The Vagaries of GPS Logging Sites

[I like Skol]

I have seen @potsy going far faster than that down hill.

Was that just before he hit the ground?

 

[Hacienda71]

Was that just before he hit the ground?

Yep @400bhp threw a bottle at him and he did a cracking impression of superman.

 

[HLaB]

Yep @400bhp threw a bottle at him and he did a cracking impression of superman.

I did a cracking impression last Friday, with the emphasis on cracking

 

[400bhp]

If you think about what GPS logging is, it's based around a gps co-ordinate and the time at that co-ordinate. So, to determine your average speed between 2 points it will need to take distance travelled divided by time.

Because gps is discrete time and space rather than continuous time and space (continuous being infinitessimly small gaps between each time/gps log) then, to some extent, there is a bit of mathematical guesswork needed to work out average speed.

Add in the fact that it wants to calculate moving average and moving time, the mathematical guesswork increases.

Different data logging sites use different mathematical models I guess.

The garmin site gives different output than Strava (Garmin usually has a higher moving average). IME Strava ignores the speed sensor (if you have one) on your bike, whereas (based on a little guesswork from looking at rides), Garmin uses GPS sensor over and above gps. IMO Garmin is more accurate than Strava for calculating moving time and therefore a moving average speed (based on experience of the time stopped at traffic lights/junctions etc).

By the way, the speed sensor might not be particularly accurate, so IMO a good combination would be to use a blend of the two (if you have a speed sensor).

I'm taking an educated guess at the above but it it's seems pretty intuitive to me.

@gam001 can add something to this.

 

[400bhp]

Yep @400bhp threw a bottle at him and he did a cracking impression of superman.

 

[HLaB]

By the way, the speed sensor might not be particularly accurate, so IMO a good combination would be to use a blend of the two (if you have a speed sensor).

@gam001 can add something to this.

Whether or not it makes a difference my speed sensor calibrates via GPS.

 

[gam001]

[quote="@gam001 can add something to this.[/quote]
Man, the differences used to drive me crazy
Stopped caring now
I trust my head unit for average speeds more than GPS approximations...not that it has anything at all to do with head unit giving faster speeds...
Not sure what the diffs are between those 2 websites though, without spending ages on google...

 

[Hill Wimp]

I have seen @potsy going far faster than that down hill.

Must have been food at the bottom of the hill then

 

[Buzzinonbikes]

On a separate note - @Hacienda71 how do you find the A537? Always struck me as quite a fast road and never thought to cycle it but could be a good option. And then is that the cycle path of the new bypass you are on there or the road? Again, not tried either.
Thanks

 

[Hacienda71]

On a separate note - @Hacienda71 how do you find the A537? Always struck me as quite a fast road and never thought to cycle it but could be a good option. And then is that the cycle path of the new bypass you are on there or the road? Again, not tried either.
Thanks

The A537 from Broken Cross is a fast road but with mostly long straights so cars travelling at speed have good visibility and see you with plenty of time to give you a wide berth or slow. Towards Monks Heath it does get twisty but people generally are pretty patient and only overtake where it is sensible. There is solid double white lines for a lot of it so if you are a reasonable distance from the verge going at a good speed they can't don't really pass that often on that stretch anyway. I do view it as a get me home road though and not a road I would ride for pleasure. There are many nice alternative options though and I tend to use most of these other routes back from Macc to Wilmslow fairly regularly as well.
I have ridden both on the road and the cycle lane on the A34 Alderley bypass. To be honest there is no need to go on the road as the cycle/shared use lane is so good. I only rode on the main carrigeway once as I was in a timed challenge on it, out and back and didnt want to go back onto the road from the separate lane to go around the roundabout and back onto the separate lane again if that makes sense.
Do you go over to Macc much?

 

[Buzzinonbikes]

The A537 from Broken Cross is a fast road but with mostly long straights so cars travelling at speed have good visibility and see you with plenty of time to give you a wide berth or slow. Towards Monks Heath it does get twisty but people generally are pretty patient and only overtake where it is sensible. There is solid double white lines for a lot of it so if you are a reasonable distance from the verge going at a good speed they can't don't really pass that often on that stretch anyway. I do view it as a get me home road though and not a road I would ride for pleasure. There are many nice alternative options though and I tend to use most of these other routes back from Macc to Wilmslow fairly regularly as well.
I have ridden both on the road and the cycle lane on the A34 Alderley bypass. To be honest there is no need to go on the road as the cycle/shared use lane is so good. I only rode on the main carrigeway once as I was in a timed challenge on it, out and back and didnt want to go back onto the road from the separate lane to go around the roundabout and back onto the separate lane again if that makes sense.
Do you go over to Macc much?

Nice one, good info. Yeah I'm from Macc originally so head back there quite a bit to visit people. I usually go through Poynton and up the back of Bollington if I fancy a bit of climbing or Wilmslow and then the road to Prestbury but turn off to Broken cross and across that way. A long way about it but quiet except the fast stretch before turning off the road to Prestbury. Or Alderly Edge isn't a bad option except for THE EDGE!

 

[400bhp]

Nice one, good info. Yeah I'm from Macc originally so head back there quite a bit to visit people. I usually go through Poynton and up the back of Bollington if I fancy a bit of climbing or Wilmslow and then the road to Prestbury but turn off to Broken cross and across that way. A long way about it but quiet except the fast stretch before turning off the road to Prestbury. Or Alderly Edge isn't a bad option except for THE EDGE!

Have you seen how bl00dy fast Hacienda commutes down there?

 

[Hacienda71]

Nice one, good info. Yeah I'm from Macc originally so head back there quite a bit to visit people. I usually go through Poynton and up the back of Bollington if I fancy a bit of climbing or Wilmslow and then the road to Prestbury but turn off to Broken cross and across that way. A long way about it but quiet except the fast stretch before turning off the road to Prestbury. Or Alderly Edge isn't a bad option except for THE EDGE!

Don't mind going over the Edge, although I am never warmed up enough for a hill like that first thing in the morning a couple of miles from my door. The nicest low traffic direct route is Oak Road up through Mottram St Andrew. I sometimes take a bit of a detour and go over the Brickworks and down through Rainow, although that tends to be when it is a bit warmer in the summer months.