Re: Type C/UP trucks

Posted by John Greenly on Apr 23, 2020; 4:50pm
URL: http://c-sng-discussion-forum.254.s1.nabble.com/Type-C-UP-trucks-tp15497p15544.html

Jim,  thanks for your response,  I wanted to make sure that I wasn't overlooking something.  

But, please--  I did not say 54" is my best estimate the wheelbase!  I said I didn't think it was that long.

Your reply is a big help though, because I was overlooking something:  the uncropped version of the flanger 013 photo in  Grandt Vol. VIII.  Using that whole photo allows a much more accurate determination of the camera position, and hence the perspective correction needed.

With this I can say positively that the wheelbase of the truck in the flanger photo is not as long as 54".   I get 49.5"- 50", based on the 26" wheel.  The main uncertainty is actually in how I'm measuring the wheel diameter.  I checked this by doing exactly the same measurements and analysis on the photo of flanger 015 on the adjoining page (p.146).  I  also get 50" for this wheelbase, but certainly this is a standard 4' C&S archbar truck.  So my conclusion is that I'm overestimating the wheel diameter at the visible point of measurement, the outer, near edge of the tire.  Based on the 015 photo, this must be more like 25" than 26.   Is that correct given the taper of the tire profile? Maybe someone could comment on this.  Or it may just be that the outer edge is somewhat rounded off, so that what is visible is smaller in diameter than the actual tire surface.   So, my confidence last night that the wheelbase is no less than 50" was definitely based on this mistake in my measured wheel diameter.  

In any case, this leads me to correct the wheelbase of the UP truck on flanger 013,  to 48".  It's a four foot truck!  

How about my estimates last night from the other two photos that gave more like 52"?  First of all I think a similar correction based on the wheel diameter is needed, so that brings them down to 50" or so.  But both of those were poor estimates to begin with for the reasons I described.  I don't believe that either of these contradict the much more accurate measure from the flanger photo .  Unless of course there were actually differing versions of these C/UP trucks, but again, I don't think the evidence we have here supports such speculation.  

I'm convinced that Michael's 4' wheelbase version is just fine, unless another really good photo turns up to contradict it.

John