Guide: Upgrade an Older Bike with Modern Components – Road, MTB & Touring

1. Start with the frame—not the components

It is easy to start by asking which groupset you want. Instead, begin by identifying which standards the frame actually uses.

Once you know this, it becomes much easier to determine how far it is reasonable to modernize the bicycle.

2. 126, 130, or 135 mm—check the rear dropout spacing

Older bicycles may have a different rear dropout spacing than more modern models. This measurement is usually given as OLD – Over Locknut Dimension and describes the width of the rear hub between the outer locknuts, and therefore the distance for which the frame is designed.

• 126 mm: Common on older 6- and 7-speed racing bikes.
• 130 mm: Standard on most later road bikes with rim brakes.
• 135 mm: Very common on classic MTB, touring, and trekking bikes, as well as later QR bikes with disc brakes.

If you want to install a more modern rear wheel, this is one of the first measurements you need to check.

On some steel frames, the rear triangle can, after assessment, be adjusted from, for example, 126 to 130 mm. This method is called cold setting. However, you should not assume that this is suitable for all frames, and the method should not be used on aluminium or carbon-fibre frames.

Measure first—buy the wheel afterwards.

3. Freewheel or cassette?

Many older rear wheels have a threaded freewheel, where the sprockets and freewheel mechanism are a single unit that screws directly onto the hub. More modern wheels instead use a cassette mounted on a freehub body.

If you want to go, for example, from 6 or 7 speeds to 9, 10, or 11 speeds, a new rear wheel with a compatible freehub body is often the simplest solution.

But check which freehub body the wheel has—not just how many sprockets the cassette has. A Shimano/SRAM HG body used for 8-, 9-, and 10-speed cassettes is not automatically compatible with all 11-speed road cassettes.

For example, Shimano CS-HG700, CS-HG800, and CS-RS400 can be fitted to the shorter HG spline M body, while most 11-speed Shimano road cassettes require the longer HG spline L body.

This is especially relevant when restomodding an older MTB. A classic 135 mm rear wheel with an HG body can often offer great opportunities to modernize the drivetrain without replacing the frame itself.

A more modern rear wheel therefore offers significantly more options for choosing the cassette and gearing according to how the bike will be used—but always check the specific cassette and freehub body combination before ordering.

4. Can modern gears be fitted to an old frame?

Often, yes. The frame does not really care whether you have six, nine, or eleven sprockets at the rear.

The important thing is that the shifters, rear derailleur, cassette, chain, and other drivetrain components work together. An older quality steel frame can therefore work perfectly well with a considerably more modern drivetrain.

That does not mean, however, that all components from different generations of Shimano, Campagnolo, and SRAM are automatically compatible. Not even the same number of gears guarantees that the components will work together.

A good example is Shimano 10-speed road. Tiagra 4700 is a 10-speed system, but its shifters and rear derailleur belong to a different compatibility family than older Shimano 10-speed road systems such as 105 5700, Ultegra 6700, and Tiagra 4600.

Cable routing, indexing, shifting geometry, number of gears, and component generation must therefore match.

On older MTBs, a modern 1x drivetrain is often an attractive option. You can do without a front derailleur and left shifter while still getting a wide gear range with a wide-range cassette. But still check the chainline, freehub body, rear derailleur capacity, and which chainrings actually fit the existing crankset.

5. Old MTBs – perfect platforms for restomods

Rigid mountain bikes from the late 1980s and 1990s in particular have become popular platforms for restomod builds. Many have robust steel frames, relatively simple standards, and plenty of room for wide tires.

The point does not have to be trying to turn an old MTB into a modern racing MTB. With the right components, it can instead become a highly capable commuter bike, touring bike, gravel-inspired all-rounder, or bikepacking bike.

A good restomod is not about replacing everything old. It is about keeping what works and modernizing what actually makes the bicycle better.

6. From frame-mounted shifters to modern shift levers

On older road frames, the shifters are often mounted on the down tube—classic so-called downtube shifters.

If you instead want to use integrated brake and shift levers, such as Shimano STI or Campagnolo Ergopower, these mounts can normally be used together with cable stops.

So you normally do not need to modify the frame. It is a small component, but a smart bridge between a classic frame and more modern ergonomics at the handlebar.

On older MTBs, the situation is often simpler because the shifters are already mounted on the handlebar. In that case, the upgrade is primarily about matching new shifters with the correct rear derailleur and cassette.

7. Bottom brackets – BSA, ITA, and older standards

The fact that the bottom bracket is threaded does not automatically mean that all threaded bottom brackets will fit. You need to check both the thread standard and bottom-bracket shell width.

Never assume that the frame has Italian threading just because the bicycle brand is Italian. Identify the standard before ordering.

Older French and some Swiss frames may use 35 x 1 mm threading. French bottom-bracket threading is normally right-handed on both sides, while the Swiss standard has left-hand threading on the drive side. These standards are much less common today, but important to recognize when working on older bicycles.

8. Do you really need to replace the crankset?

Not necessarily.

A good older square-taper crankset made of forged aluminum can still be lightweight, durable, and fully functional. There is no technical rule saying that everything old must be replaced just because the rest of the drivetrain is modernized.

This also applies to many older MTB cranksets. A classic triple crankset can in some cases continue to be used, or be converted to 1x if the right chainring is available for the crankset’s BCD and the desired chainline.

