C3 Alignment specs

[Kevin #38315]

I'm sure this has been asked before, but I'm having trouble finding it in the archives.

I have a 70 LT-1 Roadster with manual steering on new 225/60-16 tires on new 16" rallyes. The car is a nice-weather-only driver, and sometimes I like to have fun cornering. I REALLY dislike oversteer though.

In the recent Restorer article on performance tires, it suggests changes to the alignment specs for better handling. I would think there might also be changes to accomodate radial tires over the bias tires of the era.

Service Manual calls for:
Spec Front Rear
Toe 3/16 to 5/16 1/32 to 3/32(per wheel)
Caster pos 1 +- .5deg
Camber pos3/4 +/- .5deg neg7/8 +/- .5deg

From the suggestions in the Restorer article, I'd get:
Spec Front Rear
Toe 1/16 1/16(per wheel??)
Caster pos 1.5deg
Camber neg 1/2 +/- .5deg neg 1.0 +/- ?

Am I interperting this right? Is the rear Toe "per wheel"? Are there any other changes you'd suggest?

Thanks,

Kevin

[Clem Z.]

Re: C3 Alignment specs

go to www.vettebrakes.com/align.htm for some sugguestions

[Duke W.]

Re: C3 Alignment specs

The toe setting of 1/16" toe-in front and rear is TOTAL toe-in as stated in the article, so divide by one-half for toe in per wheel, which is how most modern alignment machines read. This reduction of toe-in from OEM spec is specific to radial tires.

Caster and camber (and toe) are "chassis tuning" parameters, just as initial timing and dwell angle are engine tuning parameters. The factory specs represent a nominal setting for "average" driving. A more performance oriented alignment "tune" would be to bias camber in the negative direction from OEM spec and add more caster.

Also, if your car exhibits oversteer, install hard urethane bushings in the front anti-roll bar links (the OEM rubber pillow block bushings are okay - no need to change them). Hard link bushings reduce compliance, which makes the front bar more effective and will increase understeer at the limit, which will mitigate any transition to oversteer.

With your tire set up I would recommend -1 degree rear camber and front camber of up to -1 degree WITH hard link bushings and increase caster to two degrees. If you have power steering front caster can be increased to 2.5 degrees.

These settings should improve steering response and on-center feel and ultimate grip at the limit. If the car still exhibits oversteer, back off the front negative camber to -1/2 or zero. In otherwords, use a single variable, the front camber setting, to fine tune the chassis to achieve the best handling. Chassis tuning is somewhat a matter of trial and error to find a setup that is compatible with driver preference.

For any given tire and chassis setup, Sharks should not have as much tendency to oversteer as Sting Rays. This is because GM lowered the rear roll center, via redesigning the rear strut rod bracket, which lowered the inboard strut rod pivot point. A lower rear roll center reduces rear roll stiffness, so with a given spring, bar, and alignment setup, a Shark should have less proclivity to snap into oversteer in limit handling manuevers.

Duke

[Kevin #38315]

Re: C3 Alignment specs

Well, after 19 days on order, and supposedly being "shipped" last week, I found out my 16" Rallyes don't exist.

I really need to change the rubber, so I'm back to 15" tires. I should have the 225/70-15 Firestone PV-41's (as recommended in Restorer) on tomorrow.

Does this change your recommendations at all?

Thanks again

Kevin

[Frank H.]

Re: C3 Alignment specs

Look at the 82 corvettes alignment specs, as these where the last biggist radial tired full frame corvettes, they work good on C3 and C2 even with smaller tires.For driving pleasure not racing
I set my 67s front at 2 1/2 degrees caster and 0 camber and the rear at o camber and the min toe. I did the same on a 64 coupe last summer and a 66 ragtop last week and both owners say the cars are easier to drive,but being fair both cars got all new suspension also.
Years ago I had a fat tired 70 LT-1 coupe that was all over the road until I aligned it using different specs about five times and thats where it ended up.
With the higher caster(less driver feel) the bumps and grooves in the road don't tranmit to the steering wheel as hard and the steering wheel returns to center faster,and with 0 camber it keeps the whole tire in contact with the ground and lets the radial tires do the work,you need to watch tires to get the best tire pressure for each end.
Setting the caster higher also moves the tire back in the wheelwell slightly
which has not been a problem on any of the cars I,ve seen.

[Duke W.]

Re: C3 Alignment specs

Good tire choice! The alignment specs I recommended should work well with them. Let us know how you like those tires.

Duke