Garmin race time predictor accuracy?

Garmin (Firstbeat) has updated its race predictor to make it supposedly more accurate. It's now much less useful.

It used to basically estimate your VDOT and then just give you race predictions based on that. So your marathon would probably be too fast unless you were very well trained, but it gave you a decent estimate of your aerobic ceiling and something to shoot for.

Now it tries to take ALL of your training into account, so it will estimate much slower long distance races unless you run high volume with some fast long runs. This is not a bad idea in theory, but their implementation is garbage. Mine is routinely off by 30 minutes for the marathon, even after running a marathon. Same thing with the half. For example, I did a 16 mile fartlek, alternating MP and steady miles. I split 1:15 for 13.1 inside that workout, and afterwards my Garmin congratulated me on my newfound ability to run a 1:22 half marathon.

What you should do is just take your Garmin VO2max (really it's a VDOT because it can't tell how much of your performance comes from RE and how much comes from VO2) and plug it into the Daniels table. That'll give you basically the old race predictor.

It's garbage. ran a track time trial of 15:25 but my 245 predicts a 17:17 5K

Current predictions for me with the shape I think I am actually in...

5k - 17:25 (hoping for 15:30ish in a TT next week so +2 min)

10k - 36:44 (+3 min)

Half - 1:21:26 (+6-8 min)

Full - 2:54 (probably about right... maybe +4 min or so)

I've been using this feature as long as it's been available - several years now - and my experience has always been that it predicts much faster race times than I'm really capable of doing. Like a minute or so for 5k, consistently.

I'm not sure why this is the case, my best guess is that my HR values seem to be much different than what is considered "normal". I've always had a relatively high max HR for my age and train at much higher HR values for each zone compared to "normal" runners.

The Garmin race predictor is not accurate. My Vo2 max has varied between 41 and 49 recently. It moves too much based upon a couple workouts. On Oct 31 I ran a marathon in 3:44 and it predicted under 3:30 later that day. It shows my fastest 10K from a 6.5 mile run and a week later it predicts my 10K time as 2 minutes slower. There kis no way I lost that much fitness in a week and if I did it wouldn't have known.

Sometimes the recovery time says 0 hours and I'll go on a 2 mile walk at about a 21 minute per mile pace and it tells me I need a 21 hour recovery. Two hours later I ignore the recovery and go on my 10 mile run.

Strange, because I think mine is the opposite. I also have a very high HR and my marathon prediction is about an hour slower than I can actually run. That should be a contest. Whose training watch is off by the most!

Gps was made for fighter jets and US navy ships to determine location. If you aren’t one of those then there will be substantial occasional inaccuracies.

It suck big time. If I ever run one of those times Ill send a cake to Garmin HQ

From a personal experience, the older version of the predictor sucked big time, in that it always overestimated my potential. But ever since I've been using the FR945 (always with an HRM chest strap), I'm tending to respect it more and more. It predicted 17:52 5K before my 5,000 m TT, which I ended up finishing in 17:51 (Stryd footpod predicted 17:43). Other distance predictions are well in line with my PR's and capabilities. I think the big difference in the updated version is taking climate into account.

Man Overboard wrote:

I've been using this feature as long as it's been available - several years now - and my experience has always been that it predicts much faster race times than I'm really capable of doing. Like a minute or so for 5k, consistently.

I'm not sure why this is the case, my best guess is that my HR values seem to be much different than what is considered "normal". I've always had a relatively high max HR for my age and train at much higher HR values for each zone compared to "normal" runners.

Me too, and I think your right about it not really understanding people with higher HR's. It thinks i'm waay fitter for say a 5K than I actually am right now, mostly I think because I'm 'hammering' my daily runs i.e. in the 150-160 range and not jogging them at 130.

It's a nice little data add on so people will spend more time on their apps but it is far from perfect. Probably more valuable to an untrained runner or newbie but unlikely to be particularly helpful to a veteran runner.

predicts 19:11 5k when i ran 18:00 as a hard tempo a week ago

predicts 1:28 half marathon whereas i'm actually unclear if could actually run 13 miles

HETHEREYOU wrote:

Me too, and I think your right about it not really understanding people with higher HR's. It thinks i'm waay fitter for say a 5K than I actually am right now, mostly I think because I'm 'hammering' my daily runs i.e. in the 150-160 range and not jogging them at 130.

I don't understand, if it thinks you're hammering when at 150-160 when you're really chilling wouldn't it underpredict your fitness. It would think you can only go a little bit faster in a race, whereas you can actually go much faster?

Calculators by McMillan, Tinman, Daniels are very accurate if you're using race distances which aren't too far apart.