Help a tire guy out!

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I have a project, but I just don’t have the tools. That also means I need someone to do the labor.

I want to determine what affect tread depth has on rolling diameter. I suspect it has very little effect, but I need some data to back it up.

Here’s what I need:

1) A tire shaving machine.
2) A tire mounter
3) A wheel that fits on your car or truck.
4) A tire that can be thrown away, but fits on that wheel. It needs to have a lot of tread, then we are going to shave it so it has very little.
5) A flat tape measure. Not the kind that kinks if you bend it. The kind that you can wrap around a tire smoothly.
6) A car or truck (See #3)
7) A jack (to lift the car or truck.
8) Camera. To document the measurements.
9) A smooth driveway to measure the rollout.

Anyone willing to assist me? I promise fame and glory (or something!)
 
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Rolling diameter has as much to do with specific loading, air pressure and rim width, as tread depth. They are all variables.

On 4x4's we use any tape measure and go from the ground to the upper rim edge (just a handy reference point). Get all four corners the same for a given desired pressure - say 32 PSI front for rocky trails.

You can just measure the standing height of a tire mounted any way you want and calc the roll-out ...

The footprint deformation is a bit tricky, but still nothing basic math won't account for.
 
Not to be a party pooper on the real-world experiment, but it seems like an awful lot of work. what is wrong with using math? Go measure an actual tire in a tire store, then whip out the circumference calculator linked earlier.

Load, inflation etc for each vehicle is a constant for that vehicle so can be discarded.
 
I'd be interested in seeing the results of this. I'd also be interested in seeing how load and air pressure affects rolling diameter.
 
"Effective" rolling radius is less than the "deflected" static rolling radius which is less than the undeflected free tire rolling radius.

What are you really looking for?
 
I would think the quickest way is to find someone who needs new tires but has a fullsize spare with full tread. maybe hang out at your favorite tire shop?
 
Originally Posted By: NYSteve
I would think the quickest way is to find someone who needs new tires but has a fullsize spare with full tread. maybe hang out at your favorite tire shop?

I think the size range between two of the same tires may still be too much to get any useful data?
I'd also wonder how much a tire carcass changes in diameter over a tires lifetime? That may make any data from just shaving a tire less significant as well as it may not be similar to wearing a tire out.
 
Instead spending money to shave a new tire, just find a worn out one, and get a new one to match. Just doing calculations on a 265/75-16, based on diameter, it travels 2.75 inches less per revolution compared to a new one. Of course the loaded radius would have a variable effect, which is how many new late model cars are now monitoring tire pressure instead of using sensors. All cars should be that way, which just use a regular old valve stem, which is so much cheaper, and reliable. Just can't have a pressure read out, which is not required to conform to the TPMS regulations.
 
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I was waiting for questions 10, 11 and 12 where the OP asks for....
10) date of birth
11) social security number
12) bank account numbers

...as if it was an internet scam.
 
I would suggest asking a Tire Engineer..

smile.gif
 
Originally Posted By: Nick1994
CapriRacer, you might want to post your location

Why? I am guessing he wants someone to just follow his instructions, regardless where that person lives.
 
Originally Posted By: Quattro Pete
Originally Posted By: Nick1994
CapriRacer, you might want to post your location

Why? I am guessing he wants someone to just follow his instructions, regardless where that person lives.
The way it’s worded sounds to me like he wants to physically be involved. He said he needs those things.
 
Originally Posted By: CapriRacer
I want to determine what affect tread depth has on rolling diameter. I suspect it has very little effect, but I need some data to back it up.


Is it really revolutions per mile you are looking for? You addressed this with me somewhat 4 or 5 years ago; I'm in Greenville SC with several friends who work for the small tire company here. One felt that the steel belt controlled that with a loaded tire and that tread squirm was greater with newer tires. We never, IIRC, reached a definitive answer.
 
An angle grinder could probably shave a tire down but I'll need your address so I can mail you all the rubber confetti.
laugh.gif


Couldn't you also use a long piece of cardboard, like from a refrigerator box, and a sharpie? Mark where the tire starts and ends after one revolution both when it's new and bald.

Realistically can you do this when you buy a new tire, store the cardboard somewhere dry, and continue this experiment in 4 years when the tread's spent?
 
Originally Posted By: Nick1994
Originally Posted By: Quattro Pete
Originally Posted By: Nick1994
CapriRacer, you might want to post your location

Why? I am guessing he wants someone to just follow his instructions, regardless where that person lives.
The way it’s worded sounds to me like he wants to physically be involved. He said he needs those things.

And being a tire engineer, he does not even own a tape measure?
smile.gif
 
OK, it's obvious I need to explain this.

First, I am prompted to do this by this thread: Ecomodder: Thread on LRR Tires

As you can see, the question is: Does the change in tread depth (wear) account for the change in fuel economy from new to worn out?

I already know the answer: As the mass of tread rubber is worn away, the amount of energy consumed goes down - due to less internal friction (hysteresis). In fact, when I was designing tires, if we needed to reduce the rolling resistance, we used to reduce the amount of tread rubber by making the tread narrower or having wider grooves.

But I know that the group I am talking to at Ecomodder respond strongly to data - and I was hoping to be able to prove that the change in tread depth doesn't have the effect most people are expecting. I am hoping the result would be that it changes a fraction of what would be predicted by the change in physical circumference of the freestanding tire.

OK, a couple of things folks need to understand.

First, the rolling diameter of a new tire at the rated load/rated inflation pressure is about 97% of the freestanding circumference (unloaded and hanging). That is why Tire Rack publishes Revs per Mile data with each tire. Go ahead, do the math, and you will see this is so.

Second, I've already done the rolling circumference vs inflation pressure thing and lower inflation pressure reduces the rolling circumference.

The thing to remember, is that a tire is a flexible object and not a rigid structure. The whole *Diameter times PI* thing doesn't work.

Further, there is nothing you can physically measure that will calculate out to the rolling circumference - at least not with any accuracy.

- EXCEPT -

If you do the math, the calculated diameter of the rolling tire is about the diameter of the belt - and I wonder if the belt is acting just like a tank tread, where the length of a revolution of the tire is the circumference of the belt. I called this the Tank Track Theory.

And that should mean that the difference rolling diameter between a new and a worn out tire would be almost the same.

Some other things of interest:

Tires grow. They do most of their growing in the first 24 hours. In fact we call the dimensions "24 hour growth dimensions" - and because of that, our tire testing shop used to inflate tires to 2 or 3 psi more if the test was to be conducted the next day.

There is also variability between tires. If you measure a large group of tires (for whatever parameter you wish), you will get a range of results.

That means that testing a new tire vs a worn tire won't properly answer the question - but testing the same tire would!

There is also a thing called Pantographing, where the steel belt changes angle as it rolls through the contact patch and the belt changes length and width as it does so. This angle change would be affected by the load and inflation and complicates things.

So I thought if we could find a tire, measure it's freestanding and rolling circumferences, then shave the tread off, then measure again, we could answer the question and perhaps validate the Tank Track Theory. I've measured both those circumferences before and validated the 97% value

- BUT -

I don't have access to a tire shaving machine. Without that, I can't conduct the test. While I was thinking about it, I listed some of the other things I was going to need.

While I am willing to perform the physical labor, I know that shaving equipment might be too far away for me to travel, so I listed all those other things needed to conduct the test - hoping someone might volunteer.

So there you have it.
 
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