Correct bike size for better bike fit and improved performance.

What’s inside this week:
1. Bike Size Selection
2. “Gadget” of the week. High quality kids bikes.
3. Shorts.
4. MTB video of the week.

Finding the Perfect Fit: Matching MTB Frame Sizes to Rider Height

Mountain bike geometry is constantly evolving, and if you were to swing your leg over a size medium of 10 years ago and a modern bike, you will find that they do not feel anything alike. The industry’s understanding of bike fit and muscle engagement is also evolving and so I thought I’d try to help with some pointers.

Choosing the right mountain bike (MTB) frame size is crucial for comfort, performance, and overall riding experience. Riders come in all shapes and sizes, and so do bikes. Getting the right fit involves understanding how your height corresponds to key bike measurements like top tube length and reach.

Rider Height and Frame Size

MTB frame sizes typically range from Small (S) to Extra Large (XL), often indicated by rider height:

• Small (S): For riders around 160-170 cm

• Medium (M): For riders around 170-180 cm

• Large (L): For riders around 180-190 cm

• Extra Large (XL): For riders 190 cm and above
  *Specialized have an S size indication - which works really well, but is a mind shift to remember when looking at bikes.

However, this is just the starting point. The right fit also depends on your body proportions and riding style. Also take some time to study the manufacturer’s size guide for the particular bike you are looking at. Make sure the size guide is for the right year model.

Top Tube Length and Reach

Two critical measurements that affect your bike’s fit are the top tube length and reach:

• Top Tube Length: This is the horizontal distance from the head tube to the seat tube. For a Medium XC frame, the effective top tube length typically ranges from 580-600 mm. This measurement influences your seated position and comfort during long rides.

• Reach: Reach is the horizontal distance from the bottom bracket to the top of the head tube. It directly impacts your stance and handling, especially when standing on the pedals. For a Medium XC frame, the reach usually falls between 430-460 mm. Longer reach offers more stability at speed but may feel stretched out for some riders.

Fine-Tuning Your Fit

While height provides a general guideline, personal preference and riding style are key. Aggressive riders might prefer a longer reach for better stability, while those focusing on comfort might opt for a shorter reach.

Consider also the type of riding you do. Cross-country (XC) bikes tend to have longer top tubes and shorter reaches for efficient pedaling, while trail and enduro bikes often have shorter top tubes and longer reaches to enhance control on technical terrain.

The basics (this is a starting point - if you are a competitive racer, please get a professional bike fit done to optimize your performance):

1. Saddle height, position and tilt.
Saddle height is the easiest thing to fix, and sometimes can be the one that take the longest to get right. Sit on your saddle wearing your MTB shoes and place your heel on your pedal. If your leg is nearly straight without a locked knee (slight bend), that’s a decent height. Your saddle should be close to horizontal, with the nose maybe slightly down.
Start with the saddle in the middle of the rails, then you have some forwards and backwards movement to play with after everything else has been sorted.

2. Stem length, stem rise:
Your bike will have a recommended stem length and rise. If this is however uncomfortable, you can go slightly shorter or longer and increase or decrease the rise of the stem for improved comfort.

3. Handlebar width and rise:
RideLogic suggest this to get your ideal bar width: If you’re male, multiply your height in millimeters by 0.440. If you’re female, multiply your height in millimeters by 0.426. This feels pretty accurate for me.
The rise should suit the type of bike you are riding, flat bars are good on race bikes (getting the front end low), riser bars more suited to down country and trail bikes and puts you in the attack position.
Rolling the bar forwards or backwards can also fine tune the last 5% of fit if everything else is close.

4. Stack height:
Higher stack: Leads to a more upright and relaxed riding position, with more weight on the rear wheel, which can be beneficial for climbs and when the bike is more stable. 
Lower stack: Results in a more aggressive, forward-leaning position, with more weight on the front wheel, which can be advantageous for downhill and technical sections. 

5. Cleat positioning (if on clipless pedals):
For optimal MTB fit, cleat positioning generally aims for a neutral to slightly rearward placement, aligning with the ball of the foot (metatarsal heads) or slightly behind for gravity riders, promoting stability and efficient power transfer.

Are wheel sizes proportional to rider height?

Yes and no. Super short adult riders may be more comfortable on 26” or 27.5” wheels, but honestly, a well designed modern 29-er will be just as comfortable and similarly easy to handle (with a low standover height). Preteen kids generally will not be suited to 29er wheels, purely due their adolescent stature.

TL:DR

Matching your height to the correct MTB size is the first step toward a comfortable and effective ride. Remember to pay attention to top tube length and reach, and don’t hesitate to make small adjustments or seek professional advice for the perfect fit. The right bike will feel like an extension of your body, allowing you to focus on the trail ahead.

Small adjustments that are easy to make: cleat positioning on shoes, saddle position on the rails (forwards or backwards), saddle height, increasing or decreasing stem length, handlebar rise/sweep/width and roll, and spacers under your stem (if your steerer length allows for them to be installed).

Experimentation is the best way to suss this out. If you are comfortable, that’s a good sign and good place to start.

If you want to get more in depth on bike fit, muscle engagement and fine tuning setups, let me know and I’ll do another post on that.

“Gadget” of the week: PawPaw Kids balance bikes & scooters

Anne, the owner of Paw Paw started sourcing and bringing in bikes directly from a high quality manufacturer in China. She showed me a few of her bikes and the quality is next level.

Her ethos is simple - to sell good looking bikes that last, helps with balance and a child’s development.

Designed for kids aged 18 months to 3 years (80-112cm), the PawPaw 12" Balance Bike supports key developmental milestones like balance, coordination, and confidence. Its high quality lightweight, low step-through frame ensures easy mounting, while small grips, adjustable brake levers, and V-brake cater to little hands. Features like high-volume pneumatic off road tires that promote balance, comfort and traction, a steering limiter to prevent overturning, and domed axle nuts ensure comfort and safety. The contoured saddle and durable components make it practical for parents and fun for kids, encouraging exploration and active play from the start.

These kids bikes will outlast your kid’s time ripping around on them!

To get more information or to jump on the stock while there’s still some available, get hold of Anne on 0727752294.

Q. Winter is coming - should you ride trails after rain?

A. Depends on the trails…
If the trails are established with decent drainage and you’re not riding through puddles, riding in the rain or directly after rain is not really a problem. If however the trails are freshly built, clay or muddy, or have standing puddles everywhere, you are probably going to do damage to the trails if you ride there.

Trail maintenance is hard work, so use your discretion and respect the trail builders and property owners.

About the author:
Hello, I’m Francoin, an Industrial Designer in the cycling industry based in Somerset West, South Africa.

Tools, lights, accessories and bicycle design is my daily graft.

This newsletter is to share some of the experience & industry insight that I pick up along the way, with fellow cyclists. If you are new to the sport, or been riding for many years, I plan to give you something of interest in every edition.

Thanks for subscribing and Happy trails!

FV

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