As opposed to 18 inch rims?

 

I can only tell you that I lost 2 tenths going from oem 17" to 18" 275/40's. Had to go to rear gears to get it back and keep the 18's. Regards, Jim

 

2 tenths from 17's to 18s? Wow.. that seems a bit much. Are you sure it just wasn't your driving? It could have been a number of factors, you never run 100% identical numbers.. but wow, 2 tenths?

 

Yup, 2/10. I run about three times a month until the hot weather shuts us down and I have a pretty good handle on my car and its performance gain/loss. My driving is pretty consistant (rt's and let the 5AT do the rest) and p/u my slip at the end! Wish the loss were not so, but my swap of rear gears gave me back those tenths so I am somewhat mollified I am soooo close to being a consistent 13 second 5AT that I can taste it. This fall I intend to get there with a little help along the way. I don't need/want a barn burner, but 13's in my auto Tourer w/18" rollers will fulfill me nicely. I could do it today w/16" DR's, but I want to get there w/street gear and that means 18" for me. I have a best of 13.915, but that was in Fayetteville, NC, not my home track here in AZ where I run consistent 14.2's and an occasional 14.1 thrown in. Regards, Jim

 

2 tenths sounds about right you will lose abou tthe that each inch you go up in size, unless you get some extra lightweight wheels of course. Jim hit it on the nose I noticed that years ago in my wifes old 300.

 

I replaced my 17 inch enthusiest wheels which weigh 53 pounds with tires witht the 18 inch track rims a big improvement losing like 10 pounds per tire
jimh did you weigh those wheels they look nice but are they heavy in my eyes it might be the weight there not the fact that you went up a size do you think that could be it?

 

We weighed the new wheels with the Nitto's already mounted and they are 45.10 lbs front vs. 50lbs stock. Rears are 48.4 lbs. w/Nitto's vs. 51.5 stock setup. So, as you can see, the Privat Fahrens w/much larger Nitto's, are even lighter than the smaller stock wheel(s) and smaller stock B-stones. Regards, Jim

 

Jim is definitely right. I would always hit 14.2 everytime I went to the track(not the 350z). I did it a few times in one year. Sometimes runs were 6 months apart. So I'm a consistent driver. My point in all this is that Jim is correct when he says it's the rim size that made him slower and NOT his driving

 

In my opinion, this is poof positive of the basic physics I've been spouting for months on here. I've said countless times that larger wheels have less mass towards their centers and so have a higher polar moment of inertia, thereby making it that much harder to turn the larger wheel/tire combo. This is true even if the wheel/tire combo weighs slightly less. Its not just the overall weight, its where the mass is located. If more mass is distributed out towards the outside of the wheel, then there will definitely be a higher polar moment of inertia. Thanks for helping me illustrate my long-standing point. lol

I do love the Fahrens, though. I've thought about getting some of my own, but I'd be going from heavier 18s to lighter 18s and I'd probably be better off. They look fantastic on your car, though. Nice taste!

 

Jon, I certainly ascribe to your logic here. Oh, and thx for your kind comments on the wheels and how they look on "Marilyn!" Regards, Jim