As you all know, I have an inquisitive mind, and I have my own answer to this, so I'm hoping for some good answers here...
Just trying to get technical for a bit...
Background Information
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A 13" steel wheel, has a 175/70/13 tyre installed.
A 17" alloy rim, has a 215/40/17 tyre installed.
A set of 13" wheels are fitted to a vehicle and driven down a road.
A set of 17" rims are fitted to an identical vehicle and driven down the same road.
The 13" wheels are fitted by manufacturer and the speedometer is calibrated to those sized wheels.
The Question
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1. If both vehicles are travelling at 70mph indicated by the speedo. Which car is physically moving faster?
2. If so, by how much?
3. What is the real speed difference between both sets of wheels at the indicated speedometer reading of 100mph?
Let me offer some more information...
1" = 25.4mm
13" steel wheel = 330.2mm
175/70/13 tyre = 70% the width of the tyre ?? or 70% of the diameter of the rim?
Circumference of circle = 2Πr
Π = 22/7
Hint
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Work out each circumference of the wheel and the alloy, find the difference, and understand how much further the wheel/alloy may travel over the other.
I know this is really boring! but give it ago, maybe we'll all amaze ourselves!