Was it the lawyer's touch...

that resulted in the tire pressure specification being set to a single pressure regardless of load?

I was always a bit intrigued that unlike my '99 RT which provided 3 tire pressure settings based on load and my '15 RT only specifies a single pressure regardless of load. So, I recently rode my '15 RT with the tire pressure about 2 psi below the specified set points as measured with my digital gauge. The load was one up with side bags and top box on the bike with less than 5 lbs of this and that in them. Tires are PR5GTs.

The bike handled great, felt well planted, and gave no sense of sidewall squirm . My ride was too short to claim these lower pressures were better than those specified in the manual, but it seemed to provide a bit of a plusher ride and felt so securely planted on the road I may experiment with these lower pressures a bit more.

This got me wondering if the single set point was driven as much from the risk management department than the engineering department. Better to avoid any confusion of the right tire pressure in case of any claims that to provide optimal pressures for a given load.

that resulted in the tire pressure specification being set to a single pressure regardless of load?

 

I was always a bit intrigued that unlike my '99 RT which provided 3 tire pressure settings based on load and my '15 RT only specifies a single pressure regardless of load. So, I recently rode my '15 RT with the tire pressure about 2 psi below the specified set points as measured with my digital gauge. The load was one up with side bags and top box on the bike with less than 5 lbs of this and that in them. Tires are PR5GTs.

 

The bike handled great, felt well planted, and gave no sense of sidewall squirm . My ride was too short to claim these lower pressures were better than those specified in the manual, but it seemed to provide a bit of a plusher ride and felt so securely planted on the road I may experiment with these lower pressures a bit more.

 

This got me wondering if the single set point was driven as much from the risk management department than the engineering department. Better to avoid any confusion of the right tire pressure in case of any claims that to provide optimal pressures for a given load.

Morning Paul De

That's a good question.

It could be driven by the tire suppliers as much as by BMW.

Or could just be simplified to avoid confusion (the company that I work for has used this on general consumer cars for years, but not for performance cars)

Or it could be a tire loading thing as the tires on the newer 1200RT's are getting close to max sidewall stated pressure for the loading.

Or it might just be getting the riders manual to agree with most BMW dealers that have been telling customers to use higher pressures for years.

Or is could be something else like ABS or traction control calibration needing a non varying tire.

Or possibly to keep the onboard temperature compensating TPS system reading closer to actual.

Or it could be none of the above & just new BMW engineering replacing old.

With the same tire pressures specified for both full bike loading & light bike loading then SOMEONE is compromising.

I rode an early 1200RT (water cooled) for a while as I traded bikes with a friend that didn't feel safe riding his new 1200RT w/c while waiting on the early recall parts & I couldn't stand the higher tire pressures so just used the hexhead recommended tire pressures. I rode it fast & it still kept the tire pressure gain well under the 10% pressure gain.

The tyre pressure quoted on the tyre wall isn't the recommended pressure for use.

So, is the new ride lighter?

Does it carry a different GVWR?

Are wheels same size?

Tires are getting "better" wrt design/build/wear.

Anything sold in USA better be CYLAwyer or else as there is always someone...

Saw a surfing spot in downtown Munich.

Flowing water with close edges/rock/block and a more than likely chance when you went down that you could hit the side.

Never fly over here.

A lot of fun over there.

So, what are these numbers?

Didn't realize the GT version or the PR5 was available.

Hi Pickaxe,

I use the published waterhead inflation spec is 2.5 bar (36.3 psi) front and 2.9 bar (42.1 psi) rear.

My digital gauge reads to 0.5 psi and so how I have been setting pressure for both front and rear is that I slightly over pressurize and then in little increments deflate from 36.5 to an indicated 36 psi for the front and from 42.5 to 42 psi on the rear.

My garage in the summer months is typically between 68 and 75 F and I typically check and adjust before riding.

Haha, as I wrote this it sure sounds a little too OCD-ish

Hi tallman,

What I tried was 34 psi front and 40 psi rear.

Wow.

