Tire age, inflation pressure, balancing

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Tire age, inflation pressure, balancing
Marcus Jahn

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tire

Tire age, inflation pressure, balancing

Tire age, tire pressure, tire balancing
Motorcycle tires and their problems

Even when you have found and fitted the ideal tire for your motorcycle, questions still remain unanswered: How does it behave with increasing age? What happens if the air pressure is wrong or if a balance weight is lost? We just tried it out.

Jorg Lohse, Karsten Schwers

May 14, 2018

Influence of tire age

At the beginning we put on two supposedly identical sets of tires. One pair was properly stored, the other was bombarded with high doses of UV light for a year. How does the artificially aged pair of tires compare??

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Tire dealers can sing a song about critical customers who examine the new sentence on the shop counter and let it go back with the words “It’s already too old for me!”. Any layperson can decipher the actual tire age at a glance. But when is a new tire really too old and how do its qualities change with age?

To clarify this in comparison, we stored two brand-new sets of the popular for a year Michelin Pilot Power 2 CT in two different places: one set cool, dry and dark – as recommended by the manufacturer – in the MOTORRAD tire store, the other, on the other hand, with direct exposure to the sun and heat in a greenhouse.

The aim was to age the second pair of tires as quickly as possible. So far, at least according to the knowledge of MOTORRAD author and greenhouse owner Ralf Schneider, single glazing has been able to bring down all kinds of plastics in a very short time. Rubber seals are so porous after just a few months that they literally crumble in the hand. So it’s exciting to see how the tortured Pilot Power 2 CT will fare in comparison to the more or less brand new pairing on the test track.

How can you tell when the tire was manufactured?
Each tire has a so-called DOT number (abbreviation for Department of Transport, the US Department of Transportation) – see also in the photo above on the right. The four digits stand for the week and year of production, so this tire was manufactured in the 25th calendar week of 2015.

When is a new tire considered too old??
This has now been legally clarified: A brand-new tire is still considered new five years after its completion. In this respect, a dealer can still sell tires that were manufactured in summer 2012 as new this year. As long as the tires have been properly stored, this is not a problem according to the manufacturer: Substances such as plasticizers and UV protection agents are added to the rubber compounds, which are intended to reduce deterioration in performance due to aging. Some manufacturers such as B. Bridgestone sell tires that are more than three years old at a corresponding discount. So before you reject the tire because of its age, you should talk to the dealer about a possible discount. 

When at the latest should a mounted tire be replaced?
Initially, only reaching the minimum tread depth is legally relevant: the tire has to be changed below 1.6 millimeters – this applies equally to cars and motorcycles. Incidentally, you should not use the wear marks visible in the profile channels as a guide. According to the US American DOT standard, these TWI bars (“Tread Wear Indicator”) are only 0.8 millimeters high. A tire naturally ages differently on the rim than in the tire store. UV rays, ozone pollution, moisture and heat nibble on the performance, so that the tire has noticeably decreased in its performance after seven years despite sufficient residual tread. Discoloration in the rubber is the first sign. At the latest, however, when cracks have formed in the side wall, a fresh tire belongs on the rim.

How much does the performance of tires that are too old deteriorate??
Our greenhouse simulation caused one pair of test tires to age by around four to five years – according to manufacturers’ estimates, such a tire could still be used without hesitation in real life. On the handling course, we simulate a brisk lap on the country road. Differences between our “new” and “old” tires cannot be measured. Both power sets convince with their well-known good everyday properties. The performance measurement on the wet test track, which allows the conclusion that the curing process is in full swing, becomes somewhat more familiar.

Conclusion: If the storage conditions are right, tires will last for many years. Of course, they age much faster in use. Discoloration is the first sign of the aging process, cracks form and the tire is ready to be replaced. In our test run, the artificially aged pair of tires could keep up surprisingly well. The performance only fell slightly in the extreme test in the rain.

Optimal tire pressure

Readers keep asking about the optimal air pressure for their bike. We therefore let out air and built up pressure on our test Kawasaki ZX-10R. Is it possible to suddenly set new personal bests on the home route with the inflation pressure lowered??

If you ask motorcycle and tire manufacturers about the optimal air pressure, there is usually only one standard answer: 2.5 bar at the front, 2.9 bar at the rear – that’s how (much) it has to be when it comes to widespread sports tires in radial construction. However, there are usually other recommendations for use on the racetrack, some of which are well below the extremely tough everyday requirements. Can road drivers who are committed to sports do something with it, or is lowering an absolute no-go? So let’s roll with our Michelin Power 3 pair (the new, top stored, of course) with different pressures on the test track.

How is the standard air pressure actually composed??
The tire pressure recommendation is usually determined by the vehicle manufacturer in consultation with the tire supplier. First and foremost, this air pressure adjustment follows legal standards with which the best possible level of safety is to be guaranteed. Practical aspects are more or less hidden at this point. This is the only way to explain that this “radial standard inflation pressure” of 2.5 bar at the front and 2.9 bar at the rear does not differ between light sport bikes and heavy touring bikes. First and foremost, this tough coordination is about ensuring the maximum permissible load in connection with the maximum speed that can be achieved. The air pressure information can be looked up in the operating instructions; there are usually instructions on the motorcycle itself, for example on the swing arm, under the seat or on the frame. And also very important: The information applies to cold tires. Anyone who measures or wants to refill must do this in any case before the journey.

