Crawlability Quotient
Reader: I love the idea of a crawlability quotient for your 4x4 of the Year Test (4xForward, Oct. '06). I was recently taking a look under my girlfriend's Land Rover Freelander SE3 (I know, no low range, but I am jealous of the removable top, hill descent control, and the gas mileage). It was crawlable, but super-nerve-wracking with the hot exhaust about an inch away from my face. The problem is where to measure from. Let's face it, the unibody vehicles are the major offenders here. Why not make a rule that the bottom of the rocker panels must not fall below an imaginary line drawn from the center of the front wheel to the center of the rear wheel? Since you guys are the experts you can decide what amount under that line is acceptable. My personal favorite would be an oil change test. Park it on a flat level surface and try to change the oil, or better yet the transfer-case fluid, without ramps, a lift, or a jack. The stakes get even higher if the only tool you are allowed to use is one box-end wrench. My truck passes the test, does yours? Keep up the good work.
Drew Becker
Tallahassee, FL
P.S. The Freelander passed the oil-change test. To me that is a more practical test, because it would be really annoying if I had to jack it up every time I changed her oil.
Editor: As soon as we get our current crop of competing vehicles, we'll have a parking lot crawl-off as we try to slither under the rigs to see which ones fail. Check out our full coverage of our 4x4 of the Year test in the February issue which we'll start writing in September and, which will be on the newsstand December 12.
Dept. Of Corrections
Reader: I just read your "Tall Tire Tech" (Sept. '06) and thought you might want to clean up the following comments as a service to your readership: "to increase high-speed capability, there may be 10 or more plies of nylon or Kevlar in the belts...." I can safely say that, outside of a tire fitted on the Space Shuttle maybe, there isn't a tire made today for consumer usage that has 10 plies of Kevlar or nylon in the tread. At best, you may find two plies of either material in the tread. Also, "Tires in the United States generally are constructed of two steel beads, 10 or more polyester plies, and two or more steel belts." Similar to the item above, there just aren't any tires made with 10 polyester plies today. There are numerous 10-ply-rated products available from various manufacturers, but these products typically use just two polyester plies to achieve the 10-ply rating. Years ago, 10 physical plies were needed to achieve a 10-ply rating, but advances in textiles since then allow a 10-ply rating to be achieved with typically only two polyester plies. And finally, "With a radial tire, the carcass plies and steel cords are at 90 degrees to the centerline...." I would be curious to see this tire inflated, and may model one using Finite Element Analysis (FEA) for giggles. The steel cords in a typical light truck or passenger tire are laid 20-30 degrees to the centerline. The cord angle in the first belt is opposite to that of the second belt, so that the cord paths in each belt intersect or are biased with each other. This is done to control the inflated shape of the tire and provide tread stiffness and puncture resistance, among other things. I just thought you should know.
Ken Reuille
Principal SUV & LT Tire Development
Engineer
Cooper Tire and Rubber Company
Editor: Thanks, Ken. We saw that and thought we had caught it. In fact, it was supposed to be 1 ply, not 10. As for the radial angles, they are 90 degrees to each other, not the centerline. Thanks for the good catch!