Lotus Elan

+2 rear suspension bump stop length

PostPost by: mbell » Thu Sep 09, 2021 10:34 pm

Hi,

I am currently installing TTR shocks and narrow rear springs so need to replace the aeon rubber springs. Currently trying to figure out what length bump I should use.

The original aeon rubber are 80mm and I believe normally fit on a 20mm spacer (mine were missing), so total length of 100mm.

The bump stops I have bought are URO Parts 1J0 512 131C:
uro-1j0512131c_xl.jpg and
Bumpstop

https://www.summitracing.com/parts/URO-1J0512131C

Which are for standard fit for the rear of various VAG cars. These are ~125mm long and the TTR shocks nut has a ~7mm nut/ledge on it. So a total length of ~132mm.

From what I read on here, earlier engagement of bump stops/second spring is probably a good thing and particularly in this case where the initial resistance of the bump stop is lower than the aeon rubber spring. So I thinking that fitting these bump stops at there current length is correct thing to do.

I would be interested to know:
1) how much of the strut rod is exposed at a normal ride height on the +2 (so I can see how much travel before the bump stop would engage)
2) General thoughts on length of bump stops described above

Thanks,

Mark
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: seniorchristo » Sat Sep 18, 2021 4:45 pm

My stops are 85mm which is I believe the same length as original.
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67 Elan +2
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PostPost by: jono » Mon Sep 20, 2021 1:07 pm

When I did the narrow spring conversion on my last Plus 2 I played around with dampers and springs quite a bit and ended up with 13" 120lb springs and a 65mm bump stop with the Lotus alloy spacers on top of the tubes which I seem to recall are around 25mm high - this worked well and was nicely progressive in roll. A previous set up, which I aborted, introduced a sudden increase in roll resistance in bends which was very unpleasant.

I can't recall the model of bump stop but they were Powerflex and I got them from Burtons
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PostPost by: mbell » Mon Sep 20, 2021 6:29 pm

Thanks Chris, Jono,

I am thinking that I'll try my current bump stops out. The initial compression of them is very light (easy with hand), so I am not too concerned about a sudden change in resistance due to them. My main concern is that there length will cause early engagement, leading to them wearing quickly and possibly reduced comfort on bumps. Then a minor concern if they will be firm enough at higher compressions.

Basic plan is to fit them and see how much free travel before engagement at sensible ride height I get and how it drives. Worse case I'll buy some shorter firm ones and swap them out.

I'll be running the TTR Fast/Comfort springs which are 12" and I think are 100lbs/in (marked 12E100). Which I think is only slightly firmer than the stock springs but much shorter.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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