Now this may be the dumbest question ever but on our cars when you dyno do the size or type of tire affect you dyno numbers? Had a guy I work with say his car made 17 more rwhp on a smaller rear tire (drag radial). Could this be true?:??:
does it matt...
- Thread starter Presteige
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really.... so would he be correct to say the smalley one made more power?
Yes. Remember there is Flywheel horse power and wheel horse power rear wheel in our case. Power is loss through the drive train depending how efficient your setup is. Wheels and tires take part in this. Some times very little some times a lot. Try and roll a 14" wheel on a flat surface. Now try and roll one of those massive rims with 38" tires. It is a whole lot harder to roll. Same thing your car goes through. Not to that extreme if you are going from a 17" rim to an 18" rim but there is a difference.
Now also remember dyno's are not always consistent. I have seen 20rwhp change on back to back runs. So his gains may not of been all from wheel size.
On a Dynojet - reducing tire diameter will make it look like the car is generating more HP for the same reasons that changing to a taller final drive ratio will accelerate the car faster. A Brake Dyno like a Mustang (configured as a Brake Dyno, Mustangs can also do Inertia measurements) won't be fooled by a gearing change.
Some Dynojets can do the same thing.
All I gotta say is my car put out the same numbers with the Weld (very light) drag setup with full slicks as it did with the True Forged 3 piece rear with gigantic M&H Drag Radials on it. Different days though unfortunately.
It also put out the same numbers with the built solid axle with 4.10's in it as it did with the IRS and 3.73's did.
Different days also but the graphs match perfectly on both of those combo's.
op:
Godstang like you said before if you and I had a dyno we'd be on the thing way to much lol. I would love to dyno both wheel/tire combo's the same day.
It also put out the same numbers with the built solid axle with 4.10's in it as it did with the IRS and 3.73's did.
Different days also but the graphs match perfectly on both of those combo's.
op:Godstang like you said before if you and I had a dyno we'd be on the thing way to much lol. I would love to dyno both wheel/tire combo's the same day.
Ive gone from radials, to SLICKS, to DR's with negligable difference.
Was that the same day? Same mods?
John another thing to take into account is amount of power a car makes can over come tire size a lot easier without having to regear. I had a near stock 03 GT (260bhp) and went from a 17" rim to an 18" rim and noticed a change in acceleration. Put the same rims on the Cobra (600rwhp) instead of the stock 17s and it did not bother the car one bit.
If the guy has a 140hp Honda and swapped wheels he will most likely see more of a change then you would unless you did like a 12" wheel swap.
You learn about this a lot in 4x4 when you go from stock tires to big ass mud tires but as said above some dynos you can take these things into account.
If the guy has a 140hp Honda and swapped wheels he will most likely see more of a change then you would unless you did like a 12" wheel swap.
You learn about this a lot in 4x4 when you go from stock tires to big ass mud tires but as said above some dynos you can take these things into account.
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He has a vette pushing between4-500rwhp. But I was wondering if that would matter with our cars and if he was just bs'ing.
I would figure unless he did a huge size change it would not be that big of a difference.
!2 posts with a lot of fairly good tech but still no one has mentioned rotating mass.
Y'all have dancing all around it, but no one came right out and said it.
Overall Diameter... yes it = gear ratio change, and that can have some effect.
ROTATING MASS(rotating weight for those in Rio Linda) will make a measurable difference in power available to the tire.
Rotating Mass changes have far more effect on performance than general chassis weight changes.
The diameter of the rotating mass change can amplify the effects.
If the rotating mass increases by 5 pounds but the diameter of most of that mass has also increased by two inches(the rim or barrel are heavy), it will rob more power than the same increase with no diameter change, even if you somehow equalized the gearing before hand.
Y'all have dancing all around it, but no one came right out and said it.
Overall Diameter... yes it = gear ratio change, and that can have some effect.
ROTATING MASS(rotating weight for those in Rio Linda) will make a measurable difference in power available to the tire.
Rotating Mass changes have far more effect on performance than general chassis weight changes.
The diameter of the rotating mass change can amplify the effects.
If the rotating mass increases by 5 pounds but the diameter of most of that mass has also increased by two inches(the rim or barrel are heavy), it will rob more power than the same increase with no diameter change, even if you somehow equalized the gearing before hand.
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