[Sankar]

How much effect would a 22mm spacer would have on increasing the spring rate of the spring? Does a 22mm spacer coupled with an already stiffer spring make the spring rate too high for the stock dampers to handle?

What do you think?

[mooza]

To begin with the stiffer spring, I think a stiffer spring would make the job of the damper easier, on account of the reduced suspension travel.

I personally confirmed this when I did a bounce test on my Scorpio after stiffening of the rear leaf spring. The vehicle settles down to rest much quicker now, indicating quicker damping on account of the reduced energy needed to be absorbed, I guess.

Does a spacer contribute to the spring's stiffness ? I am not too sure, but I feel it should not, unless the spacer is soft and has a measurable spring rate of its own. Else it should be doing no more than increasing the ride height.

[Sutripta]

Hi,
Do you mean the roll stiffness? If so, effect of spacers has to be worked out from the geometry. e.g. On a solid axle these have no effect!

Normally spring/ damping has to be seen as a system. And in your case, the unsprung mass would also have changed. So damping rates will need recalibration. But cant figure out "spring rate too high for the stock dampers to handle?"

Maybe better replies if posted in the modification section.

Regards
Sutripta

[Sutripta]

^^^
Please disregard last post. Brain fade time. Read spring spacer, thought wheel spacer.

Apologetic (and red faced)
Sutripta

[Mpower]

If you have a fixed rate spring, then it will have zero effect. If you have a variable rate spring, you will most likely lose the softer part entirely.

Keep in mind, that you are risking coil clash at full travel.

[im_srini]

Originally Posted by Mpower

If you have a fixed rate spring, then it will have zero effect. If you have a variable rate spring, you will most likely lose the softer part entirely. Keep in mind, that you are risking coil clash at full travel.

Hi MPower, it would be helpful if you could explain why, or how, adding a spacer results in an increase in the effective load on the spring (resulting in greater compression).

[Mpower]

Originally Posted by im_srini

Hi MPower, it would be helpful if you could explain why, or how, adding a spacer results in an increase in the effective load on the spring (resulting in greater compression).

Compressing a spring 20 mm is the same as giving it 20 mm of travel. If the rate is constant all thru the travel then you haven't achieved any rate increase. But most springs have progressive rates so you do get some increase. Its similar to adjusting preload on the rear susp of motorcycles

As you can imagine, there is risk of coil clash at max travel.

Best way to pickup rate is to cut off one turn.

[Sankar]

Originally Posted by mooza

To begin with the stiffer spring, I think a stiffer spring would make the job of the damper easier, on account of the reduced suspension travel.

Originally Posted by Sutripta

But cant figure out "spring rate too high for the stock dampers to handle?"

Hi Sutripta and Mooza,
A stiffer spring will store more energy when compressed and release that energy when its released. So i thought the stock damper may not be able to cope up with this increased rebound rate i.e., the rebound damping of the stock damper may not be enough.

Originally Posted by Mpower

If you have a fixed rate spring, then it will have zero effect. If you have a variable rate spring, you will most likely lose the softer part entirely.

Keep in mind, that you are risking coil clash at full travel.

The stock springs in my car are fixed rate springs. But the H&R's are variable rate springs. So what i thought is right the 22mm spacer added in the rear was affecting the softer part of the spring making the rear suspension stiffer.

Originally Posted by Mpower

Compressing a spring 20 mm is the same as giving it 20 mm of travel. If the rate is constant all thru the travel then you haven't achieved any rate increase. But most springs have progressive rates so you do get some increase. Its similar to adjusting preload on the rear susp of motorcycles

As you can imagine, there is risk of coil clash at max travel.

But here the 22mm spacer may not be taking up 22mm of travel, since it lifts the body by a bit too.

Best way to pickup rate is to cut off one turn.

Yes i want to decrease the rate in this case

[mooza]

@Sankar, I personally feel the stiffer (is it more bumpy ?) ride is due to the stiffer springs, and not because of the added spacer.

To confirm this, you may have to remove the spacer, if possible, and have a test drive, for the sake of comparison (if you have added the stiffer spring as well as the spacer at one go, it would be tough to separate out the individual effect of each of the 2 factors i.e. spacer & stiffer spring).

Just curious to know the response of your new suspension to the bounce test at standstill ? Do you feel the car takes longer / more number of oscillations to come back to rest ? If the answer is no, then maybe weaker dampers may soften the bumpiness of the ride, with the obvious trade off in terms of increased bounciness / swaying ride quality. Else you may have to look towards the tyres and tyre pressures to smoothen the ride a bit.

Was your overall objective towards better handling or increased ground clearance, I wonder ?

Edit :
Oops, forgot to clarify my basic doubt : Is your spacer placed within the coil pack or is it at the end of the coil pack ? My remarks above have assumed the latter.

[Sankar]

Originally Posted by mooza

@Sankar, I personally feel the stiffer (is it more bumpy ?) ride is due to the stiffer springs, and not because of the added spacer.

Yep the stiffer spring makes it bumpy but i want to revent it from being excessively bumpy if the spacer is contributing to it in any way.

To confirm this, you may have to remove the spacer, if possible, and have a test drive, for the sake of comparison (if you have added the stiffer spring as well as the spacer at one go, it would be tough to separate out the individual effect of each of the 2 factors i.e. spacer & stiffer spring).

I wanted to do this but the lack of time and the labour cost charged is holding me back.

