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Old 08-Jun-2003, 11:08 PM
pj748r pj748r is offline
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748r suspension - (DSC Suspension Guide)

has anyone got any suspension settings eg Performance Bike/Superbike for this bike as the only ones i can find are for the 748sps.bike is a 2000 model with Showa front and rear.:P
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Old 09-Jun-2003, 02:13 AM
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Ducati Sporting Club Suspension Guide

pj748r, setting up your suspension is more than just using the published suspension settings from Performance Bike. For awhile now, some DSC members have been working on a Suspension Guide to help others like you, so maybe this is a good time to let you (and other members) a peek at some of the draft sections so you can learn, offer comments and make suggestions. Hopefully it'll help get us finished. So here goes ...


3.0 ASSESSING YOUR NEEDS

3.1 Rider Skill Limitations

You need to be honest in assessing your riding skills. As they improve over time so will your suspension needs change to match your riding technique. Your particular riding technique will play a big part in refining your suspension settings. If you are an average rider, sticking with the factory recommended settings will probably be best.

But feel free to experiment. One change at a time. First reset everything back to the stock settings stock, and try a different single setting until you develop a feel for the differences resulting from each change and the sensitivity of the bike to each click on the adjuster. Always use the same road to evaluate your changes. This seat-of-the-pants testing is highly subjective so don't be surprised if your feelings about the changes are different the next time you ride. Even without any interim changes, there are days that you know that you're riding well and the suspension is just right, and days that you're not in the groove. Given that you're not an experienced test rider, you'll find that YOU are the biggest variable.

Consequently, you should probably avoid using suspension settings developed by other riders, specifically motorcycle magazine test riders who commonly tweak each new bike's suspension settings in an attempt to improve on factory settings, and then publish the results. These settings may actually be an improvement for one particular rider on one particular track but the factory settings are still the best overall comfort-performance trade-off for the average rider on an average road.

For example, a review of a dozen magazine tests of Ducati superbike compression and rebound damper settings showed that even though there is a wide variation between riders, their settings average out to the factory recommended settings. So it looks like Ducati knows its business.

If you're an experienced rider who's attended an advanced riding school, then you've developed and practiced a riding technique that works well for you, so you'll obviously want to tweak your suspension to match your riding style.

3.2 Motorcycle Design Limitations

Be realistic when selecting a motorcycle type. Once you've made your selection of a sportbike (or a cruiser) you're pretty much stuck with the performance envelope of that design. You of course can replace stock suspension components with premium cost items that, if they were installed at the factory, would otherwise make the initial cost of the bike prohibitively expensive. You can also adjust your suspension settings for a more limited range of rider preferences and road or track conditions. But you can't replace or adjust suspension components to get a sportbike that has both a cruiser's comfortable ride and a racebike's handling.

So, before you make adjustments to your suspension, you need to have a clear idea of the compromises that were already made intrinsic to your bike model's design. Adding handlebar risers, a softer saddle and some suspension adjustments after-the-fact won't make your sportbike both ride like a cruiser and corner like a racebike.

3.3 Road vs. Track Set-Up

Depending on your usage (track, road, commuting, competition etc.) your handling vs. comfort trade-off need will change. You can't set up your bike for the best track performance and still expect it to provide even a reasonable level of rider comfort for the street. A typical road surface is simply too rough for the stiff suspension settings that are warranted for the track.

Here's how Kevin Cameron puts it ...

"The sports motorcyclist wants to do the right thing, but simple tables often push aside common sense. Too often, magazine reviews say things like: 'When we got to Donington, we cranked up the damping at both ends to full-rigid with max spring preload, and got down to some serious lap times.' This implies it's always best to run the hardest possible settings. Reverse logic also implies that if you run hard settings, you must be a good rider. Like it or not, we're all a bit status conscious, so this kind of things sucks us in. Believing harder is better, all these riders are jolting around the highways with suspension set on magazine-max, when in fact they would benefit from considering the word compromise. You need traction to go fast, and on any but the smoothest surfaces, that means the suspension has to move.

A crew chief of a recent MotoGP team, once said that the rider really needs four different bikes.

1. During braking, he needs a machine with its full weight to the rear, to allow the full grip of the front tyre to be used without lifting the back wheel, with firm enough front suspension to keep it from bottoming.

