Wednesday, May 20, 2009

Tire Pressure - The Ups And Downs

The owner’s manual says 36 PSI. The tire says 41 PSI. Which is correct? Ask ten different people; you’ll get twelve different opinions. Ask me, I’ll give you a thirteenth opinion. Before we can answer this question we need to go back to the beginning. When Gork first invented the tire his only concern was moving Brontosaurs steaks around. He could easily lower the tire pressure with the use of a hammer and chisel. Increasing the pressure usually meant a new tire. In that respect, Gork was a lot like us, the tire pressure keeps going lower and lower without much attention. Many years later, one of his ancestors invented the air compressor, which is now the preferred method of adjusting tire pressure. But hey, if the hammer and chisel method works for you…

So, that still leaves the question of which is right. The book or the tire? In all honesty, I don’t know. This seems to be matter of personal preference and opinion. Ride and handling characteristics vary tire-to-tire, bike-to-bike and rider-to-rider. Weather, ambient air temperature and extreme changes in altitude can also affect tire pressure. Years ago most bike tires were pretty much the same, so you used whatever you could find cheap. Today, with the weight, horsepower and stopping ability of modern bikes, tires take on a life of their own, and quite possibly your life. When deciding on replacement tires you will always be safe going with the tires the bike manufacture recommends. Although that can be expensive, as there are many choices today. But you be the judge of what you spend your money on.

Over the past thirty some odd years, I’ve ran tires both ways; by the book and by the max pressure sidewall spec. I’ve noticed no difference in wear either way. I have noticed improvement in handling with the higher pressure. It might be all in my head, but then there’s some strange stuff floating around in there.

The reason I started to run higher pressures was a study I read a few years back. Yea, I know. Studies can be pretty darn skewed to suit your agenda. For every study I find for my side, you can find two studies for your side. I don’t recall the who, when and where the study was conducted, but I do remember the content. The study, and actual on road tests were conducted by a group of riders that I consider some of the best riders you’ll find on the road. Motor Officers. Guys that will weave in and out of 80 MPH traffic and make it look like second nature. I admire the job they do, and I would rather have them in front of me. Don't like them in my mirror.
All of the tests were done with street tires on dry roadway. No off-road or racing tires. Those are a whole different animal. They used several brands of tires, all of identical size, ply construction, speed and load ratings. There was no noticeable difference in stopping distance or control during normal riding. What made me try the higher pressure were the two following results: 1) There was a decrease in the occurrence of high-speed wobble, or “death-wobble” as I prefer to call it. 2) There was a “very noticeable” increase in control while executing high-speed turns and tight maneuvers. The reason given was the extra stiffness of the sidewalls, under the higher pressure, caused the sidewalls to resist rolling side to side. I’m not advocating one pressure setting over the other. I am saying that I run the higher pressure because I feel it gives me better control. Sometimes just the perception in your mind that you have a slight advantage is all it takes to avoid a very bad situation. But as with all things motorcycle, my final words are always “Let those who ride decide”.

20 comments:

chessie said...

Excellent thoughts you've posted here. I'm one of those idiots who just climb on and ride. I rarely think to check my tire pressures...Once I rode Angels Canyon Road into LA...about 50 miles. When I got to work at Harley Davidson of Glendale... someone said to me... "You know your rear tire is flat?"

No...I didn't...but I wondered why it felt so sluggish in the curves.
Thanks for reminding me to check my tires....

Mastercheif said...

Sorry, I don't know much about Dunlops other than the one around my waste. Sounds cool though. I'm going to check my tire pressure tomorrow.

Big Daddy said...

I use the upper scale myself and agree about the benefits you mentioned.
However ..I gotta say I'm shocked at the comments you have already got.
It takes two minutes to check your pressure and it WILL save your life and those around you riding.
Screw horsepower, Helmets and leather....Brakes steering and properly inflated tires are the most important thing a rider should attend too.

Ann said...

I make Big D check the tires on my car all the time. I suppose he'll make me do it when I start riding my own, though. :)

Dean "D-Day" said...

I tend to run mine at the higher end. I also feel that it gives me better response.

Also, I have become a regular pressure checker. I never use to give it much thought. But blowing a front tire going 65 mph in a torrential downpour has made me pay more attention to my rubber.

FLHX_Dave said...

Long runs in dry weather I run over. Wet weather I run under. Everything else I run normal.

I guess it works. I have 12,000 miles on my rear dunlop so far. It's got another 500 left or so.

Wanna save a bunch of money by switching to Geico? Nahhhh...I'll just make sure my treads are pumped to spec.

FLHX_Dave said...

Oh yeah...my front tire has 22,000 on it. I figure I have another 5k left on it.

Mr. Motorcycle said...

