T350 bump steer options
Discussion
It seems we have two camps. One says there is a fundamental, known problem with the design, the other camp says the design is fine, it just needs setting up carefully. There is obviously a lot of experience and expertise here, I have no way of telling which is right.
What does seem clear though is that I should get the car set up as best as possible as it is, and then see how it feels before making any design changes. The car has Nitron Racing Reds, no sign of leakage but they are a few years old. May be worth a refurb.
The front tyres are 225/35/18 87 XL Michelin Pilot Super Sport, the rears are 235/40/18 95 XL Eagle F1. The rear tyres need changing as they are old and developing cracks on the inner wall.
Maybe I should start another thread about tyres, that seems the place to start.
What does seem clear though is that I should get the car set up as best as possible as it is, and then see how it feels before making any design changes. The car has Nitron Racing Reds, no sign of leakage but they are a few years old. May be worth a refurb.
The front tyres are 225/35/18 87 XL Michelin Pilot Super Sport, the rears are 235/40/18 95 XL Eagle F1. The rear tyres need changing as they are old and developing cracks on the inner wall.
Maybe I should start another thread about tyres, that seems the place to start.
I don’t seem to have any problem driving mine to the limit and trust me I do although it can go light now and again I don’t find it too much of a problem, been on a few tracks with it and I found it better than all the other tvr,s I have had it certainly goes round corners better than my other TVRs mind you at Brands Hatch I ended up going backwards into the kitty litter on paddock hill bend and I went back out and it was all over the place so lost confidence and thought it was the tyres go off but found out a week later at the mot station both rear springs had snapped in half, nothing to do with my driving I think just a bad set of springs
My early Tuscan has been changed to the later wishbone and rack setup, as per the T350, as the early setup could only be corrected over a very small travel window. Having actually measured the bump steer, it needed 8mm spacers under the rack to get it to very slight bump toe out, which calms the steering down over dodgy roads.
The later cars were fitted with 10mm rack spacers as standard so the factory was aware of the issue with early Tuscans. The Sag wishbone mounts are c.15mm (IIRC?) higher than T cars, which is why they have the cranked arms. I think you'd get too much bump toe out using Sag arms on a T car, even with the rack mounted with no spacers.
I think some people confuse steering kick back and bump steer. The only way to identify and correct bump steer is to measure it, especially with TVRs, as each car will probably vary.
The later cars were fitted with 10mm rack spacers as standard so the factory was aware of the issue with early Tuscans. The Sag wishbone mounts are c.15mm (IIRC?) higher than T cars, which is why they have the cranked arms. I think you'd get too much bump toe out using Sag arms on a T car, even with the rack mounted with no spacers.
I think some people confuse steering kick back and bump steer. The only way to identify and correct bump steer is to measure it, especially with TVRs, as each car will probably vary.
"The front tyres are 225/35/18 87 XL Michelin Pilot Super Sport, the rears are 235/40/18 95 XL Eagle F1. The rear tyres need changing as they are old and developing cracks on the inner wall. "
It sounds like there is a method of making the front suspension 'better' but I do not believe us satisfied owners would drive as quickly as we do if the suspension was badly flawed.
I really think it would be worth starting with the much cheaper option of changing your tyres.
When I purchased my car the rears were old (almost bald!) Goodyear F1's but the matching fronts were in good condition. I therefore changed the rear tyres for new Goodyear Eagle Asymmetric's but I was very unhappy with the 'feel' of the car. My local tyre specialist warned me that although the fronts were in good condition they were very old and he also pointed out that Goodyear had changed the tread pattern from the old F1 to the new F1 tyre.
I therefore changed the fronts to new Goodyear Eagle Asymmetric's and the car was transformed. Either the old fronts had aged badly or having different tread patterns did not suit the car but all I can say is that I am very, very happy with the handling and road holding now (my tyres are original size specification).
It sounds like there is a method of making the front suspension 'better' but I do not believe us satisfied owners would drive as quickly as we do if the suspension was badly flawed.
I really think it would be worth starting with the much cheaper option of changing your tyres.
When I purchased my car the rears were old (almost bald!) Goodyear F1's but the matching fronts were in good condition. I therefore changed the rear tyres for new Goodyear Eagle Asymmetric's but I was very unhappy with the 'feel' of the car. My local tyre specialist warned me that although the fronts were in good condition they were very old and he also pointed out that Goodyear had changed the tread pattern from the old F1 to the new F1 tyre.
I therefore changed the fronts to new Goodyear Eagle Asymmetric's and the car was transformed. Either the old fronts had aged badly or having different tread patterns did not suit the car but all I can say is that I am very, very happy with the handling and road holding now (my tyres are original size specification).
