Correct Tire Pressure???

[Hulka]

What is the correct tire presure to run on and 1100 RT? The manual states: 31 front, 36 rear for solo rider. The Metz tires, at least the front does, states 41 psi max, while the rear does not have anything on the sidewall. Some people tell me to go by what the vehicle says and others say what the tire says. Anybody want to put in their 2 cents worth on it?

 

I am lost.

[GordonB]

MZ Z6: My 2cents, Fr 36, Rr 41-42. Works for me

[DEF]

Go by the manual and adjust slightly for your weight. A normal rider solo weighs 170 lbs according to BMW.

[ShovelStrokeEd]

Kevin,

Most here run higher pressures than that specified in the manual. Lots of reasons from soft rims that dent rather easily to a quest to get the last possible 2 miles out of a set of tires.

 

Here is an easy way to establish good working pressure for yourself.

 

First and foremost. Buy a good tire pressure gauge. Not one of those $2.99 pencil gauges the sell in Wally World. I took all my gauges into work one day when we were calibrating some of our test equipment and compared their readings against a dead weight manometer. The only gauge I took home with me was the BMW digital tire gauge. I threw all the rest away. Some of them were off about 6 lbs!!!

 

Next, set your tire pressures, cold, at some level you feel comfortable with, say 34F/38R. Now go for a nice ride, trying to keep it typical of the riding you do. Wait at least 50 miles and pull over into a safe place and check your tire pressures again. Front should have risen about 10% and the rear 10 to 15%. You did write down your original pressures, to the 10th of a pound, right?

 

If your pressure rose less than the above, start with a lower pressure on that tire. If they rose more than that, you need to add a bit the next time you air them up.

 

A couple of iterations of this and you'll have a handle on what you, on your bike, for your riding habits, need. Some other general rules. Sporting riding, you might want to drop your pressures a bit to gain a bit of flexibilty which will lead to better traction. How much? Again, it varies with the rider but 2 to 4 lbs would not be out of line.

 

Long freeway drones or even secondary road riding where you don't really expect to be carving it up much? Add a couple of pounds to your base to increase tread life. Ditto if you contemplate riding two up or are adding a bunch of luggage for a long trip.

 

While quite a few here do so, I would not recommend exceeding the max pressure, that is cold inflation pressure, shown on the side wall of your tire. If you can't find the data there, a quick trip to the mfg web site should get you the data you need.

[Al Navecky Jr]

Install a Smartire System and you can check the pressure while you are riding.

[Hulka]

OK, thanks I will try vary air pressures to see. The 32 in the front is to little for me. I am 6'1" and 230. I tried that last night going to work and it feel like the tire wants to roll of the rim on hard turns.

[motoguy128]

I think that he suspension is so compliant and smooth on the BMW's that you can run higher than normal tire pressures. I'm running 37/42 and just leave it there, solo or with a passenger. The rear tire says 42psi max, so I wouldn't exceed that on either the front or rear.

 

In my opinion, these bikes handle very well, but are not really designed for 80%+ riding, so getting heat into the tires isn't much of a concern like on a sportbike... so higher the better for less tire wear and better mileage. It will also change direction easier.

[ShovelStrokeEd]

I'll agree on the 80% thing but many riders here do ride at well over that. Part of the problem with running high pressures is the tire loses compliance and will not conform as well to small surface irregularities. If it can't conform, you will lose a certain degree of available traction. It is small but it is there. The tires are a component of the suspension system and, when leaned over, tire compliance becomes a good part of the bike's ability to remain in contact with the road as even the BMW suspension is subject to the laws of geometry.

[Rags]

Go by the manual and adjust slightly for your weight. A normal rider solo weighs 170 lbs according to BMW.

 

Is that the American manual?

 

Over inflation will increase wear on the center strip of your tire.

 

Imagine the effect of a 100 degree day doing 80-90 on black top has on expanding the air in your tire. Perhaps the cold temps recommended by the manufacturer is in line (except for loading)

[Hulka]

As for the heat thing, that was a concern for me living in Metro Phoenix with temps getting into the 110+ June through August. I am hot now with my phase 3 jacket on and it is only 90 out I can't wait till it gets to the 116+ mark to see what it is like. I can only imagine what it is going to do to my tires (the heat that is).

[BucksTherapy]

I have an 02RT and an 04ST1300. The Honda calls for 40F/40R. I found I was getting much better wear, much less cupping and just as much stickiness on the Honda so I pumped up the RT 40/42.

