Pros and Cons? Is there a noticable difference in acceleration? Speedometer difference? Typical weight difference? Tire cost? Is there a place with all of the wheels and weights listed besides tire rack?

996TT

Thanks

 

When you move up or down wheel sizes you should keep the same rolling diameter with the tire size ratio. So for example on my 997S the stock tires for 19" wheels are:
235/35/19 front
295/30/19 rear

When you move to 18" wheels you will need these size tires:
245/40/18 front
305/35/18 rear

Now the real important part is the keep the size ratio between fromt and rear with in 4% so that it does not mess up your ABS, PSM and your all wheel drive.

So if you want smaller diameter tires because you car is lowered and you would like to gear the car down via tire sizing you can go with:

255/35/18 front
315/30/18 rear

this set up will yeild a higher speedometer rating.

 

So what size tires would go on 19" wheels for a 996TT while trying to keep within the optimal diameter?

 

Yes there will often be a noticeable difference in performance. 18" wheels are generally lighter than their 19" counterparts and likewise most 18" tires and lighter than 19" tires. Depending on the wheels and tires that you choose, you could easily see 10lbs per corner of weight difference. You would definitely feel 40lbs of difference in unsprung weight.

If the weight isn't listed on Tire Rack, contact the wheel manufacturer. This is public knowledge and they should be willing to provide it willingly.

 

im looking to switch from 19 to 18 on my non-pasm caymanS. 19s look slick but ride a little rough for me.

 

I believe the impact ratio of unsprung vs. sprung weight is 3x. That means adding 20 pounds @wheel is like adding a 240# person sitting next to you (i.e., 20 X 4 X 3). If the wheels weight the same it's a wash - but most bigger wheels weight more

 

I am trying to keep within diameter requirements so the PSM, or front wheel drive doesn't blow up. Can someone post tire sizes so I can price them up? What sizes are people running on the 996TT without doing damage? I will ultimately will try and get the total sprung weight close to or less than stock with the 19" wheels.

 

If you stay with these sizes you will be at the same overall diameter as stock 19"

245-40-18 fronts
305-35-18 rear

 

Other way around. I want to stay around the stock sizes for a 996TT which has 18" wheels. But instead use 19" wheels with low profile tires that are within 4% of the original diameter. I know people are running 19s on 996TTs, I just want to know what tires they are using.

 

I recently went from a 996 with 18s to a 997 with 19s. I can say without reservation that i much prefer the ride of the 18s. My 19s are champion RG5s but i "think" my car 996 also handled a little better than the 997 does. Perhaps that's because i'm not used to the 997 yet, but it sure seems that the wheels are the determining factor. I'm actually tossing around going to 18s instead and getting rid of the 19s.

 

Go here: http://www.1010tires.com/TireSizeCalculator.asp

 

That works thanks!

Stock:

225/40/18
295/30/18

with 19"s wheels:
235/35/19
315/25/19

Looks good as far as diameter.

 

So if I go from stock 18's to aftermarket 19's but stay within the 4% of the original diameter, I may not have to change my suspension due to excessive wheel gap correct?

 

I have a 996TT. I plan on changing my suspension to some new stiffer coilovers and lowering the car. The reason I wanted to find some tires that were close in overall size but 19" diameter, was to not damage the front differential and not throw off the PSM. (that info in other posts) I am only a driver and not a mechanic and I was hoping some professionals would chime in.

 

Hey there, my name is Jim and I used to work for CEC/Techart and the 19" for the 996 was a really popular set up for us. For the 996 they had two applications...std body took a 19x8.5 ET40 Front, and 19x11.0 ET52. The recommended tires we used were 235/35-19 front and 315/25-19 rear. If the car was a turbo or C4S we ran a rear wheel that had an ET25 with the same tire set up. The 19 was very aggressive, but really looks amazing. TechArt also used coil over set ups with their 19" application, the best thing to do is look at what the German tuners have done and follow that example...because they have to test and approve each fitment for TUV, if it does not function than it can't be used.
Coilover suspensions definitely perform, but for everyday street driving they can be a little rough. Going to the 19 from an 18...you do probably feel more road, but it is not that huge of a difference. Many factors depend on how far you lower the car, what wheel width and offsets you use, and what tire brand.

I hope this information is helpful.

Jim