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A felt triathlon bike size chart gives you a starting point for choosing a frame, but the chart alone does not guarantee a comfortable fit. In this guide, you will learn how to read a size chart, measure yourself accurately, compare reach and stack numbers, and check the fit before you commit to a bike. By the end, you should have a short list of sizes to test and a clear idea of which measurements matter most for aero riding.
What a Felt Triathlon Bike Size Chart Actually Tells You
Most manufacturer size charts list a range of rider heights next to a frame size, sometimes with inseam length and seat tube or top tube measurements. Felt, like most brands, uses these charts as a guide for the typical rider in each height band. Charts are useful for narrowing your options, but they assume a standard body proportion. If your legs are long for your height, or your torso is long, the chart may point you to a size that feels wrong in practice.
Shopping for one? See our guide: Is a Road King a Good Beginner Bike? Review and Buying Advice.
Triathlon and time trial bikes add a complication. Their geometry is built around a long, low aero position, so the numbers that matter most are reach (horizontal distance from the bottom bracket to the head tube top) and stack (vertical distance from the bottom bracket to the head tube top). A bike with the same seat tube length can feel very different depending on how far forward your hands sit and how low your torso drops. For that reason, read the chart as a first filter, then confirm with reach, stack, and a proper fit.
Step 1: Measure Yourself Before You Look at the Chart
Start with accurate body measurements. You will need a tape measure, a wall, a hardcover book, and a helper if possible.
- Height: Stand barefoot against a wall with your heels, back, and head touching it. Mark the top of your head and measure from the floor.
- Inseam: Stand with your back against a wall and place a book between your legs, spine up, snugged against your crotch as if it were a saddle. Keep the book level and measure from the top of the book to the floor. Multiply by 0.67 to estimate the inseam length, or measure the inseam directly with a helper.
- Arm length: Measure from your shoulder joint to your wrist with your arm relaxed. This helps estimate how far your hands should reach on the bars.
- Torso length: Measure from the base of your neck to your hip joint while seated on a flat surface. Long torsos often need a longer reach, and short torsos often need a shorter reach.
Write these numbers down. You will compare them to the chart and to the geometry table on the bike brand’s website.
Step 2: Read the Felt Size Chart Correctly
Once you have your height and inseam, find the row on the chart that matches your height. Many triathlon charts list two or three frame sizes for each height band. When that happens, use these rules:
- If your inseam falls near the upper end of the band, lean toward the larger size.
- If you have a long torso relative to your height, lean toward the larger size for reach.
- If you are more flexible and plan to ride a steep aero position, the smaller size may suit you better, since it keeps the front end more compact.
- If you are between sizes, compare the reach and stack figures rather than the frame label alone.
Frame size labels are not standardized across brands. A 54 from one company can ride quite differently from a 54 from another. Always compare geometry numbers rather than the label.
Step 3: Compare Reach and Stack Between Sizes
Reach and stack are the two numbers that most affect how a triathlon bike feels. Felt publishes geometry charts for each model, usually in millimeters, and these figures are more reliable than the simple size label. Use this table as a way to organize what you find.
| Measurement | What It Means | What to Check on Your Body |
|---|---|---|
| Effective top tube | Horizontal length from seat tube to head tube, a proxy for overall stretch | Arm length and torso length |
| Reach | Horizontal distance from bottom bracket to head tube top | Comfort when hands are on the aero bars |
| Stack | Vertical distance from bottom bracket to head tube top | How low you can comfortably get without neck strain |
| Seat tube angle | Angle of the seat tube, which shifts saddle position | Hip position and knee tracking |
| Head tube angle | Steering angle, which affects handling | Confidence on descents and in crosswinds |
Many riders find that a bike with a longer reach and a lower stack feels faster but demands more flexibility. A bike with a shorter reach and higher stack is easier on the lower back and neck. Neither is correct in every case. Choose based on your flexibility, your race goals, and your comfort during longer rides.
Step 4: Check the Fit With a Bike Fitter or Test Ride
Size charts narrow the field, but a test ride or bike fit confirms the choice. If you can, visit a shop that carries the brand and sit on the bike on a trainer. Look for these signs:
- Your saddle sits level and you can reach the aero bars without rocking your hips.
