Suspension Questions

[Proteus]

I've been reading and thinking a lot about adjusting my suspension.

A lot of people on here have been helpful and recommended that the 250 is in stock form not designed for someone of my size - 6'1" and 210 lbs.

I've read through the different options, like heavier weight fork oil, springs designed for my size and riding style, etc.

Do all of these things apply only to ninjettes and other bikes with little-to-no suspension adjustability? Do more expensive, bigger bikes that have all adjustable suspension components allow you to set the bike up for you and your riding style from stock, or do you still have to swap out springs, etc.?

[Motofool]

Originally Posted by Proteus

........ Do more expensive, bigger bikes that have all adjustable suspension components allow you to set the bike up for you and your riding style from stock, or do you still have to swap out springs, etc.?

Metal spring rate is constant and can only be changed by replacing the spring, same for expensive and budget suspensions.
Some suspensions mix steel spring and nitrogen spring, being the rate of the last one adjustable to certain degree.

When the rate of the spring is changed, its counterpart, which is oscillation damping in both directions, must be also adjusted accordingly.

[Proteus]

Thanks Hernan.

It seems like most (if not all?) bikes are designed for ~150-180 lb rider? Does this mean that I'll need to swap the springs on any bike I ever own as a 200 lb guy?

[Motofool]

Not necessarily.
The heavier the bike, the less influence your body weight has on the stock suspension.

A Gold Wing does not behave much different between a 180 lb rider and another of 240 lb.
A Puch 50 c.c. will let you know that you need to find a bigger bike.

[InvisiBill]

Originally Posted by Proteus

It seems like most (if not all?) bikes are designed for ~150-180 lb rider? Does this mean that I'll need to swap the springs on any bike I ever own as a 200 lb guy?

Kawasaki is bad at picking spring rates. Another member here with a CB500 said that bike seems to have poor spring rates too. According to RT's calc (which may or may not be perfectly accurate), the NewGen's fork springs are good for 95lb while the rear is good for 220lb. Assuming the PreGen's rear suspension is pretty similar to the 500's, its rear spring is good for ~180lb and the fork springs are good for <30lb according to RT. Likewise, the EX500 has fork springs for <30lb and a rear spring for 130lb. The '06-'11 EX650 is the opposite, with 320lb fork springs and a 140lb rear spring.

Due to physics, the spring rate can only match one specific rider weight perfectly. It's understandable that anyone of a different size wouldn't match the springs that come in the bike. However, they seem to be completely mismatching front and rear springs, which makes the bike handle in weird ways.

Because of these facts and my experience with a few different springs on my EX500, I firmly believe that anyone can benefit from respringing these bikes to the proper rate. You might be ok with stock springs depending on your weight, but that front/rear mismatch means that even if the stock springs at one end are good for your weight, the other end will be way off. The more off your weight is, the more improvement you'll see from a respring.

For 210lb, RT's calc suggests .82-.86kg/mm fork springs, compared to the .65kg/mm stockers, which is ~30% stiffer. People here with more experience have said that RT's calc is low too. If you switch to .80-.85kg/mm springs, I think you'll see a lot of improvement.

Keep in mind that the spring is what supports the bike and lets it move. Damping is what slows that movement down (so it doesn't keep bouncing back and forth forever). If your spring matches the weight it's supporting, then the bike will be moving the proper amount to begin with, so the damping system has an easier time. If the spring is too weak, it will be flailing around, and the damping system will be trying to keep it from moving excessively. Going to a stiffer spring will keep the wheels from flying up into the chassis on bumps, giving you a smoother ride. At the same time, they'll properly support your weight and keep it from feeling squishy when you're riding hard.

Springs cost more than oil, but they're the major, initial component in determining how the suspension moves. If they're not right, you're just masking it by changing other things.

[Proteus]

0.85 kg/mm springs are definitely in my future, we're going to be moving in the next few months and I'll have a garage to work in.

This is my first motorcycle, so there are a lot of things that I have no baseline for. When it comes to fork dive, bumpiness, etc. it's hard for me to tell if there's something wrong, incorrectly set up for me, or just what bikes feel like.

[Ghostt]

Cutting the fork springs is another and cheap way.

[Qomomoko]

I feel ya,


I am in process of getting new springs... I'll let you know how they feel,

Racetech said If I am not happy with the rate, they will give me a higher one for exchange...

g luck on getting a garage man, I wish I had one

[dcj13]

Originally Posted by Proteus

This is my first motorcycle, so there are a lot of things that I have no baseline for. When it comes to fork dive, bumpiness, etc. it's hard for me to tell if there's something wrong, incorrectly set up for me, or just what bikes feel like.

I've been riding for 13 years and am a mechanical engineer. I feel the same way.

My stock pre-gen Ninjette was ok-ish, suspension-wise. My second rear shock on my BMW blew out its damping guts, so I bought a YSS Hyperpro front and rear set-up from Klaus in New Jersey: it's now very firm... My cheapo '05 KLR250 with stock suspension rides like a Cadillac over all surfaces.

Let me know when you figure this stuff out.

[dcj13]

Originally Posted by Motofool

Metal spring rate is constant and can only be changed by replacing the spring, same for expensive and budget suspensions.
Some suspensions mix steel spring and nitrogen spring, being the rate of the last one adjustable to certain degree.

When the rate of the spring is changed, its counterpart, which is oscillation damping in both directions, must be also adjusted accordingly.

True. One can also adjust the force of the spring by putting in longer or shorter spacers in the fork (and adjusting the rear spring with the big nut).

Suspensions are tricky to analyze because they are second order mass-spring-damper feedback control systems. The weight of the bike and rider matter (not all that adjustable). The spring force (pounds) and spring rate (pounds force per inch of additional compression) matter. And the damping rate (pounds force per inch per second of travel) matter.

(Sorry, but I'm old-school and don't usually talk metric in these matters. And if we do talk metric, the spring and damping rates shall be expressed in "Newtons per whatever", as kilograms are a unit of mass, rather than force).

[Motofool]

Originally Posted by dcj13

........... Suspensions are tricky to analyze because they are second order mass-spring-damper feedback control systems........

The ideal spring/damper combination for you, @Proteus, should be a critically dampened oscillator:

http://en.wikipedia.org/wiki/Damping

http://en.wikipedia.org/wiki/Harmoni....2Fmass_system

The ideal situation is to keep your mass and bike's suspended mass more or less at the same level while the tires follow the irregularities of the road, keeping traction that way.

The worst situation for the suspension is when you are cornering, because the weight of rider plus pilot increases due to centrifugal acceleration (up to 40% more) and the suspension is working at an angle (up to 45 degrees) respect to surface of the road (which makes the suspension feel those road irregularities up to 40% bigger).

The most powerful tool that we have to make whatever suspension our bike has perform its best is the throttle control during cornering.

Link to original page on YouTube.

[Ghostt]

Spacers and adjustment nut are to set the sag, does nothing to increase the actual spring weight

[dcj13]

Originally Posted by Ghostt

Spacers and adjustment nut are to set the sag, does nothing to increase the actual spring weight

Doesn't affect spring rate, but does affect spring force.