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Discussion Starter · #1 · (Edited)
Looking for affordable wider rear tires for my 2015 Base model Slingshot. 295/30R18 is about the largest size tire I can mount on my Base rear wheel. Those tires also get relatively expensive. I realized I might go wider and save some money by replacing my wheels.

I found a couple of affordably priced candidate tires on Summit Racing -

Mickey Thompson 6278 Street Comp Ultra High Performance Radial Tire 315/35R17 for $165 w/free shipping. Summit also lists the Nitto 555 G2 in 315/35R17 for $195 + $10 shipping. Both tires are rated 300AA as are the OEM Kendas.

Both tires would require me to replace the OEM rear wheel with a 17 x 10.5 wheel, which, when combined with the tire sizes above should still be compatible with the speedometer gearing for my 2015 Base Slingshot.

On the JEGS website, I found some wheels for older Mustangs that come in 17 x 8 +29.5 offset and rear spacing of 5.66” along with a 17 x 10.5 +27 offset and rear spacing of 6.81”.

According to the Rimsntires.com Wheel/Tire Size Comparer (Custom rims, wheel tire packages for your ride - RIMSnTIRES.com), I should be able to fit 17 x 8 wheels with a +29.5 offset to replace the front wheels on my Slingshot using the stock size tire (205/50R17). Fiurther research indicates I should change to a 245 tire with the 17 x 8 wheel size. Rimsntires.com also says I can use a 17 x 10.5 +27 offset wheel to replace my rear wheel/tire using either of the tires listed above with acceptable clearance and the rear wheel's actual speed at an indicated 60 mph should be 60.8 mph, but that tool assumes installation in a typical fender well and doesn't consider centering of the tire, meaning I'd probably need a spacer. One of my concerns about this info is I don't know how the rear spacing referenced above might affect the fit and the Rimsntires.com calculator doesn't allow for that measurement.:mad:

Will the Rear spacing measurement have any negative impact on doing this?
 

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Discussion Starter · #2 ·
Update - I ordered a 17 x 10.5 OE Wheels wheel from JEGS. The wheel looks nice, but when I test-fit it on the rear hub, a piece of cardboard less than 1/16" (.0625") thick barely fit between the inside of the wheel and the outer edge of the brake caliper. The interior of the wheel measured measured just under 14.375" when I measured the inside diameter of the wheel with my measuring sticks laying against the wheel's mounting surface that goes against the brake rotor. While the wheel technically fits, I'd like a little more clearance than just under .0625", so it looks like I need to return the wheel to JEGS. That's too bad because it would have cost me less than $375 to replace my Base wheels with the 17 x 10.5 " rear wheel and 2 - 17 x 8" front wheels.

I then removed one of my Base model 17 x 7" front wheel and measured the interior diameter at the mounting surface that goes against the brake rotor and got a measurement of 15.125", meaning there should be clearance of .375" between the inside of the wheel and the outer edge of the brake cylinder. This means I should be able to buy a surplus 17 x 7" base front wheel and have it widened to 10.5" for around $500, allowing me to mount a 315/35R17 Nitto 555 G2 tire while maintaining my stock wheel look. Presumably the difference between the front offset and rear offset sizes should be negligible.

This should give me the cheapest means of mounting the widest tire I can find at an affordable price. Although modding the front tire to fit a wider rear tire should cost around $500, the actual Nitto 555 G2 315/35R17 tire should only cost around $200 or so. Mickey Thompson also makes a similar size tire for around $165. All of the tires anywhere near that width in an 18" size cost considerably more.
 

