Spring Rate Suggestions for '68 Camaro

[Mkelcy]

I've finally got my '68 Camaro build on the street. It's got a 21st Century Street Machine subframe, a Lateral Dynamics 3 link rear, LS3 engine and T56 transmission. Because of the intrusion of the upper link into the rear seat area, I've elected to eliminate the back seat, so it will never carry more than two people. The car is Dynamatted but doesn't otherwise have weight added. The battery in in the trunk.

I've just gotten the car on the road. Although I've got very little seat time, my impression is that it's over sprung for my use, which is spirited local driving and long distance trips with little to no auto-cross or track time.

For the front I'm using 450 lb./in. springs, a 1.15" hollow sway bar that has a rate of 300lbs./5 degrees of twist and QA1 single adjustable coilover shocks dialed down to the softest setting. For the rear I'm using 200 lb./in. springs on AFCO double adjustable M2 coilover gas charged shocks with a remote reservoir, both compression and rebound dialed down to the softest settings and, having just checked, the former gas charge on the shocks has leaked away over the years, so they are not charged; no rear sway bar. As I said, I'm just starting to get miles on the car, so the shock settings are simply to get a baseline from which to make adjustments (and I'll throw a 50 lb./sq. in. nitrogen charge on them when I get my fill kit).

I'm thinking of stepping down to 400 lb./in. springs for the front and 175 lb./in. springs for the rear.

Anyone have any thoughts on whether that's enough of a step down (especially after I get a charge on the rear shocks) or too much; am I looking at the wrong part of the suspension (say the front sway bar, and/or adding bar for the rear if I go with softer springs); or should I get the rear shocks charged and get more seat time before doing anything?

Thoughts?

I'm looking for a little smoother ride while still allowing for excellent street handling.

[dhutton]

How much preload do you have on your coilovers? In my experience a lot of preload leads to a lousy ride on the street. The preload "fires off" when going over abrupt drops in the road which can make the ride seem harsh. I found a stiffer spring with less preload gave a better ride for me.

Just my two cents, not an expert by any means.

Don

[Mkelcy]

How much preload do you have on your coilovers? In my experience a lot of preload leads to a lousy ride on the street. The preload "fires off" when going over abrupt drops in the road which can make the ride seem harsh. I found a stiffer spring with less preload gave a better ride for me.

Just my two cents, not an expert by any means.

Don

At full extension, hardly any on the rear; I'll have to check the front, but my recollection is that I don't have much there, either. The car already rode a little high, and I didn't want to raise it more by preloading it a lot.

[dhutton]

I've got some 12" 175 pound springs if you want to try them. Just PM me your address and I can send them out this week.

Don

[Penny]

Post a pic, I am subscribing.

[Vegas69]

Twenty five pounds won't be noticeable in regards to ride. Those are light springs. I'd say it's shock valving or you need to buy a Cadillac. :geezer:

[Sieg]

How many miles on the suspension? There is a break in period for springs, shock seals, and bushings. Subtle but still a factor. Another factor is personal perception, what are you used to driving or what are you comparing it too?

[Mkelcy]

How many miles on the suspension? There is a break in period for springs, shock seals, and bushings. Subtle but still a factor. Another factor is personal perception, what are you used to driving or what are you comparing it too?

Fair questions. Perhaps 200 miles on the suspension.

I'm comparing it to '68 Camaro with 550lb./in. front springs and 200 lb./in. composite rear leaf springs

[Sieg]

Fair questions. Perhaps 200 miles on the suspension.

I'm comparing it to '68 Camaro with 550lb./in. front springs and 200 lb./in. composite rear leaf springs

Lighter motor in this one?

Brake packages similar?

Overall car weights?

[Matt@BOS]

I would guess that it is more shock than spring related. If you start to drop rates you might end up with a car that wallows a bit and bottoms out over dips in the highway. I've upped rates 100-150 lbs all around on my DSE suspension, and upgraded shocks. It rides better than with softer springs and the original non adjustable Koni/Afco shocks.

My first suggestion would be to gas up the rear shocks in case the rear is getting rattled around over bumps, without much shock control.

If that doesn't fix things, you may want to swap shocks. Trust me, in the long run you will have less headaches. My Afcos always leaked down and the verishocks seem to blow seals, and, in my opinion, they don't ride amazingly well, either. Please don't take this as an agressive sales pitch, or attempt, (I have a small fortune worth of JRi shocks and work with JJ all the time) but the fastest way to get your car driving down the road with the ride you are looking for would be to call RideTech up and get a set of their shocks. Their Ride Quality and Handling Quality series of shocks (hope I got those names right) flat out work the way they should. The cars I've driven with them ride so well I don't even think about the suspension. The ride is smooth, solid and pretty composed without clunking over bumps.

