Smooth treadless tyre to maximise roller contact

Discussion in 'Friction Drive' started by mifletz, Sep 6, 2009.

  1. mifletz

    mifletz Member

    I have 26x2.00 knobbly mountain tyres.

    Is it OK to change just the rear tyre to a totally smooth treadless 26x1.25 to maximise the contact of the roller on a Subaru Robin engine? Would there be a balance problem?

    Or does the front tyre have to be changed as well?

    What is the grip of a treadless tyre like on a normal lightly rain-wetted road? rain?

  2. wheelbender6

    wheelbender6 Well-Known Member

    You can change only the rear tire to a slick or city tire, which has a street tread.

    It should provide longer tire life. Even the cruiser tires at Walmart work well.

    I use a city tire because I do occasionally ride on the dirt shoulder or canal banks.

    I have read that a stock motorized bike will not go fast enough to hydroplane with a slick, treadless tire, assuming that you cruise around 20mph.
  3. loquin

    loquin Active Member

    The FAA has done a lot of research into hydroplaning. The only factor entering into hydroplane speeds with smooth tires is the tire pressure. As tire pressure decreases, the amount of surface area needed to support the weight increases (increased surface area with the same weight supported means decreased PSI.) The pounds per square inch supported by the tire must be equal to the tire pressure PSI. When the pressure decreases, the speed which can cause the tire to lose contact with the pavement (hydroplane) also is reduced.

    At 40 PSI tire pressure, the minimum speed needed to hydroplane is 66 miles per hour; at 60 PSI, the minimum hydroplane speed increases to 80 MPH.

    To hydroplane at 30 MPH, the tire pressure would have to be around 10 psi...

    You could keep the knobby tires on the front, they give poorer performance on asphalt, though, and can cause loss of grip when cornering on asphalt, as the knobs can deform under side-to-side load. It would be safer to put a similar tire on the front as the rear.

    The tire rubber deforms at the points where small irregularities in the road surface are present. Small road surface bumps stick up 'in to" the tire, and the tire protrudes down into tiny holes in the asphalt surface. If you have tread, it represents a non-load-bearing part of the tire, and it is NOT in contact with the asphalt. Unless a protrusion in the asphalt is exactly the same size as the width of the tread, there won't be as much traction as a slick tire.

    In addition, for smooth surfaces, there are two types of surface-to-surface friction - static friction and kinetic friction. (In automotive terms, static friction is another term for traction, kinetic friction is traction in a skid.) For a given downward force on one of the surfaces, BOTH types of friction depend on two factors - the coefficient of friction, and the amount of surface area. The friction coefficient is constant for given surface materials, so the only factor which can increase friction is the surface area. There are two ways to increase surface area contacting the asphalt with a tire: decrease the tire pressure, or, remove any tread.

    So, for a bicycle on asphalt, adding tire tread decreases the tire's traction, and it has zero effect on hydroplaning. Even on ice, or oily surfaces, or railroad tracks, adding tread reduces traction. About the only place where it may help is with snow on asphalt.
    Last edited: Sep 8, 2009