Taller versus shorter tires - what is the effect?

[bFoxGt500]

I've been running my 255/45/18 Goodyear F1 KRs for the last year on the track (on 18 x9.5 wheels). I run 'em on all fours. I've worn them out and need new (and better) tires. I am looking at some 275/35/18 or 275/40/18 tires. I want a 'Y" rated tire. These two have the same section and tread widths but one is 25.7" tall and the other is 26.7" tall. I like the idea of the taller tire, but it is 'W' rated. Is there an advantange/disadvantage to one versus the other? Thanks for your opinion.

 

[darreng505]

Taller tire will absorb curbs better and have higher top speed at the expense of some wheel torque (i.e. accel)

 

[MFE]

Do you routinely run more than 168 mph?

 

[dmichaels]

I would say it is also dependent on your gears. I have 3.73's and my 5th gear redlined at about 142-144 mph (indicated). A taller tire would give a little more actual speed in each gear, which I would prefer due to my shorter gearing. If I had 3.55's I might opt for slightly smaller diameter tires. Also largely depends on the tracks you run at.

 

[bFoxGt500]

Thanks for the opinions guys. The OE tires are 27" so I was a bit afraid of going to a tire an inch smaller but pulled the trigger on aome Hankook RS-3 285/35/18 because I got em for a pretty good price. They are 25.7" or so but a they do have a nice wide patch. I wanted Y rated so I could use them for the Texas mile because they gave me some grief with my W rated tires in the spring (never get close to 168 on the road course LOL). Turns out it didn't matter because I only got to 170 mph. I need taller tires for the mile anyway, so we'll see what happens there. I hope I am happy with them on the road course. I drive to and from so everything is a bit of a compromise.

 

[blacksheep-1]

Lets not forget that tires are de-facto springs as well and their sidewall height can effect handling, so can they effect weight distribution when going from a staggerd to a square set up.

 

[bFoxGt500]

I believe the stock tires on my 08 GT500 are 27" f/r. They are staggered but the same overall length. I've been running a square setup, not so much for the supposed 'neutral' handling but so I can rotate all four tires adn keep my costs down. If I switch to these smaller diameter tires, I'll still keep the square setup adn the load rating is OK, I believe. Besides the smaller tires, I'll also be going with a wider tire than I"ve used in the past adn that's going to change things - just don't know how much!

 

[blacksheep-1]

You're welcome...

http://bndtechsource.ucoz.com/index/tire_data_calculator/0-20

 

[bFoxGt500]

blacksheep-1 thanksa for the link. I couldn;t get it to calculate, but I'll keep trying !!

 

[blacksheep-1]

and it's metric which is kind of a PITA at times

 

[bFoxGt500]

Just thought of another question - will i have to adjust anything beside the tune to input the tire diameter; i.e., pinion angle, LCA?

 

[blacksheep-1]

I'm thinking the pinion angle should be the same so I would say "no" at first blush, if the tire diameter is close I wouldn't worry about it. Again, it's changing the spring rate so don't be surprised if you have to change something, but you'll have to drive it find out.

 

[bFoxGt500]

Thanks blacksheep. Once I get them on the wheels, I will be bringing the car in for an alignment and will try to find a good shop who can check the things out. I don;t have another track sessin scheduled / confirmed until August, to try things out ( I'll have to try harderd to get back on the track).