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The above chart clearly shows the caster settings for our cars.  The amount of caster is commonly checked by putting the front wheels on turntables and turning the wheel outward 20 degrees and setting the gauge to zero, then turning the wheel inward to 20 degrees to find actual caster for that wheel.  Does the above chart assume that caster is checked with 40 degrees total rotation of the wheel?


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Thanks Tony. I already have a magnetic bubble level. In Longacre’s instructions they are sayings to use a total of 40 degrees rotation (20 to the right and then 20 to the left). Thus, it looks like the chart above is assuming 40 degrees rotation.

From Longacre:

To read CASTER first turn the wheels 20º to the right when setting the RF and to the left when setting LF. If you don't have a set of turn plates you can use the angles machined on the corners of the gauge as a reference. Turn the wheels until the angle is parallel to the side of the car. Rotate the gauge until it is level. Turn the knurled nob in the center until the center caster vial reads 0º. Now turn the wheels back past center to 20º the opposite way - for a total of 40º.

Thank you both.

I am getting setup to modify the front upper a-arms in order to get more positive caster and have read the threads on this forum about the process of doing so.  I am currently trying to get precise measurements of caster on the car before I cut, bend, and weld my a-arms.  I am looking forward to getting better straight line handling and centering of the car on the freeway.  I will probably follow this effort with spacers for the steering rack to reduce bump steer.  That way I am only making one change at a time.

I completed the modification to the upper front a-arms to get more caster.  This modification allows for the addition of a 1/2" shim.  The next steps are to reassemble the a-arms, measure the new amount of caster, and test drive the car.  I can move shims around to get a little less caster if needed.  Electric power steering from SACC should arrive in April.

In the photo below you can see that the top bar was removed by cutting the welds, flattened in a press, and then welded back in place.



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I had 245-50 x 15s on 8" Campys touch the left front cowl drain pipe (full lock turns & hard braking when autocrossing ). Partially flattened an area about 3" long with a hammer/5 minutes.

Also had the right front tire touch the wiper motor shield in full lock/hard  braking turns. Had to modify the shield at one bend to clear. This is with 4-1/2 degrees of caster and no shock spacers. No further physical contact in 15 yrs.

Wiper shield-to-tire contact is so common, Larry Stock at PPC now offers cleaned & painted pre-flattened wiper shields on an exchange basis.

All you need in the front are 225-50-15's. They add to the Italian go-cart concept and you won't have any interferences anywhere.

Probably all that you need for high speed stability is 4-1/2 degrees like Boss has but with the power steering, you can run stock since it will add the stability without the increased caster.

If your feet are too big you may find a little interference to the PS unit. It's really close under there on the clutch side. Driving shoes are a must.

Anything over 11-1/2's, forget about it.

Last edited by panteradoug
@panteradoug posted:

I think that you are going to want power steering...and you may have this little issue with the tires hitting the fenders, but just when you turn?

The modified upper a-arms are now installed and the ball joints are shimmed all the way to the back.  I test drove the car and there is not any tire rub on either side while fully locking the rack and doing a sharp u-turn.  You can see the additional 1/2" shim below.  I measured 6.25 degrees positive caster.



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It does not have power steering yet.  I need to drive it more to get a better feeling of the car with the increased caster.  My initial impression is that the steering is heavier but not sure yet if it actually needs power assist.  I will take it out on the freeway in couple of days and try to get a get a better understanding of the change.  Before the caster change, the car tracked well (I could take my hands off the wheel when driving straight) but the car did not return to center well when turning or changing lanes at speed.

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