slightly larger spare tire & rear locker

[Methusalem]

Got it. It took me a minute to figure out that the distance above ground is the effective radius of the tire.

Naah, that's not the effective radius. Not for measuring the circumference. Although the circumference shrinks a little, like 2mbb said, it still has to cover the whole circumference (minus the little bit of shrink) of the 360 degrees of tire. Compare it with the track of a tank. If you would move half of the guiding wheels upwards, so you would get a kind of square, you still drive the same distance with one cycle of the track. The same with your tire. Just try it out. Deflate your tire 30% and measure the circumference. You will see that it doesn't differ much with the inflated tire.
About the axle and the deformed tire, 2mbb: Your explanation would be right if you would fold the ... of the tire (don't know the word - anyway, the part of the tire that touches the street). Because then the circumference would be smaller.

 

[Splangy]

Are you seriously comparing a tank track to a rubber tire?

Naah, that's not the effective radius. Not for measuring the circumference. Although the circumference shrinks a little, like 2mbb said, it still has to cover the whole circumference (minus the little bit of shrink) of the 360 degrees of tire. Compare it with the track of a tank. If you would move half of the guiding wheels upwards, so you would get a kind of square, you still drive the same distance with one cycle of the track. The same with your tire. Just try it out. Deflate your tire 30% and measure the circumference. You will see that it doesn't differ much with the inflated tire.
About the axle and the deformed tire, 2mbb: Your explanation would be right if you would fold the ... of the tire (don't know the word - anyway, the part of the tire that touches the street). Because then the circumference would be smaller.

 

[Mace]

Naah, that's not the effective radius. Not for measuring the circumference. Although the circumference shrinks a little, like 2mbb said, it still has to cover the whole circumference (minus the little bit of shrink) of the 360 degrees of tire. Compare it with the track of a tank. If you would move half of the guiding wheels upwards, so you would get a kind of square, you still drive the same distance with one cycle of the track. The same with your tire. Just try it out. Deflate your tire 30% and measure the circumference. You will see that it doesn't differ much with the inflated tire.
About the axle and the deformed tire, 2mbb: Your explanation would be right if you would fold the ... of the tire (don't know the word - anyway, the part of the tire that touches the street). Because then the circumference would be smaller.

Take that tank tread and lengthen it. Would the tank go any faster?

The speed is determined by the speed of the wheels driving the tank tread.

When you air down, you effectively reduce the radius of the tire and lengthen the tread footprint. The circumference of the tire does not matter.

Which is why a pressure difference from side to side on a locked axle makes the tires chirp.

 

[rusty_tlc]

What if the truck was on a conveyor belt.......





















































I couldn't help myself.

 

[rusty_tlc]

Naah, that's not the effective radius. Not for measuring the circumference. Although the circumference shrinks a little, like 2mbb said, it still has to cover the whole circumference (minus the little bit of shrink) of the 360 degrees of tire. Compare it with the track of a tank. If you would move half of the guiding wheels upwards, so you would get a kind of square, you still drive the same distance with one cycle of the track. The same with your tire. Just try it out. Deflate your tire 30% and measure the circumference. You will see that it doesn't differ much with the inflated tire.
About the axle and the deformed tire, 2mbb: Your explanation would be right if you would fold the ... of the tire (don't know the word - anyway, the part of the tire that touches the street). Because then the circumference would be smaller.

I do not agree.

The contact patch will get longer but the distance the tire moves will be determined the radius measured from the hub to the ground.

It took me a minute to get my head around it but what Mace said makes sense.

 

[klinetime574]

I can scan in the page in my Lockright Manual in a few hours,

But it specifically states do not change tire pressure to change the size of the tire.

So I'd say run the same brand, size, age and don't risk it.

 

[Methusalem]

Guys, I'm starting to get a headache! My brains are not used to working so hard
But I still think I'm right. Have that from my father. No fun arguing with him
No, listen. Take a fully inflated tire. Devide the whole thing from the middle of your rim to the ... (still don't know what it's called. Can anybody halp me out? Anyway, the outer ring of the tire, from now on called ... till I know better). So devide it in parts of say five degrees. Whether the tire is fully inflated or half deflated, those 72 parts of five degrees stay 72 parts of five degrees. Pi x 31" = 3.14 x 31" = 97.34" circumference. Say 250 cm. So 250 cm divided bij 72 parts = 3.45 cm per part. When the axle turns five degrees, the rim will turn five degrees and so the tire will turn five degrees. Okay, if you deflate the tire a little, it will shrink a tiny bit, but not much. So these 72 parts of ... will still be 3.45 cm each, inflated or deflated. If you say that the axle will turn faster because the tire has a smaller theoretical diameter, the rim will "curl up" the tire. And it don't. Try it. As long as you drive in a straight line (and that is what you want, right?) the big, deflated tire... will cover exactly the same distance as the smaller, inflated tire. So less degrees per cycle, so less cycles per minute than the other axle. And that is why your Aussie locker will disengage continuously. If you don't want that, you'll have to make a continuous turn in the direction of the smaller tire. But you'll never get home like that

 

[topherbecker]

[STRIKE]This has to be the stupidest thread I've ever read on mud. The circumference of your tire - the linear distance your tire travels through one revolution - is NOT affected by tire pressure.[/STRIKE]

https://forum.ih8mud.com/60-series-...ger-spare-tire-rear-locker-2.html#post6250794

 

[Methusalem]

This has to be the stupidest thread I've ever read on mud. The circumference of your tire - the linear distance your tire travels through one revolution - is NOT affected by tire pressure.

