Gary_in_NJ
Serious Thumper
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LS650 Cafe Racer
Posts: 2625
Amongst the Twisty Roads
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Shocks Much of the discussion of the forks applies to the shocks as well. The shocks define how comfortable the bike will ride – so it’s important to get them right. What makes one shock better then another? Like the forks, the primary function of the shock is to 1) support the sprung weight of the bike and rider and 2) provide damping to control the speed of movement throughout the stroke of the shaft. Without damping a spring will seek its static position as quickly as possible, overshooting its static position due to inertia. Also, just like the forks, a shock uses oil and air to create compression and rebound damping. As the shock moves it creates heat which is absorbed into the oil. When the oil gets hot it foams within the chamber and if the oil gets too hot it causes cavitation (slipping) within the chamber – impacting the ability of the shock to provide predictable (or meaningful) damping. The faster that heat can be absorbed and dissipated, the better the shock can perform its primary function of providing predictable damping. As a rule: the bigger the oil chamber the more effective the heat management of the shock.
The OEM shocks on the Savage are what are known as twin-tube shocks. Twin-tube shocks are the type most typically found on budget bikes. They are self-contained with an inner oil chamber and an outer air chamber (hence, the twin tubes). As a result of this design the inner oil chamber is very small. The damping rod (shaft) is connected to a piston that moves through the oil, creating damping. The vast majority of these shocks are typically low performance, non-rebuildable (meaning the valving can’t be adjusted), provide fixed damping and only adjustable for spring preload (usually just 5 positions for spring preload).
The OEM shocks on the Savage are under sprung and under dampened and are a significant limitation to comfort. If you’ve taken any of the above advice on your forks, then take this advice – throw your shocks in the garbage. Many Savage riders have had good success with Progressive Suspension’s 412 Series shocks. This is still a twin-tube shock, but they are slightly longer (1/2 to 1 inch) allowing for additional swingarm travel, have a dual rate spring that is more suited towards heavier riders, are nitrogen filled and “may” have better damping.
In order to select the correct part number of the 412 Series shock you will need to make a few decisions. First is your ride height. The OEM Savage shocks are 10-1/2 inches long and provide about 1-1/2 inch of travel. The 412 Series come in a number of lengths, but the closest to the OEM is an 11 inch unit offering 2” of travel and there is an 11-1/2 unit that has 2-1/2 inches of travel. Next, you will need to select the spring rate(s). There are two available rates that will work well on the Savage, depending on your body weight. The is a 90/130 lb/in spring that will work for riders up to about 200-210 lbs and a 115/155 lb/in rate that will work for riders above that weight. Finally, there are both black and chrome versions of the shocks. Looking at Progressive’s spec sheet I’ve put together the following viable part numbers. There may be more, but these made the most sense. Before ordering call Progressive and talk to a tech support person.
11 Inch Eye-to-Eye 412-4005, 90/130 Spring Rates, comes in Black or Chrome 412-4232, 90/130 Spring Rates, comes in Chrome only 412-4233, 115/155 Spring Rates, comes in Chrome only
11-1/2 Inch Eye-to-Eye 412-4006, 90/130 Spring Rates, comes in Black or Chrome 412-4200, 90/130 Spring Rates, comes in Chrome only 412-4201, 115/155 Spring Rates, comes in Chrome only
For reference, I use an 80/100 lb/in spring on my bike. My bike is probably 40 pounds lighter on the rear axle than a stock Savage. The 90/130 should work nicely for the average sized rider.
I know that some have used the shocks from the VS800/S50. I would not recommend putting these shocks on your Savage. Yes, it does have heavier rate springs but it is exactly the same crappy damping used on the Savage.
The next step up from the 412 series shocks would be a gas pressurized emulsion shock. I’ve yet to find a bolt-on replacement gas pressurized shock with the correct specifications. The short size/stroke is typically found on small displacement (very light) bikes. As a result the spring rates are typically too low and the mounts are 10mm or 12mm (the Savage has 14mm mounts). If there is enough interest or demand we might see if CL Moto can rework 280mm (11”) RFY shocks for use on the Savage. This approach world require cutting springs and reworking the bushings for 14mm mounts – but they would be a tuneable/rebuildable bolt-on replacement with unlimited preload adjustment (versus the 5 click stops).
As you can probably tell from above, I’m not a big fan of multi-rate springs in forks. Used in the forks I find progressive springs too soft in the initial stroke and unpredictable in the remainder of the stroke. I believe that proper valving is the best route towards fork “progressivity”. However, multi-rate springs are necessary for our shocks. Here’s why.
Many modern motorcycles use a mono-shock arrangement. Mono shocks use a linear rate spring. The progressivity in the system comes from the multi-link connection between the shock and the swing arm. With this configuration, as the swingarm moves up there is less leverage between the shock and the swingarm, creating additional force with increased motion. Classic motorcycles like the Savage that use twin shocks have a direct connection between the upper shock mount and the swingarm, so there is a linear relationship between the motion of the swingarm and the compression of the shock. A multi-rate spring allows the shock to apply additional force on the swingarm as it moves up towards the bike.
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