From: thatchh@hplsla.hp.com (Thatch Harvey)
Newsgroups: rec.autos.tech
Subject: Re: ++WIDDEST TIRE OF 5.5"wide RIM???++
Date: 22 Jul 92 01:33:39 GMT
Organization: HP Lake Stevens, WA

> / hplsla:rec.autos.tech / lusky@hal.gnu.ai.mit.edu (Jonathan R. Lusky) / 11:20 pm  Jul 15, 1992 /
> In article <15JUL199213101985@zeus.tamu.edu> rcg1597@zeus.tamu.edu (GUYNN, RICHARD CARL) writes:
> >>Pontiac.  They are 5.5" wide and I would like to go for the 'balloon' look 
> >>(where the ribber hangs out over the center of the rim.
> >
> >>PS  I have P195/70R13 Goodyears right now and am looking to go to a 60 series 
> >>Cooper Cobra tire-unless the 60s would look dorky in my wheel wells.
> >
> >
> >
> >	3) This would mean that the safest width of tire for your rim size would
> >	   be 5.5"/.75 = 7.3" = 185mm.  Which would indicate that you are 
> > 	   already pushing your limit.
> >
> I have a 79 Rx-7 which also has 13x5.5 rims.  I use 205/60R13 tires.
> I have a few problems with the tires rubbing the inner fenderwells at
> full steering lock (damn BFG jello-like sidewalls!), but they fit on the
> rims fine.  All of the 12A Rx-7's I've seen autocrossing in stock classes
> (ie..  13x5.5 wheels) use 205/60-13's.  YMMV.
> ----------



       I used to autocross a TR4A for several years, and I started off with
5.5 rims from a Datsun 240Z. My experience was that if the tire width is
significantly greater than the rim width you would get a performance decrease.
The ability of the sidewalls to plant the tread on the pavement is much better
when they can go straight down from the wheel rim to the tread. If they have
to make a big arc to reach the tread, there is lots more opportunity to squirm
around. If handling is your goal, the 195/70 may already be too wide. The 
Eurotire catalog (my bible) lists 5.5 as the minimum width rim for a 195/70-13.
Thus the comment above about the "damn BFG jello-like sidewalls" probably
isn't the fault of the tires but of having too narrow a rim.  I used to run
195/70-14's on my Triumph and I finally saved up enough for some 7" wide
aluminum wheels. The difference in handling with the same tires was dramatic!
(especially in autocrossing where quick transition is very important). I
wouldn't be surprised if an Rx-7 of that vintage with a good H or V rated
185/70-13 tire would be just as quick or quicker than the 205/60's.
  I now have a Merkur XR4Ti which comes with 195/60-14 Pirelli P6 tires on
skinny rims. The P6's are considered pretty high performance tires. I bought a
set of 15X7" wheels and put 205/50-15 Bridgestone RE-71's on them. It's like
a different car!  The increase in cornering capability is incredible!
   Anyway, if your goal is to look mean, the bigger tires will do it, if your
goal is to kick someone's ass, don't be deceived.

                      Thatch Harvey


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