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Tire Pressure?

Discussion in 'MX/SX General' started by nitrofc, Oct 3, 2015.

  1. nitrofc

    nitrofc PR Addict

    Hey everyone! I haven't been on Pitracer for a couple of years (life gets busy, right?) but am starting to ride again (2009 YZ450). This brings up my question....... what tire pressure should I be running and should it change based off of....?
    -Tire sizes (120 vs 110 rear, etc)?
    -Track conditions (hardpack/deep ruts/mud)
    -Outside temperature
    -Should the front and rear be the same pressure?

    Any advice is appreciated!!!!!
     
    GeorgiePorgie likes this.
  2. grantsdad25

    grantsdad25 PR Member

    Location:
    Austintown, Ohio
    Setting the correct tire pressure is probably one of the most overlooked—not to mention cheapest and easiest—maintenance tasks you can do to improve your bike's handling. It just takes a few minutes to check and adjust your tire pressure, and with a little bit of know-how from Dunlop's technical guru, Brian Fleck, you'll be armed and ready to keep the pressure set next time you go riding.

    Here are some common tire pressure questions we have received from TWMX readers, along with Brian's responses:

    1. How important is it to check/set the correct tire pressure?

    The tires not only provide traction, they are also part of the suspension of the bike. It is very important to check for proper inflation before every ride. It is best to check pressures when tires are cold.

    2. Should the front and rear always be set to the same pressure?

    No, there are normally small differences we suggest on front and rear pressure. A good baseline pressure for each is 12 psi in the front, and 13 psi in the rear. That will work in most conditions.

    3. If the area we're riding in goes through big temperature changes, how often throughout the day should tire pressure be checked?

    Air expands when it gets hotter. Think of a hot air balloon. The pressure goes up as the tire is run and gets hotter, or if the tire is sitting in the hot sun.

    If the tire is sitting for a while after have ridden, you should check the pressure, and if necessary, set it back to the safe margins of 12 psi front and 13 psi rear. If the bike sits for a few hours or temperature drops significantly it should be set again. This is especially important when racing at night, when it is warm in the day and then cools at night during the heats/main events. The temperature can drop by as much as 20 degrees at times.

    4. What pressures do you recommend for common racing conditions, such as hard pack, sand, loamy dirt, etc?

    Here's a quick general guideline:

    • Hard pack: 11.5 psi front, 11 psi rear. This would be for normal supercross-type conditions with no rocks or large square edged bumps.
    • Intermediate: 12 psi front, 13 psi rear.
    • Sand/Mud: 12 psi front, 10 psi rear. The lower pressure will help get a bite in the sand and slippery wet conditions. If it is rocky and muddy we would not suggest 10 psi in the rear.
    5. Do these recommendations apply to motocross tracks and trail riding, or would they differ?

    Motocross is a more controlled environment. It is easier to run lower pressures when there are clearly no rocks or large square edged bumps. For off road we normally suggest a little higher pressure to reduce the chance of a flat.

    For off road or trail riding suggested pressure would be 13 psi front, and 13.5-14 psi rear. If it is high speed desert terrain with many rocks we would use up to 18 psi on the rear.

    Thanks for the tips, Brian!

    Having the right rubber on your bike for the dirt conditions is crucial to good performance, but you can sabotage even the sharpest new knobs by having the wrong air pressure.

    What is the correct pressure? Read on.

    NUMBER ONE: HOW MUCH PRESSURE SHOULD I START WITH?

    Typically, 12 psi front and 12 psi rear. Except in extreme conditions, a two pound adjustment up or down is the range you should stay within (from 10 to 14 psi).

    NUMBER TWO: CAN ONE POUND MAKE A DIFFERENCE?

    A one pound change in tire pressure is almost a 10 percent adjustment. The change in casing stiffness, knob footprint and the overall effect on traction is, however, exponential. Tire pressure is so sensitive that the factories adjust in quarter-pound increments.

    When you first make a pressure adjustment, stick to a one psi increase or decrease. If necessary, fine tune from there in 1/2 psi and even 1/4 psi increments.

    NUMBER THREE: DOES RIDING A BIKE HEAT UP THE TIRE?

    Whenever the tire is spinning, the rubber gets hot because of friction. But that's not the only cause of tire heat. Sidewall flex and casing deformation also increase the temperature of a tire.

    Tire pressure increases more in the rear tire than the front, more on a hot day than on a cold day and on hard-packed track more than in loam.

    During the first three laps, tire friction will raise tire pressure by as much as six pounds (and the front by as much as three).

