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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering> Front Coil Over Shocks on a Straight Axel!
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Topic Review (Newest First)
02-09-2013 01:23 PM
jaw22w No, not even close. Sideways all the way around the track. 12" of stagger will do that for you. Takes *****s big enough to carry around in a little red wagon!!!
02-09-2013 12:33 PM
aosborn Sideways in a car with 850hp and weighs in at 1200lbs! And these drift guys think they invented going sideways with style. They are not even close.
02-09-2013 08:35 AM
jaw22w I raced dirt late model stocks. 800 hp @2350#. A lot of fun. But my son races the sprints, 850 hp @1200#. I have only driven it at home on the country road while test running before a race, Man oh Man! will they run.
02-08-2013 07:04 PM
aosborn I don't usually factor a motion ratio on a live axle rear or beam axle front. Just use 1-1. Typically they have more unsprung weight which can throw you off if you don't factor that in. Sounds like you are on the right track though.

Sprint car huh, I would love to take one of those for a few laps sometime. I had an opportunity to drive a midget for a friend of mine, but he got out of racing before we could make it happen.

Regards,

Andy
02-08-2013 06:34 PM
jaw22w I always use 60% bump and 40% rebound. Yeah, that calculator is a little awkard and is for an a-arm suspension front end . I have a straight axle. For the motion ratio, I jacked up one front wheel 4". When I did that the shock moves only 3". So I used a .75 motion ratio. Not sure if this is completely accurate. I based my original spring choice off of the sprint car. We used 250 to 300# springs on the front of the sprint. Of course the sprint only has about a 300# corner weight in front. The hot rod has a 525# front corner weight. So I decided on a 225# spring. It is not uncomfortable to drive and handles well, but could be a little softer. I was just looking for some confirmation before I spend another $200 or so on new springs.
02-08-2013 02:26 PM
aosborn
Quote:
Originally Posted by cal1320 View Post
On a street car, you would normally want the shock in the center of travel at ride height. With a 12'' spring, you have 6'' of shock stroke (3'' to center of shock stroke). A 10'' spring will have 4'' of shock stroke(2'' to center of shock stroke).
Using the same front end weight with both springs, the 12'' spring will need less spring rate so it can compress the additional 1''.
I have always used 2/3 travel in bump (compression) and 1/3 travel in rebound (extension) as a basic rule for designing mounts and specing out shocks. The length of the spring won't affect the rate necessary. The same load is applied to a 10" or a 12" coil-over with everything being equal other than shock length. The only real difference we are talking about is more travel with a longer shock which is what I would recommend.

With that being said, If the rate I am after falls between two available choices, I go with the softer spring and just add pre-load to make up the ride height. By going this route, having the longer coil-over and spring is good so you will have plenty of travel without the spring binding up.
02-08-2013 02:04 PM
cal1320 On a street car, you would normally want the shock in the center of travel at ride height. With a 12'' spring, you have 6'' of shock stroke (3'' to center of shock stroke). A 10'' spring will have 4'' of shock stroke(2'' to center of shock stroke).
Using the same front end weight with both springs, the 12'' spring will need less spring rate so it can compress the additional 1''.
02-08-2013 11:17 AM
aosborn [quote=jaw22w;1643978]
Quote:
Originally Posted by aosborn View Post

No, not referring to the preload. When I input the weights and angles for my car using a 6.3" travel shock and a 12" spring, performance mode recommends a 150# spring with .47 preload. Then when I input the same numbers but change to a 4.1" travel shock with a 10" spring, performance mode recommends a 200# spring with .52 preload. I don't understand why when changing spring lengths, the spring rate needs to change.
I think what they are doing is giving you the fully extended preload setting for each spring rate. To end up at the proper "at ride height" dimension with the different rate springs with the same given load, there might be packaging constraints (length of coil-over threads for example) figured into their formula that would require you to have a different rate to give you enough bump and rebound travel and still be within the adjusment range of the shock.

It is somewhat of an akward calculator, but I think it will get you very close to the right rate, though their ride catagories seem to be a bit on the stiff side. I would think going one catagory softer than what they recommend would be a good idea. If that makes your car a little on the softer side in springing, make up for it with stiffer anti-roll bars.
02-08-2013 07:51 AM
jaw22w [quote=aosborn;1643941]
Quote:
Originally Posted by jaw22w View Post

Are you referring to the pre-load setting they have shown? Since they are showing you three different spring choices you would need to preload each spring a different amount to support the car.
No, not referring to the preload. When I input the weights and angles for my car using a 6.3" travel shock and a 12" spring, performance mode recommends a 150# spring with .47 preload. Then when I input the same numbers but change to a 4.1" travel shock with a 10" spring, performance mode recommends a 200# spring with .52 preload. I don't understand why when changing spring lengths, the spring rate needs to change.
02-07-2013 11:36 PM
aosborn [quote=jaw22w;1643911]
Quote:
Originally Posted by aosborn View Post
That is not really how it works. I 300lb spring is a 300lb spring regardless if it is 2" or 12" long. One will just coil bind sooner than the other. 300lbs compress it one inch, 600lbs 2" etc, unless it is a progressive spring.

That is what I thought also. So why does the calculator posted above say you need a different spring when you change the length of the spring? I have been thinking about this for a couple of days. It has been bothering me. I have used coilover springs and shocks on race cars for over 20 years and I just don't understand why that calculator shows that.
Are you referring to the pre-load setting they have shown? Since they are showing you three different spring choices you would need to preload each spring a different amount to support the car.
02-07-2013 09:06 PM
jaw22w [QUOTE=aosborn;1643896]That is not really how it works. I 300lb spring is a 300lb spring regardless if it is 2" or 12" long. One will just coil bind sooner than the other. 300lbs compress it one inch, 600lbs 2" etc, unless it is a progressive spring.

That is what I thought also. So why does the calculator posted above say you need a different spring when you change the length of the spring? I have been thinking about this for a couple of days. It has been bothering me. I have used coilover springs and shocks on race cars for over 20 years and I just don't understand why that calculator shows that.
02-07-2013 08:18 PM
aosborn
Quote:
Originally Posted by Fe Block View Post
jaw22w

The more coils involved in a longer spring and shock the more vertical movement with the same impact. 10" spring moves 1" but a 12" will move 1 1/8" You use lessor weight spring but the additional movement results in the same weight after you multiply. 1 *300 or 1.125 * 275 roughly the same. I think that's how it works!!!!
That is not really how it works. I 300lb spring is a 300lb spring regardless if it is 2" or 12" long. One will just coil bind sooner than the other. 300lbs compress it one inch, 600lbs 2" etc, unless it is a progressive spring.

Regards,

Andy
02-05-2013 04:37 PM
Fe Block It is a channel weld up one inch on both sides of the frame, BUT since the mount already has holes, and there is still a buggy spring pad on the cross frame, I could easily bolt a rigid diagonal brace from the middle of the pan mount up to the middle of the frame. Thanks for the feedback. Super Idea
02-05-2013 04:32 PM
Fe Block jaw22w

The more coils involved in a longer spring and shock the more vertical movement with the same impact. 10" spring moves 1" but a 12" will move 1 1/8" You use lessor weight spring but the additional movement results in the same weight after you multiply. 1 *300 or 1.125 * 275 roughly the same. I think that's how it works!!!!
02-05-2013 11:50 AM
jaw22w My understanding of coil springs is that (as an example) a 300# spring will compress 1" with 300# on it, 2" with 600# on it, 3" with 900# on it, etc. regardless of the length of the spring.
I see from the calculator that going to a longer spring requires a lighter weight spring. I don't understand.
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