Time Trial and Triathlon Bike Size Guide: Stack, Reach and Why You Size Down, Explained

A time trial frame is sized by the position it can hold, not by the rider's height. The armrests, not the frame, carry your weight and set your reach. The frame only has to place those armrests inside a range you can actually use. That is why a height chart, on its own, tells you very little here. Browse the full range of time trial and triathlon bikes at Bikeroom.

This guide sets out the two measurements that decide the fit: pad stack and pad reach. It then gives a starting size by height, a road frame comparison, and what to check before buying a pre-owned frame.

Please note. The sizes below are indicative. They are a starting point built from official geometry charts and published rider height bands, not a guarantee of fit. On a time trial bike the cockpit matters more than the frame label, so confirm your numbers with a bike fit or with our team before you buy.

Why a time trial frame is not sized like a road frame

The mechanism is the seat angle. BikeRadar's time trial buyer's guide puts the effective seat tube angle at "around 75 to 78 degrees", against roughly 72 to 74 degrees on a road bike. MOTTIV gives the same road figure and 76 to 78 degrees for a tri frame. The steeper angle rotates your hips forward over the bottom bracket, which opens the hip angle and lets you hold a low torso for an hour.

The published charts vary more than either figure suggests. Pinarello lists 77 degrees for the Bolide F TT and 78 degrees for the Bolide F TR. Canyon lists 81 degrees for the current tri Speedmax, 80.5 degrees for the Speedmax CF, and 85.5 to 86 degrees for the Speedmax CFR TT. None of the brands states the reference point used, so compare seat angles within a brand, not across brands.

The second consequence is that frame reach and stack are not comparable with a road bike. A Pinarello Bolide F TT in size 520 publishes 413 mm of reach and 494 mm of stack. A Dogma F in size 53 publishes 383 mm and 542 mm, per the official charts in our Pinarello road bike size guide. The time trial frame is longer on paper and 48 mm lower, because its reach is measured to a head tube that then carries a long aerobar.

Pad stack and pad reach: the two numbers that matter

Pad stack is the vertical distance from the bottom bracket to the armrest. Pad reach is the horizontal distance from the bottom bracket to the armrest. Together they describe where your elbows sit, which is the position you are actually buying. Dan Empfield, writing the triathlon sizing guide for The Pro's Closet, puts it plainly: "Stack and reach are the absolute measures of the bikes height and length".

Only some brands publish the range. Canyon prints armpad stack and armpad reach as rows m and n of its geometry table on the Speedmax CF and on the previous Speedmax CFR TT. It does not print them on the current Speedmax CFR or CF SLX. Argon 18 publishes them in centimetres on the E-119 Tri+ Disc. Pinarello publishes neither figure for the Bolide.

Read the vertical range first. A Speedmax CF in size M covers 31 mm of pad stack, while the pad reach spans 111 mm. Height is the scarce adjustment on a time trial bike, so it is usually height that decides the size.

Quick size finder

Find your height, cross check the leg length, then read across. The letter column is the size most four and five size time trial frames put you on. The example column quotes a published band, so you can see the evidence behind the row.

The bands overlap because the brands' own bands overlap. Where two sizes are listed, the pad stack range decides: take the size whose armrest height covers your fit numbers with adjustment left at both ends.

How to measure yourself

Height. Stand barefoot against a wall, heels together, looking straight ahead. Rest something flat on your head, mark the wall and measure from the floor.

Leg length (inseam). Barefoot, feet about 15 cm apart, press a book up between your legs as if it were a saddle. Keep it level against the wall, mark the top edge and measure from the floor.

Torso and arm length. Measure from the top of your sternum to the hip bone, and from shoulder to wrist. A long torso with short arms usually points to a taller pad stack rather than a bigger frame.

Your current road bike. Note its stack and reach from the brand's chart. Those two numbers travel with you and let a fitter convert a road position into pad coordinates.

From road frame to time trial frame

The common rule of thumb is that a rider takes a smaller number on a time trial frame than on a road frame. That holds, but the reason is the labelling, not your body. Empfield's point in The Pro's Closet guide is that one 56 cm road rider can be several different sizes across tri brands, which is exactly what the charts show.

