Koni Shock Spring Rates

[NAZ]

Jim, the Gen-2 has a significant increase in motion ratio which is why you can't use the 225# springs others have and achieve the same result. So based on your guestimated weight and using 250# springs, if you were shooting for a 2" droop you would use 2.9" of preload. Not knowing your spring wire diameter I can't calculate your spring bind height but 2.9" of preload might have spring bind (not a good thing). A 300# spring would need 2.2" of preload to get 2" of droop. 275# spring would need 2.5" of preload for a 2" droop. I'm just using 2" droop as a SWAG but can calculate any droop you want.

Let us know how you make out with the 300# springs and if you give me the spring wire diameters I can calculate spring bind height. You want to avoid spring bind.

[33fromSD]

Jim, the Gen-2 has a significant increase in motion ratio which is why you can't use the 225# springs others have and achieve the same result. So based on your guestimated weight and using 250# springs, if you were shooting for a 2" droop you would use 2.9" of preload. Not knowing your spring wire diameter I can't calculate your spring bind height but 2.9" of preload might have spring bind (not a good thing). A 300# spring would need 2.2" of preload to get 2" of droop. 275# spring would need 2.5" of preload for a 2" droop. I'm just using 2" droop as a SWAG but can calculate any droop you want.

Let us know how you make out with the 300# springs and if you give me the spring wire diameters I can calculate spring bind height. You want to avoid spring bind.

Will do, Thanks NAZ

[33fromSD]

Hi Naz

The QA1 300# (9" Length) springs arrived yesterday for the front end. For the preload calculation, the wire diameter of the 300# spring is .4435". These are powered coated so I have no clue the thickness of the powder coating is compared to the bare wire dia. (not sure if it really matters in the scheme of things).

Let's shoot for about 1.5" droop.

Thanks for all the help.

Jim

[Jim Schenck]

Naz,

The Hot Rod motion ratio didn't change from Gen1 to Gen2, there was a second set of holes added to the arms for height adjustment but at the same radial distance from the pivot point. The Gen2 cars do have the steering rack moved for better bump-steer but that was the only geometry change other than adding the second set of ride height holes.


My only thing to add to the conversation here is that there have been changes over the course of production to both the standard and optional shocks as well as spring rates and steering geometry. The change to the nickel plated twin tube shocks and lower rates was a very significant one so just for anyone building a new car I would say finish it and drive it before deciding it has to be changed just from what others have done to earlier cars.

Jim

[33fromSD]

Naz,

The Hot Rod motion ratio didn't change from Gen1 to Gen2, there was a second set of holes added to the arms for height adjustment but at the same radial distance from the pivot point. The Gen2 cars do have the steering rack moved for better bump-steer but that was the only geometry change other than adding the second set of ride height holes.


My only thing to add to the conversation here is that there have been changes over the course of production to both the standard and optional shocks as well as spring rates and steering geometry. The change to the nickel plated twin tube shocks and lower rates was a very significant one so just for anyone building a new car I would say finish it and drive it before deciding it has to be changed just from what others have done to earlier cars.

Jim

Thanks for the input Jim

I think FFR needs to review / verify the suggested ride height in the manual for 33s running the full fender / running board package. I am running full fenders / running board and using the supplied standard Koni Shock, and the supplied 400# coil springs, even with zero pre-load on the coil spring I cannot achieve the suggested 5.5" ride height (even after driving the car and letting the springs settle). I'm at 6.75" for ride height with zero preload. I'm also using the lower set of holes as suggested in the manual for full fender 33s.

As you suggested I have driven the Koni package awhile and I agree the supplied standard Koni shock / 400# spring package is "not bad" and most folks will probably be okay with it, but it's a little too stiff for my taste and I switch to the QA1s for a little more adjustability, as well as I switched to a QA1 9" long 300# spring to get a little lower ride height (closer to the manual suggested 5.5" height for full fender cars".

Jim

[33fromSD]

NAZ

See the attached pic, these are the added holes in the upper Contro Arm Jim S from FFR is referring to. Basically it raises the suspension 1" if you're running full fenders / running boards. But it's still 7" CTC on both the lower & upper set of holes.

fullsizeoutput_69.jpeg

Jim

[J R Jones]

Jim, As you know, those are the high ride height settings. You could experiment with the three low options. With your new springs you might find the sweet spot. It just takes time.
jim

[33fromSD]

Jim, As you know, those are the high ride height settings. You could experiment with the three low options. With your new springs you might find the sweet spot. It just takes time.
jim

yup, I know. Thanks

Jim

[NAZ]

OK Jim, base on Jim Schenck's confirmation that your G-2 motion ratio is the same as my G-1, we can calculate the preload but need the front end weight to do so.

Thanks for the wire diameter info but my bad, I forgot to ask you for the number of full coils.

[33fromSD]

OK Jim, base on Jim Schenck's confirmation that your G-2 motion ratio is the same as my G-1, we can calculate the preload but need the front end weight to do so.

