Tuscan Steering Geometry
Discussion
I have been in / driven a few Tuscans and while I reckon mine handles pretty well, I would have to say that when the road gets a bit bumpy it does seem a little reluctant to go in a straight line. So curiousity got the better of me and I thought I would check the steering geometry. My car has the 18" spiders and it would appear that with the wheels pointing straight ahead the o/s front wheel is toed in around 1mm across the width of the rim and the n/s is toed out 3mm. I took the measurements with the wheels in a couple of positions to make sure that any wheel distortion was not throwing the numbers out. I am guessing that both wheels should be slightly toed in, but does anyone know what the figure should be?
I also noted that the tyre wear appears to be very even, which I guess confirms that the geometry is not wildly out. It just seems to me that there is probably a little bit of room for improvement!
I also noted that the tyre wear appears to be very even, which I guess confirms that the geometry is not wildly out. It just seems to me that there is probably a little bit of room for improvement!
Beek Auto Racing here sorted a brand new example out a year or so ago (late MkI) of which the owner said the handling was 'scary'... alignment and steering geometry were all over the place according to them, you might well be onto something here...
On a related note... how feasible is it to transfer the new steering rack and geometry to Mk I Tuscans?
>> Edited by 900T-R on Friday 3rd February 09:35
On a related note... how feasible is it to transfer the new steering rack and geometry to Mk I Tuscans?
>> Edited by 900T-R on Friday 3rd February 09:35
colin said:
with the wheels pointing straight ahead the o/s front wheel is toed in around 1mm across the width of the rim and the n/s is toed out 3mm. I took the measurements with the wheels in a couple of positions to make sure that any wheel distortion was not throwing the numbers out. I am guessing that both wheels should be slightly toed in
Toe-in is inherently symetrical. If it appears different side-to-side that just indicates that the steering wasn't exactly centered when you measured it; the true toe-in is the average of your two measurements. Obviously there are many other settings as well as the toe-in, and they all interact with each other. As to the best settings for you, having non-standard very low profile tyres will complicate this and I would advise you to talk to a suspension specialist. Joolz at Track Car Solutions is probably your best bet.
I worked it out once when I was playing around with mine and IIRC 4mm diff front to rear edge on 18" rims equates to about 1 degree, so you have around 1/2 degree of toe out, which I think is original factory spec. Mine felt better with zero or around half a degree of toe in.
>> Edited by basil brush on Friday 3rd February 11:22
>> Edited by basil brush on Friday 3rd February 11:22
You need to decide whether you are measuring combined toe-in or toe-in per side. Combined toe-in is what is normally quoted. You can measure this by measuring the distance between the wheel centerlines at the front of the tyre and then at the back of the tyre, multiply by sixty and then divide by the tyre diameter. As a rough guide, for typical wheel sizes 10mm difference represents about 1 degree of toe.
edited to correct 1mm to 10mm
>> Edited by greenv8s on Friday 3rd February 16:31
edited to correct 1mm to 10mm
>> Edited by greenv8s on Friday 3rd February 16:31
I have measured the individual 'toe in' at edge side. I established a reference line running parallel with the car (measured to the hubs of the wheels and within +/- 1mm accuracy over the wheelbase of the car). For each side I have then measured the distance from this line to the rim of the wheel at '9 o'clock' and '3 o'clock'. So the dimensions quoted relate to the position of each wheel relative to the car.
If you had 4mm toe in (combined measurement) then that would equate to 2mm deviation over the diameter of the wheel (450mm) per side and if my 'trig' is correct that would only represent an angle of 1/4 degree. So that would suggest that a combined toe in measurement of 8mm would equate to each wheel being toe in 1/2 degree? Am I getting the maths wrong? My gut feeling was that at present the wheels appear slightly toed out which would not aid stability, bit I do not want to increase the toe in dimension too much.
If you had 4mm toe in (combined measurement) then that would equate to 2mm deviation over the diameter of the wheel (450mm) per side and if my 'trig' is correct that would only represent an angle of 1/4 degree. So that would suggest that a combined toe in measurement of 8mm would equate to each wheel being toe in 1/2 degree? Am I getting the maths wrong? My gut feeling was that at present the wheels appear slightly toed out which would not aid stability, bit I do not want to increase the toe in dimension too much.
The way I worked it was that an 18" wheel is 460mm dia, therefore the circumference of a full 360 degree turn of the wheel would be 1436mm. This then gives roughly 4mm per degree. I know it's not this simple as the wheel doesn't actually pivot about it's centre line but I thought it would be near enough for what I wanted.
My maths could well be crap though, I am an accountant after all.
>> Edited by basil brush on Friday 3rd February 15:39
My maths could well be crap though, I am an accountant after all.
>> Edited by basil brush on Friday 3rd February 15:39
Toe-in quoted as a distance is measured at the tyre not the rim. The formula for converting from a distance to a small angle is 'one in sixty'. If your tyre is 600mm in diameter then 10mm difference front/rear represents 1 degree.
PS I know I said 1mm earlier, I can't trype.
>> Edited by greenv8s on Friday 3rd February 16:30
PS I know I said 1mm earlier, I can't trype.
>> Edited by greenv8s on Friday 3rd February 16:30
Gassing Station | Tuscan | Top of Page | What's New | My Stuff