Rear Wheel Track

[Railroad]

Have other Mk IV builders found the rear tires not in line with the front? Specifically the drivers side rear tire is about 1/2 to 3/4" farther out of line with the front, when compared to the passenger side.
I am at go cart stage, all tires are plumb, no camber, 1/16th toe in, all 4 wheels.
When I pull a string front to rear on the axle center of each wheel the drivers side is out more than the passenger.
The distance between the tire and top of the rear shocks reflect this same difference.
Measuring off the main frame tube out to the string on both sides is the same.
Is this normal?

[AC Bill]

I wouldn't get to concerned at this point. Take it in for a professional four wheel alignment, at a reputable shop. There is enough adjustments on our roadsters, they will easily solve it.

[Railroad]

Thanks for the reply and I hope you are right.
I cannot see how the tire can move in and still have zero or near zero camber. There is no adjustment on the lower control arms.

[BadAsp427]

Speaking specifically for the rear wheels/tires only: There are a few things to consider. One is that your floor has to be 100% flat/level or your measurements could be a slight bit out of wack and that could make some of your measurements look different. Another is that when you say your toe is xxx what is that in relationship to, the frame or the opposite side wheel/tire. Think of this, if you have your drivers side toed in a factor of 1 (but think it is perfect straight) and then you set your toe of the passenger side in relations to that factor of 1 it would be off by that much... and you would crab walk down the street. Bottom line, get it all as close as you can with the string method and you'll be good to go for a few go cart drives. Then take it to a good laser alignment shop. There is only one thing that is difficult for them to understand and that is the camber adjustment on the rear. So just about anyone that has spent the money on a good laser rack should be able to get you a good 4 wheel alignment.

As far as using the string method, I found that if you run the string across the face of the rear tire all the way past the front of the car, and then measure the string distance to the 4" tube at the rear and again at the front until you have it exactly the same, you will be able to dial it in very close to dead straight. (the key in doing this is to be sure the string is just barely touching the front edge of the tire you are adjusting. if it is too too much, then your string is not really straight.) You will have to make an adjustment and then move the string at the front until it is just touching the front of your tire after each adjustment until you have equal measurements. I hope this makes since, I know what I'm trying to tell you, just not sure it is coming across.


On a side note; As for being able to turn your front wheels side to side, I've always used 3 sheets of wax paper or parchment paper stacked under each tire. Turns real easy..


And FWIW, there are many DIY alignment videos and articles to be found via google that could help you as well.

[phileas_fogg]

To amplify what BadAsp said about the floor being level, use a couple identical-length sockets, a toe bar (or aluminum 2"x4" from Home Depot or Lowes), and a level to figure out how much tilt there is to the floor. I place the sockets in the center of the contact patches, span the distance with my toe bar, and use the level to figure out how much plywood to put under the low wheel spot. I use a couple of strips of painter’s tape to make sure I got the wheels in the same spot as the sockets.

To measure the thrust angle, I use some blocks of wood to raise the toe bar over the side pipes, and press one end of the toe bar firmly against the rear tire (I made some witness marks on the bar so that I could repeat the placement of the bar).

IMG_5535 by jhsitton, on Flickr

IMG_5538 by jhsitton, on Flickr

At the front, I use a couple of carpenter squares to measure the distance from the toe bar to the 4” round tube.

IMG_5541 by jhsitton, on Flickr

I can’t get the two squares next to each other due to interference with the body, so I use the small ruler to span the small distance between them.

I was able to get the two sides to within 1/16” of each other while maintaining camber & toe in.


John

[SteveHsr]

Rear hubs ((wheel mounting surfaces) should be equidistant (centered) from chassis centerline and prpendicular to it. Any variation in track width from front to back occurs with axle widths and wheel widths and offset. Track width differences between front and rear is common.

[CraigS]

I really don't like the string method. First you have to set the string to the car = possible inprecision. Then you measure from string to wheel = more possible imprecision. I much prefer phileas fogg's method or mine using a laser pointer. I made up this scale which is identical on the other side. I lay it over just behind the front tire, slide it under the car and then tilt it up and push the little vertical piece against the 4 in frame tube.
IMG_20170419_160800746 by craig stuard, on Flickr
Then I cut a piece of wood to fit against the rim of the rear wheel, hold the laser against it and shoot it at the scale.
IMG_20170419_160647869 by craig stuard, on Flickr
I measure the total rear toe w/ another tool and then use this process to set the thrust line so the rear wheels are not crabbed to left or right.

