This is for an FD...

Last year I had to purchase new rear tires to pass inspection and due to time and availability I went with 275/40/17s on 9.5x17 rims. KDWII. Used to run 265/40/17 but that's such a rare tire now... So I need new fronts and they do not make KDWIIs in 245/40/17s which I have normally ran in the front on 8.5x17 rims.

So do I go with 255/40/17 on 8.5 or just spend more money and replace all four so I can run 245s on the front? I do plan to track the car a few times this year but I am a beginner so please factor that into account. I'd even take tire recommendations although I've been doing a good bit of research already.

Thanks

 

255 on an 8.5" wheel is about right, as long as it clears everything, seems too easy for a real FD owner though.

 

I would go with a skinner tire on the front. stay with a 245/40/17 or a 235/40/17 front tire. with the rear I would throw on the 245/40/17 or a 255/40/17.

thats how I would set it up.

 

(Rim width" * 25.4)+20=tire widthin in mm

So 8.5 would look good wrapped in 235/45/17 4.16" sidewall
9.5 would look good in 265/40/17 4.17" sidewall

 

Go with a 255. It's the right height, it fits on a 8.5 completely fine, and it won't make the car handle like poo like a wider stagger would.

 

Those tires are too tall. stock OD for the FD is 24.8"

 

I would go with a 235/40/17 or a skinny 245/40/17 on a 8.5" wheel. you ideally want to install tires with a slight stretch to them in the front of the car. the rear is less important.

go to this presentation and look at slide 34.

Here is the Michelin tire engineers have to say for the Porsche Cup cars.

www.cb-racing.com/PilotCup_Presentation.PPT

"Well, if you are confronted with the choice of squeezing a big tire onto its minimum recommended wheel width or stretching a smaller tire onto a relatively wide rim, you might want to pause for thought."

We have found the smaller-tire + wide-rim combination, with its accompanying “high-tension” inflated shape, can be more efficient:
More direct yaw response Decreased “phase lag” between steering wheel input and vehicle turn-in
Less “overshoot” at corner exit Less of a tendency to “wiggle” at corner exit (thus upsetting the car) when you roll back into the throttle
Can result in decreased negative camber requirements, thus increasing braking and accelerating efficiency
Can improve vehicle response to air pressure tuning

 

"big tire onto its minimum recommended wheel width or stretching a smaller tire onto a relatively wide rim"

ok... but he's not increasing the wheel width. sure a 225 on a 9" wheel might be faster than a 255 on a 8" wheel, but that doesn't really have anything to do with this topic. his wheel size isn't changing.

additionally a 275/40/17 is a 25.7" tire, a 255/40/17 is a 25.2" tire, decently close....

a 235/40/17 is a 24.4" tire, which will cause all kinds of issues with the ABS because the wheels will always be spinning different speeds.

and the car will understeer a lot more...

 

I am not sure if it will effect the ABS or not but there are some people who run 235/40/17 tires on the board.

The engineers found that its better to put a tire on a wheel with a slight stretch. I would do what they recommend.

They also found that a skinnier tire width on a certain width wheel will have LESS understeer than squeezing a wider tire on the same sized width wheel.

 

By these tire sizes 235 front 265 rear. Both have a diamiter of 25.3" so no ABS problems. Feel free to check my math U'll find I'm right

 

Go much larger than a 4" sidewall and ur wheels will look factory small.
17" is already on the small side for an FD and the tire size I gave you is 25.3 front and back not 24.4.