That is lower wrt front, higher rear, than back in the day.

We used to suggest 40/42, most replied favorably.

Caveat, haven't even ridden a wasserboxer.

My experience on my WH is a couple of psi under recommendation, ride great and wear like caca.

I run a couple of psi under recommended with BT023 GTs fitted.

Interesting discussion. I've been unhappy with how my 2017 RT tracks riding on PR4s at stock or higher pressure; so much so that I will probably get a set of Metzler tires later this year.

I just noticed that my ‘04 RT at 615 lbs recommended 32 psi/front and 36 psi/rear for rider only, which I ran with. The 608 lb 2017 specs 36/42. I'll try lower pressures before changing the tires when I get back to riding it in a couple weeks.

40/42

Tried?

The weight is that close?

The tyre pressure quoted on the tyre wall isn't the recommended pressure for use.

Correct. It's the maximum pressure the carcass can withstand, with some specified safety margin on top. Kind of like your speedometer, even though it goes to 160 mph doesn't mean you should go that fast under all conditions.

The tyre pressure quoted on the tyre wall isn't the recommended pressure for use.

It matches the recommendation on many applications.

Terry.

Didn't realize the GT version or the PR5 was available.

Oops! Right, that was a brain fart....RP4GTs

40/42

 

Tried?

 

The weight is that close?

No I have not tried pressures you stated. I think maybe I have had pressures as high as 37F & 44R for about 15 miles when using gas station a pencil gauge borrowed from the gas station attendant, but it didn't feel any different than the spec settings for that short of a ride.

I tried lower on the waterhead as I run 36 & 39 PSI on my R1100RT with Metzler tires and like those pressures on that bike ( spec for that bike single rider no load was 32 & 36 PSI).

At the the 36/42 spec pressures the tire wear on my waterhead seems to be very even, with no cupping, so maybe that is part equation as my, metzlers would show cupping at the last +/- 25% of service life, but can't discount the nature of wear due to the brand difference.

Not sure what the weight question is? Close, front to back distributuon? Close between generations of RT?

40/42

 

Tried?

 

The weight is that close?

According to their specs, the weight of the R1150RT and R1200RTW are that close.

I've tried 40/42 and didn't see any improvement with the PR4 tracking. I plan to try 32/36, and don't put enough miles on to care about cupping/mileage.

40/42

 

Tried?

 

The weight is that close?

 

According to their specs, the weight of the R1150RT and R1200RTW are that close.

 

I've tried 40/42 and didn't see any improvement with the PR4 tracking. I plan to try 32/36.

Morning Roger

I presume that vehicle weight is figured like most automobiles in that it is on the base model with standard options. On the 1150RT there weren't many weighty options to increase (as used) vehicle weight.

On the newer BMW bikes there are a number of up-level options that increase vehicle weight (how much I can't say) but the tire loading/tire pressures needs to take into account "all" available options plus max passenger & luggage weight + max fuel weight unless the riders manual breaks the tire pressures down by specific weighting categories.

The older BMW motorcycle air pressure specs left it up to the rider to increase tire pressures based on intended load carrying. The newer BMW's seem to have dummied that down to one size fits all (& that is max loading)

You need to compare (as ridden) loaded weight between the 1150 that you had & your new 1200WC as ridden, then if you want to play with tire pressures keep the cold to hot pressure gain to 10% or less & watch for uneven or odd tire wear.

The other thing to keep in mind is that most vehicle manufacturers figure in a gray area on recommended tire pressures as they don't expect an owner to check & exactly set tire pressures before every usage. If recommended spec is 32 psi then it was probably tested down to 30 psi as a safe usage pressure.

To add to the above comparisons of 1150RT vs 1200RTW. My 1150 really couldn't care less (within reason) what the tyre pressures were. If the tyres were not worn out, it tracked well pretty much regardless of road surface (again, withing reason). However the Wethead seems to be amazingly sensitive DESPITE tyre pressures.However, I always follow these threads with interest to see if someone comes up with a fix that will work (for me).