodom]

I also run a 180 and 160 combo on an XC bike and just enjoy that little bit of security. Always felt like if I was quick then my front wouldn't quite do the job in an emergency, these stop me very quickly, but as Capricorn says it could be as much about having the brakes setup properly. I had mine bled and recalibrated with new pads when I changed my rotors...also changed to shimano rotors... What ever it was, a 180mm will do a better job mechanically speaking

Edited April 15, 2012 by Palaeodom