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holstein13's avatar
holstein13
Explorer II
Aug 07, 2015

Don't fight the bulge

At Spartan class this week, I learned a ton of new and interesting things, but one of the most useful is that the bulge in your tires are part of your suspension.

OK, OK, I know that hundreds of you have been saying that your tires are an important part of your suspension, but I've never heard anyone specifically say that the bulge constitutes an important part. Of course this makes perfect sense. After all, did you know that your tire width is measured at the outside of the bulge:



In class, we weighed our coaches on each corner and then looked up the charts to determine the exact PSI to set our tires. Mine was 10 pounds over inflated on the steer tires and 20 pounds over inflated on the tags so I let out air to get them to the proper pressure.

After a four hour drive, I'm happy to report that it made a HUGE difference in ride comfort. The tire and brake instructor explained that the bulge takes the first shocks and the suspension is designed to work with the tire bulge to absorb and react to bumps and vibrations.

If you needed another motivation to weigh your coach, I can only encourage you to do so and set those pressures properly. In addition to a better ride, you'll get better traction and braking as well.
Class A

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  • holstein13's avatar
    holstein13
    Explorer II
    Aug 08, 2015
    valhalla360 wrote:
    Of course the trade off of smooth ride by dropping the pressure is less efficiency. That's why semi tire go up into the 100psi range. They don't care if the driver is comfortable but they do care about the mpg.
    Intuitively, that would make a lot of sense, but I've seen no actually evidence to support this theory: http://www.popularmechanics.com/cars/a940/4199963/

    Our instructor did say that this is not true or if it is true, it's negligible.
  • holstein13's avatar
    holstein13
    Explorer II
    Aug 08, 2015
    rgatijnet1 wrote:
    Of course if you start out with the exact tire pressure needed for the weight supported, you have zero margin for safety as your tires lose air from the small amount of leakage that takes place with every tire.
    Did the class cover how much additional air you should add to protect from running the tire underinflated when you lose a few pounds?
    Yes, we did. The safety air is built into the manufacturers' recommended tire pressures. Furthermore, if you are looking for safety, overfilling your tires makes them less safe because you will get less traction and handling.

    According to Jennard at Triptek (who I also spoke to yesterday) if you are within 10 PSI of your correct pressure, you will be just fine from a safety perspective. Trying to chase 0 PSI variance is impossible.
  • rgatijnet1's avatar
    rgatijnet1
    Explorer III
    Aug 08, 2015
    Of course if you start out with the exact tire pressure needed for the weight supported, you have zero margin for safety as your tires lose air from the small amount of leakage that takes place with every tire.
    Did the class cover how much additional air you should add to protect from running the tire underinflated when you lose a few pounds?
  • valhalla360's avatar
    valhalla360
    Navigator
    Aug 07, 2015
    Thats the whole point behind pneumatic tires. Otherwise we would use solid tires as they would last longer and no risk of a blow out.

    Of course the trade off of smooth ride by dropping the pressure is less efficency. That's why semi tire go up into the 100psi range. They don't care if the driver is comfortable but they do care about the mpg.
  • TucsonJim's avatar
    TucsonJim
    Explorer II
    Aug 07, 2015
    I know I can go to a Cat Scale to get the weight of my rig. But where can I go to get the exact weight on each tire?
  • BB_TX's avatar
    BB_TX
    Nomad
    Aug 07, 2015
    It has been said time and time again on here that the correct pressure for a tire is based on the weight that tire is supporting. But there are still those who air up their tires to the max number stated on the side wall regardless of the weight.
  • WILDEBILL308's avatar
    WILDEBILL308
    Explorer II
    Aug 07, 2015
    Yes good info. Just Remember that that you need to inflate to the heaviest weight on an axel for both sides. Better said if one side calls for 92 lbs. and the other calls for 96 use the 96 for that axil.
    Bill

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