Rear Shocks

[Rtrorkt]

Apparently my rears are getting long in the tooth. What is the brain trust suggestion? 69 912 tub, stock 86 3.2 fairly stiff torsion bars. Fronts are 3 years or so old.

[Schulisco]

Basic rule: The stiffer the torsion bars, the softer the shocks...
Either Bilstein series replacement (which was the sport option from factory) or Koni red (adjustable). Never Bilstein sporty road setting! Those are the stiffest shocks by far. And for a lightweight '69 way too stiff and therefore uncomfortable. But well - they have to fit as well to the fronts. There are Bilstein catalogs with the settings as PDF and online catalogue available.
http://www.bilstein.de/fileadmin/user_upload/pdfs/classic_cars/Klassik-Katalog_08_%202010_final.pdf
https://bilstein.com/en-us/products/

Just my 2cents.

Thomas

[icarp]

Koni Red By a landslide

[PeteKz]

Koni classic (red) or Koni Sport (Yellow). If Sport, start with the softest setting. I run Sports in my 1973 with 3.2 engine.

[Rtrorkt]

Lucky me Pelican is running a KONI sale

[Rtrorkt]

alright guys, Koni reds are not available for my car. Koni yellow sport adjustable or Bilstein Green B6
Thoughts?

[Rtrorkt]

I did find a part number in the Koni catalog o f82-1962 but it seems that Pelican and Sierra Madre only carry the yellow sports.

[PeteKz]

I find Bilsteins too harsh on light cars. Koni Sports.

[AFB24911S]

Vons, level 1, digressive valving!

https://www.penskeshocks.com/blog/linear-progressive-regressive-digressive-shock-valving-differences-and-use-cases

[PeteKz]

Sure, but that's a big step up in budget.

[PeteKz]

Originally Posted by Rtrorkt

alright guys, Koni reds are not available for my car. Koni yellow sport adjustable or Bilstein Green B6
Thoughts?

Here's the Koni Red that fits 1973 cars. It should also fit your 1969. Call Pelican and ask for Glen Sager. He will know if they fit.

https://www.pelicanparts.com/More_Info/KON821756.htm?pn=KON-82-1756&SVSVSI=4247&DID=1

[Rtrorkt]

Originally Posted by PeteKz

Here's the Koni Red that fits 1973 cars. It should also fit your 1969. Call Pelican and ask for Glen Sager. He will know if they fit.

https://www.pelicanparts.com/More_Info/KON821756.htm?pn=KON-82-1756&SVSVSI=4247&DID=1

Pete, will do that this morning. The complication is when the clone was built it was done in shop doing 911 spec racers which underneath is what it is, all 80’s suspension bits. Begs the question is the fitment to the suspension or to the basic tub?

[Rtrorkt]

not that it is important, but the suggest fitment by Pete seems to be right and 2 are on their way to my shop. Thanks all for the help

[Bill Verburg]

Originally Posted by Schulisco

Basic rule: The stiffer the torsion bars, the softer the shocks...
Either Bilstein series replacement (which was the sport option from factory) or Koni red (adjustable). Never Bilstein sporty road setting! Those are the stiffest shocks by far. And for a lightweight '69 way too stiff and therefore uncomfortable. But well - they have to fit as well to the fronts. There are Bilstein catalogs with the settings as PDF and online catalogue available.
http://www.bilstein.de/fileadmin/user_upload/pdfs/classic_cars/Klassik-Katalog_08_%202010_final.pdf
https://bilstein.com/en-us/products/

Just my 2cents.

Thomas

???
???
Choosing damping ratios is a black art w/ many input variables

here's the basic model for a single wheel
ms is the suspended mass, mu is the unsuspended mass, ks is the wheel rate provided by the spring, kt is the tire rat,e cs is the shock damping, ct is the tire damping



here's what undamped over damped and underdamped looks like



a stock 911 rear has a rear wheel rate of ~107lb/in w/ a ride frequency of 1.137

this a a very comfy setup that wants ~80lb/in of damping+/-

change the t-bar to say a 27mm and the wheel rate goes to ~202lb/in w/ a ride frequency of 1.563 which wants a damping rate of ~152lb/in


ie stiffer spring wants a stiffer shock

one of the better shock choices is MCS
here is a graph of their digressive damping ratios
you can certainly find the setting that you want on these shocks


the more mudane shock cjhoices can be hit or miss

Bilstein's tend to be overdamped, which feels harsh but do a digressive revalve and they can approach the MCS for at least one spring rate selection

here's a comparison of Bilstein hd and sport rears
they have linear valving that's pretty good for 23 to 27mm rear t-bars the sports form 256mm up



here's what a digressive revalved rear would look like compared to a sport, these have a much wider range of t-bar application



it would be nice to see similar curves for the Konis

[PeteKz]

It would be nice to see the curves for Konis. I never have come across them.

IN the case of shocks, I trust my "butt shock dyno." I don't race my car, so I want a nice tradeoff between comfort and sportiness, but not all out performance. This tradeoff necessarily is subjective, as some people will put up with more harshness in their street cars than I will.

Rtrorkt: Please be sure to post your impressions of the Konis in your car.

[Bill Verburg]

Originally Posted by PeteKz

It would be nice to see the curves for Konis. I never have come across them.

IN the case of shocks, I trust my "butt shock dyno." I don't race my car, so I want a nice tradeoff between comfort and sportiness, but not all out performance. This tradeoff necessarily is subjective, as some people will put up with more harshness in their street cars than I will.

Rtrorkt: Please be sure to post your impressions of the Konis in your car.

Damping rate of ~.75 is a good starting place but tires and road conditions and MS and MT all affect that

as the ratio goes up or the spring rate goes up the ride frequency aka harshness also goes up. This also affects turn in response and other performance factors.

good rule of thumb is freq. ~1.5 +/- for street sport ~2-2.5+/- for non aero track cars, 2.5-3.0+/- for moderate downforce track cars

[Rtrorkt]

Originally Posted by PeteKz

It would be nice to see the curves for Konis. I never have come across them.

IN the case of shocks, I trust my "butt shock dyno." I don't race my car, so I want a nice tradeoff between comfort and sportiness, but not all out performance. This tradeoff necessarily is subjective, as some people will put up with more harshness in their street cars than I will.

Rtrorkt: Please be sure to post your impressions of the Konis in your car.

Pete, will do. Hoping to pick it up on Monday after I get back from working the IMSA race at Laguna

[thejobrien]

I was told Koni 82-1756 fit on a 77 rear with 3.0 cannot confirm the validity of that but I too will be going koni reds front and rear

[PeteKz]

If you are a "set it and forget it" kinda guy, the Classic/Reds will do fine. You will probably end up at the "second click" in the adjustment range. They are harder to adjust than the Sports. The Sports conveniently have knobs on the top so adjusting them is literally a one-minute per shock process. Sometimes I like to fiddle with mine, so I went with the Sport/Yellow set, even though they are a little more expensive. On the softest setting, they give very good compliance on the street in my lighter 1973 car. I don't like harsh suspensions on the street.