Thru-axles vs. quick-release
For decades wheels were held in by a quick-release (QR) skewer: a thin 5 mm rod through a hollow axle, clamped by a cam lever into open, slotted dropouts. Quick to remove, but the wheel locates against open dropouts, which allows some flex — and that became a problem when disc brakes arrived, because braking forces try to push the wheel out of the dropout.
Modern disc-brake bikes use a thru-axle: a stout 12 mm shaft that threads straight into closed dropouts and clamps the hub solidly. The result is a stiffer, more precisely located wheel that goes back in exactly the same spot every time — which keeps the disc rotor centred in the caliper.
Older — Quick-release
- 5 mm skewer in open dropouts
- Common sizes: 100 mm front, 130 mm (road) / 135 mm (MTB) rear
- Fast, tool-free wheel changes
- Some flex; can shift under disc braking
Modern — Thru-axle
- 12 mm shaft threaded into closed dropouts
- Road/gravel: 12×100 mm front, 12×142 mm rear
- Stiffer; rotor stays aligned on refit
- Slower to remove; must be torqued correctly
Mountain bikes went further with Boost spacing — 110 mm front / 148 mm rear — which widens the hub flanges for a stronger wheel with clearance for wide tyres. A "Road Boost" (12×110 / 12×148) also exists but is far less common.
Thru-axle and Boost standards are not interchangeable
with older QR wheels or with each other — the hub width and axle
diameter must match the frame. Check the numbers (e.g.
12×142) before buying wheels or a bike.
Disc brakes vs. rim brakes
The biggest visible change on road bikes. Rim brakes (calliper or cantilever) squeeze pads onto the wheel rim. They're light, cheap, simple and easy to service — but braking wears out the rim over time, performance drops in the wet, and a buckled wheel can rub or stop the wheel spinning.
Disc brakes clamp a rotor at the hub instead. They give stronger, more consistent braking — especially in wet and muddy conditions — with better modulation (fine control of braking force), and they don't wear the rim or care if the wheel is slightly out of true. That's why they took over mountain bikes years ago and now dominate road and gravel. The cost is more weight, more complexity, and the need to keep rotors and pads oil-free.
| Rim brake | Mechanical disc | Hydraulic disc | |
|---|---|---|---|
| Actuation | Cable → rim | Cable → rotor | Fluid → rotor |
| Power / control | Adequate | Good | Best; self-adjusting |
| Wet performance | Weakest | Strong | Strongest |
| Maintenance | Simplest, cheapest | Simple; adjust cable | Needs occasional bleed |
| Weight | Lightest | Middle | Heaviest |
Electronic vs. mechanical gears
Traditional gears are mechanical: the shift lever pulls a steel cable that moves the derailleur. It's reliable, cheap and field-repairable, but cables stretch, attract grit and corrode, so shifting slowly drifts out of tune and needs occasional adjustment.
Electronic shifting replaces the cable with a motor in each derailleur and a button on the shifter. Press the button, a small motor makes a fast, identical shift every time. It holds its tune almost indefinitely, shifts under load, and can shift both derailleurs from multiple buttons or even automatically. The trade-offs: higher cost, batteries to charge, and you can't bodge a repair by the roadside.
The three main systems differ in how wireless they are:
| System | Architecture | Battery | Notable |
|---|---|---|---|
| Shimano Di2 | Semi-wireless — wireless shifters, wired derailleurs | One internal battery, wired charge; lasts weeks | Fast, refined, polished shifts |
| SRAM AXS | Fully wireless — no wires at all | Removable coin-cell battery per derailleur, USB-C; ~20–30 hrs | Modular; carry a spare battery |
| Campagnolo | Wired EPS, plus a newer wireless system | Wired (EPS) or per-unit (wireless) | Now offers a 13-speed wireless groupset |
Electronic shifting is now common on mid-to-high-end bikes but by no means universal — excellent mechanical groupsets are still made and, for touring and remote riding, are often preferred precisely because there's nothing to charge and less to fail.
More sprockets & 1× drivetrains
Cassettes have steadily gained sprockets: a good bike went 8- and 9-speed in the 1990s, then 10, 11, and now 12-speed is standard on new bikes, with 13-speed appearing. More sprockets mean either finer jumps between gears or a wider overall range — often both. The chains got narrower to fit, which is why 11- and 12-speed chains wear out sooner (see the chain-wear guide).
