Bought a kit 2 years ago from Speedway = body & frame. Got it on the road last fall and now has 600 miles on it. It just beats ya to death on these Wi. roads. I can't bounce the rear pushing down with my 200 pound ****. Has a flathead, C4 w/8 rear, 25 lbs air in the tires. What spring rate are you guys running to get a decent ride in a roadster.
Every car is going to be different. You need to see what spring rate you currently have. You also should weigh the rear of the car and use a chart like this to get you in the ball park. http://static.speedwaymotors.com/images/charts/AFCOIL.gif
This is not SPAM - My friend George at Vintage Air had similar problem on his 5-window (kept a pillow in the car!) He got with RideTech with specs on the car and they sent him some coilovers that completely changed the ride - he even made a video for RideTech's site about the improvement. Check it out.
Exactly No way for us to guess what is good looks like Speedy Bill already tried that. He's pretty sharp if he can't guess we can't either.
Since it was a body & frame kit, you'd expect the spring rates to be close to correct. If you take the shock out of the car, can yo move it at all (without the spring on the shock)? Might want to check to make sure one of shocks isn't locked up. Make sure to look at the shock mounts to confirm they are in proper alignment. If they're off, you could have a bind that's preventing shock travel. Should be some easy things to check just to make sure you're not wasting money on unnecessary parts.
Are you running with the adjustable shocks? Do you have the springs pulled all the way down on the shocks with the spanner wrench? (Qual shocks and others) They should only be pulled down about 1/3 of the total. If you do have the adjustable shocks, try l backing off the spring nut (with spanner wrench) 4 or 5 complete turns. That will let your spring have more spring to it, rather than pulled down tight so there is no spring left. The spring is for the bounce, the shock is to dampen out the bumps. HellRaiser
did exactly the same thing on my 31 roadster on 32 rails, used the chart in the catalog, so damn stiff would't even bounce!
I can't tell ya what spring rate is best for your ride, but I can tell you you want the absolute softest springs for the job and the stiffest shocks you can find. I can also tell you you don't have to guess at the weight. If its rolling you can go to a scale right? But you will not be able to get a spung and unsprung easily at the public scale. Even If its not on the road yet, you can build this and be on the money no guessing & two steps. http://www.jalopyjournal.com/forum/showthread.php?t=588650&highlight=cell Step one, get a weight of entire back end of car / total Step two, support rear frame on jack stands and get a weight of the axle, wheels and misc that's your unsprung weight. Subtract second from first and that # will be your sprung weight. Sprung weight is what to use for choosing spring rates. Now you can get the right springs.
Lots of good info here..If they are ajustable remember the weight of the spring is measure by compressing the spring 1 inch.. So a 150 pound spring will move 1 inch when 150 pounds is added.. now if you ajust the spring up you spring rate will go up.. Say you ajust it up a half inck well there is a pre load of 75 pounds on the spring so to move that spring one inch then you will need a weight of 225 pounds to move it.. Saying this the problem with T buckets is they send you the spring that is right on.. The car calls for a 190 pound spring.you have no room to ajust. so with a 150 spring you can ajust it to 190 if you need it. Using the info giving on finding the weight of the car you should find out the spring weight you need. just remember dont get a spring that is right on.. get a lighter spring that you can add weight too.
how about posting a pic of your set up? can also test springs by using some store bought bags of dry cement mix. I put two bags in trunk of a Model A coupe and made a world of difference till I found a deal on some springs at a swap meet.
I wish I would have figured that out sooner. None of the mfg. charts tell you that. I guess they figure we should already know that. I''m now running 120# springs on fenderless '31 coupe.
RDAH, does your axle/trailing arms/hairpins/track bar/whatever, have complete freedom of movement with the coilovers removed??
if you have a set of springs that you do not know the rate of how do you go about checking the rate yourself? do you compress the spring one inch while measuring the pressure it took? say i took a bathroom scale and re-zero it for the weight of the spring, then ad weight on top of the spring till it is compressed one inch or some other amount?
My little plastic roadster uses 180 or 190 springs. Had one, replacement coilovers had the other. No noticeable difference.
