My initial goal was to put 285/35-20s on the front and 315/35-20s on the rear. The tires under consideration are to be Michelin Super Sports. Since the 315 calls for a minimum 10.5" wheel width, I acquired 2 SVTPP 20" wheels and sent them to Eric Vaughn to be widened to 11". I would have preferred something like a 315/30-20, but could only find competition oriented tires. I was looking for good street characteristics, something relatively quiet and a non-directional tread pattern to minmize tramlining.
One of the issues in that decision is that the 315/35 is 28.7" tall. I figured I was going into uncharted territory by going this route. Unfortunately, Michelin doesn't make a tire that wide in a 30 aspect ratio. It would have only been .25" shorter than the 285/35. My car is lowered in the rear about .8". I was sure I would have to cut out the rear bump stop bracket that is spot welded to the frame with the amount offset the widened stockers were going to give me. Having acquired a set of Zombeast's bump stop location brackets, I wanted to move the bump stop inboard, since that's needed once the bracket is removed, since the alignment would put the bump stop on the edge of remaining frame.
As part of that plan, I intended to simply move my rear wheels and tires to the front. The weekend I was planning all this, I got wind of a thread that another member had moved the 9.5x20 OEM rim to the front, but there was insufficient clearance with the Brembo caliper. He had to use spacers and ended up with longer wheel studs for even wider spacers. Not wanted to use spacers on the front end, I set out to figure out if the Ford Racing 19x10 SVTPP knockoff might be a better choice since they state it will fit with the Brembo's.
I took measurements with the front OEM wheel and determined with the offset, I'd probably be better off sticking with the offet on the 19x9.5 stockers and going with a 285/40-19 tire on them. It's 28" tall, which is a little taller than the 285/35-20, so there would be a little less rake with these anyway from putting the larger diameter 315/35-20 in the rear. This revised setup isn't far off from the radius differences between the staggered fitment of the OEM SVTPP setup. There's just going to be a whole lot more rubber in the wheel wells.
Now for a little real world math. While the 315/35-20 circumference is 28.7" vs. 27.8" (285/35-20), just how much taller is this tire in terms of actual change in gearing. Unloaded diameter doesn't tell you much. I wanted to look at the differences under the weight of the car. I look up the rev per mile data off each tire and computed the loaded radius. This measurement is going to determine how much taller that tire is from the ground to the center of the hub under the weight of car.
The stock 265/40-19 came in at 13.16" while the 285/40-19 came in at 13.57". That means the car is going to sit about .41" higher in the front. Based on my measurements, it will clear the strut and tuck the tire in far enough to stay away from the front fender. That was a go, tires ordered. Because the stud on the sway bar link sticks out a good bit into the wheel well at the mounting point on the strut, I added a couple washers in between the stud and the strut. The Ford Racing in 19X10 would have pushed the wheel inboard by about 1/4" and would be pretty tight between the tire and the strut.
Turning attention to the rear, it turns out the measurement isn't as extreme as you might think. The 285/35-20 loaded radius was 13.55" and the 315/35-20 measurement was 13.83". Hmmm.... that's only .39" taller in the rear. That's only a 3% change in the effective gear ratio. First gear is so short anyway, this might not be a bad thing. But this sucker is 12.6" wide vs. a 11.4" width for the stocker, and it's all going inboard. No question, the bump stop bracket will not be able to remain in place. I confirmed this with a test fit once the tires were mounted. Under load, the bump stop protrusion is below the rim and there is adequate clearance However, once you lift the body from the axle the tire drops down and it's "big time" rub city.
When I set out to do this, I read another members thread about his fitment using 305/35-20 Nittos drag radials on the rear of his car with the same widened wheels. He indicated he needed to remove the plastic inner fender liner because he was getting some rubbing. The liner is held in with 6 studs mounted to the wheel well with some plastic nuts. They came out easy enough. I didn't like the studs on the top hanging precariously down, so I ended up cutting them off.
This member also cut off his bump stop bracket with a grinder. I decided to use a spot weld cutter as I had seen on Justin Starkey's thread in his VMP forum. The spot welds on the bracket are somewhat of a challenge. There are four spot welds at the top of the bracket and 5 spot welds on the bottom of the bracket. I used a 3/8" Blair spot weld cutter and bought a bunch of double sided bits. Short of removing the rear axle, you will not be able to drill the bottom spot welds unless you have a right angle drill. This wasn't nearly as difficult of a task as I thought it would be, but it's not for the faint of heart. I only used two of the double sided spot weld cutter bits for the whole car. So I ended up with quite a few bits left. After about 4 spot welds, they don't cut quite as easily as a fresh bit.
What follows is a blow-by of what I did.