You can lower the air pressure yourself?
There is no regulation as to what inflation pressure you have to use when you are out and about. So the clear answer is: yes! All information is purely a recommendation. However, the manufacturers of course do not accept any liability if problems or even damage to the tire or motorcycle occur with reduced air pressure. In the ideal case, vehicle manufacturers actually make several recommendations (this is customary for cars): In addition to the full load recommendation (2.5 / 2.9 bar), it can e.g. B. give another one for the solo trip on the country road or one for the partial load operation (e.g. with a load / suitcases).

Can sporty drivers orientate themselves on the racetrack inflation pressure?
Basically, of course, it makes sense to adjust the air pressure to the actual load. Above all, with more air pressure you gain stability, and the motorcycle can also be steered more precisely and moved more easily. If you lower the inflation pressure, you gain in contact area and thus in grip and traction. The self-damping and ride comfort also increase. The lower the air pressure, the faster the tire temperature can rise – which, in the worst case, can cause the tire to overheat; then there is a risk of structural damage. The race track inflation pressures are very individually designed for the tire construction and temperatures of up to 80 degrees Celsius, which are normally not reached in everyday life.

Does the ideal air pressure exist for everyday drivers?
There is no value that can be carved in stone across the board and similar to the famous 2.5 / 2.9 bar. Even during the test on our handling course, which is not a real racetrack, but allows very sporty driving, the racetrack value recommended for Power 3 (2.1 / 1.9 bar) is not an optimal choice. Despite the pithy country road chase, the tire lacks stability and steering precision. Furthermore, higher steering forces are now required, and the pitching impulse when braking in an inclined position can be felt much more clearly. On the other hand, you cannot really perceive an advantage that the tire heats up faster and grip and feedback improve.

Conclusion: Anyone who always wants to be on the safe side should actually only rely on the manufacturer’s filling pressure recommendations. For someone who is always on the move at high speed from time to time, lowering makes no sense. Neither can racing track filling pressures be adapted for country roads. In top conditions (hot, sunny, dry), sporty country road drivers can find out whether they can reduce the pressure at the front by up to 0.3 bar and at the rear by up to 0.4 bar.

Eliminate imbalances

At the end of our three-problem test, the super sports rocket goes into the high-speed oval. To do this, we artificially created imbalances on the wheels and affixed more balancing weights than necessary. 

You will hardly find a perfectly balanced motorcycle tire in reality. Manufacturing tolerances are of course permissible, but usually do not pose a problem provided the wheel has been correctly balanced prior to installation. In this test section, our test Kawasaki ZX-10R first goes straight to the slopes. In practice, we try to find out what dangers the ninja pilot has to fight against if the wheels are not correctly balanced.

How can you tell whether the wheels have been balanced at all??
During the visual inspection, first of all, whether there are balancing weights on the rims. Theoretically, it is of course conceivable that the tire is positioned so skilfully during assembly that it is no longer necessary to attach counterweights (“matching”). However, the likelihood that manufacturing tolerances on the rim and tire will almost equalize through skillful assembly is very low. Whether the counterweights are exactly positioned can actually only be determined while driving

Which forces act on incorrectly balanced wheels??
A typical radial touring or sports tire in the widespread 120/180 17-inch dimension weighs just under five kilograms at the front and over seven kilograms at the rear. At first glance, an imbalance in the weight distribution in the tire, which can be up to 50 grams ex works, sounds quite harmless. After all, that makes up just one percent of the total weight. However, this becomes a huge problem when driving. And the faster you drive, the more powerful it gets. A calculation example: If the imbalance is only 20 grams, the centrifugal force at 150 km / h will already pull around 120 Newtons on the wheel circumference. If we turn our test ninja up to top speed, the force at 300 km / h is 460 Newtons, which corresponds to the weight of a very, very slim passenger, just under 46 kilograms.

Can you drive at all with incorrectly balanced wheels??
Where there is a will, there’s a way. Of course, it can happen in everyday life that the now widespread adhesive weights have become detached from the rim. You should definitely check this first if you suddenly and suddenly have to fight against puzzling chassis unrest or handlebar flutter. In order to simulate the loads in the worst case, we sent our tire test Kawasaki with an asymmetrical weight distribution on the bike into the high-speed oval. 70 grams more weight now rotate on the front wheel rim. The effects of strong vibrations can be felt extremely at speeds from 120 km / h. The ZX-10R cannot be driven from 180 km / h. The vibrations are so strong that after four kilometers, screws have already shaken loose from the fairing. We are now gradually reducing the extra weight. The problems remain, but only occur at a slightly higher speed: restlessness from 150 km / h, impassable from 200 km / h!

What damage can be caused by badly balanced wheels??
Even slight vibrations, which can still be felt at 15 grams of imbalance, can permanently destroy bearings and cause cracks – even in the frame. The tires also wear unevenly, which further increases the imbalance.

Conclusion: Without correctly balanced wheels, nothing can move forward. Even deviations in the ten gram range can already be felt at country road speeds due to handlebar flutter. If the speed increases, the vibrations also increase significantly. If the imbalance is more than 15 grams, there is a risk of serious damage to the entire motorcycle in the long run.

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