Lanceoldstrong

I got a 57.1 mph reading as top speed on my Garmin Edge 500 yesterday.
Garmin Connect Data: https://connect.garmin.com/activity/22120901

My ride buddy Midland questions the validity.
I have seen 52.7 mph on shorter descents on my old Shimano Flight Deck before, so I think 57.1 is possible for me, being a 200 pound rider.


What does the Bike Forums jury think?

First as to where?

It was on the longest, straightest part of the Sierra Rd /Felter Rd descent a couple miles before the right turn up the Caleveras wall. I came over the top of a little rise where I had carried a ton of speed up the rise. I peeked over the top and saw a long, long downhill straight away. Perfect conditions for a speed run.
I shifted into 50-11 and hit the drops. My cadence reached 130 rpm before I spun out, then I just tucked and held on and gravity sped me up from there before I had to brake for a turn at the end of the straightaway.

Now, is my Garmin a liar??

My Garmin actually gives conflicting info.

There are two types of information displays on the Garmin connect site: Graphs and Reports

Exhibit A: Reports - it shows my top speed listed as 57.1 mph in 2 different places in the report data.

Exhibit B: Graphs - on the graphs data shows top speed of 47.6 mph

I think I may have actually hit 57.1 and here is why.

My Garmin tracks my speed 2 ways.

A) information from GPS satellites being relayed to my unit
B) physical revolutions of the magnet on my spokes interacting with the cadence sensor on my bike.

I think the graphs are showing the exact points and times I was traveling at given speeds and they are a product of satellite data.

I think the reported top speed of 57.1 mph came from my magnet system.
The magnet is part of my cadence sensor and the Garmin communicates with if for accuracy sake.

I bet I hit 57.1 mph just for a second, and soon after the graphing data shows the location of the 47.6 mph

Time to bring in Sheldon

Sheldon Brown's gear calculator only goes up to 120 rpm. (he never counted on 130 rpm cadence made possible by the compact crank set up of 50-11)

According to Sheldon in 50-11 at 120 rpm the maximum produce-able speed is 42.6 mph.
Now consider I was cranking 10 rpm higher than that when I spun out. So I was surely going a good bit fast than 42.6 when I had to just let gravity take over.

Warning Physics Ahead!!!

An object descending under the force of gravity accelerates at an increase in speed of 32 feet per second every second it is in motion. So without a lot of math, in just 30 seconds after I spun out and just let it rip, my speed would have increased exponentially. Exponentially as in topping out at 57.1 mph

Okay, if you read this far, kudos to you. I will buy you a cup of coffee on our next ride.
Can I get your opinion? Do you think I really hit 57.1 mph?

Ygduf

Maybe.

What was the wind like? Previous high speeds on the descent?

Only way to verify is to repeat it. Certainly it's possible to his 57 on a bike. I saw 52 at the Deathride and was trimming with the back brake.

cccorlew

That's pretty darn fast. And it's a lot faster than your previous top. While it's possible, I'd ask:
Did you feel like you'd gone 5 mph faster than ever before?
Are your shorts stained?
If so, than maybe indeed you did.

BTW, that doesn't that whole 32 feet per second thing is count for falling objects, not rolling objects, and it even then, only on a vacuum.

In any event, I'm pleased to learn you didn't do a Simpson's Milk Truck on us.

Fueco

I've hit 50+ on that stretch many times, with several different bike computers... And you outweigh me by 20 pounds or so. It's certainly possible to go much faster on a bike. A friend of mine once hit 70+ going downhill through a tunnel in a peleton (obviously no wind and a vacuum effect with that many people involved!).

I've also hit 52+ on several other descents. To hit your max, try the eastside of Tioga Pass or Sagehen Summit (both on highway 120).

Hermes

Sierra Road is pretty steep so I suspect you had enough force to go 57 mph. I suspect your Garmin is right but my 705 gives me overstated max speeds at the track. I know this by measurement by other riders and by calculating the max speed from cadence data. Also, the Garmin samples data every second and I am suspicious it miscalculates max speed when bikes are accelerating fast i.e. my track sprints and possibly your fast descent. However, IMO, your speed of descent is limited by your ability to get into an aero position. If you look like the pros on TV when they are descending for max speed, then you probably hit 57 mph.

F=MA where A is gravity. However, that is for a falling object straight down in a vacuum. So in gross terms it is the sine of the % grade times the acceleration of gravity which is directly proportional to the Force. Friction (rolling resistance / bearings), aero drag (body, wheels, spokes, tires and bike) and mass (body, bike, components and wheels come into play but aero drag dominates at high speed.

1jacktripper

I get nervous driving 57 mph on my Camry, so I can't even imagine doing that on my bike. That must have been quite a rush.

bigbossman 

If the wind is right that Sagehen Summit is one fast, long roll-out. I've done 56 and 53 mph there. I've also done a mere 42, with the wind in my face.