    The simplest solution to heat build up is to go to the starting line with less than optimum tire pressure. Start with 10 psi in the rear tire. That way the tire will top off at approximately 14 psi by lap three.

    NUMBER FOUR: ARE FRONT TIRES MORE SUSCEPTIBLE TO FLATTING?

    Yes. The front tire has a smaller cavity with less air volume. With the same pressure front and rear, it takes a lot less of an impact to hammer the front tire into the rim and pinch flat it.

    NUMBER FIVE HOW CAN I TELL IF I HAVE TOO MUCH TIRE PRESSURE?

    Lack of grip and excessive wheelspin are the most obvious indications of too much pressure. If the pressure is too high, there won't be any "rim clean."

    NUMBER SIX: WHAT IS RIM CLEAN?

    Rim clean is a phrase that refers to the sidewalls' tendency to roll over the edge of the rim. A properly inflated tire will flex around the sidewalls and actually scrape the very top of the rim edge clean. If you don't see a shiny strip of polished aluminum around the top edge of the rim, you have too much air pressure.

    NUMBER SEVEN: HOW CAN I TELL IF I DON'T HAVE ENOUGH TIRE PRESSURE?

    The bike will wallow through the bumps. Similar to too much pressure, a soft front tire also won't stick in the turns. But instead of being too hard and sliding, the front goes away because the sidewalls are too flimsy and the tire is rolling over off the edge of the rim. If there is more than a 4mm swipe of "rim clean," you don't have enough air pressure.

    NUMBER EIGHT: WHAT TIRE PRESSURE IS BEST FOR MUD?

    If mud conditions reduce track speeds, a rider should reduce tire pressure down to 10 psi or lower in the back. If the mud isn't very deep and the speeds are still high, stick with your standard air pressure. If the mud is so tacky that you're fighting to keep the front end down, you might actually add air pressure to help the tire break loose easier.

    NUMBER NINE: WHAT DO I DO ON ROCKY TRACKS?

    Raise tire pressure on rocky tracks.

    NUMBER TEN: WHAT ABOUT FOUR-STROKES?

    Four-strokes transfer weight differently from two-strokes and tend to smash through more than skim over obstacles. This characteristic puts more of a load on the front tire than it does on the back. Where the standard pressure is 12 psi on a two-stroke, you should start with 14 psi in the front of your YZ-F or CRF. The rear tire can stay at 12 psi (but you might want to consider one of the new stiff sidewall four-stroke tires).
     
    loneranger171 likes this.
  3. TwentyThreeMX

    TwentyThreeMX PR Founding Father

    Location:
    chesterland, oh
    im sure that info above may be helpful but ill give you a short version, i run anywhere from 12.5-14 depending on conditions. start somewhere in there and see how you like it. I'm typically right around 13.5 90% of the time.
     
  4. Meister

    Meister PR Founding Father

    Racing Number:
    649
    13 anywhere.. Less and I get flats easily.. More, traction suffers..
     
  5. GeorgiePorgie

    GeorgiePorgie PR Founding Father

    Location:
    Ohio the 440
    Racing Number:
    740
    Rear: 9 lbs in the mud. 12 in the dry. 10 in the sand.

    Front: 11 lbs in the mud, 13 in the dry 12 in the sand.

    But I'm also 160lb.
     
  6. grantsdad25

    grantsdad25 PR Member

    Location:
    Austintown, Ohio
    Yep and almost every factory tire rep I have spoke to are right there +/- 1/2 pound depending on tire size/brand.
     
  7. hershey

    hershey PR Elite

    Location:
    Ozone Layer
    Racing Number:
    01
    The most important way to set your pressure for a baseline in normal conditions is the "rim scrape " he talked about. You want 3mm clean on the top edge. This ensures the proper pressure for your weight, tire compound and front to rear weight bias. From there you can adjust for conditions. I run 11.5 to 12 front and rear to get that. 20151004_092442.jpg

    This is 12lbs in the front in muddy conditions

    20151004_092508.jpg

    And 11lbs in the rear. For muddy conditions this is perfect rim scrapping. Shoot for something close to this and you will be good. Also this is on my yz125, I haven't noticed much difference between my 2 stroke and 4 stroke like the information Grantsdad provided. The best way is trial and error, figure out what's best for you.
     
    GeorgiePorgie likes this.
  8. MX099

    MX099 PR Addict

    Location:
    Oil City, PA
    Racing Number:
    7
    On a 450 in non slime wet conditions I've switched to a MX52 110/90-19 with 14-15 psi to get through the soft stuff and into the hard ground for bit. The rest of the time I run a MX32 120/80-19 with 13.5 psi.
     

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