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Old 04-22-2014, 06:25 PM   #1
scootrboi OP
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Does wheel size -tire height- influence lean angle?

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.
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Old 04-22-2014, 06:59 PM   #2
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Quote:
Originally Posted by scootrboi View Post
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.

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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Old 04-24-2014, 04:38 AM   #3
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lean angle




The Vespa rider doesn't lean over very far. Why is that?
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Old 04-24-2014, 05:55 AM   #4
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Originally Posted by scootrboi View Post
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.
If you're good with math and physics, you might glean some information from a Bicycle and Motorcycle Dynamics writeup.
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Old 04-24-2014, 05:58 AM   #5
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Quote:
Originally Posted by scootrboi View Post









The Vespa rider doesn't lean over very far. Why is that?
Because he's riding it like a flat tracker.

Could he lean off? Yes.
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Old 04-24-2014, 06:15 AM   #6
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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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Old 04-24-2014, 06:33 AM   #7
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A quick glance through it

Quote:
Originally Posted by popscycle View Post
If you're good with math and physics, you might glean some information from a Bicycle and Motorcycle Dynamics writeup.
Gyroscopic aspect of wheels does not affect tipping. Surprise!
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Old 04-24-2014, 06:39 AM   #8
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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.

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Old 04-24-2014, 06:52 AM   #9
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Originally Posted by klaviator View Post
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.
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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Old 04-24-2014, 07:44 AM   #10
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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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Old 04-24-2014, 01:59 PM   #11
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Quote:
Originally Posted by crofrog View Post
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.
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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Old 04-24-2014, 03:28 PM   #12
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Originally Posted by klaviator View Post
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.

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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Old 04-24-2014, 07:53 PM   #13
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Quote:
Originally Posted by scootrboi View Post

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.
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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Old 04-25-2014, 12:46 AM   #14
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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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Old 04-25-2014, 04:19 AM   #15
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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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