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NEW SIGNIFICANTLY ENHANCED VERSION AVAILABLE IN LAST POST....5/25/2019
Lee
Members:
I was frustrated at the lack of spring, sway bar, and handling information available for our C3 Vettes, so I researched the available data, measured the suspension of my car, and calculated the spring rates, wheel rates, sway bar rates, and roll rates. I put it all together in one place for all of us. Snapshots are included below. The pics are also in my albums. The original spreadsheet is loaded on Google drive. If you want a copy of that Excel spreadsheet, with all the math formulas intact, feel free to download it, here is the address:
I think there are some things unaccounted for yet. There can be a difference in how the roll bar is coupled to the suspension that will affect it's roll rate. Stock type rubber has a lot of deflection, poly has less and heim type ends with solid bushings on the roll bar have no deflection. Also a lot of the front 550 springs get shortened which raises the spring rate, as well as the rear fiberglass springs getting shortened for tire clearance, that also raises it's spring rate.
Mine for example has poly on the roll bars and both of my springs are shortened. It's not hard to figure the increase in spring rate, but the rubber, poly, heim/solid differences not so much. A lab could do it, but not so easy otherwise.
There is also center of gravity and roll center to consider. It's not too hard to change either, but making use of all the information is not an easy task for most enthusiast. On top of that we have the front to rear weight being discussed in the SB vs BB thread and the side to side weight balance, which isn't very good on stock C3's. I lowered my engine and moved it to the right by about 1/4" each way to help there.
Thanks for the positive feedback.
Agreed the suspension dynamics discussion goes way deeper than this. I found it a good way to compare major parts and possible changes. Some of the changes are almost impossible to quantify, like heim joints, roll cages and spreader bars, etc. The fine tuning must be done at the track and based on driver feel, preferences, and of course elapsed times.
Hmm.. maybe I'll find a center of gravity height measurement someday.....
Here's a good read if you want to dig into the physics of the C2 and C3 suspension written by none other than Mr. Arkus-Duntov. The 1963 Corvette Sting Ray
Thanks a lot!
Now I have access to roll center heights and center of gravity. Oh Boy!
Just remember the roll center height in the rear changed when they lowered the inner pivot of the strut rods. And the Smart Strut bracket lowers it even further.
I think there are some things unaccounted for yet. There can be a difference in how the roll bar is coupled to the suspension that will affect it's roll rate. Stock type rubber has a lot of deflection, poly has less and heim type ends with solid bushings on the roll bar have no deflection. Also a lot of the front 550 springs get shortened which raises the spring rate, as well as the rear fiberglass springs getting shortened for tire clearance, that also raises it's spring rate.
Mine for example has poly on the roll bars and both of my springs are shortened. It's not hard to figure the increase in spring rate, but the rubber, poly, heim/solid differences not so much. A lab could do it, but not so easy otherwise.
There is also center of gravity and roll center to consider. It's not too hard to change either, but making use of all the information is not an easy task for most enthusiast. On top of that we have the front to rear weight being discussed in the SB vs BB thread and the side to side weight balance, which isn't very good on stock C3's. I lowered my engine and moved it to the right by about 1/4" each way to help there.
Mike
I've been kicking that around for a future mod next time I need to pull the engine. Doing the math, the weight change/distribution numbers aren't that significant, but I'm running out of other ideas to remove or redistribute the car's weight.
Oops! I found an error in my math in the rear. There is a motion ratio on the rear spring. Changes all the rear numbers after that.
The final numbers make more sense to me now.
Many thanks to a forum member who forwarded me an S.A.E. publication from 1963 loaded with engineering drawings:
With this new information I was able to add roll center, roll rate, tire weight, camber change, and suspension alignment calculations to the spreadsheet:
Download new version here:
OK I'm finished with it now, I think. you add 12-15 pieces of info about your vette, and it will interactively show you what happens to camber, toe-in, and tire loads when you turn, brake or accelerate. I had fun playing with the math. Hopefully some of you will find it useful. Well after 6 months my hand is finally feeling better so it's time to go play with the real car! LOL
"This Dynamic Suspension Calculator is made specifically for C2 and C3 Corvettes. It will calculate many parameters that change while driving the car: Weight Transfer, Acceleration Gs, Tire Loads, Camber Changes, Toe-In changes and more. You have the capability of selecting curb weights, springs, sway bar sizes, driver weight and alignment specs. You can even add options, lower the car, change the rear roll center, or lighten the unsprung weight with lighter wheels. Just make your Selection Inputs into the Bright Yellow Boxes, and work your way through all 12 Sheet Tabs to the end. Feel free to take the protection off and modify the formulas or the data charts if you like."
Many thanks to KidVette for giving me a copy of "The 1963 Stingray Book" by Zora Arkus-Duntov and his engineers. (Earlier post). That really gave me the info I needed to dive into the deep end with this.
Fun to quantify the changes with installed springs, sway bars, and camber bracket, along with alignment.
Please confirm I read the front caster is assumed to be fixed at 2 degrees? Is there any significant change in output camber values with the C2 manual steering caster setting of 0.5 degrees (a ballpark)?
Sway Bars, cell B19, number format is set to "custom, date," and may need to change to "general" (found when entering "0").
Excellent, and thank you for the considerable effort.
Thanks,
I had fun with it and hope folks find it useful.
I used the camber curve supplied by GM. I do not believe it would change very much at all with different caster settings, or PS/MS. It is based on the 4 a-arm pivot points.
Toe-in however would drastically change when caster is changed.
But you can look at the GM graph and get an idea of how much the toe-in change drops with less caster, I'd estimate about half the toe-in change as a PS car.
If anyone puts the new upper a-arms on their car, that gives 4-5 degrees caster, that would double the calculated toe-in curve.bump-steer from Found out a little more on bump-steer from Greenwood's VIP series: Lowering the car changes the Toe-In curve dramatically. Guldstrand says a lower A-Arm Z height of 1 inch, after lowering, is ideal for a race car, and yields a front bump steer curve of almost zero under jounce. So it looks like Chevy had the ideal bump-curve built into the car from Day 1, all we have to do is align it properly, and get the front height correct. (Outer A-Arm BJ 1 inch lower than inner pivot.) My car is on jacks, so I can't tell you how much different that is from stock, only the one inch setting to shoot for.
Last edited by leigh1322; 05-28-2019 at 09:37 AM.
Reason: update
04-16-2019, 03:58 PM
Suspension Math Spreadsheet Available
you add 12-15 pieces of info about your vette, and it will interactively show you what happens to camber, toe-in, and tire loads when you turn, brake or accelerate. I had fun playing with the math. Hopefully some of you will find it useful. Well after 6 months my hand is finally feeling better so it's time to go play with the real car! LOL
