Caster/Toe Setting

How much positive caster should I have for a drag car? It may see speeds of around 120 MPH. Also, what about toe settings?

If it's drag only, I usually like to really lay them back, around 5 to 7 degrees with 1/16-1/8 toe in. Gives good high speed stability and minimal rolling resistance from wheel scrub.

Thanks Dave, I need some kind of a level tool, with degree wheel attached. Suggestions?

Find one of your local dirt trackers or road racers and borrow his caster/camber gauge....Could do it with a straight edge and an angle finder with a good method of attachment to the hub.....just have to use a clamp fixture of some sort to prevent the hub from turning. Used to have one years ago before the good gauges came out. Now I've gotten fancy and use the gauge and some turn plates salvaged from an alignment shop that went out of business. Never underestimate the powers of scrounging!!!!!!!

I thought I could go simple and use a magnetic angle finder after the axle is hung from the leafs and placed on jack stands. I could place the angle finder on the machined flat spot where the King Pin goes through and I'd know how much the axle is kicked back. This may be too simple, but since it's not ball joint type, it might work well.

The magnetic angle finder on a flat spot will work OK. That's what I used on our Super Comp car back in the day. I had a little more caster, (10 -12, as I remember) but that was a 180 mph car.

I have this cheapy from Speedway and it does an acceptable job.

http://www.speedwaymotors.com/p/2699...caster%20gauge

As far as toe gauges, you can make one fairly easily with a couple of pieces of material - mine is a 1/8"(I think - it's on loan-out) plate about 4" longer then the diameter of the tire and the height of spindle centerline. Set them against the outer sides of each wheel and carefully measure with a good tape measure, just touching the front and rear of the tire. The floor needs to be flat and the plates need to be well anchored against movement. Rude and crude, but watch the NA$CAR pits after someone has dinged the wall and you will see exactly the same kind of contraption.:D

I take a plumb bob and drop a mark to the floor on the CL of each tire, front and rear, then I measure between the marks with a steel rule.

I've also jacked each side and scribed a line somewhere near the middle of the tread and measured front and back of the tire, again at the center line of the spindle.

Any of these tape methods 'assumes' that you have straight line access between the tires and missing any engine or chassis obstructions. If there are obstructions, then you have to make up another tool, usually a rigid tram bar with extensions/pointers, again to the CL of the spindle - like the old time alignment shops did before computers and lasers.:eek: :whacked: :D

A couple of 1 1/2" x 1 1/2" x 36" pieces of angle aluminum - or steel - set on a couple of short 2 x 4 blocks that are set on edge so as to get the angle aluminum pieces up off the floor away from the bulge at the bottom of the tire work well.

Some guys drill the angles and bungee em in place.
Measure the angles transversely, equidistant from the center of the wheel hub fore & aft.
Just barely ahead of the tire's extreme fore and aft dimension horizontally works well.

I run 1/16" - 3/32" toe-in on my street driven 32 roadster.

About 6 degrees of caster makes for good handling and easy steering.
Much more than 6 degrees makes the low speed steering a little harder as far as input effort goes.
Not a problem on a comp car.

I did some research on dry lakes/Bonneville roadsters a couple years back when I started building a 31 roadster on a 32 frame for the lakes.
Some reported that 12 degrees was the way to go and others said 8 - 10 degrees.
I built the chassis for 8 degrees with room for more if necessary.
It had the capability of going back to 4 degrees if desired and that turned out handy when I decided to put the roadster on the street with 6 degrees instead of running it at the lakes or dragstrip.

Many - if not most - garage floors are tilted about 1 degree toward the door so water will run out.
Since you'll be measuring caster against a flat surface and not the flat area of the frame rails you may want to account for that by doing a 180 with the car and shooting the caster again.

Fwiw - I use one of the circular angle protractors, mine from Sears and about #10. a few years back.
They work well.

If you want real precise, get one of the shorter digital levels and make a simple aluminum block so you can adapt the digitial level to the kingpin boss.

The digital levels measure to seconds of arc.
I have a 4' model originally purchased for a plane I was building and it turned out very handy for setting up the 3 frame rails.

The shorter levels can be rubber banded to a straight piece of aluminum channel the length you desire.
That's not a bad way to go, the 4' levels are to an extent useless for most car building stuff.

Then again, there's always the hacksaw....