Disc Size Calculator
Enter your weight with riding kit, your type of riding and the rotor size your frame and fork mounts take. The calculator suggests front and rear rotor sizes, how much more braking power they give and the adapters you need.
- Rotor size
- Braking power
- Adapters
Include your riding kit, pack and water in the weight.
Bigger discs give more braking power and run cooler. Braking torque grows with rotor radius, so a 180 mm disc gives about 12% more than a 160 mm one, and 203 mm about 27% more. Trail riders often run 180 mm front and rear. Heavier riders and steep descents call for bigger rotors.
Rotor size chart
Riders up to 100 kg with kit. Search for a riding style.
| Riding | Front (mm) | Rear (mm) |
|---|---|---|
| Road and gravel | 160 | 140 or 160 |
| Cross-country | 160 | 160 |
| Trail | 180 | 180 |
| Enduro | 203 | 180 |
| Downhill | 203 | 203 |
| E-bike | 203 | 203 |
Add one size over 100 kg.
Rider weight and rotors
Trail riding. Slide the rider weight.
Both rotors are drawn to scale, with the caliper on each.
How to choose rotor size
Weight and riding. Step through it.
Weigh in
With kit.
Rotor and pads bed in over the first few rides. Do some firm stops on a flat road first.
160, 180 or 203 mm
Rotor sizes. Compare them.
Light.
All-round.
Big.
The front brake does most of the stopping, so it gets the bigger disc first.
Before you fit
Rotor checks. Tick each item.
Tick each item as you go.
Use a torque wrench on rotor bolts and caliper bolts.
What you get
Rotor sizing. Each tile explains one result.
Rotor.
Rotor.
Against 160.
Needed.
Used.
Post mount adapters are named by how much they step up, such as +20 mm.
Frequently Asked Questions
No question matches that search.
What size brake rotor do I need?
Most trail riders use one hundred and eighty millimetres front and rear. Heavier riders and steep riding need bigger.
Do bigger rotors give more braking power?
Yes. Power rises in step with the rotor's radius.
Should front and rear rotors be the same size?
Often the front is bigger, because it does most of the braking.
What rotor size for an e-bike?
Usually two hundred and three millimetres, as e-bikes are heavier and faster.
Can I fit a bigger rotor to my bike?
Yes, with the right adapter, if the frame and fork allow that size.
What does a plus twenty adapter mean?
It moves the caliper out to fit a rotor twenty millimetres bigger.
Do bigger rotors stop brake fade?
They help, as they hold and shed more heat.
Stop with confidence
Choose rotors for your weight and your riding, and the brakes stay strong to the bottom of every descent.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.