High Speed - Steering is Very Loose

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Bostn635csi
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High Speed - Steering is Very Loose

Post by Bostn635csi »

Hello, during the past summer, I was going about 100MPH and I noticed the steering got very very loose. There was a lot of play in the steering at high speeds. I tried it a few times and noticed it when I got over 80MPH. Anything under 80PMG the steering is tight. Anyone have any ideas? Thanks.
Kevin
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Re: High Speed - Steering is Very Loose

Post by Brucey »

tell us what you have checked and/or replaced in the steering. Also what offset, width etc tyres you are running.

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Re: High Speed - Steering is Very Loose

Post by Bostn635csi »

Hi Brucey, the car is still in winter storage for another month. I know the front suspension is newer including the sway bar. The upper and lower control arms are old as well as the bushings. Old steering pump as well with no leaks.
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Re: High Speed - Steering is Very Loose

Post by Brucey »

FWIW there can be all kinds of things that are not quite right with the steering, and wheels with the wrong offset exacerbate any troubles that you might be having. The steering box in an E24 (when new) is only play-free in the centre position. Over time, the steering box wears and the steering may not be play-free in the exact centre any more. You can adjust the play in the steering box (there is an adjuster for this purpose) but if you overdo it on a worn steering box you will find two tight spots either side of centre. If the steering box is at all tight, probably it is doing the gubbins inside no good at all. Even with two tight spots, a worn steering box may not be 100% play free in the centre position. Some folk adjust the track rods unevenly so that the worn spot isn't quite in the straight ahead position any more; this is OK but obviously the steering geometry isn't perfect any more and if you do enough tight turns the tyres will wear oddly.

If you have wheels with the wrong offset fitted, the effect of the scrub radius is to impose a thrust load into the steering linkage all the time. This thrust load is essentially balanced, on a smooth road, but on one that isn't smooth, it isn't balanced. You can feel if this is happening because the car will tend to follow ruts in the road, follow cambers, and the steering will be heavier than normal (you will be pushing harder to keep the line) when in a long corner. The exact same things that cause tramlining also impose higher than normal reaction loads through the steering box and will cause it to wear more quickly. With wheels that have the correct offset (and that are not too wide) these forces are very much lower and the steering box has a much easier life. [a Brucey top tip; if you have not done so already, install a magnet in the PAS reservoir (eg on the lower screen); you will pull all kinds of shrapnel (from the pump and from the steering box) out of the fluid, which gives you an indication of the state of wear/wearing, if you continue to find fresh deposits on the magnet.]

Also the aerodynamic forces at speed can be very large. In addition the rear suspension tends to 'squat' slightly under load. Your car looks like it might have a slightly lower static ride height at the rear; if you plan to drive fast, this is basically a terrible idea, aerodynamically speaking; at speed, the car is squatting under power, the rear spoiler is pushing the suspension down too, the air that gets into the engine bay through the grille is vented downwards etc and the net result can be that air gets under the car and lifts the front, unweighting the front suspension and making it feel light. [early E24s without the front spoiler were even worse for this BTW, and yes, it is actually dangerous].

There could be all kinds of things that are not right that could be helping the steering feel weird, but regardless of this, basically it is best (IME) if you set the static rear ride height to be about 3/4" higher than the rear if you want the car to handle at speed. If you have mismatched springs (stiffer at the front, still soft at the rear) it might be better to go a bit more than this.

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Re: High Speed - Steering is Very Loose

Post by masonjones »

Brucey wrote: Wed Mar 21, 2018 7:52 am Also the aerodynamic forces at speed can be very large.
You can see a real life demo of how much lift is generated on the front of the car at speed if you ever forget to latch the hood and then get on the highway. At about 75-80 mph the hood starts to raise up. Gives you a shot of adrenalin if you're not expecting it. Not sure how much the hood weighs but the lift must be taking quite a few pounds off the weight of the front end at that speed.
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Re: High Speed - Steering is Very Loose

Post by 603racing »

As always, Brucey with great info!

I will add that incorrect camber and toe can add to instability, probably throw caster in there too, but not sure how much caster plays into loose steering at high speeds. Also, worn suspension parts can lead to incorrect caster, camber, toe, and several of the situations Brucey described.
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Bostn635csi
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Re: High Speed - Steering is Very Loose

Post by Bostn635csi »

Update - suspension is being checked out by Turner Motorsports. Should have an update any day now. Thanks Brucey for the full in depth response.
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Re: High Speed - Steering is Very Loose

Post by Pod »

Bostn635csi wrote: Sun May 13, 2018 3:53 pm Update - suspension is being checked out by Turner Motorsports. Should have an update any day now. Thanks Brucey for the full in depth response.

What was the result???
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Re: High Speed - Steering is Very Loose

Post by Bostn635csi »

Sorry for the lengthy delay. Here's is what was done at the shop. This significantly tightened the steering at high speeds. I still need to replace the control arms as well have the steering pump replaced or rebuilt.

Replaced Center Link
Idler Arm R/L
Tie Rod Assembly R/L
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Re: High Speed - Steering is Very Loose

Post by Mamod17 »

Late comer to this thread! I've already got 16 x 0" wheels on my Group C tribute but they still don't fill out the guards - not much choice but to go with a larger negative offset or spacers - which will give me a positive scrub radius. Is there any way to dial this out by modifying the suspension?
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Re: High Speed - Steering is Very Loose

Post by Brucey »

Mamod17 wrote: Mon Dec 30, 2019 8:57 pm Late comer to this thread! I've already got 16 x 0" wheels on my Group C tribute but they still don't fill out the guards - not much choice but to go with a larger negative offset or spacers - which will give me a positive scrub radius. Is there any way to dial this out by modifying the suspension?
Not really, not without fabricating uprights with new double knuckle geometry (on post '82 cars; on earlier cars you are stuck, although you could consider longer/relocated control arms I suppose). BTW you probably have a positive scrub radius already; I think that the maximum rim width that can be used without scrub radius problems is 8" or 8.5" or so, and then the rim/tyre ought to be practically touching the upright. On full race cars some of this is counteracted by more negative camber (which moves the 'straight ahead' tyre contact point inwards) and this works OK on a racetrack. On the road it just scrubs the tyres out double-quick, unless you drive like a lunatic.

The double-knuckle system is complicated but in the simplest terms the upright rotates (with steering input) around a virtual centre. This is super-clever because it allows the virtual centre to be offset an inch or two outboard, i.e. beyond the ends of the control arms; this allows wider rims and more upright mac struts (better packaging) than otherwise; clever stuff. The virtual centre moves with steering angle but at any given time it can be found by projecting lines through the control arm bushings, along the length of each control arm, passing through the ball joint centre, and then carrying on beyond. Where these lines intersect is the location of the virtual centre.

I'll find a picture if I can do. (edit; I've looked and I can't find one right now)

But anyway if you fabricated different uprights with the ball joints spaced further apart, you could push the virtual centre outwards and retain a sensible scrub radius, even with wider/more offset rims. However I don't know whether it would be easy or not to retain good Ackerman geometry at the same time.

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Re: High Speed - Steering is Very Loose

Post by Mamod17 »

Thanks Brucey, that's really helpful. I won't be modifying the suspension, so will just have to live with it. Can you describe the handling issues I will have with the positive scrub radius?

Also I found this excellent offset calculator - been playing with lots of different combinations.

https://www.wheel-size.com/calc/?wheel1 ... 0mm&sr=0mm
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