Learning DIY (String) self alignment checks and fix if required

[CtrMint]

Hi, 

I've set myself a target this winter to learn how to perform a self-alignment / alignment check using the string method in my garage.   My Caterham Seven purchase was always designed to see me grow as a driver and mechanically.  I am making progress if a little slow on the mechanical side. 

Since neither car needs much at present I'm going to attempt to learn DIY alignment.  As a result, I thought I'd start a thread.  I appreciate there is plenty of content on the internet already for this, however, none of the info I've found relates to a Seven and I'm sure there's some quirks or at least particular approaches relevant to a Seven which aren't present on tin tops.

For example, and correct me if I'm wrong, but the DeDion tube and thus rear wheel position can be offset by a tiny amount hence the need for washers.  Does this mean a lateral string run against the rear wheels can't be assumed to be equal either side of the car.   This leads to questions over the exact placement of a string box based on the assumed track width.

your help and involvement in this thread as I try to learn is most appreciated.

Thanks

Mark

 

[Wrightpayne]

The string is effectively a box around the car you measure from, set away from the wheels slightly. I've not done it, but if I did I would source two rods that I could accurately centre and fix to the chassis front and back that the string can be attached to. The chassis centre to string attachment point measurement, left and right is equal on both rods.

 

[Bricol]

You don't especially need it to be equal each side, but you do need each side parallel to each other and to the centre line of the car.   Your toe measurement is then simply the difference between string and front and rear of the wheel - even if each side is different.

[JonT]

I found this website a while ago, may help (or not!) with the calculations.

https://robrobinette.com/DIYAlignmentCalculator.htm

Is your garage floor perfectly flat? Don't forget to put enough ballast in the car too. I've done DIY toe alignment on mine, and it's very satisfying to get right (although I did assume the rear was square). Much easier than most cars as you can get at the toe links without needing to jack the car or take the wheels off.

 

[Molecular--Bob]

Might give this a go, should the ballasted ride height/rake be set before the tracking is looked at?

[7 wonders of the world]

Ballast should be applied before ANY suspension of steering geometry is checked.

Surface must be level or adjusted with shims to compensate.

Slip plates or plastic bags placed between tyre and floor to ease settlement 

Remember that adjusting one area will affect others too, they don't work in isolation

 

[garybee]

I have a couple of sections of nylon cord with a strong piece of elastic in the middle.  When hooked onto the car inboard of the front and rear wheels they stretch tight across the tyres and make toe alterations a very quick exercise.  Much easier than setting up a string box around the car.

[7 wonders of the world]

I made a pair of simple but adjustable (for calibration) laser pointers and reference flags in order to check the rear axle alignment, rear radius arms are adjustable to permit this in order to correct align the rear otherwise you can never get it set correctly.

I also did the same as garybee (used and old bike inner tube) with the cords hooked into a couple of lengths of angle ally for simple checking.

[CtrMint]

Thanks all, my focus at the moment is to accurately measure the current alignment, there's no handling issues, i'll worry about load in the car when I get around to any changes.

I must admit I'm not entirely sure Garybee is suggesting, could you expand.

Thanks

[garybee]

If you stretch a piece of string across the face of both wheels on one side of the car then it will contact each tyre at two points.   If not then the wheel must be angled (toe in or out).  If that piece of string has elastic keeping it tensioned then you can adjust the toe without constantly re-tensioning the string.  Does that make sense?

[Wrightpayne]

If I'm reading that correctly, will it only work on cars with widetrack front wishbones?

[Bricol]

I'm not so sure that works, easily, on anything that doesn't have exactly the same front and rear width on the outside of the tyres - any difference introduces an angle in the string - so it might possibly contact one end at two points, but only one point at the other if it is narrower . . .?

I aligned my integrale with fishing line on axle stands - seemed to work well,  Subsequent adjustments, front and rear, done with tracking guages, reversed at the rear (so indicating toe in was really tow out) - but I've been using a trackace lazer thingie for the last couple of years - again seems to work okay.

