[Fot] Can radial and bias race tires be mixed successfully?

[Michael Porter]

jim hearn wrote:

>Does anyone know if radial and bias race tires can be mixed successfully?
>Would bais race tires on the front and radial race tires on the back be a
>good thing for autocross or not as good as all four race radials?  Thanks,
>Jim
>
>  
>
Umm, my first guess is that the results would be highly unpredictable.  
Weight shifts from braking and acceleration combined with turns could 
make the car plenty jumpy.  My favorite story about this sort of thing 
was from a dealership shop manager I used to work for (who had a 
VW/Porsche dealership once, before he lost it).  Said he had a customer 
who complained of erratic handling with his 911. So he had the guy try 
to reproduce the problem while riding with him.  The guy went into a 
very tight downhill, decreasing radius off-ramp at about 110 mph, and 
when he hit the brakes a bit, the car jumped sideways about four feet.  
"That's what I mean!," yelled the customer to the manager, who was very 
much shaken by the profound twitch, having seen a life or two flash 
before his eyes.
 

They put the car on a rack and walked around and around it, trying to 
find something out of place.  Everything looked just fine.  No bad 
bushings, no obvious alignment problems or tire wear, etc.  The tires 
were the same size and brand, all radials, etc.  Then one of his 
mechanics noticed that the tires on the right side were single 
steel-belt and the rest were fabric, while the two on the left were 
all-steel-belted.  They put a matched set of tires on it and the problem 
disappeared.


So, even radials are not all created equal.
 

Cheers.

-- 
Michael D. Porter
Roswell, NM

Never let anyone drive you crazy when you know it's within walking distance....