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Elevation gain and loss way out

Former Member over 5 years ago

Forerunner 235, with elevation correction turned off is showing over 800m of elevation gain and 1300m of elevation loss while doing a 6km flat run through central London. 800m elevation gain is the equivalent of a mountain 10kms long and 8% incline! With correction turned on it shows about 20m of elevation gain! Having read other forum questions it seems that the FR235 Altimeter is GPS based so not 100% accurate but also shouldn't be crazy like that stats mentioned above. If it was an internal Altimeter then I would assume it was just faulty. Could you please advise what may be going on? Many thanks

0 tmk2 over 5 years ago

Indeed, the FR235 does not have a barometric altimeter, and relies on GPS altitude. GPS altitude is notorious for inaccuracy. In unfavourable conditions, like Central London, fluctuations of +/- 100 meters are not unexpected. This is why elevation correction is enabled by default for devices without barometric altimeter.

0 NickMN over 5 years ago

if you take a look at elevation graph and your run location at the times of peaks/valleys it might shed light on the issues. Typically the times I see issues the most is if I am in area that would have non-detailed elevation info like off road trails where it hasn't been surveyed as well. Also if near water, cliffs, retaining walls, bridges/overpasses...etc... all can cause issue if it thinks you ran up onto the bridge, when really you went under it... or it thinks you were zig/zagging up down the river bank... when really you stayed up on the flat path along the bank. Or you cross flat bridge.. but it thinks you ran down the river bank into river... and back up the other side. etc etc... however in 6km 800m just seems a bit crazy... watch hard reboot (30sec+ power button until it turns off) could maybe help.