I've heard that while adding the look of a car, 20's can rob HP due to the larger diameter. Is it enough of a loss to not do it? Below is a pic of the wheels I am gonna get. What do you guys think? I don't see alot of Stangs with these wheels. Axis Matrix, 20x10.5 in the back, 20x9 in the front. Looks sweet, a little bit of a tuner wheel maybe, but def holding down the race look with the rivets Click pic to enlarge

 

I'm going to a Dyno day on 02/03/07, to get stock #'s. If you can wait, I'll post them up.

 

This topic gets involved with regaurding to rotational mass.Depending on the wheel,composite rims,one componet is usually heavier than the other,the center of the wheel or the outer rim.It would be wise to check wheel weight before purchasing.


One heavy rim in particular is the Boss rim which weighs around 42lbs. each.They look awesome but by the time the crank turns each component in the drive line they have to push the weight of the wheel and the weight of the tire,combined weight comes to around 50lbs each(maybe more),times four... thats one heavy set up.

 

I was debating on the ones that you have in your avatar, but went with 18's instead because of the performance.

 

Maybe there is a happy medium in a 19" wheel, too?

I can call Axis tomorrow for you and get the weight on that wheel.

 

Hey where's this dyno day going on. Is it a specific club dyno day???

 

20's were the first thing I bought for my 06 GT. I have 20x10 in the rear and 20x8.5 up front. Traction was better off the line, but I did notice a little loss of HP. Not enough to take off the wheels. I soon added a CNL CAI, UDP's and an axleback exaust along with lowering springs. You will need to lower the car if you go with 20's. If you don't, they'll make the car look taller. With the mentioned power adders I compensated the power loss and then some. A couple months back I put my 17's back on to save some tire life on the 20's since I have a 80 mile a day comute. My car felt like a rocket with the 17's. I barely had to step on the gas to get some smoke, could chirp into 3rd. I considered selling my 20's but ended up putting them back on for the looks. The only thing about the 20's that I don't like is that they make the brakes look small. Putting on a big brake kit is risky due to the fact that the spare won't fit around 14" rotors. Never know when you'll blow a tire. I'm gonna be adding a whipple pretty soon, so the heavier wheels and fatter rubber will be good for traction.

Here's some pic's of my car with the 20's.
http://i124.photobucket.com/albums/p...4/DSC01877.jpg
http://i124.photobucket.com/albums/p...4/DSC01875.jpg
http://i124.photobucket.com/albums/p...4/mustang4.jpg
http://i124.photobucket.com/albums/p...4/MUSTANG5.jpg
http://i124.photobucket.com/albums/p...4/mustang1.jpg
http://i124.photobucket.com/albums/p...4/DSC01881.jpg
http://i124.photobucket.com/albums/p...4/DSC01872.jpg

 

Why not make a slight compromise and go with the 19" size.

 

Man...I love that car.

 

Thanks. Yeah, the wheels really set it off.

 

IMO, anything above a 18" rim is sacraficing performance. Granite with a forged wheel it is lessened to some degree, when you put more mass further away from its axis point, it takes more effort to get them rolling as well as more effort to get them stopped so braking performance is something else to consider. If you go above the factory tire OD, its just like putting higher gears in the rearend as well.
On sports car revolution they did a project Acura RSX and swapped out the stock rims for 18"s(I think), and they lost 7 or 8 hp on the dyno.

 

in the newest issues of 5.0 they have an article on testing a new GT and i saw a little side note talking about the car they used for the test lossing 10hp when the 20" wheels the owner had on it was dyno tested compared to another set they used. can't remember the size of the others though.

 

Thank you for all the input, your help is greatly appreciated

 

Sorry I missed this, but the shop is in Santee and has them every couple of months, open to anyone. Keep an eye on the link below, for the next one, I'll be there.

http://www.dynoperformance.com/dynoday.php

As for my dyno pull with 20", on a stock '07 GT/CS she put down

267.77 Max Power/ 284.72 Max Torque

How does that compare with smaller rims?

 

I don't think that the numbers on a dyno will change, as you aren't moving the car, just the wheels. It would be no different than having a 100 lb person dynoing the car vs. a 400 pound person.

But, once you get on the road, you are trying to move the weight of the vehicle. So, with bigger wheels, you have more rotational weight, more curb weight, and more rolling resistance (due to more rubber). This is where you get a "loss" of HP. Technically though, you don't LOSE horsepower, you just USE more horsepower to get the car moving, and to keep it moving.

Think about it this way: do you gain any HP by removing 400 lbs. from your vehicle...NO! You just use less power to move the car

 

Axis Matrix 20X9 weighs 28.1 lbs and the 20X10.5 weighs 29.75 lbs.


Here's the link to the weights on the Axis web site:

http://www.axiswheels.com/axis_wheel..._and_lips.html

 

Wheel size WILL effect dyno numbers.
Above numbers are right on par for a stock 05,06, but not sure on the 07's yet.

 

If you say that the above numbers are right on par for a STOCK 05,06 GT, then the wheels didn't affect it.

Just looking for clarification on this. Tucker: Are the above numbers that were for a stock GT with 20's the same as a stock GT with stock wheels???

 

What I'm saying is there right on par for a stock wheeled 05-06, but I'm not sure what the 07's are dynoing at yet.
I will soon as I just picked one up I don't know if the 07 is dynoing higher or lower then the 05,06.

Jay

 

If the numbers are on par, then the wheels DIDN'T affect the HP. Mdcorney's car above was dynoed with 20's.