slightly larger spare tire & rear locker (1 Viewer)

[Methusalem]

Dude, look at your own pic of the deflated tire, what is the tread of the tire doing?

Not becoming shorter. Mace, 'm going to bed. It's one o'clock in the morning here. And in about 5 hours I have to bring my kids to school.

C-yah later, but not in this tread again. My aspirine bottle is empty

 

[Mark W]

Dear Mark, that is exactly the point at which I think that you forget something. Math wise you're right. If you decrease the circle, the arc gets smaller. But because the amount of tread in the real world stays the same (I don't swallow the idea of shrinking rubber - not that much), it's a total different story.

It not only stretches, but it also buckles and deforms. Air your tires down to where they are almost flat to see this. Look at a set of Boggers aired down to 5psi and then driven over the trail. Look at a set of drag slicks, both buckling as they rig stages and stretching as the car launches.

obviously you do not get this much buckling/stretching/deforming of the rubber at normal presures and use... but it still happens... all the time... and it makes a difference. It is simply a part of how it all works.

And I think you are misunderstanding a bit still... the movement of the tread... rotation wise.. does not have to shift in relation to the rim for it to slow and accelerate. There is no need for the tire as a whole to shift on the rim to allow a point on the tread surface to slow and accelerate independently of any slowing/accelerating of the rim. The movement closer and further from the rim is what create/allows this speed difference.

Because of the deformation of the tire... the sagging... the flat spot on the bottom... where it is forced closer to the rim by the weight of the vehicle... the tread itself HAS to slow... and then accelerate as the tire rotates and this portion of the tread is allowed to swell out to the full circumference distance again.


Mark...

 

[elripster]

You are confusing degrees of rotation with linear distance (measured a the circumference).

5 degrees at 1 foot from the center point is much less than 5 degrees at 10 feet from the center.

Your diagram clearly shows the difference if you shift your mindset a bit.

Rubber DOES stretch and deform... and so far as the point at the tread is concerned it DOES speed up and slow down.


Mark...

Another correct analogy.

Rest assured I do understand this completely. To see the effects of radii on tangential velocity check out a toroidal or conical CVT's.

If you still I don't understand this, grab your GPS and take your truck for a spin. Air down enough to deform the tire some and repeat the experiment. Your speedomoter will reflect the error do to changed effective radius.

Frank

 

[Methusalem]

Guys, I'm giving up! I don't understand half of the mathematical terms you use, especially because it's in English. But maybe that's your intention.
And no, I don't have a locker. Wish I had! I had a few in my old Isuzu Bighorn. Front, rear and centre. But never used a different spare.
So I give up and asume you guys are right, because I've lost it somewhere between page four and five in this thread. But I liked the discussion anyway!

But when I get a locker (and I will, some day) I won't have any problems with my spare tire, because I bought 5 exactly the same Goodriches

 

[meatloaf]

Wow! There is enough info here for a 12-pack... I think I am just going to get the same brand/size tire and play it safe.

Thanks to all for the input.

ML

 

[gothodgie]

C-yah later, but not in this tread again. My aspirine bottle is empty

Amen brother... i think i need a bottle of good bourbon too...

 

[Mace]

Try a good Rye, it really is tasty stuff..

 

[gothodgie]

Try a good Rye, it really is tasty stuff..