New Rear Shocks

[saltshaker]

I’d like to change the rear shocks on my Contemporary, the current shocks that came with the car are Sacks touring Shocks and the springs are 250lb. Car rides nice but leans in the turns. I have single adjustable shocks up front but my question is about the rears. Ride height for the shocks is 12” and qa1 has a shock that would work, 10” closed and 14” open American Alden offers a shock the same size as the original Koni… 9” closed and 13 open
Dies it make a difference in which shock I choose since the ride height is the same!
Jon

[Tom Wells]

Salt,

Don't know the answer directly, but I can dance around it a little ;-)

I use four Aldan PAS 654 rear shocks on my XJS rear axle, using 3.8S length swing arms and axles (longer than XKE but way shorter than XJ6.) I do think they're good shocks. They've needed rebuilding twice in 40K+ miles.

They work well for my E-M which is perhaps fairly similar to your Contemporary. Kinda depends partly on your rear axle/swingarm specs too.

When I first put the car on the track at Summit Point the builder used a shock that was too short; the interesting symptom was that when I was coming into the front straight at decent speed and cornering fairly hard, the car skipped sideways. Unsettling for me and for the car. The rear of the car literally bounced toward the outside of the corner.

The short answer is that longer shocks with a bit more travel eliminated the skipping.

My analysis was that when the car rolled a little the inside wheel unloaded and came clear of the road. As the outside tire slid the inside tire would try to bite again. Whether that's correct or not the newer shocks (same as the Aldans you noted above) seemed to eliminate the skipping. Many more track miles on many more tracks - no skipping - so I think the problem was solved.

The shorter stroke shocks may give you a similar result - or not! It depends on whether they are acting to lift the inside wheel in a turn as they get to the end of their extend stroke while the car is rolling, and on other factors such as roll bars, tires, weight distribution etc etc.

As you can tell, I'd choose the longer stroke shocks. Brand may not matter as much: QA1, Koni, Aldan and others may all give you an OK result.

Hope this helps and doesn't confuse,

Tom

[saltshaker]

I’m leaning towards the qa1’s which have more travel
Jon

[Tom Wells]

Salt,

Trying to picture what you meant by "more travel."

Looking at your 1st message I'm under the impression that you mean the QA1s have more extension (i.e., more "droop") than the other shocks which seems true.

The other consideration is whether the shock's compressed length is OK and isn't too long so as to make the shock act as a stop for the upward/compressed direction. When the suspension is fully compressed, the axle normally hits a rubber stop somewhere externally and doesn't bottom out the shock in that direction.

Again, depends on your setup. If the shock will act as a stop, maybe checking with QA1 to see whether that's OK and wouldn't beat up the shock internally would be a good idea.

Looking at your 1st post again, maybe a swaybar would be a good idea to reduce body roll? If you pursue this you'll need to decide whether to go with only a front bar or both ends. And if you do that, swaybar diameters are important. That's at least a three beer discussion; maybe six LOL.

Another option might be a bit stiffer springs at one or both ends.

Sorry it sounds so complex...

Tom

[saltshaker]

Tom, Alden 654 has a compressed height of 9.7 and extend 13.4” the qa1 compressed height is 10.125 and extended 14”….the qa1 is approx 3/8 higher when closed so I get what your saying and will check it. Ride height for both shocks is 12” and that’s what Contemporary wanted.
Jon

[Tom Wells]

Jon,

Sounds like you're on the right track with those measurements.

Just went out and had a look under the E-M Cobra after I said some swaybar things and found I have no rear swaybar. The front does have a Mustang II based suspension and sports a 1" bar. If yours has the Jag front suspension it may take a different bar - if it doesn't already have one. Body roll is minimal on my car.

I wish I could look up or recall the rear springs spec but don't know their rates.

Tom

[Tom Wells]

Jon,

My brain (if any) seems to work like one of those ink-filled 8-balls. You know, the kind that you turn over, ask a question, and then sooner or later (I'm definitely in the later category) an answer floats to the top.

The reason I say this is that body roll is more affected by swaybars and springs than the shocks. Shocks can only have an effect briefly and will continue to deflect if the springs/swaybar(s) allow it. Or in other words, shocks have an influence on the rate of roll, not the extent if that makes sense.

Here's a link that kinda says the same thing (note he does mention stiffening both springs and shocks together and ruining the ride): https://grassrootsmotorsports.com/ar...how-reduce-it/

So I think if roll control is your primary objective, you'd be better off looking first at a swaybar or perhaps a little bit stiffer springs.

I hope that makes sense.

Tom