Steering

[redcarandco]

It is not first time I use this forum where I have always got the answers to a lot of inquiries....but this time I am a little bit ashame of my inquiry which is certainly going to seem so evident to a lot of you...But as my scottish grandma (really)used to say "there 's not stupid question there is just silly answer ....so... Following an excess of optimism I put my elan out of race track during the timing practice of last race ...no big accident and car very slightly worn...but steering was touch and needs to be repaired so for 1 st time in 45 years of racing an elan I dismantled the thing and here is my question...... Is it ""normal"" that I discover that the 2 rack tie rods are not of egal length .....and when I visit all sites with lotus parts they just have one length....Am I stupid or do I have to machine both because even the longer one is shorter than the 160 mm I find everywhere??? Thousand of thanks if somebody can help...
Roger (photo is ten seconds before Iwas too optimistic)

[bitsobrits]

All of the Elan racks I've rebuilt or serviced had only one length, i.e. same both sides. A nominal 7.59" or about 193mm from the center of the pivot ball to the end of the threads.

[661]

If you are running the 26R front suspension the steering arms may have been bent inwards during set up to allow the ball joint to clear the brake disc. A bit needs to come off the track rod end to accommodate this, but usually it's taken off equally at both sides.

[redcarandco]

Dear Graeme and dear Steve ,many thanks for your interest and you are both right ...Last evening I was in touch with first owner of the car who gave me the explanation ....the car is fitted with a F A N T A S T I C 1,2 wheel turn top left to top right steering that I go on using without any trouble since I own the car(45 years) but it was in period "home made"....because did not exist so short in period and during the cutting of the rack teeth it had been necessary to offset the teeth position on the ruler for ease of machining so tie rod at teeth ruler side is shorter than the original display and if you add the obligation to shift the position of rod end ball joint to clear the rubber protection from brake disc heat.....so I am going to machine the tie rod ...and once again many thanks for answer...
Roger

[Andy8421]

It has always been my assumption that the Elan (and Triumph Herald) had the ball joint as close to the disc as it did to help with the steering geometry.

It would have been easy to have a kink in the steering arm so that the ball joint was further from the disc, but instead there is a cutout in the disc backplate so that the balljoint can stick through.

I would be careful about messing around with the steering geometry unless you know what you are doing - the distance from the balljoint on the steering arm and the balljoint on the rack needs to be the same on both sides of the car - and in the right place relative to the centre line to minimise bump steer.

When racing, a hot disc can cook the steering balljoint rubber. I have balljoints with a metal cover rather than the usual rubber boot on the car that I race that avoids this problem. I had understood that they were used on 26Rs.

[661]

TTR Front discs and steering arms.pdf

(436.21 KiB) Downloaded 284 times

This is the instruction from TTR for fitting the 26R front suspension/steering arms.
The bump steer is usually fiddled with after this on a race car anyway, but I have no doubt you are correct that it will alter it.

[Andy8421]

With all due respect to TTR's highly engineered solution (!), heating up and 'tapping' a mission critical part with a hammer doesn't fill me with enthusiasm.

I keep meaning to have a go at figuring out the sensitivity of the suspension to the lengths and positioning of various steering components, but there is a lot going on with intersecting arcs and the like and the maths gets very tricky. Allan Staniforth's excellent book 'Race and rally car source book' has a solution that uses bits of hardboard and string - his string computer - but I don't think that is sensitive enough. There is software available, but it is designed for racing teams and OEMs and costs £££.

Given that Chapman found it worthwhile to shim the height of the rack to get it right, and Triumph went to all the trouble of having the balljoint as close to the disc as was possible, I would think twice before I changed the placement or length of any steering component - including the position of the steering arm relative to the upright.

There was a recent thread (started be me) about the implications of changing the location of the lower pivot point on the suspension. The final conclusion was is didn't matter much, but I am not sure I was completely convinced.

https://lotuselan.net/forums/viewtopic.php?f=42&t=47587

Andy.

[baileyman]

When I put mine together it looked to me like the original modifiers of the 26R altered the steering geometry both to lower the front end but also line up the joints for bump steer. The upper and lower links define a quadrilateral with a messy corner where the trunnion offsets the joint and the steering axis by about an inch. It appeared to me the bending of the steering arm was intended to bring the ball joint close to in line with the steering axis looking from the front. And it looks like the joints in the rack are pretty close to the line extending from the upper inner joint to the lower inner joint.

I'm not sure about their intention, but that's how it looked. John

[661]

I think I needed to bring in the ball joint by 5mm each side.
The shimming of the rack was done at a later stage and I have virtually no deflection through 2" of bump and 3" of droop.

[The Veg]

...there is a cutout in the disc backplate so that the balljoint can stick through.

When racing, a hot disc can cook the steering balljoint rubber. I have balljoints with a metal cover rather than the usual rubber boot on the car that I race that avoids this problem. I had understood that they were used on 26Rs.

My roadgoing Plus 2 seems to have cooked a small hole in a new one in a mere five miles or so.

[Andy8421]

My roadgoing Plus 2 seems to have cooked a small hole in a new one in a mere five miles or so.

I think something must be adrift somewhere, or your roadgoing driving style is quite something to behold.

[Bigbaldybloke]

The main effect of bending the steering arm inwards will be to alter the Ackerman effect, the bump steer will be a secondary effect of this. For perfect Ackerman effect drawing a line through the kingpin axis and onwards through the steering arm ball joint should result in the line intersecting the centreline of the car where the rear axle centreline crosses it.
Bending the steering arms inwards will result in this line crossing the centre line of the chassis much further forward thus increasing the Ackerman effect. Unsure just how this will effect the outer wheel when cornering when combined with any bump steer that has been introduced by the necessary shortening of the track rods, and suspension compression changes due to roll, really needs computer modelling to understand this complex movement.

[snowyelan]

I think your Ackerman assessment is based on a rack behind the front axle?. Its the opposite effect for a front mounted rack. The front mounted rack is harder to work with due to the ideal position of the ball joint being further outboard than the steering axis. Tough to do with a brake disc occupying the same space. You can cheat this a bit by moving the rack rearwards.

[Bigbaldybloke]

You’re right my example was assuming a rack behind the axle, but if the rack is in front of the axle the point of intersection with the car centreline is the same distance but infront of the front axle instead of behind it. So the arms shouldn’t interfere with the disc, but this also depends on hub and upright design. Ideally the kingpin axis (the line passing through the centre of the top ball joint and bottom trunnion ) should hit the ground at the centreline of the tyre contact patch. If it’s much out you start to get a lot of kickback through the steering. Anyone who had an original Mini with wheel spacers on it will know that feeling well!

[snowyelan]

If the steering arms are cranked the same (closer to the centerline) as a rear rack then yes, the point would be forward. This would give 'reverse' ackerman with the inside wheel turning less than the outside. With the Elan the Tie rod ball joints are pushed outward intentionally. The point where the ground level lines on the planes of the rotating wheel intersects starts off in front (toe in), and as the wheels are turned (steered?) further it passes thru infinite/parallel to a point behind the Elan, way behind....