Ducati 998 2001 Manuel D'utilisation Et Entretien page 136

Wheels
Five-spoke, light-alloy rims for 748S and 998 models;
three-spoke rims for 748 model.
Front wheel
Dimensions:
3.50x17"
Rear wheel
Dimensions:
E
5.50x17"
Front wheel shaft can be removed.
The rear wheel is overhanging with respect to the
sprocket hub and secured with a nut and safety clip. In
this way, the rear wheel can be quickly replaced.
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Tyres
Front tyre
Tubeless, radial tyre.
Size:
120/60-ZR17 (748/748S); 120/70-ZR17 (998).
Rear tyre
Tubeless, radial tyre.
Size:
180/55-ZR17 (748/748S); 190/50-ZR17 (998).