T350 bump steer options
Discussion
I know this has been discussed a lot in the past but the solutions seemed to involve either using a Sagaris steering arm (no longer available) or fabricating your own (which I'd prefer to avoid). I believe the steering arm mod drops the track rod by about 15mm, and then using a different track rod can get you another 5mm or so, so the track rod pivot point is around 20mm lower in total.
That seems a lot! Is this right, and if so are there any other ways of achieving this?
That seems a lot! Is this right, and if so are there any other ways of achieving this?
ShiDevil said:
Why do you think you need to go to these lengths? Are you sure you have it? I don't believe t350's suffered from it. I just got my car setup correctly (not a simple geo) and job done.
Don't want to sound patronising but do you understand how bump steer manifests. No amount of geometry tweaking will solve it. If you lie on the floor and look under the car you will notice that the gap between lower suspension arm and the track rod increases as you move away from the inboard side.
This means they are working in different planes and upon bump and rebound have different lengths.
If the roads in your area are fairly smooth you won't notice as much. The roads around my way aren't, and it was very noticeable.
Thanks for your replies.
Basically the car does not feel planted in a straight line at speed, even on a motorway. I haven't been over 70 mph and frankly wouldn't want to go much faster even on a track. Overtaking a car on a B road with any uneven surface does not feel pleasant at all. Grip the steering wheel and try and keep it in a straight line.
I am open to suggestions on how to fix this, but it sounds like bump steer to me. There have been quite a few threads on here discussing the front geometry and they all point to either raising the rack, which is limited to a few mm on a T350, or dropping the steering arm pivot point.
I am sure companies like str8six would not have been offering this mod if it was not necessary. Having said that, I find it strange that it needs sorting at all. Lotus got it right 50 years ago.
M4tti, what changes did you have made to your car?
Thanks for the heads up on the re manufactured sag arms. I'll look into it.
I am sure the car would benefit from a full geo set up, but it makes more sense to me to have it done after correcting the bump steer, if that is required. So that is the question: Is there a known problem here?
Basically the car does not feel planted in a straight line at speed, even on a motorway. I haven't been over 70 mph and frankly wouldn't want to go much faster even on a track. Overtaking a car on a B road with any uneven surface does not feel pleasant at all. Grip the steering wheel and try and keep it in a straight line.
I am open to suggestions on how to fix this, but it sounds like bump steer to me. There have been quite a few threads on here discussing the front geometry and they all point to either raising the rack, which is limited to a few mm on a T350, or dropping the steering arm pivot point.
I am sure companies like str8six would not have been offering this mod if it was not necessary. Having said that, I find it strange that it needs sorting at all. Lotus got it right 50 years ago.
M4tti, what changes did you have made to your car?
Thanks for the heads up on the re manufactured sag arms. I'll look into it.
I am sure the car would benefit from a full geo set up, but it makes more sense to me to have it done after correcting the bump steer, if that is required. So that is the question: Is there a known problem here?
If your running stock 18" spiders the fronts don't have the ideal offset for the hub axis (from old threads on here). Silverstone Performance (?) developed the SP12 wheels which had optimised front offset, they also did a 3mm spacer to correct the front spider offset from ET42 to ET39, though the latter isn't ideal as it doesn't leave much hub exposed for the wheel centre bore to sit on.
non_linear said:
.
M4tti, what changes did you have made to your car?
Thanks for the heads up on the re manufactured sag arms. I'll look into it.
Uhh honestly... I sold the car... I can safely say though along poor surfaced B roads that have that patchy delaminated surface, where the car demonstrated bump steer most, and where 50mph was a workout of nerve and steering wheel dexterity, its replacement could probably double its speeds along the same section. M4tti, what changes did you have made to your car?
Thanks for the heads up on the re manufactured sag arms. I'll look into it.
That wasn't the only reason I sold it though.
I started discussing with Martin at RG earlier this year about getting hold of the sagaris arms and he said they would look into and it looks like they are.
All tweaks of ride heights and rack heights are compromise. As far as I could see the only real remedy would be the use of the sagaris or modified arms. My rack literally had a couple of mm before the hydraulic pipes would have fouled the chassis
If the sagaris arms dropped the track rod too low outboard you could remove one of the rack spacers.
It's really the one thing that let the cars down. I know a fellow PH member has had the str8six mod done and he confirmed that it brought a significant improvement to the cars handling.
The sagaris arms are the route I would take, and work everything else out from there.