BTW Dan - as Curtis pointed out, your physics is screwy. 32'/sec/sec is for falling objects neglecting wind resistance. You were not in free fall, and had wind resistance and rolling resistance to boot. Plus there is your flamboyancy, which had to count for something in this equation. Besides - Steve's a nice guy, and says nice things about me. If he doesn't believe you, why should I?

Q.E.D.

In conclusion - since you seem to want it so bad, and also because (if true) it would eclipse my best speed...... I'm sorry, but your petition must be denied.

Please pay the baliff on the way out. Thank you - next?

scorpio516

I've only got 3 bits to add:

#1 - on the trainer, at 50/12 & 140 rpms ish, I'll hit mid 40s mph
#2 - on the road, on a much, much shorter 6-8% downhill (like 1/4 mile long), I can hit 32-34 on the hoods if conditions are right, and you outweigh me by 30lbs
#3 - physics. 32'/s^2 is g, straight to the earth's core. Your traveling at an angle compared to it. If it's a 10% slope, it's a 6 degree angle. 3.2'/s^2 is translated along the angle your traveling, 29.8'/s^2 is trying to push you into the soil (which, after the coefficient of friction of your tires and your mass is accomodated, is rolling resistance). Traveling along a 10% slope gives you a 3.2'/s^2 acceleration egde over traveling on a flat, if my math is right.

Lanceoldstrong

I descend scooted back on the saddle, down in the drops with a flat back and my chin literally layed right on my stem. I don't know If I look like a pro but I get pretty low and aero.

I am starting to think I did really hit 57.1

dl33

I'm not sure where you got the top speed. For me the fastest part is the first long, straight drop but this does not end with a turn. This first drop ends with a short riser hence no braking neccessary. The part you're describing sounds like the second fastest part (at least for me) a little further down, needs some braking and is always about 4-5 mph slower.

My fastest speed for the first section is 51mph drafting GW_12 and we spun out early. Max going solo is 48mph.

bam

it's certainly possible. but your garmin seems to think you went from 3.8mph to 57 and back to 4.5 over a very short distance.


< Trackpoint >< / Trackpoint >
< Trackpoint >< / Trackpoint >
< Trackpoint >< / Trackpoint >


i'll see your 57.1 and raise you 97.2:
https://connect.garmin.com/activity/11341904

and i seem to recall one > 1000 mph, but i was going way too fast to remember

Ygduf

In folsome my garmin glitched and gave me 10,000 extra miles from nowhere. My average speed for that ride was over 2000mph.

https://connect.garmin.com/activity/20881627

bam

ygduf wins!

Hermes

IMO, the fastest descending position is grabbing the top of the handlebar near the steam (arms in tucked to chest), chest on the stem, flat back with knees together. The arms extended to the drops create more drag. Your position sounds right for a normal fast descent when cornering and braking are required.

Ygduf

Weirdly, if you go to the player on the connect site, the route never blips. I may have hit 88mph on a descent, gone back in time and returned without realizing.

powpow

When I had the 305 I never trusted the speed readings. They were always inaccurate compared to the old-fashioned magnet/sensor method. This is one of several reasons I sold my 305.

Maybe the newer models are more precise, but that drove me nuts.

8Lives

I have hit 60-61mph descending Southpark Drive a couple of times. That is according to the Garmin 305, and I haven't noticed any problems with it reading speed - it seems very consistent.

I only weigh 147, but in a nice aero tuck coming down a long steep (14%) grade guts seem to be the biggest factor :-).

ahmose

57.1 mph wow.
That seems insanely fast for me. I think i've hit around 35 mph on some descents before and that felt scary to me, i can't imagine how 57 would be like.

8Lives

Actually, rereading - yes the GPS can be inaccurate at a given moment. I pull speed from the Garmin's magnetic wheel sensor attachment, not the GPS.

Beaker

Actually for the 305, speed comes exclusively from GPS, even if you have the wheel sensor installed. The only time it uses the wheel magnet is if you turn off GPS, or it loses signal. I've noticed crazy variable speeds through Canyon on Pinehurst Rd, and climbing Tunitas Creek one time due to intermittant GPS coverage. I find that quite frustrating, but most of the time the real time speed readout is fine. I don't know if Garmin has fixed this ridiculous problem on the 500 or not.

I suspect that the 57.1 might be a blip, esp. given bam's post. I looked at the player version of the ride and couldn't see the bar hit 57.1mph even when draging the pointer manually over the profile. One thing that I've found helps is to upload the route into some other software and see what the numbers tell you, that'll help confirm or rule out whether that was a glitch in the software or the unit.

Lanceoldstrong

OK, I think now the preponderance of evidence is pointing towards a glitch.

It was fun, fast and a great time on a bike. That much I know.

BlastRadius

One reason I haven't removed my old magnet-based Cateye.

dl33

On the Edge 500, there's an auto and manual setting for wheel calibration. Assuming auto uses gps to calibrate the wheel circumference vs manually entering, anyone know if there's any difference when during normal operation?

khill

My .02 is no.....I have a 305 and I get random +10mph on descents quite often. 57 is fast fast...

spingineer

and you're complaining?