No....not true, unless racing. The difference in PSI change in street driving is minimal compared to the track, but it's not that critical, if the tire is set correctly when it's cold.

However, resting tires lose PSI as temps cool, which is why it's important to check them often.

If it's 70* and sunny one day, and 55* and overcast another, the tire inflation can vary, due to water molecules contracting inside the tire, lessening pressure.

 

Thanks Dave. It is true that pressure should be checked when the tire is not still hot off the road?

 

You can check tire pressure off the road, if you know what your tires are at, when they're hot.

My race tires were a 15% gain. I knew that at full temps and cold, what they should read. You as a street rider can do the same thing.

Check your tires cold, then ride 10 miles and check them hot. In a straight line, you'll see very little gain in PSI since straight line riding doesn't generate that much heat.

In the summer, (80* +) you'll see a varied gain, due to radiant heat from the road and direct exposure to the sun's rays.

Personally, I set mine cold, according to the tire's recommended PSI, and that's it. Most people will tell you to go by the Motorcycle's MFG decal, but tires vary with construction and brand, as do their required PSIs.

Of course, always adjsut for a passenger.

 

...Most people will tell you to go by the Motorcycle's MFG decal, but tires vary with construction and brand, as do their required PSIs...

So then, what guide do you use to determine PSI? (Is that a dumb question, veiled to me only by my ignorance?)

 

check em when they are cold before you ride...

 

I go by the recommendations printed on the tire.

If it says: Max Inflation, 40 psi, I know that HD recommends 38-40 depending on load, so I adjust accordingly.

My reasoning for this was due to racing tires getting one setting, yet the bike sticker calls for a completely different one, because it was designed for street use.

Regardless, I always use the tire's recommendations, not a generic sticker on the bike's frame.

 

I have Metzlers, they both inflate to 41 psi...good rule of thumb..around 40 on the barrel head...

 

I ran 40 psi on my front(e-glide)tire and found it too hard.I'll prolly just stick to 30-35 upfront and 35 in rear.(wifey hopps on alot) I'm runnin stockers still untill they get down to the w/bars. The DUNFLOPS say 40 psi. cold.

 

sounds good, keep em inflated...Dunlops aren't real forgiving if they are low...tend to blow out sidewalls...

 

How much do you adjust the tire pressure from listed on the tire for two up riding?

 

If the tire says max 42 psi, then no more.

Most tires for HDs are max 40-42 psi, and that's the range for 2 riders.

Honestly.....I set my rear tire at 40, and front (21") at 38 and never adjust them, 2 up or not.

Not sure if that's the best idea, but it's rare I ride a passenger, and 2 pounds of air pressure for a street bike can be the difference between one guage to another.

 

O.k i'll do another test and pay more attention to the suspension with the f/@ 40 psi.It just felt like it was skippin over the road cracks more than @ 30-35 (front only). So you say (DAVE)that you feel it's best to run the max.psi cold . indicated on the tire ?front and rear.

 

If a tire says max 42 psi, then run 38 cold and try it. If it feels good, go another 2 lbs. Find YOUR good handling range.

A tire WILL skip over the road more if the forks are under-inflated. It's like running a bad shock absorber.

The bike's sticker recommends a pressure for OEM (Dunlop) tires. My point of reading the tire, is because if you run non-OEM tires, that sticker is worthless.

The sticker doesn't know what brand tire you're running....

I generally run a tad less in the front then the rear.

40 rear, 38 front. That's me........ I know guys that run 25 rear due to tons of HP and slippage if fully inflated and 35 front.

The point is to set YOUR tires and suspension CORRECTLY, then variate it from there, to suit.

 

Good discussion gentlemen. :Thanks

 

very good discussion.. and do what dave does.. go by the tire.. and i check them before i ride .. if its been a while between .. or if the weather has changed drastically since i rode last ..

 

I run my rear softer for traction and to cushion the hardtail to it works great.the front is 12" over so i run a little low for traction as well and the front dont bounce like a ball.tire pressure is key.

 

Check em all the time!

 

Check them a lot especially after getting new tires!

The oxygen seeps out of them leaving the nitrogen...and with air being 78% nitrogen and around 21% oxygen...you need to top them up a few times to get up to the full nitrogen content. Once that is reached there is usually very little loss of tire presssure unless there is something wrong.

Guess thats why some places use nitrogen to fill tires! :thumb

 

The oxygen seeps out of them leaving the nitrogen...and with air being 78% nitrogen and around 21% oxygen...you need to top them up a few times to get up to the full nitrogen content. Once that is reached there is usually very little loss of tire presssure unless there is something wrong.

Guess thats why some places use nitrogen to fill tires! :thumb

Nitrogen still seeps from tires, only at 1 lbs per 3 months, rather then 1 lbs per month like pump air does.

The reason nitrogen is uses is because it lacks the high moisture content, and moisture expands with heat, fluctuating tire pressure.

A tire filled with nitrogen is within 1-2 lbs presssure hot, as it is cold, due to the lack of moisture molecules that expand and contract with the heat, changing pressure.

This is the reason it's uses in racing. A motorcycle/car can go out on cold tires at 28psi, run 10 laps and come back in and still be at 30-31 psi. Unlike with regular air, where there's almost a 15-20% change in pressure due to expanded moisture molecules.

I ran it with my race tires because it was less of a hassle to adjust tire psi all the time, and had less fluctuation and I couldn't afford a pit crew to do it for me. To boot, a large bottle in my trailer not only filled tires, but ran air tools, with vertually no moisture, preventing them from failing prematurely too.

and nitrogen is much better on the rubber...:nod:nod

A lot of trucking companies have been using it for years because it lacks the moisture content. Nitrogen keeps rust and corrosion from forming on steel or aluminum rims and tire carcasses last longer for recapping, with less internal damage.

 

and nitrogen is much better on the rubber...:nod:nod

 

Is it because the oxygen molecules are smaller than nitrogen molecules?

I didn't know about the moisture thing...but it makes sense!

My dealer uses nitrogen and I have it in the garage as well...( medical grade...LOL :faint )

 

Is it because the oxygen molecules are smaller than nitrogen molecules?

That's the reason that the air leaves the tire slower, yes.:thumb

 

They use nitrogen on aircraft tires and landing gear struts also plus they can pump it in at higher pressures....my old man owned an aircraft repair shop, used it all the time...