1994 Mazda MX-5 Miata: 6UL Wheeling
June 15, 2010
Let's get nutty.
Project Miata generated surprising stick on stock wheels and stock-sized tires. There are a couple of problems with that approach, though.
First, there's the future -- the stock wheels' snug dimensions severely limit our options for brake clearance, and those skinny tires will be hopelessly overwhelmed once we finally get some power in this thing. Second, the car had all the visual impact of a Vern Troyer roundhouse to the temple.
The addition of 949Racing 6UL wheels changes all of that.
A few years ago, Miata owner Emilio Cervantes observed a dearth of performance-oriented wheel fitments available for his car. He wanted a strong and light 15-inch wheel but was frustrated by the fact that rarely did they stray wider than 7 inches. Rather than gripe about the situation, he took the initiative and made the damn things himself. Thus the 15- by 9-inch 6UL wheel and 949Racing was born.
These low-pressure cast aluminum wheels are manufactured exclusively for 949Racing by a supplier of forged wheels to OEMs. Emilio acknowledges the benefits of forging in producing a stronger and/or lighter wheel. The cost, however, would have been prohibitive. Besides, these 6ULs weigh just 12.8 pounds apiece according to our scale, so we're not complaining. Stock 14-inch wheels are about 12 pounds.
You might be able to see that the tires -- 225/45 Hankook Ventus RS-3s -- are modestly stretched on the 9-inch wheel. The idea of running a slightly wider wheel than usual is to remove sidewall flex in order to enhance transient response and provide more uniform tread loading.
Visualize what happens when you're cornering hard -- the force at the contact patch puts the sidewall in tension. If you have a narrow wheel, the outward-bulging sidewall needs to be contorted quite a bit before cornering forces can build in earnest. The more sidewall deformation required, the longer the delay in the tires' ability to respond to steering inputs.
All else equal, the slight stretch provided by a wider wheel applies a bit of preload to the sidewall, which quickens its ability to react. Less time is spent taking up the slack in the sidewall, so steering response becomes more linear and direct. This strategy of removing sidewall compliance also makes your camber settings more effective. It's like plus-sizing the wheel without actually increasing the wheel diameter.
Like anything else, it's best to use this approach in moderation. At more extreme wheel-to-tire width relationships than we have, there's a higher risk of de-beading the tire if you simultaneously hit a sharp bump during hard cornering. Don't go copying Keiichi Tsuchiya's setup on your street car.
This is just about the widest tire you can fit under a Miata without getting too crazy with the fenders or with wheel offset. With only a flat-roll of the fender lips using a fender roller borrowed from our friend Steve Mitchell of M-Workz fame, we were done. The big tires fit with just a slight rub to our biggie-sized Racing Beat front stabilizer bar when at max steering lock. We can live with that, but to be fair, Emilio recommends his 6ULs in 8-inch width for Miatas that are exclusively street driven and won't be generating more than about 225 whp or so. This should also give you some idea of where we want to go with Project Miata.
Wheel offset is 36 mm compared to the stock 45 mm, which means the centerline of the wheel has moved outboard. This widens the car's track ever so slightly and increases scrub radius. We'll be sure to share impressions on what, if anything, this changes in terms of steering and handling.
To be sure, Project Miata has a truckload of visual attitude now. By looking at it you might even think it has enough power to get out of its own way. All in time.
Jason Kavanagh, Engineering Editor @ 177,072 miles.
15x9-inch 6UL wheels, MSRP $189/ea