GT6 Mk2 Suspension / Ride Height

[Nick Jackson (2)]

Having nearly finished painting of various items I'm fast approaching the point where I need to fit the suspension parts to my chassis. (Actually the diff and steering rack are already fitted).  Therefore, I wonder if I could get some thoughts from you all about designing the suspension with a view to getting the correct ride quality for my purposes and ride height for getting the right look.   I have some choice (see below) and may need to buy more kit to suit my purpose though.

A quick recap on what I have:-

It's a Mk2 rotoflex with a 2.5 'MG' prefix engine and J-type overdrive.  It's intended purpose is basically what I'd call 'fast road' use and road trips.  I'm looking for good handling while pressing on and throwing the car into hairpins, but not going all out for top speed or racing.

Assume standard spec except:-

CV driveshafts, solid steering rack mounts, Poly bush kit from Canley.
Rear shocks will be mounted onto chassis rather than the rear wheel arch
I have a choice of new shocks - Koni's front and rear, Gaz front, Spax rears
I have a choice of front springs - existing standard ones or new 440lb ones
  
Handling requirements come first of course but, by preference, I like a slightly lowered look and a flat profile when looking from the side.  I'm just not a fan of cars that sit either up at the front or back and I like the meaner/sportier look of lowered cars.  I'm also no fan of rear wheels that seem to tuck under the car (positive camber?).  Weirdly I don't mind them sitting the other way around (negative camber?), where the bottom of the wheel sits further outwards from the car.  

I'm wondering about fitting a space block between  the diff and rear spring but is this necessary and how would I balance this at the front to get the level/lowered ride height I'm after?    What else should I be thinking about?

Any comments and advice would be gratfefully received.
Nick

[tiggrr1]

Mine is an early MK3 with almost exactly the spec you are aiming at.


It's an early [s]Mk2[/s] Mk3 rotoflex with a [s]2.5[/s] 2.0 slug of an 'MG' prefix engine and J-type overdrive.

CV driveshafts, solid steering rack mounts, Poly bush kit from Canley.
Rear shocks will be mounted onto chassis rather than the rear wheel arch
I have a choice of new shocks - Koni's front and rear, Gaz front, Spax rears................ AVO rear shocks & AVO fronts (height adjustable).
I have a choice of front springs - existing standard ones or new 440lb ones................ I had 440's but went up to 650lbs on the front.

belive it or not there is still quite a lot of suspension movement in the front of the car with the damping low or you can make the front rock hard by turning up the damping.

My problem is the rear spring is very stiff, possibly off a vitesse (anyone know if they are different) either that or it is made of unspringy steel.

I'd also suggest beefing up the brakes using Mintex 1144 front pads for hard driving, for me they coped with almost anything.
That is until they were used on one or two alpine passes (or to be more correct Gaz (uksnatcher) cooked them in Andorra).
If your going to use them that hard I strongly advise a vented disc at the front to aid cooling.

Most who have driven it seem to like the way it stops and goes round corners :)

[Richard B]

Couple of thoughts;

2.5 is heavier than a 2 litre, so definitely go for heavier front springs.

Consider polyurathane suspension bush's (its a sports car. nb. I prefer Superflex)

Canleys do aluminium wishbones for rotoflex cars (helps the unsprung weight)

Alloy wheels, (I cooked the front brakes on my Spitfire regularly with 5.5 Steels fitted, also consider vented discs as Steve says)

You can always change the rear lowering block afterwards, (but I'd suggest a 1/2" or 3/4" lowering block to balance out the rear if lowered springs are fitted)

[JohnD]

No argument with tigerr's words.

You need not fear gross changes in positive/negative camber (you have it the right way around) in Rotaflex suspension as much as in the previous swing spring, but even that is vastly overhyped in normal road driving.

    Many years ago, I wrote up in the Courier my research using a two dimensional model of the rear suspension  (Rear suspension tuning the LoTec way, Courier 203 May 1997.  See diagram below).   This method may be criticised on several grounds, in particular that the spring is not a rigid arm with a constant radius.
I found that the minimum camber change occured with a 1" raise of the spring and a relocated chassis mount for the wishbone.  This "Racing" bracket puts the pivot 25mm down and 5 mm outwards from its original position, and allows a change in camber from -1 to +1 degrees from bump to droop, while it is -2 in a neutral, resting position.    If you do not wish to muck about with changing the wishbone bracket, then just a 1" block under the spring will give less camber camber change but allow significant positive in droop, which may not matter much as the wheel is relatively unloaded in that position.

