Making the rear spring more stiff

[trail_blazin_canuck]

I now own an 03yz250f and when i first sat on the bike it was way to soft for my weight at 190LBS compared to the previous owner at 150LBS.i thought about getting a stiffer spring but there was alot of room to compress the spriing to my weight and after adjusting the spring the sag is about 3 and a half inches now.My real question is why do guys that are a little heavier just go and compress the spring and save the hassel of getting a stiffer rear spring?

[Bergi600]

Hi,

there a two rates of sag that have to match.

One is the sag without rider....just the rear suspension sag that is measured when the bike is sitting on the ground.....it should be about 18-25mm (KTM PDS 30-35mm).

Number two is the sag when the rider sits on the bike....this sag should be somewhere between 95-105mm.

I assume, when the spring was correct for the 150lbs guy and you set the sag "number two" correct for your weight that the sag "nuber one" (just the weight of the bike) is somewhere around 5-10mm.......and that isn´that much-----your bike will have the tendency to kick over braking bumps!

[grayracer513]

Because compressing it only changes the preload, it doesn't make it stiffer.

To make it simple, let's say we're working on an old Triumph, where the springs are straight up and down and right by the back wheel. Now we start out with 50 inch pound springs, and let's say that they are preloaded so that the bike compresses them an inch with its own weight. For the sake of this discussion, you weigh 200 pounds. You get on the bike and it compresses two inches (2X50=100 inch pound total spring rate.) Since it's an oldie, it only has 4 inches of travel, so you decide this ain't enough. If you preload the springs another inch, you will "build in" 100 pounds of preload, and now when you sit on it, it will only compress one inch. You like that better, but now you don't have any static sag (the compression by the bike's weight). The next two hundred pounds of force will compress the springs another two inches anyway, so it still seems soft, and the suspension tops too easily.

But, if we change to 100 pound springs, and set the preload for the same half inch static sag we had before, it only sags an inch when you sit on it, doesn't top out constantly, and takes 600 pounds of additional force to bottom instead of 300.

That's why, going back to the real world again, you're told to compare your race and static sag to decide if your spring rate is correct. Set your "race" sag first, the sag with you on the bike, standing on the pegs. Then check your static sag. Too little static sag means you had to crank the spring down too far because it was too light for your weight, and now it's lifting the bike too much because of it. Too much static sag means the spring is so stiff that it supports your weight with less preload than it should have because it's too stiff. Seems backwards at first, but it will clear up if you think about it.

[dmp437]

What he's sayin' is that you need new springs. Check out MX Tech's Spring Calculator for something that will give you an idea of what to expect.

[trail_blazin_canuck]

I mainly ride HS and GNCCS so i think my spring will be okay and besides i am not doing any monster doubles.

[grayracer513]

Monster doubles aren't really the only issue. It's usually considered true that offroad springs are softer than MX springs, but there's a difference between trail riding and Hare Scrambles, too.

When the springs are heavy enough, you can back off the compression damping, which increases the overall plushness of the suspension. I think it's the single biggest improvement you can make to the suspension, and it's easy and relatively cheap. Check your sag. If you're pretty close, you won't see as much benefit from correcting the spring rate as if it's farther off the mark. Most YZ's seem to come sprung for 160-170 pound riders. I weigh 185 with out my riding gear, and replacing the springs on my own bike made quite a difference. ?

[geomoney]

I have an 03 YZ250F and had my suspension done by a reputable company. At the time, I tried to save some $$$ by not changing the springs. Even though the suspension was a lot better after the work was done to it, it didn't seem to make as much a difference as I would have expected. Fortunately, I was able to ride someones YZF who had theirs done by the same company. He even weighed within about 5 pounds of my weight, so the setup was comparable to what I would get if I had done the springs also. After riding his bike, I realized I should have spent the $$$ and got the correct springs. The suspension just works that much better. If you have the money (about $200) get the correct springs front and rear. You'll thank yourself after you do it, your bike's suspension will work so much better. PM me and I'll give you the spring weights I used on my bike.