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Discussion Starter · #3 ·
After discovering how little clearance the OE Wheels had around the rear caliper, I finally got around to experimenting with my front base wheel on the rear since we had a decently comfortable day here just north of Houston, so I removed the stock base rear 18" wheel/tire and mounted my stock base right front 17" wheel. This meant the tire was mounted with its tread facing the wrong way, but I just wanted to compare caliper clearances between the 2 wheels. Looks to me like I had plenty of clearance between the 17" wheel and the rear caliper. I attached a PDF file showing the 18" wheel's caliper clearance and the 17" wheel's caliper clearance when mounted at the rear.
Given the relatively flat interior wheel surface of the stock base wheels, I'm hoping I can find a similarly shaped 17" x 10.5" (or 11") wheel. While I've known about wheel widening for years, I've never done one before and I think using a wheel that was deigned for a certain width may be a little safer than modifying a narrower wheel. I don't recall having heard about failures of any base model wheels or spokes,but there is always a chance of adding some stress as a result of the widening process, so if I can find a wheel designed for the desired width, I'd rather buy it and matching front wheels, if possible. Plus, the wheel widening company currently has about a 4-6 week backlog.:D
I do wish I had taken some profile pics from the back to give me a better idea on how a widened wheel using the front wheel would look.:(
 

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Discussion Starter · #4 · (Edited)
I think I learned more today about the OE Wheels 17x10.5 wheel and why it didn't fit. The JEGS website didn't list the following, but I found it on the OE Wheels website - "Does NOT fit vehicles equipped with upgraded or performance brakes such as Brembo, or specialty models with larger brake calipers including Cobra, Boss, GT500, Shelby etc." The Slingshot has a 298 mm rotor and the caliper sticks out another 38 mm or so. The Cobra model referred to has a 13" rotor, meaning this wheel had reduced clearance and was more likely designed for a rotor around 11" in diameter.
I've emailed American Muscle about their 10th Anniversary Cobra wheel which should hopefully clear the Slingshot's rotor and caliper.
The American Muscle 17x10.5 wheel has +28 ofset and will position the middle of the tire a little more than 1" to the left with the right side of the wheel in the same location as the stock wheel. The wheel is similar to the stock Base wheel, but has 14 spokes in 7 pairs vs 16 spokes in 8 pairs. I think it may look OK with the Base front wheels. And it's Gloss Black compared to the Slingshot Base wheel color which is more of a metallic grey.
Here's a link - Black 10th Anniversary Cobra Style Mustang Wheel - 17x10.5 (94-04 All) - Free Shipping
Anxiously awaiting a response from American Muscle.
 

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Discussion Starter · #5 · (Edited)
Update - The 10th Anniversary Cobra Style Black 17x10.5 +28 Wheel I ordered from American Muscle ($150 delivered) was delivered yesterday afternoon. It has a significantly larger diameter (for rotor/caliper clearance) than the OE Wheel 17x10.5 I originally tried and also has a larger diameter (just under 15.75") than the 17x7 front wheel from my Slingshot (15.25"). As explained in the accompanying PDF file, the wheel pattern is enough like the Base Slingshot wheel pattern that if I repaint the Slingshot front wheels Gloss Black and also repaint the shiny rim of the AM wheel, I think the two different patterns will work together, allowing me to mount a 315/35R17 Nitto 555 G2 tire on the rear while maintaining compatibility with the speedo and safety systems, while saving over $100 compared tp buying a 295/30R18 tire that is the largest tire I can fit on the original Base 18x9.5 wheel.
The only concern about this approach is the fact that the AM wheel is +28 offset compared to the Slingshot rear wheel's +45 offset. This will cause the mounted tire to be a little off-center (see my approximation in the accompanying pics), but I don't anticipate any other problems.
I still haven't ordered the tire as I can not return the wheel once I mount a tire on it. I plan on test-fitting the wheel on my Slingshot later today.
Update - Uploaded new PDF file showing the caliper clearance with the Am Wheel mounted on the rear of my Slingshot.
 

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Discussion Starter · #6 ·
I think I'm going to go ahead and get a tire to try out the AM Wheel.
It looks like I'm going to be ordering some Nitto tires. I was torn between the 555 G2 or the Motivo All Season tires. The 555 G2s are rated 320 AA A and the Motivos are rated 560 A A. Cost per tire is about the same, although the tire replacement certificates seem to cost a little more for the 555 G2s. The Motivos also seem to have better wet road performance and a longer life, while the 555 G2s seem to have slightly better dry pavement grip.
At this point, I'm leaning towards the Motivos. Anybody have any experience with either tire?
 

