If you have a bicycle with disc brakes, you’ll soon find there are many possible choices for the rotor sizes. From a tiny 5″ all the way to a whopping 9″! The next time you need to replace a rotor, consider the following points.
Advantages of bigger disc rotors:
- Larger disc rotors obviously give much more power than smaller rotors.
- For the same braking effort, larger rotors will run cooler than smaller rotors, reducing the phenomenon known asÂ brake fade.
- Larger rotors will last longer than smaller rotors, as there is more metal present in the brake track circumference.
- In my experience with steep descents here in Tenerife,Â where brake overheating is a real problem, larger rotors will also improve theÂ wear life of the pads themselves (especially organic pads), as they don’t tend to overheat as much.
Disadvantages of bigger disc rotors:
- Each time you step up the size of the rotor, you add a considerable amount of rotational weight to your bike.
- Another down side of big rotors is that they tend to be a bit ‘grabby’ (meaning on-off-on-off braking performance)
- Contrary to what you might think, large disc brake rotors are more prone to warping than small rotors.
- The bigger disc rotors are therefore harder to keep centred & hence can become quite noisy even when pedaling along without applying the brakes.
- Many people choose to install a larger disc rotor on the front end of their bike. The reason being, the front brake more stopping power. This saves a small amount of weight at the rear of the bike and also reduces noise somewhat.
- I could only reccommend 9″ rotors for extreme downhill use.Â I’d always go with dual 8″ rotors for general downhill use.Â 7″ discs are always a good compromise between weight & power, so I’d suggest a 8″/7″ combination if you are a light downhill rider. For people weighing 90-100kg in whatever road conditions, I think a 7 or 8″ disc on the front wheel with a 6″ rear disc is a perfect choice. Otherwise, I would choose dual 6″ rotors for light, cross-country use. 5.5″ rotors are stipulated for rear brake useÂ only, obviously for light use only.
I recently installedÂ the newly released Hayes V9 9″ rotor on the front fork of my semi-downhill bike; intially, I wasn’t at all impressed with itsÂ performance… after descending I noticed that it had a huge tendency to warp like crazy after extreme braking manouvres. They are bedded in now, I treatÂ the front brake with more respect so thankfully this has not happened again. Today I rode down a 1km section of road -possibly the steepest street in Tenerife-Â which has an averageÂ gradient of 20-30%. There was zero brake fade with this setup – I’m impressed! But it is definitely overkill if you live in a flat area (and so are 8″ discs).
One thing that really gets the adrenaline going is is descending the ultra-steep streets here in Tenerife at the end of a MTB ride… for this, I only use sintered brake pads which are made of a metal compound. I’ve noticed these last waaay longer than organic brake pads.