I bought 19" TSW Bremmas two 8.5" fronts and 9.5" rears I heard jumping two sizes up on wheels causes a gear ratio change that effects the launch unless I get tires with a smaller sidewall...now this isn't familiar territory for me so any help is truely appreciated...I am unsure what to put in search option thats how lost I am...please help. So what tire size is required to keep ratio the same as OEM rims? Is there a formula to follow?

 

225/35/19 front or 235/35/19 front (might rub)
255/30/19 rear or 265/30/19 rear (might rub)

something to think about:
30 sidewall is not much protection....

 

+1
The potential for rubbing, adequate room in the wheel well, and trade-off in terms of ride quality should be enough to make you choose wisely in terms of tire size!

Let's take the OE front wheel/tire of the C32 as an example:
225/45 R17

The overall wheel diameter would be calculated as follows:
Sidewall to sidewall width multiplied by the profile:
225mm x 45% = 101.25mm (= 3.986")

Double the sidewall height (since we're talking diameter) and add it to the rim size:
17" + 2(3.986") = 24.972"

So.... the overall diameter is calculated to be approximately 25"

If you increase the rim size and you want to keep your overall wheel diameter somewhat similar, then you need to reduce the profile or sidewall height. In theory, the calculations work, but there's a little more to it than that...

You want to use your new 19" rims.

Keeping the overall diameter the same:
~25" - 19" = total sidewall height ~6"

Divide by 2 to get sidewall height:
~6" / 2 = ~3"

To calculate the profile, you convert the sidewall height (inches) to millimeters (mm):
3" x 25.4 = 76.2mm

Divide the sidewall height by the width of the desired tire (let's use hooleyboy's example of 235mm):
76.2mm / 235mm = 0.32
Your profile is thus 32.

Therefore, you need a 235/32 R19 tire to keep the same overall diameter as the OE rim + tire.

Since a 235/32 R19 doesn't exist, you have to pick the closest match.
Thus, a 235/35 R19 tire may be one of your better choices.

Again, the calculation is really only useful in estimating which tire to use. You need to take into consideration the various factors alluded to above.

 

Try this it's a little easier. Overall diameter is what you want to be the same or close as possible. Input your previous size and the size you want to compare.

Tire Calculator

 

Thanks guys I appreciate it

 

If you search for tires on Tire Rack's website, after entering in your year and model info, it'll show an option if you want to see optional sizes (i.e. 18" or 19") - if you click on 19", it'll give you the optimal sizes and tire options (that they sell, however). Best of luck in your search!

 

wont change gear ratio-gear ratio is from the rear end-it can however throw off your spedo, ect-which is what you want to avaoid (a birdie told me that the new Evo X owners are having issues with the AWD system and rear diff when changing rims out for the track.....electronics are great-to an extent).
^+1-try and keep as close as possible to the OEM diameter rim and tire combo-that can open a lot of doors if you look at it that way-

 

Thanks again guys

 

Well using both C32amg-DTM and cruzinquick I got these numbers...

for OEM 225/45/17 it says use 225/35/19 its -1.31 mph error in speedo so if it says 65 its doing 66.31 actually
for OEM 245/40/17 it says use 255/30/19 using this revs per miles is -10.91 error in speedo is -.81 mph so 65 mph actually is 65.81 while using 255/35/19 its -41.1 revs per mile error in speedo is -3.45 mph so 65 mph actually is 68.48 mph.

Now I saw the part about 30s not offering alot of protection but what you guys think in mostly Drag racing configuration?

 

Jake being the lone exception that comes to mind - most racers experience significantly worse results drag racing on a larger wheel with extremely low-profile tires. For one, it's typically a lot heavier... and two, you really want more sidewall flex when you're trying to "hook" the launch. For these reasons, most of the serious C32/SLK32/SRT6 track guys that I'm aware of will grab a set of 16" wheels (lighter the better), and mount 255/50/16 drag radials to 'em. Going to a -1 fitment for the rear, instead of +2 like you're suggesting. The Bremmas will look great on the street - but I'm not sure how well you'll like 'em on the track.

 

I only plan to use the OEM chrome 17" with Toyo R888 for drag and the Bremmas 19" with Toyo T1R on the street. I also have two 17" rims with Nitto 555R DRs I use on track. Basically I just want good performance for the street with the 19" but wanted to pick a good tire size. I'm not going to torture the T1Rs while in street use...