DeTomaso Mailing List: June 99, Message #243

Hi All,
I've been burning up my calculator doing the tire thing for a few weeks 
because I don't have a car to put them on yet but offer the following. As far 
as I can find out the original tire size on many Pantera was 185-70x15 on 7" 
wide front wheels and 225-70x15 on 8" wide rear wheels.

I must first say that I do not disagree with anything I've read about tires 
since I've been in the forum. It's a topic that can be hashed and rehashed 
for many years to come!!

One of the first things I did was figure the height of a 225-70x15 and found 
that it is 27.4" tall, then I worked backwards or something to find out that 
a 305-50x15 is 27" and 265-60 or 295-50 didn't come out to the right numbers. 
So that's kind of how I started. 
Since we are very limited for what we can get for the rear unless we go to 16 
or 17 inch. It pretty much comes down to the 305-50x15.Tire Rack lists that 
size with a "special" note saying "reinforced" and I'm not sure if that means 
the whole tire or the sidewall or the tread or how the reinforcement will 
affect performance. In any case it seems to be a feature that they think 
deserves a special note. Directly above it on the list is the 245-50x15 and 
it is also noted as being "reinforced." They are both H rated. I must admit I 
am not at all expert on how tire characteristics will affect understeer or 
oversteer. There are many other things that also affect steering so that 
changing any one of them will affect handling. Tire Pressure, Caster, Camber 
and Toe in (or out) in the front as well as the rear also affect steering. 
Then there are the sway bars, bushings, shocks, springs and I'm sure other 
things that affect steering. 

I will be doing the tire boogie in a few weeks and made myself a set of rules 
that the tire would have to meet. I was overloaded with data and info and had 
to get convert it more to a red or yellow situation. I'm sure some research 
was done during Pantera development that lead to the original size selection. 
Although I understand that a lot of this work was done depending on which 
side of the bed Guido got up from that morning. One of the things I looked at 
most were the dimension differences between the front and rear tires. Height 
difference front to rear, section width difference front to rear, 
circumference difference front to rear, sidewall height difference front to 
rear and last section width to wheel width difference front to rear. All this 
compared to the proportions of the originals was what I decided to stick 
with. 

Given that I was pretty much stuck on the 305-50x15 and 10" wide rear rim, I 
then had to do the number crunching and found that the 245-50x15 and 8" wide 
front rim comes closest to the original numbers. I was originally considering 
the 225s for the front because when I looked at 245 as a pure number, it just 
sounded to wide for this old dinosaur - I mean 245 is almost 10" wide and 
again - to this 'ol hot rodder that's a wide tire in any language!! But I do 
plan to go with the 245 because it makes the front to rear proportions close 
to the original. I just hope they don't give me too much trouble on these 
Connecticut roads - if they do, I can drop down to the 225.

Now - I'm finally going to get to the real point here. I'm not sure, but I 
think it's still true. It is not a good practice to mix front to rear tread 
designs, manufacturers, speed ratings, wet/dry performance, hydroplaning, 
etc. Front and rear should have characteristics as close together as 
possible. Now comes the tricky part - learning how to drive. Knowing that we 
all have different thoughts on tire sizes - the last thing I think about is 
oversteer and understeer. That could be because I haven't been in a ditch 
yet!! It would be nice to have a stack of different tires mounted by the side 
of a track and we could drive a few laps and then change the fronts, rears or 
both and do it again. I don't think I would be able to feel which ones were 
any better than others. What I can do is stick with my plan and little by 
little learn what my car is going to do at certain speeds when I turn the 
steering wheel. I'll learn how to drive it and unless it feels really 
strange, when the first set of tires wear out, I'll replace all four at the 
same time with identical ones (if they still make 'um!!)  

So - for all those I didn't put to sleep the summary is: It's best to use the 
same manufacturer and tire model in the front and rear. Sure we can 
experiment and mix things all over the place but I think most of use don't 
have the time or money to do that.
305s and 245s are both are H rated, available in Euro T/A and come the 
closest to original proportions.

Thanks for listening ~ peace ~ ruffscruff