The stiffest production rear spring was that fitted to Courier vans, but those have gone the way of the dinosaur.    A run of reproductions were made by Canley's but I fear those are all sold.   You could have an OE spring reforged to your own spec if you wish by going to a spring maker.   The OE specs of various springs were listed by Carl Heinlein in the Courier even earlier! (Suspensions sussed, Courier 158 August 1993, p31)

Ride hight or stiffness changes at the rear should be matched by front suspension changes.  Those can include, the spring, the shock absorber, the lower suspension arms and the anti-roll bar.
Spring:   To allow the car to ride lower, you need a shorter spring, about nine coils instead of the OE twelve.  But that lower ride height must go with a stiffer spring or grounding is likely.    450-600lb/in (the weight required to compress the spring by one inch) is really stiff, three to four times stiffer than the OE spring and will rattle your fillings out!   For a lowered-look road car, I'd suggest only twice OE stiffness at 300-350lb/in is quite enough.

Shocker:   To fine tune your ride height  you need shock absorbers with an adjustable spring platform.  You will also need two C-spanners to adjust them!  Note that for these and for replacemt springs that modern coil springs are a bit wider than OE Triumph springs,but springs and shockers are available in the narrower format.

Lower suspension arms:    With enormous serendipity Triumph provided us with brackets on the chassis to take the lower suspension arms that are adjustable by shims placed between the chassis rail and bracket, and a bracket bolt that is long enough for some serious adjustment of the front camber  I suggest you fabricate spacers from 4-5mm alloy, and fine tune the camber with OE shims,  rather than use a large stack of shims.

Anti-roll bar:   Of greatest importance if the rear spring is stiffened, but still useful with a lowered front, a stiffer front ARB will help keep the car from excess front camber change and from lifting a rear wheel.   The OE 11/16" may be uprated to a 1" bar, but you will need new brackets, which can be solid if you wish, and if you will keep them lubricated.

Hope that helps too!
John

[tiggrr1]

JohnD wrote:

The stiffest production rear spring was that fitted to Courier vans, but those have gone the way of the dinosaur.

Do you know of any way to identify these springs John ?    Or is it just the strength/springyness of the steel used.

My rear end is really very stiff (fnarr fnarr)
I bought the spring a few years ago at Stoneleigh from a guy saying it was for a GT6 or Vitesse.
I would imagine the Vitesse spring to be stiffer than the GT6, so maybe that is what I have :-/

The rear being so stiff was why I went for so high a rating at the front to balance it out, works really well on smooth tarmac but you do feel the bumpy bits!!!

[Nick Jackson (2)]

Thanks guys for the comments above.  A few responses:-

Shock's/dampers: As I've already got various new ones the only way I'll buy new AVO's is by selling all 8 I have already.   Not so likely in the current economic climate as buyers seem thin on the ground.  Although they're not adjustable on the car I think I'll go with my new Koni's front and rear for now.

Front springs: Again I've already 2 sets, so it looks like I'll start with the 450lb ones. Possibly a bit hard though.

Brakes discs/pads: Good idea on the Mintex 1144's. As for disc's, apart from bog standard solid discs I have, I acquired some EBC Turbogroove discs with blind drilled grooves & dimples.  Probably not what I would have chosen but they came as a job lot of kit and are new, so will fit these for now.

Anti-roll Bar: Hadn't thought of this and only have a standard ARB.  I'll see about an uprated one though.

[b]Canley Aluminium Parts[b/]: I was originally planning some of these items but I don't have that sort of money for now.  I suppose these can be fitted later fairly easy if need be.

Alloy wheels: Definitely on the list once I get to the end of the project.  I'm using the old steels to trundle the chassis around for now.  What about wheel size itself?  Any suggestions?