Bret/Rod please don't ever let that end up as a testimonial on your website, accompanied by that picture of my car under the Fox awning at Laguna Seca. I will get in trouble.

Matt

[Sieg]

^^^Agree. The spring rates don't seem aggressive at all, the unknown is the shock valving and without dynoing them it is blackmagic. That said, Ride Tech's shock offerings are one of the best reasonably priced pro-touring oriented shocks on the market.

[Mkelcy]

Thanks for the suggestions.

I've got a nitrogen fill setup on the way. When it gets here, I'll get a bottle from the welding gas store and gas up the rear shocks.

I also heard from David Pozzi who's tuned Bad Penny, which has the same front and rear suspensions I'm using, as well as the One Lap Camaro, which uses the same rear suspension.

David's suggesting I leave the rear spring rates alone for now and drop the front springs to 350 lb./in. He noted that 350 lb./in. springs in the 21st Century Street Machine subframe would be equivalent to a 600 lb./in. spring in a stock subframe, which suggests that the 450 lb./in. springs in there now are the equivalent of a 770 lb./in. spring in a stock subframe. In any event, I'll swap out the front springs, leave the rear alone (other than gassing up the shocks) and see where I am.

I'll consider shocks if I can't get it where I want it any other way, but springs are about $70 a set, and gas charged shocks (which I need because they're mounted upside down) are going to be $400-$1,000 plus a set.

[GregWeld]

FWIW -- I had QA1's on my Nomad --- and switched them out to Strange... which is what Art Morrison uses and sells on his chassis... it was like I built a completely different car... Until then - I had no idea a shock (really a damper) could make that much difference!


The Nomad ran coil overs all the way around.

[Vegas69]

Interesting...

[Mkelcy]

FWIW -- I had QA1's on my Nomad --- and switched them out to Strange... which is what Art Morrison uses and sells on his chassis... it was like I built a completely different car... Until then - I had no idea a shock (really a damper) could make that much difference!


The Nomad ran coil overs all the way around.

That's good to know on the QA1's. They were a set I had laying around, so it's not a big deal to replace them.

My first impression when I drove the car was the front was over sprung, over damped or both. I dialed down the shocks, which improved it a bit, but it still felt over sprung (or maybe badly damped with some stiction). I'll swap the springs, and then see where I need to go next.

It may be that the back end will be just fine once I get the front sorted out.

[Matt@BOS]

Thanks for the suggestions.

I've got a nitrogen fill setup on the way. When it gets here, I'll get a bottle from the welding gas store and gas up the rear shocks.

I also heard from David Pozzi who's tuned Bad Penny, which has the same front and rear suspensions I'm using, as well as the One Lap Camaro, which uses the same rear suspension.

David's suggesting I leave the rear spring rates alone for now and drop the front springs to 350 lb./in. He noted that 350 lb./in. springs in the 21st Century Street Machine subframe would be equivalent to a 600 lb./in. spring in a stock subframe, which suggests that the 450 lb./in. springs in there now are the equivalent of a 770 lb./in. spring in a stock subframe. In any event, I'll swap out the front springs, leave the rear alone (other than gassing up the shocks) and see where I am.

I'll consider shocks if I can't get it where I want it any other way, but springs are about $70 a set, and gas charged shocks (which I need because they're mounted upside down) are going to be $400-$1,000 plus a set.

Don't forget though, while you found the relative difference between the spring rate on a stock subframe vs the 21st Century one, you've sort of calculated one back from the other without thinking about the motion ratio and wheel rate. The 450lb spring might be equivalent to 770lb spring in a stock subframe car, but wheel rates are probably closer to 300 and 200. If you had a 550-700 lb spring on the 21st Century frame I would think it would be way too much for what you're doing.

Part of building a car is spending time after its done to get it sorted out to your liking. Even the finished cars around here always seem to be in pieces. Springs are cheaper than shocks though, so if it works for you then you're lucky you only had to make one change. :lol:

[David Pozzi]

I Found my notes.
coil rates are rounded off.

A 300 coil on a 21st century sub has a wheel rate of 156.
A 350 coil = 182
A 400 coil = 208
A 450 coil = 234

A 650 coil on a stock sub has a wheel rate of 156.
A 750 coil = 182
A 850 coil = 208
A 950 coil = 234
You will notice a 50 lb increase in 21st centruy sub = a 100 lb increase in the stock sub.

On a 21'st Century sub, multiply coil rate by .521 = Wheel Rate

Bad Penny started out at 350 went to 450 to 475 for quite a while and I think may have ended up around 500-550.
Steve always wanted to run the car super low, so we had somewhat limited bump travel. We had to go stiffer to make it work. With a higher ride height and more travel, you can run a softer spring. Shocks have a huge influence in this too.