My mechanic tells me 41 psi, so that's what I run with. It works for me.

Willy D said...

chessie: I must say that I’m surprised at that story. You deserve a good tongue-lashing;} Checking tire pressure is easier than paying hospital bills.

Mastercheif: Do it today. Don’t wait till tomorrow tomorrow tomorrow…

Big D: I hear ya, but I can’t say I’m shocked. I see low tires all the time. I’ll check my tires before I’ll check the oil. I can run just fine a little low on oil, but I can damn sure tell the difference between 5 PSI in the tires. Crashing sucks. Stupidity is avoidable.

Ann: You “make” him check your tires? Or, could it be that he checks them because he feels that it is an honor to serve such a fine woman as you? ;)

“D-Day”: A blowout at 65 in the rain? That had to suck. As far as your rubber goes, that’s none of my business :]

Dave: That’s pretty good mileage. But I will caution you that dropping the pressure to low is baddd. It can cause the center of the tread to become concave and not contact the road at high speeds.

Willy D said...

Mr.M: 41 is the upper PSI on most bike tires. That’s where I run. It works just fine for me also.

Ann said...

Willy D: No, I actually have to beg him to do it. But thanks for the nice thought. :)

Baron's Life said...

I like the higher end pressure myself and do ride at 41 or 42 PSI..It gives me better perfomance both on handling and mileage...but the danger however is a as you ride longer and faster, the tires first warm up, then heat up and there is no more room for the air to expand in the tires and that's where you risk a tire blow-up with some catastrophic results...so PREACHER you need to be careful what advice you dish out...

Willy D said...

Baron: First, I would ask why you ride at higher pressures if you think it will cause a blowout. Second, anything I write is only my opinion. Anyone is free to agree or disagree with it. As for preaching, I believe the final words were “ let those who ride decide”.

kathy said...

My bike always reminds me when I've forgotten to check the tire pressure. It's amazing the difference a couple of pounds makes in handling. For the daily commute, I check the pressure once a week. For longer weekend rides, I check it before leaving. I have a small compressor powered by my car auxiliary port that comes in very handy for the job and I keep a tire gauge in my windshield pouch so I always know where it is.

Biker Betty said...

It's interesting that you have blogged about this. A month ago I was asking the same question and getting conflicting answers. Most people were telling me to go with the recommendation of the bike, as it takes into account the weight of the bike on the tires.

It's like which came first.. The chicken or the egg? No one knows, lol.

Willy D said...

kathy: Wow! A bike that talks! I can hear it now: “I’m handling like crap, check my tires”. All vehicles “talk”. We just have to learn to “listen”.

Biker Betty: The chicken or the egg? Maybe it was the rooster. My advice, pick your favorite twisty road and ride it at both pressures. Same speed same weather conditions. If it just “feels “ better one way… Well, you be the judge.

fasthair said...
This comment has been removed by the author.
fasthair said...

I'll add my two cents here. As mentioned weight is also a factor. If you are going to be riding two up with lots of stuff (face it if your riding two up number two SHOULD be a female and they always have to bring lots of stuff) Then max out the pressure. If you read your owners manual (yah I know how does that?) it will even state this.

And Mr. Baron with all due respect you got the logic wrong. As you might know I work on Mercedes-Benz for a living. During service of these fine high performance machines I always check and set tire pressures. Each model has different settings. How do I remember all of these settings? I don't, I look in the gas door. Guess what? I quote, "for driving 100+ mph + 4PSI, for warm tires add + 4PSI."

Here is why your logic is wrong. The extra pressure actually helps the tire hold it's shape and NOT expand as much as if it had lower pressure. Just as someone else said, lower tire pressure will also affect the contact patch of the tire, i.e. the shape. Now before you say "but drag slicks only have about 5 to 6PSI" remember this, these tires are designed to run at these pressures. Plus have you seen how that tire looks at speed? The back side (in direction of travel) is almost flat against the wheel and it has grown several inches in size. This is all the effect of low tire pressures. There is also this. Lower pressures cause higher tire temperatures too. Why? Friction. This why properly inflated tires give you better gas mileage, less friction. Less friction equals less heat. A under inflated tire will actually fail sooner (Ford Explore anyone?) then an over inflated tire because of high heat. Which all add up to long tire life. So in the end, for high speed riding, max it out.

So after saying all of this can you guess where I run my tires? Yup, maxed out, 45 rear 42 front. For all of the reasons above but also because the bike does handle better and it does promote longer tire life.

Last thing for you others who don't check your tires. For the love of God please do! Not only will it be safer for you but you will save money!

fasthair

Baron's Life said...

I ride at the high end because of the ride comfort and the fuel economy, but have been always wondering what if...than you and Fasthair for clarrifyng this for me.

Road Captain said...

I like what Big D said.