Print off a 3:45 pace band if you haven't already. The Garmin will most likely catch up with itself and be there or thereabouts but you may well lose accuracy of a mile split or two around the Docklands. Definitely best to check your splits against actual mile markers.
Turn off auto lap and do what cougie says - hit lap as you pass each mile marker. If you miss one and want to look at the average per lap you just need to hit it twice at the next one. Also turn off auto pause as it will stop the timer when you go through the tunnels (there is more than one). The last thing you want is to think you're on for your target time only to find it's a minute or more out because of the tunnel.
On the pens, get into the pen early so you can get at the front of it. When they remove the ropes between them people will start to move forward so you'll probably end up further forward anyway.
I will set Garmin laps manually by the mile markers, and display average lap time to get a true min/mile pace up to the last mile marker. I personally wouldn't use the Garmin distance for any pacing if your target is important to you, although current ave lap pace will be fairly close for pacing the mile you are on.
Just don't try and make time up too quickly - you will probably burn a lot of energy. If you get held up, catch up over the next hour / hour and a half
There's no point turning off autolap because, as soon as you come out of the tunnel, the Garmin will get a signal within a few seconds and will start calculating again.
Don't agree with that Intermanaut - no point in busting a gut only to find garmin is 1 or 2% out and you miss out on your time. Best used as a stop watch in an important race - fine if the accuracy isn't an issue, e.g. trainining or a relaxed race.
I like to have the Garmin on autolap so that I have splits to look at afterwards without having to press any buttons on the way round. I'll also have "pace - lap" showing to give me an idea whether I'm in the right ball-park. Neither of these things precludes wearing a pace band and checking this against the actual mile markers on course. The more info the better as far as I'm concerned, you just have to use your common sense to realise that what the Garmin calls "mile 12" might actually be "mile 10.98 to mile 11.97" or whatever.
The two tunnels are at West Ferry Circus about 200m long and Lower Thames street about 400m long, but you may well lose the signal around Canary wharf too.
my garmin is set to pause when i pause.if you have yours set like this remember to turn the autopause off.otherwise if you stop for a pee or go in the tunnel your watch will stop and you will think you are on pace but you w3ill be out by the time stopped......
also remember that the garmins usually measure wrong because the race line can not be followed.....quite often it will measure more than 26.5 miles.so if aiming for a time make sure you run a few seconds a mile faster than that from the start to make up for the fact you will be a few hundred metres form the finish by the time your watch measures a marathon
In every mara I've done my garmin always overmeasured the distance so as the others say- if you have a set target, forget about auto lapping and trust the mile markers. Manual lapping all the way for me in all races.
Are there kilomoter markers as well as mile markers?
I found the above article when I was looking for something else....you may find it interesting in how the Garmin works and they have analysed data from a previous London marathon. Basically it is pretty damn accurate but obviously if you're not following the (blue) racing line which is impossible if it's crowded it won't be 26.2 miles anyway and there will be slight inaccuracies around the likes of Canary Wharf.
Something I've always wondered is it more difficult to connect to lock onto a satellite at the start when there are thousands of others Garmins in such close proximity or does it not make a difference. I have never had a problem before but I've never done a race on the scale of London before.
+1 for manual lap and using a pace band.
Yasunaga wrote (see)
Are there kilomoter markers as well as mile markers?
Do you know i think they have them for 5,10,15,20, 25,30,35 and 40 km....trying to remember for sure
miles mean nothing to me so I kind of rely on the Garmin if no km markers
I"f you measure your distances in kilometres, these will be marked every 5km. To find out where the mile and kilometre markers sit on the course, see our interactive course map"
..from the VLM website
..and +1 for the manual lap and pace band or stopwatch and pace band. I found that my brain was too frazzled to realise my Garmin had started to measure incorrectly around Canary Wharf
There are definitely chip timing mats at each 5k, so that and the Garmin would be enough for pacing in metric I reckon. I "ran" Paris in metric and found it quite nice breaking it into 10k chunks.
I work in Canary Wharf so do some lunchtime runs around there and my Garmin often tells me I'm running 4 minute miles towards the start of my run - are you guys telling me this may not be the case?
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