Tracking using string kit - car not square

[Piston2022]

Guys

Have one of these alignment tools

https://www.murraymotorsport.com/b-g-racing-string...

From what I gathered the notch needs to match on one side front to rear . I used the first notch and it matches on one side but other side rear is out by few mm from the front to rear( see pic attached) . The pink is string kit and black is the car

This means my car is not square . Could it mean my frame is twisted or is it some car not squared if you measure from all corners?

Also can you do caster measurement with wheel not touching ground or weight needs to be on the car?

[Krikkit]

A couple of mm runout doesn't seem unreasonable, as long as you can consistently get it the same every time you fit the jig.

All the adjustments should be made with weight on the wheels, handbrake off and a good jiggle of the suspension to settle it after jacking. Not easy to get right, hence why a lot of people use setup pads with bearings under each wheel.

[Piston2022]

Well 3 corners are good but one is 10mm out so 1 cm seems a lot suggesting either tool is no good or can isn’t square

It is mx5 mazda

I didn’t know/ get your point around pad and bearing. Any pics of what you mean?

[Krikkit]

Usually it's used with the more sophisticated corner weighting gear and hub stands, e.g.

https://www.demon-tweeks.com/uk/b-g-racing-clubman...

https://www.demon-tweeks.com/uk/b-g-racing-scale-p...

https://www.demon-tweeks.com/uk/b-g-racing-4000kg-...

However, I've seen a couple of people with home made versions, and at some point I plan to make some of a similar type.

[Decky_Q]

Have you checked that both axles are the same width? Not unusual for cars to be wider at the rear.

[Liamjrhodes]

do you have any adjustable arms? its quite possible to get one side wound in or out further than the other so the wheel is straight but as you say the overall width isn't correct, i would start by measuring each arm to ensure they are all of a similar length if that are adjustable

[Bertrum]

This is an explanation of how you do it.


Car on it wheels on a flat surface, if you’ve recently jacked it up you need to roll it around a bit so it settles
Attach the brackets and poles and ensure the poles are level and parallel with the ground (this is important)
Put the strings on the same pole notches front and back, using the ones closest to the car.

Now the faff.

I always sort the front first. Measure off the flat of the wheel as near the centre of the wheel as possible.
Get the right and left hand measurement the same by moving the pole left or right . At this point you want it close not perfect.
Now do the same at the back using the same process with the rear pole.
Then repeat until you have the measurements the same left to right at the front and left to right at the back. Note the front and rear won’t be the same. This needs to be bang on .5mm out will make a difference.

For toe you measure off the rim to the string and adjust as required

Extra info

You want to adjust in the order of
Camber
Castor
Camber (again)
Toe

All need to be adjusted with the car on the ground. You have to do camber twice as you need equal front camber to calculate Castor, then the castor will change the camber IFYSWIM

I have been doing this with string and a camber gauge for about 20 years and can get it pretty much perfect when measured with laser kit after I’ve done it. Practice and all that

[Piston2022]

So you need to measure front hub distance to string and make sure front both side match and then same on rear? Instructions seems to suggests front and rear should match.

Are you referring to using no tools/ string line and stand or the machines kit I posted in the link?

This is a good write up


https://www.studiovrm.racing/post/unofficial-instr...

Edited by Piston2022 on Thursday 7th November 21:54

[Bertrum]

Yeah the Mazda axel widths are different front and back.

Using what you posted and variations of.

That write up misses levelling the bars, also contradicts itself saying the front and rear will be different and then the same…

Edited by Bertrum on Thursday 7th November 22:00