free to be able to rate and comment on reports (as well as access 1:25000 mapping).
The main report gives a comprehensive route account. I looked in the individual reports for more guidance on using a bike. Found some bits of use but thought this focus on biking might help others.
Bike or not? - absolutely yes - takes hours off the trip - about 8 miles each way. We headed out on a day with some rain and Westerly winds of up to 50 mph forecast for tops in this area but even into that it was good cycling on the way out. The track is good - pretty smooth stones and fairly level for most of the way. Even into the wind we made pretty good time. Would have hated the walk back out at night at the end of the day and would have struggled to beat the light - this was the real winning factor. I would recommend bringing padded cycle shorts for this part. Pretty bumpy on the backside particularly coming back at more speed.
How far? Can easily get all the way to the Geldie ruin as far as conditions under wheel go (see below about river crossings). The SMC Munro’s book and my OS map is misleading - it refers to a ‘bulldozed track’ beyond that and shows it on the map as a double dotted line - it is not! The walkhighlands describes it as a ‘good stalkers path’ which is much more accurate. We initially decided to try taking the bikes further having read the SMC and did another half mile or so. My son would have gone further but I reckoned it was no longer saving me time. A lot more up and down and a track about 1 foot wide with cuttings for drainage etc - great for walking but I found slow for cycling and requiring more skill and concentration to stay on the track. We left the bikes there and continued on foot. I would leave them at the ruin if doing again. However we saw bike tracks beyond so someone had gone even further than us.
The river crossings were more significant an obstacle. Most were fairly shallow which you could cycle straight through without too much thought. A couple had stepping stones that allowed you to wheel the bike through.
The most significant was the Geldie Burn just before the Geldie ruins. It was wide and pretty deep with no stepping stones. Some else has written about having sandals - a good tip thanks! We carried a couple of pairs of flip flops in the saddle bag so took off boots and socks and waded through pushing bikes. Probably could have done it barefoot but the flips made it really easy.
Our only mistake was drying feet and putting boots back on only to discover another pretty deep crossing about 100 m further on. My son decided to go for it rather than change again. He kept to left which was ok but failed to turn back right at the last point and stalled putting one foot in deep. Having watched him I perfected his line and got right through - just! On way back I put flips on at the Geldie ruin where I was changing back into cycle shorts and was able to wade both before putting boots back on.
So in summary a big yes for bikes as far as the Geldie ruins - hope that helps!
A couple of points about the walk from there. It is a good stalkers path which takes you along past Sgarsoch beag on the north side and then down towards allt a chaoraine. Path then turns north. We went down to river to cross but this was the really hard one to cross. Lots of places with stepping stones halfway at most but with deep and fast fast flowing water the rest. Had to go a couple of hundred metres south looking for a spot. Finally found one that involved a fair jump - son first (again to check it out - I am not stupid!) and then threw rucksacks across before my jump. Choice was more last resort than a good spot!
The ground from there to the top of the Fhidhleir ridge was very wet boggy peaty and heathery with no sign of a path going our way. Hard going so get onto the ridge as quick as possible - better walking on it. Surprising for the day we had sun and a view on top.
Again similar walking at the bealach between the Munros but not quite as bad. Coming off Sgarsoch we found a path quite low under Sgarsoch beag on the west side which takes you round and along the north side then fizzles out and you have to drop down through similar boggy ground to hit the stalkers path but well worth getting back on it. This is where you would leave the bikes if you made it this far - small pile of stones marks the spot.