Tuscan front suspension facts and experiment
Discussion
I had TVR Power check/set up my geo and they couldn't get the camber within spec, so I've had to enlarge the holes in the upper wishbones. I've increased the slots by 3.5mm which should give more camber adjustment. The current camber setting is +1.8degrees (leaning in) which makes the front end unstable over rough roads. Hopefully a camber setting closer to 0.5-1degrees will be better!
Edited by MPETT on Monday 17th March 22:38
MPETT said:
After looking at many posts on the subject of bump steer issues with the early Tuscan and having experienced first hand the effect of adding spaces to my prevous '04 Tuscan, I am now aware of the small changes that can have a massive effect on the way a car feels and steers.
For anyone wanting to know more about suspension design, I would reccoment reading "The sports car and Kit car suspension and brakes high performance manual". Its hardcore reading and takes a while to sink in. I'd also reccomend getting your hands on a remote controlled buggy so that you can play with the suspension and see the relationships and effects of different settings.
I am in the throws of rebuilding my Tuscan from the ground up:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
and the latest discussion has moved onto the suspension and whether I should change the design to the later configuration.
The research I have done shows that in march 2001 the design of the front suspension changed in the following way:
Bump steer is often refered to as "The problem with the early cars". From my dealings and involvement with the SP Wheel Spacers (I was the first person to test it), I understand that tyre wall height has an effect on the scrub radius and by either increasing the tyre wall or increasing your offset with a spacer, it is possible to alter the scrub radius.
From what I have read, the scrub radius needs to pass through the contact patch of the tyre and depending on whether it passes inboard or outboard of the centre line of the wheel, it can have an effect of pulling the wheel either outboard or inboard.
Acknowledging the above, if in addition to the scrub radius, there is an effect of bump steer that will cause the wheels to point outwards (positive toe) or inwards (negative toe), the effect can be significantly amplified.
Therefore, I set out to understand suspensions characteristics on MY CAR (Jan 2000). I can only comment on my car due to the aformentioned variables.
I set up my geometry to the following default factory settings:
I used this experimental setup/technique to measure bump steer: http://youtu.be/LO07qmJ9zkk
My videos show the standard setup, and with 4mm added beneath the steering rack.
http://youtu.be/3QKvdZWyV_I
http://youtu.be/_Yt0JcNhxOA
From what I understand, the thing to look out for is not to have too much bump oversteer. When there is compression of the outer wheel's suspension in a corner, any bump oversteer (additinal toe in) of the outer wheel, causes the wheel to point into the corner more than you want to/have dialed in with the steering wheel. If this happens you'll be turning in too much, so you'lll have to take off steering lock, which reduces the load on the outer wheel, (reducing the compression), which in turn takes off the bump oversteer, which then means you're not turning in enough, so you have to turn into the corner more...... This leads to an unstable cornering car that for want of a better word, 'weaves' through the corner.
The ideal scenario, is to not have any bump oversteer on the outside wheel, so that the amount you steer in, is the amount you get. Having said that, having bump understeer on the inside wheel, (which is drooping/lower than ride height due to body roll), means the inside wheel turns in more to the corner, which helps/can be beneficial up to a point.
I also tried the experiment with 2mm spacer. This seemed to give the best compromise. The suspension's toe stayed within 0.2mm thoughout 85% of the total travel of the suspension.
Here are the lazer traces:
I did 2 experiments at normal factory settings, one and the begining of the test and one at the end, after the 2mm and 4mm tests. (to validate consistency in my set up)
Factory setup:
They both showed a bump oversteer of 1.2mm (actual measurement is divided by factor of 10) and a droop from ride height understeer/toeout of 3mm.
My modification of +2 and +4mm spacers under the rack:
These showed 0mm to 0.2mm of bump oversteer for most of the travel and both showed toe out at the extremes of travel in bump and droop.
My conclusion is that 2mm seems to be the best compromise for my suspension set up.
I would be happier if that at full bump and full suspension droop, that there was less under steer/toeing out of the wheels, but in the grand scheme of things the suspension will spend very little time at those extremes.
As a result, I think I'll stick with the standard suspension components and add 2mm to the rack to raise it upwards. If I can measure the scrub radius and it falls significantly outside the centre line of the wheel, I'll have to consider adding some spacers as before. If that doesn't work, then parhaps the new arms might then make sense? Its not a cheap mod, but it would be worth it for a stable and predicatble cornering car.
