Stealth Tires and Wheels

Not long after I bought the car, I had a moment of excitement when a frosty freeway offramp resulted in terminal understeer into a curb.

Both driver's side wheels got bent pretty badly, but luckily the impact was soft enough that the wheels took the brunt of the damage and the suspension remained unscathed.

The bent wheels caused a pretty nasty steering vibration, and coupled to the general age and corrosion of the OEM wheels, they just looked horrible. With the tires reaching the end of their life as well, it was time for new wheels and tires.

Tire Rack to the rescue!

The Tire Rack is a long-time sponsor of SCCA ProSolo, with which I was involved pretty heavily in a previous life. They also do a lot of independent testing - both of performance and fitment - and that ensures that the stuff you buy from them both works and fits.

The one downside to this insistence on fitment testing is that, especially on wheels, selection can be somewhat smaller than from other suppliers. Tire Rack's wheel search utility will occasionally miss fitments that will work on a given car, and I do wish there was an "advanced" search that would allow searching on BCD + diameter + width + offset rather than just a "by make and model" search, but the upside of the more restrictive functionality is that you can trust that the wheels that come up in the search will fit. The Stealth has a bit of a wheel fitment Weird Harold too in that the front brake caliper sits fairly well outboard and caliper clearance can be an issue with wheels that otherwise should fit well.

So then, I used the Tire Rack wheel search utility and came up with the Enkei GTC 01 in an 18" x 9.0" +40mm fitment. The GTC 01 is from Enkei's race wheel line; they are reasonably light, very strong, have tons of caliper clearance, and even come with a dual tire valve setup to allow connection to a nitrogen recirculation system for racing use. (That last feature is completely useless for a street car, but it looks cool)

I used Enkei RPF1 wheels on the Talon, and I loved those wheels. Very light, bulletproof, and reasonably priced. If I had my druthers I'd've gotten RPF1s for the Stealth, but I'd heard reports that the 18" x 9" fitments had problems with brake caliper clearance, and besides, they didn't show up in Tire Rack's wheel search. So I went with the next best thing.

With the wheel selected, now it was time to choose tires.

Again, my preference is to support a manufacturer who either does support or did support SCCA ProSolo. That would mean Khumo, BFG, Hoosier, or Yokohama. But given the amount of long-distance and foul weather driving I wind up doing in this car, I really can't afford to trade performance for former sponsor support. And Tire Rack's testing revealed a clearly superior tire in the "Ultra High Performance All-Season" category, both in winter and summer conditions - the Continental ExtremeContact DWS.

With the tire make and model selected, now it was time to consider sizes. The OEM size is 245/40R17, which specs out at 25.7" diameter and a section width of 9.6". (When buying tires, don't use the sidewall markings to determine size; use the actual manufacturer's specs for their tires) I wanted to go a little wider but keep diameter close to OEM. The choice came down to the 255/40R18 (diameter 26", section width 10.2") or the 265/35R18 (diameter 25.3, section width 10.7"). The 275/35R18 looked promising as well (diameter 25.6", section width 11.2") but my back of the napkin calculations indicated that I'd be pushing my luck with front strut clearance. They should work, but sometimes manufacturer's specs are a little bit off and I wanted to leave myself some wiggle room.

My preference was for the 255, as the larger diameter would help reduce the OEM speedometer error (mine reads high with OEM tires - there is a TSB for a new speedo gear to help reduce it) but sadly I was a victim of availability; that size was backordered.

So then, 265/35R18 it is!

Here we see the two wheels side by side. The new tires are a smidgeon smaller in diameter.

Here's a width comparison - new tires are a little bit wider.

The wheels mounted on the car.

This picture shows how the wheels and tires fit from an in/out perspective. In both pictures, a straight-edge (a long level) is placed touching the outer sidewall of the tire near the ground, and then pivoted up until it either contacts the upper sidewall of the tire (meaning the tire is proud of the fender) or the fender (meaning the tire is inside the fender). Here we see that the front tire is a little less than 0.25" proud of the fender, and that the rear tire is a little less than 0.25" inside the fender.

This is pretty good, and suggests that on an 18" x 9" rim, +40mm is about the minimum offset to keep the tires inside the fenders.

Here is the clearance between the front strut and the tire. The gap is a little less than 0.25", which suggests that offset could have been a little larger (+41mm - +46mm) or perhaps the 275 would have fit. Either way though, the 265 works fine.

I happened to have access to a Mustang Roush wheel (17" x 10" +46mm) and that wheel did not fit, as it interfered with the strut.

This picture shows front brake caliper clearance. There's tons of room, and even more room for larger diameter rotors and bigger calipers should I ever decide to install them. The rears aren't shown because there is way more room back there.

This picture shows wheel gap measurements, this with an unloaded car and 1/2 tank of gas. There is plenty of room for the car to come down... another project for another day.

As far as the ride characteristics of the new tires, they seem to handle just fine. No squealing on on/off ramps when pushed hard. Steering response is a trifle laggy when compared to something like a Hoosier A3S05, but this is a street car, not a race car, so razor-sharp steering response isn't necessary. Overall road noise seems a touch quieter than the previous tires, but expansion joints THWAP! a little louder/harsher than before. And the steering wheel shimmy is completely gone.

My overall first impressions are very positive. The wheels and tires fit perfectly and buying from the Tire Rack was completely painless.

Update June 20, 2010: Well I've put 3000km on these tires and overall I'm very happy. There is a bit of harshness and slap (probably from the short sidewalls and much higher load rating) over bridge expansion joints and the like, and that is the only complaint I can dredge up. Gripwise, these tires are very, very good with dry and wet limits that are very high. Playing in the roundabouts outside CFB Gagetown, it took work to get these tires to squawk and the resultant drift was very controllable and gentle. Steering response is not as razor-sharp as, say, a Hoosier, but it isn't mushy either - very definite turn-in, but with a little bit of softness to it to smooth off the rough edges. And in the rain, solidly planted with no hit of squirreliness.

They feel a lot like driving on R compound rain tires, but without the associated worry of overheating the tire in the dry and having it chunk. It's hard to believe this is an all-season tire with a high snow traction rating. These tires are better in the dry than state of the art dry street tires from, say, ten years ago. Very highly recommended.