a mistype! just 195r14c. speedometer under reads just a little
That was a
MAJOR typographical error!
185 R14 <=> 185/80 R14 => rolling radius = 328•8 mm | rolling circumference = 2047•1 mm
195/40 R14 => rolling radius = 255•8 mm | rolling circumference = 1607•2 mm
195/40 R14 has a 21•5% smaller rolling radius & circumference than a 195/40 R14 tyre
Hence, if one were travelling at a
true-speed of 55•0 mph, the speedometer would show an
indicated-speed of 70•1 mph; assuming the speedometer was truly accurate when 185/80 R14 tyres were fitted. However, noting that the
LEGAL tolerances for speedometer readings are 0% low & up to 10% high, speedometer manufacturers are likely to be aiming for a 5% high reading with half-worn factory-standard tyres; keeping in mind the speedometer tolerance changes by about 2%, from new unworn tyres with 7~8 mm tread-depth to barely legal worn tyres with 1•6 mm tread-depth.
Revving an engine at circa 4,000 rpm, when driving 195/40 R14 tyres at a true-speed of 55 mph or less, would be rather noisy and give a much higher fuel-consumption rate!
Also note that for a factory-standard 1968~79 VW 1600 Type 2 with 48 or 50 DIN horsepower engine, the vehicle has virtually optimal gearing with half-worn factory-fitted tyres, giving a maximum attainable
true-speed of 68 mph, so with 195/40 R14 tyres, the vehicle would be grossly under-geared, resulting in a very much lower maximum attainable
true-speed, but improved acceleration.