I hope this was useful. Please let me know if you have any comments or dissagre with my method and findings. I want to get my car right now, whilst its easy to work on, so if you've had any experience with getting your Tuscan to handle correctly, I'm all ears!v
Cheers,
Martin
Two pointsFor anyone wanting to know more about suspension design, I would reccoment reading "The sports car and Kit car suspension and brakes high performance manual". Its hardcore reading and takes a while to sink in. I'd also reccomend getting your hands on a remote controlled buggy so that you can play with the suspension and see the relationships and effects of different settings.
I am in the throws of rebuilding my Tuscan from the ground up:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
and the latest discussion has moved onto the suspension and whether I should change the design to the later configuration.
The research I have done shows that in march 2001 the design of the front suspension changed in the following way:
- The top wishbones were made longer/wider (pushing the ball joint outboard)
- The upright's top ball joint was moved outboards by circa 10mm
- A couple of different racks were used. The early (dates unknown) Tuscans used the same racks at the Chims, Griffs and the Cerbera V8 cars. (If anyone has more information on the specifics, please let me know).
- There are 2 track rod lengths quoted: 336mm (early cars, dates unknown) and 316mm (late Tuscans/T350 and Tamora).
- The King Pin Inclination was reduced.
- The longer wishbones reduced the dynamic effect on camber (leaning over of the wheel to maintain a square relationship to the road)
- The Scrub/Pivot radius was affected (assumed to have brought it inboard).
Bump steer is often refered to as "The problem with the early cars". From my dealings and involvement with the SP Wheel Spacers (I was the first person to test it), I understand that tyre wall height has an effect on the scrub radius and by either increasing the tyre wall or increasing your offset with a spacer, it is possible to alter the scrub radius.
From what I have read, the scrub radius needs to pass through the contact patch of the tyre and depending on whether it passes inboard or outboard of the centre line of the wheel, it can have an effect of pulling the wheel either outboard or inboard.
Acknowledging the above, if in addition to the scrub radius, there is an effect of bump steer that will cause the wheels to point outwards (positive toe) or inwards (negative toe), the effect can be significantly amplified.
Therefore, I set out to understand suspensions characteristics on MY CAR (Jan 2000). I can only comment on my car due to the aformentioned variables.
I set up my geometry to the following default factory settings:
- -0.7 degrees of negative (Camber)
- Shims either side of the upper ball joint (Castor)
- 1mm of front Toe in
I used this experimental setup/technique to measure bump steer: http://youtu.be/LO07qmJ9zkk
My videos show the standard setup, and with 4mm added beneath the steering rack.
http://youtu.be/3QKvdZWyV_I
http://youtu.be/_Yt0JcNhxOA
From what I understand, the thing to look out for is not to have too much bump oversteer. When there is compression of the outer wheel's suspension in a corner, any bump oversteer (additinal toe in) of the outer wheel, causes the wheel to point into the corner more than you want to/have dialed in with the steering wheel. If this happens you'll be turning in too much, so you'lll have to take off steering lock, which reduces the load on the outer wheel, (reducing the compression), which in turn takes off the bump oversteer, which then means you're not turning in enough, so you have to turn into the corner more...... This leads to an unstable cornering car that for want of a better word, 'weaves' through the corner.
The ideal scenario, is to not have any bump oversteer on the outside wheel, so that the amount you steer in, is the amount you get. Having said that, having bump understeer on the inside wheel, (which is drooping/lower than ride height due to body roll), means the inside wheel turns in more to the corner, which helps/can be beneficial up to a point.
I also tried the experiment with 2mm spacer. This seemed to give the best compromise. The suspension's toe stayed within 0.2mm thoughout 85% of the total travel of the suspension.
Here are the lazer traces:
I did 2 experiments at normal factory settings, one and the begining of the test and one at the end, after the 2mm and 4mm tests. (to validate consistency in my set up)
Factory setup:
They both showed a bump oversteer of 1.2mm (actual measurement is divided by factor of 10) and a droop from ride height understeer/toeout of 3mm.
My modification of +2 and +4mm spacers under the rack:
These showed 0mm to 0.2mm of bump oversteer for most of the travel and both showed toe out at the extremes of travel in bump and droop.