Yesssss!!! At last a MUD member who saw the light! Thanx, dude. Appreciate your common sense

 

[topherbecker]

Yesssss!!! At last a MUD member who saw the light! Thanx, dude. Appreciate your common sense

[STRIKE]A large deflated tire travels further in one revolution than a smaller fully inflated tire. The circumference of the tire does not change (meaningfully) with the tire pressure.[/STRIKE]

https://forum.ih8mud.com/60-series-...ger-spare-tire-rear-locker-2.html#post6250794

 

[Methusalem]

A large deflated tire travels further in one revolution than a smaller fully inflated tire. The circumference of the tire does not change (meaningfully) with the tire pressure.

That's exactly what I said, two posts ago. Although I fluked on math at school. But that's a long time ago and I don't wanna talk about it. So what's the conclusion of this thread? Don't use the spare tire in the rear or buy a new one with the same diameter as the rest?

 

[Mace]

This has to be the stupidest thread I've ever read on mud. The circumference of your tire - the linear distance your tire travels through one revolution - is NOT affected by tire pressure.

It'll be even worse when you figure out you are wrong.

 

[Mace]

Here's a different way to think about it.

Circumference, for topher and Meth's theory to hold water, you would have to only be on a single point of the circumference. Think tangent line... When you air down, you are actually cutting across (inside) the circumference of the tire. Instead of following the true path.

It is very easy to lose some pretty good height by airing down. And increase the "cut" across the true circumference.

 

[topherbecker]

Here's a different way to think about it.

Circumference, for topher and Meth's theory to hold water, you would have to only be on a single point of the circumference. Think tangent line... When you air down, you are actually cutting across (inside) the circumference of the tire. Instead of following the true path.

It is very easy to lose some pretty good height by airing down. And increase the "cut" across the true circumference.

So how does the circumference shorten? In other words where does the extra tread go? Are you saying it bunches up?

 

[topherbecker]

Well I'm still not "getting it", but after doing a little poking, i'm going to have to retract my statement.

Tire pressure WILL effect the distance a tire travels in one revolution. Some tire pressure monitoring systems actually measure the revolutions of an axle/wheel and indirectly calculate that a change in pressure has occurred since the axle/wheel is rotating more times to cover the same distance (in the case of lower air pressure).

Like I said, I STILL don't "get it", but that wont be the first time... Meh.

 

[Mace]

The tread does not go anywhere, you just have more on the ground at any one time. Which reduces the effective radius of the tire.

The conclusion is that as a spare tire, having a slightly different tire size and a rear locker is not the end of the world.
However, if you can keep the exact same tire (and rim) as a spare. It is a good idea (add it to the tire rotation schedule as well)

 

[rusty_tlc]

Maybe this will help.

 

[Methusalem]

Mace, Dan, come on!!! You got to be kidding me! Do you seriously think that the material between the real tire and the "effective radius" of the tire will disappear or fold? Because it has to stay sómewhere. By saying it isn't there it's not going away. The whole circumference of the tire will have to make the cycle, whether there is more or less tire on the ground. The length of the tire surface doesn't shrink (exept for the tiny bit deflation shrink and the tiny bits of less space between the profile when deflated a little. But that is almost nothing.
It's a pity that I live a few thousand kilometers from you guys and that the tunnel from Trinidad to Miami still isn't finished, otherwise we could have a good, oldfashioned indian sit-down with a few wheels with different tires and measure the whole thing

 

[Methusalem]

Another one. The plastic Coca Cola bottle. Often the label on it, is not glued properly and it's to wide. If you press your hand against the label and you turn the bottle, at a given moment the label will fold double. Same principle.

 

[rusty_tlc]

Mace, Dan, come on!!! You got to be kidding me! Do you seriously think that the material between the real tire and the "effective radius" of the tire will disappear or fold? Because it has to stay sómewhere. By saying it isn't there it's not going away. The whole circumference of the tire will have to make the cycle, whether there is more or less tire on the ground. The length of the tire surface doesn't shrink (exept for the tiny bit deflation shrink and the tiny bits of less space between the profile when deflated a little. But that is almost nothing.
It's a pity that I live a few thousand kilometers from you guys and that the tunnel from Trinidad to Miami still isn't finished, otherwise we could have a good, oldfashioned indian sit-down with a few wheels with different tires and measure the whole thing

The increased amount of tread contact area will affect the rolling resistance, agreed?

Why is that do you suppose?