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.
Fair enough
I still have a stock front anti-roll bar on my TR6 and
no rear bar.
Phil Ethier wrote:
>Not invariably for all cars. Maybe for TR6 cars and TR4 cars. But maybe not
>even for all of them.
>
>Many cars have severe roll-understeer due to camber curve and other
>considerations. VW Rabbits and MGBs spring to mind. These cars generally
>will understeer LESS with the addition of a stiff front bar.
Most road cars are engineered with a lot of understeer, because
understeer is a far more stable condition than oversteer and most
drivers will react more intuitively to understeer than they will for
oversteer. It's safer, in other words.
But Phil, I must disagree
if you go pick up a copy of Fred Puhn's
"How To make Your Car Handle" or Carroll Smith's "Tune To Win,"
"Engineer To Win," or "Prepare To Win" or any other credible book
written on the matter, you'll find this principle echoed frequently.
It is indeed invariable and applies to all cars. Race cars, road
cars, FWD, RWD, 4WD
whatever. (well, alright, maybe it doesn't
apply to a BMW Isetta) But you must understand that the basic
principle as set forth assumes that all other factors remain the
same. And you are VERY correct to point out that there are many
other factors that contribute to steer characteristics and that every
car will require different combinations of tweaks to achieve the
desired steer characteristics. But the tweaks will always go in the
same direction following this basic principle. Too much understeer?
Increase rear roll-stiffness or decrease front roll-stiffness.
Also, you would be correct to point out that there are other tweaks
you can do to effect steer characteristics without fiddling with
roll-stiffness at all. Fiddling with camber, toe, tire pressure, etc.
Funny you mentioned VW Rabbit, although I wish you'd mentioned VW
Dasher instead (basically the same car, suspension-wise) because I
used to drive a '76 Dasher. I remember one fast left-hander I used
to go around doing about 70 or 75 mph in the Dasher
but I had
temporarily removed the front anti-roll bar. Finally I got around to
reinstalling it, and was curious about whether the info in the books
I was reading would be backed up by my experience. With the bar now
installed, I went around that same bend and the push in the front end
was much more pronounced
so much so that I recall thinking I was
going to strike the telephone pole at the exit of the bend! Adding
the front bar again (increasing front roll-stiffness) DEFINITELY
increased the understeer. It is truly a universal rule in suspension
tuning. Some cars are more sensitive to it than others due to the
many other variables, weight distribution, tire pressure, bushing
deflection, alignment settings and suspension geometry just to name a
few.
I would imagine with Spitfires, because of their swing-axle rear
suspension and the limitations of that type of suspension, a guy
would have to approach these things a little differently because the
type of suspension you'd be dealing with would present other
problems, but even so
the principle always applies. Increased
roll-stiffness in the front = more understeer and/or less oversteer.
Increased roll-stiffness in the rear = more oversteer and/or less
understeer. I strongly suspect that if anyone has achieved different
results from this, they have changed SOMETHING else at the same time.
>Your guidelines are time-honored, but not invariable. Every car's handling
>is a sum of all its parts. The effect of a change may be unexpected.
Again, this eludes to the many variables that can pollute the
results. But I don't believe the principle would be time-honored if
it wasn't invariable.
>I want to get a front bar for the TR4. Then I will evaluate if I want to
>try the rear bar I have. Installing the rear bar alone would be silly: The
>car already lifts the rear wheel.
Precisely! I have a rear bar for my TR6 as well, but do not have it
installed. You're right
it'd be silly without going with a beefier
front bar. My car is already a handful when the roads around here
get slick in the winter!
Best regards,
--
Pete Chadwell
1973 TR6
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