If you instead want to use a modern crankset with external bearings, you need to check that the bottom bracket, frame, and crankset are compatible.

Newer is not automatically better. The right component for the build is better.

9. Chainline – a small detail with major significance

When older and more modern components are combined, the chainline is important. It describes where the front chainrings and rear sprockets sit in relation to the frame's centerline.

If you combine an older crankset with a more modern rear wheel and a wider cassette, the drivetrain geometry may change. If you replace the crankset, you also need to check that the chainrings are positioned correctly and do not come too close to the chainstay.

On square-taper cranks, the position is influenced partly by the bottom bracket spindle length. The wrong spindle length can therefore cause both a poor chainline and clearance problems with the frame.

This becomes especially important when an older MTB is converted from 2x or 3x to 1x. Bolting a narrow-wide chainring onto an old crankset does not automatically mean that the chainring will be in the optimal position relative to the cassette.

The correct chainline provides better shifting, less noise, and lower wear.

10. Front derailleur – braze-on or clamp?

The front derailleur can either be mounted on a fixed mount on the frame (braze-on) or with a clamp around the seat tube (clamp-on).

Many older steel frames have seat tubes with a 28.6 mm diameter, while modern clamps are often available in 31.8 or 34.9 mm. Reducers and shims often make it possible to combine modern front derailleurs with narrower tubes.

If the frame has a braze-on mount, you would normally choose a front derailleur designed for it.

If you instead convert the bicycle to 1x, the front derailleur obviously disappears completely, but checking the chainline becomes even more important.

11. Brakes – reach, mounting, and cable pull

This is a classic pitfall when modernizing an older bicycle. The fact that a brake can be bolted to the frame does not automatically mean that the entire brake system is compatible.

Therefore, if you switch from cantilever brakes to V-brakes on an old MTB, do not just check the brake arms; also check the brake levers.

The same principle applies when older brake calipers are combined with newer road-bike levers: different generations may use different cable pulls and mechanical leverage ratios.

If the frame or fork lacks dedicated disc-brake mounts, you should not assume that the bike can be converted to disc brakes. In many restomod builds, a well-functioning cantilever or V-brake system is both simpler and more logical.

12. 1" or 1 1/8" – headset, fork, and stem

Many older road bikes and early MTBs use a 1" threaded headset together with a quill stem that extends down into the steerer tube.

Later MTBs and more modern bicycles generally use a threadless/Ahead system, often with a 1 1/8" steerer tube.

If you want to keep an older 1" fork but use a modern stem, quill adapters are available that fit into the steerer tube and provide a mounting point for a modern Ahead stem.

Important: Such an adapter does not convert the headset or fork to 1 1/8". The bike still has a 1" threaded system—the adapter only changes how the stem is mounted.

Another option is to keep a classic quill stem. Models are available that combine a classic mounting system with more modern handlebars.

On a retro MTB, a wider riser or alt-bar handlebar can dramatically change the bike's character, but check the stem's clamp diameter before ordering a new handlebar.

13. Wheel size and tires – 26", 27", 700C, and actual clearance

Wheel size is one of the things you should always identify before you start buying tires, wheels, or brakes for an older bicycle.

Many classic MTBs use what is normally called 26", which for mountain bikes usually means an ETRTO/ISO diameter of 559 mm. However, 26" is not an unambiguous standard—several incompatible rim diameters have historically been called 26". Therefore, always check the ETRTO measurement on the tire or rim.

On older road bikes, you may also encounter 27" / 630 mm, while more modern road wheels are usually 700C / 622 mm. They are not the same wheel size, even though the difference may seem small at first glance.

If the goal is to make an older road bike, MTB, or touring bike more useful, a pair of good modern tires may be one of the upgrades that makes the biggest practical difference.

• ETRTO/ISO diameter of the rim and tire.
• Clearance under the brakes.
• The distance between the chainstays.
• The fork crown and fork blades.
• Clearance from the seat tube and brake bridge.

Do not rely solely on the tire’s stated width. The actual width is also affected by the rim’s internal width and the tire’s construction.

How modern does the bike really need to be?

It is easy to get stuck thinking that the latest 11- or 12-speed drivetrain is automatically the best upgrade. That does not have to be the case.

For commuting, touring, retro MTBs, and everyday road cycling, a well-functioning 9- or 10-speed drivetrain can be an excellent choice. Replacement parts are often cheaper, the systems are relatively easy to service, and wear parts are readily available.

Likewise, an old MTB does not need disc brakes, modern wheel standards, and the latest 12-speed groupset to become a fantastic bike. A pair of good tires, fresh bearings, the right gearing, new handlebars, and properly working brakes can completely transform the bike.

A quality hub, a good crankset, or a well-built headset does not become bad just because a newer standard exists.

The goal does not have to be making an old bike as modern as possible. The goal is to build a better bike for what you will actually use it for.

Sometimes the best solution is a combination of components manufactured 20 or 30 years apart. That is part of the charm of a good restomod build—and one of the reasons an older quality bike can still be well worth investing in.

Not sure what fits?

We work every day with modern bikes, older standards, retro MTBs, and custom builds in our shop and workshop in Södermalm, Stockholm. Do you have an older frame or bike you want to rebuild? Feel free to send a few photos, the components currently installed, and what you want to achieve. A few photos and a couple of measurements are often enough to find a sensible solution.