Wheels & Tyres

Rims buying guide

Category: Wheels & Tyres

Rims buying guide

Your wheel’s rim – the aluminium or carbon fibre hoop that they tyre sits on – is one of your bike’s essential components, having a significant effect on factors including your speed and ability to absorb impacts.

For road and trail riding, stiff and lightweight rims reduce rotational weight, helping you go faster for less effort. Meanwhile the latest generation of deep-section carbon rims gives competitive road racers an aerodynamic advantage.

However for high-octane biking disciplines such as BMX and downhill (DH) MTB racing, rims must be strong and wide enough to take considerable punishment without folding.

Read on for more information about the different types of rims suitable for BMX, MTB and road riding.

Learn more about:

MTB rims
Road rims
BMX rims


Rims buying guide

When upgrading or replacing an MTB rim or building a wheelset there are a number of factors to take into consideration, including not only the size of rim your bike is designed for, but also characteristics such as weight, width, spoke number and type, etc.

The vast majority of MTB rims are made from aluminium alloy although some high-end racing hoops may utilise carbon fibre – but at a price.

WHICH MTB RIM IS RIGHT FOR YOU?

The type of rim you choose must be matched to the type of riding you do – a lightweight set of XC racing hoops simply can’t withstand the beating dished out by a boulder-strewn descent, while a super-strong pair of DH rims is hard work to pedal for any length of time.

Lighter rims mean less rotational weight, which translates into improved acceleration and easier speed – perfect for fast cross-country riding and racing. However wheels for certain MTB disciplines – particularly downhill racing (DH), Enduro riding Freeride (FR) require wider, stronger rims, which can take sustained punishment without folding like a taco (not good).

MTB RIMS: IN-DEPTH

The three most important considerations when choosing an MTB rim are diameter, width and number of spokes.

Diameter
The three most common MTB rim diameters are 26”, 27.5” (sometimes referred to as 650b) and 29” (see our ‘Wheels’ buying guide for an-depth explanation as to the differences between the three and the history of the standards).

Whichever rim diameter you opt for will be determined by your bike type (you can’t put 27.5” rims on a bike made for 26” wheels, for example), which in turn will depend on the type of riding you intend to do and your personal preference in wheel sizes.

Finally, some specialised disciplines – Dirt Jumping (DJ) and Street – opt to use smaller, 24” wheels so you may need rims to suit.

Width
Narrow, lightweight rims are used for XC, marathon and general off-road riding, and tough, wider rims for more gravity-orientated adventure.

In recent years 23mm has become accepted as a standard rim width for XC and trail riding, usually matched with tyres up to 2.1” in width. More extreme AM or Enduro riders who aim to tackle rock gardens and technical terrain lean towards rims of 28mm in width, with the ability to comfortably take large-volume 2.25” to 2.4” tyres. Meanwhile DH and FR riders who put their wheels through serious punishment in the air and on the race course may choose rims of 36-40mm or even more, with the capability of using heavy, reinforced 2.5”-2.7” DH tyres.

NOTE: Remember that if you are choosing new wheels for a bike equipped with non-disc brakes you must make sure that the rims have a braking surface for the pads to make contact with. Rims without this should be marked as ‘disc’ or ‘disc only’.

Spoke number
The more spokes a wheel has, the more the load is spread and the stronger the wheel should be, while less spokes means a lighter wheel.

For general trail riding 32-spoke rims have become the accepted standard, with more lightweight race wheels featuring 28- or 24-hole drilling. More extreme riding styles call for more strength so 36 spokes are common in AM, Enduro, DH and FR wheelsets, while the most demanding jump and street riders may opt for anything up to 48 spokes in order to handle the impacts dished out by tarmac and concrete.

When buying replacement rims for an existing wheelset or when building a new wheelset from parts, be sure to match the number of spoke holes on the rim with the number on the hub – e.g. a 32-hole rim needs a 32-hole hub, etc.

NOTE: Building, lacing and truing (adjusting spoke tension so the wheel runs perfectly straight) wheels is an art in itself that demands experience, time and patience – something best left to the professionals if you are not confident. A new set of wheels may naturally go ‘out of true’ after a couple of weeks of riding and need to be adjusted – there are plenty of resources in print or online that will demonstrate how to do this, or your local bike mechanic can easily do it for you.

Finally, you can also buy MTB rims that are either ‘tubeless’ (conform to the Universal Tubeless Standard or UST) specifications or ‘tubeless-ready’. The former are designed to be run with UST tubeless tyres while the latter have special features (adapted hooks for tyre beads, shallow-drop centre sections) optimizing them for tubeless use with the aid of a tubeless conversion kit.


Rims buying guide

Lightweight, strong and stiff rims can be one of the best performance upgrades for your road bike, with reduced rotational weight offering increased speed for less effort and improving a bike’s climbing, acceleration and handling abilities.