[Railroad]

Thanks for all the help. Most of what has been said, I have done. I am just roughing in the alignment and will get it done at an alignment shop. I changed out my front tie rod ends, due to being uncomfortable with the length of thread engagement. After the new tie rod ends, putting the front toe back in the ball park, I used a string, level and tape. Everything is good, except the rear tires are not the same distance out from the car. As I stated in the first post, the 4" tube out to the string, is the same on both sides. I either have the passenger side rear tire in too close, or the drivers side rear tire out too much. I do not have the body on, so measuring is not compromised by adding blocks or set offs to clear the body.
I have not checked the floor, but is reasonably flat and level. I have a lift in the center of the floor and it did not require any shimming. The car has been leveled, working off the same floor, frame to floor at 4 corners.
Just wanted to be ready, if the alignment tech, says your wheels are spaced different????
Thanks,

[Railroad]

Rear hubs ((wheel mounting surfaces) should be equidistant (centered) from chassis centerline and prpendicular to it. Any variation in track width from front to back occurs with axle widths and wheel widths and offset. Track width differences between front and rear is common.

This is the logic, I was using and was hoping to hear that others noted the same results.
With the tires plumb, as indicated by a level and pulling a string through the center axis of the tires, alignment would have to extremely out to account for 1" of error.
The IRS lower control arms are a fixed length. This cannot be changed. Adjusting the upper control arm will move the tire out of plumb.
Again, I was hoping someone would say, mine was the same.
I guess, I will be moving on and trying to get the body on.

[BadAsp427]

Thanks for all the help. Most of what has been said, I have done. I am just roughing in the alignment and will get it done at an alignment shop. I changed out my front tie rod ends, due to being uncomfortable with the length of thread engagement. After the new tie rod ends, putting the front toe back in the ball park, I used a string, level and tape. Everything is good, except the rear tires are not the same distance out from the car. As I stated in the first post, the 4" tube out to the string, is the same on both sides. I either have the passenger side rear tire in too close, or the drivers side rear tire out too much.
Thanks,

Railroad,
I'm a little confused... I will measure mind for you since they are of the exact same vintage being a 20th.... You say that they tires are the exact same on both sides from the 4" tube so that tells me they are right on. But then you say they are not the same distance out from the car. Tell me the exact measurements you want and I'll try to get you those from mine. And just to confirm, you are talking about the rears, correct? Feel free to call me also... PM Sent.

[Railroad]

Thanks guys for replying and helping cure my problems. After Bad Asp offer, I went to the barn/shop to review, before calling him. I found the wheel in question to not be plumb after raising and lowering the car on a swing arm lift. I have double plastic sheets under the front tires, not the rear. MY BAD
The tire was about 1/8th of bubble off on a 2 foot level, from being plumb. As I raised and lowered the car, adjusting camber and then following it with a toe correction a few times. I could see the tire was moving where I thought it should be. I guess thinking the string down the side of the tires across the center hubs, toe and camber would not be critical to what I was seeing.
You can all sit back and take credit for making me go back and recheck my work.
Thanks for all the good tips, advise and offers of help. I will sleep better tonight.

[CraigS]

One thing to keep in mind is that, if you adjust camber, that changes the toe slightly.

[Railroad]

One thing to keep in mind is that, if you adjust camber, that changes the toe slightly.

I did find that and had to do multiple adjustments. Move one, check the other, adjust and repeat.
Thanks,,,,can't wait to get it on a machine with all the lasers, grids and etc.
It will be interesting to see how far off my string, level and tape work is off.

[walt mckenna]

You are getting close to the point where you will want to get a 4 wheel alignment, so I wouldn't be too concerned until you have that done. On my last alignment, the thrust angle was -.03 Percent. No adjustment to the rear was necessary to achieve that number, so the factory does a nice job of squaring those frames during fabrication.

[FLPBFoot]

You are getting close to the point where you will want to get a 4 wheel alignment, so I wouldn't be too concerned until you have that done. On my last alignment, the thrust angle was -.03 Percent. No adjustment to the rear was necessary to achieve that number, so the factory does a nice job of squaring those frames during fabrication.

Well my rear axel is out by .28 inches. Passenger is forward 0.12 in and driver is back -0.16 in. Only way to fix it is get the Breeze rod end lower control arm kit which gives thrust angle adjustment. Question: is this 0.26 in enough to worry about? Seems a bit much and don’t want to wear tires.

[walt mckenna]

Well my rear axel is out by .28 inches. Passenger is forward 0.12 in and driver is back -0.16 in. Only way to fix it is get the Breeze rod end lower control arm kit which gives thrust angle adjustment. Question: is this 0.26 in enough to worry about? Seems a bit much and don’t want to wear tires.

I believe those numbers will give you + thrust angle, but I don't know what those numbers convert to in percentage. On my alignment sheet, the tolerance of +/- .25 percent was given as acceptable. The ideal percentage is 0 and if mine had not been as close as it was, I would have gone the Breeze route.