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C5 Retirement Party

Is Bigger Better? It Looks That Way

Bob Wallace Nov 20, 2003

The right custom tire and wheel combo can make a humdrum sedan look cool and can transform a rather plain (at least as far as a Corvette can be considered plain) C5 into an eye-popping work of automotive art. My pewter '00 coupe, complete with standard silver-finish OEM wheels, used to fit into the plain Jane Corvette category--great for stealth but, well, almost boring.

The Mid America Designs "Hot Seats" custom upholstery really woke up the interior, and the simple addition of MagnaFlow's "Wide Open" exhaust with its four big polished outlets added both some distinctive character and sound to the car.

I had my excuse to go over the edge after we completed installing Wilwood's C5 Big Brake kits on the front and rear of my coupe. The car, with its stock five-spoke wheels, had been used by Wilwood Engineering for portions of their fitment process to ensure that their 13-inch front brake and six-piston caliper would work on any '00 and newer C5 with stock wheels--without the need for any sort of spacers, adapters, or modifications. The brakes were/are fantastic, but were still shrouded by stock silver-finished wheels; I now had something super trick on the car, and it didn't even show up. Stealth can be good, but it would be nice to have a standout once in a while.

Okay, I couldn't use the Wilwood brakes to justify new tires and wheels--or could I? It seemed as though we'd barely gotten the brakes bedded in when, as I mentioned at the end of the brake installation article ("Late Braking News," Oct. '03), the crew at Wilwood informed me that within a matter of weeks they'd have a wild new 14-inch, bolt-on front rotor and caliper setup for the C5 ready for evaluation, and would I like to try it out. That's a dumb question! And since the even bigger brakes required a minimum of an 18-inch front wheel, that was all the excuse I needed to go off the deep end.

HRE Performance Wheels manufacturers some of the finest, highest-quality wheels available--superb engineering, impeccable finish, and a wide array of sizes, designs, and finishes for C4 and C5 Corvettes, as well as other premium-sports and high-performance cars and SUVs from around the world. All HRE wheels are three-piece (individual forged aluminum inner and outer rims sections, and a separate center, CNC-machined from a forged billet of aluminum). The nine designs in their 540 series are completely compatible with the tire-pressure sensors on C5s. The 540-series wheels are offered in 17-, 18-, 19-, and 20-inch diameters and in widths ranging from 7-13 inches (they also offer custom widths and offsets). Since all HRE wheels are built to order, a wide array of finishes are also available.

As long as I was going off the deep end, I figured I might as well go extremely deep, and so I sat down with Mike Sweeney of Corvette Wheel Specialists to order a set of HRE wheels for my still-nameless pewter coupe. (HRE doesn't have pallet racks loaded with wheels ready to ship; each set is custom-manufactured to the customer's specifications.) I'd already figured the tire sizes I'd go with, based primarily on Z06 sizing but with a larger-diamter (18 rather than 17 inch) front wheel, and stayed with the Z06's 18-inch rear diameter for a couple reasons--there are a lot more 295-millimeter cross-section tires available for 18-inch diameter wheels than for 19s or 20s. And, the larger the diameter of the wheel, the shorter the sidewall (aspect ratio) of the tire must be to maintain a close-to-OEM overall tire/wheel diameter. I'm not a big fan of tires that look like big black rubber bands, and tires with extremely short sidewalls tend to ride extremely harsh--and the rigid sidewalls necessary (to allow the tires to be driven with little or no air pressure) on the stock run-flats are bad enough on a daily driver. While it's possible to bolt-on wider-than-Z06 wheels on C5s, I couldn't see any point in it. I'm not after extreme performance with this particular Vette; its primary duty is to be a fast, good-handling, good-looking, reliable, and comfortable commuter car.

So, I went for 18x9.5-inch wheels up front and 18x10.5ers out back. HRE's ads show six designs in the 540 series; they offer three others on their Web site. I opted for one of "the others," the rather Teutonic looking, 15-spoke model 549. And instead of the usual polished finish, I thought HRE's charcoal paint option for the centers would really compliment the coupe's light pewter metallic paint. A large proportion of Corvette Wheel Specialists' business is chrome-plated wheels. Mike Sweeney suggested that I have the outer rims chromed rather than polished, both for the slight extra flash factor and because I could pretty much forget about having to polish the rims on a regular basis. It was an excellent suggestion, one that I heeded.

