Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Brands

Bike

What Size Tri Bike Should I Get?

A triathlon bike is only fast and comfortable when it's the right size. Before you buy, know your tri bike size and how to use it for a smarter shopping process.

For access to all of our training, gear, and race coverage, plus exclusive training plans, FinisherPix photos, event discounts, and GPS apps, sign up for Outside+.

If your goals in triathlon are modest, or it’s your first year in the sport, training and racing on a road bike is acceptable, respectable, even commendable. If faster times and bigger goals are in your future, and you’re replacing a dated triathlon bike or getting your first aero machine, that acquisition should begin with knowing your tri bike size.

RELATED: How to Buy a Bike Online

(Tri) bike size matters

It’s common to be “all over” a road bike: hands on the brake-hoods, top of the handlebars, or the drops, seated in the middle of the saddle, a bit back, on the nose, and even standing out of the saddle. That kind of flexibility in the position makes comfort easier to achieve because you can refresh often with frequent changes in position while riding.

A triathlon bike, on the other hand, is intended to be ridden in one position: seated on the saddle, with elbows on or near the pads, and hands at the end of the aerobar extensions. You can – and should – move to the “bull horns” to have a wider, more stable grip for fast descents and to reach the brake levers, but in general, the tri bike is designed to be ridden in aero for extended periods of time.

Consider, too, that a road bike has five contact points: two hands, two feet, and your bum. A tri bike has seven when factoring in the arm pads. The more contact points, the more critical it is to know your triathlon bike size.

RELATED: New Triathlon Bikes are Changing Which Bike Fit Numbers Matter

How to find your tri bike size

The number-one best way to go about finding your triathlon bike size is by getting a prescriptive fit. This “pre-fit” is done before you purchase, even before you get your heart set on a certain make or model. When you’re finished with the pre-fit, you should have in your possession three key elements:

  1. Your Pad Y and Pad X (also called Pad Stack and Pad Reach). These numbers can be used to shop for the exact bikes that will work for you.
  2. A short list of bikes and the front-end configurations required on each to make them work for your position.
  3. All of your fit coordinates: saddle height, set back, saddle tilt, cockpit distance, pad width, extension length, drop, aero bar tilt, drop, and more.

This will guide your tri bike purchase. If, at the end of your fit, the bike fitter notes your Pad Y as 670mm and your Pad X as 480, you can seek out tri bikes that fit those size parameters. For example, you could ride a Quintana Roo PRsix size 54, with 90mm stem in the mid clamp position, 40mm of arm pad pedestal, the arm pad bracket set rearward, and the arm pads mounted in the mid-rear hole. You could also ride a Canyon Speedmax CF size Medium, with an 80mm stem, 25mm of spacer under stem plus 15mm of aerobar pedestal, and pads mounted two holes back from max.

RELATED: What One Triathlete Learned at his Prescriptive Fit Appointment

Fitting on multiple tri bike sizes is common

Note in the above example that one rider fits on two different tri bike sizes. That’s really common. It’s possible for an athlete to find their position on multiple sizes of bikes, even from the same make and model. In that example of the QR above, those Y/X coordinates can be achieved on a 54 (as detailed) as well as on a 50, 52, 56, and 58cm bike. The 54 is the best choice, as it offers the rider the greatest range of front-end adjustability in all directions: higher, lower, longer, shorter.

RELATED: A Fit Expert Explains the Various Triathlon Bike Options

Find a qualified bike fitter to calculate your tri bike size

A pre-fit should be done by a fitter who is educated on the triathlon position, has experience in fitting triathletes, and owns a dynamic fit bike. This is a device that allows the fitter to move the saddle and the handlebars up, down, back and forth without the rider ever ceasing to pedal. There are only 5 of these devices in existence: Guru DFU, Exit MkII, Retul Muve, Purely Custom, and a bike by Shimano that I’ve yet to see in a retail setting in the USA.

A triathlete gets measured for the right tri bike size.
(Photo: Laura Wilson)

To find your best tri bike size, it’s important for your fitter to conduct an unbiased analysis of your measurements, independent of brand. Even if your fit is done in a Trek or Specialized dealership, you still deserve to know about other brands that will work for you. To find the right fitter, make lots of calls and get them to answer key questions like:

  • Where was the fitter taught to fit the tri position?
  • How many tri fits do they do a month?
  • Do they own a dynamic fit bike and which model?

Quality triathlon bike fits can and should be expensive – often in the $250-$500 range – and they are worth every penny. Make the fitters earn your business by explaining how they help athletes like you be comfortable and fast in the triathlon position.

RELATED: The 5 Keys to Finding the Right Bike Fitter For You

Ian Murray is a USAT Elite Coach and Master Bike Fitter. Hehas served as head coach for the U.S. at the Youth Olympic Games, ITU WTS events, ITU World Cups, and more. He is Level 3 certified by USAT, Level 2 certified by the ITU and was honored as the development coach of the year by the US Olympic Committee in 2006.