Et originalt vw dæk er 629mm i diameter. Hvis du går efter 185 i bredden, skal du ha' en profil der hedder 185/65 (giver 621,5mm i diam.) 175/70 giver 626mm.
Her ka' du selv lege lidt med størrelser og se hvilke fælge der passer til de enkelte dæk.:
http://old.eurowheels.dk/ og klik på "Dækberegner".
Her lidt mere om emnet:
Since the stock Beetle tyre was 155/80 R15, then the overall diameter of the tyre has to be preserved as closely as possible, or the speedo will give you a false speed reading, which could get you in trouble with the law. The numbers on the tyre, 155/80 R15 for example, describe three variables in tyre sizing. The "155" refers to the width of the tread, in millimetres, the "80" refers to the height of the sidewall, as a percentage of the width of the tread, and the "R15" refers to the width of the rim the tyre is fitted to.
The stock 155/80R15 tyre has an overall diameter of 629mm and this is what VW calibrated their speedometers and gearbox gearing to use. While any increase in width of the tyre will require a decrease in sidewall height, an exact match is impossible, so we'll have to match it as closely as possible, so as not to alter the speedometer reading or the gear ratios.
A 185/65 R15 tyre has a diameter of 621mm, meaning the speedometer will read slightly fast for the actual speed of the car, and the engine will have to work a little harder to achieve the same speed as before. (this will adversely affect fuel economy) A 195/65R15 tyre has a diameter of 634mm which will have the speedometer reading slightly slow for the speed of the car, but will make the car slightly faster for the same amount of work the engine has to do.
While this sounds like a good idea, and you might be encouraged to fit tractor tyres to the rear of your Beetle, going too far with the height of the tyre will result in the engine straining to keep you at the same speed, and it will eventually overheat, and potentially cause serious engine damage. Still, in the case of the 195/65R15, it's only 5mm, so shouldn't cause too much strain on the old engine, and will give you plenty more contact with the road.
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