+0%
From the longer lever arm alone, before pad or caliper changes
Current disc
New disc
Pad height (radial depth of the pad on the disc face, same for both setups):
mm
| Measurement | Current | New | Δ |
|---|
Braking torque at the same clamp force
Thermal mass of the swept band
+0%
More metal means more heat absorbed before fade sets in
What a bigger disc actually changes
A brake is a lever. The pads clamp the disc at some distance from the hub centre, called the effective radius, and braking torque is clamp force × friction coefficient × effective radius. Fit a larger disc with the same caliper clamp force and the torque rises in direct proportion to the effective radius. That's the number in the table: with the pad sitting near the outer edge in both cases, the effective radius is approximately (disc radius) minus (half the pad height), which is why pad height is an input here.
Torque is only half the story: heat is the other
Braking converts speed into heat, and the disc is the reservoir that heat pours into. A larger and thicker disc has more swept-band volume, so the same stop raises its temperature less, and its larger surface area sheds heat faster between stops. This is why big-brake kits transform repeated hard braking (track laps, alpine descents, towing) far more than they change a single stop from 70mph, which on most cars is limited by tyre grip, not brake torque.
What this calculator deliberately ignores
Clamp force isn't fixed in real life. A big-brake kit usually changes caliper piston sizes too, which alters hydraulic ratio, pedal travel and front-to-rear brake balance. Move too far from the original ratio and the pedal goes long or the car locks its front axle early. The percentages here isolate the pure geometry of the disc so you can compare kits honestly; the caliper side of the equation belongs to the kit designer, and a well-engineered kit keeps overall balance close to standard.
Practical checks before buying
Bigger discs need clearance inside the wheel, typically a wheel at least an inch larger in diameter than standard for each big step in disc size, and spoke shape matters as much as diameter. Check the numbers with our wheel offset comparator if new wheels are part of the plan. Also confirm the disc's minimum thickness spec and that hub offset matches, since a disc that stands proud moves the wheel outboard just like an offset change.