Tire Pressure

[manuel.yanes]

I've heard that some racers will lower the tire pressure that is indicated on the side walls by the manufacturer, to compensate the increase of tire pressure, due to heat, while on the track and racing.

 

Is this correct, or is it a myth?

 

What is the proper procedure?

 

Or, should one follow, tire pressure indicated on the side walls by the manufacturer?

 

As a suggestion, if they use nitrogen, this gas, will maintain constant pressure, regardless of temperature.

 

Thanks, Keith, for your reply and time in this issue.

 

Manny

[Grounded]

Manuel-

Don't know the practices of racers concerning tire pressure settings. However, about your suggestion concerning nitrogen, air consists mostly of nitrogen (over 70%). Pure nitrogen expands and contracts very much like air with temperature. So pure nitrogen will not maintain a constant pressure in a tire regardless of temperature.

[stuman]

If your talking about tires used at the track, the best thing to do is ask the tire vendor at the track for a recomendation. They will know what is best for their brand of tires.

 

For the street go with the recomendations in your bike's owner's manual.

 

On the track most guys do run much lower presures, something like 31/29 f/r is common.

[Rifleman]

I think the sidewall states the recommended tire pressure when the tire is cold. The manufacture takes into account the pressure increase as the tires warm up. A lower pressure might give you a slightly bigger foot print but would cause more heat as the rubber bends and moves more.

 

All gasses have a thermal expantion coefficien. Oxygen, Nitrogen, and air (80% nitrogen 20% oxygen) are all about the same. The lowest TEC for something you might be able to lay your hands on is Argon gas. Argon gas is also three times as dense. We're splitting hairs at this point though.

[Autobahn]

The main improvement in using bottled gas is dryness. Race teams can buy air dryers from stock car retailers. Like a dehumidifier with a built-in compressor. Less humidity equals less expansion with increase in temperature. Stock car teams also use tire valve caps that can be preset to bleed off excess pressure. The caps must be removed and cleaned after each race, so its not much good on the street.

 

My 2004 Triumph Daytona came with Pirelli Corsas. They felt mushy at 30psi cold (street), but grip felt much more predictable at max lean angle at 40psi cold (street), which was still below max pressure marked on the tire. I don't know if these Pirelli have a certain "pointy" profile that requires more pressure to work, or if more pressure just makes all tires more pointy and thus more grippy at max angle. I did not take any tire temps or hot pressures. Maybe more pressure just added a needed "spring" rate to a too-soft suspension?

 

I've been riding 35 years and I'm still learning that I can't ride worth #$%&. At least I got on Speed TV this weekend, as a "wanker".

 

>>>"That's it for this week. Thanks for watching Corbin's Ride On... you wankers!"

?Brian Jackson, host of Corbin's Ride On, Tapaco Lodge, Deals Gap, NC, Triumph Dragon RatRaid, September 25, 2004

http://www.rideontv.com/episodeinfo.html

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