Now it was time for tires. I took the same approach as with the wheels; stick close to Z06 sizing and I am fairly certain there'd be very minimal chance of clearance issues. The rear was a no-brainer--Z06 size tires (295/35ZR18) were the only choice as far as I was concerned. The front skins would take a little figuring since I was using 18-inch rims. I wanted to keep as close as possible to the OEM tires' overall diameters, both front and rear, to avoid potentially throwing off the ABS and to keep from severely impacting the speedometer calibration. Front tires on a Z06 are 265/40ZR17s. The 265 refers to the cross section (overall width) of the tire, measured in millimeters; 40 is the aspect ratio of the tire, which means, in this instance, that the sidewall of the tire is 40 percent of its width (approximately 106 millimeters); Z is the speed rating; R indicates a radial ply tire; and 17 is the wheel diameter. If I step up the front wheel diameter from 17 to 18 inches and don't compensate for the 1-inch increase in wheel diameter with a reduction in the sidewall height or aspect ratio of the tire, I'd end up with a much taller front tire and wheel package. Not good, SUV size tires and wheels would look absurd on a Corvette!

The natural step is to reduce the aspect ratio; in this instance, to go from a 265/40ZR17 to a 265/35ZR18. Plus sizing is the common term for increasing wheel diameter, and the general rule is that for each 1 inch of wheel diameter increase, you add 10 millimeters to the tire cross section (width) and move one step shorter on the aspect ratio (the height of the tire sidewall). Going plus one on a Z06 front wheel and tire would then yield a 275/35ZR18. So, I decided to see how these changes would compare to the standard C5 tire/wheel packages. All of the following dimensions, except for the tire sizes, are in inches, and all dimensions were taken from Yokohama Tire Corporation's 2003 high- performance tire application booklet.

After looking over the numbers and checking with a few tuners and tire/wheel experts, I went for the 275s up front. Next would be to select a manufacturer. One of the quickest ways to find who offers what, tire-wise, is to conduct a search for the desired sizes on the Tire Rack's excellent Web site (www.tirerack.com). I found three tire manufacturers (Kumho's ECSTA MX, Michelin's Pilot Sport, and Yokohama's AVS Sport) that offer the exact combo I was after, and one (BFGoodrich's G-Force T/A KD) that offered the 295/35-18 rears, but with a 265/35-18 front. Goodyear, the OEM tire supplier for all C5s ("standard" and Z06) doesn't offer a Z06-size, 18-inch front tire in the superb Eagle F1 Supercar line, and while they have standard C5-size (and sizes for the ZR-1) in their new Eagle F1 GS-D3 ultra-performance line, there is no Z06-size tire in that product line.

I opted for the "Yokes." Why a Japanese tire on America's sports car? Goodyear, the only American manufacturer, doesn't offer the sizes I needed. BFGoodrich was close (but no cigar) for my ideal sizes and is no longer an American-owned company. Michelin, which owns BFG, makes excellent tires, but we were fitting Pilot Sports on another C5 at nearly the same time. Kumho probably makes excellent tires, but I have no experience with them and don't personally know anyone who has. I do have nearly two decades of very satisfactory experience with quite a number of Yokohama's ultra-performance tires on quite an array of automobiles ranging from a gray-market Alpina BMW to '80s and '90s vintage Mustangs, and on an extremely rare '99 1LE Firebird. I called Yokohama and ordered a set from Mark Richter, Yoke's resident HiPo tire guru and owner of an extensively tweaked C5 Hardtop that's seen more open track miles than most of us could even imagine. I had the Yokohama tires and HRE wheels shipped to CWS, and while we were waiting for HRE to manufacture the 549s (having the outer rims chrome plated by CWS added to the time required, and the wait seemed interminable), I ordered a new set of tire pressure monitors--again through CWS. As you may have noticed by tire comparison chart, I violated one of my "prime directives" and selected rear tires that are approximately 0.4 inches smaller diameter than the stock 275/40-18s--not a lot but enough to throw the speedometer and odometer reading slightly off. So I called Granatelli Motorsports and ordered a Predator tunable programmer.

The Predator offers a tremendous range of adjustments and recalibrations, and is a hand-held device that does not require a laptop to perform its many functions. Among the Predator's plethora of programming options are: adjusting or eliminating speed governors in cars so equipped; adjusting/resetting the rev limiter; adjusting shift points and line pressure (for firmer and quicker shifts) with automatic transmissions; diagnostic capabilities (it can scan fault codes, perform live data monitoring, and be used to erase or reset codes); fine-tuning fuel and timing curves (something that should be left to qualified experts with chassis dynos and air/fuel-ratio-reading equipment); and (of most immediate interest to me) the ability to recalibrate the speedometer for tire-size and/or gear-ratio changes. It also has a "performance" flash for essentially stock engines and when you go to download that "flash," it first loads the car's stock program into its memory so the stock tune can be "reflashed" at any time, should it be necessary (like if you need to have warranty work performed on your C5).