[Payton King]

I had the 21st Centry subframe and a Torque arm rear with no bar. I ran 550 lbs front and 325 rear with Bilstein shocks and 1.25 bar .188 wall in 34 inch length. 13 inch sway bar arms netted a rate of 364 lbs.

As stated above, the quality shocks valved correctly, made all of the difference in the world.

I started off with cheap non-adjustible shocks and 350 f and 175 rear with 1 inch solid bar. Quickly went to 450 f and 250 rear. Best ride was above with the best performance. Car rode way better than my wife's M3 she had at the time.

[bret]

You can guess...you can solicit advice from those who have a similar set up...or you can spend a small amount of time and really calculate what spring the car needs: http://www.ridetech.com/tech/spring-rate-calculator/

This calculator will work for any brand of coilspring or coilover. I'll spare you my personal and shameless recommendation of the RideTech shocks :)

[Rod P]

the fastest way to get your car driving down the road with the ride you are looking for would be to call RideTech up and get a set of their shocks. Their Ride Quality and Handling Quality series of shocks (hope I got those names right) flat out work the way they should. The cars I've driven with them ride so well I don't even think about the suspension. The ride is smooth, solid and pretty composed without clunking over bumps.

Bret/Rod please don't ever let that end up as a testimonial on your website, accompanied by that picture of my car under the Fox awning at Laguna Seca. I will get in trouble.

Matt

Oh no...I would never do that........:whistling: ....but its gonna cost ya!:G-Dub:

[David Pozzi]

I entered the measurements from my Morrison sub into the Ride Tech calculator. The Morrison sub is nearly the same as the 21'st century using the same lower control arm and nearly the same shock angle.

Ride Tech Calculator:
Cruiser/daily = 375
Perf driving = 425
Racing =450

Mary has been running the 350 rate since last fall.
James has 425 on OLC and it's doing very well. With the Ride Tech shocks set at mid-range, the car rides great on the street.

We had some indication of hitting the bump stops on Mary's car when she tried lower shock settings. So we will be trying some stiffer front coils. I think if you have a more streetable ride height, the 350's will work fine, but I'd turn the shocks up for an autocross.
FYI, Morrison runs/ recommends a 450 front coil on their 69 Camaro.

[Mkelcy]

I entered the measurements from my Morrison sub into the Ride Tech calculator. The Morrison sub is nearly the same as the 21'st century using the same lower control arm and nearly the same shock angle.

Ride Tech Calculator:
Cruiser/daily = 375
Perf driving = 425
Racing =450

Mary has been running the 350 rate since last fall.
James has 425 on OLC and it's doing very well. With the Ride Tech shocks set at mid-range, the car rides great on the street.

We had some indication of hitting the bump stops on Mary's car when she tried lower shock settings. So we will be trying some stiffer front coils. I think if you have a more streetable ride height, the 350's will work fine, but I'd turn the shocks up for an autocross.
FYI, Morrison runs/ recommends a 450 front coil on their 69 Camaro.

Thanks David. I ran the Ride Tech tool (nice job there, by the way) and came out in the low to mid 300's depending on shock travel. My car's not down in the weeds (my LCA's are essentially level with the ground), so I should be okay at those spring rates.

The 350 lb./in. springs came in today, as well as the nitrogen setup for the rear shocks. I'll get everything installed, drive it and see where I am. It's quite possible that a new set of front shocks are in the cards.

I have tell tales on the rear shocks, which are about 1" to 1.5" from bottoming out.

This car is primarily a long distance tourer that's supposed to be fun on curvy roads; it's not focused on auto-crossing or HPDE.

[bret]

Keep in mind that our spring rate calculator provides a starting point...rates can be tuned to satisfy a particular car, driver, tires, swaybar, shock set up.

We worked very closely with Hyperco to develop this tool. They've been building springs for awhile. We took their lengthy and complicated engineering algorithms and translated them into a tool that most of us can understand. We've found it works pretty darn well. If we get a car that is on the extreme fringe for weight or traction sometimes it can miss a little, but such cars are typically serious track units that are subjected to an appropriate amount of tuning anyway.

The other cool resource we've developed is the huge library of vehicle weights that we've gathered over the last few years. http://www.ridetech.com/tech/coiltech-2/

If you take a look at that library I'm sure you will find a combination that is darn close to yours. This will save you the trouble of finding a 4 corner scales for your own car. Then all you need is a tape measure and the discipline to use it!

[Mkelcy]

Keep in mind that our spring rate calculator provides a starting point...rates can be tuned to satisfy a particular car, driver, tires, swaybar, shock set up.

