Is urban riding on bumpy road while suspension fork locked and without slow down harming to my bike or me? I don't care about my comfort so much. I don't want to slow down or to lose energy.
Nope, and riding with it locked is quite beneficial in certain factors of riding, and if you have a locking suspension, you are very lucky compared to me, who has a bike without it.
The bike will not break from simply having your suspension locked; It still absorbs impact, just in extremely minute amounts. Seeing as many web sites have covered this, I'd thought I may as well throw some info out there.
Imagine the fact that I have 22mm tyres on my road bike; you should have about an inch and a half. Not much of a difference? In terms of absorption, I can swap my tyres for 25mm and feel a huge difference in comfort and less shock through the frame. If you have an inch and a half or even just an inch, you should be more than perfectly fine, no matter what terrain. I mean, come on, I ride a road bike off-road on bumpy-ass terrain.
On a bumpy but fairly level road, absent any suspension, energy goes three places:
- Friction between tire and road
- Wind resistance
- Vibrating your body up and down
The reason #3 is a factor is that you jiggle as you ride, and that absorbs a lot of energy -- the more you jiggle, the more energy is required.
You can reduce jiggle by using lower air pressure in the tires, but this increases tire/road friction. You can add front and/or rear suspension to reduce jiggle, but the suspension itself absorbs energy, plus it tends to make pedaling less efficient.
So it's a tradeoff -- at some point in the transition between smooth and really rough roads it probably pays, in terms of energy efficiency, to unlock the shocks.
As you have a suspension fork, I guess your bike should be at least hybrid to mountain bike.
Most hybrid start off with 32 mm tyre upwards (or 1.25 inch).
At around 38 mm upwards (or 1.5 inch), you can take on most of the pot holes, provided that you are not crashing.
I have a road bike and the difference in the shock absorbance of 23 mm tyre and 28 mm tyre on 700c wheel is already monumental (although it is not enough to mount curb or drop potholes), just to show you that wider tyre is very good and absorbing some potholes in urban area.
I also have a mountain bike, rigid fork with 26x1.5" tyre and never worry about pot holes.