- Your knee is slightly bent at the bottom of the pedal stroke, with no locking.
- Your elbows stay bent around a comfortable angle, not fully locked or hyper-flexed.
- You can breathe easily in the aero position for several minutes.
- Your neck is neutral, not craned upward to see the road.
A professional bike fit is worth the time if you plan to race or ride long distances. A fitter can adjust saddle height, setback, bar pad position, and armrest placement, and can tell you whether a frame size is truly right for your proportions.
Common Mistakes to Avoid
- Choosing by the frame label alone. Labels differ between brands, so always compare reach and stack.
- Ignoring torso and arm length. Two riders of the same height can need very different reach figures.
- Buying a race-fit position without the flexibility to hold it. If you cannot hold the aero position comfortably for an hour, you will likely ride more upright than the bike was designed for.
- Relying only on the chart for a first triathlon bike. New triathletes often benefit from a slightly more relaxed position while building strength and flexibility.
- Forgetting saddle setback and bar adjustments. Fine tuning can change how the bike feels more than a small change in frame size.
Tips for Getting the Fit Right
- Measure your inseam carefully and keep the same measurements handy when comparing brands.
- Look at the full geometry table for the exact model, not just the general chart.
- Ask whether the shop allows a test ride or offers a fit session before you buy.
- Plan for a few adjustments in the first weeks, such as small changes to saddle height or armrest position.
- If you are between sizes, the larger frame with a shorter stem is often easier to adjust than the smaller frame with a longer stem.
If you are also weighing a road bike or a hybrid for training, the sizing principles are similar. Readers comparing setups may find Road Bikes for Beginners: Endurance Geometry, Gearing and Sizing helpful for understanding how reach and stack change across bike types. For a general primer on frame size and saddle height, Bike Sizing Explained: Frame Size, Standover and Saddle Height covers the basics well. If you are new to cycling altogether, What to Expect from Your First Entry-Level Road Bike describes what early rides usually feel like.
Recommended gear
A few tools make it easier to measure yourself and check the fit at home before you visit a shop.
- A flexible measuring tape helps you record height, inseam, arm length, and torso length accurately. View on Amazon
- A hardcover book or a bike fit wedge helps you measure inseam without a helper. View on Amazon
- A bike trainer lets you sit in the aero position and check reach and stack before you buy. View on Amazon
- A clipboard or notebook keeps your measurements, the geometry numbers, and your test notes in one place. View on Amazon
FAQ
What size Felt triathlon bike do I need for my height?
Use the brand’s size chart as a starting point, then compare your inseam, arm length, and torso length to the reach and stack figures for each model. Height alone does not decide the right frame.
Is reach or stack more important on a triathlon bike?
Both matter. Reach controls how far you stretch to the bars, and stack controls how low and upright you sit. Flexible riders often choose more reach, while riders who need comfort often choose more stack.
Can I go one size up or down if I am between sizes?
Yes, many riders do. Compare the geometry numbers and consider stem length and bar pad position. A slightly larger frame with a shorter stem is often easier to adjust.
Do frame sizes match across different brands?
No. Frame size labels are not standardized, so a size 54 from one brand may ride differently from a size 54 from another. Always compare reach and stack in millimeters.
How do I measure my inseam for a bike?
Stand against a wall with a hardcover book between your legs, spine up, snugged against your crotch. Measure from the top of the book to the floor and multiply by 0.67, or have a helper measure directly from the crotch to the floor.
Should I get a professional bike fit for a triathlon bike?
A professional fit is worth it for serious racers and anyone riding long distances. It can refine saddle height, setback, and bar position for your body. If you have existing knee, back, or neck pain, consult a physical therapist or medical professional before making major changes.
Can I use a road bike size chart for a triathlon bike?
Not directly. Triathlon bikes have steeper or more aggressive geometry, so reach and stack can differ from a road bike of the same size. Use a chart made for the specific triathlon model when possible.
Conclusion
A felt triathlon bike size chart is the right starting point, but it works best alongside your own measurements and the geometry numbers for each model. Compare reach, stack, and inseam, and consider how flexible you are for an aero position. Test the bike when you can, and plan for small adjustments once you start riding.
