I'm far from expert but just for my 2 cents. My 27 with a side steer 32 box and draglink and pitmen arm set up pretty close to correct has zero bump steer. However, a couple of times with the conditions just right, which was always hitting a bad bump with the right front tire only, at a slow speed it would go into a pretty violent death wobble. I'd have to slow down to almost a stop to get rid of it. After checking everything I could think of and finding it all tight I decided to check the toe. Don't ask me how it happened but I was shocked to find almost 1/4-in toe OUT! I reset it to 1/8 toe in and have never had it happen again.
I refrained so far, but it seems to me that solid axle cars always did best with just a wee bit out. Kinda thought it had to do with how the camber is permanent to the axle, not like an IFS. Not a lot, ⅛ or less usually works. All the big car stuff I do gets just a little, no worries so far. The tie rod tension idea makes sense too, be it tension inside or outside of the balls in the ends. Full disclosure, when I say big cars I'm talking about Cl***ics that tip the scales well over 4500#, some over 5000. Makes a difference I'm sure.
Curious, what make big car 4500-5000 lbs with beam front axle? Antique pavkard, rolls or ? Hard to picture.
I have put you in the “astute guy” category!! I have dove headlong into learning about forces acting on tie rods under driving conditions. Again, just learning, but I think your comments are spot on. It seems that with my set up being front steer, toe in was putting compressive forces on my tie rod as soon as my tires began to roll. Acceleration, potholes or bumps, and braking cause tension in the tie rod. From compression to tension, and back to compression causes oscillation…oscillation creates death wobble!! I think this is why I keep finding the consensus to be “more toe in” to fix instability. More toe in, on rear steer, creates more tension in the tie rod thus keeping the tie rod from transitioning from one state to the other. The advice of replacing heim joints and fixing my steering box mount is well taken, but I think the answer to the question, is toe out “always” wrong, has been answered…not in my case!! Thx again
The tie-rod being in compression or tension is dependent on whether there is negative or positive scrub radius . A lot of FWD cars with negative scrub radius and a front steer R & P have the tie-rods under compression. They do this to counteract the thrust from the driving wheels [trying to toe-out] Now the real purpose of Toe in the front geometry is not to load up clearances in the steering components [as people want to believe] Toe-in or Toe-out is needed to counteract camber thrust. If you have camber the front wheels behave like a "Cone" shape and they try to drive apart with positive camber. So toe-in is needed to counteract camber thrust caused by positive camber. With race cars we use a lot of negative camber, so we use toe-out to counteract this. This makes the car feel unstable on a bumpy straight , but sticks on corners. Without this toe-out , the life expectancy of the race tyres is reduced significantly. The best way to set toe is with tyre temperature readings [or if you are skilled, by reading the grain on the tread]
Hey @Mimilan , is there any validity to the comments of the OP in the post above yours (#68)? Is it possible for the toe to be set at a point where it cycles between positive and negative during driving? And could this cycling state contribute to wobble???
^^^ Toe change is totally able to change during driving depending on the suspension type. On a solid axle with a solid tie rod side to side any change is during turning depending on the steering arms but in a straight ahead position almost nothing. On an independent front suspension toe can be always changing. Especially on a r&p and tie rod angles. Really see this come into play on 4x4 that's jacked up. With the tie rods pointed down towards the steering arms. When the truck goes thru a dip (suspension compression) the tie rod essentially "grows" due to it straightening out and pushing the tire or tires out thus toeing the wheels out. .
The only valid point made was the word "Oscillation" Toe-out creates an unstable oscillation whereas Toe-in is more stable. This is because of the weight transfer during oscillations [the wheel with the most load is more dominant "directionally"] If you have too much Toe-out and the Left wheel is loaded up [from a bump] the vehicle will dart to the left. When it darts to the left the weight will transfer to the right, causing it to dart to the right [starting oscillations back and forth] As I previously mentioned Road racing cars are terrible in a straight line [but luckily there is no such thing as a straight line on a road course] And braking on uneven surfaces the condition feels worse than "drum brake fade" 90% of death wobble is caused by 1 force exceeding another [the other 10% is poor condition components] A common issue is too much caster ,which should make the front more stable. But on a lightweight vehicle there is less force needed to "lift" the vehicle, than needed to straighten the steering. So instead of the steering correcting itself, it will bounce/transfer weight from side to side The caster is performing exactly what it is meant to do ,which is find a point of equilibrium between height and direction. Think about this [with too much caster] if you disconnected the tie rod both wheels would want to toe-in under the weight. Now if the L/H wheel hits a bump it would try to turn right. But the alignment already has enough toe-out to counteract this force making it feel stable. All this talk about loose steering clearances/free play is a myth. There would be more clearances / free play in the wheel bearings than the steering components.
