Many bicyclists believe that handling performance can be improved with the right bike fork. But are all road bike forks the same size? Can you just swap out your old fork for any other fork on the market? If your bike isn’t handling quite right, you may be thinking about a new fork. But what measurement do you need to know to get the right one?
Are all road bike forks the same size? There are minor variations in fork size, depending on the make and model. To get the right size fork, you’ll need to know:
- Measurement of your bike’s steerer tube
- Type of steerer tube on your bike – threaded or unthreaded
- Blade measurements of the fork: width and length
- Size of your wheel
- The type of brakes on your bike
To better understand what the small differences in size mean regarding your ability to change your fork and what that change can do for your bike’s performance, we need to look at your bike, the parts of a fork, and all the ways those parts are measured. In the end, you’ll know just how to choose the fork for the ride you are looking for.
Steerer Tube and Bike Fork Measurement
The most important measurement if you are looking to replace your bike fork is the diameter of the steerer tube. The steerer tube is the top portion of the fork. It attaches the fork to the frame and handlebars and allows the rider to steer the bike. They come in three standard sizes:
- 1”: This is an older standard diameter. Most forks with this diameter are also going to be paired with a threaded headset. If you’re working with an older frame, you probably need this size fork.
- 1 ⅛”: Most modern bikes use this diameter. They are normally paired with a threadless steerer tube.
- Tapered: Unfortunately, some high-end manufacturers have started to make what are called tapered steerer tubes. There is no standard for the diameter of these forks. This makes it hard to find a replacement fork other than the specific fork made for that specific frame. Consult a bike shop for this case.
You can’t put a fork on your bike that has a diameter larger than the diameter of the head tube on your frame without an adaptor. There is nothing stopping you from putting on almost any fork on your bike once you have determined the diameter of the frame and purchased any needed adaptors.
Type of Steerer Tube on Your Bike
The other steerer tube measurement that determines the size of the fork is the length. This measurement will be different depending on whether you use an unthreaded steerer tube or a threaded one.
Unthreaded Steerer Tube
An unthreaded steerer tube is used with an unthreaded headset. The length of an unthreaded steerer tube is one factor that will determine the height of your handlebars.
- High handlebars are usually for longer, more comfortable rides.
- Low handlebars are set for speed.
If you are of average height, this won’t be a major factor. You can comfortably adjust the handlebars to the right height with a normal-sized tube. Riders who are taller though may have to get a fork with a longer steerer tube because they’ll need a higher handlebar setting.
Threaded Steerer Tube
A threaded steerer tube is used with a threaded headset. These tubes use to be industry-standard, but with the many cost benefits to manufacturing unthreaded tubes, they have fallen out of favor. Threaded steerer tubes allow you to adjust the handlebar height with greater ease. The length of the steerer tube needs to be long enough to accommodate the headset that you are using. This means that the length of any fork you try to put on your bike will be somewhat dependent on the headset that you are using, but this should not affect performance.
Measuring the Blades of the Fork
Coming off the steerer tube is the crown which connects the blades of the fork. These blades are what connect the front wheel to the bike. The blades are measured for both length and width.
The most standard measurement on a road fork is the fork’s width. This measurement is commonly known as the spacing.
The spacing is measured between the inside edges of the end of the fork blades. Most road fork spacing measures 100mm but there are some older frames that measure 90mm. You want to make sure that your wheel hub fits in the fork spacing otherwise you risk damaging the hub.
If the wheel you want to use is too big for the fork you are trying to put on your bike; there are ways to spread out the spacing.
The best recourse would be bringing your bike to a local shop. They have special tools they can use to spread the forks safely. Or, if you really want to do it yourself, check out this article by bike guru Sheldon Brown. He explains how to spread out the fork with a method you can use at home.
Fork length is usually measured from the bottom of the crown to the center of the axle or where the wheel connects to the blade. This length can be anywhere from 363.5mm to 374.7 mm.
A longer fork length will raise up the front end of the bike. A shorter fork length will lower it. What does this mean for you and your bike’s performance?
- Raising up the front end causes a shallower head angle. The shallower the head angle of your bike is, the slower the handling.
- Lowering the front end causes a steeper head angle, which will give you the opposite result.
Try putting a fork with shorter blades on your bike if you feel like the handling is too slow.
Most aftermarket forks, forks that are sold separately, tend to be longer than the forks that come on the bike when you buy it. So, if you are going to put an aftermarket fork on your bike, chances are it will have a longer length and will slow down your handling.
The Size of Your Wheels
Wheel size may also be a factor with a new fork. You want the axle of the wheel to fit in the fork ends; otherwise, you can’t attach a front wheel to your bike. In most cases, the axle measures 9 mm and will have no problem fitting on any fork, but some manufacturers have started to make forks and wheels that will only work together.
In recent years road tires have also become thicker. This may cause an issue with clearance between the tire and the top of the blades. In most cases, this will not be an issue, but it is still a good idea to match the tire you want to use with the fork.
You want to make sure there is enough clearance between the tire and the fork when mounted or it will rub and ruin both the tire and your ride.
If you want to slow down the handling on your bike, you’ll want to try a wider wheel. That means you’ll want a fork with blades long and wide enough to allow clearance for the new, bigger wheel.
The Type of Brakes on Your Bike
The last thing you have to consider is the type of brakes you have on your bike. The type of brakes you have will dictate what kind of mounts your fork has to have.
For instance, it is becoming commonplace for high-end manufacturers to put disk brakes on their bikes. If you have one of these models, you will have to make sure that any fork you put on your bike has disc brake mounts because they can’t be retrofitted.
If you know what you need to measure, it’s not hard to find the fork that fits your brake and gives you the handling you’re looking for. As always, if in doubt, visit your local bike shop to make sure you’re on the right track.
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