We worked very closely with Hyperco to develop this tool. They've been building springs for awhile. We took their lengthy and complicated engineering algorithms and translated them into a tool that most of us can understand. We've found it works pretty darn well. If we get a car that is on the extreme fringe for weight or traction sometimes it can miss a little, but such cars are typically serious track units that are subjected to an appropriate amount of tuning anyway.

The other cool resource we've developed is the huge library of vehicle weights that we've gathered over the last few years. http://www.ridetech.com/tech/coiltech-2/

If you take a look at that library I'm sure you will find a combination that is darn close to yours. This will save you the trouble of finding a 4 corner scales for your own car. Then all you need is a tape measure and the discipline to use it!

As I said, really nice job with the coil spring rate calculator. It's a great tool and a great service to the community. I also found the library of weights which was very helpful.

My biggest area of guesstimation was unsprung weight.

I used 70 lbs. for the front - Forgeline 10" x 17" wheel, Michelin Pilot Sport 275-45-17 tire, C5 rotor, caliper, spindle, bearing pack and LCA.

I used 120 lbs. for the rear - Ford 9" with nodular iron pumpkin, Strange axles, brackets, control arms & Watts link for the 3 link, Forgeline 11" x 18" wheels, Michelin Pilot Sport 295-35-18 tires, Wilwood 12.19" internal parking brake rotors and calipers.

If I'm off, I'd guess that I'm over on the front and under on the rear. That third member is HEAVY.

[David Pozzi]

Mike,
I happened to have the parts to my Morrison sub laying around.

Front:
14" brakes 25lb
half of coil over shock 7.5
Half of LCA 10
Hub, knuckle, steering arm 20
18" Forgeline wheel with 275 tire, 47 lb
Total 109.5 lbs Smaller brakes would be a little less.

Shock angle 57 degrees which isn't available on the calculator.

A Ford 9' weighs 195 lbs with 6 piston 14" brakes, not counting suspension links or shocks. A ford 9" floater weighs 220 with brakes.

[Mkelcy]

Mike,
I happened to have the parts to my Morrison sub laying around.

Front:
14" brakes 25lb
half of coil over shock 7.5
Half of LCA 10
Hub, knuckle, steering arm 20
18" Forgeline wheel with 275 tire, 47 lb
Total 109.5 lbs Smaller brakes would be a little less.

Shock angle 57 degrees which isn't available on the calculator.

A Ford 9' weighs 195 lbs with 6 piston 14" brakes, not counting suspension links or shocks. A ford 9" floater weighs 220 with brakes.

David, thanks for the information. I was low for both ends. I measured a shock angle of about 64 degrees but, as I said, my car rides a bit high.

I got the rear shocks gassed up, but in the process of doing so, saw that the driver's side rear wheel was rubbing the canister hose. Things get tight back there with the 3 link and the exhaust. Fortunately, I'd covered the hose with some plastic wire loom for just this reason, so the hose wasn't damaged. I'll jury rig a mount for the canister in a different location, and make fabbing something pretty a winter project. We definitely have a driving season up here in eastern Washington, and I don't want to miss seat time while I get the car sorted out.

[Mkelcy]

I've got close to 1,000 miles on the car since I got it on the road at the end of April (including one 300 mile trip and one 250 mile trip), and have concluded that I need to look at damping before I play anymore with spring rates. I can't dial the AFCO M2's down anymore and I still get a pretty good jolt over slow speed bumps. It's great on smooth roads, but that's not a great test of a suspension. I think the spring rates may still be too high, but the current principal issues seems to be damping.

I'll be calling Ride Tech on Monday.

[Mkelcy]

I put a set of the Ride Tech handling quality shocks (single adjustable) on the car, together with 300 lb./in. springs in front and 175 lb./in. springs in the back.

According to the Ride Tech spring rate calculator, those rates were recommended for performance driving, and I agree, while at the same time the car rides much better than it did over bumps and pot holes. Overall I'm very pleased.

One thing I'd mention is that the Ride Tech shocks come with bearings that have a 5/8" ID. They include adapters to sleeve the bearing down to the 1/2" bolt size I was using. With the adapters installed, however, the overall shock bearing length is about 1.25".

The lower front shock trunion I had was set up for a 1" long shock bearing, however Ridetech has a trunion that will work with their 1.25" stack height.

Unfortunately my top shock mount on the subframe also required no more than a 1" bearing width and there was no modifying that mount. I ended up having the Ride Tech adapters milled down to the 1" overall width I needed.

If any of you end up needing to do this, be aware that the adapters don't touch inside the shock bearing, so you need to install them in the bearing, and then determine how much to take off each adapter.

[David Pozzi]

Keep an eye out for rear bottoming at 175 lbs.