Steering Rack Extensions - Tie Rods and Bump Steer

[4129R]

I always understood that the chin spoiler on the TCs and TCSs was for highway stability

I believe bump steer would affect highway stability.

[Clifton]

I believe bump steer would affect highway stability.

Don't believe. To gain the toe in under compression(bump steer), you would need to compress the suspension, at stock height it would need to be inches. At Highway speed, this isn't happening and if it did, it is just toe in and not unstable. If you run close to zero front toe and it goes to 1/8"-3/16" toe in, you aren't noticing.

[4129R]

Early cars use extensions (likely off the shelf male-female threaded standoffs) on the tie rods. That stopped somewhere around S2 production, presumably in the earlier half based on various murky sources. My S1 has extensions on the tie rod.

Later cars used the larger, also hexagonal extension on the steering rack itself as you've shown. Most people seem to believe this improves bump steer so your data here opposes that somewhat. Not sure if Lotus has any notes in their service bulletins or manuals regarding the reasoning for the change.

Page 7 Section H of the workshop manual seems to show the earlier version.

I have sourced the adaptor sleeves, part number 129963 I think, which replace the hexagonal extensions, and I have found a very simple way of extending the tie rods, so I can see whether the earlier S1/S2 steering rack geometry or the later TC/TCS geometry gives more stability when driving down normal country bumpy roads.

The cost of these parts appears to be surprisingly very little, so if it works, then this is an easy and cheap modification. If it does not make any noticeable difference, maybe I would need to do a 3 year university degree course in steering geometry, and a PhD majoring in bump steer to try to understand how it all works.

[Elanman39]

Sorry, but I have to disagree that bump steer will not be felt at speed on a smooth highway. Forget bumps and consider body roll.  A small degree of roll during for example a lane change at high speed will potentially increase the toe-in on one side of the car and reduce it on the other, resulting in a non-linear change of direction relative to the steering input.  On the Elise we were adjusting bumpsteer all the time until we were happy with it.  Johns paper on bumpsteer is a measure of how fixated with it Lotus were!  Lotus knew all about bumprsteer back in the sixties, look at the adjustable steering rack heights on the Elans for proof.....

[Clifton]

Sorry, but I have to disagree that bump steer will not be felt at speed on a smooth highway. Forget bumps and consider body roll.  A small degree of roll during for example a lane change at high speed will potentially increase the toe-in on one side of the car and reduce it on the other, resulting in a non-linear change of direction relative to the steering input.  On the Elise we were adjusting bumpsteer all the time until we were happy with it.  Johns paper on bumpsteer is a measure of how fixated with it Lotus were!  Lotus knew all about bumprsteer back in the sixties, look at the adjustable steering rack heights on the Elans for proof.....

You have body roll during a lane change at high speed?   

[Elanman39]

Not compared to a '57 Chevy but yes, all cars with a roll centre axis that is not perfectly aligned with the centre of mass will roll to some degree or other in any manouvre creating lateral g.  The Europa as originally sold had relatively soft, long travel suspension with fairly stiff damping as was the current best practice with period tyres. It rolls, and it rolls enough for bump steer effects to come into play so it's well worth understanding those effects. Stiffer suspension will reduce the bump steer angles of course, but modern tyres are much more sensitive to slip angle so that makes the effects all the nore critical if they are being used.

[Clifton]

Not compared to a '57 Chevy but yes, all cars with a roll centre axis that is not perfectly aligned with the centre of mass will roll to some degree or other in any manouvre creating lateral g.  The Europa as originally sold had relatively soft, long travel suspension with fairly stiff damping as was the current best practice with period tyres. It rolls, and it rolls enough for bump steer effects to come into play so it's well worth understanding those effects. Stiffer suspension will reduce the bump steer angles of course, but modern tyres are much more sensitive to slip angle so that makes the effects all the nore critical if they are being used.

 A stock Europa on a high speed road "may" have .5* of roll if the driver is a complete lane changing maniac and treats slower cars like it's a slalom. It's just not an issue.

What is your front toe setting?  If you run the book max of 3/16" in, you may notice as you are scrubbing them to death already. If you are 0-1/16" in, you are going to be under the book max with all the bump steer in. I'm saying the toe increase will never be noticed especially if a stock sprung Europa is what one desires as they are never going to be anywhere near the limit on the street where this bump steer would effect the handling, regardless of what the owner thinks. If bump steer is believed to be an issue, soft springs, soft ARB, low caster, and excessive front toe in should be higher on the list.

[chrisbeck]

The inner tie rod end should line up with the line going through through the inner control arm pivot points …. Why would the length of things change going from left hand to right hand drive?

I rebuilt my LHD rack in a new RHD case, when bolted in the new chassis it turned out that the rack is fitted off-centre (not symmetrical left/right) so I had to strip it again and swop the end stops over!

[4129R]

The inner tie rod end should line up with the line going through through the inner control arm pivot points …. Why would the length of things change going from left hand to right hand drive?

I rebuilt my LHD rack in a new RHD case, when bolted in the new chassis it turned out that the rack is fitted off-centre (not symmetrical left/right) so I had to strip it again and swop the end stops over!

Been there, done that, x 7 !!!

[fort]

 I post this on behalf of a colleague Iain who notably has owned his S2 since new! He has put in enormous amounts of time investigating and sorting Bump steer.
As noted, S1 and S2 tie rod arms are extended so the rack matches the wheel track. This was a cheap solution and leads to significant bump steer. On twin cams tha rack was extended and the tie rod arm extension was removed. As a result S1and S2 cars had individual wheel bump steer over full travel of 0.4 inch. On twin cam models this was reduced to 0.07 inch!
Mike Kimberley did a good job. Iain has worked hard on this topic and spent hours measuring.

[314159td]

By a series of circumstances involving a heinous, disgusting attempt of a 917 longtail made of old europa body sections and plywood over a heavily modified frame, I have a fairly stock complete front suspension and frame section sitting in my driveway. Imagine if you cut a Europa frame right in the middle spine and kept the front. Exactly that, maybe with weird hubs to accept very large wheels on the stock rotors

I was entirely too lazy to try to measure anything and/or simulate that on my S1, but now I suppose that I have no excuse. Dynamic CAD model is probably most useful? I think I mocked up the Spitfire setup a few years ago, should be easy to translate. I also have means to fabricate those rack-side extensions; will see what makes sense before I go build up a rack for the S1.

[314159td]

Hey OP (4129R)
Would you be able to grab some measurements on the width of your racks-the new repro, original with rack extensions, and hypothetical copper pipe one? Width measured from ball center to ball center, not the nuts. Within 1/8" of the real value should be good enough.

I'm measuring my Europa and Spitfire racks as well, I think there's some additional complications, beyond rack vs tie rod spacers. Lotus has a published dimension for ball-to-ball, which is off from other applications of the same rack.

[4129R]

From centre ball joint to centre ball joint, the new S2 rack I bought from Banks which has the tie rod extensions, measures 27" or 683 mm.

The workshop manual shows this measurement to be 27.5". Section H page 7 fig. 7. (5 + 4 + 3+ 3 +2 + 2)

My copper mock-up which shows where the centres should be to line up with the centre pivots of the top and bottom wishbones also measures 27.5".