Will it fit & work?

[Ken Scourse]

Looking to possibly put a 180/55-18 rear tire on a 2003 GL1800 ABS instead of the standard 180/60-18
Thoughts??

[WINGER3]

Looking to possibly put a 180/55-18 rear tire on a 2003 GL1800 ABS instead of the standard 180/60-18
Thoughts??

Should be no problem as the tire is going to be smaller in diameter but same width, the rear of the bike will be just a fraction lower with the 55 v 60 which is a % of the 180 width.

[joeincalif]

and you speedometer and odometer will be off more than it is now

[GoldWingrGreg]

A smaller tire has less air volume. That means it weight carrying ability is less. Therefore, a smaller tire it not a good idea. The correct size on the rear is already maxed out carrying the weight, and the demands many put on the tire.

[WingAdmin]

A smaller tire has less air volume. That means it weight carrying ability is less. Therefore, a smaller tire it not a good idea. The correct size on the rear is already maxed out carrying the weight, and the demands many put on the tire.

Not really true. You can have a bike tire that is big and fat, and has just as much carrying ability as a tiny skinny tire.

The determining factor is the air pressure, not the air volume. You need the PSI x tire contact patch (in square inches) = weight carried by tire. In this formula:

Weight on tire
------------------
PSI | Contact patch area

So: weight on tire in lbs / PSI = resulting contact patch area.
Weight on tire in lbs / contact patch area = required PSI

If you pump up a tire with high pressure, the resulting contact patch gets smaller.

If you let air out of the tire, the contact patch gets larger. This is why dirt bike riders will run very low PSI, to get the largest possible contact patch, to get the most traction possible.

A smaller tire by virtue of the geometry of the tire outer radius has less available contact patch area. So in order for it to be able to carry the same load, you need higher pressure in the tire. If the tire is rated by the manufacturer for that higher pressure, and you're OK running a smaller contact patch (which means less traction) then a smaller tire will be fine.

But both of those things are a compromise. You'd be better off running a tire of the correct size.

[Andy Cote]

Probably not relevant to OP question but the construction of the tire is a determining factor in establishing the load range. Type of construction as well as number and material of plys.

Regarding OP, You asked for thoughts and opinions. My question is why? Unless I was stuck in the middle of a trip and no correct size available I would probably not make that change as the differences are minimal. Did you have some reason?

[GoldWingrGreg]

Probably not relevant to OP question but the construction of the tire is a determining factor in establishing the load range. Type of construction as well as number and material of plys.

That is true. A tire's weight carrying ability is all about air volume. For a tire, greater air volume is achieved 2 ways. Make the tire larger so that it can carry more air volume at the same pressure, or keep it the same size and increase the pressure. However, to increase the pressure, or increase the load range, the tire must be constructed differently, and that either requires thicker cord, more cord, or a stronger cord. All DOT stamped tires have a max air pressure with a max weight carrying ability stamped on the tire.

[WingAdmin]

Probably not relevant to OP question but the construction of the tire is a determining factor in establishing the load range. Type of construction as well as number and material of plys.

That is true. A tire's weight carrying ability is all about air volume. For a tire, greater air volume is achieved 2 ways. Make the tire larger so that it can carry more air volume at the same pressure, or keep it the same size and increase the pressure. However, to increase the pressure, or increase the load range, the tire must be constructed differently, and that either requires thicker cord, more cord, or a stronger cord. All DOT stamped tires have a max air pressure with a max weight carrying ability stamped on the tire.

We're actually getting picky about terms here, but you're talking about mass, not volume. Volume is the measurement of the interior of the tire. It does not change with the pressure. If you increase the pressure and keep the same interior size (volume), you actually increase the mass of air inside the tire. The more air you cram in it (more mass), the more pressure exerted on the interior of the tire by the air to support the bike.

When talking about load range, the primary issue is heat. The more a tire flexes, the more heat it generates, and it needs to shed that heat (or not flex as much in the first place). It also needs to be able to handle the air pressure inside the tire pushing outward.

Air pressure is actually inertia. The molecules of air are constantly moving around in every direction. When an air molecule hits the inside of the tire, the inertia from the molecule transfers its energy to the tire, pushing out on it. The hotter the air, the faster the molecules move, the more often the molecules hit the tire, the more inertial energy is transferred to the tire wall, and the higher "pressure" is measured.

Anyway, I didn't want to start a discussion on physics, but I love this stuff.

Oh, and BTW...nice new pic, Greg.

[GoldWingrGreg]

In a tire we're referring to a gas and not a liquid or solid. You might have had more college physic then me; however, when studying engineering, in the three I had, we'd use Boyle's law for this. Boyle law has everything to do with volume and pressure, and has nothing to do with the measurement of mass. However, one could measure the weight of the gas, but that would sure complicate a simple relationship as seen in the expressed below. I do agree with everything else you've said especially the part about Lisa ... she does have nice mass ... I mean volume in just the right places

Boyle's Law: P1V1 = P2V2.

Air Pressure and Volume: Boyle's Law
Boyle's Law defines the relationship between a gas volume and its pressure. Think of this: If you take a box full of air and then press it down to half its size, the air molecules will have less space to move around and will bump into each other much more. These collisions of air molecules with each other and with the sides of the container are what create air pressure.

Opps ... I forgot about the Ideal Gas law. But that equation is used more for extreme temperature changes, and I don't think a tire used here on earth really qualifies for that. But that equation does use moles.

PV = nRT