27.5 – 29er – Mullet. Which is the suitable wheel size?
This multiple part post will consider the needs of an emerging, but it seems to me, slightly forgotten market: riders under 172 cm – which is realistically majority of females and junior boys under 14.
I will start with an intro about myself, for non The Fastline Bikademy (TFB) clients.
I am an OG MTBer, who started riding in 1993. A DH / DS & 4X World Cups and Champs veteran, with world cup podium, continental champion and multiple Word Games and I have a National Champs title under my belt. In the last couple year, I started GE racing. At the age of 40, I still won the Australian GE national series in elite women. I am a full time MTB coach, my skills coaching company – The Fastline Bikademy is working with an average of 70 kids weekly ; age between 8- and 18-years of age. I also have a Bachelor of Science degree specialising in coaching, which allows me to work with higher level gravity athletes. For years, I looked after the Australian U19 and non-professional elite racers in the downhill national team. My height is 164 cm or 5.4”. I am a bike brand ambassador, but I am not obliged to push the product. TFB only works with brands which we are happy with and ones we can form honest opinions about.
What wheel size?
For years I swore 27.5” wheels were the right choice for junior riders up to age 16 and ladies with average fitness.
In road bike racing, the large chainring gets locked out until generally age 16. In BMX Cross certain chainring / sprocket / crank length are recommended for certain ages. Both disciplines try to promote spinning, aka higher cadence for the juniors. However, to my knowledge, there are no gear restrictions or chainring recommendations in MTB racing.
The idea behind spinning is that the majority of the juniors don’t have good leg stabilizer muscles. Asked them to do a squat for you and their legs will act like a baby giraffe’s. They will go in any angles except straight up and down. If a junior pulls a hard gear, their legs are working against bigger resistance. With weak leg stabilizer muscles, instead of the power transfer straight to the pedals, it is partially lost & the body functions will suffer. The flexible parts, such as ankles – knees and hips will give in and start moving sideways. It may cause ligament and joint strain with juniors, particularly if they are doing longer distances for training. Not ‘pleasant’ injuries for anybody but particularly not for growing bodies. Also, higher load aka hard gear – low cadence pedalling fatigues muscles quicker. Adults are not safe from injuries like this also. I often see baby boomer riders with side way flexing knees because after years away from any sport, they discover cycling, but their leg stabilizers have wasted away. If you recognise yourself or your child from the above description, please see a physio, fitness or MTB coach and ask for help with strengthening your leg stabilizers.
Beyond changing your cadence, you can do some modifications on the bike as well. What also can slow the cadence down is chain stay length, wheel size, crank length and chain ring size. The longer or bigger are these parts the more chance to pull a harder gear by accident. In numbers, 470 mm length for a chain stay is considered to be long. Crank lengths generally are 165 – 170 or 175 mm on MTBs. To promote spinning I would recommend a 28 or 30 tooth chainring on a 1 x 12 gear with a 10/50 cassette. And then the wheel size. For years I used and recommended 27.5” wheel bikes for juniors and recreational female riders. Adult ladies with average fitness tent to spin more because harder gears fatigue the muscles quicker and they often have less muscle mass compared with their male counterparts.
However, with the refined geometry of the newer 29” bikes and the appearance of the Mullet (29” front – 27.5” rear wheel), I was keen to do some testing. Luckily for me, my trusty local bike shop Cycle Station Albury, organised a demo bike for 3 months. So, which is the suitable wheel size for junior riders and riders under 172 cm?
Please stay tuned and next week I will discuss the results of my 3 months testing of the three wheel sizes.