Bump steer on M chassis
Discussion
I remember reading a message on eliminating bump
steer in M chassis , to do with 14 and 15 inch wheels and ride height etc . If anyone has played with steering racks or steering rack positioning and was able to minimise same and is prepared to share information I would be grateful . Currently car goes from dead straight ahead at 6 and half inch ride height
to 1/4 inch toe out with 1 inch depression of front .
Any advice much appreciated .
steer in M chassis , to do with 14 and 15 inch wheels and ride height etc . If anyone has played with steering racks or steering rack positioning and was able to minimise same and is prepared to share information I would be grateful . Currently car goes from dead straight ahead at 6 and half inch ride height
to 1/4 inch toe out with 1 inch depression of front .
Any advice much appreciated .
Hi,
This is what I wrote earlier about ways of curing bumpsteer.
"To eliminate bumpsteer, (which is terrible on the M) the steering rack needs to be lowered. On my car I had to remove about 25mm off the chassis below the rack, I also modified the rack mounting bracket which
lowered the rack maybe 10mm more, I dont use rubber bushings at all so the rack is hard mounted against the mounting plate.
Even if it would seem to be so it is not for sure that the rack has to be lowered so much as to make the steering arms parallell
with ground, the suspension geometry is also dependant on the length of the A-arms. In my case I had to put 8, 1mm alu plates
under the rack to finally adjust the bump steer, so in my case the steering arms still points down a bit but not so much as before!"
The above procedure which only took about one day including adjustment almost eliminated bump steer altogether, now I have slight increase of toe in, (1 or 2mm) at fully compressed and fully offloaded suspension but otherwise constant 0 toe, this has improved behaviour especially under braking
Regards Hans
This is what I wrote earlier about ways of curing bumpsteer.
"To eliminate bumpsteer, (which is terrible on the M) the steering rack needs to be lowered. On my car I had to remove about 25mm off the chassis below the rack, I also modified the rack mounting bracket which
lowered the rack maybe 10mm more, I dont use rubber bushings at all so the rack is hard mounted against the mounting plate.
Even if it would seem to be so it is not for sure that the rack has to be lowered so much as to make the steering arms parallell
with ground, the suspension geometry is also dependant on the length of the A-arms. In my case I had to put 8, 1mm alu plates
under the rack to finally adjust the bump steer, so in my case the steering arms still points down a bit but not so much as before!"
The above procedure which only took about one day including adjustment almost eliminated bump steer altogether, now I have slight increase of toe in, (1 or 2mm) at fully compressed and fully offloaded suspension but otherwise constant 0 toe, this has improved behaviour especially under braking
Regards Hans
Hi Kevin,
The procedure I described is not very complicated even though it involves cutting away part of the chassis and do some welding but I didn't found another way to do this.
Please beware that depending on the ride height you maybe have to cut away more or less then I did, it depends on the springs you use. In my case I use non standard springs from Demon Tweeks with a rate of 250 lbs/in and free length 14", in this case I had to lower the rack approx 25mm, (lowering mounting points 25mm, cutting away lower part of the rack brackets, (the part that hold the rubber bushes) and adding 8mm of shims). My advice is to try to estimate how much you have to cut away to make the rack arms completely horisontal and initially lower the rack about 5mm more then needed in order to have some room for adjustment.
You can easily make a bump steer gauge yourself or buy one from for instance Demon Tweeks. The gauge is necessary in order to measure bump steer when doing adjustments.
Regards Hans
The procedure I described is not very complicated even though it involves cutting away part of the chassis and do some welding but I didn't found another way to do this.
Please beware that depending on the ride height you maybe have to cut away more or less then I did, it depends on the springs you use. In my case I use non standard springs from Demon Tweeks with a rate of 250 lbs/in and free length 14", in this case I had to lower the rack approx 25mm, (lowering mounting points 25mm, cutting away lower part of the rack brackets, (the part that hold the rubber bushes) and adding 8mm of shims). My advice is to try to estimate how much you have to cut away to make the rack arms completely horisontal and initially lower the rack about 5mm more then needed in order to have some room for adjustment.
You can easily make a bump steer gauge yourself or buy one from for instance Demon Tweeks. The gauge is necessary in order to measure bump steer when doing adjustments.