2. During turn-in, he needs a machine with a very short chassis for quick steering, with no suspension at all to delay the action.

3. In the turn, he needs a balanced weight distribution that doesn't overload either tyre prematurely. He needs ground clearance, but with suspension soft enough to maintain grip.

4. When acceleration begins, he needs a chassis with its weight forward, to keep that front tyre loaded enough to steer without pushing.

There is no way to combine all these separate and conflicting requirements in the bike as it now exists. There is no rule that reveals the best compromise, which is why assertions like 'harder is better' are nonsense. The more you work with suspension, and the more combinations you try, the more you learn about how to achieve a suitable compromise."


Reference: Cameron, Kevin, How Suspension Works


4.0 THE FACTORY SUSPENSION SET-UP

4.1 Stock Setup General Limitations

Any set of suspension settings is a compromise and the stock setup is no exception. The stock settings were developed by the manufacturer's test riders to give the best handling characteristics over the widest possible range of riding conditions. Consequently, they are not the best settings for a given road/track, or a personal riding technique. The factory recommended settings are simply the best starting point.

The stock settings will not provide the most comfortable ride nor will they result in the fastest track times. They will however, give you the best overall handling. Period.

The stock setup is based on some assumptions about the weight of the rider and what constitutes good handling. If you have a different idea or personal preference, and particularly if your weight falls outside the norm, then you'll need to modify the spring preload, and perhaps damping rates, ride height and maybe even steering head angle.

One point bears mentioning up front. It is important in any suspension work, to keep a record of the starting point settings and all changes to avoid later confusion regarding the effect of each change.

If you're setting up your bike for the track, the stock suspension settings are still your best starting point recognizing, of course, that your favorite track will encourage a more taut suspension setup than would be comfortable when street riding.

If you've made any sprocket changes, then make sure you've reset the ride height by changing the length of the tie-rod adjuster. (On superbike models any size changes to the final drive sprockets or chain length will usually require an adjustment of the rear axle eccentric hub that, in turn, affects your rear ride height and wheelbase.)

Further, if your bike has been in an accident, it's important to verify that the frame is not bent and that the wheels are aligned. Also check occasionally that the steering head bearings move freely and smoothly, especially if the bike has been wheelied.

4.2 Initial Suspension Setup

The human body is more sensitive to certain kinds of vibration than others, so motorcycles are designed with suspension systems having springs and dampers that modify the incoming road bumps so as to be more comfortable to the rider. But comfort is only one objective.

Motorcycle dynamics are such that handling is enhanced when the tires track the road surface bumps rather than just passing over them. Also, the motorcycle feels more responsive to the rider's control inputs if the suspension is set-up stiffer to pass more vibration and suspension movement information back to the rider.

Some manufacturers make two versions of their bikes. Monoposto (one seat) Ducatis have a softer spring in them (6.5 kg/mm) as standard because they are not capable of carrying two people. Biposto (two seat) models have a stiffer spring (7.5 kg/mm) installed to allow the bike to occasionally carry a passenger, if you temporarily increase the spring preload.

Ducati monopostos, as delivered, are set-up for a rider in the weight range of 65-75 kg (143-165 lbs.) If your weight (including gear) is significantly outside this range, you'll want to replace your springs with a more (or less) stiff unit to allow you to adjust the suspension correctly to suit your own weight. If you're heavy and you ride a biposto you'll probably still be OK but a lightweight on a biposto will definitely need a softer spring.

If your weight with gear on the bike is 200 lbs. or more, even if you've set your static preload properly, the stock spring probably isn't stiff enough to keep the rear end from bottoming out unless you crank up the compression damping.

To preload the stock spring for this heavier weight you'll need to compress it so much that you've reduced its effective range of motion. The higher preload needed for a heavier rider's weight will also cause the rear to top-out more readily requiring you to increase rebound damping to slow it down.

Too much rear spring preload will also cause your bike to ride higher in the rear. A higher rear end (or lower front) will give the front forks a steeper angle. This then results in a tendency of the bike to oversteer, where the rear wheel looses traction first so the rear end breaks loose.

The idea here is that you need to let the spring (not the dampers) control the range of motion of the suspension. Too-stiff damping causes handling problems over bumpy road surfaces. Handling is enhanced when the dampers are set soft enough to control the wheel movement, allowing the tires to track the bumps rather than skip over them. Track surfaces are smoother so higher preloads and damping of a taut suspension are less of a problem.

