Advice please on Griff Nitron settings and ride he

[steve-v8s]

Can anybody who understands suspension set up give me a quick idiot’s guide. I have just had Nitrons fitted to the Griff. My simplistic understanding is that softer is more grip harder is less. So if it under steers soften the front if the back is wayward soften the back. But stiffer is better because it keeps more of the four wheels planted. Lower is also better.

With adjustable ride height and damping in each corner I have a lot to fiddle with that I don’t understand. Help please. I am running So3s on the road and Ao32s on the hill climb, unless it is wet in which case it will be back to the So3s.

Also it would be interesting to know what the ride height of a standard Griff set-up is. Seems about four and a half to five inches from the chassis looks about right.

Thanks for your help

[greenv8s]

I'd say you have got it about right. However, lower is not always better because the unequal length wishbones will lose their geometry when you get too far from the standard ride height. Also, you should aim to use the roll stiffness and geometry to sort out the understeer/oversteer balance rather than dampers. You can fine-tune it using the dampers, but the 'ideal' damper settings depend on the mass of the car and the spring rates, and the further you go from this ideal (in an attempt to bias the handling) the less overall grip you are going to find. Final advice is to run the dampers as soft as you can get away with on a given surface, if you find you need better body control increase the spring rates before making big increases to the damper rates.

[joospeed]

Yup what Peter said :

general advice for any road cars is softer is better.

I always advise to start any damper tuning at the front .. you need the *minimum* damping to get the job done .. and a good test is to find a slightly bumpy corner and drive around it, stiffening the front end until you feel the grip tail away, then back off a few clicks and you should be somewhere about right for bumpy cornering

.. then do the same but on the brakes, hold the brakes on the point of locking over a bumpy road and start playing with the damper settings .. you'll probably fid that the optimum settings isn't the same as the cornering setting, average or bias toawards whichever you think is more important and that's fine for the front.

at the rear you're looking for two things, traction and control of the spring to stop the car spitting you off in the opposite diretion to the original slide (like highsiding a bike) .. if you dial in enough rebound you can control the recovering spring from a slide situation .. so do a lot of S bends sliding and stiffening until your car doesn't spit you off backwards (driver skill permitting)

.. then do the brake test on the bumps too .. and try to find the compromise / bias /average that suits you and the car.

On the road long stroke, soft springs with preload to get the ride height back is the way to go. On track where you're pushing the grip on a smooth surface then you can go much stiffer.

Also remember that dampers don't alter the ultimate angle of roll, pitch, dive etc, just the rate at which those angles are achieved.

Did u go for a bespoke kit or off the shelf kit? if off the shelf it's got a high level of low speed compression damping which allows novice drivers to lean on the car on corner entry and provides a degree of corner entry understeer, if you're anything like handy driver you need to alter the kit spec to suit ...

If you do that set-up technique then you'll get something that works on the road within about half an hour. But it will still be a compromise. the trick then is to drive so the *car* is doing what it wants to go fast, that isn't the same thing as what you *think* the car needs to do to go fast .. teehee.

[steve-v8s]

Thanks for the two useful replies, Clouds permitting I will put the Ao32s on and go out and have a play. The ride height is lower than before. I didn’t measure it but have grounded on a couple of speed humps that were OK before. A couple of things I am not clear about. When we first put the car on it’s wheels it was obviously very low, but I drove it to see what it was like. It was very hard but felt like it was on rails. The dampers were all set at 14clics from soft and the springs measured to be the same length as the originals.

I can’t figure why winding the springs up to raise the ride height makes the car softer. I would think a more compressed spring would be harder. The other thing is can the dampers be adjusted up and down or do you need to go all the way back to soft each time and work back from there ? I guess they are an off the shelf part and I definitely come under the “novice” heading. Incompetence and cowardice are my main specialities, trying to learn though.

[GreenV8S]

If you set the ride height too low it could be hitting the bump stops which will ruin the ride comfort and mess up the handling.

[joospeed]

unless you're running at the maximum extended damper length winding the spring platform up *doesn't* compress the spring .. think of it as the spring staying the same length and you're moving the damper body downwards so raising the ride height.. the spring carries the same load so can't be more compressed if you raise the ride height (excepting changes to the mechnical advantage of the system, which are small in this case) .. so what peter says about bump stops could well be the cause. There is a small change in wheel rate to spring rate as you raise and lower, but this is small and you'd have to be well in tune with your car to notice it. so .. something else is happening to cause it.

[steve-v8s]

I guess the bump stop theory is probably a good one. So as to understand what was happening I made a rough cardboard model of the wishbone / damper arrangement and tried to apply Joospeed’s set-up advice. I can dial in more or less under steer on one particular corner but can’t seem to detect an obvious difference on the brake test. I have decided that I will have to wait until I get on the hill, which has a much better surface than any of the local roads to fine tune it. I have a two day meeting next weekend so will treat Saturday as a test day for Sunday.

Would be particularly interested to know what damper settings and ride other people are using with the off the shelf Nitrons.

[Digga]

I've recently had Nitrons fitted by Peninsula, so I assume these aren't the 'off-the-shelf' items, but ones set up with car and use (biased towards track rather than road) in mind.

Unfortunately, I've changed a lot of other components at the same time (somthing I'd previously sworn never to do, again) including new tyres, so it's hard to be truly objective, but I'll add my experience FWIW.

The settings towards the stiffer end of adjustment seem to work best, in controlling the back end, although I'd need another day at Loton to see if I've totally cured the frightening 'kangarooing' of the back end on Cedar Straight. - It seems certain combinations of sustained gradient, accelleration and bumps are peculiar to hillclimbs only!

