In the lull here while I'm waiting for some stuff to arrive to begin reassembly of the twins, I thought that I'd discuss the rear tires used on these trikes.
First, the history lesson...
The early Tricub production had only one-piece balloon rear tires installed. These are tires molded directly to small diameter rims with tiny 3x2 bolt pattern. As far as I can tell, the early Tricubs were 5hp (model 35) only. These one-piece tires can also be found on vintage 6x6 amphibious ATVs and Honda ATCs. Various versions show up on eBay once in a while for big bucks, if they're useable. However all of these are larger diameter than the ones used on Tricubs and, in fact, I have never seen any proper-sized, one-piece tires as used on Tricubs for sale in any condition, at any price. My 2 5hp cubs both came with this these original balloons installed. The 1st unit's tires showed multiple plugs, patches, oozing green slime and some rot... not holding air, so replacement, conventional tires/rims were ultimately required. The 2nd 5hp unit (the survivor) also still has the balloon tires, but these are still very nice shape, holding air and no evidence of plugs or rot. Due to the rarity, I use this set only when displaying the unit and install alternate tires/rims for recreational activity.
Original 5hp balloons
At some point later in production, the 8hp units were launched (models 38 and 38E). My 2 38Es are the topic of this thread. I do not have any evidence other than my observations over years, but it seems that concurrent with the 8hp launch, the balloon tires were dropped for conventional tires and rims on all subsequent production of 5hp and 8hp units. The only original, later version tires that I have ever seen have been Carlisle 21x12-8 ATV mounted on 8x9 rims. These tires had a shallow, chevron tread pattern that mimicked the balloons.
Original Carlisle 21x12-8
Now the dilemma...
Up until recently (maybe 3 years ago), Carlisle AT 21x11-8s were still available and nearly identical to the original tires. I had been planning on using these for these restoration projects until I discovered that they're no longer produced and I haven't found any source for affordable old stock. Carlisle now produces the AT101 in 21x11-8 size which are similar, but chevron tread is more aggressive... more like an ag-type tread. There are many similar sized ATV tires available with knobby or modern hybrid treads, but I really want to try and maintain the vintage original look as close as possible.
Discontinued Carlisle AT 21x11-8
The unit A of this thread came with original tires and wheels. The tires were obviously shot but I had planned to use the rims. Sadly, I later discovered that the rims were also unusable due to rust-thru in a few places along the bead... too much damage to consider trying welding or any other restorative process. Anyway, the closest rims that I could find are 8x7 trailer rims with correct centered dish and the correct 4x4 bolt pattern. Unit B had some kind of trailer tires and rims installed when I got it, so I knew that I was going to replace these from the start.
At this point, I have the 1st set of the AT101s installed on the 8x7 rims and it looks ok except that due to the narrower rims, the tires end up with a rounder profile than I would like. Unless I can find some other combination that is a lot closer to the original package, I'm going with this combination.
Current Carlisle AT101 21x11-8