Tires Tire size question

Discussion in 'Bicycle Repair' started by Chain theory, Aug 8, 2008.

  1. Chain theory

    Chain theory Member

    I have an old Worksman and according to the parts and spec page on there web site there tires are 26" x 2.125" I just bought a new set of crossroads tires at the bike shop and had them installed. After reading a related thread I thought I'd take another look at them. The ones they put on are 26" x 1.95 Does anyone think this could be a problem:?:
    The tire is supposed to rotate in one specific direction and they have the front one turned the wrong way.
     
    Last edited by a moderator: Dec 15, 2015

  2. HoughMade

    HoughMade Guest

    Can't see it causing a problem on either front. The tires are a but smaller that 2.125s available, but 1.95s will work. As for directional- in wet conditions, maybe an issue- in the dry, don't see an issue.
     
  3. Chain theory

    Chain theory Member

    Thanks HoughMade
     
  4. Mountainman

    Mountainman Active Member

    Chain theory - kind of depends on what you are looking for in regards to your ride. The smaller tire will not take bumps as well. For riding in the dirt as we know - larger tires work better. For straight out speed on roadways - thinner tire is a little faster. You can easily turn your front wheel around so as to have both tires going with the thread in the same direction. Happy Riding from - Mountainman
     
  5. loquin

    loquin Active Member

    And, you should keep in mind... per Sheldon Brown, even with slicks, it is impossible for a bicycle to be moving fast enough to hydroplane. Even downhill. The tires are too narrow, and the resulting pressure (total bike w rider weight divided by the total area of the tire surface in contact with the pavement) too high for it to ever be a problem. Slicks give the best pavement performance, as it puts the most rubber in contact with the pavement. The only reason that bike tire manufacturers even HAVE tread on street tires is because user familiarity with auto tire tread design leads people to assume that bike tire tread is important. For pavement use, it isn't. In fact, for pavement use, the more tread, the poorer the cornering and stopping performance.
     
    Last edited: Aug 8, 2008
  6. Mountainman

    Mountainman Active Member

    slick tires -- rider must be careful - they do slip on slick surfaces more easily. Do we not think that motorcycle companies have not done much testing in regards to tires ? Taking that into account - why do most tires on new motorcycles come with at least some thread ?? Happy Riding from - Mountainman
     
  7. Chain theory

    Chain theory Member

    Thanks allot guys for our input. I guess I will keep them. They were kind of pricey, but at least they look good on the old bike. I had an Honda Passport back in the early 80s. I hit a oil spot in the left hand turn lane and down I went whether I had tread or not. lol
     
  8. loquin

    loquin Active Member

    Because motorcycles are capable of going much faster than bicycles, and their tires have much more surface area in contact with the pavement, tread is needed to channel water out from between the tire and the road surface to reduce hydroplaning.

    Bike tires are very narrow, (resulting in high contact pressure) and the speed is much less. Tread isn't needed for bicycle tires on pavement.

    The aircraft industry has studied hydroplaning a great deal. They've determined that hydroplaning speed depends on tire pressure, and as tire pressure increases, so does the the minimum speed needed to hydroplane. At 40 PSI, the minimum speed needed to hydroplane is 66 miles per hour; at 60 PSI, the minimum hydroplane speed increases to 80 MPH.
    Ref Sheldon Brown's article on tires. Scroll down to the section on tread.

    Also remember that tire rubber deforms under pressure. Any slight irregularity in the road surface is 'pressed into' the tire, providing traction. If you add 'Tread', you are removing rubber that would otherwise be in contact with the road surface. The only time that I could see a tread pattern helping improve traction, would be if you are riding on a snowy road.
     
    Last edited: Aug 11, 2008
  9. Mountainman

    Mountainman Active Member

    Good article on tires - but - I didn't see where any data from testing was done. No doubt Sheldon has a lot of good information posted - just wondering if some of it may be one man's opinion ? I hit a slightly wet spot the other day - front wheel started to slid out and stopped. I have a little thread - just not real sure that a slick would have been better ? Happy Riding from - Mountainman
     
  10. loquin

    loquin Active Member

    IMO, the more rubber in contact with the road, the better. Why would drag racers run slicks if they don't provide better traction?