[ScottR400D]

A number of years ago I was running a Dallata F305/7 and had tracking bars that bolted to the rear wing mount and across the front of the tub with fishing line down each side. 

Those same bars, resting on axle stands now serve to check toe on the 7! 

As said, much easier with wide track but as long as the lines are the same distance from the centre of each wheel on both sides and from each rim of the rear wheel, assuming the rears are parallel and aligned straight, It’s near enough for most things. As long as you don’t keep walking into the hard to see line.......

Having said that I might well get a cheap aligner next year, just to be sure! 

[garybee]

"If I'm reading that correctly, will it only work on cars with widetrack front wishbones?"

"I'm not so sure that works, easily, on anything that doesn't have exactly the same front and rear width on the outside of the tyres"

I wrote a quick excel spreadsheet (well, the open office version because I'm cheap, the string should have told you that though) that takes the track difference into account.  You just measure between the string and the tyre chine (or between the string and a straight edge held on the chines for toe in) and it spits out the toe measurement.  So long as you understand trig' it's easy enough.  You can make this harder and add equipment but there's no need to.

Edit: you need to know/input the total width across the front and rear axle of course.

[BobM]

I've always used a pair of lengths of aluminium angle with marks or slots on them which I can clamp to front and rear of car at wheel centre height. An alternative is resting them on axle stands. I then set it up square on the car by measuring from each hub centre to make sure it's equal on each side. Front and rear measurements may well be different depending on whether rear is wider track. Once set up it's easy enough to measure toe from the rims. I had both the car and the angles marked so I could easily reposition them on the car.

I also use a spreadsheet for the calculations.

For camber I use a piece of wood with a bolt screwed into one end along with a spirit level.

[Wrightpayne]

I'm sure someone did corner weights on 4 sets of ikea bathroom scales! (Not joking!!)

I also remember reading Dave Jackson's set up technique basically set up heights and rake then winding up the rear o/s platform a few turns. Out on the road, jam on the brakes and if the fronts lock up at the same time the corner weights are about right. He wasn't too shabby in the sprint championship!! His post will be in the archives somewhere!

Ian

[ScottR400D]

Haha. Good luck with bathroom scales!

A year or two ago I was fed up with our bathroom scales because they seemed very inconsistent. 

I went on the hunt for better and tried dozens. None of them were any better than what we already had. Carry out 3 or 4 test weighs and get as many different readings. 

God knows what they’re like near their weight limits!

[Molecular--Bob]

Would a good approximation of a set up be achieved by measuring the spring seat heights on a car and then just transferring them to the car being set up? This would assume the same chassis age / dampers / engine type and driver weight.

[7 wonders of the world]

Mark,

The readings you will see un-ballasted will be meaningless.... unless you are just playing to see how to take them ..?

 

[CtrMint]

Even on the front toe?  I appreciate camber and balance will be impacted, but I didn't think my backside would effect the toe much?

[7 wonders of the world]

Even your racing snake physique will have and effect Mark  

No seriously, any movement in the suspension will alter rake, which affects castor camber and toe too although these are more greatly affected by compression of the suspension.

Toe is always the last thing to be adjusted since the others affect it.

...and then you need to consider bump steer.....

 

[Wrightpayne]

Ohh the rack spacer debate again - should I go for 6mm or 9?? 

[7 wonders of the world]

neither...... you should check it first....  

[Shortshift]

"neither...... you should check it first..."

Well yes, but then you run into the question of how just how much bump steer you should (or shouldn't) have...  Aiming for exactly zero (which is most improbable) may not be the best approach for road driving, and then you'll find some people suggesting it's best to avoid toe-in with bump at any cost, and others who say that a touch of toe-in towards the top of bump is a good thing. 

At the end of the day, reducing gross bump steer characteristics is a sensible approach to take (and is what likely happens when people talk about raising the rack on a S3 car by 7mm or 9mm) but where to stop and leave alone probably comes down to subjective assessment on road.

Worm, can-of, opening - just some words that come to mind.

James

[StevehS3]

#21

I have changed my ride height and rake quite a lot. Is that likely to have changed the castor, camber and toe very much? Do I need to get that re-checked?