Short answer: a wheel fits your bike if five things match: hub spacing, axle type, freehub type, rotor mount and rim size. Hub spacing is the one people get wrong. Modern road disc bikes are 100x12 front and 142x12 rear, modern mountain bikes are 110x15 and 148x12 Boost, and older bikes are quick release at 100mm and 130 or 135mm.
Contents
- The five numbers that define a wheel
- Hub spacing, the number that decides fit
- Axle standards
- Rotor mounting
- Rim internal width and tyre pairing
- Rim depth and rider weight
- Spoke count, lacing and rider weight
- Hub bearings: cup and cone or cartridge
- Will this wheel fit my bike
- Frequently asked questions
The five numbers that define a wheel
Wheel compatibility feels complicated because five separate standards have to line up, and they changed at different times. Get these five right and the wheel fits. Get one wrong and it does not, no matter how good the wheel is.
- Hub spacing, also called over-locknut dimension or OLD, measured in millimetres between the dropout faces.
- Axle type, quick release or thru-axle, and the thru-axle diameter.
- Freehub type, which decides what cassette you can fit.
- Rotor mount, six-bolt or Centerlock, if you run discs.
- Rim size, 700c, 650b or 26in.
Rim width, depth and spoke count affect how the wheel rides, but they do not affect whether it fits. That distinction is worth holding onto, because most confusion comes from mixing the two lists.
Hub spacing, the number that decides fit
Hub spacing is written as width by axle diameter, so 142x12 means 142mm between dropouts with a 12mm axle.
| Bike type | Front | Rear |
|---|---|---|
| Road, rim brake, quick release | 100mm QR | 130mm QR |
| Road and gravel, disc, thru-axle | 100x12 | 142x12 |
| Mountain, older quick release | 100mm QR | 135mm QR |
| Mountain, pre-Boost thru-axle | 100x15 | 142x12 |
| Mountain, Boost | 110x15 | 148x12 |
| Mountain, Super Boost | 110x15 | 157x12 |
Two things cause most of the trouble here.
The rear road disc standard is 142x12, not 135. A 135mm quick release mountain wheel and a 142x12 road disc wheel look almost identical and will not swap. The 7mm difference is entirely in the end caps.
Boost is not an upgrade you can opt into. It moved the flanges outward to build a stiffer wheel around wider tyres, and a Boost wheel will not fit a non-Boost frame or fork, nor the reverse. If you are buying a used wheelset for a mountain bike, this is the first question to ask.
Axle standards
Quick release uses a 5mm skewer through a hollow axle, clamped by a cam lever. Thru-axle uses a 12mm or 15mm axle that threads into the frame or fork and becomes a structural part of it, which is why disc brakes moved to it: disc braking twists the axle in a way quick release was never designed to resist.
Thru-axle length and thread pitch vary by frame even at the same 142x12 spacing, so an axle is frame-specific in a way the wheel is not. If you buy a second wheelset you usually keep your existing axle. Full detail in our reference on thru-axle and quick release sizing, and the range is in axles and skewers.
Rotor mounting
Two systems, and the wheel decides which rotor you can fit, not the brake.
- Six-bolt uses six T25 bolts at 2 to 4Nm. More common on mountain and budget wheels, and easier to find rotors for.
- Centerlock uses a splined interface and a lockring at 40Nm. Faster to change and slightly lighter.
Adapters exist to fit a six-bolt rotor to a Centerlock hub. The reverse is not possible. Freehub and cassette pairing is covered separately in freehub and cassette compatibility, and rotor sizing in disc rotor standards and adapters.
Rim internal width and tyre pairing
Internal rim width, measured between the bead walls, determines what tyre widths work properly. It has moved a long way in a decade: road rims that were 15mm internal are now commonly 21 to 23mm.
| Internal rim width | Sensible tyre range | Typical use |
|---|---|---|
| 15 to 17mm | 23 to 32mm | Older road |
| 19 to 21mm | 28 to 40mm | Modern road and light gravel |
| 21 to 25mm | 32 to 50mm | Gravel |
| 25 to 30mm | 2.1 to 2.4in | Cross country and trail |
| 30 to 35mm | 2.4 to 2.8in | Trail and enduro, plus tyres |
A tyre mounted on a rim narrower than intended takes a light-bulb profile, which rolls unpredictably when leaned over. Too wide and the sidewall is unsupported. Full detail in tyre and rim width compatibility.
Rim depth and rider weight
Rim depth is an aerodynamic and handling choice, not a fit one.
| Depth | Character | Best for |
|---|---|---|
| 25 to 35mm | Light, unaffected by wind | Climbing, everyday, windy coastal riding |
| 40 to 50mm | The sensible all-rounder | Most riders, most conditions |
| 55 to 65mm | Fast on flat ground, moves in crosswinds | Time trial, flat racing, heavier riders |
| Disc and 80mm plus | Fastest, unusable in side wind | Track and time trial only |
For most riders in India, 40 to 50mm is the right answer, and it is where the useful stock sits. The Magene Exar UltraDark DB508 at ₹1,08,900 runs 50mm front and 58mm rear, which is a common and sensible pairing: the shallower front wheel is the one that catches crosswind, so keeping it shallower keeps the steering calm while the rear still does aerodynamic work.
