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Making clearance for wide tires

Discussion in 'How-To' started by Catmonkey, Feb 25, 2013.

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  1. Catmonkey

    Catmonkey I Void Warranties! Premium Member Established Member

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    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.
     
    Last edited: Jul 14, 2017
  2. Catmonkey

    Catmonkey I Void Warranties! Premium Member Established Member

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    As indicated in my objective, this is a comparison of the 315/35-20 and the stock 285/35-20.

    285 315 comparo.jpg

    315 285 comparo.jpg

    Here's a couple shots of the widened rim. I didn't think to get a shot before I had the wheels powder coated and the tires mounted. You'll notice the indented portion of the wheel is where they cut the OEM rim and welded on the new section to make it 1 1/2" wider. Nice bead work on the added wheel section.

    9 5 vs 11.jpg

    Welded rim.jpg

    Here is the wheel well before I got started. The liner is more of a fiberglass type lining that is held in place with plastic nuts on studs inside the wheel well. It's just a matter of unscrewing the nuts and removing the two push pins and then man handling it out of there.

    Inner liner.jpg

    Original wheelwell.jpg

    Here's the liner piece that was removed. I can't see that it serves a useful purpose other than to keep water out of crevices and darken the wheel well.

    Liner removed.jpg

    Notice the studs dangling precariously down. I removed the two studs on top and will probably cut the remainder out.

    Liner studs.jpg

    The wheel well without the liner. The bracket with the 4 spot welds showing is what I'm removing. The 4 spot welds on the top are not difficult, but the 5 on the bottom are a bit of a challenge and will necessitate a right angle drill unless you want to drop the axle.

    Frame bracket.jpg

    Here is a close up of the bracket and the welds. Lots of material welded into the holes.

    Spot welds.jpg
     
    Last edited: Jul 14, 2017
  3. Catmonkey

    Catmonkey I Void Warranties! Premium Member Established Member

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    Since I can't drill out spot welds and hold a camera, we'll have to fast forward to the pics of the removed bracket. If you need a tutorial for using the spot weld cutter, check out youtube. There is no shortage of videos on the process. The scratches in the paint are from using a small crowbar to pop the bracket loose.

    Removed bracket.jpg

    You can see the small indention's in the center of the built up material that remains from the spot weld. The instructions for the cutters indicate to use a punch to indent the metal. Since the weld material is not that soft, those indention's didn't keep the cutter from walking. I used a very small drill bit to make them a little deeper and it held the cutter in place. The cutter has an internal set screw so you can set how deep the cutter is allowed to go. While it may not seem like it, the cut material around the weld is flush with the surrounding sheet metal.

    Cut welds.jpg

    Now a little protection for the bare metal and cover the scratches with a little gloss black spray paint. Note the dust cover has been removed from the shock. I'm not sure it had to go, but I'm fairly certain it would rub. It's a very easy job on a Koni Sport, but you may need to cut it off of other shocks.

    Completed wheelwell.jpg

    Here is Zombeast's relocation bracket for the bump stop bolted into place. If you notice the forward screw on the relocation bracket, that is where the bump stop was originally mounted. Without relocating the bump stop, it has no bracket to contact when the axle is under hard compression and you risk breaking off the snubber and contacting metal to metal. [On edit: Zombeast no longer makes the bumpstop relocation brackets, but at this time Revan Racing has them.]

    Relocation bracket.jpg

    Here's the finished product. Notice how much better the rotors look from the first shot. They are Full Tilt Boogie Racing's two piece rotors.

    Completed wheelwell2.jpg

    Here's a shot from below with the tire mounted. It's tight with this much offset. I have a 1/8" spacer on there now, but will be going to a 1/4" spacer. However, it's going to take the installation of longer wheel studs. I'll update this thread for that project. That dust cover would have been awful close to the tire.

    Sidewall clearance.jpg

    The offset with the 1.5" width increase on the SVTPP 20x9.5 wheel is about 69 mm. I did have rubbing on off camber inclines, like a steep driveway when approached at an angle. I have not had an issue while driving, but I installed a 1/8" wheel spacer made by Maximum Motorsports. It still rubbed, but not as much and takes a little more effort to get them to rub.

    Before going to a 1/4" spacer, I knew longer wheel studs were in order. Having stacked both 1/8" spacers on one side, I was not comfortable with the number of threads engaged on the stock studs. I ordered a set of Steeda studs, which are made by ARP, but a little shorter than the long studs offered by ARP.

    Wheel studs 2.jpg

    I went this route so I could still used a closed end lug nut, although I went with a deeper lug than the stock lugs because the fitment was too tight.

    Here is a shot of the car with the wheel/tire without spacers.

    Tire orientation.jpg

    I'm editing this thread some 4 years after I posted this because Photobucket decided to extort it's free customers, so I have been uploading all the original photos to SVT's website, since all my original photos were no longer displaying and I'll be damned if I'll pay Photobucket $400/yr. for that privilege. I ended up having a custom spacer made up that was 8mm after going from 1/8" to 1/4" and still experiencing some rubbing under off-camber axle articulation negotiating driveway entrances. With the 8mm spacer, all of the tire is still under the fender. In hindsight a 315/35-20 is awfully tall and I think body roll with this tall a tire exacerbates contact with the inner fender. At the time of this edit, I have mounted a new Michelin 325/30-20 Pilot Sport Cup 2 on these rims. The 325 is the same height as the 285/35-20 that came stock on the SVT Performance Package. This sort of shows how tall the 315/35-20 is compared to the 325/30-20.

    315 35 v 325 30.jpg

    Interestingly, the 325 mounted on the same wheels comes in at a very similar cross section width as the 315 did on the 11" width wheel. However, the edge of the tread is closer to the outer fender. So much so that I went back to a 1/4" spacer. The resulting offset with the 1/4" spacer is +63mm, which I feel is optimum with this width tire. Frankly, I think this is pretty much the limit for this wheel well without looking like a jacked-up 70s musclecar to provide fender clearance.
     
    Last edited: Jul 14, 2017
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  4. Tob

    Tob Salut! Staff Member Super Moderator

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    Superb!
     
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