This single question breaks down into even more questions:

1. Why do different sites report different elevation gains when you plot out the same course? Why different values when you use the same GPX file across sites?
2. Why do different tools(watches, bike computers, etc) RECORD different elevation gains over the same course.

For the purposes of this post, I’m more interested in question 1. I’ve used the following sites in my attempt to find the best tool to get a idea of a courses elevation profile(and overall elevation gain).

-MapMyRide
-RideWithGPS
-Garmin Courses
-pjammcycling

I suspect the differences between the tools is largely related to how many “points” the tool uses to keep adding up elevation gain, but one thing that really makes me scratch my head, is how 2 different sites, using the same exact GPX file can report big differences in elevation gain!

Here is the root of my question.

I’m considering doing Ironman Finland, but I’ll never be able to fly out there to try out the course, so I need to have a good idea of the elevation profile to train properly. According to the Ironman site for that race, the elevation gain is only about 3,600 feet(although it is amusing the value that shows up in the race description is different then the value that shows up on the actual course map). I know IM race descriptions aren’t always accurate, having done Ironman Wisconsin, I know there is more elevation gain than is reported on the IM Wisconsin site. One interesting thing is that the Ironman Finland race site actually has a .gpx file download. But when I upload that file into different tools, yet again different elevation profiles. Some examples

Garmin Measurement(based on GPX file): 3,575 Feet.
RideWithGPS site(based on GPX file): 4,718 feet.

Why the difference - its the same file???

Also, I’ve seen others have created the Ironman Finland course on RideWithGPS and those courses report total elevation gain of up to 7,500 feet. And yet another site, pjammcycling, shows a whopping 9200 feet.

So my question to the community - what is the best way to try to figure out elevation gain for a course you might not get to tackle until race day? And more importantly, does anyone know the actual elevation gain of the Ironman Finland bike course :) ??

Thanks all for reading my long winded post and weighing in with your thoughts/knowledge on the topic.