My conclusion is that 2mm seems to be the best compromise for my suspension set up.
I would be happier if that at full bump and full suspension droop, that there was less under steer/toeing out of the wheels, but in the grand scheme of things the suspension will spend very little time at those extremes.
As a result, I think I'll stick with the standard suspension components and add 2mm to the rack to raise it upwards. If I can measure the scrub radius and it falls significantly outside the centre line of the wheel, I'll have to consider adding some spacers as before. If that doesn't work, then parhaps the new arms might then make sense? Its not a cheap mod, but it would be worth it for a stable and predicatble cornering car.
I hope this was useful. Please let me know if you have any comments or dissagre with my method and findings. I want to get my car right now, whilst its easy to work on, so if you've had any experience with getting your Tuscan to handle correctly, I'm all ears!v
Cheers,
Martin
1) with the spacers either dside of ball joint you run 4 degrees of castor, if you run both shims at front you get 5 degrees of castor, this is a much more conventional castor rate for a front engined rear wheel drive car with power steering and worthy of consideration.
The advantages are a better contact point on the tyre on turn in and better self centring, it also makes the Tuscan feel more stable.
2) its an accepted method to stiffen up cars to of set bump steer when dropping below the roll centres but most of the after market suspension increases spring rates on Tuscans anyway thus limiting bump steer.
Surely it is better to address and fix as the inherent bump steer/geometry issues than limit them by using stiff spring/damper settings? This simply masks the problem instead of fixing it.
It is well known the early mk1 Tuscan has major steering geometry issues. This includes the track rod pivot not being in line with the wishbone pivots, the track rod not being parallel to the lower wishbone and the top wishbone being so short it gives major camber changes on compression. Stiffening the spring/damper settings will reduce the effects of this inherent geometry problem but at the same time give the occupants a very uncomfortable ride.
There are quite a few owners on here that have spent a lot of time and effort getting this right and had a good result from it and they know limiting the suspension travel is not the answer. It is quite disturbing to read that a major suspension design company has suggested it is acceptable to reduce the inherent bump steer issues by using stiffer suspension.
It is well known the early mk1 Tuscan has major steering geometry issues. This includes the track rod pivot not being in line with the wishbone pivots, the track rod not being parallel to the lower wishbone and the top wishbone being so short it gives major camber changes on compression. Stiffening the spring/damper settings will reduce the effects of this inherent geometry problem but at the same time give the occupants a very uncomfortable ride.
There are quite a few owners on here that have spent a lot of time and effort getting this right and had a good result from it and they know limiting the suspension travel is not the answer. It is quite disturbing to read that a major suspension design company has suggested it is acceptable to reduce the inherent bump steer issues by using stiffer suspension.
This is good reading.
I have all my wishbones off at the moment, rack off, engine out blah blah...
When I was dismantling I was looking at the top wishbone thinking I would fancy more caster, ummhhh, move the spacers one sided, 7deg is probably maximum I would ever go, so if I get 5deg with two one side then that's happening. I looked at the rack and figured the track rod looked a bit low/odd, but wasn't sure as the car is in the air at the moment so I will wait until loaded up again, although the rack just felt low and I have already figured more spacers are needed. The camber I reckon is cool at 1deg, based on following my mates 2000 Tuscan in my sag and watching his wheels on an energetic drive, he doesn't run much camber up front but does on the back.
Now in bump he does very well and he has Gaz Golds which seem to be set quite hard so guess all the pointers are for a go kart ride with a touch more caster, anyone tried this???
Martin, how are the speaker pods coming on???
J
I have all my wishbones off at the moment, rack off, engine out blah blah...
When I was dismantling I was looking at the top wishbone thinking I would fancy more caster, ummhhh, move the spacers one sided, 7deg is probably maximum I would ever go, so if I get 5deg with two one side then that's happening. I looked at the rack and figured the track rod looked a bit low/odd, but wasn't sure as the car is in the air at the moment so I will wait until loaded up again, although the rack just felt low and I have already figured more spacers are needed. The camber I reckon is cool at 1deg, based on following my mates 2000 Tuscan in my sag and watching his wheels on an energetic drive, he doesn't run much camber up front but does on the back.
