REGLAGE GEOMETRIE CHASSIS SUR 748-916996-998-... (source Ducati.com) As mentioned in Checking and adjusting the suspension setting , we shall now deal with how to set the chassis geometry on those models that feature steering head, tail ride height and steering damper adjustment. While setting the suspension, i.e. spring pre-loading, compression and rebound damping for optimal dynamic balance is relatively simple, changing chassis geometry is quite tricky, as it can have unexpected effects on handling. Factory set-up is determined during the testing stage and is done in such a way that it responds to the needs of average sports usage, including racetrack riding. However, individual riding styles, track characteristics and weather conditions (wet or dry pavement) may require some changes in chassis geometry if peak performance is to be maintained. Our suggestion is to have this kind of changes done at an official Dealer. As the old saying goes, “every man to his trade”. Let me give you one example. The bikes featuring a single-sided swingarm – such as the 748, 916 and 996, have an eccentric rear wheel shaft. This means the centre of the rear axle does not lie in the centre of the wheel rim. As a result, when you tension the final drive chain you will inevitably affect wheelbase and tail ride height and you will need to somehow compensate for the resulting deviation from original set-up. Just how much room for adjustment is there when changing chassis set-up? •

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First, you can the change the steering head angle. This will be the angle of the steel tube welded to the frame that accommodates the two steering bearings. The steering head is set at 24°30'(aS-FIG.1)at the factory and can be steepened up to 23°30'(aPFIG.1). The steeper angle will not affect the wheelbase, whereas the trail (foto avancorsa) is shortened from 97mm (aS-FIG.1) to 91mm (aP-FIG.1). You can change the wheelbase by turning the eccentric rear wheel shaft. You can increase or reduce tail ride height by lengthening or shortening the rear suspension linkage (A - FIG. 2) or rotating the eccentric rear wheel shaft. You can change the position of the front fork legs relative to the steering head, i.e. raise or lower the forks in the steering head, to change front ride height.

The point is each of these changes will affect the bike's centre of gravity to varying degrees. Broadly speaking, weight distribution across the front and tail end in the Superbike family (748/916/996) is 51% vs. 49%, respectively. The trend in hypersport and racing bikes engineering is to place more load on the front end in order for the front tyre to have more grip and steering accuracy. A higher centre of gravity (theoretical point at which all masses balance out) improves handling and turn-in behaviour, however, it will give you some trouble with pulling the bike upright when exiting a bend. A lower centre of gravity improves cornering stability but may compromise handling. Good handling is invariably a compromise of all the different factors involved. An outline of the most frequent problems that might come up when you change set-up will help you understand how the different parameters involved interact. If you wish to try out a different set-up, remember to expect the unexpected. You will soon realise that the path to dynamic stability is a tricky one. •

The front wheel shakes when entering a bend until you release the brakes or start to apply the throttle. This is most frequently due to an overloaded front tyre. The front fork is set too low and nearly goes to full bump when cornering, which is the stiffest portion of its travel.

Remedies: o Increase pre-load so the fork will compress less and run in a softer portion of travel. You may need to increase pre-load significantly. Lower the front end of the bike to optimise handlebars set-up and bike balance. o If ineffective travel is too large (10 mm), lower the oil level. o Make sure there is no friction in the front fork. o The tail end might be too high or the rear shock spring might have exceeding pre-load. If so, reduce tail ride height or spring pre-load. o You might want to check on brake discs, callipers and pads. Make certain all bolts are securely tightened to the specified torque.

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The front wheel “bumps” during final application of the brakes. Remedies: o If ineffective travel is too large (10 mm), it means that the oil level is too high. Lower it. o If the fork is low and cornering behaviour is still good, increase the oil level. If the front fork feels flighty or light under cornering fit a harder spring and leave the oil level unchanged.

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The front wheel loses grip when exiting a bend. Remedies: o Rebound damping is too soft: increase it. o Exceeding front fork pre-load: reduce it. o Exceeding front ride height. Raise the fork legs in the steering head and yoke (be sure to leave enough clearance between front wheel and engine!). o The front suspension is too stiff, use a softer spring if possible..

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The rear tyre has poor grip. Remedies: o The tail end is too high, especially during the initial application of the throttle. o Exceeding pre-load of the rear shock spring: reduce it. o Rear shock compression damping is too hard: reduce it. o If the rear end feels stiff when the bike takes a bump, it means that rebound damping is too hard: reduce it. o Rear suspension is too stiff, use a softer spring if possible.

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The bike exhibits poor stability in a straight. Remedies: o Check the bike for defects, such as loose or worn steering head bearings, defective steering damper, friction in the rotating arm bearing, and so on. o Make certain the swinging arm pivot is tightened to the specified torque. o Increase the damping rate of the steering damper.

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Change the final drive ratio so as to lengthen the swinging arm by at least several millimetres. Set the steering head about 2 mm further back.

As you can see, there are many variables to be taken into account and it is not always easy to identify all of them. Again, our suggestion is to seek expert help at an official Dealer. Make one change at a time and do not forget to note the original set-up. That way, you will be able to restore the set-up you started with at any time. Note that the steering damper is there to compensate for minor fluctuation in the front end. Change setting by two or three clicks at a time and check on the outcome. Do not expect the steering damper to solve all of the problems with poor front-end stability. Do not forget that the steering lock will only operate when the steering head is set at 24°30' (factory setting). Note also that the handlebars can help greatly in making critical steering response more manageable when they are set wider open. One last question: could it be that we have to thank poor dynamic stability for top performance? The matter is open to discussion. G. Solazzo