User:Akatombo/Sandbox

Susension Information

General Information
The Ninja 250's suspension is often considered its weakest link. The budget components definately show their limitations. Good suspension is a critical part of a motorcycle, as it is the components that keep the tires mated to the road surface. Suspension makes your cornering possible. With lousy suspension a rider will never feel comfortable enough to really lean it over and get on the gas. Good suspension not only allows a rider to lean over, but do mid-turn corrections to avoid obstacles, and stay stable through bumps. The improvements in suspension system performance is felt by the rider in almost any situation.

How much faster? - light years.

Improvements can be made by spending money on shocks and forks. The stock 250 Ninja is comfortable but sloppy, so it's easy to improve.

Rear Shock Absorber
This view is from the left side of the bike, so the front is at the left side of the picture and the rear at the right.

The central piece, illustrated with the gray coil spring is the shock absorber. Its main job is to keep your rear tire on the road, as the forks do in the front. When a bump forces the tire up, the shock sends it back down. This is a delicate balancing act. If the wheel moves too much, or too little, it won't have proper contact with the ground and traction will suffer. Both are bad, but thankfully there's a fairly wide margin of "good enough", although it does get more narrow the faster you ride. More information The back bone of the motorcycle, nearly everything is connected to the chassis. It supports the forks, the engine, the seat, and, of course, the rear suspension. The Ninja 250 has a double-sided swingarm, so there is one piece on each side of the rear wheel. The wheel attaches to the swingarm via the slot at the rear. The swingarm pivot is where the swingarm attaches to the frame. The diagonal bits running from the shock linkage to the swingarm, making an indirect connection between the shock and the wheel, are the tie-rods, or 'dogbones'. There is one on each side. The elbow-shaped piece at the bottom is the Uni Trak shock linkage ('rocker arm'). This is the part that connects the frame, tie rods (dogbones) and rear shock together. The rocker arm is there so the rear shock will have more travel before transferring any bumps to the frame (which is bad). This provides for better handling and comfort.
 * Shock Absorber
 * Chassis
 * Swingarm
 * Tie Rods "Dog Bones"
 * Shock Linkage

Front Suspension
Stock is .440 Don't be surprised if the new springs you get are much shorter than the stock ones. The springs aren't designed just to fit the 250; they go in many different bikes. This helps make them more affordable. A preload spacer of the right length makes up the difference. See the preload spacer article for information on cutting the spacers.

Spring Replacement
Look at the Race Tech calculator even if you're not getting springs from them.

Kawasaki Ninja 500 Springs
If you are reasonably lightweight (check the Race Tech calculator) the Ninja 500 front fork springs from '94 and newer bikes might stiffen up your front end quite nicely for a bit less than the Racetech springs. The spring rate for these is .585 kg/mm ; stiffer than stock, less than what the aftermarket companies usually make. Part number is 44026-1555, and they cost $33 each from Ron Ayers. So for $66, you can get a much better front end feel.

Sonic Springs
Sonic produces springs now starting at .70 and .75 for the EX250. Sonic's calculator doesn't work real well for light people on light bikes, and may show different results than the race tech calculator. We like Sonic, and they are cheaper than the others aftermarket spring manufacturers. They routinely do custom-rate springs if you're a bantamweight, for an extra fee. . Sonic springs come with washers and spacer material.

Race Tech
This link will tell you everything Race Tech makes for your bike. Searching for Race Tech products at other stores may save you some money.

Progressive Springs
This ninja250 wiki does not recommend progressive rate springs for the front suspension. A test of Progressive springs showed they were really light for the first inch (~.45), about on par after the 2nd inch (1.05), and by the 3rd inch of travel they were so far beyond reasonable (1.7) that you'd never get any more travel. You limit the amount of work the forks can do which doesn't make sense. This all means that in more extreme situations, when you NEED your tires on the ground, the springs are going to fight you. Run over a 2x4 and you'll have the front wheel in the air. Hit a pot-hole mid corner and not only will it be fairly jarring, but the fast rebound will reduce the weight on the front tire and increase the possibility of lost traction. Some suspension experts, as well as forum members have expressed their opinion that progressive springs are an attempt to alleviate bad damping characteristics. However, they continue to say progressive springs cannot match the precision and flexibility of a properly tuned suspension system built on straight rate springs.

