I know that putting on smaller wheels make you go faster and thought its due to the reduced unsprung weight, diameter or rolling circumference

I have been running 19's 245 35/275 35 wheels for 2 months and had changed them a week before going FI.

When I first drove with them, I noticed a marked decrease in the cars performance and thought that maybe it was just my imagination.

2 days ago, I swapped back to my 18's 245 40/275 35 to prepare for a track day and again a felt a difference this time it was more obvious with the car FIed.

I lifted both the 18 and 19 wheels with tire and the weight difference was not much. Just went to check the overall tire diameters of both my set ups and the fronts of the 18's is only 01." smaller with the rear 1" smaller.
due to smaller wheels. Circumference diff is abt. 0.3/3.3".

I also note that handling on 19" are better, even though the width are the same and the sidewall measurements on both set of wheels are the same.

Just wondering if its me or is there really a marked difference in downsizing?

 

welp none of that makes any sense. going from 19's to 18's wont make a huge performance difference, but its not gonna hurt it any. sounds like your imagination, on the upside, you can find more competition tires for less $$$ in 18".

 

it's not your imagination at all.. it's not just the increase in weight, but youre also moving the weight further out on the wheel which compounds the loss.

 

There may be a difference but I cannot tell what you can and cannot feel.

 

When you shorten the profile of the tire (going from 275/35/19 to 275/35/18) it changes the final drive gearing. Maybe someone else can explain it better.

 

If that is really the case, I am surprised that the 1" differential makes such a great difference in response.

 

he kept the same circumference, so nothing changed there. That wasnt what he's feeling.

I leave my driveway and head down a hill with sharp turn, followed by sharp turns were I yield rather than stop. its like that almost all the way to work. Going from heavy OEM 17s to even heavier 19s was pretty drastic. Felt like driving in 6" of molasses. I even had to check my tire pressure, it felt like they were low. I can even feel a difference when changing lanes quickly. However, from my OEM G35 18s, which are nearly the same weight as my 19s, I'd say it was much less noticeable.

 

There was a difference of 0.3/3.3" F/R in the circumference. I don't think its the weight as although I did not weigh it, when i lifted both rims with tires, the difference did not feel much. I should have weighed them thou to get an accurate gauge.