Overall Suspension

[Matthew E. Herd]

All right, in a sort of followup to Bob's question about 1/4 versus 1/2 elliptical rear springs (which I do not know the answer to), I'd like to start a topic concerning overall suspension for the spridgets ... What's especially good, what's bad, etc. I'm not much of a suspension expert, so I'd like to hear some reasoning behind tube shock conversions (I understand the lever arms fade ...) and anything else that could be useful for general learning. I know some of the basics, but do not really understand the different suspension types, if anyone wants to get into that ...

 

[Trevor Jessie]

There are many books on the subject, but some things to think about...
The upper control arm of a spridget is the shock lever. Overall, it is not a bad design but it does have limitations. For example...there are no provisions for adjusting caster and camber without aftermarket components. Most lever shocks are not adjustable and I know of none that have variable resistance. By variable resistance I mean the resistance changes towards the end of the compression stroke.
It is possible to convert to a front tube shock system that will give the car a slight bit of negative camber and some adjustable shocks, but before spending money to do such a conversion it may be better to do other more basic things. Such as... a heavy anti-roll bar, poly bushings, rebuilt lever shocks (you can sell them later if you want to go to tube shocks), proper toe-in, etc.
And I haven't even started on the rear...

Before going any further I guess it is important to mention that before making any decisions you need to define what you want out of the car.

 

[spritenut]

It is possible to tweak the suspension to the point of not drivable on the street. Ask me how I know this

All poly bushings and lower springs make for great handling. On the track!
I created a monster with my 59 Sprite, first I over restored it to the point where I hated to drive it for fear of a paint chip in a flawless profesional paint job. Then I hated to use any of the NOS parts that I used in the restoration. And finally the over killed suspension made the car change lanes if I hit the white line on the hiway.
I am now running a mix of poly and rubber bushings, still with lowered springs and stock lever shocks, a 3/4" sway bar up front but nothing in the rear. I am very happy with the mix that I have. It handles very good, is still streetable and it just feels right.
My advice would be to try one upgrade at a time, drive it awhile then try another upgrade. You will know when you go too far.

 

[Matthew E. Herd]

Sounds good, as I'm looking to retain a very streetable machine. Overall, I'm only interested in making it acceptable for competition. It's supposed to be a street machine used for racing, so if it is not at the peak of performance, that's ok, as it's designed to be a learning tool.

 

[aeronca65t]

As with any analysis, set up a decent baseline first.
1. Drain all four lever shocks and refill them with new, clean fluid.
2. Grease all the suspension nipples.
3. Use plenty of silicon spray on the rubber bushings that connect the A-arms to the frame (to prevent any possible binding).
4. Tighten all suspension parts properly (rack clamps, shock bolts, etc). Check rear suspesion parts for any loosness.
5. Get the toe-in decent...even if you have to use a tape measure and straight edge...get it as good as possible.
6. Set tire pressures,

*Then* drive and see how it feels.
I agree with spritenut.......do one thing at a time after you've got everything decent.

Other thoughts:
-If you are looking for a decent Solo 2 or autocross car, the lever shocks are OK. They fade with continued use but not short runs or even fast street driving.
-As for track use: I don't know anyone who's doesn't use tube shocks all around (including me). The rear shock swap is easy and has a modest benefit. The front swap is much harder, but makes a bigger improvement (if done properly). Some of the FISC Spridgets in Europe run a trick, full coilover setup...neat, but big $$$$.
-I find the poly bushing to be fine for the street and they are much easier to replace (once the rubber bushing get stuck, it can be a nightmare to remove them). Maybe I'm not that sensitive but they don't seem any rougher to me than the rubber bushings.
-Don't lower your car too much unless you are prepared to move the rack to correct bump steer....a lot of the tuner kids end up with darty steering in their Hondas because thay ignore this.
-A good front sway bar (3/4") is a useful idea....I'm indifferent about them in the back of a Sprite. Panhard rod can help if you're running race tires.

Here's my front shock mod:

https://npmccabe.tripod.com/spritetubeshock.htm

 

[Trevor Jessie]

I agree with a baseline. I rebuilt my suspension, and was considering a tube shock modification rather than replacing my badly worn lever arms. However, another mailing list convinced me to go with the levers first so that I'd have a good point of reference. The difference is unbelievable. I'm now in no rush to upgrade to tube shocks, but I am still planning on eventually doing a conversion. My father (who builds street rods) is trying to convince me that he can engineer a good coilover system without great expense. But right now the car handles good for the street and my style driving. However, if I repower the car I will definitely need better suspension.

