GPS (Garmin) accuracy

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Old Croc Mar 2017 11:36am, 31 Mar 2017 28,395 posts	0 Old Croc Sorry for a (very) delayed reply to above. The SCPF is a value you add into calculation of calibration ride values to ensure a degree of accuracy - 0.1% added - to do exactly what is called prevent a short course measure. So you do a calibration ride and calculate 2803 clicks per km - you then add 0.1% onto that for measure ride. Then calculate based on that where each km mark is precisely. When I do a measure I make a detailed note of mile or km markers (depends on organisers preference) and take a photo - usually my bike is shown at the exact location as a guide for organiser. A description may be "3m before lampost no 235 in direction of runners" or "third fence post before gate on left hand side" - it's then up to organiser to put up the sign. The photo then reinforces that precise location. the guy who did my practical exam assessment told me to write the report and description of each point so that the man in a council van setting up at 3 a.m. before the race could find the exact spot.
Nelly Mar 2017 12:05pm, 31 Mar 2017 3,721 posts	0 Nelly Many thanks for the detailed response Old Croc. I think I came to that conclusion myself last year from further research in to the measurement methodology. Larkim - if ALL organisers (not just those that have got it wrong in the past) were only too aware of their responsibilities then why has it happened again at least twice since the issues in the NW last year? In fact, given Great Run tweeted this twitter.com in April last year and yet still managed to mess up the Great Scottish Run course in October, surely this demonstrates that the potential post race embarrassment is insufficient motivation to ensure the course is setup right!
Old Croc Mar 2017 12:17pm, 31 Mar 2017 28,396 posts	0 Old Croc Personally I am only doing smaller events but I go out with race organiser before a measure and establish the route - and have then revisited the route with them post measure if necessary to clarify any potential confusion points.
Bazoaxe Mar 2017 12:36pm, 31 Mar 2017 11,021 posts	0 Bazoaxe I wonder of the course inaccuracy is becoming more obvious now with more GPSs in use and more high profile events and social media to publicise the suspicions. Think I am coming up for 10 years garmin ownership now and I know that I was suspicious about 3 smaller races, two of which have been remeasured and were short and one which no longer exists. 2 were PBs that I have since bettered but one remains a PB which I don't now trust. I also have one other PB on a course I always garmin a bit short and I am not sure about either. In the good old days no one would have known if a course was slightly out !!! Which brings me to another point, although garmins are not 100% they are a fabulous pacing aid. I am not sure how in the pre garmin days when pacing was all doen to feel that those guys managed to get it right -
larkim Mar 2017 2:57pm, 31 Mar 2017 1,786 posts	0 larkim @Nelly - I know of at least one local race which had measurement issues and the race organisers were defiant about hiding it (St Helens 10k ISTR) a few years ago. I can't imagine that happening today, there's more "mea culpa" about it. But the reality is that mistakes happen, and often there's next to nothing that can practically be done to ensure 100% course accuracy. I admit with hindsight some of the bigger cockups do seem to have been harder to get wrong than to get right, but race organising teams are small and jobs have to be devolved down the chain of command. Perhaps its more appropriate to have a "glass half full" perspective and recognise that 99% of races seem to be organised on accurately measured course, accurately set out on the day. Perhaps I'm too sympathetic to errors? But Baz makes the point I was trying to suggest - I'm sure that in the 1960s through to early 2000s there were countless courses that were incorrectly laid out or measured, but no-one would ever know because there wasn't a way of having bucketloads of runners record the route on small electronic gadgets. These days every man and their dog has got a GPS on their wrist or on their phone, and whilst they're clearly not perfect in general the source of info about course measurement errors has largely started with that dataset being used to question things initially.
K5 Gus Mar 2017 3:22pm, 31 Mar 2017 2,112 posts	0 K5 Gus Those were the days, back in the 80's, and 90's with the trusty digital Casio and hope that the mile markers were in roughly the right position, and that your head was not too scrambled so that you could still remember what the split was at the previous marker and then do the subtraction to work out what that last mile was. Now 43:27 minus 36:49 or was is 36:43, is............. aaargh bugger it, feels alright just keep going at this effort
Nelly May 2019 8:10am, 6 May 2019 3,887 posts	0 Nelly Another high profile race the wrong distance... Belfast City marathon 460m long! theguardian.com
Bazoaxe May 2019 8:14am, 6 May 2019 14,527 posts	0 Bazoaxe Apparently it was a new course and the lead car took 2 wrong turnings which added the distance.