View Single Post
Walt Fricke Walt Fricke is offline
Walt Fricke's Avatar
Join Date: May 2004
Location: Boulder, Colorado
Posts: 6,555
Porsche Crest

Tim L:

Great idea!! Following someone else's idea, I tried something like this. It involved shooting the laser attached parallel to the rim to the garage floor behind and in front for a set distance, marking the points, and measuring across under the car. He had this down pat, I gather. I never did - my floor is rough so I had to put tape down to make the marks, etc. Plus, following the other guy's lead I made a sort of three legged standoff holder, but didn't make things cleverly enough so I could bungee it to the rims. His system had merit, but your system sounds a lot simpler. Especially if, like me, you like to run zero toe. No math with that.

Normal steering geometry guarantees that when you turn the front wheels, one will turn farther than the other. One virtue of the string method is that you can pretty much insure that the wheels are pointing straight ahead when you measure - do a preliminary measurement and then set them so they are equal for the final measurement. Maybe getting the steering wheel straight, or eyeballing the wheels, gets you close enough anyway.


As to cosines and such, I found that if I taped a bubble level (the kind you hang on a string does the trick) to a chunk of old steel tape, I could get it pretty level without much difficulty and avoid this problem. I commend that to anyone using lasers or strings and measuring to rims.

I suppose I could attach one of these to a dial or digital caliper (a vernier would be a pain) as well, but it hadnít occurred to me to try to get readings in the thousandths of an inch. Shoot, I bought depth mikes for cam chain wheel parallelism measurements - I could use those. But my instincts tell me that a millimeter rule ought to get things close enough. Havenít done the math on that one, though. Bet you have.

Randy and others:

On the question of tire or other shop professional alignment rigs and our DIY futzing, in general I see no reason that the methods used should not produce equally accurate results. IF - things are set up right - the floor/pavement is, if not exactly level, at least all in one plane. If you don't use turn plates (and what home brew guy is going to have those), you roll the car around between attempts. I think it is probably easier for us to make mistakes than a pro, and especially than a pro with a machine.

If the Hunter and other machines use, basically, a laser distance measuring system (glorified toe plate but mounted on the rim), then they ought not to be much better than strings. But I think they work by measuring where a beam shot from one side lands on a receiver on the other side, the beam being perpendicular and the plate being parallel to the rim. Or there is only a mirror on one side, and the beam comes back and the difference is measured there. Dunlop optical systems maybe worked this way without the lasers and electronic readouts? That should have an inherent resolution better than strings Iíd suspect, since you have about a wheelbase or 2xwheelbase for the radius in your equation instead of 15-18". Something like this is going on, since many of us have trouble getting an alignment shop to do our cars because they are so low these things canít see each other.

I do wonder how stringing (properly done) compares with toe plates. By toe plate I mean those stiff flat aluminum sheets with a slot or two cut in each end. Stand the plate up against a tire on each side, run a tape measure through each slot (or move from slot to slot), and compare readings = total toe. Looks to be a two person job, but about the fastest going, so great for the track. If the sidewalls are irregular or bulgy or something, things will be off. So I wonder how well it usually compares.

For camber I sure like my digital level. Let's say I determine I want to reduce camber by X on one side. Jack up the car on that side, pull a rim, and loosen things just enough. Measure the camber (doesn't matter what it is at full droop). Adjust watching the readings change until you have changed it by X. Tighten up, put rim back on, lower away, and recheck. There might be geometric differences such that a half degree change at full droop is not quite half a degree at normal ride height, but my suspicion is that it has to be small.

I donít have Tim Tís extensive race prep/support experience, but I know my DIY methods, even with less than perfect working surfaces and my tendency to call close enough good enough, do get my own cars to where they handle as I expect and have the tires wear reasonably (with lots of camber for the track tires, you canít expect even wear on the street, seems to me).

Dontcha love those fishing reels in Toddís #94 picture? But unless those guys have a centerline or other reference mark for their aluminum tubes, they have some of the setup hassles of the jack stand method (at least they know they have a parallelogram at a minimum, if not a rectangle).

I think guys with Smart Strings have some of that - I saw one used at a track and there was a fair amount of time spent measuring out from hubs, adjusting, remeasuring, etc. to get it set up. After that, piece of cake. And you can move the car.

Old 02-14-2007, 07:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #45 (permalink)