01-11-2016, 12:29 PM
So I have done a few front suspensions before diving in on the 2014 HD XL1200T. I was looking at stretching the front and rear suspensions, getting the spring rates right for solo riding and lastly getting the damping sorted out. I got the rear sorted out first, then switched my attention to the front.
Pic 1: In testing the front, I found it had really weak springs, a surprise. I also verified the working range of the right fork, 3.63”
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2011%20spring%20analysis_zpslamqhzpv.jpg.html]![[Image: 1ed05acca64e8f8a10bd59cf5b39c38a.jpg]](https://cb1100forum.net/forum/uploads/imp/201601/1ed05acca64e8f8a10bd59cf5b39c38a.jpg)
Pic 2: Then I got into a good discussion on another web site (caters to sportsters) on spring rates. I wanted to run a higher rate spring. The thing about linear rate RaceTech springs, the stiffer the rate, the shorter the spring. In the pic you see the oem 40 lb/in spring vs the 56 lb/in (I think) spring. I had a RaceTech emulator left over from a GL650 project, so it was going in the 39mm Showa fork too. You can see the parallel magenta lines from the damper rod to the folk lower. These are reference lines to depict how high up in the fork the damper rod sits. That got me to thinking how much over the top of the damper rod the oil level is set. Per factory specs, the oil level is more than 7” above the damper rod. This told me the oil level is not set for damping purposes but to set the overall spring rate. This ment I could play with the oil level to try and get as linear a rate “spring” in the front suspension.
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2014%20spring%20analysis_zpsjquxvdvu.jpg.html]![[Image: 3226c9e8ca68da3c8845c79af4af77e4.jpg]](https://cb1100forum.net/forum/uploads/imp/201601/3226c9e8ca68da3c8845c79af4af77e4.jpg)
Pic 3: Here is the result of testing with water. I put all the components in the fork then fill the fork with water. Then, I pour out all the water and measure the water converting the water weight to volume. You can see the max volume in the fork is 16.3 oz. Now, I flll the fork with water to the spec limit, then pour the water out, weigh and convert to volume. Based on my testing, I can see with the factory spring and proper oil level, the oil volume is 70% of the max volume. I collected other fill heights and calculate the fill volume. With the multiple data points, you can build a curve to help figure out how much less oil I can run.
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2012%20spring%20analysis_zpslknl8160.jpg.html]![[Image: f2ecd383990767a312768e05d56a0981.jpg]](https://cb1100forum.net/forum/uploads/imp/201601/f2ecd383990767a312768e05d56a0981.jpg)
Pic 4: Back to testing. I assemble the fork with just the spring and check for spring only capability (brown dotted line). Then I add the factory oil (water really) level and test for capacity (green line). You can see adding the oil increases the max capacity from 214 lbs to 270 lbs (66 lb increase!). In fact the green curve tells you the spring is going to behave like a progressive spring (there is no reason to buy a progressive spring when oil makes you linear rate spring act like one). Now, I add to the 76% oil fill (only 1” higher fill over factory levels) and you can see the fork is not going to fully compress (will never compress 3.63”).
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2015%20spring%20analysis_zpsc8cstg3a.jpg.html]![[Image: b6ca58c92009197aa584737cce0a564a.jpg]](https://cb1100forum.net/forum/uploads/imp/201601/b6ca58c92009197aa584737cce0a564a.jpg)
Pic 5. Here is the pic of the fork testing. In pic 1 above, the fork easily compressed with 225 lbs. IN this pic, 385 lbs will not fully compress the fork
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2013%20spring%20analysis_zpseplekpsc.jpg.html]![[Image: 7ab9b2d8914630256efa6c9e5bf172cc.jpg]](https://cb1100forum.net/forum/uploads/imp/201601/7ab9b2d8914630256efa6c9e5bf172cc.jpg)
So I learned you CAN use a higher rated spring if you back off the oil a bit. The short spring allows you to run a lower oil level which reduces the air spring affect. This netted a more linear spring rate which helps you dial in the suspension easier and makes the bike easier to ride more aggressive because the suspension is more linear and easy to predict what the bike is going to do.
Clear as mud right?
Jerry
Pic 1: In testing the front, I found it had really weak springs, a surprise. I also verified the working range of the right fork, 3.63”
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2011%20spring%20analysis_zpslamqhzpv.jpg.html]
Pic 2: Then I got into a good discussion on another web site (caters to sportsters) on spring rates. I wanted to run a higher rate spring. The thing about linear rate RaceTech springs, the stiffer the rate, the shorter the spring. In the pic you see the oem 40 lb/in spring vs the 56 lb/in (I think) spring. I had a RaceTech emulator left over from a GL650 project, so it was going in the 39mm Showa fork too. You can see the parallel magenta lines from the damper rod to the folk lower. These are reference lines to depict how high up in the fork the damper rod sits. That got me to thinking how much over the top of the damper rod the oil level is set. Per factory specs, the oil level is more than 7” above the damper rod. This told me the oil level is not set for damping purposes but to set the overall spring rate. This ment I could play with the oil level to try and get as linear a rate “spring” in the front suspension.
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2014%20spring%20analysis_zpsjquxvdvu.jpg.html]
Pic 3: Here is the result of testing with water. I put all the components in the fork then fill the fork with water. Then, I pour out all the water and measure the water converting the water weight to volume. You can see the max volume in the fork is 16.3 oz. Now, I flll the fork with water to the spec limit, then pour the water out, weigh and convert to volume. Based on my testing, I can see with the factory spring and proper oil level, the oil volume is 70% of the max volume. I collected other fill heights and calculate the fill volume. With the multiple data points, you can build a curve to help figure out how much less oil I can run.
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2012%20spring%20analysis_zpslknl8160.jpg.html]
Pic 4: Back to testing. I assemble the fork with just the spring and check for spring only capability (brown dotted line). Then I add the factory oil (water really) level and test for capacity (green line). You can see adding the oil increases the max capacity from 214 lbs to 270 lbs (66 lb increase!). In fact the green curve tells you the spring is going to behave like a progressive spring (there is no reason to buy a progressive spring when oil makes you linear rate spring act like one). Now, I add to the 76% oil fill (only 1” higher fill over factory levels) and you can see the fork is not going to fully compress (will never compress 3.63”).
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2015%20spring%20analysis_zpsc8cstg3a.jpg.html]
Pic 5. Here is the pic of the fork testing. In pic 1 above, the fork easily compressed with 225 lbs. IN this pic, 385 lbs will not fully compress the fork
[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2013%20spring%20analysis_zpseplekpsc.jpg.html]
So I learned you CAN use a higher rated spring if you back off the oil a bit. The short spring allows you to run a lower oil level which reduces the air spring affect. This netted a more linear spring rate which helps you dial in the suspension easier and makes the bike easier to ride more aggressive because the suspension is more linear and easy to predict what the bike is going to do.
Clear as mud right?
Jerry