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Discussion Starter · #7 · (Edited)
OK. I finally ordered the Nitto 555 G2 315/35R17 tire from Discount Tire Direct and had it mounted at my local Discount Tire. I put it on the Slingshot a few hours ago and went for a short 15 mile ride. I included a couple of pictures showing the side view of the tire/wheel and a mounted pic of the Nitto on my American Muscle 10th Anniversary Cobra 17 x 10.5" Cobra Wheel. The AM wheel has an offset of 28 mm compared to the Slingshot's 45 mm offset and according to Willtheyfit.com should be offcenter by about 3/5", but it doesn't look bad to me. The wheel was $150 or so and the tire was around $240 with tax and road hazard coverage.
NittoPics.jpg

I forgot to mention I also used hub-centric adapter rings with an inside diameter of 66.1 mm to adapt the hub to the AM wheel's hub-bore of 70.3 mm. I got them from JustForWheels.com.
Here's the link to WillTheyFit for a visual comparison of the two tire/wheel combos - Will They Fit - Online Wheel and Tyre Fitment Calculator
 

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Discussion Starter · #9 ·
Dirty Yellow, yes. I had it painted by a local young man who was thrilled to have a chance at painting the Slingshot, but his idea of a good job and mine weren't the same. I wanted an affordable, cheap paint job and it looks good from several feet away, but get within a couple feet and the flaws can be seen. Overall, it's probably worth the $800 I paid for it, but I'm seriously considering trying it myself, even though I've read about enough problems with painting to know it won't be easy. (I keep telling myself there's a reason I need a bigger compressor!)

I just got back a short time ago from a short 75 mile ride that included a few turns and some high-speed lane changes on the Interstate and I really like how the new tire feels. According to a phone speedo app I have, the wheel turns about 1 mph faster than indicated at 65 mph, which is about what the Discount Tire Tire Calculator predicted.
 

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Dirty Yellow, yes. I had it painted by a local young man who was thrilled to have a chance at painting the Slingshot, but his idea of a good job and mine weren't the same. I wanted an affordable, cheap paint job and it looks good from several feet away, but get within a couple feet and the flaws can be seen. Overall, it's probably worth the $800 I paid for it, but I'm seriously considering trying it myself, even though I've read about enough problems with painting to know it won't be easy. (I keep telling myself there's a reason I need a bigger compressor!)

I just got back a short time ago from a short 75 mile ride that included a few turns and some high-speed lane changes on the Interstate and I really like how the new tire feels. According to a phone speedo app I have, the wheel turns about 1 mph faster than indicated at 65 mph, which is about what the Discount Tire Tire Calculator predicted.
Now that you've had a little more time with your new wheel, are you still happy with it's performance?
 

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Discussion Starter · #11 ·
I've since taken the Nitto 555 G2 tire/wheel combo off since I still have plenty of tread left on the Nankang NS-20 275/35R18 tire I've got on my factory rear wheel and haven't installed my turbo yet.
As far as the Nitto 555 G2 315/35R17/American Muscle 10th Anniversary Cobra Style wheel combo goes, I am looking forward to having it once I get my turbo installed. I decided to go with the 555 G2 over the Nitto Motivo Ultra High Performance All Season tire in the same size as I try to avoid riding in rain (unless I get caught out in a storm) so I opted for the slightly better dry road performance rating of the 555 G2. Since I have managed to spin the G2 w/o having a turbo, I may give the Motivo a try when I need to replace the G2. The G2 has a 60K mile warranty (30K miles when used in a non-rotatable situation), so I might try it if the G2 wears more quickly than I'd like.
 

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My turbo SS still breaks loose that fat ass Toyo 345 I just installed. Hoping after a couple hundred miles it will start sticking better. Right now it breaks loose about like the factory Kenda did.
 

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My turbo SS still breaks loose that fat ass Toyo 345 I just installed. Hoping after a couple hundred miles it will start sticking better. Right now it breaks loose about like the factory Kenda did.
Those tires don't like cold pavement and cool weather. Just wait until the roads are clean from a good rain and it is warm out.
 
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