Dyno - Does Wheel Size Matter

[NUT515]

Hey guys just a quick question. We all know that increasing rim size and there fore overall rolling circumference of our tyres can throw our speedos out but can we make more horsepower and if yes is it signifigantly difference between different size tyres.

[R31Nismoid]

Wheel size can affect read out.

[adamskill]

Hey guys just a quick question. We all know that increasing rim size and there fore overall rolling circumference of our tyres can throw our speedos out but can we make more horsepower and if yes is it signifigantly difference between different size tyres.

yes in theory it can.

No, dont got and put 22's on your car.

[MagicMikeZ32]

Yes it can/does effect readings, but really you should just be using the combo you use on the street. Because, well that's what you use.

[NUT515]

Just had me wondering. I normally run 20s but am only taking 18s to powercruise so wasn't sure if. Should be expecting, more, less or the same figures

[scotty nm35]

Power shouldn't change much but torque will. Has anyone else run their car up in 3rd to see the difference?

[BeastVS]

I got my dyno tune done by Tunehouse here in sydney, They actually took the wheels off the car and measured from the hubs.

Edited August 17, 2012 by BeastVS

[MagicMikeZ32]

Hub dyno will read higher than rolling road.

[BeastVS]

^^^ True, which is why they do both

[mad082]

lighter wheels with skinnier tyres will make a difference too, as you are spinning up less weight with less resistance

[NUT515]

^^^ True, which is why they do both

Wat was the difference between the 2.

[*LOACH*]

I am interested how the wheel diameter difference affects the horsepower the dyno reads?

I understand the skinnier tyres/lighter wheels but if these are equal and the only difference is the actual diameter of the wheels why would the horsepower measured change?

Power=forcexdistance / time

Force in the dyno is calculated by the accelaration of the drums (not measured through the spark reading for engine RPM) and the weight of the drums which is a known constant as is the distance (the circumference of the drums).....I am probably missing something obvious but I really don't see how rim size affects horsepower.

[mad082]

you have a point regarding the equation. i was wondering the same thing about that. i think that is why using a different gear doesn't alter the readout by much. however i think there is still a slight variance in there. and going to bigger wheels gives a taller ratio which will have a small effect on power. but i think more of it probably comes from the weight difference of the bigger wheels.

and if it does make a difference, this may play a part in how some people are able to get higher readings from a car running a stock ecu/turbo, other than the usual "happy dyno" call.