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# Personal Bests within a race distance tolerance (Read 1084 times)

Bear with me on this one! Here goes:

When entering race details, I use the exact distance from my GPS, rather than the advertised race distance (which is often wrong in Thailand!). But this means I’m seeing my PBs for very specific distances (2 decimal places), rather than grouping them by 5k,10k etc.

For example, a half marathon race may actually measure in at 20.8km instead of the official 21.1km. However on the personal bests page it would show my time as a PB for “20.8km” rather than “half marathon”. So for all my half marathons I see 5 different PB times rather than just one PB. I understand why this is, but in my mind I still entered a proper half marathon and want this to reflect in my personal best.

My idea is to allow a % tolerance around a race distance then adjust the time to an equivalent PB time for the intended race distance. For example, during a Half Marathon race I ran 20.80km in a time of 1:22:48. This is distance is 1.4% less than the true HM distance, let’s say it is within an acceptable tolerance of 5%, for example. Then, my adjusted race time for half marathon would be (21.1/20.8)*1:22:48 = 1:24:00. So the personal best screen could show:

Race Distance: Half Marathon
Actual Distance: 20.80km
Actual Time: 1:22:48
Pace: 3:59
Event: Thailand International Half Marathon
Date: 2/26/2012

Maybe not all users would want this, so the %ge could be configured by user. Setting the tolerance to 0% as default would give the same results as the site currently gives, but some users may want to allow maybe 3% or 5% tolerance when grouping their races to create personal bests. And it may require a different tolerance for above and below the distance (because if you ran 1% short then you may not want to include as a PB at all, but 3% long may be OK).

Sounds slightly complex I know, but I found myself doing this in a spreadsheet to work out my true PBs!

Simon

Hi Simon,

The PR calculations already have a tolerance built in.  Selecting a proper tolerance is tricky.  The problem is while it may work for a given distance unit (e.g. kilometers), it may erroneously place the race into a separate distance for a different distance unit (e.g. km).  For example, I had to put in special code to keep an 8k race distinct from a 5 miler (8045 meters).

To avoid false positives, the tolerance value is smaller than what you suggested.  The only safe way to do it is to allow the user to specify the tolerance amount.  An alternative is to omit these races from being included in the PR calculation, which you can do by selecting the "Exclude from PR" checkbox next to the workout type dropdown.

Thanks Eric,

I think your suggestion of "exclude from PR" will do the job in cleaning up my PR page, albeit manually.

What are the current tolerances for a Half Marathon and a 10km? These are my most common races but the tolerance isn't working that well for me at the moment (maybe because I'm in Thailand where they don't always measure distances very well!).

It would certainly be a valid argument that if the distance is at all short (even only 0.2km short for a 10km, for example), then it's not truly a PB because you didn't run the distance. But not true the other way around: my 10km PB is actually in a race which measured 11+km on GPS, and that PR definitely stands for me!

I didn't think of the 5 mile / 8km example. Maybe another way around that would be for the user to select the "event distance" or "race type" that they ran for each race. Maybe that would work for half marathon too, to differentiate it from a 20km event.

Thanks a lot for replying so quickly!

Simon

Trouble is, the discrepancy may be due to a poorly measured course, or it may be inaccurate GPS.  If there was an automatic adjustment to the nearest standard distance, it could wrongly adjust your race time when it should not be adjusted.

Well at least someone here is making relevance to the subject. - S.J.

Trouble is, the discrepancy may be due to a poorly measured course, or it may be inaccurate GPS.  If there was an automatic adjustment to the nearest standard distance, it could wrongly adjust your race time when it should not be adjusted.

+1.  My GPS is wrong, roughly, all the time.  Especially on trail races.

I update the distance to match the official distance.  I even did this for a 5K that virtually everyone at agreed was really more like 3.23 miles, even though it made me want to scream.  I obviously leave the time alone, and I leave the splits so I can see/keep the GPS data.

If the course was too short, I'd exclude it from PR.  Not just measured too short by my GPS--definitely too short.  And I'm not sure what threshold I'd use for that, either.

"When a person trains once, nothing happens. When a person forces himself to do a thing a hundred or a thousand times, then he certainly has developed in more ways than physical. Is it raining? That doesn't matter. Am I tired? That doesn't matter, either. Then willpower will be no problem."
Emil Zatopek

Yep.  GPS is wrong ALL THE TIME.  If it's a half marathon, it doesn't matter what the ole GPS says, ITS A HALF MARATHON.  If I have any information or strong evidence to convince me that the course was either long or short I don't adjust my times - I check the Exclude From PR box .