Regards Hans
i seem to recall the group going over this before but i don't remember what the determination was. the consensus seemed to be that the m chassis was designed for one steering arm or one wheel size and received another when the chassis went into production. did anyone ever figure out what the steering arm should be and what the donor car was? or is there simply nothing for it but to wack off the rack mounts? could the steering arm be drilled and a bolt on style rod end be sustituted and shimmed as in some race cars? would love to here some of the other members chime in as i also am about to address the dreaded bump steer problem and don't want to cut up the rack mounts.
frank
frank
Hi,
According to an article in the US TVR car club magasine the M chassis was designed with steering arms, (the arms that sit out at the wheel, not the rack arms) from one type of Triumph,
(probably TR4) and when the production started they use steering arms from a TR6 instead and didn't realised that these steering arms are different, the TR6 drop more so the rack arms will point down, with the TR4 arms the geometry is different
so the rack arms are parallell to ground.
However when I posted this info on the forum Richard Sails answered that the real cause of the bump steer problem was that the M was designed with 15" wheels that where later changed to 14" wheels and the ride height increased which introduced the bump steer problem.
I dont know what is correct but it could be a good idea to investigate the different steering arms from TR4, TR6 and other Triumph cars. Using other steering arms could solve the bump steer problem without the need for cutting away part of the chassis, (I suspect however that there could still be bump steer even with TR4 arms or 15" wheels so adjustment of the steering rack height could be needed anyway).
Regards Hans
According to an article in the US TVR car club magasine the M chassis was designed with steering arms, (the arms that sit out at the wheel, not the rack arms) from one type of Triumph,
(probably TR4) and when the production started they use steering arms from a TR6 instead and didn't realised that these steering arms are different, the TR6 drop more so the rack arms will point down, with the TR4 arms the geometry is different
so the rack arms are parallell to ground.
However when I posted this info on the forum Richard Sails answered that the real cause of the bump steer problem was that the M was designed with 15" wheels that where later changed to 14" wheels and the ride height increased which introduced the bump steer problem.
I dont know what is correct but it could be a good idea to investigate the different steering arms from TR4, TR6 and other Triumph cars. Using other steering arms could solve the bump steer problem without the need for cutting away part of the chassis, (I suspect however that there could still be bump steer even with TR4 arms or 15" wheels so adjustment of the steering rack height could be needed anyway).
Regards Hans
valve said: Hi,
According to an article in the US TVR car club magazine the M chassis was designed with steering arms, (the arms that sit out at the wheel, not the rack arms) from one type of Triumph,
(probably TR4) and when the production started they use steering arms from a TR6 instead and didn't realized that these steering arms are different, the TR6 drop more so the rack arms will point down, with the TR4 arms the geometry is different
so the rack arms are parallel to ground.
However when I posted this info on the forum Richard Sails answered that the real cause of the bump steer problem was that the M was designed with 15" wheels that where later changed to 14" wheels and the ride height increased which introduced the bump steer problem.
I don’t know what is correct but it could be a good idea to investigate the different steering arms from TR4, TR6 and other Triumph cars. Using other steering arms could solve the bump steer problem without the need for cutting away part of the chassis, (I suspect however that there could still be bump steer even with TR4 arms or 15" wheels so adjustment of the steering rack height could be needed anyway).
Regards Hans
Yes Hans, we are both right and the US magazine is wrong!
Changing the length of the arms will reduce or increase the toe in / toe out, when the tracking is adjusted this is how it is done.
The reason for the longer arms is that the TVR wheelbase is slightly wider that the TR6 and if you fitted a TR6 rack with TR6 arms it will not be possible to adjust the tracking correctly.
I have seen several M's that have has extension bushings fitted to the arms to correct the problem that occurs if you think that the rack is standard TR6 and do a exchange. If your rack needs re-building get your actual rack re-built, do not swap it for another TR6 rack!
The first M's had the 15" Vixen finned wheels fitted with rather high profile tires (they also filled the arches much better than the 14" wheels). The result that with the correct spring/shocker length the steering rack arms were parallel with the ground hence reducing the bump steer. If you look at the chassis you can see that the rack mounts raise the rack to ensure that the rack WAS at the correct height.
I don't know why TVR changed from the Vixen type 15" finned wheels to the 'T Slot' 14" wheels (or 14" Wolfrace on some cars), (I will ask Martin Lilley next time I bump into him in the pub), but was probably to keep the car looking modern (at the time!) or due to wheel/tire availability and/or price.
With 14" wheels it is necessary to use a longer length spring/shocker (or more pre-load - same effect), this causes the rack arms to be down at an angle and you get bump steer. The rack mountings should have been lowered when the 14" wheels were fitted but they were not.
As you state above, the simple fix to reduce bump steer is to reposition the rack lower to bring the arms horizontal.
The rack itself is indeed a standard TR6 item with longer arms, I think TR4 arms, I had mine re-built for one of my M's with a larger pinion to give a slightly quicker lock to lock, I would not recommend it as it made the steering even heavier.
