Contact patch size probably depends mainly on pressure, not tire size. Contact patch shape is what changes when you change tire size. If there's 450 pounds on a tire with 45psi (pounds per square inch), it's going to have 10 square inches of contact patch. On a ten inch wide tire, that's a 1 inch long contact patch. On a 5 inch wide tire, it would be 2 inches long. On a 2 inch wide tire it would be 5 inches long.

Assuming the same pressure and a significantly larger tire, rolling resistance is reduced significantly. Oversizing while keeping the same inflation is effectively overinflating.

my valkyrie holds 5.3 gallons, but 1.14 gallons is reserve.I fill up as soon as possible when I hit reserve, I switch to reserve between 180 and 200 miles , usually takes 4 gallons to top off. mpg drops a couple of miles when carrying a passenger. I came to this site to get some info, I am grateful for that info by the way, but I am tired of having to defend my mods and my ride, and having my honesty questioned, so I am out of here.

By pressure, do you mean the weight that the tire carries?

2-up on a 700+ lb. moto with 205 60 16 car tire vs 180 70 16 standard Valkyrie rear tire.. which do you think might have larger contact patch?

I'm sorry you feel that way, there are many here hypermiling with non-conventional vehicles not known for mileage. For example, my primary vehicle is a V-8 4x4 pickup truck that I can get the EPA highway rating driving in city traffic. Holy Cow also has a 4wd pickup that he hypermiles with as well. Phillip hypermiles with a stationwagon. This is a great site for information on hypermiling with vehicles that people don't usually hypermile. Other sites generally have the attitude that if you're not hypermiling a Prius or a Geo Metro then you're wasting their time.

-Jay

No. "Pressure" in a tire discussion is always about tire inflation pressure, the pressure of the air inside the tire. That's why I was talking about overinflation and such.

Tell me the weight on the tire and the pressure in the tire, I'll tell you the contact patch. I don't need to know the tire size.

Let's say 400 pounds of those 700 are on the tire, and there's 30psi in it...there would be a 13.3 square inch contact patch. The 205-60-16 is 8 inches wide so the contact patch will be 8 inches wide by 1.66 inches long. The 180-70-16 tire is 7 inches wide so the contact patch will be 7 inches wide by 1.9 inches long.

I assume that a motorcycle tire is generally rounder in profile than the square-shaped profile of a car tire, which would mean that the motorcycle tire may not effectively be as wide; I'd guess that the width measurement is at the sidewall, not where the tread meets the road. The motorcycle tire will have to do a lot more flexing and deforming to make that contact patch, which would increase rolling resistance. OTOH, the motorcycle tire is probably a fraction of the thickness of the car tire, so that would probably reduce rolling resistance.

My estimate: Valkyrie 700-720 lb., rider 200-220 lb., passenger 160-180 lb., total approx. 1060-1120 lb. 36 psi in tire. What's the contact patch size?

All that weight is on one tire? I would expect the front tire to carry some of the weight too.

1060-1120lb at 36psi is 30-31 square inches.

You didn't specify the front and rear weight ratio..

Contact patch is 30-31 square inches for all sizes of tires?

I asked how much weight was on the tire, not how much weight was on both tires.

Given the weight (on that single tire) and the inflation pressures I worked with, yes. The math is pretty simple. You have pounds, and you have PSI (Pounds per Square Inch). Divide out the pounds and you're left with square inches.

Different tire rubber/silica/material compound does not effect the contact patch size?