Diff/Rear Spring Space: I'm undecided on this. 1/2 to 3/4" seems to be usual but I've seen talk about having to use drop links with these.  I think this refers to the Vertical Links but could someone explain the issue and what is needed.   At the moment the 'default' option is to use a 1/2" spacer I suppose.  I think I can get away with this without needing longer studs.  

Rear Spring: I assume my spring is standard and I wasn't planning on changing it.  My only concern is that it would be a real pain to change later once the car is on the road?

Poly Bushes: I've already started fitting Red Polybush bushes from a Canley kit.  Blue might have been a softer ride perhaps but I had to hop one way or the other.  I used Superflex on the 2.5PI and they're fine but I went for Canley's Polybush as they sold a complete kit. They look a quality bush with metal inserts so I'll hopefully they'll be okay.

It looks like I need to fit and play for a while but I don't want to spend a lot buying alternative kit so soon after finishing a major body off restoration.  

Nick

[JohnD]

Nick,
Wheel size.   Don't bother with bigger wheels, unless appearance is your only criterion.  Wid wheels and tyre only work on modern suspensions with near zero camber change,as the stiff side walls of low profile radials cause them to lift the trae off the road if tilted.

Drop links (to the vertical links??) for a raised spring would negate the fitting of the spacer as they would reverse the desirable change the spacer makes, raising the supension and lowerig the car.  And they would insert an additonal pivot point losing all control of the wheel angle.   Drop links are what connects the ARB to the suspenison arm.

Don't try to fit a spacer with OE diff studs.  Longer ones make fittong much easier - fit the spring with them untightened, then close up when connected to the vertical links.

But it looks to me as if your prevuious purchases will drive your choice of components.   Fit what you have within those constraints and see how things go.    IF you have the Spring Lifter Tool (see Workshop Manual) then replacing a Rotaflex spring later is only a fiddly job.

JOhn

[JohnD]

tigrr, copy of table from Courioer article below.
You will see that the Courier spring has 8 leaves and by far the lowest free arc height.
An estate spring will do as well. but equally hard to find.
JOhn

[tiggrr1]

Thanks for that John :)

My spring has 6 leaves, so it is a GT6 MK3 spring according to your chart.

But the free arc height looks to be more than the suggested 116mm :-/     possibly an uprated spring from somewhere.  

That's an old photo so I can't check without taking it off the car again.

[Nick Moore]

Regarding the front springs - if you make them too stiff, the chassis could start flexing instead! My Herald ran 450lb/in springs for a while and while it was compliant enough on the open road, it was a bit too harsh around town. It now has progressive front springs too, and is much nicer to drive. A GT6 wouldn't be as harsh on 450s due to the heavier engine, but I wouldn't go much harder without reinforcing the chassis. My GT6 Mk3 will get progressive springs as well.

As for shock absorbers, I prefer Konis over Spax for ride comfort. My Herald had Spax for years and they were very hard even on their lowest setting. Konis aren't height adjustable though, so you might have to use spacers if the front of the car rides too low.

Otherwise, fitting solid rack mounts and replacing the steering linkage with a UJ will make for a nice and direct feel, but shouldn't transmit too much vibration.

[Richard B]

Nick who supplied the progessive front springs. I appreciate you are the other side of the world to me!

What spec is this spring?  :-/

[Nick Moore]

Oh dear, I knew someone would ask who makes them. I'll give you a clue... they're from your side of the world, maybe even the UK (although it could be Portugal or Estonia, we're never really sure). No idea yet? OK. It's Gareth Thomas.

(Ducks)

What, no smiting? OK, I'll explain. Gareth has made several small batches and, like Bristol cars, they're marketed mainly to a select few faithful. If you ask nicely he might have some, or might remember you for next time if he makes some more. In any event, I love my Herald's springs, which mean that it's nice and comfy in usual driving but firms up when spanked around corners. They're something like 300/500, from memory. To be honest, I have no idea why more suppliers aren't making them - possibly it's a lot harder to make a progressive spring than a constant rate coil? Anyway, full credit to Gareth for making something no one else can be bothered to get right (in my slightly biased opinion anyway).

