Suspension tuning

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motorcycles

Suspension tuning

Suspension tuning
The right twist

If you want to raid the curbs with momentum, you not only have to have yourself fully under control, but also your chassis.

Gerhard Lindner

08/11/2000

In terms of sport, we motorcyclists live in rosy times. Numerous adjustment options on the trolleys allow an exact adjustment to the desired area of ​​application.

But playing around with all the many buttons and wheels with up to 40 adjustment options is not always a blessing. If the attitude is wrong, what was originally an agile racehorse quickly turns into a stubborn mule. MOTORRAD tested three days in Imola, Italy, in order to create a suspension setting for ten coveted athletes that fits on almost every racetrack in Europe. The fine-tuning on site – depending on the driver’s weight, driving ability and driving style – then has to be done by everyone.
If you want to experiment with the set-up, you should adhere to a few basic rules both on the country road and on the racetrack.
1. Before tinkering with all possible buttons, first write down the series setting or check the driver’s manual to ensure that it is listed there.
2. When voting, never make several changes at the same time, but proceed step by step.
3. All setting values ​​for rebound and compression are always given from the closed maximum position.
4. Hardness is not everything. The same applies to sporty driving on the racetrack: as soft as possible, as hard as necessary.
The most common weak points that need to be combated in very sporty use with standard chassis are the front wheel pounding when braking hard, stubborn steering behavior in curves and sluggish handling in chicanes, lack of ground clearance, inaccuracies in the curve radius and a pumping rear when accelerating out. So a lot of problems, the cause of which, especially with the Japanese machines, is mostly to be found in the very soft, comfortable basic set-up. By gradually adjusting the spring base, which causes the front or rear to be lifted, spring travel reserves can be mobilized at the front and rear. Turning off the compression damping and the associated reduction in the compression speed also help to prevent unintentionally strong deflection.
More rebound ensures a slower rebound movement and can calm uncontrolled rocking like a pumping tail. In addition, the resulting minimized intrinsic movement of the vehicle has a positive effect on handling and target accuracy and also has a stabilizing effect when cornering and accelerating out.
Raising the rear section by adjusting the level by means of a threaded spindle, as is the case, for example, with Kawasaki is found, also promotes agility. If there is no adjustment option, the same effect can be achieved by pushing the fork tubes through, i.e. lowering the front of the vehicle. But you shouldn’t overdo it, because too high a rear end means unstable straight-line stability and decreasing grip on the rear wheel.

Adjustment options fork

Whether tele or upside-down fork, the main task is the guidance and also the suspension of the front wheel. The stiffness of the fork tubes cannot be changed by setting, nor can the spring rate, i.e. the hardness of the spring. The spring base can be adjusted using a threaded plug at the upper end of the fork tubes. The adjustment screw for the rebound stage, which controls the rebound movement, is always located in the middle of this plug. The pressure level can be regulated with the screw at the lower end of the fork. This dampens the compression movement of the fork and thus also acts as a support for the spring. In addition, the handling of the machine can be noticeably influenced by lowering the nose of the vehicle using fork bars that have been pushed through.

Adjustment options shock absorber

Unlike the fork, the shock absorber does not have to take care of the guidance of the wheel. If a suspension strut is articulated via a lever system, the spring force increases progressively despite the linear spring. In the expansion tank, a gas-pressurized separating piston prevents the oil in the damper from mixing with air. The adjustment screw for the compression damping is located on this container. The rebound stage is hidden at the lower end of the shock absorber. As with the fork, the setting can be changed in steps (clicks) or without a grid. Likewise, the spring preload, which is adjusted in several stages or continuously via a thread. Raising the rear of the vehicle using a threaded spindle changes the handling, but is rarely possible with standard struts.

Basic vote in front

First determine the negative spring deflection, i.e. the downward deflection of the fork. With the driver, it should be around 30 percent of the total suspension travel (usually 35 to 40 mm). Too little negative suspension travel can lead to loss of grip when accelerating and the handlebars slapping. Too much reduces the suspension reserves. Adjustment of the rebound damping: After being compressed while standing, the fork is allowed to swing around 20 millimeters above its starting point and then has to sag back onto it. The correct pressure damping is a little harder to feel. It usually only emerges on the track. A cable tie on the standpipe or sliding tube ensures that the actual use of the existing spring travel is checked while driving.

Basic vote in the back

Again, first measure the negative suspension travel with the driver. The best value for sporty driving is around 25 percent of the usable suspension travel and is 25 to 30 millimeters. Adjusting the rebound damping is not that easy to explain. Turn from the open position until the tail no longer rebounds like a bouncy ball after being compressed. The damping should be felt well, but the rear should not take longer than half a second to return to its starting position. The compression damping is only noticeable with a very fast compression movement. The following applies here: First start with the series set-up and readjust if necessary while driving. The same applies to the height adjustment at the rear, if available.

