What would I have to do to correct the speedometer if I wanted to use a non-standard tire size on a 09 SS/TC? For example, instead of the stock 225/4R018, I want to use 225/50R18. There is about a 7% difference in tire rotation speeds which will be very noticeable. How do I correct this error? Do I get the PCM tuned or do I change out the speedometer gear?

 

i believe you have to go through the pcm

 

HPT tuned

 

bump for best answer !!

 

HPT !!! or trifecta

 

HPT will do it, also , why would you want to run a 225-50
that is a massive sidewall, even if you want a bigger sidewall id go 225-45 at most,

 

agreed !!

 

I am considering 225/50 only because I can get Goodyear Assurance TripleTreds in this size. I have those tires on my Crown Vic and they're like summer tires and snow tires all in one. I am not sure how the thicker sidewall would affect handling, but the treadwear rating is 780. The difference in sidewall from stock is about 1" at most.

Would the HPT/Trifecta void my GM powertrain warranty?

 

It depends on your dealer, but as I understand it GM is cracking down on people who tune their PCMs. If you are concerned with warranty I think I've heard of people simply asking the dealer to re-calibrate via Tech 2.

Anyway, in case someone stumbles on this in the future, here is how to recalibrate for a different diameter in HP Tuners:

----------------------------

Plug in your tire size here: http://www.onlineconversion.com/tire...conversion.htm



Take the diameter, plug it in to the Speedometer section of HP Tuners, and hit Commit:

Before:


After:

 

225/50/18's are too big buddy. I can pretty much guarantee they will rub. Don't run all season tires on an SS/TC. They will only provide mediocre traction all year. Get some snow tires and 17" wheels for winter and stick with performance tires in the summer.

 

17" wheels won't clear the Brembos from what I have read.

I also don't intend to run summer tires once I get done with the stockers. I've done it in the past and don't want to store an extra set of rims either. I guess I'll stick with the Michelin Pilot A/S or ContiExtremeContact in 225/40R18 unless anyone has better suggestions for all-seasons.

 

QFT. If you have a taller sidewall, then your tires will better absorb bumps and impacts from the road. Your rims/tires will be less likely to get bent/torn/blown out. Those are the positive things that may result from a taller sidewall (50 aspect ratio vs 40).

The negative things that may happen are less cornering ability. The taller sidewall will flex more and roll over causing poorer handling and loss of traction. Your ride will be less responsive to steering inputs. Imagine a sliding scale that measures handling with sport car on one end and family sedan on the other. Your slider will move slightly toward family sedan.

Your ride may be smoother and more comfortable, while sacrificing some performance.

Braking, accelerating, and cornering will be affected. The overall tire diameter will be larger so straight line accelerating and braking may improve.

 

okay my 225/45/17's even rub !!!!

(sportlines)

 

stock SS/SC 17's will fit over the brembos with no problem. my friend in his 09 did it. i just mounted my snow tires to my stockers. but they will fit no problem.