Just curious to know the response of your new suspension to the bounce test at standstill ? Do you feel the car takes longer / more number of oscillations to come back to rest ? If the answer is no, then maybe weaker dampers may soften the bumpiness of the ride, with the obvious trade off in terms of increased bounciness / swaying ride quality. Else you may have to look towards the tyres and tyre pressures to smoothen the ride a bit.

No there is no larger number of oscialltions than normal, pressing it down is sure harder than with stock! The car is new so dampers are healthy i suppose. With the stiffer spring there was no sway or any body roll even while cornering hard.

Was your overall objective towards better handling or increased ground clearance, I wonder ?

It was for better handling and that is acheived. GC doesn't matter to me much, but the excessive bumpiness matters. The spacer was added because i had upsized tyres (185/7013 from 155/80/13) and it was rubbing the rear fenders. But that was cured permanently by cutting off a bit of metal from inside the fender and sealing the metal with sealant to prevent rust. So now i suppose i can do without the spacer and see how it goes. Wif i had 175 section tyres it wouldn't have rubbed.

Edit :
Oops, forgot to clarify my basic doubt : Is your spacer placed within the coil pack or is it at the end of the coil pack ? My remarks above have assumed the latter.

The spacer is at the end of the spring. Not the other type.

[Sutripta]

Originally Posted by Mpower

Compressing a spring 20 mm is the same as giving it 20 mm of travel. If the rate is constant all thru the travel then you haven't achieved any rate increase. But most springs have progressive rates so you do get some increase. Its similar to adjusting preload on the rear susp of motorcycles

Don't see how adding a spacer will compress the spring. Weight remains the same, so will the compression to support that weight. The spacer will increase ride height.

Agree about the possibility of coilbind at limit of suspension travel.

Originally Posted by im_srini

Hi MPower, it would be helpful if you could explain why, or how, adding a spacer results in an increase in the effective load on the spring (resulting in greater compression).

Agree with your point of view.

Regards
Sutripta

[Mpower]

Originally Posted by Sutripta

Don't see how adding a spacer will compress the spring. Weight remains the same, so will the compression to support that weight.

Hmm..when the wheel is jacked up, the spring is held in the pocket by the shock. You have to compress it to fit the spacer right??

EDIT: actually you are right, once you bring it back the spring retains its normal height and the body is raised by 22mm. I was confusing it with an adjustable lower perch.

But either way, there should be no change in rate

[Sankar]

Originally Posted by Sutripta

Don't see how adding a spacer will compress the spring. Weight remains the same, so will the compression to support that weight. The spacer will increase ride height.

It depends on what kind of suspension the spacer is used. For example in a mcpherson strut there is a maximum extension limit possible for that strut and the spring is contained within that limit. The spring is compressed by a spring compressor when screwing the top of the mc pherson strut to hold the spring in place, otherwise without the spring being compressed the top cannot be screwed with the spring in place. once the top is tightened the spring compressor is taken off and the spring sits tightly & slightly compressed within the strut. So if a spacer is added between the mcpherson strut top and the spring, the spacer compresses the spring more for it to fit inside the maximum extension of the strut. So it sits more compressed than without a spacer.

Same with the rear suspension in my car, there is a maximum limit to the damper's extension, the damper will let the axle to fall down only within its limit, the spacer when added contributes to compress the spring so that it has to fit within the max extension of the damper. Damper has to be unbolted from the axle to fix the spring with/without the spacer. And to bolt the damper back into place the axle has to be jacked up, compressing the spring, to bring the hole of the damper in line with the axle stud. With the spacer this takes more effort. You don't want the springs to jump out of its perch if the axle drops down, isn't it, so even at max extension of the axle the spring stays slightly compressed.

So the addition of the 22mm spacer did not yield a rise in body height by 22mm, the rise in height was less than that, due to the fact that the spring was compressed.

This scenario will not be applicable to suspension where the dampers have more travel than the uncompressed height of the spring. If the damper has more than enough travel then adding a spacer of 22mm may result in an increased height by 22mm.

[Sutripta]

^^^
Hi,
When the spring is mechanically constrained (when at each extreme of suspension travel), the spring will be more compressed as the remaining space is taken up by the spacer. Because then you are fitting a spring and a spacer into an externally defined space.

When the spring is doing its work as a spring, supporting the weight of the car, there should be no change in its compressed length, as long as there is travel available about its equilibrium position.

Regards
Sutripta

[mooza]

Originally Posted by Sutripta

When the spring is mechanically constrained (when at each extreme of suspension travel), the spring will be more compressed as the remaining space is taken up by the spacer. Because then you are fitting a spring and a spacer into an externally defined space.
When the spring is doing its work as a spring, supporting the weight of the car, there should be no change in its compressed length, as long as there is travel available about its equilibrium position.

Yes, I agree with your logic.

Further, in my opinion, if the pre-compress force in each spring on account of the spacer is, say 25 kgs (x 4 corners), for example, and the vehicle is slowly lowered from a set of jacks, the springs will begin to travel only after over 100 kgs of the vehicle has begun to sit on the springs, as the jacks are being lowered.

In other words, if the weight of the vehicle is 800kgs, then the net / final spring travel will correspond to only 700 kgs weight, on account of the pre-compress. So even in a ride without any load, the spring will behave as it does in a ride with 100 kgs load, I feel.

As Mpower says, maybe the travel of the soft part of the spring is the first to be eaten away in case of the variable rate springs with the spacer, leading to a stiffer ride.