Despite the obvious suffering they cause us, hills deliver both challenges and rewards. When describing races or trails, people tend to focus on the distance of the route. While this is important, it doesn’t give a clear indication of how difficult the route actually is. Ten kilometres sounds pretty easy, until you realise it’s up the Swartberg Pass. This is where a far more crucial statistic comes into play; ASCENT. – Paulo Conde & Gresham Enerson (Rookie Project – MTB for Average Bros)


Ascent is defined as the total number of vertical metres gained over the duration of a ride. Obviously the more you climb, the more you’re fighting against gravity, and the more effort you will need to exert over the given distance. It therefore stands to reason that more ascent typically equates to more suffering.

Looking at distance or ascent individually is a bit like watching a 3D movie using only one eye. The picture isn’t very clear and you’re bound to end up with a migraine. It is only when you look at distance and ascent together that you can get an accurate understanding of how difficult the route is likely to be. Sure, things like terrain and weather also play a part, but let’s focus on the topic at hand for now.

Measuring ascent

There are two fundamental methods of measuring ascent; barometric pressure and GPS triangulation.

Devices that use barometric pressure rely on changes in atmospheric pressure to determine a change in altitude. These devices are relatively straightforward as they rely on processing a single input variable, although their accuracy can be affected by changes in the weather, or by debris clogging their sensors. They are however widely accepted as the most accurate and consistent. Just look at the latest sports tracking devices – even though they are equipped with both GPS and barometric sensors, they opt to use the barometric sensor readings to measure ascent. To understand why, let’s have a closer look at GPS.

GPS devices rely on satellites to triangulate your position. While this may sound like infallible space-age tech, there are a number of issues with this method.

Firstly, location accuracy is dependent on the accuracy of the GPS device used. Cellular phones have weak GPS receivers and are only accurate to within a few metres, whereas GPS-based sports devices have much stronger receivers and are accurate to within a few feet. So even with a state-of-the-art device, standing still while recording a workout would pick up minor movement based on the inability of the device to precisely pinpoint your exact location.

Secondly, accuracy is affected by the network of satellites used to determine your location. The more satellites there are casting their beady eyes on you, the more precise your location accuracy will be. Newer GPS devices make use of both the US (NAVSTAR) and Russian (GLONASS) global network of satellites resulting in much greater accuracy.

Thirdly, obstructions like mountains and buildings interfere with GPS signals, so riding in a built up urban area or a very remote mountainous area can also adversely impact location accuracy.

Finally, in a bid to overcome the myriad of inaccuracies, GPS-based devices pass the raw GPS data through an algorithm to smooth out the profile and this means that each device can (and will) report a different ascent given the same GPS data. In addition, some GPS software cross-references the raw GPS data against geographical survey data in a bid to further ‘improve’ accuracy, but the data they are cross-referencing against is usually mapped as ‘tiles’ that are between 10 and 30 metres wide, so any dips / rises within these tiles are not accurately reflected either.

Not one to believe all this theoretical mumbo-jumbo, we strapped on our arsenal of devices and hit the trails for a decidedly unscientific test. As it turns out, the guys in white coats were on the money.



While the barometric devices (Polar and Garmin) were both consistently within a few metres of each other, the GPS devices were all over the place. Endomondo tended to under-report the ascent by anywhere between 8 and 30% of the average barometric readings for the ride, while Strava proved to be more indecisive than a teenage girl getting dressed for a date. The fact that both GPS readings were obtained on the same ride, using the same device, yet they varied by around 30%, really puts things into perspective.

So what are race organisers using?

Cool. So we’ve established that finding out ascent is important, but it’s become clear that we also need to know how the ascent was measured so that we can compare apples with apples. To this end, we decided to ping some of the more prominent race organisers to get their thoughts.

What we found extremely interesting is that it is not always possible to pre-ride the route because races often traverse lots of private land. Access to this land often involves taking fences down and unlocking gates so the route only comes together a few days before the actual event. In this case, some race organisers opt to use Google Earth to plot the route and get an estimation of the distance and ascent. While this may not be entirely accurate, it’s leaps and bounds better than going into the race blind.

When it is possible to pre-ride the route, the devices used to measure ascent and distance were typically sport-specific GPS devices, but they range from older Garmin 705’s to newer Mio GPS units (a relative newcomer to the SA market).

In a very interesting development, Francois Theron from Advendurance advises that they are fully aware of how important accurate information is, especially in their ultra-marathon races. To assist us average bro’s in deciding whether or not to tackle one of their races, they’re piloting a ‘rate your race’ system using Vavavox. The idea is that riders can go on to the website and leave comments on any of the MTN National MTB Series races they have ridden. They’ll also be introducing a ‘difficulty rating’ in the near future that will allow riders to rate the technical difficulty, physical difficulty and overall race quality. Over time, the accumulation of all of this feedback will give prospective riders a very good picture of what the race entails.

How does this affect us average bros?

The year we trained for our first Hill-2-Hill Ultra Marathon, we did most of our riding in the sugar cane fields around Umhlanga. Although we were covering the 100km race distance in our training rides, we got lulled into a false sense of security because (a) the ascent was nowhere near the ascent we had to cover in the race, and (b), the terrain was mostly open dirt roads whereas the race had a large proportion of singletrack, which is a lot more energy sapping. Needless to say, we shed a few (manly) tears on race day!

The moral of the story is that it is important that your training for tough races simulates the race as closely as possible, so you should make every effort to get your hands on a route profile that gives you accurate distance and ascent. Knowing how the ascent was measured will allow you to compare apples with apples. A difference of a few metres here and there won’t kill you, so one could argue that the accuracy of the reported ascent is a bit of a moot point.

One final pearl of wisdom from us on this topic: We highly recommend that you double-check the accuracy of the reported ascent figures wherever possible. We had a few sleepless nights when, a week before the race, we found out that the Sani2c organisers had made a minor typo on the ascent figure for day 1. Instead of the claimed 450m, we discovered it was actually 1450m! With the proliferation of high-end cycling computers these days you should be able to find route profiles on race websites, online forums or dedicated sports portals such as Strava or Garmin Connect. A five-minute internet search is a small price to pay for the peace of mind that comes with knowing you are fully prepared for what’s to come!

Gresham Enersen and Paulo Conde are not pros; just a couple of average bros that love riding their mountain bikes – in the real world… They’re on twitter: @grusomegresh and paulotheporra


TREAD Magazine is sold throughout South Africa and can be found in: Spar, CNA, Exclusive Books, Discerning bike shops and on Zinio

*Originally published in TREAD Issue 28, 2014 – All rights reserved



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