The other shift is 1× ("one-by") drivetrains: a single front chainring and no front derailleur, paired with a wide-range cassette. Mountain bikes have almost entirely moved to 1×; gravel bikes often use it too. You lose some fine gear steps and top-end range, but gain simplicity, less to maintain, less to go wrong, and no dropped chains at the front. Traditional 2× (and old 3×) setups keep more closely-spaced gears, which road riders and tourers often still want.
Older / road-traditional
- Two or three chainrings + front mech
- Closely-spaced gears, wide total range
- More parts, more to adjust
- Still ideal for road racing & touring
Modern MTB / gravel
- Single chainring, no front mech
- Wide-range cassette does the work
- Simpler; fewer dropped chains
- Bigger jumps between gears
Tubeless vs. inner tubes
Traditionally a tyre holds an inner tube that you inflate. Tubeless removes the tube: the tyre seals directly to the rim, and liquid sealant inside plugs small punctures automatically as you ride. Benefits: fewer flats, no pinch punctures, and you can run lower pressures for grip and comfort. Costs: a fiddlier initial setup, sealant that dries out and needs topping up every few months, and messier roadside repairs when a puncture is too big to seal.
Many tubeless road/gravel rims are now hookless (no bead hook), which caps pressure at around 72.5 psi and requires tubeless-approved tyres. Older high-pressure road tyres are not compatible. Always match tyre and rim.
Wider tyres & clearance
One of the clearest shifts in thinking. For years narrow, hard tyres (23 mm at ~120 psi) were assumed fastest. Testing showed that wider tyres at lower pressure often roll as fast or faster on real roads, while being far more comfortable and grippier. Road bikes moved from 23 to 25, 28, and now 30–32 mm as standard, and modern frames are built with the clearance to fit them. Gravel pushed clearances to 45–50 mm and beyond. If you ride an older frame, its tyre clearance is one of its biggest practical limitations.
Bottom brackets: threaded vs. press-fit
The bottom bracket (BB) holds the bearings the cranks spin on. Classic frames use a threaded BB (the common standard is BSA, 1.37 ″ × 24 tpi) that screws in — simple, serviceable, and reliably creak-free. To fit larger, stiffer axles, makers introduced press-fit standards (e.g. BB86/BB92) where bearing cups press into the frame. Done well they're light and stiff; done poorly they became notorious for creaking.
The newer T47 standard is a response to that: it uses the large 46 mm diameter of press-fit but threads into the frame like BSA, aiming for the best of both. If you're servicing an unfamiliar bike, identifying the BB standard is the first job — there are many, and tools are specific.
Integrated cabling & cockpits
On older bikes, brake and gear cables ran outside the frame — easy to see and service. Modern performance bikes hide cables and hoses fully internally, often routed through the handlebar, stem and headset for a clean look and a small aero gain. The downside is real: jobs as basic as changing a headset bearing or adjusting bar height can mean disconnecting hydraulic hoses and re-bleeding brakes, turning a five-minute task into a workshop job. It's a genuine trade-off of looks and aero against serviceability.
Materials & other standards
- Carbon fibre went from exotic to mainstream, allowing lighter frames and aero shapes — but demanding torque-wrench discipline and careful handling.
- Wheel & tyre sizing settled: most adult bikes now use 700c/29″ or 27.5″ (650b) wheels; older 26″ mountain-bike wheels are largely gone from new bikes.
- Dropper posts became standard on trail mountain bikes, letting you drop the saddle on the move.
- Freehub & axle standards multiplied — SRAM XD/XDR and Shimano Micro Spline bodies exist to fit modern wide-range cassettes with small 10- or 9-tooth sprockets that the old freehub couldn't.
The trade-off, summarised
Modern bikes are, broadly, more capable and lower-fuss to ride — better brakes, gears that stay tuned, tyres that puncture less, and stiffer, more precise wheels. The cost is more complexity to own: more standards to match, batteries and bleeds and sealant, and some jobs that now need a workshop.
An older bike, by contrast, is usually simpler, cheaper to run, and easier to fix yourself — which is exactly why steel-framed, rim-braked, mechanical bikes remain a favourite for commuting, touring and anyone who values working on their own machine. Neither is "better" outright; they're tuned for different priorities.