handy1882 Posted May 30, 2012 Share Posted May 30, 2012 Hi All, Probably a daft question, but where do you measure the size of a wheel rim? I was under the impression that the 30 cwt wheels I have for the Vulcan were 24" rims, as they are supposed to have 33 x 4.5 tyres on them. However there doesn't seem to be any part of the wheel that measures 24", is it one of those odd tyre sizing things that i'm unaware of, or are they just not 24"? I thought i'd better find out before i start buying tyres! They measure 24 3/4" across the fixed rim on the back of the wheel, and the rim itself measures 22 5/8", and 4 1/2" across the outside of the fixed and split rim. Front. Back. Measurement across the fixed rim. Measurement across the front of the rim. Any help or explanations muchly appreciated! Quote Link to comment Share on other sites More sharing options...
N.O.S. Posted May 30, 2012 Share Posted May 30, 2012 33 x 4.5 gives a 24" rim, and surely your rim measures about 24" diameter on the inner face where the tyre bead sits Quote Link to comment Share on other sites More sharing options...
N.O.S. Posted May 30, 2012 Share Posted May 30, 2012 Excuse the horrific looking modern rim - only drawing I could find online in a hurry! Quote Link to comment Share on other sites More sharing options...
handy1882 Posted May 30, 2012 Author Share Posted May 30, 2012 Thanks for the reply N.O.S, The rim measures 22 5/8 dia on the bead where the tyre sits, so it's 1 3/8" smaller than the 24" i was expecting, i could understand if it was a bit undersize but that seems like it would be far too loose for a 24" tyre? Quote Link to comment Share on other sites More sharing options...
N.O.S. Posted May 30, 2012 Share Posted May 30, 2012 The subject of old tyre sizing has come up before. They used to be specified by overall diameter and section height. So in the case of the 33 x 4.5 Vulcan tyres the rim diameter would be 33" less 2 x 4.5" giving 24". Another example is the old 34 x 7 tyre used on GMC 6x6 trucks. This was 34 - 14 giving 20" rim. This way of sizing changed (I guess around the war period?) to rim diameter and section width. In the GMC case the size became known as 7.50 x 20. A modern truck tyre sized at 385/65 R22.5 means 22.5" rim (R is radial) and width is 385mm but section height is 65% of the width i.e. much shallower tyre than the older profiles which were almost as high as they were wide. Quote Link to comment Share on other sites More sharing options...
handy1882 Posted May 30, 2012 Author Share Posted May 30, 2012 (edited) Nope, you're not boring anyone at all! All very usefull stuff! :thumbsup: I can understand the old tyre sizes, they make a bit more sense to me than modern ones anyway:-) The 33 x 4.5 tyres should give a 24" rim, yet they measure a lot less than that, 22 5/8 across the bead. i would have thought 24" tyres would just fall off those rims. Would 22 5/8" rims have been a standard size? Seems a bit of an odd size. I'll go and dig an old 33x4.5 out of my collection of worn out tyres and have a measure tomorrow. Edited May 30, 2012 by handy1882 Shoddy spelling! Quote Link to comment Share on other sites More sharing options...
N.O.S. Posted May 30, 2012 Share Posted May 30, 2012 They do state rim diameter as being 'nominal', but with that difference it does seem a bit too nominal for peace of mind Quote Link to comment Share on other sites More sharing options...
N.O.S. Posted May 30, 2012 Share Posted May 30, 2012 It certainly seems to be a minefield. I've just found some 34 x 4, 34 x 4.5 and 34 x 5 tyres for sale online which are shown as being for 25" rim fitment!! Also found out that the use of rim size in tyre spec (e,.g. 7.50 x 20) started in 1925. Interesting then that the earlier sizing was still being made in ww2 - unless they had pressed old moulds back into use due to the critical tyre shortage maybe? Quote Link to comment Share on other sites More sharing options...
