I've made the decision to upgrade to 19x9 and 19x11 wheels. I am using the V12 as an example because I hope to land in the 520HP range with the future supercharger. Having said that, and the previous discussion of fish-tailing, I wanted more traction. Now the question is what size tires would look and perform best. I am going to lower the car 20mm with H&R springs but I don't want to loose too much size of the over all wheel and tire. The standard wheel and tire are 26.4" (F) and 26.58" (R). To maintain this size, I would need 255/35 in front at 26.03"(F) and 295/30 at 25.97"(R) or I could go with 305/30 wich would bring the rear measure to 26.2". Has anyone done this or increased the width of their tires this way. Will this present any problems with rubbing or anything else? I would appreciate any info, opinions and pictures.

 

I've weighed in on this before, but I think probably that stock sizes from the V12 vantage are the way to go. You know there will be no rubbing issues since the body of the V12 car is not modified. The 305s will probably fit...they COULD possibly have rubbing issues, depending on offset of the wheels you use, but I'd be surprised. It seems like at least one person used that size without any problems, but I don't know for sure. Generally I've found that moving up one size from a stock wheel option is pretty safe. Beyond that you'll probably have problems.

As for wheel circumference, of course the 295s will give you more speedo error than the 305s, but will also in effect shorten gearing...giving probably imperceptible increase in acceleration and loss of top end. Given the added power, that's probably not much of a concern. Top speed comes at 6800 rpm in 6th, so now matter how much power you add you will not increase the top end much unless you change the gearing or increase the rev limiter.

 

Explain what you mean about speedo errors.

 

The speedo is calibrated for wheel/tire size, among other things, so any changes in diameter/circumference will result in the speedometer not being accurate. Smaller than stock diameter tires result in overestimation of speed and larger than stock diameter tires result in underestimation of speed. This is why aftermarket tire stores like TireRack make specific recommendations to keep tire diameter as close as possible to stock size even if you are getting wider tires. I figured that's what you were referring to when you mentioned the tire diameters of the sizes you are considering.

Here's an article describing it:

http://auto.howstuffworks.com/speedometer4.htm

Also, a smaller diameter and thus circumference wheel is equivalent to a shorter gear so it effectively shortens the gearing, and a larger diameter wheel does the opposite.

 

Thanks for the knowledge.