Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site floyd.UUCP
Path: utzoo!linus!decvax!harpo!floyd!gjw
From: gjw@floyd.UUCP (Greg Wroclawski)
Newsgroups: net.auto
Subject: Re:280Z Tires
Message-ID: <2025@floyd.UUCP>
Date: Tue, 6-Dec-83 09:18:56 EST
Article-I.D.: floyd.2025
Posted: Tue Dec  6 09:18:56 1983
Date-Received: Fri, 9-Dec-83 01:21:11 EST
Organization: Bell Labs Whippany NJ
Lines: 25


	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.