Now in bump he does very well and he has Gaz Golds which seem to be set quite hard so guess all the pointers are for a go kart ride with a touch more caster, anyone tried this???
Martin, how are the speaker pods coming on???
J
The first thing I did after getting my mk1 was move the spacers to give maximum caster. This helps but isn't a magic wand fix. The track rod ball joint has to be in line with the upper and lower wishbone inner pivot points. This is well documented on here as early as 2002 and any car suspension tuning literature will tell you this is of primary importance to maintain correct geometry through entire suspension travel.
Lifting the rack helps fix the out of parallel problem between the track rod and lower wishbone but I think machining a new steering arm with the correct offset
Lifting the rack helps fix the out of parallel problem between the track rod and lower wishbone but I think machining a new steering arm with the correct offset
Ab Shocks said:
2) its an accepted method to stiffen up cars to of set bump steer when dropping below the roll centres but most of the after market suspension increases spring rates on Tuscans anyway thus limiting bump steer.
Is there a competition running "most ridiculous post ever"OK take the shocks off and put 1 inch box section in there place, bump steer cured
Is it bump steer or kick back?
I ask as I suspect that bump steer would not be cured by wheel spacers yet these seem to be held high as the most effective, cost/ease etc. fix. Consider also that the results from the OPs BS graph experiments were favourable. The early mk1 mod, moving the top ball joint and effectively altering the king pin inclination will have more effect in part lock to geometry than it would wheels straight ahead, correct??
What think?
J
I ask as I suspect that bump steer would not be cured by wheel spacers yet these seem to be held high as the most effective, cost/ease etc. fix. Consider also that the results from the OPs BS graph experiments were favourable. The early mk1 mod, moving the top ball joint and effectively altering the king pin inclination will have more effect in part lock to geometry than it would wheels straight ahead, correct??
What think?
J
Agreed to some extent but it still remains you need the three suspension pivot points in line i.e.upper, lower wishbone and track rod in line. Couple this with the other issues mentioned above and over the last 12 years and you have a poor handling car. It can and will not ever work properly. I am even more stunned to read that the alleged answer by a supposed respected suspension design company is to stiffen the springs and damping to lessen the travel. This is the most ridiculous answer I have ever read. This is totally irresponsible to purchasers as too stiff springs or/and damping will cause the tires to skip over a road surface instead of staying fixed to it. This will provoke even more problems as well as the initial inherent issues mentioned once or twice above over the years. It's not surprising these cars are slated for their handling when the suspension 'experts' are saying to keep going more and more stiff on what is relatively stiff settings from the factory.
Edited by Andy_mr2sc on Friday 14th March 22:53
Sagi Badger said:
Is it bump steer or kick back?
I ask as I suspect that bump steer would not be cured by wheel spacers yet these seem to be held high as the most effective, cost/ease etc. fix. Consider also that the results from the OPs BS graph experiments were favourable. The early mk1 mod, moving the top ball joint and effectively altering the king pin inclination will have more effect in part lock to geometry than it would wheels straight ahead, correct??
What think?
J
Hi John, while your engines out Will you be raising your rack height?I ask as I suspect that bump steer would not be cured by wheel spacers yet these seem to be held high as the most effective, cost/ease etc. fix. Consider also that the results from the OPs BS graph experiments were favourable. The early mk1 mod, moving the top ball joint and effectively altering the king pin inclination will have more effect in part lock to geometry than it would wheels straight ahead, correct??
What think?
J
So went out on a drive this morning down to silverstone for the Sunday service. What weather! I'm pleased to report that the suspension is now much much better than it was before. I've managed to firm up the shocks so that it now stops undulating over the bumps and feels properly under control. It was a few years ago that I had an 04 tuscan with spacers, but it doesn't feel bad to me right now at all!
Can anyone comment about when the early suspensions felt bad. Was it all the time, did it tram line a little bit or was it just when pushing hard? I was thinking about doing an airfield day to play around with the suspensions settings to see what works best.
Can anyone comment about when the early suspensions felt bad. Was it all the time, did it tram line a little bit or was it just when pushing hard? I was thinking about doing an airfield day to play around with the suspensions settings to see what works best.
Hi Martin
What changes did you finally settle on making to the front geometry? I have read a lot of threads on here dating back years regarding modifying the front geometry and am slowly getting my head around it. When looking underneath at mine there are some major geometry faux pas but I'm interested to know which ones to address to make the most difference.
