avon roadrider

[John Park]

Well, I have to say it

Put the 4.00 Avon on there and you'll notice a positive difference in the handling

Get more contact patch as well

Contact patch area is function of air pressure, so unless you plan to drop that the contact patch size won't change. A wider tire will flex less in forming that patch area so less heat is produced,and the wear is spread out over a larger area - all potentially beneficial - but all you can generate at say 30 psi is 30 psi.
300 lbs on a 30 psi tire is 10 square inches, wide tire or narrow.

[Steve]

300 lbs on a 30 psi tire is 10 square inches, wide tire or narrow.

Sorry, but my little mind is having trouble wrapping itself around that idea.

There is more than just air holding up the bike, there is at least SOME strength in the carcass of the tire.

Drop your pressure down to 15 psi, I'll just bet that you won't have 20 square inches of rubber on the pavement.

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[posplayr]

Sorry, but my little mind is having trouble wrapping itself around that idea.

There is more than just air holding up the bike, there is at least SOME strength in the carcass of the tire.

Drop your pressure down to 15 psi, I'll just bet that you won't have 20 square inches of rubber on the pavement.

.

Well you may have a point there, but I'm struggling with how a wider tire will not generate a larger contact patch??

[tkent02]

Sorry, but my little mind is having trouble wrapping itself around that idea.

There is more than just air holding up the bike, there is at least SOME strength in the carcass of the tire.

Drop your pressure down to 15 psi, I'll just bet that you won't have 20 square inches of rubber on the pavement.

.

Let all the air out and you have no contact patch at all? That doesn't work for me. Put in 100 PSI and get three times the contact patch? That doesn't work either.

200 PSI and the tires don't even touch the ground, the bike just flies away?

Maybe that's why our airplanes have 220 or so PSI, to help them fly. Funny all this time I fought it was the wings.

[John Park]

Sorry, but my little mind is having trouble wrapping itself around that idea.

There is more than just air holding up the bike, there is at least SOME strength in the carcass of the tire.

Drop your pressure down to 15 psi, I'll just bet that you won't have 20 square inches of rubber on the pavement.

.

There is some casing stiffness factor, BUT, that stiffness will result in heat, so it's a reason why narrow tires have to have so much flexibility built into the tread design. A stiffer tire will have a smaller contact patch at the same pressure; making a tire wider will reduce the degree of casing flex and allow a lower pressure for a given amount of heat, plus it will spread the heat over a larger area of tire. But functionally, casing stiffness is pretty minimal compared to air pressure and the variation between tires rather small.

At 30 psi I don't think you'll find much difference between a wide and a narrow tire; it will be down to the individual design. Yes, an infinitely flexible tire will have the largest contact patch at a given weight/pressure. I used to run between 8 and 15 psi on a 4.00 18 trials tire back when and the thing ended up like a tank track, but the bikes only weighed about 200lbs and went slow.

The sobering calculation is that adding a 150lb passenger over the back wheel which has 400lbs bike and rider rear load to start with should require an increase of 40% pressure. If I'm running 32 psi that means about 44 if I want the same contact patch and flex. Realistically, we usually go for about half that increase and either accept the heat or slow down. This is where a wider rear tire really shines.

Another problem is that air cooling maximizes at about 50 mph; IOW speeding up the airflow is a diminishing returns game. So tire temperatures really soar as you speed up past that.

The problem is that motorcycle tires have to be 'spherical' yet conform to a flat surface so there's inevitable scrub, which is why they wear out at a deplorable rate. Car tires can be made to have pretty minimal scrub. Who ever heard of a $150 car tire that wore out in five to ten thousand miles at legal speeds? So we have half as many tires as a car that wear out about ten times as fast. But ain't it fun?

[Steve]

Well you may have a point there, but I'm struggling with how a wider tire will not generate a larger contact patch??

A wider tire (than the bike is designed for) is designed to be put on a wider rim, as well. If you squeeze it down onto a narrow rim, it will be forced into a tighter radius, which will reduce the contact patch.

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[John Park]

A wider tire (than the bike is designed for) is designed to be put on a wider rim, as well. If you squeeze it down onto a narrow rim, it will be forced into a tighter radius, which will reduce the contact patch.

.

No, it will flex the casing more to reach the same contact patch - with a slight adjustment for casing stiffness.

Let me repeat, a wider tire does not have a larger contact patch. It will have a more gentle radius and more available surface area, but the amount you are using at any one time is pretty much a function of air pressure, unless you've got a really stiff, kludgy casing. In general, you can run a wider tire at a lower pressure and - bingo - larger contact patch. A wider - read more gentle radius - tire will tend to generate a wider contact patch as the pressure drops; narrow, tight radius adds length faster. For cornering, a wider contact patch is probably more effective but the freedom of design afforded by modern construction to use softer rubber compounds is responsible for most of the traction increase.

Actually, wide tires can be made for narrow rims - see mountain bikes - just by continuing the sidewall further around the circle. But the angle at the bead gets pretty kooky and the 'waddle factor' from lack of lateral support may get out of hand. If you want to get into radial/belted designs, the short sidewall/wide rim is how it is.

If you look at Moto GP and Moto 3 bikes - 1 liter and 250cc respectively - you see the small bikes using a skinny rear but the riders still dragging their elbows and mid corner speeds being almost the same. The fronts aren't that much different as the bikes don't weigh all that much different. But the big motors would shred the skinny rear tire almost immediately. Entering the corners, the back wheel is almost off the road and the front contact patch is doubled; leaving is the opposite with total transfer to the rear. If you're going to transfer all the weight to the back and apply massive hp at major speeds, a 4.00 18 isn't really capable; well, not for long.

[JTGS850GL]

An excerpt from Motorcycle Industry Council Tire Guide and some good reading on motorcycle tires:

http://www.mic.org/downloads/mic_tire_guide_2012v1.pdf

Because a motorcycle is a single-track vehicle and leans as it turns, motorcycle tires are quite different than car tires. Whereas car tires have a fairly flat profile and a contact patch that varies little in size or shape, motorcycle tires have a U-shaped profile and a contact patch that changes size and shape during cornering. Motorcycle tires are also relatively narrow, which makes their gripping capability (“traction”) a limited commodity.

[John Park]

An excerpt from Motorcycle Industry Council Tire Guide and some good reading on motorcycle tires:

http://www.mic.org/downloads/mic_tire_guide_2012v1.pdf

Because a motorcycle is a single-track vehicle and leans as it turns, motorcycle tires are quite different than car tires. Whereas car tires have a fairly flat profile and a contact patch that varies little in size or shape, motorcycle tires have a U-shaped profile and a contact patch that changes size and shape during cornering. Motorcycle tires are also relatively narrow, which makes their gripping capability (“traction”) a limited commodity.

I'd hate to depend upon whatever else this guy wrote. He seems to be under the impression that a motorcycle tire can magically turn the lateral cornering forces about 45 degrees and turn them into downforce. Vector voodoo.

Actually, the contact patch on an outside car tire changes during cornering, but that's from weight transfer from the inside tires. All we got is outside tires.

And traction is always a limited commodity. I hope he knows that….

So I think he's wrong. Did he go on any longer?