From: Pete & Aprille Chadwell <pandachadwell_at_mac.com>
What are: (a) Caster, (b) SAI, (c) Included Angle (appears
to be the sumof Camber and SAI) and (d) Thrust Angle, and what do they tell us?
I'm pretty certain that SAI stands for 'Steering Axis Inclination',
which I'll describe shortly
Caster and SAI are very, very similar. To illustrate caster, think of a
bicycle's front wheel, fork and steering head. When viewed from the side, it
will be immediately apparent that the axis around which the forks and wheel
rotate when steered left or right runs at an angle that is nowhere near
vertical. That axis is tipped back in such a way that if you draw an imaginary
line on the axis, you'll find that the line intersects the ground IN FRONT of
the wheel/tire's point of contact with the ground by a considerable distance.
This is referred to as a POSITIVE caster angle. NEGATIVE caster refers to a
steering axis which is angled such that it intersects the ground BEHIND the
wheel/tire. If you have a bicycle handy, get on it and steer the front wheel
right or left and watch what happens to the CAMBER of the wheel. That is,
notice that the farther you steer the wheel in one direction or another, the
wheel itself leans considerably and is no longer in a vertical plane. You'll
notice the same thing on a road car when the wheels are steered sharply the
camber of the wheels change with steering input. How does this happen? Back to
the bicycle analogy: Imagine that you designed a bicycle so that the steering
axis was angled back so far that it was PARALLEL to the ground. Of course, you
wouldn't be able to steer the bike at all. Turning the handlebars would only
lean the wheel over.
Why have caster at all? Why not just run the steering axis vertical?
Good question. Ever notice when you're steering through a corner that IF you
were to let go of the steering wheel, it would snap back to center? That
tendency is due to the positive caster angle. The greater the angle, the
greater the self-centering force. Caster has a huge impact on the directional
stability and steering effort. That is,
the greater the positive caster, the lighter the steering effort (to a point, I
believe) AND the greater the tendency of the car to wander. Lesser caster
angles give great directional stability, but the steering effort becomes
greater.
Steering axis inclination is very similar. The caster angles described
above are observable when looking at the car from the side. SAI is observable
when looking at the car from the front (or rear). Both angles tell us something
about the steering axis. If you view a front wheel from the front of the car, the
axis around which that wheel rotates when steered left or right is also
slanted, almost always so that an imaginary line drawn on the axis intersects
the ground near the center of the tire's contact patch. The other end of this
imaginary line would (theoretically) intersect the axis of the opposite wheel's
steering axis at some point in space above the car. In other words, the
steering axis is inclined toward the center of the car. This inclination also
has an impact on steering effort. Usually the axis is designed to intersect the
ground NEAR the geometric center of the tire's contact patch. But usually it's
offset so that it intersects the ground INBOARD of the geometric center of the
contact patch. The distance of this offset is called 'steering offset'. The
greater the offset, the more steering effort is required. SAI and steering
offset are manipulated especially in front wheel drive cars to tune out 'torque
steer' to some extent.
I'm not sure I'm familiar with 'included angle'.
I am considering
putting a front and/or rear sway bars. Who has done this and how much
improvement was there? I see that VB has a 3/4" ADCO sway bar for front
and 5/8" for rear for $170 a piece. Rather pricey, but I would bite the
bullet if it was worth it. Also, should the bushings be upgraded to urethane
for added rigidity?
From: Randall Young : ryoung_at_NAVCOMTECH.COM
I am reasonably
certain that the kits sold by VB are made by ADDCO, and are available through
other sources at a lower price. I got
mine from JC Whitney many years ago, but I see they are still listed in the
printed catalog (even though I couldn't find them on-line). ADDCO has a web site at
http://www.addco.net/ where you can learn more about their kits. I installed
both bars on TS39781LO, and was quite happy with the result on (nearly) stock
size tires. I used all rubber bushings
in the rear, but switched the front vertical link bushings to polyurethane to
reduce oversteer. The bars completely eliminated the problem where the rear
axle hits the frame on hard corners. The installation is pretty
straightforward, the only permanent modification to the car is 8 holes, 2 in
each of the front frame extensions, and 4 in the rearframe. The bolt through the
center of the front wishbones gets replaced with a longer bolt (not included in
the kit I received), to carry a metal bracket.
I used Nyloc nuts to avoid having to drill the bolt for a cotter pin. On
the rear suspension, the existing U-bolts were long enough to remove one Nyloc,
add the metal bracket, and install a new Nyloc. I did have a few installation problems, had to contact ADDCO for
some modified parts, but they were very helpful, and I would assume they've
updated their kits by now.
VB's catalog is flat
wrong. (which is not unusual) Addco's web site at http://www.addco.net/products/triumph.shtml
specifies 'post-58' (which isn't strictly accurate, but ...)
The issue is that the
Addco bar (which I have) mounts to the front bumper supports on the 3A-3B. Those supports are considerably different on
the TR2/3, with no flat surface to mount the swaybar pivots to. TRF sells the
same sway bar kit from Addco . BTW, I have the rear bar too. Definitely helps reduce understeer
From: Randall : randallyoung_at_earthlink.net
> TeriAnn wrote:
I've spent a lot of time chatting with TR3 & 4 racers about suspension. The
short answer is you want a stiff front and a stockish rear suspension. Almost
no one is racing with a rear say bar on a TR3 because it makes handling less
predictable and it doesn't really help high speed cornering.
It might be worth
pointing out here that the TR2-4 (and some TR4A) are beam-axle cars. Which means their handling (and what works
to improve it) is quite a bit different than the later IRS TRs. And, they have a somewhat unique rear axle
setup, with the axle going over the frame, which introduces some unique twists
in their handling. Pushed to the limit,
a stock TR2-4 will suddenly go from slight understeer to gross oversteer, when
the axle hits the frame on the inside rear wheel. Fortunately, once the outside
rear tire loses traction, the suspension unwinds and the inside tire plants
again, giving you another chance to recover instead of just instantly tossing
you over the high side. The net result is that the rear ends 'skips'
sideways. IMO this effect is worth
eliminating, even if it compromises other aspects of handling. Thus, a heavy
front bar, although it induces more understeer, is desirable because it also
helps keep the axle from hitting the frame.
The beam axle TRs also
have a quite stiff rear suspension, and fairly drastically mis-matched roll
centers, which leads to lifting the inside rear wheel off the ground in hard
turns, even when it doesn't hit the frame.
Again, you can sacrifice some ultimate cornering force, in return for
being able to accelerate through the second half of the
turn, and wind up with
a quicker car.
From: Rikrock_at_aol.com
Normally, Spax shocks take 13 or 14
clicks going from full soft to full hard. If you turn the screw counterclockwise far enough it will bottom.
That is, you will get to a point where it won't turn farther. That's full
soft. Each click is about 1/2 turn of
the adjusting screw.
My experience has been that you can turn the screw clockwise
"forever". It won't stop after 14 or 20 or 30 or more clicks. Continuing to turn the screw clockwise after
14 clicks will not alter the setting, you'll still be at the hardest (14th
click) shock setting.
This "feature" is why people like me who have a lousy memory
and don't always write things down count the clicks it takes to return the
shock to full soft before "cranking it up" again :-)
As a side note, these shocks are "single adjustable". The adjustment is for rebound only.
Compression is not affected by the adjustment.