Don Terrill’s Speed-Talk

ijames wrote:

Belgian1979 wrote:I have yet another question. After a small testdrive, I noticed the car was nervous with regards to steering input. Could this be caused by too little toe in or by too much ?

If the problem is toein, too little will make it nervous, way too little will make it do donuts by itself, and too much will just scrub rubber off the front tires and wear them out faster and faster as you go to more and more toein.

I was thinking along the same lines. I will put in some more toe in and see what it does.

I have a newer model without the strings and have used it quite a bit. If after the heads are installed the car is rolled any amount without the heads staying level it will throw your toe off. Were the heads compensated on the wheels prior to alignment? Too much toe will just bind up the front but shouldn't make it darty, I would guess your toe is off. Straight ahead is still not too bad, but toe out could make it darty. Too little caster will make self centering go away and you will have to steer into and out of a corner. FYI, tightening the nut on the steering arm will change toe .010 on my stuff, so I have to lead this a bit.

mbrooks wrote:I have a newer model without the strings and have used it quite a bit. If after the heads are installed the car is rolled any amount without the heads staying level it will throw your toe off. Were the heads compensated on the wheels prior to alignment? Too much toe will just bind up the front but shouldn't make it darty, I would guess your toe is off. Straight ahead is still not too bad, but toe out could make it darty. Too little caster will make self centering go away and you will have to steer into and out of a corner. FYI, tightening the nut on the steering arm will change toe .010 on my stuff, so I have to lead this a bit.

Handbrake was on all the time, so I asssume it was not rolling. I didn't compensate the heads on the wheel as for some reason the front heads button will not work. Steering wheel was block during setting toe as per instructions.

I redid the alignment, but it didn't seem to come back to the same measurements. The distance from the rear of the front rims to the string was the same left to right and also at the front of the rear rims. So I assume at least they have the same amount of toe.

Toe at the rear is 1/8 at the front a tad more than 1/32 (0.04")

The caster is at 5°34' left, 5° 37' right. Cannot get them any closer as the shims are not that thin.

Cranking in a bit more toe and retesting is a good and rather easy suggestion. If this cures the problem you might want to check camber in that positive camber can cause darting that toe-in can compensate for. Toe out and positive camber cause an unsteady condition in that the more weighted tire turns the car to the weighted side which in turn causes to opposite tire to become the weighted and controlling tire, etcetera.

I have a feeling like I'm running after my own tail. Hm

When I have my buddy check out my alignment, I sit in the car.... Even with a perfect alignment, I still usually end up adding a 1/4 to a 1/2 turn toe-in, I go by how the car feels..

I'd love to have my own rack...

pitts64 wrote:When I have my buddy check out my alignment, I sit in the car.... Even with a perfect alignment, I still usually end up adding a 1/4 to a 1/2 turn toe-in, I go by how the car feels..

I'd love to have my own rack...

i have enough old weights and lead to put a driver and passenger in mine. picked my hunter d111 up for $500.

Belgian1979 wrote:

flyingwedge wrote:>>Mr. 1979, you have checked and negated bump steer, throughout suspension travel range ? Scrub radius is acceptable ? Eccessive Ackerman can act "darty". Good Luck, flyingwedge.

concerning bump steer, it still is stock and on a 1979 corvette there is actually some bump steer. To get that minimized would mean changing/modifying the center steering link, which is not possible.

Wait a minute.
Youve radically changed the caster... now you MUST correct the bumpsteer.

You need to learn the proper way of altering your tie rod end pivots.

My Belgian friend, can you expand on how the car feels to you? At what speeds does it feel not right? What are you asking of it and how is it responding?

As stated, caster changes bump steer and makes the car more responsive or ''darty''.On my dirt l/m we set the l/f straight and all the toe out in the r/f.

To expand on earlier posts, increasing caster above stock has the secondary effect with a front steer system of raising the outer tie rod/steering arm joint, which in turn creates more toe-in in bump. (Worse than toe-out as it causes unstable roll oversteer.)
On our tube frame road racer, we got the bump steer over 3" of travel down to ~ 0.010", then later backed off the caster from 5° to 2° due to the excessive effort with the unassisted steering. Problem was we forgot to go back and re-do bump steer. When we checked, it was almost 0.500" over 3".

Toe in aids stability while toe out makes for searching back and forth as first one wheel and then the other becomes the dominant steering wheel.

Greenwood was a pretty successful Corvette racer.

I've long been struck by His comments about the suitability of Stock suspension bushings and front OEM geometry, at least for the best tires and wheels of the period.
http://www.corvettefaq.com/c3/vip.pdf

Recommended alignment specs on page 47.

The use of the wheel rim bead edge as an alignment reference strikes me as mighty risky, unless the axial/lateral runout is checked, and excellent, or compensated for.
I'd say if the desired toe-in is in the range of 0.125", any wheel's runout would have to verified be less than 0.010" .

The front alignment is actually set off the rear the rear axle must be square with the chassis

Hey Belgian1979, any further observations on the Corvette's handling?