What size bike do I need? A South African sizing guide

A lot of resale ads and courier returns start with the same three words: it didn't fit. A bike that's one size too big or too small doesn't just feel awkward — it loads your hands and lower back, kills your confidence on descents, and never quite lets you settle in. And because so many bikes here are now bought online, sight unseen, getting the size right before you pay matters more than it used to.

The good news is that sizing isn't guesswork. Most riders land on the right frame from two numbers — height and inseam — plus a couple of sanity checks. Below are the charts for road, mountain and kids' bikes, and then the checks that confirm the fit before you commit.

Height is where everyone starts, and for most people it's enough to pick a bracket. But two riders who are both 175 cm can need different frames — one is all legs, the other all torso. That's why the charts pair height with inseam (your inside leg). It's the most useful single measurement for standover clearance and saddle height, and you can take it at home in two minutes (there's a how-to in the FAQ).

The other number that matters, especially on road and mountain bikes, is reach — how far you stretch forward to the bars. You can't measure it on yourself, but it's why sizing up for 'a bit more room' usually backfires: you end up over-stretched, perched on the nose of the saddle, with sore hands by the end of every ride.

Notice the height ranges overlap. Mountain bikes are sized by reach more than seat-tube length, so a 174 cm rider can genuinely go either way. The rule of thumb: a shorter frame is more playful and easier to throw around on tight, technical trails like Tokai or Jonkershoek; a longer one is more stable and planted when the trail opens up and points down. On wheels, 29 inch is the default for almost everyone now — smaller riders and dirt-jump setups are where 27.5 still makes sense.

Ignore the age labels on the box — kids the same age vary wildly in leg length. What matters is the wheel size, matched to the child's height and inseam, and that they can get a foot down comfortably. Resist the urge to buy a size up 'to grow into': an oversized bike is harder to control and puts kids off riding, which defeats the point.

Once the bike is in front of you, three checks catch most sizing mistakes:

1. Standover. Straddle the top tube with both feet flat. You want a few centimetres of clearance on a road bike, and a good fist or more on a mountain bike. If the top tube is jammed into your crotch, it's too big.
2. Saddle height. Set it so your knee keeps a slight bend — about 25–30° — at the bottom of the pedal stroke. Quick formula: inseam in centimetres × 0.883 gives the distance from the centre of the bottom bracket to the top of the saddle.
3. Reach. Hands on the hoods or grips, you want a relaxed bend in your elbows and your back at roughly 45° — not stretched flat, not scrunched up. Locked out and reaching for the bars means the frame or stem is too long.

If you're riding more than a couple of times a week, or something aches after an hour in the saddle, a professional fit is the best money you'll spend on the bike after the bike itself. A basic static fit — saddle height, setback, cleat position — typically runs R500 to R900. A full motion-capture or Retül-style fit, where they film you pedalling and dial in every contact point, is usually R1 500 to R2 500 and often includes a follow-up tweak.

Plenty of shops offer it and a few specialise. Browse the bike shop directory to find a fitter near you. Still choosing the bike itself? Our buying guides and the marketplace show what's available right now, in rand.