Bumpstop science

[DownSouth]

Scenario:
I replaced the stock springs with Mopar 2 inch
I later purchased and replaced the Socks to RS 9000s for 2 inch lift.
When I compared the shocks with the original factory ones I noticede they were the same size extended or compressed
I later added a 1 inch spring spacer all round.
I noticed my shocks now had very little down travel and I felt my flex was compromised.
As the shocks were new and exxy I decided to add a bottom bracket on all 4 corners compressing the shock by around 50 mm

Having done this I now notice that my up travel is limited before the shock reaches full compression.
It would seem that bump stops need to be increased.
I am also running 33s

Questions:
How do I work out what size bump stops I will need?
And general interest, Does adding more bump stop limit the down travel (Flex) in any way?

Appreciate some feedback as I don’t want to destroy my shocks just yet.
Also I will not be replacing these shocks so comments within the parameters of the scenario will be more useful
Cheers
John

[wranglertj]

bumpstop want effect down travel, atleast very minimally as i understand it as they other side compresses and hits bumpstops does the side with the down travel then also stop. Been asking this questionalso as cant get my head around it but this is not the pivot point per se so i have been told

[SeaComms]

Unfortunatley as you have found out the recommended 9000's for a 2 in lift are actually shorter than the stockers! I did a lot of research into the shock lengths and the base 9000's are 4mm shorter in the front and 23mm shorter in the rear than the stock JK ones (providing you are using the ones I am referring to of course - info is all compiled in this spreadsheet).

Based on my calcs, the front shocks had about 40mm remaining when suspension was compressed to bump stop, so if you dropped the shock by 50mm, then they will bottom out about 10mm before you hit bump.

Ignoring all that though, if you extended the shocks 50mm, stick in 50mm bump stop extensions.

[Bandit]

Originally Posted by DownSouth

Questions:
How do I work out what size bump stops I will need?
And general interest, Does adding more bump stop limit the down travel (Flex) in any way?

Appreciate some feedback as I don’t want to destroy my shocks just yet.
Also I will not be replacing these shocks so comments within the parameters of the scenario will be more useful

Just replace the shocks... sry just having a dig

If you want to get it spot on then I recommend the following:

1) Put the chassis rails up on truck stands
2) Remove the wheels, Swaybar End links, coils & soft bumpstop sections
3) Cycle your suspension & get out the tape measure
---- Full compression both sides
---- Full droop (just for your reference purposes if you do look at changing shocks in future to see what kind of increases in down travel you'd be looking at)
---- Right side Full flex / Full compression on one side (metal to metal bumpstops)
---- Repeat above for Left side (Panhard causes axle placement to be different so measurements may differ ever so slightly)

*If your bumpstops are limiting uptravel as they should be then each measurement should be the distance the shocks have left to travel (eg. 20mm) then you can decide whethere or not to further reduce the amount of bumpstops to maximise travel.
** Conversely if your shocks are limiting uptravel, then you can measure the gap between metal to metal bumpstop contact and determine the increase in bumpstop height you require to avoid shock damaged.
*** It's important to do the flex measurements because the bumpstops contact points naturally change on such angles, on long travel shocks it starts looking a bit wrong...

I'm not a mechanic but that's what I did, seemed logical.

Hope that helps.

PS. Sorry for the messy layout, indenting and general formating is cr@p house in forums / I don't know the tags well enough...

Cheers,
B.

[jktom]

I drove my JK up on ramps, right front, left rear, with timber under the ramps to get a little higher. I made several 70mm round disks out of 10mm timber, slid them in between the coils, 5 at first, then removed them one by one to work out how much bump stop i needed.

[SeaComms]

Originally Posted by jktom

I drove my JK up on ramps, right front, left rear, with timber under the ramps to get a little higher. I made several 70mm round disks out of 10mm timber, slid them in between the coils, 5 at first, then removed them one by one to work out how much bump stop i needed.

So what did you do then? Glue/bolt those ones in or buy "real" ones?

[jktom]

I removed them and used proper ones. I had a mate make me some 35mm front stops before I did this, but he took a while, as I was planning to go away, i just bought some 2" ones. I have the incorrect upper bump stops, but the 50mm ones are to tall for my shocks. but now I am using the SOLID steering stabiliser reloacation, I may need the 2" ones. need to spend more ime under there.

For the rear I had used RHS 75 x 50 cut it about 90mm long to 2" bump stops

Originally Posted by SeaComms

So what did you do then? Glue/bolt those ones in or buy "real" ones?