Join Date: Apr 2008
Location: Proctor, VT, USA
The answer is, for a tire to perform at its best it has to reach, but not exceed, the temperature at which the rubber compound gives the maximum grip.
The difficulty is, predicting the temperature that the tires will actually reach for each combination of bike model, suspension set-up, rider weight, cornering and throttle technique, air temperature, road temperature, road surface and curvature ... just to name a few variables. This is why tire testing is so important, and also why so much time is devoted to it by race teams.
For street bikes, Ducati plays the averages. When they do development work on each bike model, Ducati test riders and engineers work with their OEM suppliers, Michelin and Pirelli, to come up with a tire that gives a good overall performance (wet, dry, good milage, etc.) Along the way, the tire pressure that works best for these OEM tires for AVERAGE ROAD USE is determined, and thatís the number that ends up in the Owners Manual. As power increased and tire construction and rubber formulations changed over the years, so have Ducatís recommendation for tire pressures. Early 916ís for example, had a recommended pressures of 32F/35R, but 30.5F/32R is now recommended for 99Xís.
So when you move to a tire that isnít OEM, then you have to do your own tire testing to determine the best pressures FOR YOU, and you have to hope that the tire manufacturer has done the necessary development work to give you a good starting point.
The non-Ducati OEM tire manufacturers play the average-game as well, so when they recommend tire pressure starting points, they do it for an average bike, whatever that means. The trouble is the tire manufacturers donít ever tell you whatís the optimum tire temperature for the rubber formulation for each kind of tire. Some reps will tell you the optimal increase (%F/%R) in pressure from cold to running condition, which is more useful information than cold tire pressures.
So itís really all up to you. You'll get a lot of opinions on what tire pressure to run, but the correct tire pressure for you is not a matter of polling other rider's opinion or asking the manufacturerís rep at the track.
Here are the basics you'll need to decide for yourself.
For the street, start with the bike manufacturer's recommendation in the owners manual or under-seat sticker for OEM tires and similar models from other manufacturers. This is the number that they (Ducati and the OEM tire makers) consider to be the best balance between handling, grip and tire wear. Just as you would for a car, increase the pressure 2 psi or so for sustained high speed operation (or two-up riding) to reduce rolling friction and casing flexing.
In order to get optimum handling a tire has to get to its optimum temperature which is different for each brand of tire. Most of us don't have the equipment needed to measure tire temperature directly so we measure it indirectly by checking tire pressure since tire pressure increases with tire temperature. Tire temperature is important to know because too much flexing of the casing of an under-inflated tire for a given riding style and road will result in overheating resulting in less than optimum grip. Over-pressurizing a tire will reduce casing flexing and prevent the tire from getting up to the optimum operating temperature and performance again suffers. Sliding and spinning the tires also increase tire temperatures from friction heating.
S0, the technique for those wanting to get the most out of their tires on the street is to use the 10/20% rule.