GT6. Correct toe-in. Can it be tweaked?

[Pete Lewis]

i dont quite see why you would go over it backwards

driving backwards will give a reversed reading  if the setting is parallel it shouldnt change much and sit at 0

rotaflex with its wishbones should not have direction quirks 

so what reading did you get going forwards ????

Pete

 

[Mark B]

4 hours ago, Pete Lewis said:

so what reading did you get going forwards ????

Trying to remember, it was a year or so ago, think there was very little deviation on the rears staying more or les on 0 going forward, but a larger deviation going in reverse. I only measured it in the reverse direction as I had to pull the car out of the lock-up, the flatest surface I could find, and was curious.

I will add that the Trakrite I have was given to me,  and is very old and very well used, but i still get the feeling the tow changes at the rear wheels when reversed.

Vitesse drives well and there is no unusuall tyre wear, front or rear (1000 miles).  Got side lined replacing the doughnuts on my Gt6.

I will have another look at this though, and double check and record the readings.

[chrishawley]

Picking up on the above:

I'm ok on measuring toe-in: I've got a hi-tech tool with a precision of better than 1/128th inch (ok, three bits of angle iron welded together and a 1/4 unf screw acting a a fine gauge).

Negative amber on the front? The data I've got is about 2 degrees positive. Is this right?

So nest week will be to experiment with the caster and gain some experience  with judicious road testing.

Anti-roll bar. I suppose I should replace the 'fat' one anway. I've got a Spitfire Mk4 one. Would that do?

I replace the lower steering joint with a UJ type from MevSpares, 'Upgraded' the blurb said but I wasn't expecting agricultural! It was huge! So became quite a performance to fit as it would bind up on the edges of the turret. Machining required. Tough, for sure. Fits straight out of the box - no chance!

[Clive]

Your traking gauge is more advanced than mine. I use 2 bits of steel bar (as straight timber seems impossible to find), 2 bricks to sit them on, a tape measure and my glamorous assistant. 4 wheel done using string, 4 axle stands, a tape measure, having set f+r to parallel first.

ABB for a mkIV spitfire (70-74) is also the thick version. Youwant one off a mk3 or earlier spitfire, herald or vitesse. Or GT6 except late non roto mk3

I would set front camber to approx 1/2-1 degree negative. 

 

[PeteH]

How much is the tracking/camber affected by loading?. My instinct would suggest that with the Rear spring setup, It would be necessary to have the car in the "in use" condition?. A bag or 2 of sand on each seat?.

Pete

[Nick Jones]

After extensive experiments with my Vitesse I arrived at:

Toe:
Parallel to 2mm toe in. Parallel or even slightly toe out gives sharpest turn-in but tends to wear the inside edge or the tyres and make it a little wriggly under hard braking. This with blue PU wishbone bushes. Rubber bushes may allow a bit more deflection when rolling meaning you need more initial toe in.
 

camber
1.0 deg negative.

castor
I was aiming for 4 deg. Not completely sure that’s what I got, but it’s the same both sides and the car is stable even at well over 100mph. The steering is heavy though (using a Herald rack doesn’t help!)

Rear toe
2mm toe in (important it’s even both sides)

Rear camber is about 2 deg negative at normal ride height. Car is about 1.5” lower than standard.

Standard skinny arb. I’ll take a bit of lean in preference to ploughing straight on…..

Need to check the castor on my GT6 as it’s very much less stable than the Vitesse at speed. Steering is nice and light though!

Nick

[JohnD]

No argument with Nick, except to say that it depends!   On how hard you drive, your wheel and tyre sizes and how hard is your springing.   Tyre wear is a good guide, or a bit quicker, tread temp after a run.    You need to be very quick if you use an IR pyrometer, but a proper tread thermometer with a needle probe allows a more leisured assessment.

[chrishawley]

Hurrah! Adding a 1/16th shim to each rear (and readjusting the toe in accordingly) has been a significant advance. Good steering behaviour at low speeds and reasonably stable on the straight up to 70mph. Not what you call 'rock solid' but way better than it was. On a hands off test at 65mph the vehicle follows it's own line well. Steering remains light and has not gone heavy. Although not quite there, increasing the caster has certainly helped

Shims are now L1f2r, R1f2r.

Is it worth an experiment wit pushing the caster one step further (one more shim)? From what I understand from the above if the steering gets unduly heavy the that indicates toe-in excessive.

And I've found a Herald anti roll bar. Will that do as a replacement for the incorrect 7/8ths one currently fitted?

 

Ideas?