Aprilia RSV mille

the Aprilia RSV mille is one of those candidates who inherently have a high level of sportiness. The spring rate and damping reserves are sufficient at all times, both at the front and at the rear. The adjustment range is large enough and offers enough leeway for readjustment even under extreme conditions such as high temperatures. Disadvantages in handling compared to the R version equipped with lighter wheels can be almost compensated for on the standard Mille by lowering the front section. Straight-line stability and ground clearance do not suffer from this intervention. The Mille combines agility and stability almost ideally.

Ducati 748/996

The Ducati continue to set standards in terms of driving stability. Nevertheless, the youngest vintage is not entirely convincing. After the switch from Showa to Sachs, the struts of the structurally identical models show 748 and 996 slight weaknesses. While the somewhat soft spring with 15 millimeters more preload still offers enough reserves, both rebound and compression damping are overwhelmed. Both valves must be turned to the stop so that sufficient damping is built up and the rear does not start to pump when accelerating. In conjunction with the lowered front, the Ducati can then also be kept on a fairly tight curve radius.

Honda CBR 600 F.

It is always surprising how easy it is to control the CBR 600 around the course. Its spring elements are anything but sporty and tight. Much too soft springs and too little damping cause unnecessarily strong unrest in the chassis. A fully pre-tensioned spring on the shock absorber increases the ground clearance and cornering stability, but leads to a not entirely uncritical driving behavior due to the insufficient damping: The degree between tire grip and sudden loss of grip becomes very, very narrow. So live with a little less spring preload, but more safety reserves.

Honda CBR 900 RR

Unlike the 600, Honda shows how to do it right with the CBR 900 RR. Everything is actually right here. Optimal spring rates at the front and rear and a wide, above all sensible adjustment range of the damping ensure equally balanced driving behavior on country roads and racetracks. Only a level adjustment at the rear by means of a threaded spindle or a screw-out eye on the shock absorber could finally be donated by the Honda engineers. A plus in agility can only be achieved here by pushing the fork through five millimeters and reducing the spring preload.

Honda VTR SP-1

Even if Honda’s two-cylinder engine shows impressive performance in the Superbike World Championship, there is no flower pot to be won with the standard suspension. The SP-1 can still be fine-tuned for country roads, but fails on the racetrack due to its poorly tuned suspension elements. Due to the slack suspension strut, the V2 hangs a bit on the ropes at the rear, which gives it a sluggish, indirect driving behavior. Unfortunately, there is no height adjustment, lowering the front to 17 millimeters overhang of the fork tubes helps to improve handling. If you are really serious, you can’t avoid a retrofit strut and other fork springs.

Kawasaki ZX-6R

The little Kawasaki is similar to the Honda CBR 600 F, but still much more stable. The adjustment range of the damping is almost exhausted in super sports use. The ZX-6R could use even more spring preload on the shock absorber, even if this reduces the static negative spring travel. The controllability also suffers as a result: The limit area before the rear wheel suddenly slips away is then difficult to identify, even for savvy professionals. In contrast, the stepless level adjustment via the threaded spindle on the upper strut mount is exemplary.

Kawasaki ZX-9R

The biggest problem with the ZX-9R, the mysterious fork flutter, was largely eliminated by installing less aggressive brake pads. Nevertheless, the front suspension is not quite convincing. Like the fork of the 600, that of the nine also offers no damping reserves. Satisfactory results can only be achieved with the tension and compression stage completely turned off. On the other hand, the ZX-9R shines once again in terms of handiness. With a raised tail and a slightly lowered nose, it turns out to be a true curve sweeper. But be careful, here too the limit area becomes narrower due to a stronger spring preload on the shock absorber.

MV Agusta F4 750 1 + 1

There it is, finally, the new two-seater from MV – and presents itself as confident as the single-seater F4. It doesn’t matter whether it’s about the response behavior, the basic tuning, the setting range or the possibilities of changing the geometry? the MV is the measure of all things. Reserves in all directions allow optimal coordination both on country roads and on the racetrack. Comfortable or tough, the MV masters the whole repertoire. With a slightly raised rear, it even gains something in handling, without losing a touch of sovereignty and line-fidelity.

Suzuki GSX-R 750

Once again the Suzuki shows what it is made of. High-quality spring elements ensure a fantastically safe driving experience. However, a little more damping reserves could not hurt the multiple test winner. After all, even after 20,000 kilometers you still want to have enough leeway when setting up the chassis. Placing a five millimeter thick washer under the upper strut mount and lowering the fork by nine millimeters is a significant plus in handling. Liability problems remain alien to the Suzuki in every situation despite the clearly more front-heavy chassis geometry.

Yamaha YZF-R1

Without a doubt a bike for experts. If things are going really fast, the 150-horsepower bolide demands a lot of concentration from its pilot. Although the basic set-up of the R1 is quite comfort-oriented, the damper elements can still be trimmed to make it sporty. Unfortunately, the Yamaha dealers have also saved a level adjustment on the shock absorber. The only option left here is to push the fork through eight millimeters in order to train the R1 to behave more smoothly in an inclined position. Easier, more precise turning in and a narrower line selection from the apex of the curve are thus possible.

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