We will be passing it down
@Petakabras catch!!!
If he passes, then I will host the next round in his place.
I will be handing this down, so tmcc 14 is yours agb7.
OK then, I will come up with a rule set within 72 hours.
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A quick post script on the tire realism section, after a bit more research:
G-width tires, roughly 235 wide, did exist in factory fittings, with G70-15s seen on some full-size offerings, too large to be in the hunt here. G60-15s, with their shorter sidewall, started showing up on factory high performance cars in 1970, too late for this competition. Wider options could be found aftermarket, but it seems the roughly 235 wide G width were as wide a factory fitted tire got before proper radials started showing up, and many cars, even high performance models, stuck with slightly narrower F-widths.
When this round started, I looked for conversion tables. The ones I found show G cross-plies to be much closer to 205. They also show L width, indicating that it is close to 230ā¦ with an aspect ratio of 78. They do, also, include a little disclaimer about interchangeability.
Looking at the dimensions of a G60-15 tire, they have a section width of 9.76", or 248mm, and a tread width of 8.4", 213.4mm. Since bias-plys have a rounder shape when inflated, comparing straight section width to section width doesnāt give a good comparison to radials, and I am in no way asserting that a G60-15 has a wider contact patch than a 245 section width radial. But, considering even the tread width, let alone the section width, is wider than the 205mm section width of a modern radial, I have a hard time seeing how they could be closest to a 205 wide modern tire in width.
Iād say, the effective width of a G60 would fall between a 235 and 225, but out of curiousity, Iām going to try to take some measurements of reproduction bias-plys as comparison and future reference when car show season starts.
Iām not saying this is accurate, itās just what I found and am using for reference. I am, of course, more working with a very basic approximation of overall height, not actual fitted.
From right to left, it shows a 225/70 x 15 is close to a G78 (with 78 being aspect ratio), 225 x (70/78) = 201.9mm
Looking at the Firestone web page, they say G70-14 has an o/d of 26.8" (680mmā¦ ish), something like a 215/70.
I should have done the math from the start instead of guesstimating, we have all the information we need to determine this with some algebra given fixed conditions, and I do enjoy a bit of algebra.
We know that the tireās overall height is (sectionwidth*(profile/100)*2)+wheelsize.
So, for the 215/70r14 example you provided, the overall diameter would come to 656mm, 25.85". Given 14" is 355.6mm, we get:
(215*(70/100)*2)+355.6 = 656.5mm, or 25.85". This lines up with the rounded figure given by tiresize . com
So, since we know the G70-14 from Firestone or Goodyear show an OA diameter of 26.8", 680.72mm we can actually calculate itās width by solving for x.
(x*(70/100)2)+355.6 = 680.72
x.72 = 325.12
x1.4 = 325.12
x = 325.12/1.4 = 232.23
So, not taking into account pressure, fitment, weight, etc. we can come to the conclusion that a G70-14 has an effective width of 232.23mm, not too far off a 235.
We can use use the same math for an F70-15. 15" is 381mm, and Firestone shows a F70-15 OA diameter also at 26.9", so:
(x*70/100)2)+381 = 683.29
x1.4 = 302.29
x = 302.29/1.4 = 215.92. So on that math, an F70-15 is damn close to a 215/7015.
How about the quite common F70-14. Goodyear and Firestone show 26.2" diameter, 665.48mm
(x*(70/100)2)+355.6 = 665.48
x1.4 = 309.88
X = 309.88/1.4 = 221.34.
So, based on this, we can see that the letter width ratings are not exact, but seem to vary based on the wheel size and tire profile.
For fun, lets see what we get for the biggest, baddest factory sizing from the era: the G60-15. Goodyear shows their Wide Oval G60-15 at 26.8" diameter, so:
(x*(60/100)2)+381 = 680.72
x1.2 = 299.72
x = 299.72/1.2 = 249.77. A whopping 250 section width on the highest performance cars of the early 70s!
So, based on this math, that the letter-width ratings used at the time scaled based on sidewall profile and wheel size, as this G-width G60-15 is considerably wider than the G70-14 we calculated earlier, despite both being rated G.
My only point of confusion on that, both the chart I posted, and the other one I found, show 78 a/r, not 70. Naturally, a 70 series will allow for wider rubber, but were they 70 in reality? What if they were 67 but marked 70:
The F70-14 (665.48) diameter on a 14" rim would then be 230 wide, wouldnāt it?.
It more implies that the letters were a range of widths at the manufacturers discretion, not a scaling value: they wouldnāt need to have the aspect ratio moulded on if that were the case.
I did the math on an F70-14 above and got 221.34, where are you getting 230 from?
Switching to DM, so we donāt clutter the thread any further.