 

Guess what, much better wear, much less cupping, stickiness just as good, ride uncompromised(Wilbur shocks).

 

I think Honda has this one figured out given my experience. I am currently running Metzlers on the ST and Pilot Roads in the RT.

 

Pump m up and try it.

 

PS I have low profile soft tires on my car and couldn't get 30k out of a set of expensive tires without cupping so severe I had to change tires. A country mechanic in a little town in northern Maine told me to forget the factory spec of 35lbs and pump them up to 45lbs as per tire spec. Guess what, no cupping, none, much quieter and much better wear.

 

Good luck!

[leikam]

For commuting use, I like low-30s in the front and high 30s for the rear. Anywhere in there and I'm happy.

[Mike O]

...Front should have risen about 10% and the rear 10 to 15%....If your pressure rose less than the above, start with a lower pressure on that tire. If they rose more than that, you need to add a bit the next time you air them up.

Ed,

 

This seems very methodical (and as an Engineer, I appreciate) On the other hand, I'm eager to understand where the "10 to 15%" came from? (yes, I know it's going to rise because of heat, buy why not 5-10% or 20-25%...)

 

Regards,

 

Mike O

[ShovelStrokeEd]

Old school rule of thumb. Back before infrared pyrometers were cheap and easy to get, race guys used this method to set tire pressures. Internal temperature of the tire is really not a good indication of tread temperture which is why most have gotten away from it. It is, however, a really good indicator of how the tire is flexing in response to loads and road surface irregularities. The 10$ range means the carcass temperture of the tire has risen just about the right amount.

 

Gimmee a minute or two to go dig up my HP 49 and I'll run some temperature rise numbers for you that will illustrate the point.

 

Crunching numbers makes my head hurt so it might take a bit.

 

Proposed: Harley riders are people too. Discuss.

 

OK, I'm back. Tire internal pressure will vary directly as the internal temperature in degrees Kelvin. Please nobody get on me about non-ideality factors and air not being an ideal gas, it's close enough and I'm gonna round the numbers to follow anyway.

 

Assuming an 80 deg F starting temperature, a pressure rise as it reflects internal temperature will look like this.

 

start = 80F Internal temp 80 F.

5% up Internal temp 107 F, a bit cool

10% up Internal temp 134 F, just about right

20% up Internal temp 188 F, pretty hot for rubber and cord material

 

Clearer now?

[Mike O]

...Clearer now?

Yes...And so that others understand, the beginning temp (80F) is the ambient air temp, and the internal rise in temp is due to heat generated by external tire friction. Makes sense.

 

How did the 'race-guys' determine that 134F is 'just about right? I'd guess this was on the basis of handling characteristics for the particular tire, weight, road surface etc. but I'll let you set me straight.

 

Regards,

 

Mike O

 

Proposed: Harley riders are people too. Discuss.

No, that would just start YAHBT...no thanks.

[ShovelStrokeEd]

Yes...And so that others understand, the beginning temp (80F) is the ambient air temp, and the internal rise in temp is due to heat generated by external tire friction. Makes sense.

 

Almost, just a small correction. Most of the internal temperature is generated by the flexing of the tire's carcass and internal friction within that carcass. Tread temperature can vary quite a bit from that temperature (rubber being a pretty poor heat conductor). Maintaining internal temperture in the 130-140 deg F range is more about preserving tire life. There is, of course, some transfer of heat from the tread to the internal but it's a pretty long term proposition.

 

Likely it is safe to say that perhaps 80% of the heat comes from carcass flex and the remainder from transfer from the tread itself. Just about all the components of a tire are poor conductors of heat when you stop to look at it, the excpetion possibly being metal belts. Rate of conductive heat transfer being a function of two things, temperature differential and thermal conductivity of the components. In the case of a typical motorcycle tire, both those factors are pretty low so there isn't much interaction.

 

You'd probably be better off talking to a tire engineer about this stuff, I'm just a generalist (knows less and less about more and more till he knows nothing about everything) as opposed to a specialist. (knows more and more about less and less until he knows everthing about nothing)

[Rags]

Some comments from my experience:

 

The 140 degree optimum operating temps for racing tires sounds reasonable. The converse is, Z tires are woodlike when first out in the cool am. They have virtually no traction until they heat up.

 

Running road (high mileage) tires in 100+ temp at high speeds can throw cleats of rubber. I was told they are "low hysterisis". The rubber's tensile strength is compromised

 

Running fast in hot weather requires a tire air top off in the evening when it cools (I don't know where the air goes.)

 

my .02

 

Thanks Ed for the analysis...