Meanwhile deep-section aero rims are designed to offer straight-line aerodynamic advantages for competitive racing, although they can compromise overall handling in crosswinds (depending on their depth).

While many road rims are made from aluminium alloy, the upper end of the market is dominated by premium carbon hoops, most of them with an aero profile of some degree. However these are more commonly sold as complete wheelsets.

WHICH ROAD RIM IS RIGHT FOR YOU?

Road bike rims differ in many ways, from size (diameter and width) and construction (materials used, number and type of spokes) to intended use (all-weather training or race day performance).

The choice ranges from good-quality budget and mid-range aluminium offerings to the latest generation of carbon fibre aerodynamic wonders. The right rims for you will depend not only on your budget but also on the type of riding you enjoy.

Sportive and leisure riders, for example, may be served best by aluminium alloy ‘all-rounder’ rims offering a balance of light weight, durability and ease of repair, while competitive riders may choose to invest in carbon fibre rims as part of a ‘race day only’ wheelset which delivers stiffness, light weight and superior aerodynamics – but at a price.

ROAD BIKE WHEELS: IN-DEPTH

Construction
A typical road bike rim consists of an aluminium or carbon fibre hoop laced to the wheel hub with spokes, the number, pattern and type of which depends on the design and intended use of the wheel. Rims may be designed to take the more common clincher tyres or the tubular type (‘tubs’).

Rims also vary in construction and materials – the traditional ‘box-section’ rim is still found on wheels at the lower end of the price scale and is ideal for leisure riding, commuting or touring, but most mid-range wheelsets and up now use deep-section aero rims for added stiffness, strength and aerodynamic performance.

Sizing – diameter, width and depth
Road bike rims come in a variety of sizes with the most common diameter being 700c (for most adult road bikes) and 650c (smaller racing bikes for juniors and ladies, some high-performance time trial and triathlon bikes).

Rim widths also vary, with narrow rims – for narrow tyres that can be pumped to a high pressure for more speed – the standard for high-performance bikes and commuters/tourers requiring wider rims.

Rim depth is also to be considered. The new generation of aero rims and wheelsets feature deep-section rims for improved speed and stiffness but as they affect handling, ultra-deep section rims may not perform well under specific conditions (i.e. when it’s windy).

NOTE: Sizing for tubular rims is different to clincher rims with manufacturers still using imperial sizes (26” equates to 650c and 28” to 700c). The large variety of wheel sizes and measuring methods has always given rise to confusion, leading to the development of a universal sizing system by the ISO (International Organisation for Standarisation). This system was formerly known as the ETRTO system, developed by the European Tyre and Rim Technical Organisation.

Manufacturers now also provide an ISO/ETRTO number which gives a rim’s width (measured between the flanges) and diameter (of the bead seat) in millimetres. For example, a 700c wheel has a diameter of 622mm, so the ISO/ETRTO number of a 700c wheel with a 15mm rim would equate to 622×15.

If you are unsure of the exact sizing of a wheel rim or tyre to match, check for the ISO/ETRO number to be certain.

Spokes
The more spokes a wheel has, the more the load is spread and the stronger the wheel should be, an essential consideration for touring and training wheels that need to be durable and long-lasting. However less spokes means a lighter wheel, so manufacturers of performance wheels and rims especially have worked hard to develop spoke designs and spoke patterns that cut down on the number of spokes required, without compromising strength or lateral stiffness – the evolution of stiff, deep-section aero rims having played a big part in this.

A ‘traditional’ road rim may therefore have between 28 and 36 spoke holes, while lightweight aero wheels may have as few as 20.

NOTE: Building, lacing and truing (adjusting spoke tension so the wheel runs perfectly straight) wheels is an art in itself that demands experience, time and patience – something best left to the professionals if you are not confident. A new set of wheels may naturally go ‘out of true’ after a couple of weeks of riding and need to be adjusted – there are plenty of resources in print or online that will demonstrate how to do this, or your local bike mechanic can easily do it for you.

COMMON TYPES

‘Traditional’ vs. ‘aero’
There are two basic designs of rims, named after their cross-sections – the more traditional ‘box-section’ (roughly square or rectangular) rims and the ‘aero’ shape deep-section rim (roughly triangular).

The deep-section rim has a number of advantages – it is stronger and laterally stiffer, meaning less spokes can be used to build the wheel, and its aerodynamic profile provides a speed advantage by reducing drag forces. Deep-section rims can also be built using carbon fibre for a reduction in weight and improvement in stiffness, further boosting acceleration and speed.

However the major disadvantage of deep-section rims is that the steering and handling can be impaired while riding in a cross-wind; the deeper the rim, the worse the effect (taken to extreme by disc wheels which are generally only used indoors or in flat calm conditions).

Therefore many riders may opt to choose wheels with different rims or rim depths for different conditions or race situations.

