Does wheel size -tire height- influence lean angle?

Discussion in 'The Perfect Line and Other Riding Myths' started by scootrboi, Apr 22, 2014.

  1. scootrboi

    scootrboi Long timer

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    I would like to know more than I do about the changes in handling that occur in relation to the height of the wheels. I am good with geometry and physics.:ear
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  2. Al Goodwin

    Al Goodwin Long timer

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    Smaller diameter wheels more twitchy, quicker turning...like a Vespa,,,SQUIRRLY...

    Larger diameter=more stable.....

    I came from the 80's, and the era of 16in. front wheels...believe me...17's are much better on the sportbikes.

    Now, tire sidewall/profile is another story...depends on the tire manufacturer mote so than size...

    My 1990 FZR1000 Came with Pirelli MP7 tires, the front a 130...very triangulated profile...off handling ....
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  3. scootrboi

    scootrboi Long timer

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    The Vespa rider doesn't lean over very far. Why is that?
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  4. popscycle

    popscycle Fahren Away

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    If you're good with math and physics, you might glean some information from a Bicycle and Motorcycle Dynamics writeup.
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  5. Yossarian™

    Yossarian™ Deputy Cultural Attaché

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    Because he's riding it like a flat tracker.

    Could he lean off? Yes.
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  6. crofrog

    crofrog Long timer

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    It doesn't really effect lean angles. Tire contact patch shape does and that can be influenced by the differences in tire design of different size wheels.

    Smaller wheels have the following traits though:

    • Stiffer
    • Less unsprung mass and steering inertia
    • They have less gyro which allows the use of a wider (and heavier) tire with out undo effort at the bars
    • They drop farther into holes and have higher suspension velocities (and ergo more demand on the suspension) when exiting holes. This produces a rougher ride over uneven ground and reduces the tires contact with the road
    • For a given tire section (tread width) a larger wheel puts more rubber on the road. This is the trade off (smaller wheel needs a bigger tire section to produce same contact patch size, but it ends up being lighter and stiffer overall)

    This list was paraphrased from Motorcycle Handling and Chassis Design: The Art and Science
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  7. scootrboi

    scootrboi Long timer

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    Gyroscopic aspect of wheels does not affect tipping. Surprise!
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  8. klaviator

    klaviator Long timer

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    Size of wheels doesn't affect lean angle for a given speed and curve. However, scooters with small wheels usually have limited cornering clearance which limits how far you can lean before scraping hard parts.

    As far as handling in general, smaller wheels tend to result in easier & quicker reactions to steering inputs. Bigger wheels = slower & more stable steering. Riders who are used to more stable bikes tend to think of small wheel scooters as twitchy and unstable. Personally I like prefer to think of it a quick and responsive.

    I have a scooter with 14" wheels. Fairly large for a small scooter but small compared to a motorcycle. I think the overall handling and steering is fantastic. However, lack of cornering clearance doesn't allow me to take advantage of that fantastic steering & handling on a twisty road.

    [​IMG]
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  9. crofrog

    crofrog Long timer

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    That's only indirectly related to the wheel size though. They could have built the rest of the bike higher or with greater clearance. Of course, then you'd have to have it be narrower (or taller) both of which would mean you couldn't step through like a scooter.
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  10. Rgconner

    Rgconner Long timer

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    Having owned:
    P200 10"
    Vespa GTS250 12"
    75 Honda CB550 18"
    12 BMW F700GS 19"

    The most nimble of the bunch is the P200, not twitchy thanks to a good front end shock. (actually better than on any of the bikes)
    the CB550 is the most stable
    The GTS250 is the most twitchy
    BMW has the most neutral handling, not as stable as the CB550, but not twitchy.
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  11. klaviator

    klaviator Long timer

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    There are other factors besides wheel size but most scooters have a CVT and the engine & drivetrain is all part of the swingarm.This means that the back of the CVT at least is centered on the rear axle and sticking out the side. With a small wheel it is going to compromise clearance on that side. I rode behind a guy riding a Buddy 125 once on a twisty road. His CVT cover was close to touching the ground in every left hand turn. It made me nervous to watch. The buddy has 10" wheels.