Mine drives like most do from what I have read. It's ok at lower speeds but when you start approaching three figures it almost feels like you are not in control of it. When accelerating hard when overtaking for example it feels very 'floaty' and it feels like it could easily wander into the side of the car you are passing. The car wanders and when you try and correct it the car doesn't react to input like you would expect and it does not inspire any confidence to drive hard in to a corner. It drives best when on a very flat straight road but on a road with lots of camber or other undulations it feels very skittish and out of control to the point where I'm backing off. It is worst on twisty B roads which is really frustrating as these should be the most fun; anyone can go fast in a straight line! I had two Chims before my Tuscan. One was a very late, low mileage on Nitrons and the other a very early tired one on standard dampers. They both drove massively better and inspired the confidence and feedback needed to push on hard.
Just before I bought my Tuscan it had had its nitron dampers rebuilt and a full geometry set up at a well known local tvr specialist so I strongly believe it is a bit more than altering a bit of camber here and toe in there to sort this.
What changes did you finally settle on making to the front geometry? I have read a lot of threads on here dating back years regarding modifying the front geometry and am slowly getting my head around it. When looking underneath at mine there are some major geometry faux pas but I'm interested to know which ones to address to make the most difference.
Mine drives like most do from what I have read. It's ok at lower speeds but when you start approaching three figures it almost feels like you are not in control of it. When accelerating hard when overtaking for example it feels very 'floaty' and it feels like it could easily wander into the side of the car you are passing. The car wanders and when you try and correct it the car doesn't react to input like you would expect and it does not inspire any confidence to drive hard in to a corner. It drives best when on a very flat straight road but on a road with lots of camber or other undulations it feels very skittish and out of control to the point where I'm backing off. It is worst on twisty B roads which is really frustrating as these should be the most fun; anyone can go fast in a straight line! I had two Chims before my Tuscan. One was a very late, low mileage on Nitrons and the other a very early tired one on standard dampers. They both drove massively better and inspired the confidence and feedback needed to push on hard.
Just before I bought my Tuscan it had had its nitron dampers rebuilt and a full geometry set up at a well known local tvr specialist so I strongly believe it is a bit more than altering a bit of camber here and toe in there to sort this.
Andy_mr2sc said:
The track rod ball joint has to be in line with the upper and lower wishbone inner pivot points.
the inner ball joint (were the track/tie rod is fixed to the steering rack) also has to be in the correct relationship with the inner wishbone pivots, some early cars have the wrong length rack onhttp://www.thetvrshop.com/TVR/Parts_details/TVR%20...
Edited
Edited by Walford on Monday 17th March 15:06
Sorry I did mean the inner track rod pivot point. I saw a suggestion on here to make a threaded spacer between the rack and the track rod to extend this pivot point outwards. Did anyone ever try this with success? Much cheaper than buying a new rack! Theoretically then shorten the track rods by the same amount and lengthen the thread if necessary.
Andy_mr2sc said:
Sorry I did mean the inner track rod pivot point. I saw a suggestion on here to make a threaded spacer between the rack and the track rod to extend this pivot point outwards. Did anyone ever try this with success? Much cheaper than buying a new rack! Theoretically then shorten the track rods by the same amount and lengthen the thread if necessary.
I think Raceproved starting doing a kit with those a few years back. It seemed to go quiet pretty quickly.Mine as standard was worst on mid corner compressions and under hard braking over bumps / camber changes. Nitrons helped but it was still scary at times. Having played around with it a bit, even a tiny amount of bump toe in makes it feel very uneasy, whereas bump toe out just numbs the steering the more you have. From memory, I ended up at about 1mm toe out at 1" bump which makes it much easier to drive quickly on less than perfect roads.
bananaface said:
ive had a chimp, cerb, griff, tuscan mk1 and finally a t350.
nothing scared me like the tuscan.
the only one that ever span me off the road without reason or warning and the only one that ever changed lanes in the time it took to blink.
I wonder why the Cerbs don't have the same issue as the front end setup is identical to the early Tuscans AFAIK.nothing scared me like the tuscan.
the only one that ever span me off the road without reason or warning and the only one that ever changed lanes in the time it took to blink.
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