Thanks

[Clive]

7 hours ago, chrishawley said:

Hurrah! Adding a 1/16th shim to each rear (and readjusting the toe in accordingly) has been a significant advance. Good steering behaviour at low speeds and reasonably stable on the straight up to 70mph. Not what you call 'rock solid' but way better than it was. On a hands off test at 65mph the vehicle follows it's own line well. Steering remains light and has not gone heavy. Although not quite there, increasing the caster has certainly helped

Shims are now L1f2r, R1f2r.

Is it worth an experiment wit pushing the caster one step further (one more shim)? From what I understand from the above if the steering gets unduly heavy the that indicates toe-in excessive.

And I've found a Herald anti roll bar. Will that do as a replacement for the incorrect 7/8ths one currently fitted?

 

Ideas?

Thanks

Yes, the herald ARB is the same as GT6 (except late swing spring type)  You will need new clamps/bushes unless the herald one has these attached.

Good news on the adjustments. Is it worth further adjustment?  It is not difficult to do and reverse if necessary, so yes. Either add another shim to the rears,  or take one out of the front, depending on how your camber looks. Ideally a little negative camber /---\

[Ian Foster]

Chris

Sounds as though you are moving in the right direction. I think I would add one further to the rear on both sides which will give you just a tad more castor and neg camber.

I think you will be pleasantly surprised by the change to the thinner ARB.

Look forward to further reports.

Ian

[chrishawley]

Oops  - forgot to order any bushes and clamps. Doh!

So I'll increase the caster one more step and see what that's like. Then try the skinny ARB. Further pondering is telling me the ARB is more of an issue that I originally supposed. Puts me in mind of a XJ6 I had: Even the most minimal mods (e.g. hard bushes, slightly firm shocks) would not alter any dimensions at all but absolutely wreck the feel.

I never had a small chassis Triumph as problematic as this one for getting susp/steering right. But then this one is VERY heavily restored. I'm getting a feeling that although 'by the book' geometry provides a sound datum it's not the whole story and some judicious experimentation is required as well.

[Clive]

3 minutes ago, chrishawley said:

I never had a small chassis Triumph as problematic as this one for getting susp/steering right. But then this one is VERY heavily restored. I'm getting a feeling that although 'by the book' geometry provides a sound datum it's not the whole story and some judicious experimentation is required as well.

There are plenty of garages that can offer geometry setup, but sadly there are far fewer operators. Typically as long as each reading is in the "green" they are happy, but if at opposing ends of the the total is too marginal, and not satisfactory. Every reading needs to be band in the middle of the range.

And a big clue, a heavily restored car ia unlikley to need the same shims either side, possible, but unlikely. As to castor, again, few seem to measure/check. But it seems you are making improvements. Ideally you want to check castor is the same each side.

[Nick Jones]

The problem with the book figures, apart from them probably not being in the alignment machines computer, is that they are quoted in the running position, meaning you need to add significant weight to each seat….. and who EVER does that. It’s nuts.

Also assume standard ride height, standard wheels and tyres of the time.

All of which is why a bit of careful experimentation can work wonders.

Nick

[Pete Lewis]

the gt6 data gives some unladen figures   from memory static laden to unladen makes aprox 3mm difference at the tyre

pete

[chrishawley]

Yet more hand holding required. I'm afraid. Let's make sure I've understood the formula for calculating caster correctly.

If the above is a tolerable approximation across equal and narrow values, then; If one turns the wheels (I have turntables) from 20 degrees out to 20 degrees in then that's T2 - T1 = 20 -(-20) i,e 40 degrees. Similarly if C1 is 2 degrees positive and C2 is 3 degrees negative (hypothetically) then that's 2 - (-3) = 5 and NOT 2 - 3 = I degree.

Right? Wrong?

 

[Clive]

9 hours ago, chrishawley said:

Yet more hand holding required. I'm afraid. Let's make sure I've understood the formula for calculating caster correctly.

If the above is a tolerable approximation across equal and narrow values, then; If one turns the wheels (I have turntables) from 20 degrees out to 20 degrees in then that's T2 - T1 = 20 -(-20) i,e 40 degrees. Similarly if C1 is 2 degrees positive and C2 is 3 degrees negative (hypothetically) then that's 2 - (-3) = 5 and NOT 2 - 3 = I degree.

Right? Wrong?

 

Correct, but just use the simpified version? For 20 degrees either way, castor is 1.5x the change in camber, in your example 5, giving castor as 7.5 degrees. 

[Pete Lewis]

as i said  on turntables or on the floor to measure  castor you must brake the wheel i must not be able to rotate 

or you get useless readings  its a  standard procedure

Pete

[Nick Jones]

37 minutes ago, Pete Lewis said:

on turntables or on the floor to measure  castor

Stand each wheel on a newspaper on magazine.  Red neck turntable……. 

