I've noticed when people spec out spring rates for people for the back of the SV650 they seem to use numbers derived from them Penske website, or numbers close to them. I've been thinking about that recently and I think those numbers are too hard for the street.
If you go to Race Tech's site and spec fork springs for the SV you'll see that you get street springs that are about 9% less stiff for street riding, Sonic's calculator is also gives about 9% less stiff for "normal Street" and about 5% less stiff for "aggressive street"
Penske spec'd a 650 pound spring for me, as did GMD Computrack, but the number just seems high. I went with a 600# spring instead.
This is just something to think about for people getting an aftermarket shock. I commute and do a lot of easy riding and didn't want to have a spring that's set up for the 5% of hard riding I do. Take the Penske numbers with a grain of salt
As it's winter here in New England I haven't had a chance to test my theory but I'm pretty confident I will be happy with it.
I split the difference and went with 625# spring on a Penske 2-click. I'm 180+ on a 1st gen, 0.85 springs in front with 20 weight oil. Short (no freeway) commute and spirited weekend canyon riding. I'm really pleased with the behavior of the rear. Next suspension improvement will be a Traxxion emulator for the front. That should take some of the bite out of the bumpy back roads in my neck of the woods.
This will wind up being pretty close to where I am with a custom valved Fox and a 600# spring. I have .85s up front with Gold Valves as well. I am still working those out, though.
If you look at the recommended racing front spring for Race Tech I think it's a .915, with a .85 recommended for street. If you look at the rear shock Penske racing application for us it would be a 650# spring. Using the same correction factor that would work out to be a 600# spring in the back.
Harder springs are not racier. If you don't need them to control pitch from super hard braking (are you lifting the rear regularly on braking?) or super hard acceleration (are you opening the throttle 100% on corner exits?) you don't need a full race spring.
In fact, you should really use the softest spring you can get away with. If you think of it this way a bump that is 1" tall will deflect the motorcycle up with 650# of force with a 650# spring, but only with 600 with a 600 pound spring. The spring will actually keep the tire in better contact with the ground (the point of suspension) with a softer spring and will upset the chassis less up to the point that there is not enough downforce to follow the ground contour.
So unless you are using a lot of speed and need that extra down force to keep the rear wheel in contact with the back side of bumps you should really use the softest spring that will keep the attitude of the motorcycle. It's better for control too. Granted it's all compromise, but I have ridden race spring motorcycles on the street because people feel if they want to be fast they need that. It's no fun.
Those charts are made for racing. It took me a long time to sort out that and what it meant. You can go faster easier with a spring that's right for you, not one that's right for Colin Edwards.
Thanks for the reply. It's good to know the 625 and the .85s will be ballpark for me. I have only snuck out on warm days for a few min here and there but I'm confident the setup is good.