Here is another opinion on tires.
Jeff
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Subject: Reply to Steve, Rich and Jarrid
Author: GDWF22A@prodigy.com (MR RICHARD T TRENK SR) at INTERNET
Date: 9/11/97 6:03 PM
Steve; the Alpine does have a nice X member frame as well as rails forward
of the firewall to which the cross member is bolted.
Jacking points were mentioned to you a day ago and this is all correct.
Also, you can floor jack this car and also position support stands under
any portion of the lower cross member, lower A frames, side frame members ,
rear axle housing and rear springs themselves. This car is light and those
various places can handle the weight without deforming or bending.
Avoid jacking under the thin wall portion of the rocker panels or other
actual body sheet metal.
I see NO reason not to trust four properly placed stands or supports.
use of drive-on ramps is OK and certainly are solid but they encroach too
much around the front car area and hamper certain work areas.
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Rich; you mentioned using BR60x13 tires with 42 and 45 psi front and 40
psi rear. No wonder you slide around a lot !
These are radial tires and as we know, they look somewhat bulged or
underinflated when set at recommended psi.
The idea of the radial (which makes it so much better than a bias ply tire)
is that when a radial is inflated PROPERLY, it will not lift it's trear off
the ground in a hard corner and will instead just keep it's tread hard on
the ground and allow the side wall to flex over to one side.
A bias ply tire in a hard corner, keeps its sidewall rather straight but
lifts the tread off the road.
To get a better handle on this, stand up with your shoes a few inches apart
and just lean your body to one side. The shoes remain flat on the floor but
if you had ridgid ankles, you would have tipped up or lifted up the outside
edge of your shoes, like tilting a statue off it's base.
Now....when you air up a radial way too high, you make it act like a bias
ply tire. It cannot flex and keep it's "footprint" on the ground properly.
Also, whenusing too much air, the front-rear length of foot print is
shortened a lot . The result of all this is as you alreadu found ! No grip
and lots of skidding.
By law, tires are marked on the side with their MAXIMUM load carrying
capacity when aired up to a certain MAXIMUM pressure. This marking is
misunderstood by far too many people in the tire and garage business.
The marking represents a max pressure you "could" use if you had to carry a
max weight on that tire.
A typical text may read: " Max allowable weight 1020 lbs @ 35 psi
inflation". This sidewall pressure marking is NOT the pressure you would
normally inflate the tire to for road use!!!
By law, cars sold here after approx 1972 (?) must display a sticker telling
the tire pressures (cold temps.) for normal driving and normal loads. If the
mfr. wants some increase in pressure for heavy loads or high speed driving,
this must also be on the sticker !
Your BR60x13 certainly won't have normal footprint size nor flexible side
wall action at the pressures you have used.
I am rusty on this subject but will guess you need around 24 psi front and
22 psi rear (cold setting) to obtain proper "radial tire grip". Perhaps
some reader with current data or tire industry technical book can reply
here and supply the actual correct data if I am off a bit.
Also be aware....different brand tires as well as different construction
variations makes for different psi requirements (2 ply, vs. 4 ply , steel
vs nylon or rayon cord belts etc. etc.).
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