[PeteH]

1 hour ago, Nick Jones said:

Red neck turntable……. 

And the Xmas Lights on all years round?.🤣

Pete

[chrishawley]

Thanks for all the comments above. Here's the progress (inviting further comment):

• Pushing the caster up by one shim each side produced a definite improvement in stability a 60  - 70 mph. Nothing measured, just empirical. Adding another (now f1r3 each side) made no additional difference. Still not 100% right, but definite improvement.

• Then replaced 7/8ths anti roll bar with 11/16th (and soft rubber bushes, not polybush). Never done a back-to-back test of different ARBs before and the contrast was marked. Whole front end softer and more 'feeable', less harsh over rough surfaces, cornering less precise and go-kart-ish (but absolutely fine) and a further improvement in high speed stability and even if still not 100% at least one can get some feel for what the wheels are doing.

So it's within a gnats of where i think it should be. Having messed with everything experimentally I suppose I should go over all the measurements again in laden condition. But are there further possibilities to optimise the situation? I'm on fairly fresh Toyos 155/80/13 and wonder if there's anything to be gained by going 'upmarket' with the tyres? There was also a suggestion of using an undertray to control aeodynamic lift - is this a realistic option and how would one do it? Plus I'm still open to suggestions that help teh steering be as good as it cab be.

 

Cheers

C

[GrahamB]

On my Spitfire 1500, I secured a board over the gap between the chassis rails in front of the radiator using existing mounting holes.  The idea was to prevent the air entering via the front grill from escaping under the car and so force the air to flow through the radiator and aid cooling.  As a secondary effect, it did subjectively appear to improve stability when travelling along the A1(M) at 70 mph but again nothing measured.

[Ian Foster]

Clive

Pleased that you seem to getting there. Where are you with tyre pressures?

Interesting to hear your comments on the change to the thinner (standard Rotoflex) ARB. I definitely found an improved turn-in, ie less understeer, with the thinner bar, albeit I do have a rear spring that has been uprated with the addition of a centre leaf.

I presume you have rechecked the toe in after the addition of rear shims. 

I have always used 175/70 R13's as my car had 5 1/2" rims on it when I bought it back in 1977. Currently shod with Kumho Solus KH17s which are better than you might think. 

Might be time for another visit to the laser alignment chaps.

Ian

[Clive]

15 hours ago, Ian Foster said:

Clive

Pleased that you seem to getting there. Where are you with tyre pressures?

Interesting to hear your comments on the change to the thinner (standard Rotoflex) ARB. I definitely found an improved turn-in, ie less understeer, with the thinner bar, albeit I do have a rear spring that has been uprated with the addition of a centre leaf.

I presume you have rechecked the toe in after the addition of rear shims. 

I have always used 175/70 R13's as my car had 5 1/2" rims on it when I bought it back in 1977. Currently shod with Kumho Solus KH17s which are better than you might think. 

Might be time for another visit to the laser alignment chaps.

Ian

I *think* you meant Chris?

But FWIW I have 185/60 14 Michelin Crossclimates that are brilliant all year around, running 25psi all round on my tyre gauge (others all seem slightly different)

Talking of front ARBs, I used a ratty herald estate as an everyday car and also used it for 12 car rallies, but also autosolos. That ended up with 440lb springs at the front, with std ride height, plus a Courier rear spring. I eventually removed the front ARB altogether, and the car indeed improved in the corners. Firmer front springs outweighed the ARB. That car was brilliant, but eventually needed too much doing. I remember a friend and his daughter borrowing it for an autosolo, they both had quicker times than a TR7V8, proving power is not everything, agility is very important.

Anyway, I ought to give my spitfire suspension a check over, I fiddled with teh rear spring a couple of years ago to give slightly higher ride height, but nworth checking rear toe again now it has settled. Just need to finish welding my Dolomite to get that out of the garage, about 4-6 weeks I expect at the current rate of progress.

[Ian Foster]

Clive, sorry, yes Chris....confused me??!!

[chrishawley]

Yup, adjusted front toe in when changing the caster.

Tyre pressures approx 26f 28r (but none of my TGPs agree with each other!). Tried pushing the pressures up but that led to marked skittishness.

So, one more round of measurement and then perhaps leave it alone for a few hundred miles; the car is still pretty fresh on it wheels and definitely settling/softening as miles accumulate. On the first few test drives it was absolutely appalling  - boneshaker would be an understatement. And I still have a very thick lowering block on the rear spring which was required to get the ride height down to something normalish. But I suppose that with the passage of miles that will need to be changed for a skinny block or none at all.

And thanks for all the comments and advice without which it would have been creeks and no paddles.