https://www.strava.com/activities/391650465/analysis/8471/8744
Pretty solid downhill, but I find it hard to believe I hit 53.5mph. A friend who also did this MS ride says he hit 54.1mph (he didn’t make the turn at the bottom), but I almost believe both are in error rather than both were that fast. Does my Garmin 500 use wheel size or GPS to determine speed at any given point?
Most likely a GPS error.
Does my Garmin 500 use wheel size or GPS to determine speed at any given point?
It depends, do you have a speed sensor, and is it paired with your Garmin?
It’s very possible to hit that speed on a steep descent. I do it all the time and I only weigh around 60kg.
Does my Garmin 500 use wheel size or GPS to determine speed at any given point?
It depends, do you have a speed sensor, and is it paired with your Garmin?
PowerTap G3 wheels, feeding into the 500.
I’ve had many rides when Strava messed up my max speed. I think I had a ride this summer with a 60mph top speed on strava which was only 40mph on my bike speedo sensor.
Max speeds on GPS are a bit buggy.
Average speed will be fine - but any one data point might be a bit off.
I’ve recorded north of 50 when I know I wasn’t doing much more than 40.
My top speed was 56 mph with a wheel magnet computer and I was with a tail wind and pedalling out my top gear. Of course - a lot depends on the hill you’re descending.
Were you actually riding 100’ to the right of the road in the woods? That’s where your GPS tracked you. Your speed was calculated from the GPS points that are not very good so no, you did not hit 53 mph.
I don’t really believe what Strava shows as my max speed on a lot of rides.
Just own the pace. Garmin makes me a much faster athlete than I truly am at times. Have gone 28 miles running for three minutes and my last ride I was going 78 miles an hour up hill for 10 seconds. It all averages out in the end, but no need to invalidate your Strava result as everyone gets these readings from time to time and Strava does a good job of spotting them and evening it out.
Also, if you are a decent or better cyclist and descend without staring at your computer, you’ll be surprised by how fast you end up going and this could very well be accurate. You didn’t set a CR there either, so it may also be a fast stretch of road.
Are you telling me my max speed of 145.90 mph that my Garmin recorded a few years ago was in accurate?
It’s very possible to hit that speed on a steep descent. I do it all the time and I only weigh around 60kg.
Indeed. It looks like about 100m elevation loss over 800m. I would say 50+ mph is definitely possible.
I wouldn’t trust the absolute maximum speed itself, but to say you averaged around 50mph in the last 100-200m of that descent would be correct.
Totally possible, 50mph isn’t that difficult to hit on a good downhill. Even for the smaller guys - we just need to pedal the whole time!
Both - you could have gone that fast, and/or got a wonky reading.
No KOM on that? Grow a set. 
Z00M into the area on the map, its not even close to the center of the road so the GPS points add a lot of distance with the actual recorded time.
That descent has double digit downward grades so easily possible. I’ve hit 48 mph going downhill on -4, -5% grades.
From what I see, your path is way off the road and perfectly straight. Seems to me you lost GPS signal for a while. Looks like the software calculated speed based upon time and the distance between where you lost and got the signal back. I’d say it’s a bogus reading. FWIW one time I paused my FR305 for a while and forgot about it. I restarted it after a couple hours. I can’t remember the exact speed, but Garmin connect calculated me going something like Mach 2.
Z00M into the area on the map, its not even close to the center of the road so the GPS points add a lot of distance with the actual recorded time.
That’s why I said I wouldn’t trust the maximum speed, but to think an average of 50mph was reached for a small stretch, yes.
https://www.strava.com/activities/391650465/analysis/8471/8744
Pretty solid downhill, but I find it hard to believe I hit 53.5mph. A friend who also did this MS ride says he hit 54.1mph (he didn’t make the turn at the bottom), but I almost believe both are in error rather than both were that fast. Does my Garmin 500 use wheel size or GPS to determine speed at any given point?
Rode up Federal Twist on Saturday morning and saw two riders going the other way - the guy in front was in a decent aero tuck and I’d say he was probably around 50mph. My riding partner mentioned after we dropped down Tumble Falls Road that he’s seen a lot of people hitting between what he estimated at 50-60mph on Federal Twist.
Eye-balling the difference between the curve length and the road length where they separate and estimating the right triangle angle I’d guess the GPS added 53.5=x/cos(15 degrees) ==> x = 53.5*(.965) = 51 mph. I’ve gotten to 50 mph on 6% straight descents, so it’s probably close to real.
Was it fun?