Hot Rods rough ride

I have an old school 30 A tudor with coil overs and ladder bars . The bars connect to the trans.crossmember. The ride is prettty harsh when you hit a bump so was wondering how , if any way so soften the ride. I posted a thread a while ago about a "rattle" in my engine. Turned out to be just the collector gaskets. Go figure.

 

Coil overs.
Are the shocks adjustable?
If so, back the screw off a half turn and go for a ride.
Do you know what the pound rating of the rear springs are?
For a sedan, I'd guess 250, or 275 would be good. Max would be 300 lbs.

My '31 Victoria has 225 lbs Alden rear coilovers. They recommended that spring. The ride was fine. I put over 100k miles on that setup.

The Vic weighs 2450, empty

 

My ride sucks, 4 bar coil overs. Hopefully with the full fender rebuild (previous it was a hiboy) it will behave a little better.

 

The biggest mistake in suspension tuning is the wrong choice of springs


The Model A Tudor has a curb weight of 2400 lbs , now assuming there is 50/50 weight distribution = 1200 lbs rear weight
1200 lbs minus approx 200lbs unsprung weight = 1000 lbs or 500 lbs each rear corner

Soften the rear spring stiffness and have between 5" to 6" spring load [somewhere between 90 lb/in and 110 lb/in max]

Measure the spring height as it sits on the ground ,and try and buy a softer spring with a 5"-6" longer static height [the longer needs to be softer]


Then look for a way to ditch the Ladder Bars for something that allows body roll.
As soon as you install ladder bars the car is "over sprung"

With ladder bars if only one wheel hits a bump the whole rear travels upwards together [so the bump is absorbed by both springs instead of just one]
Usually this results in frame twist [the harsh/shudder you feel through the whole cars]

 

let me tell you about my experience with coil overs with my '32 Ford roadster. I won't mention the brand of coil overs, but they used what they called "progressive" springs. The bottom four or five coils were touching and you couldn't get a business card between them. To me, that's a spacer, not a spring. I drove my car for about three years and chalked the rough ride up to the car being a hot rod. I was at the Nat's in Louisville one year and stopped by the Pro Shock booth and talked to them about the ride. The salesman told me that if I wanted, over the winter, send them all four shocks and springs and they would test them and let me know what they find. Well, all four spring rates were wrong and the front "progressive" shocks were blown. I purchased what he recommended from Pro Shocks and I couldn't believe how great my car handled and how nice the ride was. Even my wife commented on how nice the car rode on her first ride. As Kerry points, spring rate is everything and many people do not understand how to calculate the correct rate. There's no reason a hot rod shouldn't have a good ride if all the components are sourced correctly.

 

Assuming g the rear coils aren't coil bound an easy test is whether the ride improves with some weight in the rear. Couple of beefy buddies should do it.

Chris

 

A 250 lb spring rate is at least double what it needs to be, just as Kerrynzl has posted.
see this all the time with old rods, way oversprung on the rear like they were going to fill the trunk with spare parts like it was a truck, and the back seat with passengers, all the time.

Quite a few are that way because they don't have room between the axle and the frame for enough suspension travel with a correct light rate spring....so they overspring it to keep the axle from hitting the frame.

 

Try a 140-in-lb. coil set.

 

Let me know if it does not.

 

I would be surprised if the weight of a couple of fenders, brackets and maybe half the weight of running boards will make a noticeable difference !

 

It seemed to when I mocked them up before the tear down. But maybe it was just in my head

 

Find some race scares and weigh it
Don’t crank on the coil adjuster thingy to get the ride height

 

This except once the corner weights are known , support the frame on 4 x jack stands and disconnect the shocks/springs and weigh the 4 wheels [to get the unsprung weight]
With a bit of elementary school math you can calculate the sprung weight.

Even this is too stiff for a street vehicle.

For example a 1969-70 Mustang fastback only has a spring stiffness 85 lbs/in [ # C9ZZ-5560-A ]
It has a "spring load" of 700lbs [a deep arch] so if 700lbs was actually loaded on it , it will settle 8.23"
[700 ÷ 85 = 8.23"]