pros & cons of a 21" front wheel vs. large 16" wheel/ tire

Discussion in 'Some Assembly Required' started by boatpuller, Nov 21, 2012.

  1. kellymac530

    kellymac530 motorcycle addict

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    Again SB, you are missing the point of the OP. The question was not about HIS bike, just what would work better in a certain condition.

    I have always contended that a 19" front is the best multi use tire for a moderate dual sport bike.

    As to BPs sportster I do not know exactly what he plans for his suspension. If he is doing anything like JTH sportster then a 21" is still the best option.

    I am really curious though if you have ever tried a 19" tire on your CR450F for the desert?

    I am not sure if you noticed the measurements, but that three fifty actually measures narrower than the 21" on your 450f. Maybe be an optical illusion though.

    I just went out to MY garage and measured MY 1965 Yamaha Ym1 rear tire, which is a 3.50-18 and it measure exactly 3-1/2" and so does the more knobbie looking tire that came off of it. And yes I have ridden it in the dirt. I also measured my airhead R80G/S which has a 90/90-21 and it measures almost 3-3/4" wide although optically looks narrower that the smaller diameter on my old yami.

    If this discussion was whether or not the taller sidewall was better in the dez for flats or pinches...different discussion.

    PS: I love old and vintage things so none of this is because I think old is bad....my daily driver is a 1949 Studebaker truck with a V8 conversion....not a small block chevy like most but a 1963 Studebaker V8 conversion that I did myself. It still runs the stock 3 on the tree with OD and the stock 5.56 geared Timkem split center diff. No A/C. No PS. No PW....my current motorcycles are a '96 RT, an '86 G/S, an '83 Honda POS project and a 1965 Yami Ym1 305cc 2 stroke twin...I obviously love old and vintage.
    #41
  2. Haar

    Haar Adventurer

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    Bio: 63 yrs. old, ridin' 49 yrs. Owned many types, styles etc. From '67 Big Bear to Tenere. Not all that many (serious) miles, just for fun and pleasure. Both sons ride (1-- all over the place, now on Tenere). I rode WABDR with him this summer on my DR650. Other son on DR and Seattle son on Tenere. Also have NX650 (21" front). I live in N. Mich., lots of gravel, sand (some deep). For MY riding "pleasure", I first noticed nice tractability on gravel at moderate speed seemed better on the TDM (that I recently purchased) and that urged me to try the Tenere. (btw: sold FJR - not practical for up here). I really ENJOY the Tenere's handling of gravel, washboard, eroded, some light sand and that it seems to be the ideal bike for my old (titanium hipped) ass. I surely do not have the experience of ya'll, but as an avid rider and fairly analytical of my riding, I can see where the argument for a chubby, 19" front may be the ticket for enjoyable handling in somewhat precarious riding environments. Your analyses are duly noted and I only wish I had done the riding that a lot of you were able to do. Different lives, times, demands. Just trying to help, BP.
    #42
  3. boatpuller

    boatpuller Been here awhile

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    Finally got to read some unread motorcycle magazines over the weekend, and found a very interesting editorial in the July issue of Motorcycle Consumer News (a bare-bones no advertising fairly technical motorcycle publication I really enjoy. The editorials tend to be very engineering oriented, and thought-provoking).

    The topic was on gyroscopic effects of motorcycle wheels and tires. The biggest contributor to gyroscopic effects, mathematically, is diameter.

    Could the benefit of a 21" wheel in the dirt be the increased stability provided by the gyroscopic affect of the larger wheel/tire at the slower speeds usually ridden off pavement, especially in conditions that tend to cause slippage or side-loading due to the rough or loose terrain?
    #43
  4. kellymac530

    kellymac530 motorcycle addict

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    I believe that article to be true. No single factor makes something work or not work.
    I do know that when Honda tried the 23" front back in the late 70s early 80s that was the issue, very HEAVY steering feel. An example of too much of a good thing. This I believe is also the reason why a street bike with a 21", like a DS bike has a heavier turn in feel and usually requires a bit more counter steer input to make it turn. Not that it handles much worse per say, just more steering input.

    The diameter of a wheel also effects turn in I think effects it in more than one way. A wheel being round that is smaller in diameter will turn a tighter radius with the same input. That is just my feelings, no scienece behind it that I have, just my own experiences. If you drop a washer and it lands on its edge but leaning on an angle it will roll in a pretty small circle, if you MC wheel on its edge {tire} at about the same angle the circle it will roll is much larger. Add gyro effect and you have a genuine formula for how a bike might handle with a 17", 19", 21" front wheel.
    #44
  5. foxtrapper

    foxtrapper Been here awhile

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    Well, as one who has one of those 23" tired Hondas right now, I can say today that the steering is not heavy on it.
    #45
  6. motu

    motu Loose Pre Unit

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    I've been a gravel road rider all my life, and I used to believe a 21'' was the only way to go....then I realised I didn't believe that at all. This is a bike I rode in the '70's, great in gravel, and got it going the other day...still a good bike in gravel. 3.25x17 front and rear.

    [​IMG]

    Rode this in the '90's, orsome in gravel. 3.50x19 front.

    [​IMG]

    This is my 21st Century gravel road bike. 4.00x18 front and rear.

    [​IMG]

    None of them heavy steering and excellent in gravel. You will notice a theme - Dunlop K70's. It's a lot to do with profile - your modern tyre has a radius, 1/3 will have contact with the road, then the 1/3 on the sides gets used in corners. But in gravel those 2/3d's have stones under them, stopping that central section from getting down to the traction. That's why your bike handles like shit in gravel. The competition trials tyre that those desert racers had on are a similar cross section, and get down and hook up.
    #46
  7. Solo Lobo

    Solo Lobo airhead or nothing

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    Having ridden tons of highway miles on my 21" wheeled G/S and GS I would say that sucking is an overstatement if you are running today's street biased knobbies (ex: TCK80). While the smaller front wheels of the street bikes I have owned are certainly better, the 21" front does not limit my riding.

    I'm not really that slow, but I certainly don't operate well above posted limits any longer.

    If I was going on a long trip and expected to do dirt, I would (and do now) go with the 21".
    #47
  8. tHEtREV

    tHEtREV Captain Awesome

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    Slightly of topic, but aren't speedway bikes using 23 inch front wheels?

    For a bike that is never really going in a straight line on nicely groomed tracks I thought they would benefit from a smaller tyre... :1drink
    #48
  9. PeterW

    PeterW Long timer

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    My experience was that it's mostly diameter and the fact that 21" fronts tend to be narrower. Don't get me wrong, I'm sure there is a gyro effect, but it's rolling over shit rather than climbing and/or sliding sideways that made the biggest difference to feel.

    Overall the bike I have now with a 19" front is faster and more stable on gravel than the lighter 21" dirt bikes I used to ride, well, until the size of the lumps goes up, then it gets unpleasant.

    Pete
    #49