A hub is the central part of the wheel, making them a very important component of the bike as a whole. Despite being a small piece, bike hubs have a lot more to them than meets the eye. In this article, we will discuss all the factors there is to consider for you to be able to buy the ideal set of road bike hubs.
Factors to consider before buying road bike hubs
Front & Rear Hubs
For all kinds of bikes, including road bikes, hubs for the front and rear wheel are going to have different constructions. A front hub consists of all the basic components – hub body/shell, bearings, flanges, and end caps. If the wheel uses a disc brake, then there will be an additional mounting for the brake rotor. The center of the hub body is hollow to allow an axle to be inserted.
Rear hubs also have the same components. However, they also have an additional component called the freehub on the drive side. The freehub is where a cassette is installed. It also contains a ratchet mechanism that engages the cassette when pedaling but also allows you to coast on the bike. It is responsible for the clicking noise you hear.
Road bike hubs are not usually designed to be exceptionally sturdy. Compared to mountain bike hubs, they are subject to less punishment. Therefore, just about all road hubs are made of either aluminium or carbon fiber to keep weight to a minimum. Carbon fiber hubs are lighter and stiffer, but they are significantly more expensive.
Hubs have bearings on either side to allow the axle, and hence the wheel, to rotate smoothly. In general, there have always been two types of bearings. Cup and cone bearings with loose ball bearings made of steel are cheaper but more difficult to service and adjust properly. Meanwhile, cartridge bearings are pricier but have sealed ball bearings. This makes them longer-lasting and better rolling.
Nowadays, high-end road hubs feature ceramic ball bearings instead of steel ones. The ceramic bearings are lighter and provide improved performance. The downsides are that they are expensive and they can get worn out quickly when riding over rough terrain.
All bike wheels are attached to the bike frame with the use of an axle that runs through the hub body. Axles can have different lengths and so, the hub must have a corresponding width. There are two types of axles – quick-release (QR) skewers and thru axles. QR skewers have a 100 mm length on front wheels and are 130 mm on rear wheels. All of them have a 9 mm diameter. Thru axles are a relatively newer design built to be stronger and stiffer than a QR. They have a 12 mm diameter, and a length of 100 mm and 142 mm on the front and rear wheels respectively.
Freehub & Drivetrain Compatibility
The right side or drive side of the rear hub is where the freehub is situated. It is what holds the cassette and transfers power to the rear wheel. It is important to ensure that the freehub and the drivetrain are compatible, even though most 11-speed models are backwards compatible now.
For the last 20 years, the spline system hasn’t gone through much change at all. The only exception being that 11-speed requires a wider freehub. Cassettes that are 8, 9, or 10-speed can be used with an 11-speed freehub with a spacer. Also, it is possible to use 11-speed cassettes with a 10-speed hub. But you might need a medium cage derailleur for that. Unfortunately, you cannot replace a Shimano 10-speed freehub with an 11-speed one.
Older 10-speed freehubs had a narrower body with tall splines that do not work with other speed cassettes. So, beware of that. SRAM and Shimano 10 and 11-speed cassettes all use the same spline system. Hence, they are all interchangeable. A few freehub models are even cross compatible between Shimano 11-speed and SRAM XD and the new XDR 12-speed standards. However, not all offer such versatility.
Shimano Micro Spline
After the rise in popularity of 12-speed drivetrains, Shimano introduced its own 12-speed freehub named Micro Spline. It is able to accommodate that extra tiny cog on a 12-speed cassette. Initially, they were used only for MTB wheels. But eventually, road bikes have started using these as well.
Campagnolo freehubs are very different from Shimano and SRAM in terms of diameter and spline size. Therefore, Campagnolo freehubs should be matched with the drivetrain speed. However, 12-speed Campagnolo cassettes can be used with 11-speed freehubs of the same brand. It is possible to get replacement freehubs that allow you to switch to a Shimano or SRAM drivetrain and vice versa.
SRAM XDR and XD driver
As mentioned before, SRAM 10 and 11-speed freehubs are compatible with Shimano drivetrains and vice versa. The XD driver for MTB and the XDR driver for road bikes by SRAM are new designs that are 12-speed. They were developed due to the rise of 12-speed drivetrains and the desire for smaller cogs with less than 11 teeth. The XD and XDR freehubs can use cogs with 9 teeth only.
The engagement speed of a hub describes how much the pedals need to be turned before the cassette engages the wheel. It is proportional to the number of points of engagement (POE) of the freehub. The higher the POE, the smaller the angle through which the pedals turn without transferring power. This translates to a faster engagement speed. Faster engagement speeds are preferred by most riders as the pedals feel more responsive and provide faster acceleration.
Brake Rotor Attachment
For road bikes with disc brakes, the hub needs to have a mount or attachment for the brake rotor. This can be either the six bolt type or the centerlock type. Six bolt mounts use, well, six bolts to fix the rotor to the hub. Centerlock rotors attach directly to one of the splines on the hub using a lockring. The level of performance is pretty much identical. Neither one is better than the other. But it is important to know this so that you buy the right rotor and hub combination. If you want to use mix and match, you can buy an extra adapter to make it possible.
Types & Number of Spokes
Most road bike wheels feature one of two types of spokes – J-type and straight pull. J-type spokes are so called because they have a hooked shape at the end that attaches to the hub. Other than straight pull spokes being slightly lighter, there is not much of a difference between them. Your hubs should be compatible with the type of spokes you want.
Another aspect is the spoke count or the number of spokes. The number of spokes on your wheel should match the number of holes drilled on the hub flanges.Road wheels may have anything between 24 and 36 spokes. More spokes equal more strength but also more weight. So choose according to your requirements.
Frequently Asked Questions
Q1. What is the difference between road and mountain bike hubs?
Ans.: Due to the wildly different natures of the two cycling disciplines, road and mountain bike hubs differ in quite a few ways. The main differences between them are in,
- Hub width/Axle standards – MTB wheels have larger axles for increased stiffness
- Materials – MTB wheels are sometimes made of steel for enhanced strength
- Spoke holes – MTB wheels have a higher spoke count
- Freehubs – MTB drivetrains require a cassette with more speeds
Q2. How does a freehub work?
Ans.: The freehub contains ratcheting teeth and pawls which combined is called the ratchet-and-pawl mechanism. When you pedal, the cassette moves the pawls which engage with the teeth and that transfers power to the wheel. When you stop pedaling, the pawls also stop rotating. However, the wheel and the ratcheting teeth keep spinning. As they spin over the pawls, it creates the clicking noise you hear when coasting.
Choosing a new hub for your road bike can be quite a daunting task considering all the different aspects to look out for. However, hubs are an integral part of the bike. And choosing the right one can improve your experience on the bike. Carrying out your own research is important and hopefully, this article will provide enough information. Nevertheless, your best bet would be to visit your local bike store and talk to them to find out exactly what works for you.