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Path: utzoo!watmath!watnot!watrose!tohaapanen
From: tohaapanen@watrose.UUCP (Tom Haapanen)
Newsgroups: net.auto.tech
Subject: Re: The ART of choosing tires
Message-ID: <7848@watrose.UUCP>
Date: Wed, 26-Feb-86 10:47:34 EST
Article-I.D.: watrose.7848
Posted: Wed Feb 26 10:47:34 1986
Date-Received: Fri, 28-Feb-86 05:48:23 EST
References: <2096@dutoit.UUCP>
Reply-To: tohaapanen@watrose.UUCP (Tom Haapanen)
Organization: University of Waterloo, Ontario
Lines: 70

In article <2096@dutoit.UUCP> ssp@dutoit.UUCP writes:
>
>Can someone explain what difference wheel/tire size makes to a car's
>	
>	acceleration
>	top speed
>	economy

None, unless the overall diameter is different.  In that case your
speedometer will be off as well.

>	road noise
>	ride

Better performance often means more road noise and a rougher ride.

>	road holding
>	handling 

Here the big differences.  The improvement comes from a number of
sourrces:
	1. Wider wheels provide more support for the tire
	2. Lower tire sidewalls don't flex as much
	3. Stiffer sidewalls don't flex as much
	4. Better compounds provide better grip
	5. Aggressive tread provides better grip (not in snow!)

>Also what the different numbers mean:eg. 185/60 HR 14 80 H tires
>on 6 J x 14 wheels, alloy/steel etc.

185 / 60 H R 14
 |  |  | | |  |
 |  |  | | |  --- Rim diameter
 |  |  | | --- 'R' means radial.  Bias ply has no indication
 |  |  | --- Speed rating.  V  > 210 km/h
 |  |  |                    H <= 210 km/h
 |  |  |                    U <= 190 km/h
 |  |  |                    S <= 170 km/h (the last 2 from memory)
 |  |  --- Aspect ratio.  100 * (overall height) / (overall width)
 |  --- A slash.  Indicates that this is a tire.  :-)
 --- Overall width.  != tread width

The /60 or whatever is optional; eg. 165SR13 is valid and indicates a
165/78SR13 or 165/80SR13 tire (depends on manufacturer).

>And are there any physical limitations on the wheel/tire choice for
>a given car?

Yes.  If it doesn't fit, you can't use it.  :-)  As in, if the bolt
pattern is wrong, or the tire is too wide to clear suspension and
fenders.  You should also retain approximately equal overall diameter.
This can be calculated as follows (in millimetres):
	OD = (rim size) * 25.4 + (overall width) * (aspect ratio/100) * 2
This is only approximate, though; the actual aspect ratio of a given
tire will vary with the rim width (wider rims will 'spread' the tire
and give a lower aspect ratio, lower OD, and better handling).  An
example of various tires with same approximate OD:
	175/70SR13 on 5.5J13
	205/60HR13 on 6J13
	185/60HR14 on 6J14 (known as 'Plus 1')
	195/50VR15 on 6J15 (known as 'Plus 2')
As you go down the list, both price and performance increase...


				   \tom haapanen
				   watmath!watrose!haapanen
I'm all lost in the Supermarket
I can no longer shop happily
I came in here for that special offer
Guaranteed personality				 (c) The Clash, 1979