# Torque and wheel size of a car

• Automotive
So lets assume I have 100 Nm at the wheel of a car, with a wheel size of 25 in diameter

If I put wheels that are 24 in diameter, so 4% smaller, what exactly will change ? Will I have 4% more torque ?

Waaat.

You'll have exactly the same amount of torque. Something will change at the contact patch through.

Isnt there some formula that might be applied here ? ... F = T*r ? Doesnt a change in wheel size of a car act like a gear change ?

• billy_joule
Ohhh...its F=T/r ... I get it now.

If F is the ground force on the wheel then T- F.r = IG

Also your rpm changes. The circumference (pi*D) is less on the smaller diameter.

no you won't have more torque .. torque is a function of gear ratios at wheel torque = engine torque*gear ratios*differential ratio
So when you are considering change in tyre dimensions assume it constant. so for changing wheel selection following things will occur.
in this case your tractive force will increase..
say you have 100Nm of torque which is constant
now you used 25inch tyre= radius=0.3175m
so tractive effort = 100/.3175=314N

Now you used 24inch dia tyre=radius=.3048m
so tractive effort = 328.08N