Combined Shape Bike IQ

Grade Detection

The gradient on screen should match what your legs are saying. Bike IQ reads the road from your iPhone's barometer, the same sensor that knows you have gone up a flight of stairs, so it feels the hill rather than guessing at it from a map.

Grade detection works on the free version. There is nothing to unlock.

Why Not GPS

GPS is good at telling you where you are and poor at telling you how high you are. Its altitude wanders by several metres even standing still, and on a bike those wobbles turn into a gradient that swings from 2% to 9% on a road that never changed. That is the number most apps show you.

Air pressure drops as you climb, and your iPhone can measure that directly. It is a physical reading of the air around you rather than a calculation from satellites, it does not care whether you are under trees or between buildings, and it notices a change of a metre or two. It is the reason the grade in Bike IQ settles instead of flickering.

Pressure Alone Is Not Enough

A barometer tells you that you climbed. It does not tell you how steep the road was, because the same height gained over a hundred metres and over a kilometre are two very different climbs.

So Bike IQ puts the two together: how fast your height is changing, against how fast you are travelling. That is what gradient is. Reading both at once, many times a second, is also what keeps the number steady, because a gust of wind or a door slamming in a car can nudge a pressure reading, and Bike IQ can tell the difference between that and a real hill by checking it against the speed you are actually doing.

What the Grade Feeds

Gradient is not only a number on the ride screen. It is one of the main inputs to everything else Bike IQ works out:

  • Your power. Lifting yourself and the bike is most of the effort on a climb, so an honest gradient is what makes an honest watt figure. See Virtual Power Meter.
  • The road ahead. The elevation of what is coming is shaded by how steep it gets, so you can pace a climb you have never ridden. See The Road Ahead.
  • Your ride afterwards. Elevation gain, climb detection, and the colour of the route on the map all follow from it. See Ride Report.

Which iPhones

Every iPhone Bike IQ runs on has the hardware for this, so grade, elevation and estimated power work across the range. Older models report height slightly differently, and Bike IQ handles that on your behalf. Newer phones settle a little faster after a sharp change, which you would have to be looking for to notice.

If the gradient looks wrong, the usual cause is Motion & Fitness access being switched off, since that is the permission the barometer sits behind. System Status in your profile will tell you in one line. See Troubleshooting.

Related Guides