Nomenclature for tyres

[Max Martin Richter]

Hej,
yesterday, I got a copy of the Power Pull set and just for fun I have looked into our library, if the BIG tyre is available. I found it, but it has an odd name.
I left a comment on the part's page. Steffen BFC'ed the file in the meantime - thanks for that.
Now I was looking for the right name. I checked the wiki and the old Lugnet entries.
And I found out, that our naming system is a bit chaotic (for me). Sometimes it is like the version in our wiki and sometimes it starts with the diameter (like on some Lego tyres). I have checked the rim for the tyre, too. Here it is the same. It doesn't correspond with the wiki.

And another thing: I have no idea, where I should do the measurement at the tyre. At the widest width, at the inside width (because it's a balloon), should I include the bead for the rim in the "percentage" measurement or not and and and.

It would be really great if we could find a way to describe this in a good way.


/Max

[Philippe Hurbain]

A nice Christmas gift you got - two days in advance
I thought that the wiki naming was mainly used for small System tires that have no marking on them. But I think that, for big Technic tires that have a name embossed, it would be a mistake not to use this name since it is the widely known one! Now I admit that for the PP tire I cheated, since there is no marking on this one...

[Chris Dee]

The LDraw nomenclature "width_(mm) / profile_as_%age_of_width x rim_diameter_(mm) [optional qualifier]" was defined to try and match the ISO standard, which is what is used by TLG for the imprints on some tyres.

The "width" should be the maximum outer width. The rim diameter should be measured where the rim meets the tyre - so that (in theory) the dimension for the "rim diameter" of the tyre should match that dimension in the wheel rim nomenclature "width_(mm) x rim_diameter_(mm) [optional qualifier]".

The 32998.dat on the Parts Tracker has not been updated to match this nomenclature, but should be updated before becoming official. As with any eveolving standard, there are some legacy files in the official library that need recycling through the tracker to bring their names into line. Any help with that is, of course, welcome.

[Magnus Forsberg]

I've made this picture as an attempt to describe how to measure a rim and a tyre.

[Magnus Forsberg]

Which "width" is used to measure tyres?

The "width" should be the maximum outer width.

Of what? The tyre or the rim?

The rim to be used here is 22969.dat, "Wheel 56 x 46 Technic Racing".
Maximum width: 116ldu x 0.4 = 46.4mm
Maximum visible diameter: 2 x 68ldu x 0.4 = 54.4mm
A new name for this rim could be: "Wheel Rim 46 x 54 Technic Racing"

The dimensions of this tyre, 32998 is:
Maximum outer diameter: 2 x 131ldu = 104.8mm
Profile height is: 131 - 68 = 63ldu x 0.4 = 25.2mm
Maximum width of rim (same as above) = 46.4mm
Maximum width of tyre: 76ldu x 2 x 0.4 = 60.8mm

A new name for this tyre would be...
if we use "max rim width": "Tyre 46.6/ 60 x 54 Off Road"
or, if we use "max tyre width": "Tyre 60.8/ 50 x 54 Off Road"


My opinion is like this:
Wheel:
(width_(mm) x rim_diameter_(mm) [optional qualifier])
"width" means "maximum rim width" in mm (without decimals)
"diameter" should be without decimals, unless it is below 10mm, then one decimal

Tyre:
(width_(mm) / profile_as_%age_of_width x rim_diameter_(mm) [optional qualifier])
"width" means "maximum tyre width" in mm (with one decimal)
"profile" should be rounded up to the nearest ten
"diameter" should be without decimals

Should both tyre and wheel use the same definition of "width", or should they have different definitions?

[Chris Dee]

I agree with your opinion - the the width should have different defintions for tyres and the rims. Not sure if 1 decimal place is needed anywhere - rounding to the nearest mm is unlikely to produce duplicates. Profile is not rounded in the ISO specification and should not be rounded here.

[Magnus Forsberg]

OK, thanks for the clarification.

It would mean that this tyre should be called "Tyre 61/ 41 x 54 Off Road"

btw
there is an easy way to calc the outer diameter of a tire.
(tire width x (profile/100) x 2) + rim diameter = outer diameter
On this tire it is (61 x 0.41 x 2) +54 = 104.2mm