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Are ride height and bump/droop interlinked?
jps - 11/2/19 at 10:47 AM

I'm very carefully trying to understand everything before I commit to spending several hundred pounds on coilovers for my Haynes. Now i've got onto thinking about droop and bump - what I understand as being how much the suspension will travel down, or up, from the standard position when the car is when it's either static, or on a flat road at a steady speed.

I'm also thinking about the ride height I want to achieve.

Let's say I have a 14" open length damper - with spring of a set length.

With that combination I can run a ride height of 150mm - at which point the damper length will be 13" open. I know this because i have put the chassis on wooden blocks at that ride height and measured between the two shock mounts - and got 13".

I assume that means I have 1" of droop - because the 14" damper could extend by another inch before it was fully extended. I appreciate that the extra drop' at the wheel will be a little different - because the damper is angled.

If I wind the spring seat by 25mm so there is now 25mm more space for the spring to go in - I assume this means the ride height will become 25mm less -down to 125mm.

This means I now have 2" of droop?

Have I understood things correctly?

[Edited on 11/2/19 by jps]

[Edited on 11/2/19 by jps]

AdamR20 - 11/2/19 at 10:52 AM

Yes, but rattly springs at full droop are bad news, and that extra inch where the spring isn't doing anything is insignificant.

[Edited on 11/2/19 by AdamR20]

MikeRJ - 11/2/19 at 02:21 PM

quote:
Originally posted by jps
Let's say I have a 14" open length damper - with spring of a set length.

With that combination I can run a ride height of 150mm - at which point the damper length will be 13" open. I know this because i have put the chassis on wooden blocks at that ride height and measured between the two shock mounts - and got 13".

I assume that means I have 1" of droop - because the 14" damper could extend by another inch before it was fully extended. I appreciate that the extra drop' at the wheel will be a little different - because the damper is angled.

If I wind the spring seat by 25mm so there is now 25mm more space for the spring to go in - I assume this means the ride height will become 25mm less -down to 125mm.

This means I now have 2" of droop?

Have I understood things correctly?


In the simple case of wheel rate=spring rate (e.g. McPherson strut) you are correct that droop and ride height are inversely proportional when you have adjustable spring platforms. As Adam say though, extra droop will do you no good unless the spring is adequately compressed so that it doesn't lift off the seats at full droop.

With a basic double wishbone suspension the wheel usually moves further than the damper since 1) the damper is mounted somewhere inboard of the outer balljoint on the wishbone, effectively making the wishbone a lever that is applying mechanical advantage to the damper & spring 2) The damper is almost always inclined, further increasing the mechanical advantage from the wheel's perspective. This is the difference between "wheel rate" and "spring rate".

Angel Acevedo - 11/2/19 at 04:23 PM

I am shooting for 1/3rd of travel for droop and 2/3rds for Bump.

Ride Height is determined by Shock Lenght, position of inner Shock pivot and how you adjust your perches.
If RH does not fall where you want, you may need to alter one or more of these.
You state your Damper Open Lenght, but not your Closed lenght, or your Damper travel.

150 mm is pretty high (to me)

If at Ride Height you have 13", yes, you have only 1" Droop travel.

As stated, you need to have your perches adjusted in such a way that at full droop ypu still have some spring compression. Preload.
On my shocks, I will have this with the perches retracted all the way, that is even at full extension, I need to compress the springs in order to be able to install them.

I hope this makes sense and is of any help.
Regards
AA

Oddified - 11/2/19 at 09:09 PM

Slack/loose springs on full droop is also an MOT fail (assuming it's a road going car of course), but some times it's unavoidable and you can use softer (than the main spring) flat section helpers to fix the problem. Faulkners do them amongst others.

Ian

phelpsa - 11/2/19 at 09:36 PM

Be careful to check the coilbound length of the springs you are using if you end up with a lot of bump travel, you really want to make sure the damper goes metal to metal before the spring does.