Other options in stock include the Pardus MVMT M-Bronze 50 at ₹69,990 and, for gravel, the Magene Exar Pro GR45 at 45mm. Crosswind sensitivity scales with depth and inversely with rider weight, so a light rider on 65mm rims will be working harder than a heavy one.
Spoke count, lacing and rider weight
Spoke count is the most useful specification nobody reads.
| Spokes | Suits |
|---|---|
| 20 to 21 front, 24 rear | Light riders on good surfaces, racing |
| 24 front, 24 to 28 rear | Most road riders |
| 28 to 32 | Heavier riders, gravel, Indian road surfaces |
| 32 to 36 | Touring, loaded riding, tandem |
Rear wheels usually carry more spokes than front, because the rear takes most of the rider's weight and all of the drive torque, and because the drive side flange is pushed inward to make room for the cassette, which makes the rear wheel inherently less balanced.
If you ride Indian roads regularly, bias upward. A 24-spoke rear wheel that is fine on European tarmac will need truing far more often here. The extra 200 grams of a 28-spoke build is a better trade than repeated wheel work.
Spokes are either J-bend, which hook into the hub flange, or straight-pull, which pass through it. J-bend spokes are available in any bike shop in the country. Straight-pull spokes are proprietary to the hub and often have to be ordered. That matters more in India than the small stiffness difference between them.
Hub bearings: cup and cone or cartridge
Cup and cone bearings, which Shimano still uses, run loose balls against machined surfaces in the hub. They are adjustable, serviceable indefinitely with basic tools, and if maintained they outlast the wheel.
Cartridge bearings are sealed units pressed into the hub. They need no adjustment and are replaced rather than serviced, which is quicker but means buying a part.
In monsoon conditions the practical difference is that cup and cone hubs can be opened, cleaned and regreased at home for the cost of some grease, while a contaminated cartridge bearing is a replacement. Neither is better. Cup and cone rewards attention, cartridge tolerates neglect until it does not.
Replacement hubs and freehub bodies are in hubs, including SRAM 900 12x148mm Boost, Token D1 and M1 thru-axle hubs, and XDR freehub bodies for Token, Parcours and Zipp wheels.
Will this wheel fit my bike
Run these five in order. Stop at the first mismatch.
- Measure your dropout spacing with the wheel out, front and rear. This gives you the first number.
- Check the axle. Quick release skewer, or a threaded 12 or 15mm axle.
- Check the freehub against your cassette: Shimano HG, Shimano Micro Spline, SRAM XD or XDR, or Campagnolo.
- Check the rotor mount, six-bolt or Centerlock.
- Check rim size against your tyres and frame clearance.
Only then look at depth, width and spoke count, which decide how it rides rather than whether it fits.
Frequently asked questions
Can I convert a quick release wheel to thru-axle?
Sometimes, and only by changing the hub end caps, never with an adapter that bolts on. Many modern hubs from Token, Novatec, DT Swiss and Hope accept swappable end caps that convert between 135mm QR and 142x12, and the caps cost far less than a wheel. Older hubs with fixed axles cannot be converted. Check the hub manufacturer before assuming either way.
Are 650b and 27.5in the same wheel size?
Yes, identical. Both describe a 584mm bead seat diameter, and the two names exist only because road and mountain biking arrived at the same rim from different directions. A 650b gravel wheel and a 27.5in mountain wheel share a rim size, though they will differ in internal width, spoke count and hub spacing, so sharing a size does not mean they are interchangeable.
How often should hub bearings be serviced in monsoon conditions?
Once at the end of every monsoon as a minimum, and immediately after any ride through standing water. Water forced past hub seals emulsifies the grease and corrosion starts within days, long before you hear anything. Cup and cone hubs can be stripped, cleaned and regreased. Sealed cartridge bearings that have taken water in should be replaced rather than cleaned.
Can I fit a road wheelset to a gravel bike?
Usually yes on spacing, since both commonly use 100x12 and 142x12, but the rim is often the limit. Road rims with 19 to 21mm internal width will not properly support a 45mm gravel tyre, which needs 21 to 25mm. Check the internal width before the hub spacing here, because that is the specification that will actually stop you.
What do I need to know before replacing a broken spoke?
The spoke length, which is specific to that wheel and often different on the drive side and non-drive side of the rear. Length is calculated from hub flange diameter, rim depth and lacing pattern, so it cannot be measured off a neighbouring spoke reliably on a rear wheel. Bring the wheel in rather than ordering a spoke by guesswork.
Check before you buy
The full selection is in wheelsets. If you are unsure whether a wheel fits, ask TBA Guide with your bike model and year, or bring the bike to our Kondapur workshop and we will measure the dropouts for you. It takes two minutes and it is a great deal cheaper than a wheel that does not fit.
