Shite tracking

[dieselnutjob]

I recently replaced the front right wishbone, lower balljoint and wheel bearing following a knock on my Pug 607.

The tracking was clearly way off from how badly it drove, but I didn't want to pay for wheel alignment as I will have to change steering rack bellows and the balljoint on the other side within the next few weeks.

According to t'internet the front and rear track is the same whilst the owners manual says something like 5mm narrower at the back, so not a lot then.

Therefore I just got a straight edge and adjusted it so the each front wheel lines up with the back. A bit of school boy trigonometry tells me that if I am 1 degree out then that would be about 8cm over the 4.8m wheelbase and I'm sure I got it much closer than that. (tan 1) X 4800 = 83.8

The thing is, it seems to drive quite well now.

I popped into Quickfit and had a look at their wall chart. I think it says +1mm or +0.08 degrees. A bit more internet searching tells me that this means a bit of toe in, but what does "1mm" mean?

0.08 degrees would be about 6mm at the rear wheels but I suppose it actually means 3mm on each side (6mm in total). Probably too small to measure with a straight edge and eyeball.

I just can't figure out how 0.08 degrees equated to 1mm.

Once I've changed the bits on the other side I'll probably take it to a fancy four wheel alignment place near work just to make sure the rear didn't get damaged as well.

I think eventually I'm going to buy a laser pointer and a mirror and lash something up though.

[Mr_Bo11ox]

Isnt the 1mm, the difference in track/width between the forward edge of the front wheel rims and the rear edge?

[red5]

If it's in mm the measurement can vary on rim size iirc.

[seth]

Yes, the measurement will relate to the difference between the distance between the front of the wheels and the back of the wheels. So I guess you could work out the angle by using 1/2mm and the diameter of the rim.

 

I have frequently set tracking by eye, looking past the edge of the front wheel/tyre to see where that line intersects with the rear. Works fine on older stuff with a bit of slack in the system but possibly a bit low tech for modern fully adjustable jobs.

[dieselnutjob]

ah yes, that actually works (maybe)

standard rims are 15" which is 381mm

(tan 0.08) X 381 = 0.53mm

so do they mean 0.08 degrees on each side which gives you 1mm in total for both sides?

[CIH]

Wheel alignment angles can be measued in either mm or degrees and minutes (either 1/60 or 1/100 just to really confuse). 1mm equates about 8 minutes, assuming 1/60. It's the same thing just measured in a different scale (like Miles and Kilometers).

Weel size is irrelevant in this case.

Also you're using the rear as the baseline but do you know if the rear is straight ? - though if it's a beam and you have no issus with the rear you can safely assume it's sraight enough.

So I just in-made my own point there.....

[dieselnutjob]

if 1mm equates to 8 minutes then there must be 2700 of them in a complete circle

(360 x 60) / 8 = 2700

therefore we are taking about a circle with a diameter of 859mm

2700 / PI = 859mm

so if you attach a stick to each side of the car each of which is 859mm long and if the sticks are 1mm further apart behind the wheel compared with in front of the wheel then you have +1mm of toe in.

Correct?

Why 859mm ?

 

(tan 0.08) X 859 = 1.2mm so 0.08 deg isn't equal to 1mm either, but getting close.

if you said that 1mm is 9.6 minutes then it would agree with kwikfit's wall chart

[dieselnutjob]

you know what

the diameter of the tyre is approx 660mm

(tan 0.08) X 660 = 0.92mm which is getting near to 1mm

is it possible that it just means that the front edge of the tyres are 1mm nearer than the back edge?

In other words it's the tyre diameter than counts rather than the rim?