Careful measurements matter more than extra decimal places. Here is what each result means.
01 / DRIVETRAINWhich gear makes climbing easier?
The gear ratio is the number of chainring teeth divided by the number of cog teeth. A 32-tooth chainring with a 51-tooth cog gives 0.627: the wheel turns about 0.63 times per crank revolution. On the same wheel, a lower ratio means less distance per pedal stroke.
Development (also called rollout) takes the wheel into account too: development (m) = circumference (m) × chainring ÷ cog. Compare the lowest development for climbs and the highest for fast sections. The range is the highest divided by the lowest, multiplied by 100.
Gear inches use the effective wheel diameter in inches. Gain ratio divides the effective wheel radius by the crank length and multiplies it by the gear ratio. The calculation does not guarantee derailleur compatibility, enough chain capacity or freedom from cross-chaining.
02 / RHYTHMHow do you convert cadence into speed?
Cadence is the number of full crank revolutions per minute (rpm). Multiply the development by the cadence and by 0.06 to get km/h. To go the other way, divide the speed by development × 0.06.
Example: with a 2,100 mm wheel, a 50-tooth chainring and a 25-tooth cog, each pedal stroke covers 4.2 m. At 90 rpm that is 22.68 km/h. Holding 30 km/h in the same gear takes about 119 rpm. This describes the motion only; whether you can sustain that pace depends on the conditions and the rider.
How to measure wheel circumference
Inflate the tire, mark the contact point on the ground and roll forward one full wheel revolution with the bike loaded. Measure the distance between the marks in millimeters. “29er” or “700c” alone does not determine this distance: width, load and pressure all affect it.
03 / WHEEL BUILDThe measurements that determine spoke length
ERD runs to the ends of spokes correctly threaded into the nipples. Measure across more than one diameter of the rim, using the nipples and washers you will build with. PCD runs through the centers of the holes in each flange. Also measure from the hub center to each flange.
We use L = √(R² + r² + d² − 2Rr cos θ) − h/2, where R = ERD/2, r = PCD/2, d = effective lateral distance, θ = 4π × crosses ÷ total spokes and h = hole diameter. All measurements are in mm. A positive offset to the left reduces the left d and increases the right d.
The result is shown to one decimal place for geometric comparison. It is not a shopping list: check tolerances, available lengths, thread engagement and the manufacturer's recommendations. The formula does not apply to straight-pull spokes, paired spoking or 2:1 lacing.
04 / GROUND CONTACTBike tire pressure: why is there no universal PSI?
Load per wheel and actual width change the pressure you need. RatioRide uses its own heuristic: P(bar) = 4 × (load per wheel / 42.5) × (28 / width in mm)1.5 × surface factor × setup factor. The reference point is 4 bar for 42.5 kg and 28 mm, on smooth pavement with a tubeless setup. It is not a SILCA or SRAM formula.
Surface factors: smooth 1; rough 0.92; hardpack gravel 0.85; light trail 0.80. With an inner tube we multiply by 1.08. These are explicit modeling choices, not certified coefficients. The formula does not account for casing, temperature, speed, impacts or grip; software tests are no substitute for real-world validation.
Conversion: 1 bar = 14.503773773 psi. The model covers tires from 23 to 80 mm and a total mass of up to 200 kg. Once you confirm compatibility, a result is shown only if it falls within the range you entered. Hookless rims with inner tubes are outside our scope, even though some manufacturer-approved setups exist.
Hookless pressure caps and our conservative rule
Schwalbe technical reference for TSS: 25–29 mm: 5 bar; 30–34: 4.5; 35–39: 4; 40–44: 3.5; 45–54: 3; 55–64: 2.5; 65–74: 2; 75–84: 1.5. Below 25 mm we give no hookless recommendation.
The source refers to “tire width” without distinguishing nominal from measured width. To stay on the safe side, we pick the cap using the larger of the two and continuous bands (28.9 mm stays below 30). This is a RatioRide decision, not a rule attributed to the source. Lower limits set by the manufacturer always take precedence.