I'm sure you are right, getting the tyres right is the first step. As the fronts are Pilot Super Sport and pretty new I need to get something compatible on the back. I'm leaning towards Pilot 4s on the standard profile 235/40/18, as they come from the same stable and are supposed to be almost as good as the PSS.
Other option would be some more Super Sports on a slightly different profile, 245/35/18, but they are quite a lot more expensive and might foul the bodywork.
I've asked Michelin to comment, will report back.
Other option would be some more Super Sports on a slightly different profile, 245/35/18, but they are quite a lot more expensive and might foul the bodywork.
I've asked Michelin to comment, will report back.
I think some people confuse steering kick back and bump steer. The only way to identify and correct bump steer is to measure it, especially with TVRs, as each car will probably vary.
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As above the 225/40's on the front certainly improved the roadholding, steering kickback, tramlining on rough roads.
As for bump steer - I've had the rack raised, Suspension Geo done on Nitrons. All improvements but incremental.
Front tyres would be my first change and take it from there.
That is interesting. I believe the T350 was originally launched with 225/50/16 on front and back. I have seen a T350 owners manual that gives that tyre size. That profile gives a rolling diameter of 631mm, The RD for 225/35/18 tyres is 615mm. If no suspension components had been changed that would alter the scrub radius. Your new tyres at 225/40/18 have a RD of 637mm, very close to the original figure. This would bring the scrub radius back to being very close to the design figure.
Great debate guys. Following with interest. After reading I think my cheapest next option is also tyres and see how that makes a difference. I’m debating getting the powers wheels which will throw all of my set up all up in the air again. Do it look for a quick fix and try new tyres or get powers wheels and get it all looked at again. Hmmm ???!!
non_linear said:
That is interesting. I believe the T350 was originally launched with 225/50/16 on front and back. I have seen a T350 owners manual that gives that tyre size. That profile gives a rolling diameter of 631mm, The RD for 225/35/18 tyres is 615mm. If no suspension components had been changed that would alter the scrub radius. Your new tyres at 225/40/18 have a RD of 637mm, very close to the original figure. This would bring the scrub radius back to being very close to the design figure.
More sidewall on the 225/40's makes a difference, interesting the comparison with the 16'sSome folk have posted that 225/40's rub on full lock on the front. I don't seem to have that issue. Each body is slightly different I guess.
I have 255/35's on the rear. There's some rubbing on the bodywork going over the more noticeable compressions in the road but generally fine.
NBON said:
More sidewall on the 225/40's makes a difference, interesting the comparison with the 16's
Some folk have posted that 225/40's rub on full lock on the front. I don't seem to have that issue. Each body is slightly different I guess.
I have 255/35's on the rear. There's some rubbing on the bodywork going over the more noticeable compressions in the road but generally fine.
ditto I have same tyre combination, fronts fine and rears rub under full compression but Normal use fine both Michelin PSS Some folk have posted that 225/40's rub on full lock on the front. I don't seem to have that issue. Each body is slightly different I guess.
I have 255/35's on the rear. There's some rubbing on the bodywork going over the more noticeable compressions in the road but generally fine.
New tyres are supple and will give you an improvement. Check the date codes and throw off old stuff as they harden over a few years and it's noticeable on a lightweight car. It's the cheapest place to start.
Great thread, learning lots, but crap roads don't suit 18in wheels and tyres with these cars. 16s were standard on the Tam for sure, but they look under-wheeled (and I've never had them on mine). Depends what you want but there'll be a compromise to be made somewhere...
Great thread, learning lots, but crap roads don't suit 18in wheels and tyres with these cars. 16s were standard on the Tam for sure, but they look under-wheeled (and I've never had them on mine). Depends what you want but there'll be a compromise to be made somewhere...
Any one looking at sorting the root cause of the bump steer may be interested in the last post on this thread.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
https://www.pistonheads.com/gassing/topic.asp?h=0&...
i read here several time "new dampers and a geo setup sorted everything"....definately true, but not the "real" reason....
as those dampers are coilovers, the "new" settings will also involve ride-height.
the ride height has an immediate effect on the angle of the wishbones AND consecutively of the steering-arms AND consecutively on bump-steer.
if the correct settings would have been done without fitting new dampers the result smight have been the same.
most cars out there (not only TVR´s ) with a double wishbone-design, plus coilovers, plus adjustable camber, castor, tracking are driving far out from the optimum settings, hence they drive like a pig.
whats most important for a majority of car-owners: wide wheels, big tyres, low suspension and loud exhaust.......but they forget that low, & wide is not how the cars left the factory...and if you go low, you need to adjust also other parameters (like tracking and camber) otherwise the car handles like a Lada..
as most owners nor their garages have the right knowledge, solving those issues, the owners loose interest, after one season the car will be sold...next owner, same game...1 season, car sold.....and it happens that such cars are out there on the road for several years far away from their potential..
