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Discussion Starter · #1 ·
I made this post because I read somewhere that the STI could not use 2 diffrent tire sizes becaue it would mess up the trans or the diff.

Stock STI tire size 225 x 45 x 17 = 24.97

225 x 40 x 18 = 25.08
255 x 35 x 18 = 25.02

Run a 18 x 7.5 rim up front 37mm offset.
Run a 18 x 8.0 rim in the rear 42 mm offset

If you think this is not posible then think of this then. Your STI comes with 225 x 45 x 17 = 24.97. Tread depth is about 3/8th of an inch. So when you buy your STI new the tire sizes are equal. The STI will wear down the rear tires faster than the front in a ratio of 1 to 2. Long story short if the front tire is about 24.97 and the rear tire has worn down the tread to 24.17 then the sizes dont match. Thats the diffrence of .80 of an inch. This will not damage the the trans or the diffs. So being off by .06 will not cause any problems.

For the math guys here is the formula to figure out tire diameter.

Tire width X Tire ratio X 2 divided by 2540 + rim size.

Example below for STI tire 225 x 45 x 17

225 x 45 x 2 = 20250
20250 / 2540 = 7.9724409
7.9724409 + 17 = 24.97

Below is a link to a STI with Volk GTNs 18 x 7.5 with 225 x 40 x 18 = 25.08 offset 37mm

http://www.imprezawrxsti.com/postnu...c&t=4347&sid=e9c31fb323da224e1431461c16269e59

could you imagine what the stance would be with 255 x 35 x 18 =25.02 on all 4 rims 18 x 8 Volk GTNs with a 42 mm offset.

I was also thinking of getting 18 x 8 Volk GTNs with 245 x 40 x 18 = 25.71. This would allow for quicker 1/4 mile times as I would not have to switch into 5 th gear to go through the 1/4 mile.
 

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What would be the point of putting smaller tires in front then the rear? All thats going to do is promote understeer. Also its not easy to fit 255's on a wrx, especially on the rear and expecially with a stock suspension.

And as for quicker quarter mile times you will also be dragging a whole lot extra weight on the wheels and tires and the car will pull slower in each gear so that may negate the time you save with the extra shift.
 

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Discussion Starter · #3 · (Edited)
I guess you can not see what I am talking about.

225 x 45 x 17 = 24.97
225 x 40 X 18 = 25.08
255 x 35 x 18 = 25.02

First of all these tires have one thing in common there are the same height. The diffrence in width from 225 to 255 is 30 mm or 1.25 inches.
There is 1/2 an inch or 12.5 mm of cleaance from the back of the rim to the strut. I measured. It is actually a little more but I am giving myself room. There is a also 3/4 inch or 19 mm from the front of the wheel to the inner side of the fender. All of this has been measured with stock 17 x 7.5 stock BBS wheels.

Now I know the front is no problem its the back where things get tight. If you can put a 225 x 40 x 18 = 25.08 and move the offset from stock BBS 53mm to 37 mm. Then you can see that this tires size 255 x 35 x 18 = 25.02 will fit. 19mm on one side and 12 mm on the other side = 31mm. The diffrence between te to tires is 30 mm.

The rim would be 18 x 8 with a 42 mm offset. This rim is designed by Volf to fit the STI. By moving the rim out to a 42 mm offset you have now cleared the shock by 6 mm more which would be 3/4 of an inch or 19 mm clearance. The rim in the pic is also desighned for the STI and it has a 37mm offset. The 7.5 wheel and the 8 inch wheel will have the same clearance from the fender side becasue the offset being 5mm more than 42 vs 37 when used. This is acomplished becasue the 42 mm offset is on 5 mm more than the 37mm offset but but the 8 inch wheel being 1/2 an inch wider will have 6 mm of over hang on each side of the wheel. So if you check it out a 255 tire and 8 inch wheel will fit without rolling the fender.
 

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Discussion Starter · #4 ·
Now you said that you can see no reason for putting a wider tirer on the rear of an STI. Well here are some reasons for you.

Ask anyone who has lowered their STI and put swaybars and strutbars how th car handles. They will tell you that the car oversteers or swings its tail out. By putting a larger tire on the rear you will make the car more neutral.

