gjw@floyd.UUCP (Greg Wroclawski) (12/06/83)
I have a 1980 RX-7 with the same problem you appear to be having. The weight ditribution is almost the same 51%/49% front rear and both have about the same power to weight ratios. The previous owner had put 205/60-13 tires in place of the original 185/70-13's. The car's wet weather traction was poor and in the snow even worse. The rear tires were very easy to break loose in the rain. As soon as the tires got reasonably worn I changed back to 185/70-13's (Bridgestone 207's in this case) and wet weather traction was vastly better. An important point to remember is that a tires wet traction comes from the fact that the water between the tire and the road gets channeled into the treads and the rubber is allowed to contact the road. When this can no longer happen the tire is said to be hydroplaning. This channeling of water is helped by increasing the weight per unit area and by tread depth and pattern. Therefore, all other factors remaining the same increasing the tire width decreases the weight per unit area on a given car and decreases wet traction. Also as a tire wears and its treads get shallower the tire's wet weather traction decreases although dry weather traction and handling gets better. A similar situation exists in the snow where you want the tire to dig in and get a good bite. So snow tires are designed with large chunky treads and the more weight on the driven wheels the better. Dry weather traction (lateral acceleration also) and transient response are affected by a totally different set of parameters and in general wider tires will improve traction in these conditions. So one must pick tires which are the best compromise between the two extremes depending on one's location and driving habits.
ralph@inuxc.UUCP (Ralph Keyser) (12/07/83)
I've just re-shod my trusty RX-7 ('81), and I'll pass on what I
picked up in the process.
Wider tires will increase your car's lateral acceleration *on dry
pavement*, but not automatically in the wet. The biggest thing
that affects wet weather handling is how well the tires channel
water away from the rubber/road contact patch.
I elected to swap my stock 185R70-13's Bridgestones for a set of
of Phoenix Stahflex 3011 195HR60-14's. The tires are just a bit
wider than normal, and the shorter sidewalls are stiffer which
increases the car's lateral acceleration. This particular tire also
got a high rating in Road and Track's last tire test from earlier this
year for wet weather traction. I've been nothing short of amazed at
the difference in the way the car sticks nowdays.
This is all kind of expensive though, since you need new wheels in
the deal. If you don't want to go to all that expense, you might
be better off with a standard size "performance" radial.
I'm not familiar with the Michelin model you mentioned, but I'm
thinking of the Goodrich Comp T/A, Goodyear NCT, Pirelli P6, etc
type tires.
Just remember that wide tires will hurt you in the wet unless the
tread pattern is really "aggressive". Nobody runs slicks in the
rain.
Ralph Keyser
inuxc!ralphrobert@hp-pcd.UUCP (robert) (12/10/83)
#R:floyd:-202500:hp-cvd:2700006:000:580 hp-cvd!robert Dec 8 11:42:00 1983 I live in Oregon where it rains *all* winter. I had a set of Rikens on my rabbit. I am a *hard* driver and the wet weather traction of the Rikens left a lot to be desired. When the time came for new tires I went wider for better dry road traction and went with Comp T/A (H rated) tires. WOW! I was amazed! Even with 205/60's the wet weather traction was awesome. I could go around corners 5 mph faster in wet conditions than I could have in dry on my old tires! I highly recommend Comp T/A in wet weather. Robert (animal) Heckendorn ../hp-labs/hp-pcd/hp-cvd/robert