tire speed ratings and why they matter

[Thorin]

I'm looking for winter tires for one of my cars, and there are two tires rated first and second by Consumer Reports that have two different costs.  So I thought I'd read up on the details.  Well, one of the differences is the tire speed rating.

The tire speed rating is determined by spinning the tire under load at faster and faster speeds until it fails.  It's a letter rating with a top speed attached, where the top speed is how fast the tire can spin under load continuously.  Here's a chart:



Okay, I normally never drive anywhere near those speeds, although I have taken a car with Q rated tires (160km/h safe) up to 190km/h for a minute.  So if those top speeds don't matter, do I care?  Surprisingly, I found the answer is YES.

What is pointed out here: http://www.agcoauto.com/content/news/p2_articleid/235 and here: http://www.barrystiretech.com/speedratings.html is that higher-speed-rated tires are sturdier and less likely to warp under heavy load (such as when panic braking while trying to swerve around an obstacle at highway speeds).  This could mean the difference between @%&# in the pants and a rapidly beating heart, and having to pay to replace another bus shelter.

I do wonder how much better the snow tires will be in the snow - my Mazda6 has almost gotten stuck with me at the helm a couple of times in the last week, and it's still on all-seasons (and old ones at that - they're five years old and at the end of their tread life).

...

Also, the original owner of my Mazda6 didn't like the 17" wheels and bought 16" wheels and tires, and 1. didn't keep the (what I consider) beautiful original rims (and the ones he bought I think are ugly as sin but my wife likes them) and 2. went from a V rated tire to a Q rated tire which is a pretty significant reduction in tire sturdiness.

[Lazybones]

I only bothered with winter tires in the last few years, they made a substantial difference in traction and control.

[Thorin]

Yeah, I know that there'll be an improvement.  What I found really interesting, though, was that the tire speed rating should actually be called the tire sturdiness rating, or perhaps the tire resistance-to-deformation rating.  And this is important in panic situations, because the less a tire deforms abnormally, the more the car will go where you're trying to make it go.

One thing's for sure, the part-time 4WD system in the truck (and that was previously in the Suburban), even on all-seasons, substantially improves the traction on snow.  Just not when trying to stop.  But I drive slower when it's bad weather out, so I haven't slid into anything in a long, long time.