It is important that in beginning any suspension setup that the spring preloads should be adjusted first (including correct determination of required spring rates.) It's important also to note that all of this should be done before any adjustment of damping rates, or steering head angle. So return these settings to stock before continuing.

You need to set the front and rear spring sag amount for your own weight plus gear and a half tank of gas. The way this is done is by measuring the suspension change with you on the bike sitting in the riding position, leaning forward with enough weight from your hands on the handlebars to mimic your riding at speed. See your bike's service manual for the procedure for setting the bike's spring preload and measuring sag.

After doing this, you can then adjust the suspension's rebound and compression damping.


5.0 TYRE ADJUSTMENTS

One integral (yet often overlooked) part of a suspension system are the tyres. They are selected and tested by the bike manufacture to obtain the best handling behavior and match-up to the bike's chassis characteristics. When you change the tyre pressure, size, aspect ratio, side wall construction, tread pattern, and rubber compound you change the bikes handling, so be prepared for some additional suspension tuning to balance out any adverse effects of different tyres.

5.1 Tyre Selection

It's difficult to evaluate published tyre test comparisons made using other makes of bikes, or use recommendations from other riders who have different riding techniques. As a practical matter, modern motorcycle tyres from major manufacturers all have similar-enough handling characteristics, such that looking at their subtle differences is the only way to differentiate them. However, the effect of tyre size, aspect ratio, and pressure is less subtle.

5.2 Tyre Pressures

If tyre pressures are not in line with manufacturer’s recommendations, too-high or too-low pressures can either mask or exaggerate what you might believe to be suspension problems. For instance, if a rear tyre is under-inflated you might feel the back end squirm initially when you lean the bike hard over and then again when you apply power on the exit of a corner.

You could be forgiven for thinking the problem might be too soft a spring or not enough compression damping. But a soft (as in low pressure) rear tyre will display some of the characteristics of badly set-up suspension and you could end up mistakenly changing a whole lot of settings (or even an entire shock) for the sake of an airline and an accurate tyre pressure gauge.

So, before you start making any suspension adjustments, use an accurate gauge to set the tyre pressure to the bike manufacturer's recommended pressure for the street. For the track, drop the front tire pressure by 10% and the rear tire pressure by 20% from the recommended street pressures to accommodate increased heating. (Ref 6.)


8.5 Steering Head Angle Adjustment (Set Last)

On some manufacturer's models (notably Ducati superbikes) you can change the steering head angle, the angle that the forks make with the vertical. On most road bikes changing this angle is not an option, but Ducati gives you the choice of two settings.
The steering head angle is set at 24.5 degrees at the factory (the recommended setting), but can be steepened by changing the setting to 23.5 degrees.

Making the change to the steeper angle does not affect the wheelbase, but the trail dimension is shortened somewhat. The trail dimension, a measure of the distance that the front axle is placed ahead of the steering axis, is important to the motorcycle's steering stability, so making it shorter reduces the tendency for the steering to naturally realign to a neutral position after hitting a bump or object in the road.

The steering head angle should only be altered after all the other suspension changes have been finalized.

You need to first be comfortable with the overall suspension settings. If the bike displays any instability problems they need to be sorted out first, because the steeper steering head angle change will magnify these problems, and also because part of its effect mimics changing the rear ride height. Remember that the fork angle also changes when the front ride height or the rear ride height are changed.

8.5.1 Effect of Changes

Changing to steeper steering head angle will make the bike have less straight-line stability, steer into corners faster, and hold a tighter line through turns. This is not necessarily an improvement.

If it suits your riding style, this makes it easier to brake late into turns and still hold a tight line. However, one consequence of using this riding technique is that the greater braking load on the front end will cause the forks to bottom out more readily and the front wheel to chatter under hard braking. So more front spring preload and compression damping may also be required, at the sacrifice of riding comfort under more usual riding conditions.

The other drawbacks are that you will loose a significant amount of steering range of motion (lock-to-lock) making low speed maneuvers more difficult, and that the ignition steering head lock won't engage in the steeper position. Also, given that the steeper angle gives less steering stability, an adjustable steering damper may be needed to control handlebar movement under certain rough pavement conditions.
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Old 09-Jun-2003, 12:53 PM
adam adam is offline
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