Shock shortening question?
Thread Starter
|
Ultimate HDF Member
Joined: Jun 2007
Posts: 9,193
Likes: 494
From: Richmond, VA
Shock shortening question?
My buddy rides a 1997 Dyna convertible. Its got 12.6 Shocks. Not sure what brand but they aren't stock any more. My question is about shortening shocks. Skull Enterprises shortens shocks for $69.00. A lot cheaper than buying lowering shocks.
http://www.skullenterprises.com/shocks.html
It "looks" as if he just disassembles the shock end, cuts and rethread's the shaft and cuts a coil off the spring. What happens to the ride quality of the shock with a coil missing? Do the shocks get stiffer or softer??? I just can't place it in my head what happens to a spring with a coil gone. Do the shocks get rock hard or get so soft they bottom out all the time?
http://www.skullenterprises.com/shocks.html
It "looks" as if he just disassembles the shock end, cuts and rethread's the shaft and cuts a coil off the spring. What happens to the ride quality of the shock with a coil missing? Do the shocks get stiffer or softer??? I just can't place it in my head what happens to a spring with a coil gone. Do the shocks get rock hard or get so soft they bottom out all the time?
Cruiser
Joined: Jan 2011
Posts: 125
Likes: 0
From: Rowlett, TX
If you shorten a spring, it's spring rate WILL go up.... Because for the same amount of travel, the remaining coils will have to compress further (because there are now less of them).
Let's say that you have a spring with ten coils, and it's 20 inches long. And let's say that this spring has a rate of 20 lbs\inch. If you load that spring with 100 lbs, it's going to compress 5 inches. And each coil wii compress .5 inches. It's important to remember that....each coil compresses .5 inches when the spring has 100 lbs on it....
Now, cut a coil off and put the same load on it....what happens? Each coil still compresses .5 inches, but since there's only nine of them now, the spring only compresses 4.5 inches total under the same 100 lb load. The rate of each coil is unchanged...but the rate of the whole spring has gone up! Obviously, I chose numbers that make for an easy example, but the principle is the same for all coiled springs.
I'm not trying to disparage you...the new spring rate may turn out to be better suited for your situation that the current one. But it will be stiffer! How much stiffer all depends on the specifics of the spring.
Let's say that you have a spring with ten coils, and it's 20 inches long. And let's say that this spring has a rate of 20 lbs\inch. If you load that spring with 100 lbs, it's going to compress 5 inches. And each coil wii compress .5 inches. It's important to remember that....each coil compresses .5 inches when the spring has 100 lbs on it....
Now, cut a coil off and put the same load on it....what happens? Each coil still compresses .5 inches, but since there's only nine of them now, the spring only compresses 4.5 inches total under the same 100 lb load. The rate of each coil is unchanged...but the rate of the whole spring has gone up! Obviously, I chose numbers that make for an easy example, but the principle is the same for all coiled springs.
I'm not trying to disparage you...the new spring rate may turn out to be better suited for your situation that the current one. But it will be stiffer! How much stiffer all depends on the specifics of the spring.
Road Warrior
Joined: May 2010
Posts: 1,382
Likes: 4
From: Kennewick, WA
If you shorten a spring, it's spring rate WILL go up.... Because for the same amount of travel, the remaining coils will have to compress further (because there are now less of them).
Let's say that you have a spring with ten coils, and it's 20 inches long. And let's say that this spring has a rate of 20 lbs\inch. If you load that spring with 100 lbs, it's going to compress 5 inches. And each coil wii compress .5 inches. It's important to remember that....each coil compresses .5 inches when the spring has 100 lbs on it....
Now, cut a coil off and put the same load on it....what happens? Each coil still compresses .5 inches, but since there's only nine of them now, the spring only compresses 4.5 inches total under the same 100 lb load. The rate of each coil is unchanged...but the rate of the whole spring has gone up! Obviously, I chose numbers that make for an easy example, but the principle is the same for all coiled springs.
I'm not trying to disparage you...the new spring rate may turn out to be better suited for your situation that the current one. But it will be stiffer! How much stiffer all depends on the specifics of the spring.
Let's say that you have a spring with ten coils, and it's 20 inches long. And let's say that this spring has a rate of 20 lbs\inch. If you load that spring with 100 lbs, it's going to compress 5 inches. And each coil wii compress .5 inches. It's important to remember that....each coil compresses .5 inches when the spring has 100 lbs on it....
Now, cut a coil off and put the same load on it....what happens? Each coil still compresses .5 inches, but since there's only nine of them now, the spring only compresses 4.5 inches total under the same 100 lb load. The rate of each coil is unchanged...but the rate of the whole spring has gone up! Obviously, I chose numbers that make for an easy example, but the principle is the same for all coiled springs.
I'm not trying to disparage you...the new spring rate may turn out to be better suited for your situation that the current one. But it will be stiffer! How much stiffer all depends on the specifics of the spring.
I'd never recommend lowering a bike and loosing any of that much needed travel, but if you do, just buy a shock that is already rated for your weight in the shock length desired. The internal valving is also designed to work with the coil spring, so that you neither pogo nor not rebound fast enough when hitting a bump or a washboard road.
Go ahead and try it. If it doesn't work you will still end up buying new shocks. Nothing ventured, nothing gained..............
Thread Starter
|
Ultimate HDF Member
Joined: Jun 2007
Posts: 9,193
Likes: 494
From: Richmond, VA
Thanks guys. Great explanation. I knew there was some science to it but for the life of me I could not figure it out. So shortening them makes them stiffer. Hemiorange, I couldn't agree more. Though not in my sig pic, I run 13 inch 440's for exactly the reason you stated. I also have those short covered ones just so I can lower the bike every once in a while should the need hit me. But for most of the year, the longer 13 inchers are great riding shocks that I would never get ride of. But hey, my buddy wants it lowered and he's a cheap a$$. 
Road Captain
Joined: Apr 2011
Posts: 597
Likes: 0
From: Louisiana
If he doesn't take the route above, he can always pick up a pair of 11" progressive 412s on ebay. I'm running 11" on my wide glide and I love the way it looks. However, it does make the ride a little rough, but it sure looks good!
Thread Starter
|
Ultimate HDF Member
Joined: Jun 2007
Posts: 9,193
Likes: 494
From: Richmond, VA
Thats the advice I gave him, but they run about $206. He's thinking that shortening them is still about a third of the cost. And since 11's do ride pretty rough anyways the shortening might be the option. I have to say, I am just a little curious to see how they ride if he does it. I'll certainly let this forum know how they turn out if he goes threw with it. Thanks.
Last edited by bikerlaw; Apr 3, 2011 at 06:55 PM.
Thread
Thread Starter
Forum
Replies
Last Post
126, 1996, conv, convertible, dyna, harley, long, lower, motorcycle, progressive, review, shock, shocks, shorten, shortening, spring, stock