This is one of the reasons rear drive cars like the 240sx, RX7, 300zx, 350Z, Supras, Ferrari, Lotus, AWD cars like the 911TT, Skyline, Lamborgini run a larger rear tire to make up for the xtra power to control the car from swinging around or oversteering.
 

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No I understand exactly what you are talking about. But your measurements are static not dynamic, macpherson struts have alot of camberloss which is where the rubbing comes from. Im not saying they wont fit as i have seen 17 inch 255s fit on all 4 corners on a car with JIC coliovers, I just said its not easy to get them to fit.

As for the bigger tires in the rear. Your telling me that you reduced the grip of the rear tires by adding a sway bar and now you want bigger tires to get the grip back? Take off the swaybar and your problem is solved. All swaybars do is reduce grip wherever you put them by making the suspension less independent. Just use them to tune under and oversteer dont use them to get rid of body roll use spring rates for that. If the car is oversteering after you have dropped it and added swaybars then use the swaybars to tune the over understeer and put a smaller one on the back, it will increase the overall grip of the car.

And you comparison of cars that run bigger rear tires is not a very good comparison half of the cars you mentioned are RWD and the awd cars you mentioned all have a engine mounted over the rear wheels, as well as a different torque distribution, weight distribution and suspension set up. Look at the stis that they track in japan and they use the same size rire all around typically with a half inch narrower wheel in the back to get a progressive break away.
 

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*eyes glazing over*
*decides to just do what subaru says and trust their engineering; it got me this far*
 

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I can not see one damned advantage of running smaller tires up front. No matter how you cut it you would be doing the same thing faster with 255's all the way around.
 

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hahah... what is the point in multiplying width by aspect ratio by rim diameter... that's not how you calculate the height at all.

[Try Width * (Aspect / 100) + (Rim Size * 25.4)] * 2 = The height of the tire (diameter) in mm.

Your calculation just produces crap... their not even in the same f'ing units.
 

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LOL I never actually read his calculations I was just arguing because its a really dumb idea regardless if its possible or not:D
 

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How about running:

245/40 X 17 on a SSR Type C (48mm) 17 X 8.5

I'm pretty sure the 235/40 X 17 will work, but anyone running a 245/40 X 17 ??
 

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I was going to try some but I couldnt find any good tires in that size. Except for hoosiers probably. I will be running 235/40/17 v700s soon though.
 

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Im an autoxer though and the kumho v700 are way better then the yoks at an autox, there also only $134 for 235/40/17. As for the street Im just sticking with 225/45/17 Azeni sports.
 

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Article in Grassroots motor sports may disagree with you on the Yok A032 -- what compound have you used soft or hard for the A032R? The Yok was 0.7 - 1.0 second faster than the Kuhmo and I think the Proxies came in last. The Yok has a very stiff sidewall so it may take some setup adjustment.
 

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Wasnt that test on a track though? On a road course yes the yoks are better, but from what I have seen on autoxs the yoks cant get enough heat into them to work, I know guys who have autoxed on all the tires you can think of and they just think the A032s are a little better then azenis and nothing compared to a hoosier, and still slower then victoracers.
 

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Thanks afpdl,

You just gave me an interesting idea for my situation. Rather than get a set of Hoosiers and add a hitch for a small trailer to drag around out west next summer I could get a set of Victoracers, change them for the weekend, and drive to the events. They would be shot by the end of summer, but with all the heat cycles, who cares if they are bald too?

The Hillclimbs I go to use the SCCA rule book for stock classifications.
 

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V8VENOM gets credit too with "4000-7000 mi on them". For tyres, a hillclimb is a long auto-x. Cold start, and posably higher speeds.
 

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Web Foot STi said:
Thanks afpdl,

You just gave me an interesting idea for my situation. Rather than get a set of Hoosiers and add a hitch for a small trailer to drag around out west next summer I could get a set of Victoracers, change them for the weekend, and drive to the events. They would be shot by the end of summer, but with all the heat cycles, who cares if they are bald too?
I drove the Impulse RS to every event on the Kumhos. I never saw any sign of wear from that part of the event. So long as your alignment is not super aggressive, it should be fine.
 

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Snacks, did you go to Larson Rock in Oakridge, or Bible Creek? The ferry drives I worry about are the ones like the 1,800 mile round trip to Black Otter in Billings MT.
 
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