Why did I wait so long???

I can't believe the difference. The suspension is happier, the car feels more settled and stable, etc.

Sincerely,
Composed Cornering
Original Post
I made a major upgrade with new wheels. I went from 17" to 15".

Car feels transformed. Wheels and tires are much lighter. It is so much quicker with the lower unsprung weight.

The car follows road irregularities with ease, the ride is much better and there is more grip. The shocks/springs feel relieved and are no longer working very hard.

I don't know why I waited so long to do this as I ran 15s on my other cars. I kept putting it off for no good reason.

LSJ
quote:
Car feels transformed. Wheels and tires are much lighter. It is so much quicker with the lower unsprung weight.

The car follows road irregularities with ease, the ride is much better and there is more grip. The shocks/springs feel relieved and are no longer working very hard.

PCNC member Marcus Wohler reported similar results when he switched from larger Campy clones back to his original Campys. He couldn't believe how much better the car felt and handled on the road. Congrats!
Thanks!

I must admit that I sorta "knew the answers" already but I'm just so excited about the changes.

It feels like a new car.

LSJ
Lashdeep,

Is this on the GT5?

Julian
Yes, and I went from 17" Aluminum to 15" Magnesium.

I drive my car spiritedly and the dynamic improvements are substantial.
Other than the 17 inch wheels were you still running with all the original suspension pieces?

Shocks, springs, bushings, a-arms, etc?

Larry
Umm...yes.

On this car, the shocks are non-typical but likely factory installed.

Regardless, they were obvoously made for the 15s.

My old car had the standard, OEM suspension, stock wheels and modern rubber.

I drove it back to back with an identical car which had 17s and modern rubber installed. There was no comparison.

The stock wheeled car did everything better than the one with 17s. It felt faster, lighter and handled much more predictably.

On my current car, I can take the slightly bumpy section of my favorite road 10mph faster than before.

The suspension is controlling less weight now and following the undulations in the road is easier. The increase in grip is impressive. There is less need for mid corner corrections due to road surface changes.

Inspired by this, I am going to experiment with a narrower (and lighter) tire stretched a bit. I am going to use a state of the art 2017 tire in an R compound to compensate for the loss of section width.
I had similar experience when I replaced 15 inch Gotti wheels/tires with 17 inch Hall Ultras on my wide body car. It made the car feel heavy, acceleration was noticeably slower, braking distance was longer. It was not as stable and did not handle very well. I did not like it at all so, I switched back to 15 inch lighter Gottis. After the change car felt very stable and much quicker with shorter braking distances.

Shah
While lighter wheels is a great plus the only reason the larger wheels didn't handle correctly is because the shocks were not doing their job with the extra load of a heavier wheel. A correctly tuned shock with larger wheels wille perform as well over rough roads and sporty cornering when setup correctly.

The lighter wheels is a great benefit that helps with the feeling of it being more nimble but you will get some of that feeling back with the larger wheels and a tuned suspension. This is why you can't just throw parts on your car and expect everything to work correctly without making sure the parts selected are correct for the particular situation and adjusted correctly.

Not trying to take anything away from the positive results from going back to the originals. I am very happy they work so well. Just didn't want people to think that going to larger wheels will make their car handle worse. It may if not setup right but a larger wheel will work fine with the right shocks.

Respectfully submitted...

Scott
Scott raises some good points, I think what also needs to be considered is the wheel and tire combination; tire profile and rolling diameter play a significant role in the feel and response.

I'm betting all the perceived acceleration difference is simply due to tire diameter effectively impacting final drive ratio.

Higher profiles on 15" tires make for a more compliant sidewall as well, where the low profile modern tires are stiffer.

It is also interesting to note that the two examples quoted are both wide body cars, where the effect is likely pronounced due to the wheel offset.

A lot of wide body cars always look 'jacked up' with aftermarket wheels due to the aforementioned tire diameter change, this significantly raises the cars center of gravity, it should feel different!

If we are comparing wheel weight the only true comparison is between two wheels in equivalent diameter and tire size, anything else is really apples and oranges.

Julian
Scott and Julian are right.

And, I would add another 10-12 things that would need to be analyzed and possibly changed to get back to where you started with the smaller and lighter wheels.

I drove over a rough patch of curves that I have always dreaded yesterday. Previously, a downshift and teeth clenching were necessary. Yesterday, the chassis just ate up the irregularities. The dampers are no longer confused in any manner. I didn't even let up on the gas the second time around after how good it felt the first time.

Maybe 10-15mph faster overall through all of the corners?

It feels like I just got a new car.

LSJ

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