Lotus Elan

Steering Rack Limiters

PostPost by: bill308 » Fri Feb 23, 2018 2:16 am

Brian Buckland says Elans use rack limiters as follows:

S1-S3 driver side= 0.281 in, passenger side 1.75 in.
S4-Sprint driver side=0.53 in, passenger side 2.00 in.

Presumably these dimensions compensate for different OEM wheel/tire combinations and are intended to prevent the tires from rubbing on the sway bar?

What do 26R's use with wider rims and tires?

Another tidbit I learned from Ken Gray at Dave Bean Engineering is that they offer a slightly shorter rack that minimizes the effects of bump steer. This rack puts the inboard tie rod joint in a better location.

Bill
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PostPost by: Gray » Fri Feb 23, 2018 8:34 am

The bigger rack limiters on the S4 were due to 155 tyres instead of 145 to stop rubbing on the anti roll bar on full lock.

I don't know about the 26R rack.

I had a very interesting discussion with John Miles many years ago, he found developing cars for manufacturers other than Lotus that zero bumpsteer made them unstable. He suggested a very small amount might be worth trying on the Elan, starting with a 0.5mm additional shim.

I've driven Elans and Plus 2s where the rack height had not been correctly set which tended to wander, much improved with the rack correctly set. I suspect the wander may have been caused by uneven heights each side of the rack.

When I eventually get my S4 back on the road I'll try it with some additional shims and report back, but could be a long time.
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PostPost by: bill308 » Sun Feb 25, 2018 2:44 am

Hi Gray,

I believe you are correct that the 1/4 inch increase in rack stop length on the S4-Sprint are due to the tire size increase from a 145 to a 155. Interesting that my S2 SE was also fitted with 155's.

To me it is the distance from the wheel mounting surface to the inside of the tire where it can contact the anti roll bar that is critical. One strategy would be to mount extra long rack limiters and trim to length in situ. Another strategy would be to slit a tube, cut to length, and secure the C-halves directly on the rack ends with ties of some sort or drill and tap for 4 retaining screws.

Once my rack is set up, I really don't want to take it apart to trim the limiters. Maybe a die grinder with a cutoff wheel could work but one would have to be careful in preventing abrasive from getting in the grease or inside the boot.

Bill
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PostPost by: miked » Tue Mar 06, 2018 12:47 pm

I have found racks low with the so called correct shims. Upon doing the set up they usually need lifting. I have done this as much as about 8 or 9 mm to dial out all bump and then adjusted to put a small amount of "toe in" on bump.
The amount of toe on full bump with a low rack can be quite dramatic. As Gray says the rack mounts can be at different heights. Hence anybody doing that measuring from the top pin can be out. Bump gauge is the only true way in my opinion.
Sorry Bill for thread drift.
I did a modified car and split the rack limiters horizontally so i could play with wheel to body clearance. I then pulled the rack out and carefully welded the halfs back together. Saved splitting the set up rack joints and shims.

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