Geometry advice
Discussion
I've replaced virtually everything that moves on my Griff yet my handling is still unpredictable at times, the best description I can come up with is "twitchy". I think the problem is bump steer but I'd like some advice.
On a Griff the standard geometry is 145mm from the deck at the front, 160 at the rear. With these settings neither my wishbone or track rod is parallel to the ground. I'm using the pre-load adjusters to alter the ride height. In an ideal world, what should be parallel, the track rod or the lower wishbone? I'm assuming it's actually the track rod? I'm happy to move away from the standard ride height if it improves stability.
My ride height may need to be a little different from standard anyway as I've gone up 2" on the rim size and lowered the profile accordingly. I'm aware that can increase tramlining but that's at an acceptable level for now. I've had 4 wheel alignment done and everything is within tolerance. I can put the actual readings up if it helps.
What should I be adjusting to decrease the sensitivity to road imperfections?
What's been replaced:
Shock absorbers with uprated adjustable Protech dampers
Steve Heath rose jointed drop links
Powerflex ARB bushes front and rear
Wishbones
Wishbone bushes (Powerflex)
Upper and lower balljoints
Track rod ends
Rack has been refurbed
Steering knuckle joints
Running Toyo Proxes @24 front, 26 rear (2PSI above standard)
ETA:
Picture of the offending article.
On a Griff the standard geometry is 145mm from the deck at the front, 160 at the rear. With these settings neither my wishbone or track rod is parallel to the ground. I'm using the pre-load adjusters to alter the ride height. In an ideal world, what should be parallel, the track rod or the lower wishbone? I'm assuming it's actually the track rod? I'm happy to move away from the standard ride height if it improves stability.
My ride height may need to be a little different from standard anyway as I've gone up 2" on the rim size and lowered the profile accordingly. I'm aware that can increase tramlining but that's at an acceptable level for now. I've had 4 wheel alignment done and everything is within tolerance. I can put the actual readings up if it helps.
What should I be adjusting to decrease the sensitivity to road imperfections?
What's been replaced:
Shock absorbers with uprated adjustable Protech dampers
Steve Heath rose jointed drop links
Powerflex ARB bushes front and rear
Wishbones
Wishbone bushes (Powerflex)
Upper and lower balljoints
Track rod ends
Rack has been refurbed
Steering knuckle joints
Running Toyo Proxes @24 front, 26 rear (2PSI above standard)
ETA:
Picture of the offending article.
Edited by HRG on Tuesday 10th June 15:54
HRG said:
Can't put mine in upside down thanks to the taper in the hub. I was cunning, I replaced the suspension a corner at a time so I had the original as a point of reference in case I forgot anything 
I wasn;t so cunning I am afraid, took me ages to figure out why the threads wouldn't reach the nyloc .. the answer was sooo simple!HRG said:
I think the problem is bump steer but I'd like some advice.
At risk of asking a stoopid question, have you actually checked for bump steer?It's not that difficult to do; any decent suspension set-up guy will be able to do it for you, or you can even do it yourself with care, a dial gauge and a few quids worth of DIY materials... full details and description of how to build a bump steer gauge are shown in Allan Staniforth's books (Competition Car Suspension and the Race and Rally Car Source Book).
My Griffith tended to tramline a bit even when correctly set up, so you may find that at least part of the issue is the standard trait, possibly exacerbated by the changes you've made to the wheels, but it would certainly do no harm to rule out bump steer if that's what you (probably correctly) suspect as part of the problem.
My Griffith also exhibited uncertain characteristics under certain transitions of road camber, too - mainly when pulling out to overtake over the crest of the road camber. This trait was reported by several magazine road tests when the car was new, and my suspicion was that it was caused movement of the rear roll centre upsetting diagonal weight transfer. It wasn't something I felt inclined to provoke in the interests of testing, though, as it made the car very nervous, and TVR declined my request for the geometrical data that would have allowed me to properly analyse the problem on paper.
Bottom line is that if you want a car that handles, don't buy a TVR.
Edited by Sam_68 on Tuesday 10th June 22:35
Tramlining I can cope with, it's the unpredictability when encountering undulations and crossing cambers as you say. I'm sure part of it is me over correcting as I split my driving with a wallowy old Volvo 850 that's more like turning a ship than something with a quick rack.
I just know it has the capability of being more stable than it currently is if I get everything set up correctly.
