Tracking - converting toe in to degrees
Discussion
Following the PAS conversion on my Tasmin I need to get the tracking checked.
I have the track and toe in measurements in mm but all the local tyre shops and garages want the values in degrees. I think I can work this out ok but I need a couple of points of confirmation first.
The tracking figure quoted in the manual is 1436mm with a toe in of 3.2mm
I asume the tracking relates to the center line of the wheel (axle center line as shown on diagram)
Therefore with a toe in of 3.2mm the front line A on the diagram will be 1432.8mm from wheel rim to wheel rim and line B will therefore be 1439.2.
Is this correct?
With this info I can then use a bit of triganomety to work out he angle of the wheel relative to a straight line drawn front to back of the car. Hooray for maths
I have the track and toe in measurements in mm but all the local tyre shops and garages want the values in degrees. I think I can work this out ok but I need a couple of points of confirmation first.
The tracking figure quoted in the manual is 1436mm with a toe in of 3.2mm
I asume the tracking relates to the center line of the wheel (axle center line as shown on diagram)
Therefore with a toe in of 3.2mm the front line A on the diagram will be 1432.8mm from wheel rim to wheel rim and line B will therefore be 1439.2.
Is this correct?
With this info I can then use a bit of triganomety to work out he angle of the wheel relative to a straight line drawn front to back of the car. Hooray for maths
No,
on your drawing toe in of 3.2mm means that A is 3.2mm less than B
3.2mm is 1/8"
Do not use the nominal track to do the sums (it is not exact) - use the rim diameter and you should be in the ball park.
Most old fashioned tracking gauges have a handy little calculator attached that made it very easy!
>> Edited by Rubi on Wednesday 26th April 12:45
on your drawing toe in of 3.2mm means that A is 3.2mm less than B
3.2mm is 1/8"
Do not use the nominal track to do the sums (it is not exact) - use the rim diameter and you should be in the ball park.
Most old fashioned tracking gauges have a handy little calculator attached that made it very easy!
>> Edited by Rubi on Wednesday 26th April 12:45
Draw a circle round the outside of each tyre roughly in the middle of the tread. Take the point at the front of the tyre and measure the distance to the corresponding point on the tyre on the other end of the axle. Do the same for the point at the back of the tyre.
The difference between these distances is the linear toe-in on that axle, the average is the nominal track.
You can roughly convert the linear toe-in for the axle to an angular toe-in (per side) by multiplying it by 30 and dividing by the diameter of the tyre.
This is for linear toe-in measured at the tyre rather than the rim: I think this is conventional, but ymmv. I'd expect any decent mechanic to understand the relationship between them and be able to do the conversion for you, so I'm a bit puzzled that all these places you went to can't work on the basis of the figures you gave them.
The difference between these distances is the linear toe-in on that axle, the average is the nominal track.
You can roughly convert the linear toe-in for the axle to an angular toe-in (per side) by multiplying it by 30 and dividing by the diameter of the tyre.
This is for linear toe-in measured at the tyre rather than the rim: I think this is conventional, but ymmv. I'd expect any decent mechanic to understand the relationship between them and be able to do the conversion for you, so I'm a bit puzzled that all these places you went to can't work on the basis of the figures you gave them.
GreenV8S said:
I'd expect any decent mechanic to understand the relationship between them and be able to do the conversion for you, so I'm a bit puzzled that all these places you went to can't work on the basis of the figures you gave them.
That's what I was hoping but unfortunately I'm getting the "it's not in the computer so I can't do it" response
Naughty cross poster you 
GreenV8S said:
Draw a circle round the outside of each tyre roughly in the middle of the tread. Take the point at the front of the tyre and measure the distance to the corresponding point on the tyre on the other end of the axle. Do the same for the point at the back of the tyre.
The difference between these distances is the linear toe-in on that axle, the average is the nominal track.
You can roughly convert the linear toe-in for the axle to an angular toe-in (per side) by multiplying it by 30 and dividing by the diameter of the tyre.
This is for linear toe-in measured at the tyre rather than the rim: I think this is conventional, but ymmv. I'd expect any decent mechanic to understand the relationship between them and be able to do the conversion for you, so I'm a bit puzzled that all these places you went to can't work on the basis of the figures you gave them.
I disagree here. I'm pretty certain that the values are quoted at the rim rather than the tyre perimeter. The tracking gauges that were common when Tasmins were built were those that touched against the outermost part of the wheel rim at opposite sides of its diameter rather than those that hang on the tyres. I therefore feel tha tthe initial sketch is correct and that the hypotenuse of the triangle used in the trig should be the distance from the leading edge of the rim to the trailing edge across the centre of rotation of the wheel.
I agree with the figures in the original post.
Trying to measure to the middle of the tyre is a non starter.
Try finding a garage with a slide gauge. It is placed on the floor and you drive over it with one wheel. As you drive over if that wheel is trying to turn in it will slide the gauge outwards showing you have to much toe. If toe is correct the gauge does not move. It does not need to know degrees or measurements it's just right or wrong.
Steve
Trying to measure to the middle of the tyre is a non starter.
Try finding a garage with a slide gauge. It is placed on the floor and you drive over it with one wheel. As you drive over if that wheel is trying to turn in it will slide the gauge outwards showing you have to much toe. If toe is correct the gauge does not move. It does not need to know degrees or measurements it's just right or wrong.
Steve
Yes, that's what I imagined he was talking about. I've used a set a few times and the pointer shows the amount of toe-in (or out) as the wheel slides over them. The one's I used (can't remember if they were this particular make) were all plastic and driving over them three or four times gae slightly different results each time. That's what made me a bit suspicious.
That is the beast I was thinking of but was (perhaps incorrectly) under the impression that toe in for a given car was related to the suspension design (of which I know nothing) and that when that design/toe combination was correct there was no scrub and therefore the gauge would stay still.
If this is not true then toe in is continually wearing out my tyres everywhere I go.
Steve
If this is not true then toe in is continually wearing out my tyres everywhere I go.
Steve
steve_D said:
That is the beast I was thinking of but was (perhaps incorrectly) under the impression that toe in for a given car was related to the suspension design (of which I know nothing) and that when that design/toe combination was correct there was no scrub and therefore the gauge would stay still.
If this is not true then toe in is continually wearing out my tyres everywhere I go.
Steve
It's not quite like that. The tyres don't point exactly in the direction they are rolling so there is some sideways deflection, but it's mainly a matter of twisting the tyre slightly rather than making is slide against the road if you see what I mean. This twisting and distortion makes a big difference to the way the tyre generates side force which in turn determines the steering response and stability. You only get scrubing on the tyre if you have really excessive toe-in or camber.
Gassing Station | Suspension, Brakes & Tyres | Top of Page | What's New | My Stuff