I have not had time to test this with road riding so take it with a grain of salt and I feel the difference there will be minimal, unless you live in Colorado. I use a Garmin Edge 500 & a Garmin Instinct watch. Adding the wheel sensor made a huge distance difference when riding mountain bikes with significant altitude gain & loss. On one ride w/o the sensor pared to my Edge it showed 8.4 miles with an average speed of 6.3 mph, the watch pared to the wheel sensor showed 9.99 miles with an average speed of 7.0 mph. This was with 1220 ft elevation gain and the same loss. A 17.3% difference is pretty big to me. The watch reads 2 GPS signals, the Edge 1, they never matched distances but were not real far apart. After that ride I bought 2 more sensors for my other bikes. Get one to match the unit you are using, set it up properly by actually measuring the circumference of your tires at the running pressure to enter them, you won't regret it.
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