Best way to inflate this tyre profile?

[Steve1]

Hi,
V5

I have traced the tyre profile from a photogrammetry wheel.
I see its about 16 inch dia.
The tyre is marked 18 x 7

clearly it was under-inflated when I was there. should be 18inch dia.

I want to assume no stretch of the tread area, or of the short angled straight wall.
The curved part heading out from the rim will be less curved in order to attain the 18 inches.
and perhaps the tread takes on a slight more curve.

How can I change these to get them to the 18 inch line marked.
tyre profile to chaange after inflation.3dm (39.5 KB)

Cheers

Steve

[encephalon]

i am not sure if that can be replicated accordingly, since the tire would also inflate not only in its with, but also expand vertically at least a slight bit i assume while the tread would at least flatten out maybe even expand slightly either. but i am not an expert, it looks like a tire from a plane just guessing.

i would use scale 1d with the axis intersecting your black curve as a starting point the outer part at the first dimension as the reference point then simply pull it over to the outer dimension as the target point, given that the vertical diameter does not expand. you can try to limit the scaling by only marking a limited amount of control points, and scale from the same position as mentioned to retain more of the original tread curvature.

there is also the stretch command, which would work the same as scale 1d her, but that will change the cp very slightly but therefor retains more of the original curvature.

[davidcockey]

To understand how a tire changes shape how a tire is constructed needs to be considered.

A pneumatic tire is not a ballon. It does not uniformly stretch when the air pressure inside is increased. In addition to the rubber which is visible on the outside a pneumatic tire has reinforcement cord (or fabric on very old tires). The reinforcement can be steel, polymers such as aramid/Kevlar, nylon, polyester, or in very old tires natural fibers such as cotton.

There are several types of tire construction including radial which is the most common today, bias ply / crossply which was predominate prior to the late 1960s and is still used in some applications, and bias belt which was popular in the late 1960s and 1980s.
https://www.continental-tires.com/kh/en/b2c/tire-knowledge/tyre-construction/

Radial tires have a belt under the tread, typically made of steel cords, which are close to the circumferential direction. There are also reinforcing cords in the radial direction. The circumference of a radial tire changes very little with air pressure.

Bias ply / crossply tires do not have a belt. There are reinforcing cords running around 30 to 40 degrees in the radial direction. Bias ply tires do change circumference with air pressure. The change in size is not uniform.

Bias belted tires are a hybrid of radial and bias ply construction. There is a a belt under the tread and the circumference changes little with air pressure.

[Steve1]

Hi,
Tyre is a WW2 RAF Bomb trolley tyre.

Does anyone know of any of these available ? note the straight grooves around the tread area with the little dividers, THE WAY of identifying a wartime or pre war pattern make.
.
Failing that same 18 x 7-8 size with delicate patterned tread area. Not the awful Fork Lift truck things with tread the size of your hand.

I am assuming the tread area stays same shape, the short straight slope likewise, and the curved wall straightens out a bit to attain the 18inch dia.
It must not stretch.
I think these had wires inside ?
I could check that.
for the purposes of this quick, ask, someone saying send them the profile, I have this, as the owner doesnt like to inflate to the full 40psi, incase they go bang.

so what is best way to straighten out the side wall keeping its curve length the same.
Scale1D would surely stretch it ?

I do the Scale1D and 2.311 becomes 2.843 curve length. 1.23x growth

What command to straighten a curve retaining curve length ?

Actually it looks like the rubber is going to have to stretch as even a 2.311inch straight line cannot reach the short side slope when its moved 1 inch fwd !

1.23x stretch though seems a lot.

Cheers

Steve

[encephalon]

did you try the command Stretch as a comparison?

@Steve1

What command to straighten a curve retaining curve length ?

try FixedLengthCrvEdit, that is very limiting in its handling though it will change the end points of the curve to retain length when you edit it.

but i also must say i am not quite sure to understand what exactly you are trying to achieve, some sketch would help.

[Steve1]

Hi, let me explain better, the photogrammetry gives a profile where tyre is 16 and abit inches in diameter.
Its marked 18x7 so it should be 18inch.
A tyre comppany said send the profile shape.
so I need to ‘inflate’ the tyre more as its at 20psi.
I disdnt envisage the rubber stretching, just he bowed sides straightening out .
However it seems 1.28x stretch of the rubber is needed to get to that 18inch dia.

as per scale1d.

I had thought if the side bulge straightens up, retaining its length, I can redraw the profile and get to 18inch.

I dont now think its possible doing some simple drawing. that rubber is going to have to stretch ! a lot.

Steve

[eons]

I don’t think ‘expanding’ it is the right approach: to expand and get a larger diameter you would also be increasing the perimeter - i.e. stretching the tread around, which is not possible by just inflating a tyre. Could it be loss of diameter due to worn tread?

[eons]

Also- did you physically measure the tyre or are just relying on the photogrammetry measurement?

