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Power And Performance From Weight Loss

Posted in How To: Wheels Tires on October 1, 2011 Comment (0)
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Power And Performance From Weight Loss

It was time to put our money where our mouth was, so to speak.

We’ve all heard that less rotating weight has a big impact in overall performance. We have been living it all the way back to our backpacking days, where ounces really mattered. “An ounce on the foot is like a pound on the back” in backpacking parlance became “A pound of rotating mass is like 10 pounds on the Jeep” for us Jeep-speakers. We’ve known both sayings to be true for a long time through personal observations. We’ve also been telling you that less rotating weight directly translates into benefits on the Jeep that you might not be aware of. Things like more power, better economy, and faster acceleration are but a few of the things we’ve talked about over the years.

For our cover section on losing weight to gain performance, we decided we’d do some actual testing to get real numbers, and whether we were right or wrong, we’d publish whatever we found out.

As it turns out we were right about the whole “less weight is more” thing, but we managed to surprise even ourselves with the numbers we came up with.

The Players
Auto Meter - Helped keep an eye on transmission temperatures to keep acceleration results consistent from pass to pass. 866/248-6356, autometer.com

B&M Racing - Without the Supercooler we’d have smoked the transmission in the first few acceleration passes. 818/882-6422, bmracing.com

Casio - Gotta time the stuff somehow. Used the stopwatch on a PRW-240 to keep tabs on stuff. 800/836-8580, casio.com

Discount Tire - The low-price online dealer of literally thousands of tires and wheels. Often available delivered to your door mounted and balanced for cheaper than can be had locally. 800/589-6789, discounttire.com

General Tire - Provided the heavyweight tire of the test. When the zombie apocalypse comes we hope we have General Grabbers under our Jeep. 800/847-3349, generaltire.com

Goodyear - Donated the bantam-weight contender to the test. And, provided us with the 40-60mph test idea. 330/796-2121, goodyear.com

OPEC - Took way too many of our hard-earned dollars to feed the test mule 87 octane.

Raceline Wheel - The first company we spoke with about this story years ago. Manufacturer of stout beadlock wheels and soon to have a low-weight stout beadlock wheel. 714/893-4160, racelinewheels.com

SR Motorcars - Our long-suffering associate shop that does really cool engine swaps and tuning with little cars. Also has a dynometer and humors our goofy big Jeeps with low power numbers. 310/516-1003, srmotorcars.blogspot.com

Trasborg - Anal-retentive personality who ends up doing most of the hands-on side-by-side shootouts and tests. Often bringing down the wrath of his company’s bean counters upon himself by doing so.

The Test Mule
Vehicle: ’98 Jeep Cherokee aka Mileage Master
Engine: 241,000-mile 4.0L inline-six
Transmission: 241,000-mile AW4 automatic
Transfer Case: NP242
Axles: Dana 30 (front); Dana 44 (rear)
Axle Gearing: 3.55:1 (front and rear)

The Test Track
Location: Secret location in one of the many deserts of California
Temperature: 98 degrees
Elevation: 2,389 feet

Basic Test Criteria
We found out early on that the hotter the transmission got the slower the Jeep accelerated (go figure). We have two temp gauges on the transmission. One tests the hottest spot: right when the transmission fluid dumps out of the torque converter. The other tests at the coolest spot: about midway between our B&M Supercooler and the transmission on the fluid’s way back to the transmission. We ran every acceleration run with the cool side at 180 degrees and the hot side at 220 degrees for consistency.

For the 0-60 tests we came to a complete stop on a straight stretch of abandoned road with no elevation changes and hit the stopwatch at the same time we hit the gas. For the 40-60 tests we stood on the gas at 30 mph to get the transmission to downshift and started the clock as we came up through 40 mph. The 60-0 stop tests were performed with Trasborg on the brake pedal, one guy verifying that the brakes were applied the same place every time, and one person measuring to a fixed point on the Jeep after the full stop had been achieved.

For all tests, we did at least eight repetitions and threw out the high and low values before averaging the results for the numbers that you see here.

The Contenders
We pitted the lightest tire and wheel we could come up with against the heaviest tire and wheel. We used tires of the same type (mud terrains) and size (33x12.50R15) and we have accumulated well over 10,000 miles on each set. We know these tires. We like both of the contenders. All tires as tested were the same diameter (323⁄8 inches) and had the same tread width (10 inches). We wouldn’t hesitate to suggest either to anyone (and we have, in fact, suggested both many times since we first tested each tire).

Goodyear Duratrac
The Duratrac is a relatively new tire to Goodyear’s stable that blends the lines between the MT/R and the typical street-oriented Goodyear all-terrain. In fact, depending on where you get your Duratracs they are listed as either a mud-terrain or an all-terrain. They are great in all kinds of snow, be it on- or off-road in addition to being a great tire for most off-road-based light wheeling. With the high-void content of the shoulder lugs they do quite well in the mud and have a similar rubber-on-ground contact pattern as the Grabber.

Goodyear Duratrac on MB Wheels model 72 wheels

We were surprised when our search for the lightest 33x12.50R15 we could get turned up the Duratracs. Our past testing hadn’t revealed just how light these tires are. We wrapped them around MB Wheels model 72 aluminum wheels from Discount Tire in a matte black finish, which weighed in at 19 pounds. Total tire and wheel weight: 68 pounds.

General Grabber
Pure and simple, the Grabbers are tanks…but without the pain-in-the-butt of having to maintain those tank treads. With a seven-ply tread and three-ply sidewall this is the tire we just don’t worry about. Cactus? Cast-off wood that may or may not have nails? Curbs? Shale? 4 psi in the tire? 1,000 lbs in the back of the Cherokee? Not a problem. We’ve run over all of that stuff and abused the tires and not put a single hole in them.

General Grabber on Raceline Rock Monster wheels

So when our search turned them up on the heavy end of the scale, we weren’t surprised. A tire that wears like a tank also weighs like a tank? OK, makes sense. So the Grabber got the unenviable position of being the heavyweight of the test. We then pulled another bulletproof tank-like item in the form of Raceline Rock Monster beadlock wheels. We’ve got nothing but good things to say about how well these wheels deal with the abuse we’ve given them over the years. Total tire and wheel weight: 96 pounds.

The Tests
Like all of you guys back home, all of these tests started with bench-racing sessions. The 0-60 test was on the books from when this story was but a flicker in our minds. The 40-60 test came in while talking to Goodyear about this story. The 60-0 test reared its head after we had bolted the Duratracs to the Cherokee with the Grabbers inside and had our first brake check in SoCal traffic. The mileage numbers are derived from Trasborg’s obsessive note-taking at every fuel stop. The dyno runs were the wild card from the beginning. We just couldn’t predict what the dyno would show, but like we said at the beginning, in for a penny, in for a pound.

154 1110 04+gaining through losing+dyno chart
Light Tire and Wheel (68 pounds each) Heavy Tire and Wheel (96 pounds each) Change (28-pound difference each)
0-60 mph 16.32 seconds 18.35 seconds 2.03 seconds
40-60 mph 8.32 seconds 8.98 seconds 0.66 seconds
60-0 mph 132 feet 6 inches 156 feet 8 inches 24 feet 2 inches
Mileage 15.93mpg 15.3mpg 0.63mpg
Dyno Numbers 147.95hp 169.35-lb-ft 141.17hp 163.38-lb-ft 6.78hp 5.97-lb-ft

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