springs
Roger, Greg
This is the posting I sent two months ago regarding my TR250
handling quirks. What I didn't specify is that the springs
used were the TRF replacements:
>>I recently rebuilt my TR250's suspension, front and rear. This
>>included new shocks, bushings, and springs. In the rear I also
>>replaced all U-joints, sliding shafts, and hubs. Having gotten the
>>car back on the road I now notice a peculiar effect from the rear
>>suspension. As I approach a turn, I brake, turn in, and at the apex I
>>accelerate out of the turn. The problem I notice is that as the car
>>approaches the apex it increasingly leans, when I get on the
>>throttle the car settles into a leaning and slightly squatted
>>attitude, as the car exits the turn, the lean goes away but when I
>>get off the throttle to resume cruising speed the rear of the car
>>wiggles. It seems as though the semi-trailing arm bushings are so
>>compliant that they allow excessive toe-in ( or toe-out) durring
>>the cornering process, and as the throttle is applied when
>>accelerating out of the corner the orientation of the drive wheels
>>does not allow the toe-in/toe-out to relax. When the throttle is
>>ultimately released to resume cruising speed, the toe-in is able to
>>relax. The semi-trailing arm bushings are stock repacements from
>>The Roadster Factory. Have any of the netters had similar
>>problems? If my hypothesis is correct, I am contemplating going
>>to the harder ($12.00/bush) bushing the TRF sells.
I'm now running the original springs and the hard rubber TRF bushings
and the handling is right on. Its hard to say whether the bushings
OR springs solved the problem because I installed them both at the same
time. However, when I had a 4-wheel alignment done on the old system,
with a full tank of gas the rear geometry was within spec, and the
handling quirk was present regardless of the weight in the car. I
am reasonably certain that my compliance hypothesis was correct. You
should see the difference between the old bushings and the hard rubber
ones, the old one's are very very soft.
The Triumph Competition Preparation Manual for the TR250 says that the
original spring rate was 350lb/in and that a factory uprated
replacement road spring was available with a rate of 450lb/in.
I sent my original springs to Coil Springs Specialties in Kansas
(913-437-2025) to have them tested and to have 450lb/in springs
made. The originals had:
free height: 10.75"
N = number of coils: 6.75
D = diameter of spring
center to center: 3.15"
W = wire thickness .5"
tested at 1104lb spring height was 8" = 401.5lb/in
Theoretically K = ((W^4)G)/(8N(D^3)) = 404.6lb/in
G = 12(10^6) for steel
I'm having Coil Springs Specialties make a set of 450lb/in springs with
a loaded height .75" less than the originals. These are costing me
$118.00 for the pair. I'm going a little lower because with my Panasport
alloys and 185/70x15 Yokohama 008R tires the original springs are a
bit to high. Beware though, the competition preparation manual warns
not to allow the suspension to bottom since stub axle failure WILL
occur. They suggest cutting the bump stop to allow more suspension
travel and spacers on the springs may be required if the suspension
bottoms when cornering hard. Put a dab of grease on the bumpstop
and do some hard cornering to see if it bottoms.
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