What you are describing is mechanical "bump steer" which can be difficult [but not impossible] to engineer out. Most IFS the bump steer is kept within a workable range. If you lower the front etc you can create bump steer issues [due to heights/ arcs etc] and usually require a wheel alignment On some race cars the designers lower the whole steering components to be parallel with the lower A-Arms so the bump steer is consistant with the arc of the lower A-Arm. This ^^^ also needs to factor in caster [or the steering will be too high] and also ackerman or the tie-rods will be too short. I have seen some well set up front suspensions where they had fixed length tie-rods. The toe was set by using an adjustable sleeve nut on the drag link [so it never altered the bump steer] By having the steering components parallel with the lower A-Arms, the upper A-Arms could also be adjusted to alter the roll-center [dynamic camber] without affecting the other settings
Yes it could be part of the problem. Wobble is usually a combination of 2 or more issues. The most common one is lack of lateral location of the front end [especially with cross steer] This can be "split-bones" causing the whole front end to parallelogram itself during wobble. Incorrect shackle angle on cross leaf front ends [with split bones the shackles need to be close to horizontal as possible] When somebody reverse-eyes the main leaf they end up changing the shackle angle. Another common problem is too much scrub radius [caused by smaller diameter wheels and/or wider wheels] There are so many variables that could cause wobble, So lightweight cars [eg early 70's dragsters and Altereds] can have up to 20 deg caster without an issue. [thefront axle on these cars are usually located quite good] Now here is a "curve ball", the rear end can cause wobble in the steering. If I use a 70's Altered as an example. Usually after ****oning off after a burnout, the car will dance from side to side on the slicks.[engine torque reaction pre-loads the tyres then is suddenly released ] This rocking motion is transferred into steering wobble because the caster is trying to correct this height/load difference. Now if a car builder has the rear suspenion "instant centre" higher than the axle centreline, the rear will be very unstable [roll oversteer] Rear roll oversteer can trigger front steering wobble if there is a lot of caster.
My thoughts are that with fixed length tie rods you would have no way to change the distance between the ends of the tie rods, therefor no way to change toe unless you changed the caster or camber settings. To me the only thing an adjustable drag link can do is to center the steering wheel, unless what you are calling a drag link is what I learned as a center link. Continental differences?
That particular reply I made was in reference to IFS front ends. The adjustable Drag-link is known as a "center link" in the USA [the rest of the world calls it a drag-link] example here: https://ecl***ics.com/acp-fl-es001-..._vnoXaPP1A6PWTK66vmLCgwbDxaOUcdRoChlQQAvD_BwE By lengthening/shortening this link will change toe settings without altering the tie-rod lengths. So the Arc of the tie-rods will remain consistent with the A-Arms. The car I saw this on , was a homebuilt front engined sports racer [Lotus 7 / Mallock U2 type] It had an aluminium steering box when everyone else used a R & P . The top A-Arms had outer heim joints and the Trimph Herald" uprights which had threaded bolts on the uppers [by adjusting 2 nuts the Roll Center could be raised or lowered]
Full disclosure, they're NOT mine. I have been really hands-on with those 3, and a whole lot like em.
Another toe question…I understand that from toe in, the tire starts to straighten up as it rolls down the road. With a standard spec’d camber and caster rear steer and let’s say 1/8” toe in, at what point would you think the tire gets to its maximum “straighten up”( for lack of a better term) position? 10mph? 20? 60?
I'm under the impression that it happens pretty quickly, as soon as the 'slack' is taken out of the steering components. Other thoughts on this question?
Not trying to hijack the thread but my car seems a little squiggly at 60 mph or so at times. From what I am reading, that could be a result of toe? Dropped axle, 9 degrees caster.
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