Actual Crawl ratios from tyre height and vehicle speed

[Wooky]

Are you on the SJ 4x4frica whatsapp group with Henri Mouton from Zombi Offroad?

Not on the whatsapp group.... just to many messages.
On a few of the SJ facebook groups

[XJ Junkie]

Measuring my tyre diameter isn’t working out so lekker. When I let air out I can’t get my measuring tape under the tyre. But it’s fine on top.

[Wooky]

Measuring my tyre diameter isn’t working out so lekker. When I let air out I can’t get my measuring tape under the tyre. But it’s fine on top.

Not quite following you with the "measuring tape under the tyre"
I just used a straight edge across the tyre tread at the top and measured from that down to the ground vertically

[Wooky]

the squirm in the tread when heavily deflated tends to increase the rolling radius to about the same as normally inflated - over inflated tends to push it up even higher.

Come to think of it. The tread circumference won't actually change much with tyre pressure as that is fixed by the length of rubber around the tyre.
The change is only in the shape that circumference takes on ie flat on the bottom, but the distance it travels per revolution will remain about the same.
Over inflated as Apoc mentioned above will have a slight increase.

[XJ Junkie]

That’ll not be overall diameter then.

[david bfreesani]

I'm sure for the sake of this exercise, a person can purely just go on the size of the tyre as indicated by the manufacturer. Or do as Apoc suggested, to measure the rolling distance of exactly one revolution of the wheel. From 33 to 35, mine changes by about 1.39 meter per minute, or 0.0834km/h in speed. I suppose we can get anal about it.

[Wooky]

That’ll not be overall diameter then.

It will be the outside diameter - outer edge to outer edge in a vertical line.

[Wooky]

I'm sure for the sake of this exercise, a person can purely just go on the size of the tyre as indicated by the manufacturer. Or do as Apoc suggested, to measure the rolling distance of exactly one revolution of the wheel. From 33 to 35, mine changes by about 1.39 meter per minute, or 0.0834km/h in speed. I suppose we can get anal about it.

Hey that's scientist and engineers for you.... we calculate everything to 7 decimal places and in the end round it all down and quote it with no decimals

[Apocalypse]

I'm sure for the sake of this exercise, a person can purely just go on the size of the tyre as indicated by the manufacturer. Or do as Apoc suggested, to measure the rolling distance of exactly one revolution of the wheel. From 33 to 35, mine changes by about 1.39 meter per minute, or 0.0834km/h in speed. I suppose we can get anal about it.

Hey that's scientist and engineers for you.... we calculate everything to 7 decimal places and in the end round it all down and quote it with no decimals

well, if you get the input figures good and accurate then the result can be rounded off....

if you start rounding off the input figures, things get wildly inaccurate by the result stage! Just ask a politician!

[Apocalypse]

Is this what you are talking about?
IMG-20190826-WA0024.jpg
IMG-20190826-WA0025.jpg

Winces.

so you have to cut the intermediary shafts in half and weld them up into a frankentranny? Eish.

it's also worth mentioning that when High Range is an under drive (as in this case and , e.g. a Defender) the ACTUAL reduction multiplier available through the transfer case is Low Range Divided by High range:

viz 4.16/1,57 - so an actual reduction of 2,65 .


i.e. for any given rpm in any given gear in high range, you will divide the speed by 2,65 when you engage low range - not 4,16

[david bfreesani]

Alex, am I at least on the right track with my spreadsheet?

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[Apocalypse]

Alex, am I at least on the right track with my spreadsheet?

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didn't see it? will go back and look....

[Apocalypse]

Alex, am I at least on the right track with my spreadsheet?

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okay, found it took a look, yes, all looks good.

Instead of typing out 'Pie' to 4 places (the 7th part of an Australian 7 course meal - the other 6 courses being recycled beer in a can...) you can just use " =PI ' on a spreadsheet and you'll get the full value for a lot less effort...

[david bfreesani]

Yip, saw that in your first post. I built that spreadsheet a few years back, not bothered to change it now. Done its job for me long ago. Only thing I added "recently" when you had your crawler thread on the other forum, was the torque calculation.

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[Wooky]

I'm sure for the sake of this exercise, a person can purely just go on the size of the tyre as indicated by the manufacturer. Or do as Apoc suggested, to measure the rolling distance of exactly one revolution of the wheel. From 33 to 35, mine changes by about 1.39 meter per minute, or 0.0834km/h in speed. I suppose we can get anal about it.

Hey that's scientist and engineers for you.... we calculate everything to 7 decimal places and in the end round it all down and quote it with no decimals

well, if you get the input figures good and accurate then the result can be rounded off....

if you start rounding off the input figures, things get wildly inaccurate by the result stage! Just ask a politician!

It is also about what the final data is to be used for. In this case working to 2 decimals all the way through would be more than sufficient, possibly over kill. In the end , as you said, the actual numbers are not all that important. If I come out at 67: or 72:1 in the real world it is pretty much the same thing.