Hello,
I'll echo what Pete Chadwell said to this topic - in order to do the job
justice, you really need to read a book or two on the subject. I'm a big
fan of Puhn's "How to Make Your Car Handle" too.
Your Triumph is an IRS car. The changes that you make in the rear or the
car are very different that what you could do if you had a solid axle TR.
Before you would go about making any changes to your car's suspension
consider the following: engineers most likely spent much time and effort to
come up with what's on the car in the first place. If you muck with one
thing, you'll likely upset something else. The key here is balance.
Now, in a nutshell (and from a racer/autocrosser prospective) I'll offer
the following.
1. the primary concern _for a racer_ is the rules/sanctioning body. You
need to be aware that certain changes will move you into classes that you
may not want to run in. So in addition to Puhn - you need a rule book or books.
2. road racing and autocrossing are completely different entities when it
comes to setup. A road racer would likely be sprung less heavily and
primary design criteria would be for smooth transitional forces.
Autocrossing requires stiffer springs, bigger sway bars and stiffer shock
settings. In autocross a moment of transitional delay means lost time.
3. if you make a car "dual purpose" it will do niether purpose well. For
example, a street car cannot be an effective racer. An autocrosser would
make a lousey road racer. Granted you can have fun with cars set up this
way, you just cannot extract maximum performance.
Now, I just happen to have two Triumphs that are set up for autocrossing.
One is also a street car. We'll call the street car CarWon and the racer
Khartu.
CarWon has urethane bushings, it is lowered with Moss competition springs
and it has Addco sway bars front/rear and Spax adjustable shocks in the
front, rebuilt Armstrongs in the rear (with the Apple Hyd. "heavy duty"
valving). I run _stock_ alignment specs owing to the fact that the car
drives between 5K and 10K miles every year. This car corners fairly flat,
so excessive camber settings are not needed. Note: when you lower the car,
you get negative camber both front and rear. I had to dial some camber
_out_ of the car.
Khartu, on the other hand has lowered TriumphTune sprint springs (more
stiff than the Moss units by at least 15%). The frame is about 3 inches
from the ground. I run GoodParts bars front/rear - this is to add
adjustability to the car, e.g. on a wet day i can dial _out_ rear bar). I
run the same shocks front/rear as CarWon. Now, despite having driven this
car for two seasons, I have no idea what the alignment specs are. There is
almost no negative camber in the front, probably 1 degree tops. The rears
are set for almost no negative camber. I believe front and rear toe are
close to zero with maybe a tad of toe out in front and matbe a tad of toe
on in the rear. The car tracks dead straight, so it is aligned - I'm just
not clear on actual numbers. The car has never been "on the rack".
Now on the race car, there is _no_ body lean - well, maybe a degree or so.
Because of that, having larger than 1 degree of camber is a waste. Also,
real racing slicks are bias ply, so they don't need a whole lot of camber.
If you run radials, you might benefit from more negative camber, but the
only way to know for sure is to get the car on a skid pad and measure the
tire temps.
If you want to go for total adjustability, then coilovers all the way
around are called for, but this is a large exercise of effort and it will
be expensive and you'll have to play a lot to get the car dialed in.
Repeating the theme - Triumph did a fairly good job designing the cars'
suspension and you can do a lot just by "tweaking". Wholesale redesigns are
not called for unless you hit into limits that are due to the existing designs.
For example: if you lower the car significantly, you can get into a
situation where the front toe changes a lot under suspension
loading/unloading - aka bump steer changes. To remedy this, you might need
to switch from stock outer tie-rod ends to heims joints (aka "rose" joints)
and spacers to maintain the geometry relations between all the parts.
Bottom line, you can do a lot of stuff before you have to start
redesigning. Just keep in mind "system" (e.g. it's a system and all the
components effect the other components) and "balance" (e.g. don't just toss
on a huge front bar and think everything will be okay.) The shotgun
approach usually ends in making the car undrivable.
Regarding suspension adjustments, in the stock form, an IRS TR4 and
TR250's/TR6's offer precious few tweaking points. In essence you can play
with toe, you can play a bit with camber, but caster is hard to change (but
it is changable) - to get more tweakability to your car, you have to resort
to serious modifications like hacking the upper A arms and that sort of
thing. Def. not for the Weak at Heart.
Now, it's fairly easy to play with ride height on these cars just by
playing with tire sizes. A stock TR6 tire (185/80-15) is about 26 inches
tall. If you go to 225/45-15's, your car will be at least 1.5 inches lower
than stock - this is a no-brainer handling improvement. In fact, this was
the first thing I did to my street TR6 a few years back, and I was amazed
at the transition/handling. Adding in that I was on "real race rubber"...
yeee ha!
If you start playing with the suspension to lower things, then you have to
be aware of the interaction between the parts. A big drawback to lowering a
TR Triumph - you have to be very careful about bumps in the road, raised
storm drains - entering driveways... my street TR6 has the frame 4 inches
from the ground. I have bottomed out on curb transitions etc.
Anyway, figure out how you want to use the car, look at the rules books and
then figure out what you want to do.
I can talk at great length about this topic, but I'd rather just drive!
Regards,
rml
TR6's
----------------------------------------------------------------------
Bob Lang Editor, New England Triumphs | This space for
TR6 Owner lang@isis.mit.edu | rent.
Voice:617-253-7438 Home:781-438-2568 |
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