Visit The Dirt Forum for More Information

Author Topic:   13 inch to 15 inch rear spring
Xtreme12x
Dirt Forum Champ
Total posts: 874
posted July 21, 2004 10:17 AM  
i've got 13 inch rear springs in now... going back on top of the housing on the left rear i would like to get more travel outwards....
will a 15 inch spring compress to the same height with weight on it as the 13 will or will i need to jack the car around quite a bit to lower it that much... i always thought the longer spring compressed more and then when it exteneded was longer

fastow
Dirt Maniac

Total posts: 168
posted July 21, 2004 11:14 AM  
let me xplain this as i see it when a spring is rated its rated in lbs per inch of compression ie: if you had a 100 lbs spring and set 200 lbs of wieght on it it would compress 2 inchs. A 200 lbs spring with 200 lbs on it would compress 1 inch. So if its a 100 lbs spring 13 inch free hieght when you but 200 lbs on it in theory it would be standing at 11 inchs. I you started with a 15 inch spring then load the same wieght on it it would be standing at 13. So going to longer spring will not give you more travel in the rebound direction unless you change your spring rate. It does increase your bump travel but there is usaully other things limiting your bump travel way before your spring binds. My thought would be make the spring as short as you can with out any danger of coil bind. I hope I explained that clear enough .

zeroracing
Dirt Forum Champ
Total posts: 1875
posted July 21, 2004 12:07 PM  
good points, also shorter springs act slightly stiffer.

smayo964
Dirt Maniac

Total posts: 194
posted July 21, 2004 01:42 PM  
I agree also with the shorter spring. One other point to consider with the longer spring is the bowing effect vs. compression you get as the spring gets longer.

Ego Racing
Dirt Forum Champ
Total posts: 724
posted July 21, 2004 03:09 PM  
You also want to consider that the weight center of the car should be above the top of the springs so when on the gas the chassis pushes down on the spring. If the top is to high the weight of the car will be pushing accross the spring, this will not let weight transfer to the rear springs.
I have seen several Pro Latemodel teams keep the same spring weight and change from 12 to 8 and even 6 inch springs for changing track conditions. It allows them to taylor the way the car acts on the springs. A shorter spring of the same weight will compress more due to the weight having more leverage on the spring, as long as the top of the spring is lowered on the chassis.

fastow
Dirt Maniac

Total posts: 168
posted July 21, 2004 07:07 PM  
Ego your deal with the c of g hieght vs: top of spring hieght was my next point. but my post always go to long I have never worked with a car and changed from say a 13 inch spring to a 8 inch the car I work on now could very easly be changed from one to the other its just a matter of finding \ buying springs how much of a difference you think it would be ? I am thinking about the side bite at the right rear wouldn't it get better with the shorter spring ? Then again if this is a big thing why would so many guys put the right rear spring right on top of the rear end and use a big long spring or is that one of them monkey see monkey do things LOL

Ego Racing
Dirt Forum Champ
Total posts: 724
posted July 22, 2004 08:04 PM  
There are always some things that are easier to work with that fall outside the norm. I watched a car with a mono leaf/coil slider left rear and a 4 link right that almost got lapped in the heat almost lap the feild in the feature and they changed nothing between races.
I have seen several other latemodle teams here going to a short spring and they go from a 200 10 inch to around a 325-350 8inch. We have not had a chance to try it yet on our mod or LM to figure it out. I was planning on trying to talk to one of the guys doing it this weekend and see whay he says. I have seen it on more Rocket chassis than any others so it someone you know has one the factory my offer some advice to them if they call.

Back to the Archives