as those dampers are coilovers, the "new" settings will also involve ride-height.
the ride height has an immediate effect on the angle of the wishbones AND consecutively of the steering-arms AND consecutively on bump-steer.
if the correct settings would have been done without fitting new dampers the result smight have been the same.
most cars out there (not only TVR´s ) with a double wishbone-design, plus coilovers, plus adjustable camber, castor, tracking are driving far out from the optimum settings, hence they drive like a pig.
whats most important for a majority of car-owners: wide wheels, big tyres, low suspension and loud exhaust.......but they forget that low, & wide is not how the cars left the factory...and if you go low, you need to adjust also other parameters (like tracking and camber) otherwise the car handles like a Lada..
as most owners nor their garages have the right knowledge, solving those issues, the owners loose interest, after one season the car will be sold...next owner, same game...1 season, car sold.....and it happens that such cars are out there on the road for several years far away from their potential..
Edited by GinG15 on Wednesday 6th December 20:54
My personal experience.
Exactly as you described even I a straight line @ 70 felt extremely twitchy. Had different but good tyres on each axle. Changed those- maybe made a bit of difference but not much. Full geo. Yup better.
2 yrs later ( purchased from a former main dealer , been back to them 3 times) & I discover a cracked rear spring (Yup through the mot too). Changed rear springs for Tuscan S springs & so much better........but guess what- came across a ph post giving a factory ammendment to tyre pressures. Now everyone had advised the manual pressure of 23psi. This now said 28psi.
Omg what a difference. Tis the simple things in life !
Exactly as you described even I a straight line @ 70 felt extremely twitchy. Had different but good tyres on each axle. Changed those- maybe made a bit of difference but not much. Full geo. Yup better.
2 yrs later ( purchased from a former main dealer , been back to them 3 times) & I discover a cracked rear spring (Yup through the mot too). Changed rear springs for Tuscan S springs & so much better........but guess what- came across a ph post giving a factory ammendment to tyre pressures. Now everyone had advised the manual pressure of 23psi. This now said 28psi.
Omg what a difference. Tis the simple things in life !
My T350 would suffer from bump steer, I had the Geo done and new rubber , it did make a difference but it was still there.
After speaking with Ben Lang who designed the Sagaris suspension I opted to have the Sag steering arms fitted and the rack spaced; I have to say even though I thought it pricey it made a heck of diffference, the bump steer vanished completely.
I sold the car a year or so ago, the arms were fitted probably 3-4 years ago if I remember correctly.
I now have a special Sag ( more on this later ) that I am building, couldnt find the arms anywhere so I had no choice but to have a batch made, but like anything to do with engineering it was expensive to do even with mates doing it. Pics on the TVRCC site.
After speaking with Ben Lang who designed the Sagaris suspension I opted to have the Sag steering arms fitted and the rack spaced; I have to say even though I thought it pricey it made a heck of diffference, the bump steer vanished completely.
I sold the car a year or so ago, the arms were fitted probably 3-4 years ago if I remember correctly.
I now have a special Sag ( more on this later ) that I am building, couldnt find the arms anywhere so I had no choice but to have a batch made, but like anything to do with engineering it was expensive to do even with mates doing it. Pics on the TVRCC site.
Edited by bubblebobble on Saturday 7th April 10:25
bubblebobble said:
My T350 would suffer from bump steer, I had the Geo done and new rubber , it did make a difference but it was still there.
After speaking with Ben Lang who designed the Sagaris suspension I opted to have the Sag steering arms fitted and the rack spaced; I have to say even though I thought it pricey it made a heck of diffference, the bump steer vanished completely.
I sold the car a year or so ago, the arms were fitted probably 3-4 years ago if I remember correctly.
I now have a special Sag ( more on this later ) that I am building, couldnt find the arms anywhere so I had no choice but to have a batch made, but like anything to do with engineering it was expensive to do even with mates doing it. Pics on the TVRCC site.
I unfortunately have let my TVR club membership lapse, so cant get on the member areas. How many of batch did you get made, would you be willing to pass on dimensions or drawings. I may have a go at manufacturing some myself as i cant afford the price of the sag ones listed on powers After speaking with Ben Lang who designed the Sagaris suspension I opted to have the Sag steering arms fitted and the rack spaced; I have to say even though I thought it pricey it made a heck of diffference, the bump steer vanished completely.
I sold the car a year or so ago, the arms were fitted probably 3-4 years ago if I remember correctly.
I now have a special Sag ( more on this later ) that I am building, couldnt find the arms anywhere so I had no choice but to have a batch made, but like anything to do with engineering it was expensive to do even with mates doing it. Pics on the TVRCC site.
Edited by bubblebobble on Saturday 7th April 10:25
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