Everything else was on hand when the HRE wheels were delivered at CWS, so I arranged to have the tires mounted as soon as possible. Tires and wheels can be high-dollar items for cars like C5, and what looks good (or doesn't appeal) can be a very personal matter. When I first saw the HRE 549s, I was ecstatic. The finish and craftsmanship was impeccable, and the look was almost exactly what I'd visualized many weeks (well, it seemed like it) before. To me, the tire-and-wheel package actually looks better than I'd hoped or expected.

The new tire and wheel package fits the car perfectly; there are no clearance issues whatsoever. Before manufacturing the wheels, HRE obtained engineering drawings from Wilwood so they could be certain that their 18-inch diameter, 540-series wheels would fit with the 14-inch Wilwood front Big Brake kit. Anyone contemplating installing the 14-inch Wilwoods can be assured that they'll have no problems with wheel fit if they go with the 18-inch (or, of course, larger) HRE wheels.

Shortly after getting the new tires and wheels installed, I brought the car and Predator programmer into the Primedia Tech Center. We, technician Jason Scudellari and I, were curious to what if any changes could be measured from the performance "flash." Mainly, I wanted to get the speedo and odometer calibrated for the new, slightly shorter diameter tires.

The Predator comes with a comprehensive, 50-plus page instruction manual with a series of step-by-step directions on installing the "performance tune," restoring the "factory/stock tune," modifying parameters, and using the diagnostics capabilities of the controller. Hookup is extremely simple; the Predator plugs into a C5's diagnostic port, which is located under the driver's side of the dash facing the floor. The Predator guides the user through the procedures to make changes in the factory programming via instructions on the unit's screen. Jason probably spent all of 15 minutes loading the "performance tune," then recalibrating the speedometer so we'd have the correct readings with the new tires. The speedo recalibration only took 2-3 minutes.

The chassis dyno results--or lack thereof--really didn't surprise me. We made two baseline pulls, which were essentially identical to the final dyno runs at MagnaFlow earlier in 2003. The two pulls with the "performance tune" were almost identical to the baseline runs; there was not enough difference (no more than 1-2 hp and 1-2 lb-ft of torque variance at any rpm level, 1/2 to 2/3 of 1 percent) to be of any statistical significance. I really didn't expect much because stock late-model cars with computerized electronic fuel-injected engines are so finely tuned and so thoroughly optimized with sensors monitoring and reacting to changes in milliseconds, that there's not really a lot to be gained by fiddling with the factory settings. If the C5 was modified beyond the most basic of bolt-ons, i.e. cat-back exhaust and X-style crossover pipe and, still to come, a freer-breathing induction system, then the Predator's abilities to reconfigure the parameters could make a significant difference in the power output. If I wanted to change over to a lower temperature thermostat, I could use the Predator to kick on the engine's twin electric cooling fans at a lower-than-preset temperature. But with the car essentially stock, well, there doesn't appear to be a lot to be gained.

On the other hand, a lot was gained by retiring the C5. This formerly subtle, sedate, and understated Corvette now stands out from the crowd. It's purely a subjective judgment, but it now rides much smoother on the "Yokes" than on the OEM Goodyear run-flats. Its handling is much crisper, the grip feels significantly higher, and the steering feels more responsive. That's an interesting transformation--better ride and better handling.

This new tire and wheel combo also provides improved grip for the 13-inch Wilwood Big Brake kit that we installed a couple months ago ("Late Braking News," Oct. '03). We snuck over to our nearby and highly illicit test facility (a local, very lightly used industrial street), plugged in our trusty old Tesla G-Tech Pro, and ran a quick series of 60-0 stopping distance tests. In totally stock form, the '00 coupe had repeatedly stopped from 60 in a quite credible 122 feet. With the 13-inch Wilwoods lurking within the stock 17- and 18-inch wheels, still shod on OEM run-flats, the coupe had given us a string of 60-0 stops in 111 to a best (on our last stop of a half dozen) of 109 feet. With the improved grip of the AVSs, we saw six straight stops (three going west followed by three headed east) from 60 mph in just 103 feet! No fade, no drama--just the prodigious stopping power of superb ultra-performance tires and serious, race-bred brakes.

The only downside to the new Yokohama AVS tires is that they set up quite a howl on some (but far from most) types of the grooved pavement we have on local SoCal freeways. What looks gorgeous to one person may be ugly as sin to another. My subjective opinion of the HRE 549 wheels is that they are stunning! I think they look great. In the three or four weeks since the new tire and wheel package was installed, I've had several Corvettes--and a new Porsche cabriolet--pull alongside at stops and want to know who made the wheels and where could they get a set. I've never experienced that before.

