How steep a hill can a bike be ridden up?

Factual Questions
1

Most mountain biking forums have people posting outlandish claims about the steepness of climbs they’ve taken on their bikes. Its quite common to overestimate the grade of a climb IME, so I was wondering what the SD of the matter is; how steep a hill can one ride up on their bike? (I reckon there is enough factual content here to merit a GQ.)

To define some terms: Say we’re talking about a sustained climb of half a mile. To make things simpler we’ll deal with a flat road surface, and the guy riding up it is your local club cyclist, ie not a professional but a fit guy nonetheless. How steep before they die in a fire of lactic acid?

Also, consider a very short and steep section, the like of which is typically found on mountain bike trails. Say 10 metres long, what gradient do you think can be cleared?

2

I predict that the grade will be under 90 degrees.

3

If the bike can be a trike (so you don’t have to worry about keeping balance), I think the limit may be the tire road friction (at a certain point it will be so steep that the bike will slide down even with the wheels locked)

Brian

4

To answer your second question, look into trials riding, sometimes called observed trials, which is not so popular in the U.S. as in Europe. The best riders can climb almost any surface as long as there are some small flatter spots to hop up and down and regain balance. Competitors try to make it through sections of a course without putting their feet down. I’m guessing the steepest 10m section of one of these courses might be a 60-70% grade.

Here’s one website:

trashzen.com

and another with videos:

http://www.discovermountainbiking.com/videoclips.asp

Even more astounding is observed motorcycle trials, in which the competitors climb the same nearly vertical surfaces on specially designed bikes without putting their feet down.

5

I about match your rider description. Looking back on guide books the best that I have done is about 1000’ vertical over about 1 mile so what is that about 20%?
Keep in mind that this is mountain biking and usually what wears me out the most is the quick 5 foot technical sections that you have to slam on, if those come too close to together that’s usually what gets me touch a foot down. If it were just a smooth dirt road I’d guess I could around 35% would be possible for 1 mile.

6

This guy tried, and failed, to ride up Dunedin’s Baldwin street (38%.) More telling, when asked, by a tourist, to pose for a photo at the top, he found himself sliding backwards, so it would seem that the limit of tire grip is something less than 38%.

7

Thanks for the link Death Ray. It seems that a 30% gradient is at the limit of what can be ridden up for any length of time by most folk, on the road. Trials riders can ride anything, and the short steep climbs I was talking about in the OP can probably be cleared up to 50%, maybe.

8

I very sceptical: that guy is saying there is an actual pave maintained town road that is so steep you’ll slide down it on rubber in the dry? Nah. Don’t believe it. He has to be exaggerating.

9

Yeah, good point. There must be some formula for working out the grip limit for a bicycle tire.

10

I doubt if the limit is determined by grip but by the layout of the bicycle. At extremely steep angles it would be difficult to keep the center of mass of the bike and rider in front of the contact patch for the rear tire. The center of mass also has to be sufficiently far forward that the torque on the rear wheel from pedaling doesn’t cause the front wheel to lift and send the rider over backwards.

Perhaps someone could design a mountain bike similar to the special motorcycles used for hill climbs. The swingarms for the rear tire are stretched to ridiculous lengths so the weight of the rider and engine is far enough forward to not cause a backflip.

11

I’ve ridden up Rosedale Chimney Bank in North Yorkshire a few times, once with saddlebags full as I was youth hostelling at the time. This hill gets to 33% in places, and where it does, its fairly straight, you simply can’t zigzag uphill to ease the gradient becuase its so steep that it just turns your front wheel downhill when you switch zig to zag, or vice versa.

If this road is damp and you have high pressures, say 140 lbs, then your wheel will spin, seen it, done it.

http://www.paulcurran.ndo.co.uk/Articles/1987/871025-NationalHillClimb.html

The main problem is that your front wheel lifts if you are not incredibly smooth pedalling, and the angle of the hill is so acute that its difficult to get over the top of the bottom bracket because your handlebars are so much higher than the rest of the bike and effectively rotated backwards.

I have also ridden Hardknott Pass, which is also very nearly as steep as Rosedale, but longer, and to keep the front wheel down I had an handlebar back which I filled with rocks, this worked fine but made the steering somewhat interesting.

Given a low enough gear, and a highly modified frame along with low pressure tyres, you might be able to get perhaps near to 40%,but on a racing cycle I think that Rosedale and 33% is pretty near to the limit.

I should perhaps add that Rosedale is rather steeper on the inside of the notorious hairpin, steep enough to lift the wheels on cars which have limited suspension movement, but realistically this part is very short, and if you time it right you can take the longer way around it but you then are going on the wrong side of the road so you have to watch out for traffic.

This picture does not really do it justice.

http://www.cs.uvic.ca/~msanseve/england03.NOPERMS/lincoln/index.php?image=IMG_1546.JPG&d=d.html

This is better, but this is not the steepest part, and the bad hairpin is just at the vanishing point of the road as it sweeps around left.(you can see the rider cheating by zig zagging across the road, around that top corner you can’t do that any more and you tackle it dead on)

The grassy bank that runs upward from centre upwards to the left is a very good indication of what lies ahead as that is the road edge.

http://www.cs.uvic.ca/~msanseve/england03.NOPERMS/lincoln/index.php?image=IMG_1547.JPG&d=d.html

12

I wonder if Copenhagen’s Roundtower Unicycle Race is helpful here - recall that being rather steep… and variably graded.

This blog has a couple of photos of the inside of the tower, although the perspective may not be helpful.