Mention of the Welsh Wizard is always divisive, so I'm going to hide in the garage with a saucepan on my head  ;)

[Nick Jones]

I've just got some progressive springs for my Vitesse from the same source..... Still haven't had the chance to get them fitted but they look very nicely made and I'm really looking forward to trying them!

Nick

[JohnD]

Has anyone considered the "beehive" spring, used for intake/exhaust valves, in this application?

GT's design works as the spring compresses, when the closely wound coils touch and become coil bound.  A coil spring's rate is given by:
Rate = (Torsion modulus of steel wire x wire diameter^4) / (Number of coils x coil diameter^3 x 8)

In effect the spring suddenly becomes much shorter, with less coils active.   But "Number of coils" affects rate in inverse proportion to the number.  So the rate will change suddenly and to a not very different rate.

A beehive has a number of coils at one end wound on a decreasing diameter, which factor affects the rate in inverse proprtion to the CUBE of the number as the coils are compressed.  Because the coils progressively get narrower, they will bind in series and a beehive spring has a constantly varying rate as it compresses and releases, instead of a sudden change.

I can only find beehives for the valve application.  Anyone know why not for suspensions?
JOhn

[uksnatcher]

Heres a bit more technical info inc rear camber info from an old thread on here...  ;)

http://clubtriumph.eu/cgi-bin/forum10/Blah.pl?m-1276120356/s-all/

[GT6 M]

John, lots of moderns have em on.
the Ladd behint me has them on  a Astra. as I helped him fit em.
about 8 inch high, and about 8 inch across, with a wrapped bottom biit,
turning inside its self as weight gets on it.

M

[mikeyb]

JohnD wrote:

I can only find beehives for the valve application.  Anyone know why not for suspensions?
JOhn

I'm sure that I have some TR7 springs stashed somewhere that are beehived . . . .

[thebrookster]

I don't know about beehive springs for cars, but I am fairly certain GT's springs are NOT beehived, which appears to be confirmed by the pictures posted of them?

Also, again as far as I am aware the GT springs are a straight swap, whereas beehive's would presumably require different spring seats?

John et al - have you tried looking for motorbike springs/manufacturers?? I seem to recall from previous investigations that this is where progressive springs were first really used as OEM, though I may well be winding you (and myself) up! (See what I did there  :P ;D :P ;D :P ;D )

[GT6]

The bike I have, which was already an old design when made in 1962, has progressive springs as standard. If you know what you want a spring maker should be able to help?

[Nick Jackson (2)]

So going back to the original thread, I'm thinking now I'll refurbish the original Rotoflex spring (assuming I can get the thing apart).   Apart from new spring eye bushes and graphite grease, is there anything I can do to improve this spring?

Nick

[Nick Jones]

You'll probably find the tattered remains of a number of hard rubber buttons which sit in imples between the leaves.  Best replaced with nylon/teflon items though you'll probably have to get them made as I'm not aware of anywhere that sells them.

Some like to wrap the spring with special tape (Denso tape?) to keep the grease in and road muck out.

Bradford Abbas tonight?

Cheers

Nick

[GT64fun]

Hi Nick(s)

I have used Denso tape on my Mk2 spring.

It is used in the construction industry typically for wrapping burried metal items etc. and should be available from good builders merchants.

'Orrible' stuff to handle but the surface does evently become less tacky as it matures and it certainly keeps the spring 'nice and fresh'.

Regards

Ian F  ;)

[Richard B]

Nick_Jones wrote:

You'll probably find the tattered remains of a number of hard rubber buttons which sit in imples between the leaves.  Best replaced with nylon/teflon items though you'll probably have to get them made as I'm not aware of anywhere that sells them.

http://www.ebay.co.uk/itm/TRIUMPH-HERALD-GT6-SPITFIRE-VITESSE-REAR-SPRING-THRUST-BUTTONS-INSULATOR-PADS-/370600042741?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item56497be0f5

Here they are in rubber. Don't know who sells them in nylon.

[Casper]

Denso
http://www.frost.co.uk/automotive-suspension-tools/denso-tape.html
Other suppliers are out there.

C.

[Nick Jackson (2)]

The Dutch Spitfire Club sell teflon ones.  See this thread:-

Sorry , link no longer available