 

[Matthew E. Herd]

Again, thanks for the input. Can you define bumpsteer? It's never been satisfactorily explained to me. Is the "dartiness" a result of a change in camber or castor? Also, as I know nothing about the history of the vehicle, it is possible something was done (but the bushings certainly WEREN'T and are in need of replacement immediately). The front coils, when the car is on the lift and the wheels are hanging, have only about 2.5-3" travel before they hit the bump stops. I didn't try to measure it when its on the ground, but that's not a whole lot of room for lowering anyway ... can you define how the handling is improved with the front tube shock kit?

 

[aeronca65t]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Matthew E. Herd:
Again, thanks for the input. Can you define bumpsteer? It's never been satisfactorily explained to me. Is the "dartiness" a result of a change in camber or castor? Also, as I know nothing about the history of the vehicle, it is possible something was done (but the bushings certainly WEREN'T and are in need of replacement immediately). The front coils, when the car is on the lift and the wheels are hanging, have only about 2.5-3" travel before they hit the bump stops. I didn't try to measure it when its on the ground, but that's not a whole lot of room for lowering anyway ... can you define how the handling is improved with the front tube shock kit?<hr></blockquote>

The buffer travel distance of 2.5 to 3 inches tranlates to more at the wheel (nearly double that...right?)
Tube shocks *keep* working and don't fade....for short runs (autocross) they are not that much different.
Bump steer relates to the fact that the tie rods are at an angle. That angle is aways a compromise and toe-in/tow-out changes as the suspension moves up and down. If you lower that car, the angle of the tie rods will change and spoil the "best-compromise" setting. It might seem that if you lower tha car 2", you could simply raise the rack 2" and fix everything, but there are a variety of other factors that enter the problem. To set bump steer, a car is set at its static ride height with springs removed (using floor jack). The car is dropped to it's minimum expected rided height and toe is measured. Then the car is raised to its max expected ride height and toe is measured again. If bump steer is good, the toe change will be minimal (for that car). The idea is to get the toe change to be least within the expected suspension movement. Adustments are made by moving the rack up and down or putting spacers on the tie rod ends (if it has spherical rod ends). There are a number of books (such as Carrol Smith's) that have long chapters on this subject).

 

[Matthew E. Herd]

Oh, and another thought occurred to me about improving the effective performance life of the lever arm dampers.
1. In essence, the damper fluid absorbs energy
and heats up.
2. Viscosity is the primary factor in damper
performance, if I'm not mistaken.
Now, I'm also fairly sure that an oil based fluid is used in these dampers. It is a known fact that oil viscosity is very unstable with respect to temperature. As oils heat up, they drop in viscosity. Therefore, a synthetic fluid with more consistent viscosity characteristics at high temperatures could dramatically decrease fade. Furthermore, a simple heat sink, if it is possible, with fins and some airflow, could add to cooling effects. This could make the dampers far more reliable under stressed conditions. Any thoughts? I haven't done any math with this, its just a theory I developed right now (don't ask, I come up with strange ideas all the time

)

 

[Dave Russell]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Matthew E. Herd:
Oh, and another thought occurred to me about improving the effective performance life of the lever arm dampers.
2. Viscosity is the primary factor in damper
performance, if I'm not mistaken.
more consistent viscosity characteristics at high temperatures could dramatically decrease fade. This could make the dampers far more reliable under stressed conditions. Any thoughts? <hr></blockquote>
True, the viscosity of the average fluid changes by about six to one between 100F & 200F & the damping changes accordingly.

How hot does the fluid actually get? The lever arm shocks have aluminum bodies bolted to a semi heat sink which gives good heat transfer to the considerable air flow around them. Maybe heat sink compound between the shock & mount would help. I'm not sure that they get very hot under spirited street or highway driving. I have reached in & felt the shocks after a hard run & they don't seem to be much above ambient temp.

A fast, rough rally course or a bumpy track could cause considerable heating of the shock & fluid.

It would be interesting to see real world instrumented temperature readings of shocks. Manufacturers can do this on a shock dyno but I have never seen anything published.

Just something for you to investigate.

D

 

[Matthew E. Herd]

I didn't know they were made of Al ... could investigate attaching fins directly to the body of the damper. However, simply changing the fluid's about all I think I will do in the immediate future. I'm already working on too many projects