The mounting brackets are also standard TR6, you can change either the rubbers for harder poly bushes or replace the mounting bracket for solid items.
PS, I quite like the bump steer, my green M suffers a lot from it while howling along bumpy lanes, it makes for a more exciting ride!!!
Hi Richard
It seems to be a slight misunderstanding, when I refer to steering arms from TR4 and TR6 it is the ones that are located out at the wheels, not the rack arms. Appaerently the TR4 and TR6 steering arms are different and when the TR4 arms are used the rack arms are horisontal.
The rack on the M is from a Triumph 2000 saloon, this has been described in various magasines and I can guarantee that it is true as I changed my car from RHD to LHD and got the steering rack I am using now from a Triumph 2000s saloon car, this one is an identical mirror view copy of the one that was mounted on the car originally.
Regards Hans
It seems to be a slight misunderstanding, when I refer to steering arms from TR4 and TR6 it is the ones that are located out at the wheels, not the rack arms. Appaerently the TR4 and TR6 steering arms are different and when the TR4 arms are used the rack arms are horisontal.
The rack on the M is from a Triumph 2000 saloon, this has been described in various magasines and I can guarantee that it is true as I changed my car from RHD to LHD and got the steering rack I am using now from a Triumph 2000s saloon car, this one is an identical mirror view copy of the one that was mounted on the car originally.
Regards Hans
richard sails said: The first M's had the 15" Vixen finned wheels fitted with rather high profile tires (they also filled the arches much better than the 14" wheels).
I don't know why TVR changed from the Vixen type 15" finned wheels to the 'T Slot' 14" wheels (or 14" Wolfrace on some cars), (I will ask Martin Lilley next time I bump into him in the pub), but was probably to keep the car looking modern (at the time!) or due to wheel/tire availability and/or price.
Main reason (as told to me by Martin L) was that the 15" 'Vixen' style wheel was 5½" wide and, as you say, filled the wheelarch nicely. TVR wanted to fit wider tyres and as a 195/70x15 would foul the rear wheel arches under hard cornering, they went to a 6x14 wheel and fitted either 185x14 or 195/70x14 tyres.
If you do bump into Martin in the pub, tell him I said Hi!
which once again brings us back to the steering arms.
were the same steering arms used on all chassis that used tr6 vertical links; vixen,2500,2500m, etc? did the earlier cars use tr4 or something else? some parts suppliers have said there is no difference while some parts catalogs list different part numbers. i guess it would be to easy to just bolt on a different steering arm to cure this problem.
frank
were the same steering arms used on all chassis that used tr6 vertical links; vixen,2500,2500m, etc? did the earlier cars use tr4 or something else? some parts suppliers have said there is no difference while some parts catalogs list different part numbers. i guess it would be to easy to just bolt on a different steering arm to cure this problem.
frank
With all due respect to Mr. Lilley and my friend Richard Sails, I beleive it is safe to say that the bump steer problem as found in the M series cars is not caused by wheel size so much as it is the angle of the steering tie rods relative to the suspension A arms. A quick perusal of this explanation should serve to illustrate that point: www.racerpartswholesale.com/longtech3.htm
Therefore, there are two ways of correcting the bump steer problem. 1. Lower the steering rack in the frame. Certainly the more diffucult solution. 2. Modify or replace the steering arm (drop link) with one that corrects the geometry.
Why don't wheels affect the bump steer problem? Changing wheel diameters only alters the ride height, not the steering geometry. If, on the other hand, cars which were designed to use a different size wheel AND because of that, were fitted with different length springs, the suspension/steering geometry would be altered to some extent. That WOULD contribute to bump steer but not as much as using the wrong drop link! This is something to be kept in mind when using a height adjustable coil-over on the car. The use of shims at the point where the outer tie rod is bolted to the steering arm could help to correct the slight error induced by moving the spring perch higher or lower.
Therefore, there are two ways of correcting the bump steer problem. 1. Lower the steering rack in the frame. Certainly the more diffucult solution. 2. Modify or replace the steering arm (drop link) with one that corrects the geometry.
Why don't wheels affect the bump steer problem? Changing wheel diameters only alters the ride height, not the steering geometry. If, on the other hand, cars which were designed to use a different size wheel AND because of that, were fitted with different length springs, the suspension/steering geometry would be altered to some extent. That WOULD contribute to bump steer but not as much as using the wrong drop link! This is something to be kept in mind when using a height adjustable coil-over on the car. The use of shims at the point where the outer tie rod is bolted to the steering arm could help to correct the slight error induced by moving the spring perch higher or lower.