I'm running about 400 lb front springs, and 325 lb rear. As Pete might point out, this is softer than many sprint/hill TVRs, but I'm fairly happy with it.

If there were such a thing, I think an up-rated rear anti-roll bar might help my car.

[joospeed]

if that's a griff you got there, they're very stiff springs, especially at the back ..

[Paul V]

I have just fitted Redline shocks with Nitron springs to the Griff, it has 400 lb on the front and 325lb on the rear, the back does seem very bouncy at the back, I can wind the shocks up to stop this but then it makes the car too stiff, I think I may try the 300 lb springs to see if that makes a difference.

[joospeed]

Paul V said:

I have just fitted Redline shocks with Nitron springs to the Griff, it has 400 lb on the front and 325lb on the rear, the back does seem very bouncy at the back, I can wind the shocks up to stop this but then it makes the car too stiff, I think I may try the 300 lb springs to see if that makes a difference.

yup, you can wind the adjuster up of course, but because you can't separate the compression and rebound you end up with a ride that's on the firm side .. if you're a press on driver who likes a lively back end (phnaaar) then it's ok. also good for luggage carrying of course! but a bit stiff for good traction, you would certainly want to take the rear anti roll bar off for instance. 400 lbs at the front is a great compromise / biased spring for track use though ..

[Digga]

325 is relatively stiff, and in my opinion, not a great idea if you do a lot of raod miles.

My car (yes it is a Griff Jools! - see profile pic) is used predominatly for track stuff, and I'm prepared to compromise.

I'd say though, that there are other sprint/hill TVRs with stiffer springs, particularly at the front - 700 lb and more.

[greenv8s]

Digga said:

I'd need another day at Loton to see if I've totally cured the frightening 'kangarooing' of the back end on Cedar Straight.

This sounds mysterious, what are the symptoms?

[Digga]

greenv8s said:

Digga said: I'd need another day at Loton to see if I've totally cured the frightening 'kangarooing' of the back end on Cedar Straight. This sounds mysterious, what are the symptoms?

I think it was due to running the dampers too soft, although it was possibly compounded by hitting the bump stops.

Basically, I had to get off the throttle only 1/3 of the way up Cedar Straight (which as you know, is anything but straight!) because the back end started to bounce in ever increasing amplitude.

This pic:

is on the steep uphill from Fallow to Museum - lots of throttle - and I wonder if the rear may be set too low, and/or too soft?

[Paul V]

The back does look very low in that pic, I have been told that Griff’s don’t like being too low at the rear.

[joospeed]

yup if you go too low you increase the roll couple, going low generates *more* roll for any given suspension spring and damper and roll bar, something you'd like to avoid! .. also going too low alters the roll axis, which can alter the handling balance mid corner, something else best avoided.. also going too low runs the car on the bump rubbers, effectively a very stiff spring which reduces traction dramatically .. something else to avoid ..

as you can see, there's a lot of very good reasons for not running your car too low!!

[Digga]

[quote=joospeed]yup if you go too low you increase the roll couple, going low generates *more* roll
quote]

My hideous 'experiment' at Loton would appear to confirm this!

However, in the same trim, the car was 3rd in class yesterday at Anglesey (first time there), and felt like it had some more to go, with someone better behind the wheel. So now I'm scared to change it!

I can certainly see how it affects geometry, and I also think the 'bouncing' episode in the earlier Loton runs could be a combination of the geometry, bump stop, and (definately) insufficient damping.

[greenv8s]

joospeed said:

the bump rubbers, effectively a very stiff spring

Vert stiff, also undamped. This would leave the car bouncing on the tyres and bump stops which would be quite unpleasant I imagine!

[Digga]

greenv8s said:

joospeed said: the bump rubbers, effectively a very stiff spring Vert stiff, also undamped. This would leave the car bouncing on the tyres and bump stops which would be quite unpleasant I imagine!

Your imagination of this is fairly accurate.

As an utter, well novice is perhaps the most polite description, how can I sort this?

Can I wind the ride height up with the spring/damper assembly in situ? Is there a standard sized c-spanner I need?

[greenv8s]

Digga said:

Can I wind the ride height up with the spring/damper assembly in situ? Is there a standard sized c-spanner I need?

Yes. No.

First thing to do is to see how much bump travel is left on the dampers at the normal ride height to see if we are looking at the right problem. You can do this by jacking up one of the rear corners, taking the wheel off and then lowering the hub back on to a stand that holds it the same height off the ground as it would be with the wheel fitted - iyswim. The suspension will then be taking the same weight as normal. Looking through the springs you can see how much damper rod is visible, this tells you how much bump travel is left. How much bump travel you need depends on what spring rates you're running and what sort of road surface the suspension needs to cope with, but for a typical road car I think 2" of bump travel at the wheel is sufficent, this corresponds to about 1.4" of travel at the damper. If you have a lot less than this then we're probably looking at the right problem and need to raise the rear ride height. Also check the front to see if they have a similar problem.

You can adjust the ride height fairly easily without any special tools, just jack the car up and take the wheel off, then grab the body of the spring with both hands and turn it firmly; the spring seat will go with it allowing you to wind the spring seat up or down the damper body. Obviously in this case you want to wind it upwards to increase the ride height. If the damper body is badly corroded you might find the spring slips on the spring seat and the spring seat doesn't turn, in this case grab the spring and spring seat together and turn then together - just make sure you don't trap your hand between the spring seat and the suspension, if you're curious yes it does hurt.