DeTomaso Mailing List: February 1997, Message #97
     



From: MikeLDrew@aol.com

Subject: Pantera Tires

Date: Fri, 14 Feb 1997 01:51:12 -0500 (EST)



Hey Guys!



It's way late, and I've got to get up early again tomorrow to ride to work,

so here's a quick reponse to some of the things you've been writing about:



1)  Tire compounds/sizes.  Shane says he isn't wild about mixing tire

compounds.  Actually, I see nothing wrong with this.  The Pantera tends to

understeer, and this condition is aggravated when wider rubber is fitted at

the rear.  The fundamental handling limitation of the Pantera is the

inability to fit enough rubber in the front (ask Jack DeRyke who autocrossed

his car for years).



Fitting STICKY rubber in the front is a work-around to the problem.  Terry

Aultman is running old Goodyear 265/50 VR Gatorbacks (no longer made) on his

10-inch Campys, with Yokohama A-008R super-goopy 225/50's in the front on

8's.



I have determined that it's possible to fit a 245/50 in front on an 8-inch

rim, and that's what I've done.  I've never driven my car though, of course.

P.J. Couillard took my advice and is running the Euro T/A 305/50 on 10-inch

Campys in the back (this is an H-rated tire, by the way, not V-rated as

previously reported), and he pitched his Euro T/A fronts and replaced them

with BFG's Comp T/A Z-rated 245-50 on his 8-inch fronts.  He says the

difference is like night and day, the car sticks solidly now and gives a very

secure, confident feeling when he flings it into a corner (and fling he

does--I've been with him when he tossed it into 45 mph corners at about 100,

and the car just corners like it's on rails).



So I think that's the hot setup for 8 and 10 inch wheels.



If you're sticking with the stock 7 and 8 inch wheels, I'd run a 225/50 in

the front, but definitely something larger than 245 in the rear.  BFG makes a

V-rated Comp T/A in 275/60 which is almost identical in size (just a bit

wider) than the original Arriva.  Jack DeRyke is running ancient Pirelli

275/55's in the rear with 245/50's in the front.



Lots of people will tell you you should never mix tires of different aspect

ratio.  Well, we do it all the time with GT5/Group 4 cars; I think the rules

are different when you're dealing with mid-engined cars with wider rear

wheels anyway.



I wouldn't run anything with less than a 50-series in 15 inch, however.

Besides looking sort of goofy and throwing off your speedometer something

awful, they might do weird things to your handling.  Better to go with

something greater than 50-series, although 50-series is probably ideal.



2)  Good point raised about the increased loads transmitted to an

unsuspecting chassis by stickier tires.  This is in fact that cause of the

concern raised about Pantera brakes; there's nothing wrong with the brakes,

folks.  They were simply designed to absorb X amount of energy, any more and

the skinny OEM tires would lock up.  Now we've got tires capabable of

transmitting twice as much energy to the brakes, and they're overwhelmed.

Not a design flaw, but if you're upgrading one part of the chassis (the

tires) you've got to consider the effects upon the rest of the system.



3)  With all the hand-wringing about the lack of suitable tires for 15-inch

wheels, I'm surprised nobody has mentioned running treaded race tires.  My

427 Cobra came with Goodyear Blue Streak Sports Car Specials, bias-ply

super-sticky roadrace rubber.  They're probably only good for about 2500

miles of combined street/track driving, but they're cheap, and once warmed up

they stick like crazy.  Don Welch has been running them for years on his

427-powered Targa Pantera, and they look like a great alternative.  Being

bias-ply, they ride a bit harder, they'll flat-spot if you leave the car

parked on them for any length of time, and they leak air something fierce

(they'll lose 5-10 lbs per week if you don't run them with innertubes), but

it's worth considering.



Besides, with that giant "Goodyear" logo, they look bitchin'!



I've got another friend with a 427 Cobra who runs hand-cut Indycar slicks on

the street.  They're cut by a sprint-car tire specialist, and have quite an

aggressive tread pattern, and a surprising depth to the tread.  They're only

good for 2000 miles on the street/track too, but hey, they look tough and

stick well!



Finally, Hoosier makes a really sticky DOT autocross or roadrace compound

tire, I think in 275/60.  John Wehrheim used these things on his car and

knocked a bunch of time off his previous year's record at the Shelby Club

Virginia City Hillclimb.  Cobra guys dig these things too.  They're only

about $115 apiece, and again, probably only last for 2-3000 HARD miles.  Bias

ply, too.



4)  Wheel stress.  Sorry Shane, it's true, magnesium DOES age, especially

when it's exposed to the air uncovered by paint.  It becomes brittle and

porus; Jim has a valid concern.  However, I don't think an overly-large tire

is going to damage a wheel, but realize that they're simply not as strong as

a steel wheel when it comes time to hammer over potholes.  At worst, when a

steel wheel might bend, the magnesium will probably shatter.



Keep this in mind when you're stripping your wheels to refinish them.  Strip

them, then IMMEDIATELY paint them with zinc chromate, or they'll crumble away

to powder in no time.  Once the corrosion process begins, painting or

powdercoating just locks in the corrosion and it continues under the paint.



I've got a coffee table made from an 8-inch Campy and Arriva combo.  It

developed a hairline stress crack which made it unsuitable for road work;

when I prepped and painted it, then inflated the Arriva, within an hour the

air pressure created a 2-inch bubble under the paint!



5)  Hate to break it to you all, but 10-inch Campys are dropping in value as

people become concerned about the lack of tires available for them.  Doesn't

matter if they're early or late, most people seem to be buying a complete set

of four wheels and tires (8's and 10's) for $1200 or so; I'd imagine a bare

set of 10-inch wheels is worth something less than $1000 used.  New, they

still cost a fortune, $1300 each or so if I recall.



Okay, bedtime.  Hope this is suitable grist for the mill!



Mike Drew