2018 RTL OEM Rear Spring Rate Question

[h0gr1der]

Wanted to add, this is a bit technical, but the Spyder I believe, but could be wrong, is utilizing a pretty typical 3:1 leverage ratio. With no linkage, and a shock near vertical, there is no rising rate built into the design. No rising rate for the spring or damper.

The airspring is inherently rising rate. Add to this, the oem rear spring is progressive. Combined, the oem coil and the airspring provide selected ride height and on earlier models a form of adjustable preload.

Asking a straight rate spring to accomplish progressive spring duties can result in compromises elsewhere in the travel.

Consider, the rear end of the Spyder is controlled by 1 1/2” of shock shaft movement. With that, any error in choosing a spring rate or control by the spring is a factor of 3 at the axle.

On dirtbikes, with linage setups, I have tested straight rate springs, and multiple variations of crossover points of progressive springs, plus each in various rates. I found the straight rate spring was best at holding the rear end up during the initial part of the stroke. This made for holding a steeper head angle and lively steering. The downside though was the straight rate spring tended to blow through the stroke and bottom easier. The progressive spring settled a bit more when cornering, but had better feels on small bumps and did not bottom violently. Each has merits and each has drawbacks.

Mr. PMK,
Thanks for all the input, this is exactly the stuff I don't know. Someone suggested, and I can see from pictures of aftermarket shocks, the possibility of combining springs to make a dual rate spring. Not quite as good as a truly progressive spring, but better than the linear setup. I can buy the Hyperco 2.25" x any length up to 9"" long x whatever rate linear springs for about $69 to my door. I may buy a couple to experiment. I'm not a racer, so as long as it doesn't break my back I really don't think I'll notice. I think in the end I'll probably settle on the lowest spring rate that gives me the ride height I want without excessive pre-load to get it. That should provide the plushest ride, and most closely emulate the air bag and progressive spring working together. Whatcha think?

[PMK]

Mr. PMK,
Thanks for all the input, this is exactly the stuff I don't know. Someone suggested, and I can see from pictures of aftermarket shocks, the possibility of combining springs to make a dual rate spring. Not quite as good as a truly progressive spring, but better than the linear setup. I can buy the Hyperco 2.25" x any length up to 9"" long x whatever rate linear springs for about $69 to my door. I may buy a couple to experiment. I'm not a racer, so as long as it doesn't break my back I really don't think I'll notice. I think in the end I'll probably settle on the lowest spring rate that gives me the ride height I want without excessive pre-load to get it. That should provide the plushest ride, and most closely emulate the air bag and progressive spring working together. Whatcha think?

Dual rate springs. Have run them on bikes in the past. I like dual rates for the reason you can alter tender coils and main coils independent of each other.

Another benefit is that straight rate springs are easier to wind and obtain proper rates. Progressive springs can vary and often the point of variance is the concern. In short, where does it begin to transition.

Dual rates have a less known, but awesome feature. Most people believe that dual spring setups rely on coil binding the tender coil. Not true. By tuning the spring separator perch, the defined transition can be known for when the tender coil is no longer functioning.

Downside of dual springs, unless you make a wear sleeve, the spring separator can make a bunch of noise as it destroys the shock body.

I just installed a Hypercoil on my trials bike. They make a nice product.

I know you like to tinker, but honestly, you will be time ahead and possibly close on cost buying a complete rear shock.

Consider too, if you can deaden a coil or two, and retain ride height, the oem spring might do what you ask of it.

I have two oem front shocks off a 14 RT series here. Actually, even have a pair of spare Fox Shox. If you want to send me a rear spring. I can borrow my buddies spring tester and find out the rates of all three.

[PMK]

Mr. PMK,
Thanks for all the input, this is exactly the stuff I don't know. Someone suggested, and I can see from pictures of aftermarket shocks, the possibility of combining springs to make a dual rate spring. Not quite as good as a truly progressive spring, but better than the linear setup. I can buy the Hyperco 2.25" x any length up to 9"" long x whatever rate linear springs for about $69 to my door. I may buy a couple to experiment. I'm not a racer, so as long as it doesn't break my back I really don't think I'll notice. I think in the end I'll probably settle on the lowest spring rate that gives me the ride height I want without excessive pre-load to get it. That should provide the plushest ride, and most closely emulate the air bag and progressive spring working together. Whatcha think?

Rates and preload...My experience knows excess preload tends to make the bike pitch. Little preload can make the bike vague. Typically road bikes run a softer spring and more preload on account of the vehicles weight. 1100 pounds plus fuel and stuff is over 4 times the riders weight. On off road motorcycles, the motorcycle and rider are more similar in weight. This allows optimizing preload for grip and feel, while running a firmer spring for control.

Keep in mind too, the Spyder has no appreciable rising rate, so that mandates the basis for spring choice to control bottoming. Preload does not change rate, but can change end forces. Rate first, preload second. If preload is excessive, you need a firmer spring, if too little preload, a softer spring. But the spring still must remain supple and not bottom harshly.