Front
Caster
Left 5.21
Right 5.45
Camber
Left -0.10
Right -0.42
Toe
Left 0.06
Right 0.04
Total 0.10
Rear
Camber
Left -0.54
Right -0.58
Toe
Left -0.01
Right 0.11
Total 0.10
Thrust Angle -0.06
Secondary Angles
SAI
Left 13.31
Right 14.17
Included Angle
Left 13.22
Right 13.35
Setback
Front 7mm
Rear 8mm
Track width difference -7mm
wheel base diff -1mm
I just know it has the capability of being more stable than it currently is if I get everything set up correctly.
Front
Caster
Left 5.21
Right 5.45
Camber
Left -0.10
Right -0.42
Toe
Left 0.06
Right 0.04
Total 0.10
Rear
Camber
Left -0.54
Right -0.58
Toe
Left -0.01
Right 0.11
Total 0.10
Thrust Angle -0.06
Secondary Angles
SAI
Left 13.31
Right 14.17
Included Angle
Left 13.22
Right 13.35
Setback
Front 7mm
Rear 8mm
Track width difference -7mm
wheel base diff -1mm
Properly adjusted, my Griff was pretty stable in a straight line (to the point where I felt comfortable exceeding 160mph on occasion) and the tramlining and steering kickback was perfectly manageable, but just very occasionally it would give me a serious brown-trouser moment when crossing a camber under hard acceleration - like I said, my suspicion was roll centre movement, coupled with very average standard damping, but since TVR weren't interested in helping me solve the problem I decided to cut my losses and get rid of the thing before it killed me!
Bump steer is a definite suspect, given what TVR would laughably refer to as manufacturing 'tolerances' with the suspension geometry, so you'd be well advised to hand the car over to a specialist (someone like Steve Gugliemi, for instance) to sort the geometry properly... lots of the places that do 4-wheel alignment have plenty of fancy computer equipment and know how to set the cars to Manufacturer's Specifications, but don't really understand the underlying principles of what they're trying to achieve. For a start off, they'll be working on the assumption that most performance cars will have been properly designed and manufactured to eliminate bump-steer, which simply isn't the case with TVR's, and won't even think to be checking it!
Bump steer is a definite suspect, given what TVR would laughably refer to as manufacturing 'tolerances' with the suspension geometry, so you'd be well advised to hand the car over to a specialist (someone like Steve Gugliemi, for instance) to sort the geometry properly... lots of the places that do 4-wheel alignment have plenty of fancy computer equipment and know how to set the cars to Manufacturer's Specifications, but don't really understand the underlying principles of what they're trying to achieve. For a start off, they'll be working on the assumption that most performance cars will have been properly designed and manufactured to eliminate bump-steer, which simply isn't the case with TVR's, and won't even think to be checking it!
Interesting topic, doubly so in that (i believe) tvr suspension designer neill anderson studied under lee noble .. and on the basis that the student should always go on to do better than the teacher you can only assume that even though lee noble seems to deliver better handling cars out of the box, he wasn't a very good teacher?
trackcar said:
...(i believe) tvr suspension designer neill anderson studied under lee noble ...
I'm surprised. I used to know Lee Noble reasonably well back in the early days of the Mk. 1 Ultima and the Noble 23, and I wasn't aware of that. Where did you learn that, and what's the story?Bear in mind that the Mk. 1 Ultima was created in (I think) about 1983, and Anderson was with TVR from 1987... so that would imply that Lee trained him as a design engineer in the first 4 years of the Noble company (pre- Noble-Moy), when he was just another a small kit car manufacturer?
For what it's worth, Lee himself would cheerfully admit that some of his early designs were quite badly flawed. The suspension on the Mk. 1 Ultima was pretty awful and even the Mk 2 wasn't perfect; early Ultimas won races mainly because they had relatively big engines and a couple of guys (Bob Light being the worst offender) threw an enormous amount of money and technology at crushing the opposition in what had previously been a very low-budget, low-horsepower, amateur championship. The Noble 23 was nice, but nothing special, either (the Xanthos 23 is a much better car all round). It wasn't until the Noble M12 that it all finally gelled and he created a car with truly exceptional handling and performance.
Edited by Sam_68 on Thursday 12th June 22:26
You didn't dream it - it's true. (Although whether the term "studied under" is strictly accurate is perhaps, more open to debate)!
I think it's also worth bearing in mind that not everything the engineers at TVR wanted to do actually GOT done. This was for a variety of reasons but there were always pretty major cost and time constraints under which the cars were designed and developed!