If your too stiff in the rear,but have the room to move ether top shock mount inward or bottom shock mount outward=can make softer the more angle ya get on shock[don't go more then 45* though=45* cuts springrate in 1/2 vs 90* is full
I personally think the biggest mistake a hotrod builder makes with their cars is "The Wrong Choice Of Springs" [ Usually Too Stiff ] First thing you need to understand is "spring rates" are different to "wheel rates" due to mechanical design of the suspension [ motion ratio ] The formula is "spring rate divided by [ motion ratio squared ] = wheel rate. So a road race Boss 302 mustang with 900lb/in springs and a 2:1 motion ratio has a wheel rate of 225lbs/in [ 900 divided by 4 = 225 ] The same road race Boss 302 mustang would probably have 170lb/in rear leaf spings [1;1 ratio ] Motion ratios can be adjusted by moving the springs inboard or out, or by laying them over similar to early motocross bikes [ or early Grand Prix cars ] You also need to look at sprung weight vs unsprung weight ,a motor in the front is sprung weight but a heavy axle in the rear is not [ it is not supported by springs ] example: a 3500lb car with 55/ 45% front to rear weight would have 1575 lbs on the rear tyres, but if you deducted 200 lbs for the rear axle weight it would be 1375 [ or 687 lbs per side ] sprung weight This same example would be closer to 59/ 41% front to rear sprung weight so the rear springs need to be softer Other factors to be considered is "spring load" and "spring frequency" ! Spring frequency is like comparing a "valve spring" with a "pogo stick" . the valve spring has many cycles per second [ high RPM ] whereas the pogo stick is all "bouncy bouncy" So the higher the speeds the car goes the higher the frequency of springs Drive around a Road Racing track at 30 mph and you'll think you don't need suspension at all, but at racing speeds they can "bottom out" on bumps, so spring frequency is actually a compromise of average speeds of intended usage. Race cars have a lot higher frequency than road cars! Spring load is the point of equalibrium [ of height ] that a spring settles when a load is upon it. For example a 50lb/in spring will support 500lbs weight but it will settle down 10 inches doing so. For comfort a lower spring frequency is desirable, so there is a greater difference in spring static height and load height, which explains why spring compressors are needed to install coil springs on road cars but on Racing Cars with adjustable coilovers the springs need to be tied in. In most aftermarket applications the springs are usually only cl***ified by lbs / in rates ,but the auto factories they are also cl***ified by load. In a leaf spring the load is an indication of the shape of the arch, in a coil it is the static height . For example: two springs could have the same rating but one has a greater arch for a heavier vehicle. examples here:[ I'll use rear leaf springs as the wheel rate is the same as the spring rate ] Ford Mustang Boss 302 rear springs [ # C9ZZ-5560-J ] have a rate of 152 lbs/in and rated at a load of 550 lbs , so it will settle 3.62 inches with 550 lbs load but because in reality it would get closer to 700 lbs upon it ,the ride height would be 4.6 inches lower than static [ Boss Mustangs sit 1 inch lower from the factory ] Normal Ford Mustang 6 cyl p***enger rear springs [ # C9ZZ-5560-A ] have a rate of 85 lbs/in and rated at a load of 700 lbs [ it has a greater arch ] so it will settle 8.23 inches with 700 lbs load , so because of the greater arch it would sit 1 inch higher than the Boss 302. This all makes sense when you jack the car up, you need to jack it quite a bit to get the wheels off the gound. All this talk about almost 200 lb springs is insane,Road Race cars have less than that [ except banked ovals ] The sprung weight of the rear of a 27 roadster is minimal weigh the rear, pull the springs out while the car is on jackstands and the weight the 2 rear wheels with a pair of bathroom scales to get the unsprung weight, then do some maths. I would guess that an 85 lb /in spring would be on the "heavier side" of sporty in the rear of a 27 roadster [ I've seen 70 lb/in springs in a T bucket that was a pleasure to drive ]
My spring rate tables indicates:- 140lb for a T-bucket; 160lb for an 28-30 RPU; 180lb for a 32-34 roadster or coupe; 200lb for a fendered 32-34 coupe; 220lb for a 28-34 sedan; 250lb for a 35-36 coupe; 300lb for 37-40 coupe; and 350lb for a 35-40 sedan.
We have built several hot rods simular to yours over the past 40 years. I would think you would use a 110# to 120# spring with a common coilover shock with a 14-14.5in. installed height with a 12 in. spring. installed at no more than a 30 degree angle. The way we tell if we have a correct spring is. With 1in. of thread showing at the bottom of your adjuster,it should measure no less than 14in. and no more than 14.5-center to center on your mounting holes. This on a car with 110- 125 in wheelbase. Not saying that it is correct, but has always worked well for us. Bob
Looks like the first thing I'll check to make sure everything back there moves freely with the springs off the coilovers. If that's OK I'll move the spings down & the shock bolt up. If that does'nt help I'll take it to a scale & weigh the rear of the car. I think I posted this question on Monday the 26th & just found it today 29t.h
These numbers have some bearing on mechanical design, for example if the springs were vertical standing "coilovers" they are on the stiff side. But lay the coilovers inwards 30 degrees and it changes the motion ratio and the wheel rate significantly We are talking ride comfort here [ this thread ] , if there is too much bodyroll anti-roll bars should be added In a race car controlling roll stiffness is more important than comfort , so on high speed tracks the roll stiffness is usually controlled by using stiffer spring rates. On low speed tracks [ where the G forces are the same but the speeds are slower due to tighter corners ] the suspension is softened but the anti-roll bars need to be heaver to control roll stiffness. A very common mistake is to use heavy anti-roll bars with too stiff springs [ on the front this causes understeer, so they usually dial in too much negative camber to try and fix this ] On a street car the springs don't need to be as stiff most people think, just the fact that the sprung weight of the vehicle is a lot lighter increases the spring frequency
Forgot this. http://www.hotrodphotos.co.uk/SpringRates.htm Just a guide to set up on a street driven car, not a race car. I've no idea on race suspensions. As an example my steel '35 tub, a lot heavier than a 'T' uses 2 x old and worn OEM Jag coil over shocks on each axle, I believe to 200lb each so 400lb combined for each side. Others say they are 160lb and 180lb depending on year and model. Again from memory they are roughly 13" fully extended and compress to 9" but I've never heard of anyone compressing this far. At ride height they are roughly 11" eye to eye. Ideally the shock would be at 1/3 downward stroke at ride height leaving room for extension and compression as you drive. On solid axles, the further out the shock is towards the wheels, more stable the car is. There are inherent differences when mounting shocks vertically (Upright) as well as canted over too much (Inclination). The mounting angle will effect ride quality and efficiency. My $0.02 worth
A street driven car, and a race car both use the same calculations and laws of physics [ just the perimeters for the calculations are different for the intended usage ] one of the issues with laying over coilovers is the motion ratio constantly changes with compression [ jounce ] it actually makes the wheel rate slightly softer. That link you sent is a very good article but has a few areas that could be misinterpreted depending on what side of the Atlantic you're on [ or Tasman ]
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