Runflat Posted May 31, 2012 Share Posted May 31, 2012 I was under the impression that the 30 cwt wheels I have for the Vulcan were 24" rims, as they are supposed to have 33 x 4.5 tyres on them. However there doesn't seem to be any part of the wheel that measures 24", is it one of those odd tyre sizing things that i'm unaware of, or are they just not 24"? An article on the VSW in Motor Transport, February 21st, 1927, ends: The single tyre equipment consists of 33 x 5in. pneumatics on all wheels, and the twin of 32 x 4 1/2in. on all wheels - twin tyres on the driving wheels. Applying the formula mentioned above this would mean 23in. wheels. Does that help? Of course, that's not to say you actually have 23in. wheels... Quote Link to comment Share on other sites More sharing options...
handy1882 Posted May 31, 2012 Author Share Posted May 31, 2012 Thanks for that Runflat, That would make a bit more sense if they were 23" front wheels, they still seem a bit small but 3/8" undersize seems a bit better than 1 3/8"! Maybe it would be best to take the rims to some vintage tyre suppliers and try before i buy. Quote Link to comment Share on other sites More sharing options...
N.O.S. Posted May 31, 2012 Share Posted May 31, 2012 In my post above I meant to put 33 x 4, 4.5, 5. This was from Longstone Tyres, where they showed 33" tyres as being suitable for 24" rims. They do however list various 32 x XX tyres for 23" rims, see here: http://www.longstonetyres.co.uk/search?searchMethod=searchTerm&searchScope=site&searchUrl=&sortBy=&category=&searchTerm=1061&x=18&y=5 I'm sure they will confirm if your rims are ok at 3/8 below nominal size. Straight sided tyres may well need this tolerance for fitting. I have a M5 bomb trailer which came with 18" rims, but with one 18" and one 19" tyre - the previous owner had been using it on the road for years with heavy loads! :cool2: Good luck! Quote Link to comment Share on other sites More sharing options...
Richard Peskett Posted May 31, 2012 Share Posted May 31, 2012 Although not directly connected with the Vulcan, the Dennis 30 cwt model of the late 1920s if fitted with single rear wheels - 34 x 7 , the fronts were 33x 5 as standard a problem arose over the spare to be carried. This was overcome by supplying a disc wheel with solid tyre. Richard Peskett. Quote Link to comment Share on other sites More sharing options...
handy1882 Posted May 31, 2012 Author Share Posted May 31, 2012 Thanks for that N.O.S, i'll have to give them a call and see what they think. Richard, that is interesting, I have a picture of the another Vulcan taken in the 1960's which shows a disc wheel with a solid tyre, I always assumed that it belonged to something else but maybe it was the spare? Some interesting clutter in the background too..... Quote Link to comment Share on other sites More sharing options...
Ian L Posted June 1, 2012 Share Posted June 1, 2012 Thanks for that N.O.S, i'll have to give them a call and see what they think. Richard, that is interesting, I have a picture of the another Vulcan taken in the 1960's which shows a disc wheel with a solid tyre, I always assumed that it belonged to something else but maybe it was the spare? Some interesting clutter in the background too..... Hi Rob looks like an Austin K5 in the background ? Quote Link to comment Share on other sites More sharing options...
handy1882 Posted June 1, 2012 Author Share Posted June 1, 2012 It could be Ian, looks very similar to yours. Quote Link to comment Share on other sites More sharing options...
Richard Peskett Posted July 1, 2012 Share Posted July 1, 2012 Further to previous I have now found in various write ups in 'World's Carriers' late 1928 /1929 that in addition to Dennis also Vulcan, Guy and Albion all used solid spare tyres when using the 33 x 5 and 34 x 7 tyre combination on their 30 cwt. range. Richard Peskett. Quote Link to comment Share on other sites More sharing options...
handy1882 Posted July 3, 2012 Author Share Posted July 3, 2012 Thanks for that Richard. I saw a 1920's Dennis a few weeks ago with that exact set up, so seems reasonable that the Vulcan would have had a soild spare too. I've not found any evidence of a spare wheel carrier yet, unexplained holes in the chassis etc.. so i assume it would have been mounted in the rear body somehow? Anyone got an old 8 stud solid spare wheel laying around that they want to get rid of? Quote Link to comment Share on other sites More sharing options...
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