[ON EDIT] I had Tob unlock this thread to upload the pics that were linked through Photobucket. I don't believe in extortion, so I will not pay them $400 annually to provide third-party hosting. This thread is over 4 years old at the time of the edit and I have added a few updates. There are more tire choices than there were 4 years ago too.
One of the issues in that decision is that the 315/35 is 28.7" tall. I figured I was going into uncharted territory by going this route. Unfortunately, Michelin doesn't make a tire that wide in a 30 aspect ratio. It would have only been .25" shorter than the 285/35. My car is lowered in the rear about .8". I was sure I would have to cut out the rear bump stop bracket that is spot welded to the frame with the amount offset the widened stockers were going to give me. Having acquired a set of Zombeast's bump stop location brackets, I wanted to move the bump stop inboard, since that's needed once the bracket is removed, since the alignment would put the bump stop on the edge of remaining frame.
As part of that plan, I intended to simply move my rear wheels and tires to the front. The weekend I was planning all this, I got wind of a thread that another member had moved the 9.5x20 OEM rim to the front, but there was insufficient clearance with the Brembo caliper. He had to use spacers and ended up with longer wheel studs for even wider spacers. Not wanted to use spacers on the front end, I set out to figure out if the Ford Racing 19x10 SVTPP knockoff might be a better choice since they state it will fit with the Brembo's.
I took measurements with the front OEM wheel and determined with the offset, I'd probably be better off sticking with the offet on the 19x9.5 stockers and going with a 285/40-19 tire on them. It's 28" tall, which is a little taller than the 285/35-20, so there would be a little less rake with these anyway from putting the larger diameter 315/35-20 in the rear. This revised setup isn't far off from the radius differences between the staggered fitment of the OEM SVTPP setup. There's just going to be a whole lot more rubber in the wheel wells.
Now for a little real world math. While the 315/35-20 circumference is 28.7" vs. 27.8" (285/35-20), just how much taller is this tire in terms of actual change in gearing. Unloaded diameter doesn't tell you much. I wanted to look at the differences under the weight of the car. I look up the rev per mile data off each tire and computed the loaded radius. This measurement is going to determine how much taller that tire is from the ground to the center of the hub under the weight of car.
The stock 265/40-19 came in at 13.16" while the 285/40-19 came in at 13.57". That means the car is going to sit about .41" higher in the front. Based on my measurements, it will clear the strut and tuck the tire in far enough to stay away from the front fender. That was a go, tires ordered. Because the stud on the sway bar link sticks out a good bit into the wheel well at the mounting point on the strut, I added a couple washers in between the stud and the strut. The Ford Racing in 19X10 would have pushed the wheel inboard by about 1/4" and would be pretty tight between the tire and the strut.
Turning attention to the rear, it turns out the measurement isn't as extreme as you might think. The 285/35-20 loaded radius was 13.55" and the 315/35-20 measurement was 13.83". Hmmm.... that's only .39" taller in the rear. That's only a 3% change in the effective gear ratio. First gear is so short anyway, this might not be a bad thing. But this sucker is 12.6" wide vs. a 11.4" width for the stocker, and it's all going inboard. No question, the bump stop bracket will not be able to remain in place. I confirmed this with a test fit once the tires were mounted. Under load, the bump stop protrusion is below the rim and there is adequate clearance However, once you lift the body from the axle the tire drops down and it's "big time" rub city.
When I set out to do this, I read another members thread about his fitment using 305/35-20 Nittos drag radials on the rear of his car with the same widened wheels. He indicated he needed to remove the plastic inner fender liner because he was getting some rubbing. The liner is held in with 6 studs mounted to the wheel well with some plastic nuts. They came out easy enough. I didn't like the studs on the top hanging precariously down, so I ended up cutting them off.
This member also cut off his bump stop bracket with a grinder. I decided to use a spot weld cutter as I had seen on Justin Starkey's thread in his VMP forum. The spot welds on the bracket are somewhat of a challenge. There are four spot welds at the top of the bracket and 5 spot welds on the bottom of the bracket. I used a 3/8" Blair spot weld cutter and bought a bunch of double sided bits. Short of removing the rear axle, you will not be able to drill the bottom spot welds unless you have a right angle drill. This wasn't nearly as difficult of a task as I thought it would be, but it's not for the faint of heart. I only used two of the double sided spot weld cutter bits for the whole car. So I ended up with quite a few bits left. After about 4 spot welds, they don't cut quite as easily as a fresh bit.
What follows is a blow-by of what I did.
[ON EDIT] I had Tob unlock this thread to upload the pics that were linked through Photobucket. I don't believe in extortion, so I will not pay them $400 annually to provide third-party hosting. This thread is over 4 years old at the time of the edit and I have added a few updates. There are more tire choices than there were 4 years ago too.
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