Edited by m4tti on Wednesday 15th November 22:40
Interesting thread I was looking into it myself, my t350t has had a full geo set done which made a hell of a difference. But on B roads around were I live it's still skipping around if pushed, maybe it is just the nature of the car ? But something I'd like to improve, I've read of a mod that put a spacer between the existing steering arm and the hub, but this would then throw out the geo set up. There was a guy who's sold his a while back stating in his ad it had a bump steer mod. Keep us posted
It is difficult to read a thread like this without wondering if what is being described is just the nature of TVRs. Before buying my T350 I drove a couple. It became instantly obvious that the T350 is a very light car with a very fast steering. Good tyres at the correct pressures help, but if you do not relax your grip on the wheel you end up 'fighting' every movement and the car starts to dart around. Keep a loose touch and the car is fine - I happily 'throw' mine around B-roads and Country lanes with the only problem being grounding the front or back diffuser on really big bumps. I do know what bump steer is and I have witnessed it a few times (normally with much heavier cars) and the result is a single and dramatic movement not the 'floatiness' of the T350. If you drive other very light cars (Elise, Caterham) they also have the same feeling as the T350 although I think the fast/light electric steering of the T350 is the biggest problem.
plasticman said:
Do you think the track rod should be parrallel to the wishbone ? You are not taking the top one in to account .
No... the wishbones might be parallel but the track rod is doing it own thing. Are you telling me this has no impact on the drive.
Edited by m4tti on Thursday 16th November 13:18
I am out of my depth.
I know the theory fo zero bump steer
but I can't see from just looking at the suspension if the design will have inherent bump steer or not.
Nothing I feel in my T350 suggests that it has a bump steer problem. The steering runs straight and true over all surfaces but I do accept that T350's are 'twitchy'. I still think this is a factor of the very fast and over-assisted steering. The bad bump steer I have witnessed in other cars actually made the car go off-line and needed to be corrected.
I know the theory fo zero bump steer
but I can't see from just looking at the suspension if the design will have inherent bump steer or not.
Nothing I feel in my T350 suggests that it has a bump steer problem. The steering runs straight and true over all surfaces but I do accept that T350's are 'twitchy'. I still think this is a factor of the very fast and over-assisted steering. The bad bump steer I have witnessed in other cars actually made the car go off-line and needed to be corrected.
The top wishbone is not parrallel to the bottom and as the trackrod rod is not on the same horizontal plane as the lower wishbone you would expect it to be inbetween the angle of the wishbones but obviously closer to the lower . We do not need to talk theory as the track rod angle is known to be wrong . From memory I moved the ball joint mounting on the steering arm down 10mm and out by 7mm to add some ackerman .
I cut off the triangular section of the steering arm at an angle ( about 10 degrees but can find out exactly tomorrow ) and swapped with the opposite arm cut at the mirror image and welded them on 10mm lower . This also gives you a slightly improved turning circle as the inner wheel can move turn further .
Cool thanks for this. I think a similar concept is described here by CraigCaf
https://www.pistonheads.com/gassing/topic.asp?t=12...
https://www.pistonheads.com/gassing/topic.asp?t=12...
non_linear said:
Thanks for your replies.
Basically the car does not feel planted in a straight line at speed, even on a motorway. I haven't been over 70 mph and frankly wouldn't want to go much faster even on a track. Overtaking a car on a B road with any uneven surface does not feel pleasant at all. Grip the steering wheel and try and keep it in a straight line.
I am open to suggestions on how to fix this, but it sounds like bump steer to me. There have been quite a few threads on here discussing the front geometry and they all point to either raising the rack, which is limited to a few mm on a T350, or dropping the steering arm pivot point.
I am sure companies like str8six would not have been offering this mod if it was not necessary. Having said that, I find it strange that it needs sorting at all. Lotus got it right 50 years ago.
M4tti, what changes did you have made to your car?
Thanks for the heads up on the re manufactured sag arms. I'll look into it.
I am sure the car would benefit from a full geo set up, but it makes more sense to me to have it done after correcting the bump steer, if that is required. So that is the question: Is there a known problem here?
My car, a 2003 T350t, was very skittish on any bumpy B road. I took it to Center Gravity in Atherstone, had new Nitron dampers and new tyres fitted, with a full geo set up and the problem disappeared. The difference was remarkable. Before the visit to CG, I lost confidence and backed off at 50mph on a bumpy back road. After CG finished I could take the same road, with confidence, 30mph faster. My strong recommendation is to get the car properly set up on decent dampers and tyres before attempting any changes.Basically the car does not feel planted in a straight line at speed, even on a motorway. I haven't been over 70 mph and frankly wouldn't want to go much faster even on a track. Overtaking a car on a B road with any uneven surface does not feel pleasant at all. Grip the steering wheel and try and keep it in a straight line.
I am open to suggestions on how to fix this, but it sounds like bump steer to me. There have been quite a few threads on here discussing the front geometry and they all point to either raising the rack, which is limited to a few mm on a T350, or dropping the steering arm pivot point.
I am sure companies like str8six would not have been offering this mod if it was not necessary. Having said that, I find it strange that it needs sorting at all. Lotus got it right 50 years ago.
M4tti, what changes did you have made to your car?
Thanks for the heads up on the re manufactured sag arms. I'll look into it.
I am sure the car would benefit from a full geo set up, but it makes more sense to me to have it done after correcting the bump steer, if that is required. So that is the question: Is there a known problem here?
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