Big Bang Front End

[surypap3]

I have Spax adjustable front shocks and I think 140lb springs. When I cross a depression in the road (not a pot hole), I get a big enough bang to startle me. It is like something has hit bottom in the suspension. Not like hitting the road. Just the compression reaching its limit, I think. Has anyone had this experience? The shock spring seat adjustment is all the way down, as far as the shock permits. Attached is a picture of the ride height. Not totally aggressive. Any thoughts here?  I did a quick search (to avoid topic duplication) without luck.

[Grumblebuns]

With the lower spring seat all the way down, you have no pre-load on the front springs. What was your reasoning for that? Also what spring length are you using?

[jbcollier]

Check for missing, loose and worn bushings in the front suspension first.  Commonly it's the roll bar.

[EuropaTC]

How old are the dampers ? I've had rear failures on the Elise at under 10k and that felt like someone was hitting the floor with a hammer, a real thump.

Otherwise as John says, rubber bushes are the usual culprits, you might have to jack up each side and use a pry bar to look for movement.  140lb springs aren't too far from stock on the front and should feel relatively soft. If they are significantly shorter than OEM free length and you don't have enough preload you might be reaching the travel limit on the damper ? Normally there's a bump stop to soften the effect though.

Brian

[surypap3]

Will need to pull down the shock to measure the spring length. Its been a long time since installed. I think the seat is all the way down for lowering the front end. I do not remember the springs to be unloaded, but I can't remember how much preload there may be. All the suspension has limited miles on and was all renewed, but it has been years with limited use. Bump stop is gone. I think I left them off.

I will check the bushings. I know the roll bar bushings are pretty beat at the bottom. I never changed those.

[TCS4605R]

It looks like you have a lot of negative camber in the front or is the photo deceiving?

Tom
74 TCS - 4605R

[Clifton]

I run Spax on the front  and pretty low. I can bottom mine on the aggressive cross drainage dips. Easiest way to check for travel is to put a zip tie around the shaft. As it compresses, it moves the zip tie up the shaft toward the bump stop. If you have buried the zip tie up into the bump stop on small dips, then an aggressive dip is hard bottoming.

[surypap3]

Clifton. Did you leave a bumpstop on your shocks. Also, I'll try the zip tie idea .... I like that. Since you are experience bottoming, do you have ideas for a setup to avoid that? Good use that advice.

TCS4605R. Been so long but I think I have 3/4 to 1 deg negative camber up from up front. I need to put it on an alignment rack and get the current measurements. I did my setups in my garage with strings and things.

[Clifton]

The Spax I have are only rebound only. There is no damping on compression. I don't know what other Europa shocks have but compression damping helps in bottoming.

I have the bump stops that came on them, short black rubber. I don't have it happen often enough that it is a problem. Some of the streets by me have cross streets where the crown in one roads meets the other has a depression that is even lower. Dips don't bottom me, but those do. There's only a few but only a problem if I don't slow way under the speed limit. I'm running a 250# spring too so that helps too.

Only way to check is the zip tie. Don't guess or assume.
It could be something else. You can run longer and different stiffness bump stops. I run a harder one in the rear as the factory QA1 ones I had were too soft and split. These may not work for you. https://www.summitracing.com/parts/ENS-9-6110G A few other companies make

If you are smashing into that bumpstop that often and run a longer bumpstop to slow the bottoming it could compress it in a turn enough that it will increase your effective spring rate. If you don't get to the limit, it won't matter but it would create more understeer. A zip tie will let you know.

Here's a  few other options.

http://www.advancedracingsuspensions.com/products/bump-stops/
https://performanceshock.com/index.php?main_page=index&cPath=67_102_217
https://www.resuspension.com/bump-stops.html

[Clifton]

I use the 4" zip ties from Lowe's/Homedepot.