At the start of this article I asked the question, "Is bigger better?" In this specific instance, my answer is an unequivocal and resounding, "Yes!"

EDITOR'S NOTE (We'll be back next month with the installation and tests of Wilwood's 14-inch front brake kit. In addition to the normal street compound pads, we're going to install, bed-in, and test a set of Wilwood's PolyMatrix "E" pads--a slightly streetable compound that's engineered for serious track usage. I won't be surprised if we end up with some sub-100-foot stopping distances from 60 mph.)

23

When Mike Sweeney of Corvette Wheel Specialists pulled the first HRE 549 wheel out of its box, I was almost speechless (and that's a real rarity). The custom hoops turned out even better than I'd expected.

After regaining some semblance of self control, we took the HREs, Yokohama AVS tires, and my trusty coupe to a nearby installation shop that CWS recommends highly. In with the old, and an hour later, out with the new.

This is a factory C5 tire pressure sensor, from the backside, the part that faces the inside of the rim. As you can see, the valve and stem are part of the sensor body. Air enters (and exits) through the slot (arrow). Walt Thurn covered programming a new set of sensors in his Jan. '03 article about fitting '96 Grand Sport tires and wheels on a '99 Hardtop, so we won't regurgitate that information.

Here you can see how the sensor fits against in inside of the wheel. The whitish streak is a silicon-based sealer that HRE applies after the inner- and outer-wheel halves are bolted together to make their wheels airtight.

With the sensor held in place, our installer hand-threads the chrome-plated factory retaining nut, then tightens it securely with a deep socket.

If the nut is not tightened enough, you will have a slow (3-5 psi/day or more) leak from the wheel.

Two views of the new sensor, securely tightened and...

...ready for a tire to be mounted.

With a wheel positioned on the mounting machine, our installer lubricates the inner and outer beads with a special soapy solution to help the tire slip onto the wheel easier.

Then he carefully works what will be the inner bead of the tire over the outer lip of the wheel, making sure that no metal touches the exposed surface of the wheel.

Next, he rotates the tire and wheel on the machine and works the outer bead over the lip of the wheel. Neither the plastic wheel nor his pry bar is allowed to contact the lip of the wheel.

Once all four tires and wheels are united, it's time for high-speed, computerized spin balancing. The John Bean VPI balancer pinpoints exactly where any imbalance is located and how much weight is required to eliminate the imbalance. In this view, you can see where the wheel center is bolted to the inner- and outer-wheel halves. Forty high-strength stainless-steel nuts and bolts are used to secure the three parts that make up each HRE modular wheel together as a unit.

Weights are affixed to the backside of the wheel (where they're out of sight) with high-strength pressure-sensitive adhesives. An arm and roller on the balancer actually pushed the weight into place with enough pressure for it to hold to the wheel.

Off with the old...

...and on with the new.

These are the old and new right-front tires and wheels. What a contrast--and a great example of plus sizing. The old and new combos are nearly identical in overall diameter, yet the original tire is 245 millimeters wide overall on a 17-inch diameter wheel, while the new tire is 30 mm wider (275 millimeters) on an 18-inch diameter wheel.

This is the Diablosport Predator for Gen III V-8 powered vehicles which we ordered from Granatelli Motor Sports. On C5s, it plugs in to a data port under the dash near the steering column. It offers numerous tuning and adjusting parameters that should NOT be used by anyone other than an expert with access to a dyno with air/fuel ratio reading capabilities. It also has many features, like the ability to recalibrate a speedometer for gear ratio of tire-size changes, which makes it very worthwhile for any C5 owner who's contemplating minor modifications.

While Tech Center technician Jason Scudellari was loading our coupe's stock program, prior to downloading the Predator "performance flash," we nabbed this shoot that indicates roughly where the data port is located. Part of the connector (arrow) and the cable can be seen trailing down from beneath the dash.

This is a typical display on the Predator. It guides the user, step by step, through the various adjustment parameters it offers and is very user-friendly.

Just for grins we ran before-and-after tests on the Primedia Tech Center's Dynojet to see if the "performance flash" made a measurable difference. It didn't on this essentially stock C5, but modified ignition and fuel curves would probably make a much larger and very measurable one on a Vette with more than just some bolt-on, cat-back exhaust tweaks. Technician Chad Vogele is running the car while Jason Scudellari kicks back--mere inches away from a rear tire and wheel that's being driven on the roller at about 140 mph!

Sources

Yokohama Tire Corporation
Fullerton, CA 92831
800-722-9888
http://www.yokohamatire.com
HRE PERFORMANCE WHEELS
Vista, CA 92083
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