[Steve1]

Hi,
relying on the photogrammetry, its accurate to 0.1mm, though not tested it but work so far has no issues.

the side wall would straighten out, but almost straight doesnt get to the target dia of 18inch.

moving the tread out to the 18 inch line. thendrawing a circle from the short side, the curved side needs to touch that, and even straight its too short a reach.
I cant envisage the tread area bowing that much, perhaps it does ?

I try FixedLengthCrvEdit but cannot fathom it out, it made the curve not any less curvy retaining curve length.

Steve

[jeremy5 (Jeremy)]

@Steve1

Tyre is a WW2 RAF Bomb trolley tyre

Which type of trolley?

What diameter is the wheel? What width between the rims?

Edit:
And have you seen these pics of an 18 x 7 tyre on a wheel? Bomb trailer wheel rim - HMVF Classifieds - HMVF - Historic Military Vehicles Forum

HTH
Jeremy

[davidcockey]

@Steve1

relying on the photogrammetry, its accurate to 0.1mm, though not tested it but work so far has no issues.

@Steve1 What software are you using? If Photoscan/Metashape, Photomodeler or similar then the results have to be scaled based on a known distance/dimension. It is entirely possible to get the scaling wrong - I’ve done it.

What is the rim diameter based on your photogrammetry?

[Steve1]

Hi,

Hi, Jeremy, oooh thanks for the link, will ring him in the morning.

That’s a Post War tread pattern and better than the modern HS treads (hand size), the rims are the same.

Which type of trolley, The Type B, Type C and Type D as well as the Type F all used these 18 x 7-8 tyres. Though in WW2 they just had 18 x 7 on the walls,

Dia of wheel supposedly 18inch from those markings.

Measured from Photogrammetry 16.3 though inflated to 20psi and not 40psi, as may go bang he says.

6 inch inner to outer rim edge he measures, my CAD was 6.315

CAD/Photogrammetry has 10.1097 for rim dia but getting it measured on a real one.

the scaling down to get 6 from 6.315 would give 9.6 but I recall at least 10 on those over the years measured. I have site notes to dig out.

My ruler method is very carefully done, and I have at least two cooking at the moment !

rim thickness 0.25inch.

@davidcockey

What software are you using? If Photoscan/Metashape, Photomodeler or similar then the results have to be scaled based on a known distance/dimension. It is entirely possible to get the scaling wrong - I’ve done it.

I am using Metashape standard, (or if it fails to align all Photos then Photoscan which invariably aligns all, then continue in Metashape)
and laid into the many photos as a secondary smaller photoshoot, same focal length etc etc, is a ruler.
I marry that chunk in Rhino to the first chunk, rather than use Agisofts chunk aligning., which I have yet to get to work !

Orient3Pt then scale if need be. turn layer on and off and see a good match.

Run a section through the ruler , divide 30 then line through points, and with both meshes grouped orient that line horiz, then scale the meshes to the ruler, then use sections on rim to re orient the rim ortho etc.

Steve
( I am the UK expert and co-ordinator on WW2 RAF Ground Eqpt)

[jeremy5 (Jeremy)]

@Steve1

Measured from Photogrammetry 16.3 though inflated to 20psi and not 40psi, as may go bang he says.

That’s a very cracked and dessicated piece of rubber and I think he’s right not to inflate it! (Nowadays you shouldn’t use a tyre over ten years old on the road.) I wonder whether, as a result of the aging process, the tyre has shrunk, accounting for the difficulty in reshaping it to an 18" o.d.?

[Steve1]

Hi, Jeremy
I owe you a pint. TRULY !!! Tyre bought. Whilst not a WW2 pattern tread (always denoted by straight line grooves, this was zig straight zag as I call it. Should scrub up to look decent, far better than those folk are having to use with tread the size of ones hand.
The rubber can be anything from really nice for over 80 yrs old (top of the montage, and an AM marked at that ) to far too much sun and starting to flake. foot of montage the newlu acquired tyre.

Top is Champagne glass pattern, then space Invader, then choc Block. Poor thing seems doomed to remain there, seller wouldnt play ball and cut the axle from a worthless farm trolley with no other wheels. then get £180 scrap. being mega rare WW2 that hurt me deep. then sun damaged , all WW2 so far, then the post WW2 just bought.
You asked of which Trolley Type, my radar tells me you might have a slight knowledge or interest, also knowing of HMVF etc )

So how do I buy this pint ?

Cheers

Steve

[jeremy5 (Jeremy)]

No, no special knowledge. I was intrigued by your tyre profile issue and did some googling to try and find more pictures of a bomb trolley tyre and it appeared there were different wheel sizes for different types, so I wanted to narrow it down.

As for a pint, unless you too live in Sussex, it seems impractical. As always in that scenario, I thank you for the offer and ask that you buy a pint and down it yourself on my behalf.

Cheers
Jeremy