Question about Tire Sizing

[Rick]

Is there a calculator online for scratch math-ing the effects of acceleration/speed/traction/wutnot when changing tire dimensions?

Wanna make some predictions about the performance of two slightly different builds.

[Jason]

Changing only Tire Size
The general rule of thumb, all things remaining the same, if you make a larger diameter tire, you will have less acceleration but more top speed. If you shrink your tire diameter, it will accelerate faster but not have as high of a top speed.

Changing only the Sprocket on the Axle (assuming a single reduction, motor sprocket, to axle sprocket)
Assuming you stick to the same chain size, #25 for your existing kart, if you move to a higher tooth count 80t to 90t (this means a bigger diameter sprocket) you will have less top speed and more acceleration. If you go from 80t to 70t (smaller diameter sprocket, you will have more top speed and less acceleration.

Changing only the sprocket on the motor "Pinion" (assuming a single reduction, motor sprocket, to axle sprocket)
Assuming you stick to the same chain size, #25 for your existing kart, if you move to a higher tooth count 11t to 15t (this means a bigger diameter pinion sprocket) you will have a higher top speed and less acceleration. If you move from a 11t to a 9t (smaller diameter pinion sprocket) you will have more acceleration and less top speed.

Changing the voltage
Ignoring a lot of other things. Changing your voltage to a higher voltage, will equal more RPMs from the motor and in general net you a higher top speed. Reducing the voltage will lower your peak RPMs and net you a lower top speed. Even a fully charged battery vs a lower charged battery may be the difference between 1-2mph at the top end.

Allowing more Current
The speed controller you currently have limits current at roughly 30a. This is good as we race with a 30a fuse. However if you could dump 40a at start up, you will take off quicker (better acceleration). Oppositely if you were to limit the current to 20a you would have worse acceleration.


There is more that go into each one of these categories. Efficiency, what the equipment is designed to run at, temperature etc etc. However, those are the general guidelines that can help you dial in the speed/acceleration you want per track.