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Old 05-Apr-2004, 01:23 PM
Andyl Andyl is offline
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Can someone help me through the tyre pressure b******t

I have just read Icoic's thread re corsas and it strikes a nerve for me regarding tyre pressures. Does anyone have a difinitive answer to the apparent black art?

The owners manuals for Dukes always quote in the region of 30f-32r with minor variations depending on model. I recently bought some Bridgestone 012ss for my 999s and was told to set them at 36f-42r.

These as far as I am aware are pretty standard pressure for most Japanese sports bikes but are vastly different from the 30-32 that most Ducs seems to run on.

I know there is much b******t around about tyres and I am fairly confident with my knowledge of the differences between road and track use but does anyone know why tyre manufactureres quote these inflated figures (Oh no - what a pun - sorry!) and why they are so different to the ones in the manuals.

[Edited on 5-4-2004 by Andyl]
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Old 05-Apr-2004, 01:42 PM
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no is the simple answer maybe ducati manuals assume the pressures are for track use which should certainly be somewhere in the 29/32 ish range.
and 36 42 is definitely good for 'average' road taking into accout potholes and the like obviously these will drop in good weather or on smooth surfaces.
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Old 05-Apr-2004, 02:04 PM
Triple Nine Triple Nine is offline
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I checked with Ducati when I got my 999 and they confirmed 30/32, as per the manual, lower than the 916/996.
I have run with these settings for 6K on road and track without a problem (but I am a bit slow)
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Old 05-Apr-2004, 06:42 PM
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A couple of years back the tyre manufacturers got together and agreed to just recommend one set of tyre pressures which I recall being the 36F-42r, which to me is quite high but is probably done for legal reasons.
When I first started racing I joined the Perelli riders club run by CPK, they would supply me with Pirelli Dragon Corsa's at a highly discounted rate, for track use they recommended 31f-30r without tyre warmers and 1 psi less in each if using tyre warmers. On the road I tend to run 32f-34r as I like the feel I get from my tyre at these pressures.
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Old 05-Apr-2004, 08:37 PM
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The answer is that 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. Further, if you're running alloy wheels on poor pavement, consider adding 2 psi to the recommended tire pressure just to reduce the likelihood of pothole damage. 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. Check your tire pressure regularly as they say.

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.

A technique for those wanting to get the most out of their tires on the street is to use the 10/20% rule.

First check the tire pressure when the tire is cold. Then take a ride on your favorite twisty piece of road. Then, measure the tire pressure immediately after stopping. If the pressure has risen less than 10% on the front or 20% on the rear, you should remove air from the tire. So for example, starting at a front tire pressure of 32.5 psi should bring you up to 36 psi hot. Once you obtain this pressure increase for a given rider, bike, tire, road and road temperature combination, check the tire pressure again while cold and record it for future reference.

Each manufacturer is different. Each tire model is different. A tire design that runs cooler needs to run a lower pressure (2-3 psi front) to get up to optimum temperature. The rear tire runs hotter than the front tire, road and track. So the rear tire cold-to-hot increase is greater. Dropping air pressure has the additional side effect of scrubbing more rubber area.

As an example, when I used the tire pressures recommended by Ducati (32F/35R) for my 916 on my favorite road, I got exactly 10/20% on a set of Bridgestone BT-012SS. So I guess I'm an average rider, and the BT-012SS runs at an average operating temperature compared to other brands.

For the track you'll have to drop the cold tire pressures an additional 10/20%. Track operation will get tires hotter (increasing the cold-to-hot pressure range) so starting at say 32/30 psi now should bring you up to the same temperature (and pressure) that 35/39 psi gave you for the street. Don't even think about running these low track cold pressures on the street.

Finally, dropping tire pressures on street tires for track use has its limitations, so street compound tires on the track often get too hot and go beyond sticky to greasy. That's why you have race tires. Race tire compounds are designed for severe operation at these higher temperatures for a limited number of thermal cycles. On the other hand, a race tire on the street usually won't get up to the appropriate temperature for good performance. At street speeds, the race compound often won't perform as well as a street tire.
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Old 05-Apr-2004, 08:54 PM
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don't know about the rest of you but thats just confused me
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Old 05-Apr-2004, 11:01 PM
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For the last 3 years Bridgestone used to rec pressures very close to the Ducati handbook pressure for BT010's on the st4s, and a number of other Ducs.

As of 2004 Bridgestone have now changed all recommendations to the standard catch all 36/42.

I've never had any probs with the lower pressures over the last few years under a variety of conditions. A curious thought though is if someone was unfortunate to have a serious accident and presuures were checked how would you stand running supposedly much lower than the new approved pressures?

Must try Shazaams guide and see if the new or old Bridgestone figures are right.

[Edited on 5-4-2004 by bigdaftgeordie]
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