I can't see anyone agreeing, anywhere, on either Jag-Lovers or our Forum, or anywhere else on the Net for that matter, what the actual value in
degrees/minutes is the equivalent of the oft-quoted Jaguar figure of
1/16" - 1/8" of toe in at the rim, note the manual refers to a
rim and not
rims.
The only thing everyone agrees on is that it's Toe-In
Like Jesper's original post said, nowadays all wheel geometry is expressed in degrees/minutes, so I thought I'd have a stab at expressing the E-Type toe-in in those terms.
The principal obstacle, as Steve rightly points out,
is that you first have to decide what Jaguar's values actually refer to.
To keep it simple, I'm going to work it out on just the higher 1/8" figure.
1. Is it a TOTAL toe - which might mean the difference in the distances between the leading and the trailing edges of
both front wheel
rims plural.
If so, then each rim moving 1/32" inward at the front, and 1/32" outward at the rear gives a toe of 1/16" per wheel, or 1/8" for the pair, which equates to
13' per wheel (that's 13/60 of a degree).
(Note - Rim edge actually has 8.25" radius, as our famous 15" refers to the
tyre seating diameter ; and tan-1 of 1/32 divided by 8.25 equals 0.217 degrees, or 13 minutes of arc
https://www.calculator.net/scientific-calculator.html)
2. Or is it the toe of just ONE rim, singular.
And if it were the toe of just ONE rim, what does that mean ?
You can take it to be just literally how much the
leading edge of the wheel rim is turned inwards, in which case 1/8" per wheel gives a TOTAL toe figure of 1/2", and the angular measurement is then
52'.
Or you can interpret it as the total toe of one wheel, in which case it's 1/16" turned in at the front, 1/16" turned out at the back, and the angular expression is
26'.
So you can read it as
13', 26', or 52' according to how you interpret the upper limit of the original expression, and
7', 13', or 26' if you take the lower value.
That's a variation of from 1 to 8.
Now, my reflective guru in Connecticut, who sets up Italian racing cars - same period as ours - for a living, Goodwood, LeMans, Monaco etc, said this is how he would read it :
Toe per wheel. So if the rearward side of the rim is zero reference, the forward side is 1/16-1/8 inwards. Total toe of the set (front or rear) would be 1/8-1/4. As a side note I never run toe in on the front unless the Ackerman is really big like a go kart. For a road car it wont make too much difference. Road cars usually are set up "safe" to understeer, and toe in helps that.
So because of that, I'm nailing my colours to the mast
for
TEN minutes of pinch on each wheel
It will put some conviction in my step
when I next go to my measuring guy.
Incidentally, I'm now SOLD on the use of the suspension-setting tools that Jaguar insisted be used when making these measurements ; without them you are never measuring the same thing twice.
Feel free to pick holes in my maths.
