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+--- Thread: Wheel diameter (/showthread.php?tid=211)
Wheel diameter - David.H - 08-09-2017
When were 17" spoked wheels introduced? Or were they a go-faster goodie?
RE: Wheel diameter - Ruairidh Dunford - 08-09-2017
I feel certain they were introduced in 1934, along with the first Ruby.
More info for you here however: http://archive.a7ca.org/wp-content/uploads/IC_A7_BS.pdf
RE: Wheel diameter - Ian Williams - 08-09-2017
I agree the 17" wheel was standard fitment on home market Ruby, Pearl, Opal, certainly not a "go faster goodie"
RE: Wheel diameter - David.H - 08-09-2017
Thanks, I wondered if they were used to lower "sporting" specials etc post war. The effect on the gearing would have improved acceleration, but done nothing for cruising speeds of course!
RE: Wheel diameter - AustinWood - 08-09-2017
Most standard Austin Sevens were badly over-geared.
Fitting a lower axle ratio usually improves the the top speed.
The sports models with low-ratio axles have the highest cruising speed of the standard cars. The Nippy I had 20 years ago was comfortable cruising at 60mph.
This was augmented by close ratio gears, otherwise the intermediate gears were too low.
Fitting a Nippy axle and gearbox will transform performance - however they are rare!
Also it must be remembered that at the same time as the 17" wheels appeared the tyre section was also increased so rolling diameter was much the same.
RE: Wheel diameter - Ruairidh Dunford - 08-09-2017
I understand the outer diameter of the tyres used in both 17" and 19" tyres are all but identical.
RE: Wheel diameter - Ian Williams - 08-09-2017
It is well known that lowering the final drive ratio on some sevens will actually increase the top speed, this is particularly true of 4.9 rear axle ratios, most post war specials ran on 15" wheels although this size is less acceptable in some quarters today. Several publications cover gearing well, as does Dave Armstrong's Speedex site.
Edit, Although close in size a 400 x 17" is marginally smaller than a 350 x 19" it all depends on the tyres used
RE: Wheel diameter - Erich - 09-09-2017
This brings up a question I have. My Ulster Rep has 19 inch wheels with 3.50 tyres and a 4.9 rear end. I also have a set of 17's with 3.50 tyres. I had thought that would lower my ratio. Is this going to make a difference, or am I mistaken? Next year, I am planning on competing in the only hill climb in the area(and one of the few in the US) that is open to prewar cars and so does not require fuel cells, roll bars, etc. It is run on the oldest paved road in Washington State. The course is 3.6 miles long, 8 hair pins and nearly 600 feet of gain for a 5% average grade. Any thoughts on whether changing to the 17s will help or should I think about a rear axle change to 5.25? Here is a video shot in a TR6 for an idea of the course. I should mention the car runs very well, has a torquey cam, larger valves and a Ruby head, all built by Pigsty. I do not know what the power is. https://www.youtube.com/watch?v=RWKaJ2fZOrg
RE: Wheel diameter - Charles P - 09-09-2017
Erich
Change that 4.9 to 5.25 and make sure that you have a CR box with 16/26 or 16/25 constant mesh gears (if you're 3 speed). You will not regret the changes - they'll make a big difference. Better than 17" wheels.
Charles
RE: Wheel diameter - Shuttle - 09-09-2017
I've been dealing with a '35 AAK that's fitted with 18" wheels.
Purves states it should be on 19" and it would seem 18" were only ever fitted to vans and export models.
Can anyone enlighten me please, or is it a case of "if that's what the customer wants, then that's what the customer gets"?
Could explain why the original colour was 'Westminster green' which doesn't seem to be an A7 option although it was in Austin's catalogue.