Thanks for the wire diameter info but my bad, I forgot to ask you for the number of full coils.

7 full coils NAZ unless you count the outside coils too which have the flattened spots for the spring sets then it's 9 full coils

Jim

[NAZ]

Jim, I'll give you the theoretical preload for three different front end weights to achieve 1.5" of droop:

1250lbs needs 1.8" of preload
1300lbs needs 1.9" of preload
1350lbs needs 2.0" of preload

All these preloads will allow full shock travel without coil bind.

[33fromSD]

Jim, I'll give you the theoretical preload for three different front end weights to achieve 1.5" of droop:

1250lbs needs 1.8" of preload
1300lbs needs 1.9" of preload
1350lbs needs 2.0" of preload

All these preloads will allow full shock travel without coil bind.

Perfect, Thanks NAZ

Jim

[33fromSD]

Lot of work into the suspension with many hours on my back on the floor removing and reinstalling shocks with different spring combos. I still quite honestly don't know how you guys build your whole car without a lift, doesn't help I'm in my mid-50s and the ground is no longer my friend but still, kudos to you all.

Also, a lot of extra $$ tied up in the QA1 shocks, but more so the various spring sets I purchased (if anyone is interest in some sets let me know) but in the end I'm going to call this suspension issue closed as I believe I now have the right shock / spring combo on my car. I still have some fine adjustments on the knobs for all the QA1 shocks but the major work is now done.

Here is the combo that feels best to me for my 33:

* Front = QA1 DD403 Proma Star Double Adjustable coil over shocks with 9" long 300# springs
* Rear = QA1 DS601 Proma Star single Adjustable coil over shocks with 12" long 300# springs

With the longer springs in the back I needed to do the modification to the shock mounts where to take a 2-1/2" hole saw and cut slightly more than 1/2 a hole of the material away so the spring clears the mount, but I knew that coming into this. No biggie there, just a heads up to anyone else swapping to 12" springs.

The beauty of the rear shock / spring set up, is this is the first time since I completed the car and started driving it, that I have not bottomed out on all the really bad bumps and dips I know of in the city. Certain tweaks I made with the Koni Shocks / 250# spring with the kit kept me from bottoming out on some of the lesser severe bumps / dips but not 100%. This morning when I took out the car when I finished the new set up, I purposely looked for and drive over every really bad bump, dip, gap, seam or pot hole I came across verses avoiding them and not once did I bottom out....FINALLY!! Still need to do the same route with a passenger in the car but I'm fairly confident it will be fine.

Someone mentioned it above (can't find who now) and they are 100% correct, each of these 33s are unique regarding build / set up, so my taste / setup in shock / spring combo may not be to the liking of someone else but it this is why we tweak on our own rides and make them our own. It was a great learning experience, I learned a ton from them with the wealth of information everyone provided (especially NAZ).

Thank You everyone!!

Jim

[RoadRacer]

I suspect I'll need longer rear springs.. or stiffer. My car is almost through the 'glass above the tire now. But I'm waiting to final fix more when I have my sway bar on (next weekend) and larger tires (not sure when). Also may add more bumpstops.. so a lot up in the air.

[NAZ]

James, if the tire hits the fender over bumps you have too much suspension bump travel for your fender clearance. The fix is not stiffer springs, that doesn't guarantee the tire won't rub -- it just requires a bigger bump to make contact. And stiffen the springs on the rear enough and it will lead to your car handling like a drift car and longer stopping distances as traction diminishes at the rear.

A bump stop is the cheap and easy fix. Bump stops come in extra lengths that you can cut to the size needed or you can stack bump stops to get the length you need.

[sread]

Bump stops are a versatile method to fine tune suspension travel - they come in all sizes and hardness (durometer). GM 1/2 ton suvs of the early 2000 vintage have bump stops that that are in contact at normal ride height. They are made of a dense foam type material and when they age they will start to crumble and deteriorate. When you go to the GM parts catalog for replacements they are actually called "auxiliary springs"

[NAZ]

Elastomers can be used as springs. I've designed punch press tooling stations using polymers for short throw springs. They outlasted steel springs and are not as susceptible to harmonics from the sudden and repeated impacts over millions of strokes like steel springs. At 400 strokes per minute, 24/7 punch press tooling takes a real beating.

[J R Jones]

As long as this thread has "mission creeped" a bit: I have a fondness for air suspension. Back in the 60s air shocks for trailer towing made the unloaded suspension rough. Air Lift air bags inside coil springs were great. Operating pressures (5-20) were much more comfortable and the ultimate spring rate seemed progressive. I never measured the actual boosted spring rate. I see that Air Lift is making an "Airover" shock unit currently, but I have not tried it. One can tune the spring rate and ride height with air pressure.