    Go to a scooter shop some time and look at how much clearance they have. Generally speaking bigger wheels = more clearance and small wheels = poor clearance.
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  12. scootrboi

    scootrboi Long timer

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    [​IMG] [​IMG] [​IMG]
    Leaning this scooter over till the floor hits is routine for removing wheels. The floor hits first. I can't imagine leaning this far while in motion.
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  13. klaviator

    klaviator Long timer

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    I believe your scooter is different from most modern scooters by not having a CVT or swingarm mounted drivetrain. That makes a big difference.

    Also, keep in mind that if you were on the scooter, suspension would compress and your actual cornering clearance is less than in the pic.
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  14. Pecha72

    Pecha72 Long timer

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    " if you were on the scooter, suspension would compress and your actual cornering clearance is less than in the pic"

    Exactly.

    And furthermore, if you hit some potholes or bumps mid-corner, when leaned over, it all gets even more complicated.
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  15. outlaws justice

    outlaws justice Long timer

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    This is more complicated than that.

    Tire size (Width and height and circumference) are all calculated to provide the bike with certain dynamics and changing the size of a tire will effect the bike in several ways. It can effect the rake and trail of the bike therefor effecting the steering geometry either positive or negative depending on what changes you make and how the bike was designed to handle and which way you make the change. Changing a tire profile can also effect the ground clearance even if it is minimal. Changing the profile can also effect the bike and how it turns in. does it turn in slow and take a lot of effort to steer or is it twitchy and turns in quick. If you have problems you can sometimes change the problem by changing the brand of tire to a tire with a different shape, or changing the size profile of the tire you are using.

    Tire width can impact the size of the contact patch as well. Some people may believe that a wide tire will give you a bigger contact patch, but this is not usually the case either, as you are putting a wider tire on the same width rim and doing so makes the tire bend more to fit the rim and can actually have the reverse effect you might be looking for.

    There is a lot involved when we start talking tires and the effects on the motorcycle, it's geometry and traction. I would be happy to discuss further but we could go on for days.
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  16. lnewqban

    lnewqban Ninjetter

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    [​IMG]

    [​IMG]

    The cross section to diameter ratio of the tire makes the bike lean a little more or less, as well as the height of the combined CG (bike+rider).

    Fat tires + low CG requires higher lean angle for same turn and speed.

    [​IMG]

    [​IMG]
    #16
  17. scootrboi

    scootrboi Long timer

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    Now this is interesting. Particularly since I figured out those are not BMW logos. The phrase 'higher lean angle' seems awkward when it means leaning over more.
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  18. scootrboi

    scootrboi Long timer

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    Thank you for sending this. This is exactly the kind of information I am looking for and can understand. Geometry, physics and diagrams! I am surprised at what it is telling me but it makes sense. This will help me to understand the effects of tire tread profiles and widths and steering effort, and the peculiarities of scooters.
    #18
  19. scootrboi

    scootrboi Long timer

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    A question comes to mind: some scooters with a very low center of mass also have relatively little mass, and a full size human rider. The rider is a large percentage of the mass involved. The motor is small and light. This raises the center of mass significantly. Scooter tires are not very wide either. A motorcycle like a Goldwing or Harley has a lower center of mass than a scooter, I suspect. I wonder how it shuffles out with other motorcycles that are over 600 pounds.
    #19
  20. Rgconner

    Rgconner Long timer

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    Err.. no.

    Unless you are talking about a 70 or 80s Vespa, most modern scooters weigh as much as a bike, with lower center of gravity. The engine is inches off the ground, and you have very short wheelbases. 48 inch wheelbase for my '77 P200, 238 lbs. 8.5 inch ground clearance. Handles like you are on roller skates.

    Some of them weigh more. The BMWs weigh a good 100lbs more than my F700GS, as well as longer wheelbases.
    Those are pretty easy to out turn in the twisties.

    Something in the middle, like a 300cc Jap or Korean bike is 350Lbs, 58 inch wheelbase, 16" wheels usually. They handle like a similar sized bike all told, like a CB360, as there are not many road bikes in the 300cc range anymore.
    #20