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Playing with string - wheel alignment


Shortshift

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Fishing line, rather than string, actually.  And I'm not sure if people are nowadays familiar with this technique or not.  If not, the pictures below might be useful.

It all took a bit of time to set up (the main challenge was finding two bars of adequate length to span the width of the car plus a bit) but after a some fiddly setting-up I was pleased with the repeatability and apparent accuracy of the method.  It's some time since I had done this!

I disagree with much of the advice that you often see online about this technique, which in my view often fails to take into account the errors that can creep in where the front and rear tracks (and wheel widths, come to that) are different.  I believe it's essential to take the time to have a pukka rectangular box correctly - squarely - arranged around the car, with the distance between the lines at the front being exactly the same as the width at the rear.

Anyway, the CSR has independent rear suspension that can be adjusted individually, side-by-side, for rear wheel toe-in and toe-out.  This means that you cannot rely on the rear wheels being square to the the vehicle axes and you have to use the hub centres as the basis for ensuring that the fishing line rectangle is properly arranged around the car - with sides that are parallel to each other as well as to the centre-line of vehicle.  But with the set-up completed, I was able to get the same alignment results time and time again to an accuracy of around 0.5mm. 

For info, I set the fronts to just a smidge of toe-in (probably tracking parallel when the car is in motion) and the factory specified 1.5 mm of toe-in on each side at the rear.  All this for road use only - I am not intending to track this car, where a touch of toe-out at the front would likely aid initial turn-in but at the expense of on-road tramlining and sensitivity.

Took a bit of time and effort to get it right but the final outcome was quite a change from where the car was at the start of the work - and this time the steering rack is also centralised when the steering wheel is in the straight-ahead position.

James

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IMG_0605.thumb.jpeg.96118c524dddc0d04a95c27bfa9fc8af.jpeg 

Align.thumb.jpg.bbad3612b98c361dcc2c32e2b18b5369.jpg

 

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Or kick the fishing line!

I have exactly the same set up. Bars that I made back in 2012 when we were racing an F3 Dallara. Only difference is my bars still have the brackets that connected to the front and rear of the F3 car. 

It’s accurate enough for setting toe IMO, which fit me these days is just the front and yes, you do need the bars to be parallel!

I now have ball jointed top joints so it’s a few minutes work to go from parallel/low camber to toe out/higher camber for the track, with one adjustment each side. 

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Looks like you have that very well set up *smile*

I've fixed two laser spirit levels to a plank of wood, one with a pivot mount and adjustment bolt. I place it close to the wall to mark where the beams hit and then move it three feet away to check the beams are parallel. I then place it on blocks a measured distance in front of the front wheels. And used a marked piece of (high tech) cardboard to read the distance of beam to the wheel rims. I set the front rims parallel, because that's how Caterham set them initially and it drives nicely, plus it is easier *smile*

The disadvantage over your system is I suspect it wouldn't be accurate enough to do all four wheels (lucky I have an S3).

It does have the advantage of being quick to set up, and after adjusting, I can roll the car backwards and forwards to get the suspension settled again without disturbing the beams.

Duncan

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I made lasers and rear flags for checking and adjusting rear axle alignment of the DD to the chassis, you can use these to centralise the steering and for bump steer to.

Calibration is easy via a 2m length of ally box and clamp one either side to measure the beam.

For alignment these are simple and very repeatable.

https://www.demon-tweeks.com/uk/trackace-laser-wheel-alignment-gauge-t-atag01/

 

Again all checks and adjustments must be done with the car ballasted to the appropriate level otherwise your wasting your time.

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At the rear you can use the rear silencer fixing points to make a fixed support for the rear square tube, in that tube you slide another tube for the control line , at the end of the smaller bar you cut a slot so that the line doesn't move. This smaller bar is fixed with a butterfly bolt. At the front use ARB blocks on the lower wishbone to fix the support tube. And if you are in a hurry to check the rear  on a live axle then clamp a 2m square tube to the rear disc both sides and measure toward the chassis front and back.

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I have also modified the original fishing line method. I use a couple of laser pointers inside aluminium tubes with two sliding nylon blocks that slide along the tube that can adjust for wheel size. The blocks then rest against the wheel rim and are held against the wheel with a couple of bungee cords. The target is a length of aluminium channel on axle stands at the other end of the vehicle. Cost about $80 for the bits and pieces.

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  • 1 month later...

Two key things I have found when doing an alignment, no matter which method or device is used to measure:

- Mark 4 wheel positions on the floor with tape and then use a spirit level with a long straight edge to confirm they are all level with each other, using shims of a suitable material to put under a tyre in a low spot to make up for a floor that isn't level.

- To ensure there is no lateral binding of the suspension I use two pads of wood 40mm thick under the wheels on one side of the vehicle and two pieces of plywood and 4 short pieces of 25mm dowels (totalling 40mm thick) under the wheels on the other side of the vehicle. This allows the suspension and track rods to be adjusted and settled with no lateral binding due to the plywood rolling on the dowels, without having to roll the car backwards and forwards several times after an adjustment.

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  • 4 months later...
  • Leadership Team

I would think so - so long as you ensure that the edge of the phone sits correctly on the bridge piece you're talking about (thinking about buttons sticking out the side of the phone causing it not to sit 'true').  Maybe fasten (cable ties?) the phone to the timber piece.  And put a screw in close to each end of the piece of timber so that the screw head will sit accurately on the area of flat just inboard (radially) from the edge of the rim.  You can then use that to adjust the device to ensure it's properly calibrated for zero/ninety degrees, etc.

There - wood, cable ties and screws; a pukka engineered solution!

James

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