In the seventies I was doing interstate service work with occasional heavy loads in my mid-size Chevy wagon. I put (used) Air Lift bags in the rear coils. Late one night on the interstate in NW WI I was carrying a load at speed passing 18 wheelers in the left lane. A loud report came from the rear, I assumed it was a tire, the car sagged, but was stable. One of the bargain bags blew but I did not use the system lines for service, I serviced them individually. I moved the load over the good bag and moved-on.
Seems to me not interconnecting the Airovers would provide the ability to balance weight.
jim

[NAZ]

Jim, my hauler is a F550 I ordered new with all the bells that fit my needs. They only come as a cab and chassis so you have to finish the vehicle. When it arrived at the dealer I drove it straight to my shop to start modifying it for my particular use and the first item on the agenda was pull all the steel springs and install an air ride suspension including a four-link rear. I set it up with auto leveling in the rear and have a dump valve that makes it squat when attaching one of my trailers or even offloading by hand so it's easier to reach the load. I love air ride on a truck and it rides twice as good as the OEM springs. The auto leveling adjusts the air pressure based on load so the truck doesn't ride like an old farm wagon when not loaded.

The next thing was fabricate a lightweight aluminum bed which looks better than store bought. I love that truck but I think it'll be the last Class-5 truck I purchase, the annual insurance and license fees are more than all my other seven road driven vehicles combined. I think the next truck will be a 1-Ton, they're way less expensive to operate.

[J R Jones]

NAZ, One has to assume there is something behind (high) insurance rates; it is not obvious to me.
In the old days air shocks lifted the chassis to inappropriate height and loaded shock mounts with spring load, also inappropriate. The air bags did not lift to an extreme, but would lift overloads to original ride height.
The Air Overs are an odd configuration with the air chamber around the shock body. Quite different from bag in coil. Seems like an opportunity for innovation, especially for the Hot Rod, like a mono-bag in front. "Soft Nose" TM.
I have been visualizing a unique front anti roll device as well.
jim

[RoadRacer]

Jim, (33fromSD) I sent you a PM about some spring questions when you have a chance. Thanks.

[33fromSD]

Jim, (33fromSD) I sent you a PM about some spring questions when you have a chance. Thanks.

Just responded, sorry about the late response, trying to pack some of the toys away for the upcoming down turn in weather so I've been off line a bit.

Jim

[5mspeed]

Took your advice on QA 1 took 3 months to get but what a great ride now thanks Gary

[33fromSD]

Took your advice on QA 1 took 3 months to get but what a great ride now thanks Gary

Awesome!! Yes, the ride is night & day between Koni & QA1. Little spendy, but worth it in my opinion. I also like the adjustability of QA1.

Jim

[RoadRacer]

JR, the front motion ratio on the Gen-1 cantilevered upper arms is ~1.37:1.

I know NAZ is no longer around unfortunately, but I've been thinking about the spring rates a lot since starting autocross. I keep getting a little more serious about making my car faster

So, I want to make sure I'm thinking about this cantilever the right way. Many folks (roadster, coupe) run high spring rates, i.e. 700-800lbs front. I'm at 650, btw, but I think the cantilever is working against me? Can anyone confirm.. given that the inner arm is ~7" and the outer arm ~10", the 650 spring is the equivalent of a ~475lb (650/1.37) spring in a cobra? I can't believe it works the other way, i.e. equivalent to a 650x1.37 = 890lb spring?

If this is the case, it would explain a lot.. cos 450lb would seem to be awful light for a competitive autocross car.

[33fromSD]

I know NAZ is no longer around unfortunately, but I've been thinking about the spring rates a lot since starting autocross. I keep getting a little more serious about making my car faster

So, I want to make sure I'm thinking about this cantilever the right way. Many folks (roadster, coupe) run high spring rates, i.e. 700-800lbs front. I'm at 650, btw, but I think the cantilever is working against me? Can anyone confirm.. given that the inner arm is ~7" and the outer arm ~10", the 650 spring is the equivalent of a ~475lb (650/1.37) spring in a cobra? I can't believe it works the other way, i.e. equivalent to a 650x1.37 = 890lb spring?

If this is the case, it would explain a lot.. cos 450lb would seem to be awful light for a competitive autocross car.

I don't autocross James but I'm only run-in 300# springs in the front with dual adjustable shocks.

Jim

[RoadRacer]

Yeah I get it Jim, sounds crazy I know. different animals!

My point being though that compared to other cars without the cantilever, the extra 1.37 leverage means that your car is like a normal car with 220lb springs

* actually very simplistic because all cars have some leverage and we’d have to measure their distance on the lower a-arm to determine theirs. It’s not 1:1 for a roadster..

[Dgc333]

I have read through this thread and find the info to be very informative. I do have one question:

Why would you want to use a spring that is shorter than what the longest length the shock can accommodate?

Assuming the same spring rate a longer spring will minimize the chances of coil bind.

[RoadRacer]

I have read through this thread and find the info to be very informative. I do have one question:

Why would you want to use a spring that is shorter than what the longest length the shock can accommodate?

Assuming the same spring rate a longer spring will minimize the chances of coil bind.

Agree at the back.. but at the front of a 33 the longer springs can touch and interfere with each other. I only use 7” springs on the front now.