I think it's also worth bearing in mind that not everything the engineers at TVR wanted to do actually GOT done. This was for a variety of reasons but there were always pretty major cost and time constraints under which the cars were designed and developed!
I think he went to work for Lee Noble briefly after graduating and before moving to TVR. In all honesty, I will probably never get right to the bottom of it but I think he did a fair bit on the suspension side leaving Lee to concentrate more on the body. It has to be said that Lee's bodies were among the best in the kitcar industry in that era!
As far as TVR is concerned, the development budget was much smaller than most people would imagine with such a "glamorous" vehicle. I vaguely remember one conversation between a highly respected ride & handling consultant and someone at TVR:
Consultant: "I think I know what the problem is - those suspension bushes - not enough shear stiffness per unit volume. Why did you choose them"?
TVR employee: "'cause they were 76p each and had a 7/16" hole down the middle. You don't get much shear stiffness per unit volume for 76p"!
Ok, it's a bit of a silly one, but it's a good illustration of the cost constraints under which we had to operate. The point I'm trying to make is that I think most people would accept that the TVRs of the 80s and 90s offered huge performance per unit cost compared to their competitors. Obviously, they had to make the savings somewhere. Clearly the people who designed the cars had their shortcomings - of course they did, but not everything that was bad about the cars was down to the ineptitude of their creators!
Similarly, they DID know about bump steer and they DID get it as good as they could - being lumbered (on the Griffiths) with a Sierra front upright with an integral steering arm and a steering rack based on another vehicle with inner balljoint centres that weren't necessarily the perfect distance apart for the rest of the suspension geometry. Obviously, it's also perfectly possible that what came off the production line wasn't, in all cases, QUITE the same as what came off the drawing board, so there were often significant improvements to be had by paying someone who knew what they were doing to take the time to set the car up as well as was possible - at least within the constraints of the original design.
As far as TVR is concerned, the development budget was much smaller than most people would imagine with such a "glamorous" vehicle. I vaguely remember one conversation between a highly respected ride & handling consultant and someone at TVR:
Consultant: "I think I know what the problem is - those suspension bushes - not enough shear stiffness per unit volume. Why did you choose them"?
TVR employee: "'cause they were 76p each and had a 7/16" hole down the middle. You don't get much shear stiffness per unit volume for 76p"!
Ok, it's a bit of a silly one, but it's a good illustration of the cost constraints under which we had to operate. The point I'm trying to make is that I think most people would accept that the TVRs of the 80s and 90s offered huge performance per unit cost compared to their competitors. Obviously, they had to make the savings somewhere. Clearly the people who designed the cars had their shortcomings - of course they did, but not everything that was bad about the cars was down to the ineptitude of their creators!
Similarly, they DID know about bump steer and they DID get it as good as they could - being lumbered (on the Griffiths) with a Sierra front upright with an integral steering arm and a steering rack based on another vehicle with inner balljoint centres that weren't necessarily the perfect distance apart for the rest of the suspension geometry. Obviously, it's also perfectly possible that what came off the production line wasn't, in all cases, QUITE the same as what came off the drawing board, so there were often significant improvements to be had by paying someone who knew what they were doing to take the time to set the car up as well as was possible - at least within the constraints of the original design.
Edited by Avocet on Monday 23 June 23:35
As promised mate,
Feels very balanced but haven't had a chance to try it properly yet
Perhaps a few peoples views pls ?
Thought i'd stick it on here & Rob's other thread rather than starting a new one but if you lot don't comment i'll get a fresh one going
Set up was done by Lee at Supertyres,Maldon,Essex Great service by him, Damien & Warren....
Bit of a mix between what he has set TVR's up to before & what i thought/how i wanted it to feel!!
So feel free to flame me if it's all cock !!!
ETA
Supertyres have said if i feel it needs a little tweek to run it back in
Feels very balanced but haven't had a chance to try it properly yet
Perhaps a few peoples views pls ?
Thought i'd stick it on here & Rob's other thread rather than starting a new one but if you lot don't comment i'll get a fresh one going
Set up was done by Lee at Supertyres,Maldon,Essex Great service by him, Damien & Warren....
Bit of a mix between what he has set TVR's up to before & what i thought/how i wanted it to feel!!
So feel free to flame me if it's all cock !!!
ETA
Supertyres have said if i feel it needs a little tweek to run it back in
Edited by Del 203 on Wednesday 25th June 19:20
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