Trek Rail 9 AXS wheel circumference setting for 29x2.4 tyre?

[alextrek9]

My bike is a Trek rail 9 axs.

Trying to find correct wheel circumference for 29er with 2.4 tyre.

@Greg Watts

 

[Greg Watts]

For a 29 x 2.4 tyre, the real-world rolled circumference lands very close to 2295mm — give or take 10mm depending on brand, casing and pressure. That's the number most riders end up at after measuring rather than trusting the sidewall.

How to verify it properly (takes 30 seconds and beats any chart):

• Pump tyre to your normal riding pressure
• Mark the tyre at the valve, mark the floor below it
• Roll the bike forward one full revolution with your weight on it
• Mark the floor again, measure between marks in mm
• That's your true circumference

Do it under load — an unweighted measurement will read 20–30mm long because the tyre isn't squashed.

Why the published numbers lie

A "29 x 2.4" varies wildly. A Maxxis Minion DHR II 2.4 EXO+ measures differently to a Schwalbe Magic Mary 2.4 Super Trail, which measures differently again to a Specialized Butcher T9. Rim internal width also changes the seated profile — a 2.4 on a 30mm rim sits taller than the same tyre on a 25mm rim.

For reference points from the community:

• Stock 29 x 2.6 Specialized tyres measure ~2.45" wide on a 25mm rim, per @1oldfart
• Amflow's stock 29 x 2.6 Minion comes in at 2356mm circumference
• A 27.5 x 2.6 Eliminator measures 2251mm (per CatEye calc, @mustclime)

So 2295mm for a 29 x 2.4 sits sensibly between those.

If this is for speed derestriction

Then you want the displayed wheel size, which on most systems is the real circumference multiplied by the derestriction factor (typically 0.677 for a 1.5x speed lift, or 0.621 for ~1.6x). For 2295mm actual:

• 0.677 factor → set display to ~1554mm
• 0.621 factor → set display to ~1425mm

Which factor depends entirely on your tuning method/dongle — tell me what you're running and I'll be more specific.

If it's just for a cycle computer / odometer

Punch in 2295 and you'll be within 1% of reality. Measure your actual tyre if you want that last percent.

What bike and what's driving the question — speedo accuracy or derestriction?