Just changed my tires and wheels yesterday from the stock 235/55R17 to 265/35R18's. Lost about 1-1/2" in tire height. I knew that was going to happen but what I didn't expect was the car to loose a little throttle response. Going into the dealer this weekend to have them reconfigure the car for that tire size. Does anyone know if this is because the PCM is sensing a change of drivetrain enviroment and needs to be adjusted?

2007 Mustang GT
Pypes Catback M80 exhaust
No other mods yet

Nope it is because of the greater rotational mass. When I was n/a I was at 312hp and I went down to 298 by switching from 235's to 275's + rims.

Andrew

Felt my loss immediately when the 20s went on. Then later the lost torque down low when the o/r h went on.

Did you tune for the larger tire size? That would help.

Bigger wheels = worse performance. Period. There is no amount of tuning that can reduce rotational mass. My car came with the 18s. It didn't take me long to ditch them for some 17s.

ORIGINAL: Androdz2

Nope it is because of the greater rotational mass. When I was n/a I was at 312hp and I went down to 298 by switching from 235's to 275's + rims.

Andrew



That's why I love the dynapack.

ORIGINAL: Androdz2

Nope it is because of the greater rotational mass. When I was n/a I was at 312hp and I went down to 298 by switching from 235's to 275's + rims.

Andrew



I can't believe it would go down that much. My 18 rims and 285 tires are only a few pounds heavier then my stock 17s and tires.

Does the better grip, counter act the lost in hp?

ORIGINAL: bkid

Did you tune for the larger tire size? That would help.


[sm=funnypostabove.gif]

ORIGINAL: Lito

ORIGINAL: Androdz2

Nope it is because of the greater rotational mass. When I was n/a I was at 312hp and I went down to 298 by switching from 235's to 275's + rims.

Andrew



That's why I love the dynapack.



can you put engine load on a dynapack?

ORIGINAL: SuperSonic05

ORIGINAL: Androdz2

Nope it is because of the greater rotational mass. When I was n/a I was at 312hp and I went down to 298 by switching from 235's to 275's + rims.

Andrew



I can't believe it would go down that much. My 18 rims and 285 tires are only a few pounds heavier then my stock 17s and tires.

Does the better grip, counter act the lost in hp?



Yah but the rims could be a little bit heavier. + the tire has more weight towards the outer radius of the tire which would then = more rotational mass.

Andrew

You can simulate any load you want, you can even control the speed of the engine with the load. You can have your car WOT and it won't let it move from that certain RPM you want.

The thing is that you can review what a shot of nitrous does to the car not worrying about traction, or don't expect having a different reading because you changed the tires, you've lost 5psi on them or you tied you car a little harder this time.

ORIGINAL: bkid

Did you tune for the larger tire size? That would help.


HaHaHa, I know what he meant, but still funny....

That is somewhat strange. According to this website: http://www.wallaceracing.com/Calculators.htm
With your new tires your actual gears are 3.81, provided you have 3.55. Seems like you would have gained some throttle response. I also put on new tires. I had 255/50/17 and now have 245/45/17. I have 3.55 but according to the calcutalions my gears are 3.79. My car does feel more repsonsive.

Your tire height is about the same as mine. Have you noticed an increase wheel gap?

Big wheels are pretty, but you will feel the power loss; no doubt. I plan on getting some staggered 20s soon, but I have a set of 3.73 gears in my garage to I can counter the bigger wheels' extra rotational mass. With 20's, I may even by able to get away with some 4.10's if the tire is tall enough. I saw another post here with a website that calculates your gear ratio with your tires sizes......I'll check it out. I got time to figure it out.

I'm sure a gear swap will give your power back and let you keep the bigger wheels. The gears themselves are cheap; the installation will cost you more than the part itself.http://i15.photobucket.com/albums/a379/rugedraw/StangSide.jpg