Ok. I have a set of 19" TSW thruxton which I ran on a couple of weeks ago. To my disappointment the best I could do was 14.46@97.19 MPH. Here's the slip:
60' 2.177
1/8 9.385
mph 76.67
1/4 14.469
mph 97.19

Needless to say, a far cry from the time in my sig which is my best ever. So I was worried something was wrong with the car and all. So since the winter is coming I put my stock 18"'s back on and decided to run the car again today.

Ran 13.96@100.6

slip:
60' 2.13
1/8 9.057
mph 80.03
1/4 13.966
mph 100.62

So she's healthy again, except for the clutch starting to slip on the launch and the 1-2 shift.

Anyway, I've always heard that bigger, heavier wheels affect performance but damn I didn't expect to lose 4 tenths and 3mph+ by going big. I love the way the car looks on the 19s but I don't know if I'll put them back on the car. It bothers me that they slow me down that much. Maybe it's time to fork up for some Volks. Those should be much lighter. Anybody else noticed a drastic difference by going with bigger wheels? Please comment if you have.

But wow, I still can't believe it how slow the 19's made me.

 

Wow-that seems a little exaggerated. Im sure the 19's contributed to running slower but not completely. You did have a slightly better 60ft on your 18" wheel run. What were conditions for both runs? What size rear tires, maybe you made the FD taller with the tires you chose? Regardless Id never run the 19's again!

 

I was thinking the same. But I've ran with my 18s countless times before and I've always trapped around 99-100mph. Last night it was about 47 degrees and my clutch was slipping a lot, so I could have ran faster.

When I ran with the bigger wheels it was around 65 degrees. Same track. Same launch method.
I was running 275-30-19, which should have made my gearing more aggressive.

 

your final drive prolly changed a little. But the bigger issue is the weight. When i was lookin at rims i read a study that said something like 1lb of rotational mass is equivalent to liek 8-10 lb of static mass. so if u add 1lb heavier rims on each tire, you basically added 40 lb (rounding because 1. i dont remember exact numbers 2. easier lol) plus if u get bigger rims, you push the weight farther also, which also makes it worse. remember wider/ larger rims means you are adding weight to the outermost part of the wheel(lets not forget about tires).....this is why i hate rim shopping, because i always want the lightest, problem is cash....one day i would love to have magnesium wheels like on the mosler, now those are extremly light. Now the same philosophy applies to stuff like flywheels and even rotors.

 

My 19's dropped me exactly one tenth.

 

I would not like to race with fat *** 19 inch wheels, but I think your comparison is extreme.

 

Hmmm...you make a lot of sense. Especially with the 19" wheel I was running. Such a fat lip and such thin spokes, all the weight is on the outside, and then the meatier 275 tires... I never really thought about that when I was shopping around. Oh well, found out the hard way. But I did talk to one other 350z owner who was running 20"s and he said it dropped almost a full second off his times.

 

How much do those wheels weigh?? I ran a 13.4@103 with 19x10s on 275s toyos out back, my wheels were 1lb heavier in rear and 1lb lighter in front than the 17's stockers.

I think it has more to do with weight than size.

 

Sorry for the year long delayed response, but the 19" Thruxton wheel apparently weighs about 31-32 lbs.

 

Weather difference between the runs could easilly make up the difference in performance.

 

Both runs were made in fairly cool weather, though there was an 18 degrees difference, which would account for probably half a tenth of a second at the most. Don't know what the actual DA was on those days though, but like I said, I've always trapped 99-100 every other time I've been to the track with my 18s on. The first time I've trapped 96-97 was with the 19s on.

 

As has already been stated, additional rotational mass (ie. heavier rims and tires) will obviously contribute to a slower time. But also as already stated, the difference seems extreme.

I'm hoping to lose 1/10th with light weight 18's (running the stock 19's now).

 

^

Actually your front wheels are already 18's but your rear wheels are 19's..

 

Yup.

 

Imagine a 20lbs 18in tire, and then imagine a 20lbs 19in tire, same mass, but the smaller diameter tire has its mass more spread out. Even though the entire combo can be lighter, the weight at the edge can actually be heavier.

TK