Dynojet power numbers and tire size?

[427dart]

If you make a dyno run with a certain size and weight rear tire combo and than later make another run with a smaller lighter weight tire what effect if any on the new dyno numbers?

[lefty o]

everything ive ever seen suggests on a chassis dyno for every pound removed as rotating/drivetrain weight = 1HP.

[In-Tech]

I don't think it matters which chassis dyno you use. If you change the mass of rotating, you change the reading.
I made a 175hp difference on an electric dyno changing from a 40" tire to a 27" tire. I'm sorry I don't have the weights, it was done because "they" didn't believe the HP was so low. Then, after, we towed it across town to a dynojet and with NO changes picked up another 75
People race dyno numbers, all I care about when on the dyno is increasing where we baselined.

[Orr89rocz]

I have seen some small difference in power numbers when pulling in different trans gear ratios. I can imagine some difference occuring in tire type and size. Different loss factors from friction and weight etc

[NewbVetteGuy]

Mustang swaps between heavy 20" wheels and 17 lb lighter 18" wheels and does back to back pulls. 34 lbs less rotating weight = 17.35 hp or about 5% HP improvement:

https://www.youtube.com/watch?v=5MUnG5hrEEI

Also an old Engineering Explained on the subject: https://www.youtube.com/watch?v=CxuER0qIWJk


Adam