Hello Solo II, I think that you are correct that changing the wheel size from 15 to 14 inch will not by itself change bump steer.
It can be eliminated with 14 inch wheels without moving the rack, however you end up with a ride height of about three inches and the car scrapes the ground all the time. It is because of the smaller wheels that the spring shocker length has to be increased which is the cause of the bump steer.
The reason for the dramatic change is that the tyres fitted to 15" wheels were of much larger circumfrence that the 14" wheels.
It can be eliminated with 14 inch wheels without moving the rack, however you end up with a ride height of about three inches and the car scrapes the ground all the time. It is because of the smaller wheels that the spring shocker length has to be increased which is the cause of the bump steer.
The reason for the dramatic change is that the tyres fitted to 15" wheels were of much larger circumfrence that the 14" wheels.
Hi Hans,
The identical racks were used on a number of Triumphs at the time.
You are right I did misunderstand which bit you were talking about!
I have three M's, all 1972 cars, one is a very early car (with the original 15" finned alloys), all three have TR6 front vertical links fitted with TR6 bits.
It may be however that TR4 steering control arms on the hubs do have a different profile and will improve the situation on the 14" wheel cars but I am sure that they were not fitted as standard from new.
The identical racks were used on a number of Triumphs at the time.
You are right I did misunderstand which bit you were talking about!
I have three M's, all 1972 cars, one is a very early car (with the original 15" finned alloys), all three have TR6 front vertical links fitted with TR6 bits.
It may be however that TR4 steering control arms on the hubs do have a different profile and will improve the situation on the 14" wheel cars but I am sure that they were not fitted as standard from new.
Hi Richard
I will call it steering control arms in the future in order to avoid misunderstanding.
When I wanted to change my car from RHD to LHD, (which is quite easy BTW) I read in a Brookland books collection of car Magasines, (TVR 1960 - 1980, I think many know what book I am taking about) that the rack on the M was from a Triumph 2000 saloon and one common cause for critcism of the M was the very slow rack with as much as 4.2 turns.
Anyway I went out to a car scrapyard where I located a Triumph 2000 saloon and I removed the rack and the half shaft assemblies, (as they are also used on a M).
Back home in my garage I compared the old rack with new one and as I said they are identical, (except that one is LHD and one RHD).
Do you know if the same rack was fitted to all M cars? How about the 3000S, I read somewhere that it has a quicker rack.
Regards Hans
I will call it steering control arms in the future in order to avoid misunderstanding.
When I wanted to change my car from RHD to LHD, (which is quite easy BTW) I read in a Brookland books collection of car Magasines, (TVR 1960 - 1980, I think many know what book I am taking about) that the rack on the M was from a Triumph 2000 saloon and one common cause for critcism of the M was the very slow rack with as much as 4.2 turns.
Anyway I went out to a car scrapyard where I located a Triumph 2000 saloon and I removed the rack and the half shaft assemblies, (as they are also used on a M).
Back home in my garage I compared the old rack with new one and as I said they are identical, (except that one is LHD and one RHD).
Do you know if the same rack was fitted to all M cars? How about the 3000S, I read somewhere that it has a quicker rack.
Regards Hans
All M-series cars were made with the same Triumph rack. As far as I know, the rack itself is the same as used across most of the Triumph range, but you need to specify T2000 track rods. The 3000S had the same standard rack as the other M models, my 3000S has a 'quick rack', only because I fitted one during one of it's annual rebuilds
valve said: Do you know if the same rack was fitted to all M cars? How about the 3000S, I read somewhere that it has a quicker rack.
I have read from several sources that the steering arm from early TR4's are a direct swap and don't drop as much though I have yet to confirm that myself. An acknowledged expert whith whom I have spoken agreed that there are suitable replacement arms and suggested I trace out the arm on my car with particular attention to its mounting locations. I haven't gotten around to this yet but on my honor, when I do I will pass the word!
Thank you for all your input . We used TR4 Steering levers which area approx 24mm higher than the TR6 steering arm levers .I am no expert in old Triumph bits and assume there are a few variants . They are also approx 25mm shorter in lenght which improves the rack quickness . This steering arm lever also reduces the Ackerman effect which suits me . we finished up raising the rack 12mm to achieve virtually no bump steer . There was a bit of work involved with tie rod lengths etc but , all in all , not too much . I have not driven the car since but the physics are correct so I expect it will be fine . Has anyone played around with the rear end bump steer ? I suspect we are getting a bit of rear end steering , lurching into oversteer without too much warning , we are running 3mm toe in on the rear and do not wish to go any further ,ant suggestions ?
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