Progressive springs also have a reported problem with quality control. One of our suspension techs on the board reports seeing a couple springs that were drastically different from one another when pulled out of the same forks for service.

Gold Valve Emulators
Gold Valve Cartridge Emulators replace the damping rod's orifices as pressure regulators, making damping rod forks perform more like well-tuned cartridge forks. In short, the forks become more responsive to small bumps, increasing usable traction, and stiffer under load. It makes the most of the suspension system's capacity, allowing other modifications such as stiffer fork springs come alive. Emulators are tunable valves that sit on top of the damping rods and are held in place with the main springs. They are simple to install and completely tunable for all conditions and rider preferences. Forum members rave of the results they gain from the mod, come citing it as the first mod they should have done. Part # is FEGV S3501, and installation requires some tools. MSRP is 169.99

Rear Suspension
The stock EX250 shock is produced by Showa for Kawasaki. It is a budget shock with no adjustability and is designed for the "average" beginner to intermediate lightweight rider. A common misconception is that more advanced shocks are for "racers only". Without a doubt, a higher quality shock will help the bike handle better and provide more comfort and safety. At the same time, a rider must be aware that just because a shock is from a larger displacement motorcycle that doesn't automatically mean it's a "better" shock for your EX250. Don't fall for that hype. There are largely two upgrade paths for the ninja 250. one is shocks from other bikes, the other is aftermarket replacements.

Any thought of changes to the functional parts of your motorcycle should be carefully weighed before making a buying decision. A new shock will not cure all handling and riding woes. In order to perform at its optimum, a replacement shock needs to be wisely coupled with careful adjustment, chassis geometry monitoring, quality tires and a properly tensioned chain.

Some factors for replacement shocks are the type of riding done, expected loads, adjustability and budget constraints.

Type of riding: Many street riders just want a "better" shock, perhaps with minimal adjustability. Racers and more aggressive riders tend to opt for a firmer shock that has more adjustability and resists fading under extreme conditions.

Load: The stock EX250 shock is simply not well suited for heavier riders, and can easily bottom out riding two-up or in aggressive cornering over bumps.

Adjustability: Shocks can have several modes of adjustability. The most common are:
 * Preload: Adjusts the initial compression of the rear spring. This determines sag and, to some extent, height.
 * Compression damping: Strikes a compromise between soaking up bumps and squatting under acceleration.
 * Rebound: Can sometimes be set correctly before you ride the bike. Bounce down on the seat to judge return rate.
 * Ride height: Controls the overall length of the shock, but can be built-in to the dogbones or mounting points.

Adjusting a rear shock is an art, and an iterative process. Make small changes, and keep notes on what works and what doesn't.

Budget: Aftermarket shocks can be expensive, reaching $1000. However, there are less expensive solutions for those that do not want or need all the bells and whistles of the high priced shocks and like to get their hands dirty.

A stock EX250 shock measures approximately 12 1/4" "eye-to-eye". Increasing that distance means the bike will ride higher. Decreasing it means the bike will ride lower.

Stock shock spring rate is 440 in/lbs. Length from center of upper to center of lower eyelet is 320mm. The good thing is that shock springs are pretty much interchangeable. Nearly everything made from 1990--> has a 2.5" ID, and just vary in length, and possibly thickness, of the wire. So, if you have a shock with a 6" spring and the wrong rate, you'd just look for the right rate spring in 6" (and some shocks could take a 7", too). Most suspension places have lots of pre-loved springs lying around.
 * Recommended rates:
 * For real lightweights, up to 140 lbs: 450 in/lbs
 * 150~190 lbs: 475 in/lbs
 * 200-250 lbs: 500 in/lbs
 * 275+ lbs: 550 in/lbs

The once-popular SV650 shock, at 550in/lb, is only good for the truly heavy.

It is not recommended to play with the length of the dogbones in order to get a different shock to fit. Racers will sometimes do this, but we won't recommend any shock here in the FAQ that requires dogbone modification.

Shocks from other Bikes

 * Kawasaki ZX600C
 * Suzuki GSXR(1000, 750) 1990-1995
 * Suzuki SV650