oops you already did it. I'm curious to see what your numbers will be. I know at the track my car is a about .3-.5 slower with my 20's on due to the weight. I have heavy axis wheels also, but they look good though.

 

Results are in so you guys can ignore the previous dyno since the tuner found out that the machine was not calibrated correctly hence the strange gain and drop off at the end.

Today I did a back to back dyno with the 20" then with the 18" and to say the least the results are eye opening.

 

Gabe,

Can you put any of the data into Excel for analysis?

It would be great to compare notes.

 

Tony,

Here it is, the performance loss is drastic throughout the entire revband and the peak power kicks in later as well. Higher TQ and HP are for the 18" obviously.

 

Awesome! We have agreement on two completely independent tests!

 

Yeah, but unfortunately for me I took a pretty bad hit in performance especially on the Torque. Oh well, at least it looks better...perhaps those TP you will develop will help me gain that power back hehe

By the way doing these mods I got these following peak values; 249.3hp@6250/223.6tq@4750 as oppose to before 248.0hp@6500/215.5tq@4750. Perhaps due to the lighter rotors that took off a total of 9lbs total for both side on the rear.
-Interstate Battery, finally had to replace my 6 year old OEM one.
-MD Coolant Control Valve
-UR lightweight underdrive pulley (-5.2lbs)
-UR lightweight flywheel (-15lbs)
-Southbend OFE stage 3 clutch, just to replace my 90k old one.
-Girodisc 2-piece rotors (-9lbs rear and -11lbs front)
-SxExCx ground kit

 

Wow you take a good hit rolling on 20's. I'll do the same test in the next couple of weeks also.

I'll ask the shop and see if they have any 17's laying around for me to use my numbers on their dynojet are 249hp and 231tq on my 20's.

 

Something you might want to keep in mind. Eventhough both the test Tony and I did shows significant losses, they show it in two different ways; one as a measure of time, the other as a measure of engine speed. Looks like if I did a test on the same dyno as Tony's, the losses would not be the same or there at all, since his test yielded no peak power loss.

 

While the wheel size doesn't change the engine power (it cant), it can certaintly change the delivery of power to the asphalt.

Just like a final drive gear set. They don't change the power, but they certainly can make your car accelerate faster.

 

Agreed

For the three test that you did, can you stretch the 17" curve and shrink the 20" curve so that they can have the same sampling rate as the 18". Curious to see how that looks. Also can you fit a quadratic trendline on each of the curves? Thanks.

 

Great thread! I always knew bigger/heavier wheels like 19's/20's threw it off, but never knew it was quite this much.

 

Give me a email. I can send you the file.

There are too many possibilities for trend lines.

 

Did you ever get a chance to do it. It'll be interesting to see a third data point.

 

Could you repost your dyno, it's not showing up now?

 

the shop didn't have any 18's or 17's laying around. I plan on going to get a retune for my 3in maf housing at the same shop on my 18's next week.