Re: boge & tire pressures, alignment

[phile@swamp.stpaul.gov (Philip J Ethier)]

Eliot Lim writes > 

> the car is now running with just a tad less than 1 degree of front negative
> camber.. factory specifies +/- 0.5.. i have not noticed any difference with
> the new setup, unfortunately.. front toe is set to 0.7 degrees. 

Toe in or out?  I assume out, as the front is driven, and the theory is
the the suspension is "pulled" towards zero tow at speed.  0.7 degrees
overall?  On a 23" tire (guessing on tire size) that is 0.281".  A full
quarter-inch toe out?!  No wonder you have tire wear on the inside!  This
number must be wrong.  I can't imagine anyone wanting to run this much
toe-out on a street machine.  Autocrossers may want to run that much on a
FWD that does not turn in smartly enough, but never on the street.  If you
meant 0.7 degrees PER SIDE, it would be really outrageous.

> i 
> recently rotated my tires and found that the inner edge of the front
> tires were more worn than the center or outside... so i guess 45psi front
> is *not* too high for this car.

The inner edge of the tire is worn from the negative camber, and possibly
too much toe-out.  If you have been working the tires hard in cornering
and there is no roll on the outside, and the wear is all on the inside, I
believe that 45psi IS more than you need on the front.  As an autocrosser
(and I do not use the special stiff-sidewall tires from BFG which
invalidate these theories) I know that main reason to run tires higher
than the max on the sidewall is to prevent roll-under.  This is not a
problem with my Lotus, but I have spent some time fighting heavier cars
under stock rules, too.

If you are still seeing wear on the inside edge, you ought to reduce your
tire pressure and re-test.  

In any case, I fail to see that "45psi front is *not* too high"  follows
from "the inner edge of the front tires were more worn than the center or
outside".

Before I replaced my old street machine with a Quantum Syncro I ran one
degree of negative camber (all I could get) and 1/16" toe out on
The Mighty K-wagon with 36psi on .  I like to corner.  I still wore the
tires on the OUTside first.  The car with the transplanted five-speed and
the uprated springs used to surprise a lot of people.

My Lotus has significant negative camber all round, and tire wear is even.  Of
course this car spends a lot of time autocrossing at full cornering loads I
can't recommend for street use.  On dry public roads, you can't challenge the
car at anything slower than truly irresponsible speeds.

I have not yet put any significant wear on the Syncro's tires. It came to me 
with even wear on each tire, but the fronts were worn much more than the
rears.  What makes this odd is the the "fresh" tires on the rear are
Dunlop GT Qualifier HR4.  These are supposed to be long-discontinued.  But the
mostly-worn-out fronts are Dunlop (mumble, mumble, can't remember the
alphabet-soup designation) which SUPERSEDED the GT Qualifier HR4!  In an
effort to get the car to stop better in the snow, I swapped the tires end
for end.  This achieved the desired effect, but power-on oversteer is
another result in the snow.  Fun, but pay attention.  I ought to replace
all four 195-60-14 tires with 175-70-14 all-weathers for winter, but my wallet
says wait.

phil.ethier@stpaul.gov