Folding Bikes - Dahon Speed Pro poor at hill climbing
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07-28-07, 05:13 AM
Hi fellow folders :)
I've got a 2006 Speed Pro (amongst other folders) which I generally enjoy riding. There is a very noticable tendency for the bike to lose a lot of speed when meeting any kind of incline, when compared to any of my larger wheeled bikes.
Do people think that this is just a side effect of the very light wheels which don't have as much inertia compared to a larger wheel?
One solution might be to fit larger, heavier tires, which would help soften the ride a bit too.
If you've ever ridden rollers, you know that accidentally riding off the side of the rollers onto the floor doesn't shoot you across the room. You actually stop right where you hit the floor. The inertia in the wheels is miniscule compared to the inertia of the mass of your body.
Riding up hills is about power-to-weight and efficient rider position.
I always get dropped on hills, and have smaller wheels than you do. Even/especially when the other riders stay in their saddle. (I'm always in my saddle.)
It's probably technique. In theory, smaller wheels are better for hill climbing. This is mostly because they wheels have less inertia! When accelerating or climbing, you want the lightest wheels possible.
Of course, your bike is heavier than a road bike and has an internal hub, which doesn't help, but probably also doesn't hurt much either. Heavier tires will definitely make things worse, not only by increasing the weight, but also by possibly increasng your rolling resistance. Heavy tires tend to be lower pressure and have tread. However, they might improve the comfort of your ride. (Thus, if you are riding on very uneven surfaces, it might improve your speed.)
Does anyone know of a good posting on optimal hill climbing technique?
07-31-07, 05:28 AM
I understand that that the total amount of momentum stored in me (90Kg) plus the bike (10Kg) is going to be more significant that the inertia stored in the wheels, but there is definately something else going on here. I only notice this effect at the start of a hill, once steady state conditions are met the climbing speed of the bikes is about the same. One of the reasons that I feel the wheel/tyre inertia is significant is that my Brompton (smaller, but heavier wheels and tyres) does not suffer from this as much, although the bike is a terrible climber generally.
Perhaps it is simply that I can put down more power on a big bike, or the Brompton compared to the Speed Pro. My technique remains the same - I never come out of the saddle, and am pretty quick up hills.
Couple of things come to mind.
1) The Speed Pro has an SRAM Dual Drive. When you are not in the 1:1 range of the dual drive you will take a small, but real, efficiency hit. I recall that the middle range of the dual drive is 1:1. So, if when hitting a hill you shift into the low range, you suddenly will be faced with that additional power drain.
2) User error. I seem to fumble the shifts at the beginning of steep hills more on my folder than on my big wheel bike. I don't know why. If, like me, on a particular bike, you screw up the shifts, then you would percieve yourself slowing more than you usually would. Once I get moving up hills I get organized and in the right gear, but there is definitely a wall effect at the bottom of steep hills.
I think efficiency, and user posture. If you're more efficient at pedalling your other bikes compared to the Speed, then this will have a BIG impact on hill climbing. Bike fit should make the biggest difference here. Forget inertia for now.
07-31-07, 09:08 AM
It's that SRAM Dual Drive. I have a single speed boardwalk with a 16 cog in the rear and 53t chain ring, and I'm taking hills without even breathing.
07-31-07, 05:59 PM
The SRAM dual drive hub efficiency theory sounds very plausible. I spend almost all my time in the top hub gear and rarely use the derailleur beyond tweaking when cruising. It is quite annoying that on a small wheeled bike gear changes seem more necessary.
I have a feeling the cranks might be shorter too, but not as short as the Brompton. I'll have to try keeping the 1:1 ratio going uphill.
I believe Dahon uses a 170mm crankarm... that's what mine has. 170mm is pretty typical and probably the best choice for the average consumer. What are you comparing it to? (Do you have another bike with 172.5, 175, or something different?)
08-01-07, 12:37 PM
Both the Brompton and the Speed Pro are running 170mm cranks, whereas my road bike is running a 172.5 by the look of it. I like to try a 175 I think. Will try to test the dual drive theory this week.
I wouldn't increase crank length unless you are very tall. It won't be any more or less efficient than changing your chainring size, but it will do a number on your knees. Even if you are tall, be careful going up in crank size, and make sure to completely refit your bike (move the saddle, adjust cockpit, etc.). This isn't to be taken lightly. Moreover, you will get much more bang for your buck by adjusting your gearing. It doesn't matter where the lever length is!
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