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Triumph TR6 - Suspension Tuning

I'm looking for some advice on adjusting my front suspension to reduce or eliminate the "loose" feeling I get at speed in my 73.

I'm running stock springs with Koni shocks on the middle setting. All the bushings are new polyurethane, wheel bearings are new and all the fasteners seem tight. Tires are new Pirelli P4000 215's Z rated, wheels are stock steel and recently balanced. Steering rack is stock with poly mounting bushings.

Above about 90 kms per hour the front end seems to get loose and light feeling - doesn't feel as firmly planted as it should.

I'm thinking a bit more toe-in. Anyone have any thoughts.

As usuall I'm trying to solve the problem by learning rather than taking it in to an alignment shop.

Thanks in advance

John Parfitt
Calgary, Canada
1973 5speed.
John Parfitt

Lower the air pressure on tires...running my 205/70/15 at 25 psi...lower them 5 psi and test drive...
Angel L. Traverso

The Pirelli P4000 are a "special" tire. They are the only Z rated 70 series sidewall tire made and are original equipment on some grand touring Jaguars. In order to get that Z rating on such a tall aspect ratio, the tire is designed to hold 51 psi - very high pressure obviously.

I bled mine down to about 47 psi. But soft tires will mask a suspension problem. I'd rather get the geometry such that the thing is more stable. I think it has to be not enough toe.

JP
Calgary, Canada
73 5 speed.

John Parfitt

47 psi??? Talk about a rough ride!! Are you sure that's not the pressure for the max load rating? A TR6 shouldn't be anywhere near the max loading.

I have to agree with Angel - I have 205/70/15's (P4000) and also run them at 22/25 psi.
Brent B

John,

I have to agree, way too much air pressure, the 51 psi (should we convert it to Pascals as an academic exercise for the SI crowd?) on the sidewall is a max inflation for the tire. I typically run 24F/26R on the street tires with a TR6. Another trick to help in higher speed, straight line stability is to go to/increase the positive camber. The down side is that it will hurt "turn in." This is for front only. I personally prefer the better turn in and run some negative camber up front. What would bother me is that it feels all loosy goosy at a speed that is not really high at all. At 90 mph instead of km/h, it would be a little different story.

You also have to consider the rear. You have both toe and camber to worry about back there too. If you are not right at all four corneres, the whole thing will feel out of whack.

BTW, steam cleaned and drained my W57 tranny the other night. Reasonably clean oil, very little attracted to the magnetic plug. Looks a good box to play with.
SteveP

47psi???!!! How are the hemorrhoids? With such high pressure you probably rattled every nut and bolt loose. I have never heard of any car running that high a pressure. Formula 1 cars even run at a very low pressure usually below 20psi and they don't want to hide or mask suspension problems.

I run my 205/70HR15 at 20 fr and 24 rr. I have had them as high as 35 and the ran so poorly
Steven

OK, OK, I get the message boys, I drained the air down to 35 psi all around. I also tightened my hub; seems the new bearing clearance was a bit too much. Took her for a run and it feels more planted but it should still be better. I'm going to have an alignment done. I'v changed so many things that this is really test-and-tune time. Bigger swaybar on the front, big bar on the rear, rear shock conversion, new springs etc; lots of variables so need to spend the time to dial it in and get it hooked up.

SteveP, your tranny will work good. Just run some RedLine oil in there and it will be smooth as silk. I'v now got nearly 1000 break-in miles on my car and I'm starting to drive it like I stole it and I'm having no problems with the Trany conversion other than getting used to a "vauge" 5 - 4 downshift (I missed it twice!) I'm also happy with the cam I used on the rebuild as it brings the torque on at just the right place for running in 5th gear at around 2,200 rpm. Anything below 2,200 starts to bog in my car. You could imagine running a race cam that brings it on at about 4,000 rpm - the only time you could use 5th would be at about 85mph or you'd be lugging it all the time.

Sorry for digressing - I guess it was all the extra hot air I'v been packing around....

John Parfitt
73 5 speed.





John Parfitt

Excuse my 2 cents worth, but all this talk of suspension mods and tire pressures makes me wonder (or maybe I don't drive fast enough). Although all rebuilt, my car is standard, but set up with great care, and I cannot make her misbehave. Just drove home in the rain and flung her into the bends feeling a 'Wow'that she simply goes where I put her without any expectation of surprises.My first TR, I love this car like no other.Peter
Peter Gooch

John,
I guess you've had the stering stripped down so try tightening the bolts that pinch up the splines on the universal joint just above the pinion on the end of the steering column. They are pigs to do up really tight, but a little play there translates into an uncertain feeling in the steering when on the straight.

I use 22psi tyre pressure (205 section)

Peter
P H Cobbold

Hi Peter,

Your not drunk enough. (But seriously, TR6's misbehave by design.

JP
John Parfitt

Sorry, cannot agree with that last statement. Went for a thrash tonight with a quarter moon, and really pushed my baby. Standard, but with all urethane bushings and everything adjusted tight. She will not misbehave, I just fling her around and she is a joy to drive.As the license plate says - PUR-FUN. Peter
Peter Gooch

I wanted to thank the members for thier advice on improving on the "loose" feeling front suspension.

I'v now got the suspension hooked up and feeling very stable by doing the following things:

1. Tightened the steering rack u-bolts.

2. Tightened the wheel hub castle nuts about one full turn on each side.

3. Adjusted the koni's to 1/2 turn from the stiffest setting, which in the koni is not too stiff on the compression stroke and pretty stiff on the rebound which settles things down.

4. Set the tire pressures to 37 front / 38 rear.

John Parfitt
73 5 speed.
John Parfitt

Glad you got it all sorted out, my post may be too late to be useful.
1) The function of the air in the tyres is to support the weight of the car; since the volume of air contained by a tyre of that section width and profile is likely greater than the standard ones it should be fine at the pressures recommended in the owners manual.
2) A z rated tyre usually has a very stiff sidewall which gives precise steering, higher pressure should not be needed to "stiffen" the tyre to improve its response.
3) For a 5.5" rim width a 215 is very wide, and the tread may not sit flat on the road, thus the extra width gives little or no more grip, however you may like the look.
4) The size and weight of those big tyres will increase the gyroscopic effect, meaning the car may feel as if it is reluctant to turn into corners, though this effect may be fairly subtle.
5) Wider tyres may make the car follow grooves in the road more than it did before.
6) For "sporting" driving, ie to reduce understeer, reduce the pressure differential between front and rear tyres and generally increase pressures. Do this gradually, 40 plus pounds sounds too high even for track use, to me anyway.
7) Toe in adjustment is important to the cars sense of "straight ahead"; if alignment is off the car may feel darty, especially on roads with a high crown.
Sorry this is so long. Hope at least some points are helpful.
Simon R.
Simon R

John and Simion,
I run Pirelli P6000 215/65R15 at 19Front 22rear
Up to 120kph I would say the car handles predictably.
Upward of that and the car runs very much as John
describes it, twitchy, light and unpredictable.
Poly urathane bushings allround, shock conversion,
and I can only asign these misbehavings to old tech.
My 2003 Subaru (stock) Impresa doesn't have such problems. John, lower those tire presures, you'll
see a great improvement in handling.
Christopher Trace

This thread was discussed between 02/07/2003 and 10/07/2003

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