Date: Sun, 12 Nov 2000 23:38:53 -0500 From: Rob Levandowski <roblnopsamhiz.com> Subject: Re: 1999 9-5 Tire question
in article bC4O5.8205$I8.988551nopsamoon.southeast.rr.com, Scott Turnamian at wahoonopsamd.rr.com wrote on 11/7/00 11:26 PM: >> I have a 1999 9-5SE 5 speed. It came from the factory with V-rated >> 215/55 >> R16 Michelin Energy MXV4s. I just replaced them (they had about 39000 >> miles >> on them) with a new set of the same tire but H-rated. The tires have >> been >> balanced 3 times and there's still lots of shake, vibration, and shudder >> in >> both the steering wheel and seats. Before I replaced the tires, the car >> was >> rock steady at any speed. >> >> Is there anything special about the wheels or tires on the 9-5? Are >> they >> (the rims or tires) directional? Are the Michelins it shipped with >> specially made for Saab? Are there special requirements for mounting >> and >> balancing? Well, you've replaced the factory tires with tires that aren't designed to handle the speed and torque produced by your car. Depending on the way the tire is manufactured, this may mean that the sidewall is less stiff, resulting in the kind of symptoms you suggest. A V-rated tire is designed for use at speeds up to 149 MPH, which is the approximate top speed of your Saab. A H-rated tire is only designed for speeds up to 130 MPH. While you may never reach those speeds, you're now using a tire that is not designed to handle the performance of your car. Should you ever find yourself using your car flat out, your tires would be beyond their design limits and prone to failure. More importantly, the speed rating affects the design of the tire in ways that affect handling, such as cornering and braking. You may find that your new tires, while the same brand and model, do not perform as well as your old tires. That's because H-rated tires are inherently lower-performance tires than V-rated tires. It's generally a Bad Idea to replace factory tires with tires that have a lower speed rating. The manufacturer generally wants to keep their costs down as much as possible to keep the price of the car palatable, so they will tend to use the least expensive tire that will perform reasonably well and be safe given the car's design and intended use. Using tires with a lesser rating may cause safety and performance deficits that the manufacturer wasn't willing to accept. Also, where did you get the tires replaced? There's a good chance that your average tire shop would have damaged the rims or the car in some fashion -- my experience is that most tire shops are staffed by people who know very little about how to treat a car. For example, if the car was jacked up by a suspension member or the drivetrain, instead of using the proper jacking point illustrated in the Owner's Manual, part of the suspension could have been damaged, causing the problem. If the installer used a pneumatic wrench to tighten the wheel bolts, instead of using a proper torque wrench, the bolts may have been overtightened, possibly warping the wheel and/or rotor. And they almost NEVER get the inflation pressure correct... -- Rob Levandowski roblnopsamhiz.com (Opinions expressed are solely my own and not a statement from my employer)
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