In reply to Minneconjou Sioux: It would depend mostly on the friction between the back wheel and the road. I find the limiting factor on climbs like Hardknot pass is either keeping the front wheel on the ground when I sit down, and stopping the back wheel spinning if I stand up.
Both these things tend to start happening at around 25-30%. If there was more friction from a thicker back tyre or a really grippy road you could stand up, lean forward and then the limiting factor would be your gears and leg power.
I would imagine my limits are around 25% on a fairly slick wet road, with normal winter tyres on a road bike. 30-35% sustained in good conditions with normal tyres. I don't have a clue about if I was to change the gearing and stick on a mountain bike tyre on the back - short sections of 50% perhaps?
It would be pretty tough to find out though because you would have to first build a new road or ramp to test it. Steepest at the moment is thought to be Baldwin Street at 35%.
In reply to ablackett: Just seen and read the link, some interesting thought but his power numbers are too low. Top riders can push 500W all the way up a climb and sprinters can do 2000 for short sections. So that isn't going to be the limiting factor.
He ignores at the end how the amount of weight and therefore friction, going through the back wheel changes as the riders weight goes forward. From my experience this is the limiting factor so fairly useless piece of work! Still, an interesting read.
> (In reply to ablackett) Just seen and read the link, some interesting thought but his power numbers are too low. Top riders can push 500W all the way up a climb and sprinters can do 2000 for short sections. So that isn't going to be the limiting factor.
But there were riders pushing their bikes at 27% in the Tirreno-Adriatic?
> (In reply to ablackett)
> But there were riders pushing their bikes at 27% in the Tirreno-Adriatic?
Bicycle geometry as opposed to theoretical power levels would be more relevant on really steep inclines. It would probably be possible to design a bike where your weight distribution and position would be such that it'd be easier to cycle up steeper inclines. Though it would probably be very inefficient elsewhere and a dog to cycle on longer flat sections. Or in simple terms power means nothing without having the ability to transmit it.
In reply to Minneconjou Sioux: That's because a lot of them were over-geared, not because they weren't physically capable. Particularly in the wet at that angle you need to keep it reasonably smooth. Hardknott is steeper than 27% and fine in the wet if you're set up right or fresh enough to turn a high gear with control. The surface is slightly different to the relatively smooth Italian tarmac but I'm not sure if that's helpful or not!