10 replies to this topic

[mach1000]

Hei everybody,

I have a perhaps quite simpel question I am thinking about, it is concerning spring preload.

This attached picture is from a Seat Leon Supercopa with koni shocks without any normal options of adding preload.

But my question is:

As you can see on the picture i have attached that the helper spring is fully compressed, and the spring it self is also a bit compressed by the spring perch. This is in "static" mode when it not even is mounted on the car, and I can't figure out wether this will add a bit of preload on the spring. I of course now that it raises the rideheight, but what happens when the weight is being put on that spring. I have never seen an application where the helping spring is fully compressed without any load from car.

Thanks in advance

[DaveW]

As you can see on the picture i have attached that the helper spring is fully compressed, and the spring it self is also a bit compressed by the spring perch. This is in "static" mode when it not even is mounted on the car, and I can't figure out wether this will add a bit of preload on the spring. I of course now that it raises the rideheight, but what happens when the weight is being put on that spring. I have never seen an application where the helping spring is fully compressed without any load from car.

It is common for tin tops to use compound springs (main & helper), but (now) to run with the helpers well coil bound. The helpers are used as "fillers" to stop the main spring load falling to zero & to help push the wheels out of the wheel arches for changing tyres quickly. I don't recall seeing the configuration you described & can't think why it should be that way, unless it is desired to limit droop travel for some reason.

[cheapracer]

At a guess it's just a filler spring and it's there compressed rather than a spacer because when the main spring goes 'boing' the wrong way the filler will expand and stop the main flicking off it's seat.

I'm also guessing that they had to do this to get the correct ride height with that rate spring, they could only get the spring in that set length and at full droop the spring was dangerous close to being fully extended.

[Greg Locock]

Lack of rebound travel in the shock does not change the load in the spring when it is installed and the car is on the ground. There are very good reasons for restricting the wheel travel of front wheel drive cars.

[DaveW]

If the top mount is fixed, & no spacers are added or removed from the spring assembly, then the length of the spring assembly will remain constant when it is supporting the weight of the vehicle. That remains the case whilst the helper spring is coil-bound in that condition, & the damper is free to move. Hence the position of the lower spring mount on the damper body will determine the vehicle static ride height & the available damper travel. Top mount shims can also be used to trim static ride height. The combination can be used to set both damper travel & static ride height.

Normally, the wheels of a racing tin top are buried in the wheel arches, & an excess of rebound travel is required to change wheels/tyres without releasing the top mounts. That is the usual reason for including helpers in a spring assembly. Your example appears to negate that function.

[Fat Boy]

Normally, the wheels of a racing tin top are buried in the wheel arches, & an excess of rebound travel is required to change wheels/tyres without releasing the top mounts. That is the usual reason for including helpers in a spring assembly. Your example appears to negate that function.

Point 1: correct
Point 2: correct.

The only reason I can see to have those tender springs on like that is for ballast.

[DaveW]

I wonder if either the length of the damper shaft has been reduced, or an internal droop limiter has been installed, as a "quick fix" following damper failures?

[mach1000]

Thank you for all of your good replies, it gives me something to think about:)

Greg could you or somebody else please describe some of the good reasons for restricting wheel travel at fwd racecars?

Thank you all in advance, it is fantastic with a forum with lots of qualified people to pass on their knowlegde

[Greg Locock]

Greg could you or somebody else please describe some of the good reasons for restricting wheel travel at fwd racecars?

Not what i said.

[DaveW]

Another random thought:

The Koni struts I have seen on a Leon have rebound controls that are not "detented", making precise setting of rebound damping something of an art form. It is also possible, I suppose, that the rebound control might occasionally self-adjust in use. If that happens, and the change is to reduce damping, then the vehicle will tend to "jack up". A droop stop would then control how far the vehicle can get "out of shape". Pure speculation, of course, but something to look out for, perhaps.

Edited by DaveW, 07 February 2010 - 10:43.

[cheapracer]

I wonder if either the length of the damper shaft has been reduced, or an internal droop limiter has been installed, as a "quick fix" following damper failures?

Or an internal droop spring and they use the small outside one to set the rate.