after making the change to 18 or 19inch wheels,what would you say was the best improvement or negative if any. I'm not too please with the unsprung weight increase , but tyre choices are much better ..

 

18s are the way to go...for now. You get the most choices so that you can fit the widest tires and can run the lowest sidewalls. This will give you the most grip and the least tire flex. Once there are more choices in 19s, then they will slowly wind up as the better setup, but I think that we are starting to get to a point of diminishing returns. The only negative with 18s over 17s is the cost.

 

What he said.

 

With lightweight race wheels, you might easily see a drop in unsprung weight, not an increase. Inside the same overall diameter of a wheel and tire package, wheel can weigh less per inch than tire.

 

It also depends on the car. For a lot of cars, there aren't ANY advantages to larger wheels than 17". I prefer our 17" wheels on our Audi A4 due to the better ride. And I fail to see any use at all for 19" wheels on any car. Too much risk of curb rash and rim denting, in addition to the rougher ride, increased weight, and increased tire cost.

 

I thought that we were talking strictly track use. For the street, I would want as much sidewall (within reason) as I can get.

Jack, I have to disagree with you on the weight. 1/2" of additional sidewall weighs much less than the corresponding amount of wheel spoke required to make up the difference. Our cheaper 17" SSR wheels weigh less than our expensive BBS magnesium centered 18" wheels.

 

What kind of car?

What kind of use?

 

Track use only ,
A 18 inch tire and wheel combination is going to weigh more than a 17 inch setup so the unsprung weight goes up. is this offset by the better tires available in 18, as 17 inch tires are limited in slicks.

 

As mentioned, BBS, SSR, Enkei, OZ, and others make lightweight racing wheels 17-20" . I have 18 OZ that weigh 16lbs which is not bad at all.

Bigger is better when it comes to contact patch with the road for most part.

There is also a gearing/performance impact when upsizing, but that is another topic.

 

DaMan 993TT,
This is what i'm getting at , it does not matter who makes what as it is academic that a 17" bbs wheel is lighter than a 18 inch BBS wheel.
what i'm asking is there anyone here who mde the shift from 17 - 18 inch wheels and had a performance advantage ( this takes into account the unsprung weight increase if any , gearing impact etc. ) or did you have to do other changes to take advantage of the larger tire etc....

 

You just can't make blanket statements when it comes to changing wheel diameter.

Here's some data I was able to find quickly on wheel and tire combos:

HRE 547 17 x 10 - 23 pounds
HRE 547 18 x 10 - 25 pounds

Kumho V70A - 335/35R17 - 32.1 pounds
Kumho V70A - 335/30R18 - 29.8 pounds

The 18-inch combo would be .3 pounds lighter than the 17-inch combo. (Overall diameter decreases by a third of an inch.)

Fikse FM-5 17x8.5 16.0 pounds
Fikse FM-5 18x8.5 18.0 pounds

Kumho V710 - 245/45R17 - 23.8 pounds
Kumho V710 - 245/35R18 - 21.6 pounds

The 18-inch combo would be .2 pounds lighter than the 17-inch combo. (Overall diameter is reduced by .9 inches, in this case.)

Granted, I wouldn't put 335's on a 10-inch rim. And granted, I wouldn't trust all the data that's out there on the internet. Many increases in wheel diameter also mean an increase in overall tire/wheel diameter, because of the quirks of tire sizing. In those cases, the weight would probably skew in the opposite direction.

But it's safe to say that increasing wheel diameter doesn't always mean the rotating mass also increases.

And by the same token, there are instances where your overall wheel/tire diameter decreases when you increase wheel diameter.

 

agree Jack,

But does it transfer into a faster car by going to the 18"s , does it make sense to switch? or the improvemnts is one of many to get a faster car than just changing from 17-18.

 

I changed wheel/tire widths when I changed wheel diameters, so I can't speak to wheel diameter as an isolated change. While there's a theoretical advantage to shorter sidewalls, I don't think it will be nearly as significant as a change in tire width or overall diameter would be.

In your shoes, I'd look at the specific tires you'd be running with each size. Compare the overall diameters to see how it's going to change your gearing and ride height. Also, get the specific weight of your current wheels to compare to potential 18-inch replacements. Then look at tire cost and availability of tires in each diameter, and make your decision based on the sum of all those factors.

 

I thought one of the bigger reasons to go to a larger wheel (18-19) was to get larger brakes??

 

keep in mind the tire is part of an entire suspension system. If your springs and damping rates aren't set up for a really stiff sidewall you can potentially lose performance going up in rim diameter. The same applies in the other direction. This is why street cars that upsize significantly lose a lot of performance - the sidewall is too stiff for the damping and spring rates.