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Old 07-07-2006, 07:05 AM
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Softening the Ride with Rear Coil Overs

We have rear coil overs with 12 inch 200 lb/in springs on our 1939 Olds street rod. Weighs about 3400 lbs I would guess. The 200 lb/in springs compress 2.25 iches with the car empty which equates to about 900 lbs rear weight on the springs. We just use the car for cruising. The current shocks are "drag shocks".

The problem is the ride is very firm in the rear and car oversteers.

The lower coil over mount is adjustable. I think I can easily get 14 inch springs on the car.

Would the basic approach be to go to longer but softer springs and change out the shocks to standard shocks?

John

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Old 07-07-2006, 07:27 AM
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answers to some questions on ride

hello, first what type of suspension system? 4 link? triangulated link? are shocks adjustable as most rear drag shocks are setup to dampen squat so valveing is stiffer on compression. the springs at 200 lbs are to heavy for your vehicle rear. a 125 lb spring would be better. a longer spring is going to be stiffer as it takes more to compress. if shocks are not adjustable then think about replacing.
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Old 07-07-2006, 12:45 PM
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The rear axle rests on trailing arms with panhard bar. Lower shock mounts are welded to axle and have numerous mount holes to vary ride height 5 inches. Drag shocks have three settings (30/70, 40/60, 50/50) -- I think they are set on 50/50 right now.

My thinking was that since I have room for longer springs I could go to those and use a lower spring rate. A spring rate of 150 lb/in for example would compress the springs 3 inches and probably still have 2.5-3 inches of additional compression available.

I don't understand the statement that longer springs are harder to compress and would feel firmer. I think the firmness is a function of spring rate and shock valving.

John
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Old 07-07-2006, 01:12 PM
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sofer ride

what i should have said was to keep ride height the same and putting longer springs in would need to compress them further to compensate which would then give you harsher ride even with softer rate springs. if you have enough adjustment holes and shock travel allows for longer springs you could use them but you are only going to get allowable travel due to shock length. i built a 63 nova shoebox with full four link set up for a customer and installed 75lb 12 inch spings in rear, which would be very close to weight ratio as your car, and car rode very well with mt sportsman 31x18.5 - 15 tires under it . dual batteries and 20 gallon fuel cell in trunk and full interior with rear seat and car never bottomed out. hope this helps
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Old 07-07-2006, 02:28 PM
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Tread40,

Yes, I would need to find shocks with travel to match the longer springs. If 14 inch 150 lb/in springs (for example) are compressed 3 inches with empty car load, the shock ride length would need to be about 11 inches plus 3 inches for the upper and lower mounts, or about 14 inches. Remaining reserve spring compression would be about 3 inches.

Much softer 14 inch springs like 100 lb/in would compress 4.5 inches, leaving only about 1.5-2 inches of addtional travel before coil bind. I don't think that is enough travel to handle two more passengers in back seat and bumps in the road?

The car is a 1939 Oldsmobile, 4 door sedan which I estimate weighs 3300-3400 lbs. (Originally weighed 3000 lbs before street rodding).

John
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Old 07-07-2006, 04:42 PM
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The ride quality is determined by spring rate and damping. The only place coil length comes into play is like you said: how much bump travel you have till coil bind. You can never let the coils bind. You will need to install bump stops to keep them from binding.

Some softer springs and adjusting the shocks should go a long way to better ride. You could also lean the shocks in which would in effect lower the spring rate (it will also reduce the damping).
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Old 07-08-2006, 02:07 PM
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Ride is subjective. One man's OK is another man's "holy $%^&".

Your measured compressed height sounds within limits. 2.25 out of "5.5 or 6" (you said), and I guess you are running a linear spring, not progressive.

I think that most ride problems come from too stiff of shocks.

You are running a valving of 50/50 but that is only the balance between rebound and compression. You need a shock that is softer when it moves through its stroke.

First I would try a softer shock, and then a progressive spring. A longer softer spring might work depending on the adjustment range you have on the coil over. You have to keep your loaded height at about 50-60% of your shock stroke.

You should consider a front anti-roll bar to balance that handling.

I would suggest looking at as many cars as possible that might be similar in design to yours and talking with the owners. It could save $$$$$$ of experimenting.

WE are trying, but without being there about all we can do is give meaningful generalities.

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Last edited by xntrik; 07-08-2006 at 02:37 PM.
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Old 07-08-2006, 03:22 PM
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Just a thought but do you have enough space, diameter wise, to throw away the coil overs and add Shockwave airbag shocks. I have coil overs on my Model A, I hate them, way to harsh. I put airbags on my Model T, it rides much better.
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Old 07-08-2006, 04:19 PM
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Lakeroadster,

I probably don't have room. The coil over springs are 2.5 inch ID and I only have about .25 inch clearance between them and the exhaust pipe.

There isn't any inherent reason that coil overs have to be harsh is there? Can't you achieve the same ride with coil overs as with separate springs and shocks as long as you have enough length to avoid real stiff springs.

I see a lot of street rods with 10 inch or even 8 inch springs on the rear, I guess because the cars are lowered. These must have to be stiff to avoid coil bind in the spring.

My car is not lowered, and I have sufficient room and adjustment on the bottom coil over mount that I can go to 14 inch springs if that helps.

So, basically I am asking if longer softer springs is the way to go, and does anyone have a suggestion on softer shocks. I see some non-adjustable shocks relatively cheap, and single or double adjustable for $150 to $250. Hopefully I can avoid these real expensive ones.

I am just looking for a comfortable, safe ride on the interstate and around town. No racing or carving mountain roads.

John
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Old 07-09-2006, 12:51 AM
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Longer springs would be a good thing if you can fit them.

Before you go spending money on shocks try adjusting them away from the stiffest setting (where they are at now).
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