Loose Steering or something like that

[kirby]

"I always follow the TYRE manufacturers recommended pressures. When the bike was designed and built there were A,B,C tyres available. Now the tyres available are X,Y,Z - the vehicle manufacturers recommended pressures are no longer valid because they never took into account the way that tyres X,Y,Z were going to be designed."




I don't have the words for that one!

I'm sure you understand my meaning, even if my words were a little abrupt.

I'm sorry but your way off in the deep end with that one.

[riceburner]

"I always follow the TYRE manufacturers recommended pressures. When the bike was designed and built there were A,B,C tyres available. Now the tyres available are X,Y,Z - the vehicle manufacturers recommended pressures are no longer valid because they never took into account the way that tyres X,Y,Z were going to be designed."




I don't have the words for that one!

I'm sure you understand my meaning, even if my words were a little abrupt.

I'm sorry but your way off in the deep end with that one.

If I change your highlights to include the preceding word is it better?

My intended meaning is more along the lines of : "Once you start using tyres that are 10 years younger than the bike they're on, then the bike manufacturer's recommended tyre pressures are less valid than the tyre pressures that are recommended by the manufacturer of the new TYRE."

To put it another way: in ten years, tyre technology and design has moved on, the bikes (our R1150Rs) have stayed (more or less) the same. So - when the bike was built, the tyres available at the time responded best at certain pressures, because of the way they were designed. The tyres manufactured now are very likely to be built in a different manner, to different designs and specifications, using different materials which perform in different ways. So - the pressure that they work best at is very likely to be different than the best pressures for the tyres that came with the bike originally. Knowledge, technology, materials, design all change in time.

Even though the given spec of the bike (weight/handling characteristics/performance characsteristics/desired useage etc etc etc) has not changed - the tyre materials/design/manufacturing method may well have changed. Tyre manufaturers are well aware of this and so the recommended tyre pressure for a given specification of machine will be calculated (or found by experimentation) during the design process of the tyre. Each tyre model has different characteristics and so will have differing recommended pressures. (eg Michelin tyres that are ostensibly for the same usage as Pirelli tyres will have very* different recommended pressures - as we have discovered on this very thread).

The BIKE manufacturer in the meantime, has moved onto other things and will not go testing all their bikes on the new tyres to then re-publish the recommended pressures (even though that would be a good idea, and car manufacturers might do it a little - but I'd wager they would see it as somewhat "above and beyond" their duty of care to their customers).

Does that make a bit more sense?




* If I rode my Rockster with Pirelli tyres, but used the pressures recommended for Michelins (see links I posted here : viewtopic.php?p=255580#p255580) - I'd very definitely feel the difference in a negative manner. Michelin's pressures for the Rockster are 0.2bar front (2.9psi), and 0.4 bar rear (4.8psi) LOWER than those recommended for the Pirelli Angel GT. I've ridden bikes with the pressures off by that much - and it's definitely noticeable and not fun.

[kirby]

We are probably never going to be on the same page with this one.
Tire manufacturers, regardless of the changes of rubber compounds and manufacturing techniques have not changed the basic construction on the radial tire since its been available to the riding public.
They purposely (liability concerns and safety) design for example the 120/70 tire to work well in the range of 32-42 psi (42 being the upper limit on them all since they have been available) To do otherwise could be a disaster(literally). The pressure you run is your choice, to your tastes.

However the recommended pressures stated in the manuals and placards from the machine manufacture still stands and will work fine. Generally for stability and longevity.

I have a classic bike (old) that had 90/90/18 front 110/90/18 rear bias ply tire from the factory. So when continental came out with a radial in that size I wanted to try them so called (bike company out of business) continental for recommended pressure because of the change of tire (bias vs radial) construction. I talked to their engineering department(am a member of the SAE) and they told me that the new tire was designed for the old machines and that I should use the pressures recommended by the manufacture (bike).

This is just one example and saying that the recommended pressures specified by the manufacturer is not valid ... is in error.
Construction technology, profile, and compound has little if anything to do with changing the pressure requirements. As you ride you change the profile as the tire wears, do you change the pressure?

If you are sensitive enough to recognize a difference of 1 to 2 psi then by all means change to what you like. I would bet that most folks riding out there couldn't tell you what pressures they are running or even what the manual/placard shows.

Like I said we are probably not going to agree on this and that's fine...

Enough...

:-)

[skylarmav1]

Low rear tire pressure equals sluggish steering at low speeds. I've had this happen a couple of times. Also, as the tires were near their acceptable end of life, the same phenomena would occur. Generally sloppy low speed handling but they still passed US inspection.

[Bogdan]

Must say I'm surprised by the content of this thread. My ride, my first oilhead, a 2004 R1150R with 27k miles, exhibits the same characteristics described: rock solid at over 100mph, fine in the twisties but....pulls, a bit, toward the turn at low speeds. I thought this was simply normal paralever behavior and not especially bothersome. I should add that I bought the bike 20 months ago from a BMW mechanic up in Canada. This man used to be a dealer who now works out of his garage. On meeting him I was impressed with his expertise. This bike was his main ride for a couple of years. I didn't/don't think he would sell me a ride with a glaring fault. Also..on his advice I do keep the tire pressure rather high - 38f and 40r. Could it be, cgguy, that you're chasing a problem that doesn't exist? or......that I'm living with a defect that I thought normal?

Bogdan, puzzled in Colorado

[maccraith]

I am sending you a link to a Ohlins suspension owners manual. And while you may not have an Ohlins suspension, I think you will find a lot of information in the manual about suspension and steering behavior, and suspension and steering adjustment. I think you may find some worthwhile information here that may be pertinent to your problem. Good luck.


https://drive.google.com/open?id=0BzTBY ... W9aWjV3bk0

[EasyBee]

rock solid at over 100mph, fine in the twisties but....pulls, a bit, toward the turn at low speeds.

Does it easily fall into the corner or does it really pull you into the corner? And is this to the righthand corner a bit more than into a lefthand corner?
To newcomers on these Beemers, they seem to fall a little bit into a slow corner. This is because of their low point of gravity and because of it's design (these two big cilinders hanging low and sticking far out). Where you have to steer with most 4 cilinder bikes, these beemers steer at the blink of an eye. Because of its design they tend to do this a bit more to the right, than to the left. Eving standing still with the engine running, if you open the throttle ist tends to the right, the weight of the crankshaft.
Check your tyres, stick to the advised PSI of the manufacturer of the tyre (it's a lot newer than your bike), Are your springs and shocks still in a good condition a adjusted to the right settings?