    A slippery surface is a slippery surface. Tread or no tread. But, having LESS tire surface in contact with the surface reduces the traction on a slippery surface.

    The ONLY reason that auto & motorcycle tires need tread is to channel standing water away from the tire face/road. Auto tires, in particular, need this, because a) they're flat, with a large tire surface in contact with the road, and b) they travel at a high rate of speed. This means that there's a point, at some speed, where the tire can't push all the water out of the way.

    A bike tire has so little surface in contact with the road, that the contact pressure is substantially higher than an auto or motorcycle tire. And, it presents a rounded surface. this, in conjunction with the fact that there's more time (since a bike is slower than a car) to push the water our of the way.

    Wikipedia mentions the formula that Brown referred to. (the actual formula is speed (in knots) equals 8.6 times the square root of the tire pressure in psi) And, they mention
    And, at How Things Work, mention is also made of this.
    Wikipedia also mention that narrow tires, and tires at higher pressures are less succeptable to hydroplaning, and that underinflated auto tires contribute to hydroplaning.

    There are lots of references to hydroplaning and speed. The only factors mentioned to determine hydroplaning speed is tire pressure. If you are approaching the speed at which hydroplaning will occur at your tire pressure, at that point, a tire's tread WILL help you out a bit, by channeling some of the water away. But, it does so by removing rubber that is in contact with the road, and thus reducing traction at all other times.
     
    Last edited: Aug 13, 2008
  11. loquin

    loquin Active Member

    If an auto weighing 3200 pounds, loaded, has 32 psi tire pressure, the area of rubber in contact with the road is 3200 pounds/32 pounds per square inch, or 100 square inches. That is therefore, an average of 25 square inches per tire. If the load weight goes up or down, the tire surface area goes up or down, accordingly.

    An auto tire (assuming a 6 inch wide tire face) with the above assumptions, traveling at 60 miles per hour, is moving at over 1000 inches per second. This means that a point on the tire face is only in contact with the road surface for about 0.004 (4 one-thousands ) second. A slick auto tire would have to push water on the road, up to three inches to get it out of the way. However, if you manufacture groves in the tire, this distance is shortened considerably, which is why this is done in auto tires.

    Now, lets talk about a bicycle. Road bikes are run at high pressure - 100 psi (or more.) For a 170 pound rider, and a 30 pound bike (heavy for a road bike, I know,) that's 200 pounds of weight, divided by 100 pounds per square inch, means that only 2 square inches of rubber in contact with the road, or 1 square inch per tire. Cruisers & mountain bikes, with their fatter tires, are often run at about 50 psi. For the same weight of bike/rider, we're looking at just 2 square inches per tire, in contact with the road surface in this case. Since the bike tire is rounded, you end up with (as one site mentions) a canoe-shaped surface. (it's actually an flattened circle, or ellipse.)

    However, a bicycle tire has a MUCH narrower 'face' in contact with the road than does an auto. A road tire might only have a half inch 'face' in contact with the road, whereas a balloon tire would have an inch or so. And, at 25 miles per hour, while a point on the tire would be in contact with the road for about .005 seconds, the average distance to move water is only a quarter inch for a road bike, and half an inch for a balloon tire. But since the tire surface in contact with the road isn't rectangular (like a car) but 'pointed,' similar to the bow of a ship, the bike tire is able to squeeze the water out from under the tire MUCH more easily. Kind of like an Olympic diver going cleanly into the water, versus me and my belly-flops!

    Sheldon did present the results of the testing. The speed needed to hydroplane is approximately 9 times the square root of the tire pressure (speed in knots, pressure in psi.)
    For miles per hour, multiply knots by 1.151, or, change the constant from 9 to 10.35
     
    Last edited: Aug 14, 2008
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