Bumpstops and spring rates

[Dominic TVRetto]

Running Gaz suspension, I have never been able to get rear spring rates right for my set up - the initial (soft) spring rate being compliant but bottoming out, and harder spring rates skittering over uneven ground.

I heard that some early Griff/Chims had progressive rear springs - and this seems like the ideal solution. Previous posts have suggested that correct valving was critical with these, so as I am having my dampers refurbished, a quick call to Gaz was in order I thought...

I relayed my thoughts regarding progressive springs, and received an alternative suggestion to consider running softer springs (with rates nearing those that had previously bottomed out), with 2 celotex (spelling?) bumpstops (20mm total?) and a striker plate on each damper - which would give the softer more compliant ride, increasing the spring rate once the bumpstops were reached...

I have looked into this a little, and found this interesting thread here:

https://forums.nasioc.com/forums/showthread.php?t=...

I wonder whether our relatively short damper travel would have any bearing on whether this is a good idea...

Does anyone have any knowledge in this area of suspension design, and if this is a workable idea given our suspension limitations...?

Thanks!

Dom

Edited by Dominic TVRetto on Wednesday 23 January 21:19

[fredd1e]

Cant comment on specifics of a Griff (assumed) but the Sagaris Bilstein dampers had longer bump rubbers compared to other T-Car Bilsteins so its something TVR did consider as part of T-Car chassis tweaks along with other stuff like moving wishbone pickup points (possibly to reduce/remove a tendancy for the effective spring rate to fall as the wheel /hub moved upwards).

[spitfire4v8]

Bump stops should more suitably be called spring assisters. They ramp up the effective spring rate when they come in to action.

The trick is to know how stiff to make your spring assister, and at what point in the damper travel you want it to come in. This is governed by many factors including the springs you initially choose, the ride height, the use the car is put to, driver preference on balance once the spring assister comes in to action etc etc

Also consider that a spring assister which is brought in to action more often will have a shorter operational life .. ie heavily used assisters often split so might become a service item, certainly a service-check item.

If you can't / don't want to employ the services of a suspension engineer then arm yourself with lots of "bump stops" of varying hardness and lots of solid packers to space them and have a play.

Gaz won't necessarily be able to help you other than to give you some parts, as they would need to see your car, see how you like to drive, etc etc to work out what's going to work best for you (but it will still be a compromise).

[QBee]

Do also consider how low you have your ride height set - so many of our cars bottom out over any serious bump because the current or past owner thought it looked better virtually slammed to the floor.

[s6boy]

QBee said:

Do also consider how low you have your ride height set - so many of our cars bottom out over any serious bump because the current or past owner thought it looked better virtually slammed to the floor.

^^^^^^^^
True dat