I have the privilege, since the summer, of having access to the 3 most common mountain bike wheel sizes, 26”, 27.5” and 29”. My son wasn’t using his Trek Fuel EX8 so I brought it home when we last visited. It has 29” wheels and is a 2014 model. Moving it around, in the garage for instance, it feels bigger and more unwieldy than my 2016 vintage Boardman FS Pro.
The distance between the axles of these bikes is very similar but the bigger wheels make the Trek 3” longer and it’s surprisingly noticeable in tight spaces. Of course out on the trail there’s plenty of room and today’s ride would give me a chance to see what difference the bigger wheels make to the ride.
The evolution of mountain bikes is so rapid that neither of these bikes are exactly up to the minute. Bikes are getting longer and it’s all for the sake of stability, which is one of the justifications for bigger wheels. A bigger wheel rolls more easily over bumpy ground and is less easily diverted off course. The volume of air in the tyre is greater, giving more cushioning, further enhanced by being able to use lower tyre pressures. The other big changes which have been developing in the last decade are summed up in the mantra “longer, lower, slacker”. Longer means the wheelbase but this is tied in with slacker. To make the steering more stable and keener to go where you point it without being diverted, the angle or rake of the forks has been changed, making them less steep. This has pushed the front wheel further away from the rider, making it far less likely that you’ll go over the handlebars. The rider has also been moved further back with the use of shorter handlebar stems which give a more direct feel to the steering. To fit the rider in the pedals and saddle have moved by extending the central part of the frame. This would put the rider too far over the rear wheel which, whilst improving rear wheel grip, would reduce front wheel grip. To get the balance back the rear wheel has also been pushed back, hence bikes are now longer. To help matters further in terms of stability, the bottom bracket, where the pedals attach, and the handlebars have been lowered to bring the rider closer to the ground. My Boardman is as low as I’d want with it’s 330mm bottom bracket. I already catch pedals on rocks quite often. The Trek seems a little higher in this respect. The handlebars are 780mm wide on the Trek which to me is 40-60mm too wide. They are too easy to catch on trailside trees etc. It seems that 800mm has become the benchmark but I’d be tempted to cut them down to something more sensible.
I decided to ride 3 laps of Healey Nab, my local hill, today. We’ve had a massive amount of rain so myy lap times would be of little significance but I did want to be consistent. I rode to the north end of the hill and started my laps half way up the long climb. I realised that with an old school transmission with 3 front chainrings and a narrower range 10 speed cassette I’d be better starting the steep climb in the smallest, easiest ring and change to the middle ring towards the top. I’d then return to the small ring just before the big climb. It’s easy to understand why gears which change at the front have gone out of fashion. It requires more thought and is much less intuitive. I rode the first lap in 8 minutes 36 with an initial burst of energy. This energy took me to the top in 4 minutes. On the second and third laps I was around 15 seconds slower on the climb but similar on the twisty and action packed downhill. My times were 8 52 and 8 58 but I did hit a tree root on lap three which had me tumbling to the ground. I was concentrating on maintaining speed at the time. I should, perhaps, have taken it easier on the first climb but wasn’t too inconsistent. Basically the reason for seeking consistency is that you can do multiple laps quicker at the same speed, whilst becoming more and more tired as the laps progress.
So how did the bike ride with it’s bigger wheels? I think it’s definitely smoother over bumpy ground so ultimately it will impede progress less allowing you to go quicker. I don’t think the bigger wheels are significantly more awkward around tight corners, you just need to be a little more forceful. Over a series of bumps on the approach to one corner, where you also need to brake, the big wheels give a good improvement in smoothness and hence control. You could definitely brake later and harder because of this. I enjoyed my ride and feel sure that I’d only consider 29” wheels for any trail bike which I buy in the future.