[Tschamp]

Inside the radio box of my RT-P it stated 37 front 42 rear.

[ShovelStrokeEd]

Some of us choose to use other numbers, despite what is stated on a sticker. There are all sorts of factors in that decision.

[Ghostdad]

I run 40F, 42R, which is what is recomended on the side of the tires. My thought is that the tire manufacturer is given the best all around recommendation for pressures. ie) a good compromise between tire longevity and traction. Granted you could probably easily go with higher pressures and get better tire life yet.

Just remember you will never have both, maximum tread life and maximum traction. Find what works best with your type of riding and stick with it.

 

Dave

[ShovelStrokeEd]

Dave,

 

Run what you wish, of course, but, a closer look will show that the number on the side of the tire is the maximum recommended cold inflation pressure, designed to allow the tire to run at its maximum load rating. It is far from the best in terms of traction and handling. Since even a big, heavy bike like an RT doesn't often see those loads, you can safely reduce those pressures.

[Ghostdad]

Dave,

 

Run what you wish, of course, but, a closer look will show that the number on the side of the tire is the maximum recommended cold inflation pressure, designed to allow the tire to run at its maximum load rating. It is far from the best in terms of traction and handling. Since even a big, heavy bike like an RT doesn't often see those loads, you can safely reduce those pressures.

 

 

I didn't say that you would get the best traction and handling from the stated pressures.

What I did say was that that is probably the best compromise between tire life and traction.

My belief is that the tire manufacture has done tests with different tire pressures and their recommendation is a good all around number to be at for decent tire life and decent traction/handling. Granted if you dropped the tire pressure a bit you will get better traction/handling but at a cost of tire life... Or higher tire pressure would probably give you better tire life but less traction/handling.

Personnaly 50% of my riding is 2up riding which puts me close to max payload for the bike. So for me running the tire manufacturers (recommended) max pressure is giving me the best compromise between max tire life and and max traction/handling.

I doubt we will ever see a tire capable of providing both outstanding tread life and outstanding traction/handling all at the same tire pressure.

Like I said this is my belief and I'm not trying to start an argument with anyone. It all depends on what you want out of your tires in the long run. I prefer to get as much life out of my tires while still maintaining decent traction/handling.

Dave

[ShovelStrokeEd]

OK, I'll buy that but, please understand that the number on the side of the tire is meant to indicate the MAXIMUM SAFE INFLATION PRESSURE. It is not the recommended pressure for normal running nor is it in any way a comprimise, thus, the word maximum.

 

Likely, you are not at near the maximum load on the tire either so it is no big deal. Rather than just blindly following your belief, why not do a little work and follow my recommendation above. You might just find a better compromise and, in the process, get the bike to stop rattling the hands off your watch.

 

Both my Honda Blackbird and my 1100S were equipped with Metzler ME Z-6 tires at the moment. Honda says 42/42, BMW says 34/36. Both bikes weigh within a few lbs of each other. All the tires have a 42 stamped on their sidewalls. What is a guy to do? At 42/42 the Blackbird's ride is so harsh as to make it uncomfortable to ride for more than 150 miles or so. Switched to 37/39 and it's a whole 'nother bird. When I go twisty strafing, which is all too infrequently these days, tire pressure goes down to 33/33 on both bikes.

 

I really don't much care about tire life. Mine usually square off long before they wear out and once there, the feel in transition into turns pisses me off so much they are gone at the next dealer I get to. Considering that I run between 30K and 40K miles a year, most years, that is at least 4 rears and 3 fronts, although I don't really expect the D208 that replaced my worn to the cords in the center Z6 at 9K miles to last much more than 4K. Next set will be Pilot Roads just to try them.

[ttorborg]

I had been a faithful 40/40 guy until this spring on myR1150RT with ME Z-6's. I store my bike away from my home for the winter at a relatives house. This spring I forgot my tire gauge so instead of pumping up the tires to 40/40 I rode the bike home with the tire pressure that remained after sitting four months. It was like a new bike, It felt better in the corners and was smoother on the flats. The next day I check the pressure and I had 35/35. I will never go back to 40/40 even if running lower pressure shortens my tire life.

[Hulka]

Right now I am running 36 (F) 38 ® and that seems to be great for me. I also noticed I have a lot bigger footprint on the road now compared to before which I think is good. Better for stopping since there is more surface area touching the ground. The bike for me handles well in the turns and well on the straight aways. Wehn I loose some weight I might kick it down a notch but until then this is where I am going to stay! Thanks for the input guys.