I have recently replaced the stock 18" oem wheels with some inexpensive aftermarket 19" and found the acceleration significantly slower at every gear levels due to the weight issue. I initially thought only the low gears would be impacted and there shouldn't be an issue once the car has built up the momentum. I was apparently wrong.

Now I have two alternatives to move on. Either move back to 18" wheels or replace my 19" with lighter wheels to make the weight equivalent to the 18" OEM.

I then wonder if anyone would know the difference on the acceleration between the 18" and 19" wheels assuming their width and weights are identical?

I am struggling between moving back to 18" and buying lighter 19" wheels. Both are costly options though.

 

The oem 18 are actually quite heavy and typically a cheaper 19 actually weighs about the same.
Does it just feel slower or did you time it? Adding hp might be a cheaper option than changing the wheels and tires if you like the 19s you put on.
There really isn't an affordable option for you there on either size. Forged light weight 18s or 19s are a pretty penny.

 

From a performance standpoint 18s will always win out. Take a look at what Porsche Cup cars run on. 996/997/991/GT3/RSR....all on 18s.. Ideally you want lightweight forged 18" wheels with taller tires that will give you more sidewall. My 18x10x13s weight 18.9lbs and 21.9lbs respectively. Weight of tires also plays a big role. Look at a Bridgestone compared to a Michelin PSC2 for example. Same size but the Bridgestones will be substantially heavier. Up to several lbs per tire heavier and in the worst place possible, the outer perimeter of the wheel. Pick the right wheel and tire combo and you can easily save 10lbs per corner over a mediocre 19 with heavy tires.

 

What hard data do you have to indicate that your car is actually slower?

 

technically, its the not the weight. Unless you are going to tenths on a race track, you wont tell 15 lbs difference, if its even that much. You will experience a change in gear though. Bigger tire means a shorter gear. Going to my 19s I can get another 4mph out of the car at top speed.

 

That really tire diameter not wheel size though. You can accomplish the same on 18s.

 

That is true. I run taller tires because I hate rubber bands. I just figured the same for most others.

 

I did not really measure the acceleration and it was just more of a feeling, yet I believe I can tell the difference as I have been driving the car for a while. I missed a couple of points that on top of the weight, the rolling diameter of my rear wheels has indeed increased an inch after I moved from 295/30-18 to 295/30-19. Plus the offset pushed the wheels more towards the fenders.

I believe all these factors contribute to the result. I have decided to move back to 18" now, just a matter of back to the OEM or some light 18" rims such as the OZ alleggerita.

 

Rotational mass matters! Ok, less so on a 450 bhp car but if your ****-bhp-meter is astute you can definitely tell the difference. 19 inch wheels are for show 18's are for performance. Stock 18's (hollows) weight wise are actually hard to beat; 18x8 = 9.65kg, 18x11 = 11.9kg. You can get 19's of a similar weight but they won't be cheap! And don't forget the tyre weight as well.

http://www.caranddriver.com/features...d-tires-tested

 

What you are feeling (for the most part) is the difference in the overall diameter by going to taller tires. When you increase the diameter, you increase the top speed but the car will feel like it has less torque to it because you have essentially changed the gearing of the car. You should also have noticed that your revs are higher at certain speeds than you were at with stock diameter tires.

 

My 19" wheel/tire combo weighs less than the stock 18" hollow spoke setup Not crazy expensive either.

What type/brand wheels did you get? I'm also guessing that the weight of the wheels + the larger overall diameter is causing the phenomenon you are noticing.

 

Sorry mate but this simply isn't correct.

Going from 18's to 19's should result in the same diameter or near-about. If not, than totally wrong wheel/tyre combo is in place. You need to be especially mindful of this in the 996TT! If you change the overall diameter, chances are your PSM will be off and you will eventually chew through your front diff.

 

I was responding specifically to the OP in regards to this statement:

He states that the total diameter of the tires did change when he moved up to 19 inch wheels.

 

Aha. Misunderstanding then. ;-). Up 1 inch! :-0.

 

Unfortunately it is a combination of the added rotational mass and the tire diameter effectively changing your gearing/acceleration. I can confirm that you can actually feel it. It also effects turn in response and braking too. Like putting weights on your feet plus the gearing issue.