Reach and Stack Explained: Bike Fit Beyond Frame Size

The problem with frame-size labels

Frame-size labels look like they should tell you whether a bike fits. They rarely do the whole job. One brand's "large" is another brand's "medium", and a road frame marked "56cm" from ten years ago can feel very different from a "56cm" bought last year. The number usually refers to seat-tube length, and on modern frames with sloping or compact top tubes the seat tube no longer tracks how the bike actually fits your body.

That matters most when you are buying used. You are comparing bikes from different brands, different model years and different design eras, all sold under size labels that were never standardised. Trusting the label alone is how people end up with a bike that is technically their size and still feels cramped or stretched.

Reach and stack cut through it. They are two measurements, both in millimetres, that describe the fit of the front end regardless of what the size sticker says. Get comfortable reading them and you can compare any two frames on equal terms. You can browse bikes for sale and judge them on geometry rather than a label that means something different from one seller to the next.

Cyclesite Tip. Before you shortlist anything, write down the reach and stack of a bike you already know fits you. Those two numbers are your reference point.

What stack is

Stack is the vertical measurement. It is the height from the centre of the bottom bracket, where the pedal axles turn, straight up to the top of the head tube at the front of the frame. Because it is measured vertically from a fixed point rather than along the tubes, it does not change with the angle of the seat tube or the length of the frame's other tubes.

A taller stack lifts the front of the bike, which raises the handlebar relative to the saddle. That puts you in a more upright position: easier on the back and neck, and better for long days and general riding. A shorter stack drops the front end, lowers the bar and stretches you into a more aerodynamic, racier position.

If you find drop-bar bikes leave you aching after an hour, you probably want more stack than you have been riding. If you like being low and long, you want less. Stack is the number that captures that comfort-versus-speed trade-off at the front end, and it is printed on every manufacturer's geometry chart.

What reach is

Reach is the horizontal partner to stack. It is the distance measured forwards from the same point at the centre of the bottom bracket to the top of the head tube. Where stack tells you how high the front end sits, reach tells you how far away it is.

A longer reach stretches you out. It moves the bar further from the saddle, opens up your body and, on a road bike, tends to feel racier and more planted at speed. A shorter reach brings the bar back towards you for a more compact, upright and manoeuvrable feel. On mountain bikes in particular, reach figures have grown over the last decade, so an older "large" can have noticeably less reach than a current one wearing the same label.

Reach is the single most useful number for judging whether a frame's length suits you, because it is measured to a fixed point and cannot be fudged by tube angles. Two frames with the same reach will put your hands a similar distance forward, whatever their seat tubes measure. You can look up reach and stack for a specific model on our bike geometry pages, or start from your own measurements with the bike size calculator.

Cyclesite Tip. Reach and stack are frame numbers, not fit numbers. They describe the bike, not your body, so always read them against a bike you have actually ridden.

How to use reach and stack to compare used bikes

Start from a bike that fits. That might be your current bike or one you have ridden and liked. Find its geometry chart, note the reach and stack for your size, and treat those as your target. If you have never checked, our bike size calculator and bike size guide give you a sensible starting range to work from.

Then, for any used bike you are considering, find the same two numbers on its geometry chart and compare. Ignore the size label to begin with. A frame within roughly 5mm to 10mm of your reference reach and stack is likely to feel familiar out of the box. Differences of that order can usually be dialled out with small changes to your setup. Larger gaps mean a genuinely different fit, and no amount of adjustment will fully close them.

Watch the two numbers together rather than in isolation. A bike with your reach but much less stack will fit lengthwise while sitting you lower and more aggressively. A bike with your stack but more reach will feel stretched even though the front end is the right height. It is the combination that decides how the cockpit feels.

Where you can, line up shortlisted bikes and check the figures against each other. Our compare tool puts specifications next to one another so you are reading like for like rather than flicking between listings. For road bikes specifically, the used road bike guide covers the other checks worth making once the fit numbers stack up.

Adjusting fit within limits

Reach and stack are the frame's fixed skeleton, but they are not the whole fit. A few components let you fine-tune the cockpit around them, which is why a bike that is close rather than perfect can still be made to work.

Stem length is the main lever for reach. A shorter stem pulls the bar back and effectively shortens a slightly long frame; a longer stem does the opposite. Most stems come in 10mm steps, so you have useful room to move. Handlebar reach and the position of the brake hoods add a little more adjustment on drop bars.

Stack is easier to add than to remove. Spacers under the stem raise the bar, and flipping the stem to a positive angle raises it further, so a frame that is a touch low can be brought up. Going the other way is limited by how far you can drop the stem before you run out of steerer. Saddle setback and fore-aft position change your weight balance and effective reach too, though the saddle should be set for your pedalling first and not used to paper over a frame that is the wrong length.

The honest limit is this. You can tune a frame that is close, but you cannot stretch or shrink one that is fundamentally the wrong size. If a used bike's reach is 20mm or 30mm off your reference, adjustment will not rescue it, and you are better off holding out for a closer match. If you want to go deeper on setup once you have the right frame, our bike fit guide covers the finer points, and it is worth getting a rough valuation before you commit so you know the price fits as well as the frame.

Common questions

What is the difference between reach and stack?

Stack is the vertical distance from the centre of the bottom bracket up to the top of the head tube, and reach is the horizontal distance forwards from the same point to the top of the head tube. Stack controls how high the front end sits, so more stack means a more upright position. Reach controls how far away the front end is, so more reach means a longer, more stretched-out position. Both are given in millimetres on a manufacturer's geometry chart and, unlike the size label, they describe fit consistently across brands.

Why do two bikes with the same size label fit differently?

Size labels are not standardised. A "large" or a "56cm" usually refers to seat-tube length, and brands measure and design their frames differently, so one company's large is another's medium. On modern frames with sloping top tubes, seat-tube length no longer tracks how the bike fits at the front end. Reach and stack are measured to fixed points and do not vary with tube angles, which is why comparing those two numbers is far more reliable than trusting the label.

How do I find the reach and stack that fit me?

Start from a bike you have ridden and found comfortable. Look up its geometry chart, note the reach and stack for that size, and use them as your reference for any bike you are considering. If you have no bike to compare against, a size calculator gives you a starting range, but numbers from a frame you have actually ridden are always more reliable. Fit is individual, so treat published figures as a guide and confirm them against real-world experience.