Not a daRn thing, both have enough mechanical advantage to get you out of low points in your life to the tops of many hills. Both are vehicles for great physical and mental journeys. When their wheels are spinning they are both actually moving forward. Even though the ride might me a little bumpy you have to get their under your own power your aways satisfied when you finnish, fortunately some are tandem so they have no problem sharing the ride so your partner has equal value. They're often found riding in groups where people are smiling and having a fantastic time.
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