Found on the internet:

There's a lot of bicycles still in the Finnish army and they are really taken into a good use during service. In wartime situation the former Jaeger units now act as mobile elite or better class units - as they used to be - but nowadays use APC's. However, in a country like Finland bicycle is sometimes much better means of transportation than truck or even APC, as in many places (not to mention remote areas) good roads are rare. Heavy modern organizations can't be moved via small village-roads, or even if they somehow manage make their way forward, in local terrain it's extremely easy to make blockages, set up ambushes etc. It's extremely risky to deploy large valuable troops in restricted open areas with no room to maneuvre - even more today than in the past (russians demonstrated some disastrous examples of this kind of deployment during WWII).

In this kind of environment any infantry troops, not considering whether they are elite or conscript status, can make a great use of bicycles if only the distances are short enough (well less than 200 km maybe). The most obvious disadvantage of the bicycle is that heavy equipment can't be carried. But in the circumstances Finnish army uses them, heavy equipment is not necessarily needed. When everything the organization needs (whether it's squad of battalion) is carried by bicycles, it's not dependent on terrain or obstacles in anywhere near the same scale that partly motorized/mechanised units.

During my national service we had a couple of big exercices where our company bicycled some 100km during day with all gear and participated battles at night - and everything worked very well indeed. The regular infantryman in bicycles can easily carry his personal equipment and food supplies, with assault rifle and maybe one additional weapon or squad equipment (single-shot at-rocket, at-mine, radio etc.). The only means of accommodation generally needed is a piece of fabric which can be used to put up a tent. Unit equipped in this manner is extremely flexible and maneouverable (though not very fast over long distances).

Against infantry and maybe light APC's this kind of bicycle infantry (in Finnish use) trusts in it's knowledge and good use of local terrain and basic combat skills - not in heavy fire support. And against MBT's - well, if you're enemy is dumb enough to haul a few in the area where bicycle troops are deployed, and successfull in doing that, the bicycle troop will be long gone.

How about the threat of enemy undirect fire? Always there, but it's not at all easy to locate small units without large equipment from the sea of woods, and generally not at all wise nor effective to deploy barrages or air raids against them (a single one of them is not such a valuable organization).

The conclusion - in certain circumstances or in right kind of environment bicycle units can still be prevailing troops.