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Discussion Starter #1
I'm taking the scientific approach to selecting springs for my S4 and will be doing calculations based upon the sprung vehicle mass. To calculate the sprung mass the unsprung mass needs to be subtracted from the vehicle weight.

Does anyone know the weight of the front and rear suspension components or could weigh them, e.g. rear axle, front spring pans, springs, front spindles, front hubs, rotors, calipers, etc? I have heard that they can be 10-15% of a vehicle's mass.

This forum has a wealth of information and insights which is extremely valuable. When I've read and the information in the spring database spreadsheet is confusing. I'm hoping to use a little engineering to understand which springs are optimized for what.

FYI - a forum post puts F/R weight distribution for a S3 at 52%/48%. It should be good enough for my purposes.

References:
The Race Engineer: Springs, Part 1
Automobile Ride, Handling, and Suspension Design
Suspension systems and components

Thanks,
John
 

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Discussion Starter #3
We have the same problem... all our unsprung parts are on the car. I plan to reverse engineer the spring rate calculation starting with the information in the spring database (search this forum), guesstimating the sprung mass and work backwards to determine the front and rear chassis frequency. I'll upload the results in a few weeks.
 

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I have the entire front suspension apart on my 1976 Alfa Spider, Spica. All parts have been cleaned thoroughly, iron phosphate dipped, and powder coated. All bolts, nuts, screws, washers, have been thoroughly washed, cleaned to bare metal using a bench grinder wire wheel, and zinc re-plated with yellow chromate to match the original colour and patina.

Box with all the fasteners, weighs - 10.8lbs.

Box 1 with; Spring pans/seat, Wheel hubs, spring caps (not the shims), tie rod outer tubes, weighs - 17.6lbs.

Box 2 with; Spindles(steering knuckle), Lower arms, Lever support shaft, Rebound buffer plates, Steering lever, weighs - 41.2lbs.

Box 3 with; All new, Adjustable Upper control arms, Ball joints, All tie rod ends, Elastic bushings (lever support shaft to lower control arms), weighs - 20.0 lbs.

I'm not sure if brake callipers, brake dust shields, sway bar, wheel bearings, or new after market yellow front springs are required. I have everything either new or refinished if you need more information. I'm not 100% sure of terminology, I used the descriptions from my Spider Workshop Manual.
 

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Discussion Starter #5
Franco - thank you for the information! From the description of the parts

"iron phosphate dipped, and powder coated. All bolts, nuts, screws, washers, have been thoroughly washed, cleaned to bare metal using a bench grinder wire wheel, and zinc re-plated with yellow chromate to match the original colour and patina"

your spider will be a really nice when you are finished.

I need the weight of the brake calipers, brake dust shields, brake rotors, wheel bearings, and front springs.

The mass of the lever support shaft is not needed as it is a non-moving part.

My goal is to get the weight of the front and rear unsprung suspension within 5%. For a fast street car that should be adequate. From forum posts it appears most people use anecdotal evidence for suspension selection and setup. When I looked at the ratio of front and rear spring rates, I discovered the stock Alfa Spider's front springs have a spring rate that is 4.0 to 4.3 times greater than the rear spring rate. The Shankle springs have a similar front/rear ratio. The Alfaholics springs have a F/R spring rate ratio between 3.3 and 4.4. Race springs have a F/R ratio between 6 and 7.3. GTA springs have a 4.9 ratio. I'm assuming the spring database is accurate.
 

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Discussion Starter #6
I found an old front caliper and it weighs 10# and a front rotor that weighs 12#.

I'm assuming the weight of the lever support shaft that Franco included will be the approximate weight of the splash shield. I have not included the mass of the brake pads

Adding all the unsprung mass, except wheels, results in a 131.6# of unsprung mass in front plus the mass of the wheels.

I still nee the mass of the unsprung rear suspension components.
 

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I have an axle assembly in my backyard. It is "dry" (no oil) and complete with the exception of the brake calipers and rotors. Not a hyper accurate measurement - I balanced it on an old bathroom scale - but I got 114 lbs.
 
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