The Pinarello and Canyon size labels are official. The road frame column is indicative, since road size labels are not standardised between brands. Use it to place yourself in the chart, then confirm with stack, reach and pad numbers.

How the brands label time trial sizes

• Pinarello labels the Bolide in millimetres of seat tube: 450, 485, 520 and 550. Dealer listings write the same size as 45, 48.5, 52 or 55, or as 520. They are the same four frames.
• Canyon uses letters. The tri Speedmax CFR and CF SLX run S to XL, the Speedmax CF runs XS to XL, and the UCI legal Speedmax CFR TT runs XS to L.
• Scott pairs a letter with a number. The Plasma RC Pro is listed as XS/49, S/52, M/54, L/56 and XL/58 by retailers including Bicycle Superstore.
• Argon 18 lists the E-119 Tri+ Disc in six sizes from XXS to XL, with the armpad ranges printed in centimetres.

UCI position rules and triathlon freedom

A time trial bike raced under UCI rules has to fit inside a box. Article 1.3.013 puts the tip of the saddle no more than 5 cm behind the vertical through the bottom bracket axle. Since 1 January 2023 the extensions are limited by rider height category, per the UCI's own announcement. The limit is 80 cm forward of the bottom bracket below 180 cm, 83 cm from 180 to 189.9 cm, and 85 cm at 190 cm and above. The permitted height difference rises with it, from 10 to 14 cm, and the forearm support inclination went from 15 to 30 degrees.

Triathlon is not bound by any of that. BikeRadar notes that triathlon bikes are "not constrained by the UCI rules", which is why they carry deeper tube shapes and integrated storage. In practice a triathlon frame gives you a steeper effective position and more forward pad reach than a UCI legal frame in the same size. Our guide to time trial bikes versus triathlon bikes covers the wider differences.

Between two sizes?

Take the smaller frame if you want a lower front end and you already ride a low road position. Take the larger frame if your pad stack figure sits near the top of the smaller size's range, because a cockpit at the end of its travel leaves you nowhere to go. A long torso with short arms points up a size, long arms and a short torso point down.

One caveat applies across the category. Integrated cockpits limit how far a frame can be rescued by parts. On a one piece aerobar the spacers, extension length and pad plates are often model specific, so the frame size has to be right before the cockpit is adjusted.

What to check on a pre-owned time trial bike

• Cockpit adjustment left. Ask for photos of the pad plates and spacer stack. A cockpit already at its lowest and shortest setting cannot go lower or shorter.
• The spacer set. Time trial cockpits use proprietary shims and riser blocks. A bike sold without its spacer set can be expensive to bring back into range.
• Extension shape. Extensions, risers and pad mounts are frequently brand specific and not always sold separately. Check that the parts on the bike are the ones you want.
• Seatpost and saddle rails. A reversible or offset post changes the effective seat angle. Confirm which orientation the bike is in and whether it is UCI legal, if you race under UCI rules.
• Model year of the chart. Geometry changes between generations under the same model name. Match the chart to the year of the frame, not to the current page.

Our practical guide to buying a pre-owned triathlon bike goes further on condition and paperwork.

Shop time trial and triathlon bikes at Bikeroom

• Time trial and triathlon bikes for the full category, Pro-Owned, Pre-Owned and New.
• Pre-owned triathlon bikes for complete bikes that have already been ridden.
• New triathlon bikes for current season stock.
• Triathlon framesets if you are moving a known fit onto a new frame.

If you know your pad stack and pad reach from a fit but not which frame size covers them, talk to our concierge with those two numbers and the bike you are considering.

Disclaimer: the sizes in this guide are indicative and given in good faith. Stack, reach, pad and seat angle figures are official manufacturer data read on the brands' geometry pages on 21 September 2026, and they change between model years and versions. Always confirm against the specific bike you are buying and, where possible, with a professional fit.

Sources: BikeRadar, Simon von Bromley, updated 17 June 2024; The Pro's Closet, Dan Empfield, 22 February 2021; Canyon Speedmax geometry; Pinarello Bolide F TT geometry; Argon 18 E-119 Tri+ Disc; UCI, time trial regulation changes; MOTTIV, updated 17 February 2025.