Most springs for cars and motorcycles have a linear spring rate. If the spring rate is 100 pounds per inch that means it takes 100 pounds of force to compress it one inch. If you load your motorcycle down the spring compresses. It is under tension but it's spring rate is still the same. It still takes 100 pounds of force to compress the spring another inch. The problem is your motorcycle is now loaded up with more weight so when when you hit a dip you are more likely to bottom out due to the inertia of your cycle. This is true even if you have increased the preload. It would be great if you could increase the spring rate when you load up a cycle but the preload does not do this.

Some shocks have progressive spring rate springs. The spring rate might start off at 75 pounds per inch but after the spring compresses the spring rate would increase to 125 pounds per inch. Some progressive spring rate shocks are made with 2 springs. One spring has a low spring rate. When this spring completely compresses the 2nd spring takes over. This 2nd spring has a higher spring rate. Some progressive springs are just one spring but one end of the spring is smaller diameter and easier to compress.

The purpose of a progressive spring rate is to give a low spring rate on the smooth roads. When you hit a big dip and compress the suspension then the spring rate increases to be much more firm before the suspension bottoms out.

 

I searched a bunch of threads, but I don't have a ton of time to read at the moment. Is there anyone who can tell me if my 96 fatboy will withstand 2 up riding w me and my ol lady. I am about 280, she is about 210. I feel like that's gonna be a strain for it. I've been riding a VTX for years and had no problem...but this is my first HD and it seems on the light side.

 

After reading this thread from end to end I see that I now have many options for air shock upgrade on our 2008 Ultra Classic. The problem is that 14K miles ago I installed Progressive 416s and don't want to spend more money chasing "the best rear shocks."


When I originally decided to make the swap, I read or was told the stock shocks were not rebuildable and I didn't verify it for myself. Damn! Because of very good prior experience with Progressive fork springs (a few different touring bikes), and the H-D cartridge kits, I arbitrarily decided to install Progressive 416s in the rear.


My wife and I are not large, and she has a bad back. I take care to monitor the air shock pressure, but we have not been satisfied the result justified the expense. (We have since installed a Road Zeppelin seat, which I love and she likes.)


Progressive tech support verified 416 shock oil can be drained & refilled without disassembly. So yesterday I replaced the original SAE10 (fork) oil with SAE20 (fork) oil. The drain pan should have collected 4oz, but the 416s only drained ~3oz -- and after 14K it was nasty!


Yippee -- February in NH it's easy to find some rough roads, and a 50°F test ride felt like a definite improvement. I attribute this to some combination of clean oil, proper quantity, and the SAE weight. Going forward, I intend to drain and refill the rear shocks regularly.

 

I've read a lot about rear suspension upgrades and actually rode a buddies bike who had Ohlins remote reservoirs with the yellow cans on his 2014 FLHTK. He wanted to ride my bike to see what power my 106CI has and I wanted to try how comfortable his bike with Ohlins rode. I weigh 185lbs and he weighs 190lbs so we didn't adjust anything. Although I only rode it a few miles I must say that I was really impressed with the overall feel of the bike but when he told me he spent well over a grand I was like damn.. Too bad that money is an option for me. I ended up buying Bitubo WME 330mm for my 2014 FLHTK for $550 brand new and I am completely satisfied with it. I think Bitubos are an option in addition to shocks mentioned in all these posts and in my opinion there not that expensive considering they are rebuildable.


If money was not an option I will definitely get a set of Ohlins with the remote reservoirs. till this day I have never rode a more comfortable bike.

 

Wrong. It takes an ADDITIONAL 100 lbs to compress the spring the second inch. So, if the spring is uncompressed; it takes 200 lbs to get 2 inches. If the spring is preloaded an inch it will take 100 lbs + 200 lbs = 300 lbs to get 2 inches of suspension travel. So how would a suspension that provides 2 inches of travel through an applied force range of 100-300 lbs not be stiffer than one that provides 2 inches of travel through a range of 0-200 lbs? I've strapped quite a few suspensions down for drag racing and they go from compliant to bone jarring when I compress/preload/tie down (or whatever you want to call it) the coil springs.