Leisure riders and tourers may appreciate the comfort and simplicity of traditional box-section rims, while aero rims with a lower profile may be ideal for sportive events, climbing or all-round race riding as they provide a balance of improved stiffness and reduced weight without the trade-off of poor handling.

Meanwhile for time trials in calm, flat conditions, track racing and even triathlon stages a set of proper deep-section aero wheels (or even disc or baton wheels) may come into their own.

Tubular vs. clincher
Finally road bike wheels are also available with tubular or clincher rims to fit two different types of tyres.

Clincher wheels and tyres (used with inner tubes) are by far the most common type. This is where the rim of the wheel features a ‘hook’ into which sits the bead of a clincher tyre.

Tubular tyres are sealed units with an inner tube sewn into the casing of the tyre. Rims for ‘tubs’ do not have the hook for the bead (and so are lighter), the tyre being glued in placed with tubular cement or secured using special tape.

Tubular tyres and rims have long been the choice of the racing professional who values their performance advantages – lighter overall weight, better rolling resistance due to higher inflation limit, round profile aids in cornering – but for leisure riders clinchers are generally considered the better option due to their convenience, availability, affordability and ease of repair.

NOTE: ‘Tubeless’ or ‘tubeless-ready’ rims are also available for road bikes, but they have yet to gain acceptance in the same way that they have among MTB riders. This is for a number of reasons. Firstly, one of the main advantages of the tubeless system – the ability to run tyres at lower pressures for improved grip without the risk of pinch or ‘snakebike’ flats – isn’t as important on the road, where tyres are generally run at much higher pressures. Secondly, road tubeless systems are regarded as offering few weight or performance advantages compared to tubular road tyres or even high-end clinchers. Many road tubeless systems weigh more than equivalent clinchers, while tubular setups will generally be even lighter. However development is continuing in this area so you can expect to see ‘tubeless road’ become a more common standard as manufacturers introduce lighter-weight, high performance tubeless tyres and rims. 


Rims buying guide

WHICH BMX RIM IS RIGHT FOR YOU?

BMX rims come in a variety of incarnations with the main considerations being size (diameter and width) and spoke count (more spokes for a tougher – but heavier – wheel).

Racers may require narrow, lightweight rims with fewer spokes to shave precious grams and take slim, speedy racing tires.

Stunt, street and flatland riders meanwhile will opt for burly 36-spoke rims wide enough to take chunky tyres, while big-air jump riders might even find themselves looking for 48-spoke hoops,

However most riders will be satisfied with a durable ‘all-rounder’ rims – e.g. 36 spokes suited for tyres of between 2” and 2.2” – that will serve them well on the street in the skate park, but equally be able to race or jump on in a pinch.

Also – they have to look cool, so take your pick from snazzy anodized rims, neon colour schemes, urban camouflage or graffiti-inspired decals.

BMX RIMS: IN-DEPTH

Size
Unlike MTB rims, the vast majority of BMX hoops come in the standard size of 20” diameter, although smaller 18” wheels are available, as well as 24” models for ‘cruiser’-type BMX bikes.

As to rim width, multiple sizes are available with 32mm being the standard ‘all-rounder’ size. Smaller riders (riding mini- or junior-sized bikes) or racers looking for a speed and weight advantage may opt for narrower rims (30mm) to mount slimmer tyres and reduce rotational weight, while hard-hitting street and stunt riders may look for a wider rim (36mm) as part of a burlier wheel package.

Spoke count and spoke pattern
BMX wheels can be laced using different numbers of spokes to influence their strength and weight – the more spokes used, the stronger the wheel is, but the bigger the weight penalty.

Again, a good ‘all-rounder’ figure settles at a 36-hole rim – tough enough for most applications but not so heavy as to be a misery to ride. Race riders looking for a lighter wheelset and less rotational weight will likely choose a 32- or even 28-hole rim, although these sometimes have a rider weight limit. Meanwhile BMXers who really put their wheels through their paces – and have destroyed multiple ‘standard’ hoops – may opt for burly 48-spoke models.

COMMON TYPES

BMX rims can be pinned or welded, which describes how each end of the aluminium hoop is joined to the other to create a circle. Welded joints are the stronger of the two options, but pinned rims – where a small piece of metal joins the rim ends together – can still be found on lower-end and factory-spec wheelsets. If you’ve found yourself busting a pinned rim (or more than one), it might be time to step up to welded seams.

Rims also differ in their internal wall structure, with multiple-walled ‘box-section’ rims featuring hollow internal chambers, as opposed to single-wall rims which don’t. As you might expect, double- or triple-walled rims are stronger than single-wall (or ‘single-skin’) rims owing to the extra structural support, but the extra metal involved in their construction means an accompanying weight penalty.

Double-walled rims are regarded by many as the best ‘all-round’ option, giving the best strength to weight ratio for most riders’ needs. Single-walled rims may be used by race riders while triple-walled could be best for big hitters.

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