Yep.  GPS is wrong ALL THE TIME.  If it's a half marathon, it doesn't matter what the ole GPS says, ITS A HALF MARATHON.  If I have any information or strong evidence to convince me that the course was either long or short I don't adjust my times - I check the Exclude From PR box .

This is the proper approach. If you raced a 5k, just put the distance at 5 kilometers, and enter the time. If you raced a half marathon, put the distance as 13.1 miles, and enter the time.

There is no reason to assume that your GPS is more accurate than the course was measured (unless the course was measured very poorly, and then of course it would be obvious.)

I agree that putting in the correct distance works, but doesn't fix Simon's problem.  One thought would be to have a separate Nominal Race Distance field, which defaults to the entered distance, but can be overridden if the GPS distance is desired.

BTW, I have a problem with the current tolerance built in, because 1600m races are included in the 1 mile PR.

Lou, (aka Mr. predawnrunner), MD, USA | Lou's Brews | lking@pobox.com

BTW, I have a problem with the current tolerance built in, because 1600m races are included in the 1 mile PR.

Organizing a 1600m race rather than the well-established 1500m or mile distances is just perverse!

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Organizing a 1600m race rather than the well-established 1500m or mile distances is just perverse!

The 1600 is the standard in many high schools, and the track is built much more naturally for it, and splits are much easier as well.

It's a 5k. It hurt like hell...then I tried to pick it up. The end.

I agree that putting in the correct distance works, but doesn't fix Simon's problem.

I'm unclear on what exactly that problem is.

If you ran a race denominated "half marathon", then you come away from the event with a race time.  That time divided by the HM distance yields your official pace for the HM.  Anything else is just not reality.

So if Simon DOES want his 13.05mi or 13.15mi (or whatever distances, you get my point) races to be half-marathons and RA doesn't automatically recognize them as such, he should just type "13.1" in the distance field.  RA will auto-adjust it to "half marathon" and (properly) calculate pace based on the default HM distance.

If Simon DOES NOT want his 13.05mi or 13.15mi races to be half-marathons, he should either:

1. check the "Exclude from PR" box.  The only remaining issue I can see is if RA automatically recognize those races as HMs anyway and adjusts them to HM default distance (but I can't see why someone would run a HM, have his Garmin record 13.05mi, and then NOT want to recognize it as a HM); OR
2. create a workout type called "Race...ButNotreally" or somesuch, and classify the activity entry as such.  Then RA doesn't see it as a Race to begin with and therefore will never try to make it a default HM distance.  Since Simon doesn't recognize the event as a real race, either, this aligns his interest and the RA log entry.

"I want you to pray as if everything depends on it, but I want you to prepare yourself as if everything depends on you."

-- Dick LeBeau

That's all useful, thanks. My objective is only to know the best possible estimate of how far I really ran, so I can compare my true pace across races. I would like my log to show this distance rather than the advertised race distance, IF the race distance was wrong.

It looks like most other people would trust the race distance over any GPS reading, in which case the answer [to my PB page problem] would be simple, to overtype the GPS data. However, especially in Thailand I have some doubt about how accurate the race distances are, so my assumption has so far been that GPS is more accurate.

To validate, I always search Garmin connect for other people who have done the same race, to make sure my reading is consistent. Every time I think a race is long or short, I find that other people's garmin GPS devices are saying the same thing. So it looks like a minimal amount of error between different devices, but of course they could all be wrong. I guess this could be explained by the relative position of satellites or calibration errors in the device. One thing I haven't done is check other types of GPS such as mapmyrun etc. Does anyone have any experience of big differences between types of GPS devices?

In support of the people trusting the official race distances, I raced a 16.8km organised by Adidas this morning. So this really should be accurate, a) because it was a large, competitive event organised by a large organisation and b) because 16.8km is such an odd and specific distance, it would have to be correct! Interestingly enough, my garmin GPS measured it short, at 16.3km, and everyone else on garmin connect also measured it short. If the other types of GPS devices give the same, I may still be trusting Adidas on this one!

One other option, short of a Jones counter, is to map it here using Google/RA maps.  At maximum zoom, these are very accurate - assuming you know exactly where you ran.  Yeah, and Google doesn't always have the highest resolution available.  I don't know how well they've done in Thailand.

Well at least someone here is making relevance to the subject. - S.J.