 

With stock shocks, ride 2-up. There will be much by way of improvement in ride. Don't forget to make sure you have 30 lbs. of pressure in them.
Don't ride 2-up? I don't do a lot either. That is why I bought HD premium shocks with a pre-load adjustment and also installed Progressive Monotubes up front. Although not the "best", they are a huge improvement over the stock "send me to the moon on bumps" shocks, they are very nice. I bought them with bonus money from my local stealer. These "minor" improvements others talk about sounds like what you are after. If you want a softer ride, you will lose some handling. But I'm sure you already know that.
Sounds like you need to spend some hard earned cash. Good luck.

 

If the spring rate is 100 lbs per inch it takes 100 pounds to compress it one inch. It takes another 100 pounds to compress it another inch. Each inch takes another 100 pounds to compress further. This you said in your opening sentence. Think long and hard about that. If the spring is on a bench it takes 100 pounds per inch to compress. Same if it is on the cycle. If you put a 100 lb. weight over the rear wheel of a cycle it will compress 1 inch. That is true if the cycle is empty and even if it is fully loaded. That is true if the preload is set to maximum OR minimum UNLESS you top out or bottom out the shock. If there is only one inch left before you bottom out then it will take 100 pounds to compress the spring another inch. (Harley's have 2 shocks and springs in back so 200 pounds total).

Now lets talk about the suspensions you strap down to a trailer. This is not weight but a strap pushing the suspension down. So if your strap presses the suspension down 2 inches it is SIMULATING 200 pounds of weight. Another 100 pounds will not compress the suspension another inch. You need too press down with 200 pounds of force before the straps even START to get loose. You need to press down with 300 pounds of force to compress it another inch. If the suspension is compressed this way it will seem to be rock solid until you press down with more than 200 pounds of force.

This is not how preload of a shock works unless you set the preload so low or high that the shock bottoms out or tops out. Those are the only times that preload comes into affect. For example it is possible to set the preload so high that the shock is already topped out before you go anywhere. Now it is like the dragster that has a strap compressing the suspension instead of weight.

Understand? This is a good debate and I don't mind explaining it. Preload and spring rate are often misunderstood.

 

Durango Dave , you are not correct and adding preload does stiffen your shock and thus increase how fast it rebounds and decreasing preload softens your shock and slows rebound. The springs all having a Newton rating , I don't have a chart in front of me so I will make up numbers to give you an idea of how it works. Say a 25Nm rated spring , it will have a resistance of say 100lbs per inch , so you put it on your bike and add preload (not sag) of 1" , it will now have 100lbs of resistance , I add another 1" of preload , the resistance is now 200lbs , so now I have 200lbs of resistance pushing back , thus the shock is stiffer and rebounds faster , I reduce preload and the shock is softer and rebounds slower , again these numbers are not correct as I don't have a Newton conversion chart in front of me but this is the basic principal. Sag is what you get with the weight of the bike and rider compressing the shock , preload is achieved my manually compressing the spring on the shock with the spring tension adjuster nut

 

[QUOTE=Durango Dave

This is not how preload of a shock works unless you set the preload so low or high that the shock bottoms out or tops out. Those are the only times that preload comes into affect. For example it is possible to set the preload so high that the shock is already topped out before you go anywhere. Now it is like the dragster that has a strap compressing the suspension instead of weight.[/QUOTE]

I'm not talking about strapping down to a trailer, I'm talking about strapping it down to itself which is exactly the same as preloading. We must have a different idea of what preloading is, to me it's compressing the spring to require a larger starting force before deflection occurs. When I turn the adjusters on a coil over, I'm compressing the spring. Since I now have a starting force to overcome, I won't get the same amount of deflection when I sit on the bike.

 

Bsmug , you are right it takes more force to compress , what you are missing is the other rating on the spring is the resistance you get by compressing it , the more you compress it the more the spring pushes back , the rate is consistent like I stated above but increase with preload , like my example if it is 100lbs per inch it is not 100lbs per inch to compress it but 100 lbs of force per inch it is pushing back , so the more preload the harder the spring is pushing back , thus yes it takes more energy to start to compress it