[chrisguyw]

Chris ,many thanks for a concise answer ,I expect never racing at tip level lead me to wonder why such a rim was developed .I fully understand that the increase in diameter for more speed ,this is used in drag racing but the concave bit in the corners I found a bit of a puzzle .I raced in the 60 ,s but only at club level and have never heard of injecting tyres with air before .We were still sticking tyres to the track with wintergreen .

Steve

Hi Steve, In the 60's we were all treating our sponge tyres with wintergreen or castor oil. ........in the 70's, stickier tire additives became the norm due to the increased power of the increasingly "hotter" motors. As virtually all racing during this time (60's/70's/80's) was done on sponge tyres, which compressed well, and had gobs of grip via traction compounds, alternate designs were not needed, nor beneficial.

It is the current use of  comparatively "hard" tyres  (rubber/silicone/urethane) in most 1/32 plastic chassis based racing that was the impetus for looking for a way to "soften" the tire..........and the NSR "air" wheels, were the first design to address this issue. They did not show up until somewhat recently (I am guessing 10/12 years) , so you rightfully would not have seen/heard about these in the early days.
 
PS I think Pendle were one of the first shops to ban the "Syringe" practice.

Cheers
Chris Walker