FORMULAVEE.ORG

Hi,

Could somebody explain how to square up a car from scratch? Assume all wheels were off, and the trailing arms and tie rods were removed.

I have a Lynx B that has been modified over the years and as a result the frame is not straight, one corner seems higher by 1/2". I'm told this has little effect on handling because I run a zero roll suspension.
When driving the car, I find it to switch very fast from understeering on corner entry to oversteering while cornering.I think this may have something to do with toe changes. I could be wrong but regardless, I need to properly square the car, and this has been tricky as the frame is not square.

This is what I tried. I started with the rear wheels to get a baseline, since the front wheels can be oriented and complicate the process. Using toe plates, I set the toe at the rear making sure each rear wheel measurement (at the front of the tire) is equidistant to the bottom frame member on the same side. I thought this would be a good way to generate a reference alignment, as you can't do this with the front wheels since they can be oriented. I then switched to the front where I tried eyeballing when the wheels look straight. I ran a line around all 4 tires, and adjusted the front tie rods until I had the impression each front tire was contacting the line in a similar way. I would then adjust toe at the front.

Doing this, I always end up noticing that the rear right wheel is always in by 1/2" compared to the rear left.

At this point I came to the conclusion that I could never win with this frame, played a bit with the rear right wheel so it would point a bit less to the inside and went racing.

Any advice on how to properly set toe from scratch will be greatly appreciated.

Another question related to front toe: I measured the variation of the front toe vs ride height. By using shims I could get the front to develop either positive or negative toe under braking, same thing for accelerating.
By setting the front so I get toe in under breaking, I guess I end up with a car more stable under braking, but harder to get into the corner (until the nose comes back up). By developing negative toe under breaking I guess the car gets a bit less stable, but I get more byte in the corner on entry.
Is there a consensus on where you want to setup your front end in terms of bump steer, or is it a driver preference?
The same goes for the rear, but there is little I can do on my Lynx. For now I am setup to specify camber, whatever the toe variations are at this ride height.


Jean

I prefer to make sure the four tires are traveling on an identical path rather than basing everything on the chassis or centerline of the car. Since the vees have virtually no adjustments to square up a car, you're pretty much locked in to what you have. Your ride height difference is another issue. Either a component is installed wrong, a H-beam or tranny, or the frame is twisted. Zero roll can compensate for some of that but if your car is not reacting the same in both directions, then you have to chase down the source and fix it.

Instead of stringing a car off a fixture on the frame, I wrap a string around the 4 tires to make sure all four tires are all pointing in the same direction. By setting the toe in, front and back, with the distances from the tires to the string being the same from side to side, you will have the tires going in the same direction. Since the front wheel base is wider, I use a spark plug to space out the string. You will be measuring the distance from the rear of the front tires and the front of the rear tires. I temporarily equalize the front measurement then set the rear toe. The front will come later. Since all vees are virtually the same, when the toe is around 0 to 1/8, there should be somewhere between 6 and 10 mm from the tire to the string on both sides on the rear tires. The I go to the front and set the tow, once again, with the measurement to the string being the same. The fronts will be from 10 to 15mm depending on tire size. If you try to correct the wheelbase with the rear toe, the rear will be pointing off to one side. If the wheel base is off, side to side, it means the tires are creating a parallelagram. In this case, the only option you have is to shim the H beam on the short side. Hope this helps.

Call Brian. he can walk you through it.

Also: Here's a good reference from Jim at SR.
http://www.sracing.com/Tech/veetech.htm

smsazzy wrote:Also: Here's a good reference from Jim at SR.
http://www.sracing.com/Tech/veetech.htm

Wow. I just read that again. It IS pretty good isn't it ?

Yea really, Jim's entire book is really worthwhile. One thing is that I prefer to use the scribe method on the tire instead of using the rim or tire edge. It will eliminate any run out of the wheel and tire and give you a honest straight line.

Stupid question I'm sure, but what do you guys use to scribe a line? I find that my tires usually have enough crap picked up (small stones, rubber bits, etc..) that if I try to use something fine enough, it'll be bouncing all over the place and the line doesn't always connect to the starting point hehe..

Maybe I should just try cleaning up my tires a bit....

Tiago: Just clean the tires off first.

Also, when scribing, dont push so hard that a rock will bump the scribe out. A nice light pressure works best. Use an awl or something pointed and have at it. A small phillips even works in a pinch.

I can do an align by eye and get dam close. Formula ford guys used to use a jack handle on the rear uprights and the tires and "shoot" the front end..you do the same on a Vee. Looking down the inside of the rear tires you should see the same spot on either side of the front beam. (I forget what the spot is..)

Forget wheelbase..if it's within a 1/2" your ok.

Hi:

Thanks for the replies.

Brian: I used a string around all 4 corners right away and got the car pretty square. Typically I would first try to get the rear aligned then use the string to get the front square too. I guess this wasn't very effective.

The car measures square now, I even got to fix the bump steer. A couple of years ago I upgraded to a taller front roll hoop which increased the angle of the steering column from the horizontal (I run with a straight steering column). As a consequence the Pittman arm angled increased which translated into lots of bump steer (I have quick steer spindles). I never bothered and/or noticed until last race where it became obvious something was wrong with the front end of the car.
Bump steer seems very limited now.

Jean

Vees have limited opportunities to to reduce bump steer. I try to have the tie rods level and parallel to the ground at ride height. If you have a lot of bump steer, locating the steering arm pickup slightly lower than the pitman arm end, the car will increase toe in under braking. You really don't want a car going to toe out under braking.

It is OK to do the eyball thing if the chassis isn't square to get the car to go somewhat straight but if the chassis was welded up out of square you will have differences in wheel base from side to side. At the Glen last weekend I was helping a new guy trying to get his car aligned and the wheel base was over 1" difference from side to side and I noticed that the front of the frame was visibly out of square. This is the second Protoform that I have seen this way. If you want the car square and I thing it should be you need to mark the center of the chassis at the front and rear and use a straight edge or string on those points and then using shims make the front beam square with the senterline of the chassis. After doing this you will always be able to align the car and have the wheel base the same on both sides when done.

I always center up the front wheels and then do the front alignment first. Then I measure the wheel base next off of the top link pin to front of the axle tube and after checking the rear toe make the required adjustments to end up with the correct toe and equall wheel base on both sides in the rear. This way the car will really be square and track straight down the road.

If you have different wheel base measurements when the car is aligned straight you proabaly have a car that was not square when made or bent or a bent front beam.

Ed

Ed's correct.

Alignment on a Vee is kinda goofy, and I've seen some Vees driven by knowledgeable racers where the alignment was unbelieveably screwed up, in an effort to get the wheelbase the same. Of course the object is to get everything headed in the same direction, and shimming the beam can cure a variety of ills caused by either damage or poor build quality, including wheelbase issues. However, shimming the beam pushes the envelop for many home based drivers.

I can't tell you the number of arguments I've gotten in over the process of shimming the link pins, much less getting into bump steer or ackermann, but that's another issue.............