Thread: load = ride comfort = what spring rate?

Originally Posted by uninformed

Dougal,

do you have a Load leveller, and is it working?

whats your front rate and front weight?

Yes and I think so, but it is 27 years old. Fronts are 180 lb/in, front half weighed ~1170kg back when I weighed it.

1170kg, pretty good considering the Isuzu.

Originally Posted by uninformed

1170kg, pretty good considering the Isuzu.

Yeah, unloaded only 20kg over max axle weight.

But I've now got an alloy gearbox bellhousing, it's probably only 12kg over now.

Where is the front pulley in relation to the front axle centerline?

Originally Posted by uninformed

Where is the front pulley in relation to the front axle centerline?

My solidworks model thinks they are about 40mm apart. It looks more than that in the metal, but I guess it's just another illusion.

Forward or rearward.....bloody 300TDi

Originally Posted by uninformed

Forward or rearward.....bloody 300TDi

Err, sideways. To the left.

Fore/aft it's ~75mm clear of the front cross-member, which is something like 290mm forward of the line between the two front shock turrets.
That is the front of the second crank pulley that drives the AC belt. It's ~22mm less if you don't have that one.

Originally Posted by uninformed

Hey all,

My 98 110 tray back has a short cut down alloy tray, the vehicle is minimalist type set up. I run 250lb springs in the rear. I find the ride a little harsh. The other day I had 150kg of steel (2m lengths from head board to hanging over rear of tray a little) behind driver. The ride was much more what I like and am after.

Can anyone hazard a guess as to what spring rate I would go down to, to give a similar ride unloaded?

Yes I am aware it will affect loaded ride, but Im looking to install my load leveller for that..

IMHO the ride you felt with the heavier load can be replicated by changing the spring rate to achieve the same natural frequency.

Natural frequency is proportional to square root (spring rate / weight)

From this you can determine the required spring rate knowing the rate of your current springs and the weight on the springs when you were loaded and normal.

i.e. sqrt(K1/W1) = sqrt(K2/W2) where:
K1 is your current spring rate
K2 is the rate that you want for better ride with normal load
W1 is the weight on the spring when you were loaded
W2 is your normal load

The natural frequency (normally measured in Hz which is cycles per second) for rear springs should be a little less than that for the front springs. This is because the front wheels hit the bump before the rears but you want the motion caused by each to finish at close to the same time - obviously different speed and wheel base affect this.