From:
doctorduke_REMOVE_384846_THIS_@yahoo.com
--- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100046209130">cosworthvegas@y...</a>, cosworth0078 <<a href="/group/cosworthvegas/post?protectID=091233212180056219138097203245129208071">no_reply@y...</a>> wrote:
> Duke, you run a Cosworth competively, don't you? I need your
advice.
> I am in the market for a good street/autocross tire and am leaning
> towards a 205/60VR-13 Kuhmo VictoRacer. You have previously stated
> that there are very few good 13 inch performance tires. I usually
> stick to Goodyear but they have "nothing" in my size. What I am
> wondering about is whether I should buy these Kumhos even though
they
> have a reputation for "throwing gravel". What is your opinion of
> this tire for occasional street driving and once a year
autocrossing?
> Even if I do not drive on gravel roads, will I chip the paint on the
> sides of my old Cosworth? Also, if I go with this size and aspect
> ratio, won't it cause "speedometer error"? I remember Karl at
> Hutton's in the early 90's changing out the tranny's "speedo gear"
> because it was the wrong one for my stock size (BR70-13) tires
> (having been changed first in the 70's when I ran wider autocross
> tires). Also, won't using a "205" tire cause interference at the
left
> rear inside fender well? I remember using an aluminum spacer in the
> 70's and 80's when I ran wider than stock tires.
> Clark
In addition to the Kumho, you can buy the Toyo Proxes RA-1 in the
205/60R-13 size (V-rated). This is the tire I am now running. I
can't give you a blow by blow comparison of the Victoracer and RA-1 as
I have never compared them back to back. The Toyo is basically a road
racing tire and needs some heat to work really well. Even at normal
highway running temps in mild to warm weather these tires have
exceptionally high grip, but they don't get sticky enough to pick-up
and throw pebbles unless you are hot lapping a track at which point
they can pickup debris when you slow down and go through the paddock,
but they are like driving on flypaper and generate an easy 1.0+ g of
lateral grip. I overfill my oil by one quart when I track the car,
and I am running 2 degrees negative front camber with 1 1/16"/7/8"
front and rear bars with poly bushings on the front links.
The 205/60R-13 size will make your speedo/odo about 5 percent
optimistic. A couple of ways to correct this is to either install a
properly geared adaptor or, what I did was have my speedo recalibrated
by decreasing it's gain by 5 percent. A speedometer shop can do this
by altering the magnetic flux of the head, but the odo will still be
high. If you have a four-speed you might be able to get a 24T
driven gear that will replace the 23T original and mesh properly with
the drive gear. The five speed has a 25T driven gear, and I am not
aware of any 26T driven gears that exist.
I had to reshim my Panhard bar to give more clearance on the RH side.
Since the axle moves slightly to the left in jounce, RH clearance is
reduced over a bump. If I approach or depart a steep ramp at an
angle, I can get still get slight interference on the RH inside, but
one only accomplishes these manuevers at low speed. I keep the RH
wheel wheel chalked to check for interference, but I have never had
any in normal driving. Unfortunately, the '75s do not have the '76's
shim adjustement for the Panhard bar.
The Toyos have a DOT wear rating of 40, but I project normal street
driving mileage of at least 10,000. A once a year autocross won't
reduce this by a significant amount, but 150 miles a day on a race
track sure will if you do that a lot.
I'm very happy with the Toyos and recommend them to all, but there is
one downside. They are very harsh riding because of the steel
stiffener in the sidewall. This give fabulous steering response, but
at the cost of ride harshness, especially on old patched pavement.
I think the Victoracer might be a better autocross tire. You should
go to some local events and see what guys who run the 205/60R-13 size
are using. I know the RA-1 is a spec tire for an RX-7 road racing
series, but I'm not sure if it's popular in autocross.
Duke
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