Introduction: Converting a Mountain Bike to a Single Speed Bike.

I have recently had my bike taken apart and resprayed.

I am trying to learn more about bike mechanics as I reassemble it, with the help of my bike mechanic beau.

I never got on with the gears on the bike before the respray, so I have decided to turn the bike into a single speed machine.

This Instructable covers the following:
  • Installing bottom brackets (the cylindrical shaped part that goes through the frame and allows the cranks to spin.)
  • Installing the cranks (the bits between the bottom bracket and the pedals.)
  • Installing pedals (hope you know what pedals are)
  • Installing a single speed conversion kit.
You will need these tools:
  • 5mm Allen key
  • 8mm Allen key
  • Flat bladed screwdriver or chain ring bolt tool
  • Bottom bracket spline tool
  • Large adjustable spanner
  • Pedal spanner
  • Chain tool
  • Cassette lock ring tool
  • Bike grease
These are specialist bicycle tools, if you don't have them, look for a community bicycle workshop in your area.

Step 1: Assemble Your Crank and Chain Ring.

My bike had a fairly standard mountain bike triple crank set, as pictured in the first photo of this step.

As we're converting to single speed, we only need a single chain ring at the front.

We found a double crank set from an old racer and removed the largest chain ring. (Sorry- no photo of the double rings.)

To undo the chain ring bolts, you need a 5mm Allen key and another tool to hold the back of the chain ring bolt. If you haven't got a chain ring bolt tool, you can use a large flat bladed screw driver.

As we removed the large chain ring we had to space out the chain ring bolts with washers so they would tighten properly. You can just see the washers in the third photograph.

We also moved the chain ring to the outside of the crank spider as we knew it would help the chain line in the long run.

Step 2: Installing the Bottom Bracket.

We are using a sealed cartridge bottom bracket, so you will need to find a different Instructable if you've got an old fashioned adjustable bottom bracket! Sorry.

We kept our old bottom bracket (1st photo of this step) from when we stripped the bike, it was knackered, but we measured it and replaced it with a new one the same size.

Make sure you grease the threads on the bottom bracket  (2nd photo of this step) as this area of a bicycle gets a lot of abuse and can often seize if not well greased.

You need a bottom bracket spline tool to install the bottom bracket, don't try and do it without this tool as you won't succeed! Spline tool shown in 3rd photo of this step.


Slowly thread in the right hand side of the bottom bracket into your frame taking care not to cross thread.

Regularly inspect from the left hand side through the bottom bracket hole in the frame to make sure it's going in true.

Fully tighten the right hand side using the spline tool and a suitable spanner.

Install the left hand side of the bottom bracket using the same technique, but remember, this is a normal right hand thread (righty tighty lefty loosey.)

Photo 5 of this step shows the bottom bracket fully installed.

Step 3: Installing Cranks.

Start with the right hand crank which has the chain ring.

Grease the bottom bracket spindle before installing the crank. The spindle is the piece sticking out both sides of the bottom bracket.

Our bottom bracket and cranks are the square tapered type. There are other types of bottom bracket and cranks but the method is very similar.

Push the right hand crank on to the spindle. As we're installing new cranks on this bicycle there's a chance that the crank or the chain ring might rub on the frame. As you can see from photo 1 of this step, ours clears, although only just.

If your crank doesn't clear your frame, you'll either need to find a different crank set, or install a wider bottom bracket.

Grease the threads on your crank bolts and wind it into the spindle as shown in photo 2 of this step.

Using an 8mm Allen key tighten the crank bolt as shown in photo 3 of this step.

Install the left hand crank using the same method.

Crank bolts need to be very tight. It's one of the few things on a bike where you need to give it as much welly as you can! A good time to Google "mechanical advantage".

Photo 4 of this step shows both cranks fully installed.

Step 4: Installing Pedals.

We are reusing the pedals from the original bike.

When we held the axle and gave the pedals a spin they felt a bit rough so whilst holding the pedal from the axle we dropped some heavy oil down into the bearings and gave them a good spin which helped free them up- as shown in photo 1 of this step.


Look closely and your pedals will be marked "L" and "R".

Screw the pedals into the cranks by hand. It's very easy to cross thread the steel pedals in the alloy cranks so be careful.

Then fully tighten the pedals with a pedal spanner. A pedal spanner is a special bicycle tool which is a thin 15mm spanner.

The pedals need to be nice and tight.

Photo 3 of this step is a good example of "Mechanical Advantage" in action!

Step 5: Installing Single Speed Conversion Kit.

We are reusing the old mountain bike wheels.

Our rear wheel is a free hub as opposed to a freewheel.

A free hub rear wheel has the ratchet mechanism attached to the hub, whilst a freewheel has the ratchet mechanism combined with the sprockets.

It's possible to buy a single speed freewheel if you have that type of rear wheel.

For our free hub we bought a single speed conversion kit. The kit includes the sprocket, a number of spacers, and a lock ring. The different sized spacers allow you a lot of freedom as to where the sprocket is placed on the free hub body.

It may take a few attempts but you want your sprocket to be in line with the chain ring on your crank. The chain wants to be as straight as possible when it's finally installed.

The spacers and sprocket are held on the free hub body with the lock ring. You will need a cassette lock ring tool to fully tighten the lock ring. If you need to undo the lock ring you need to hold the sprocket, usually with a chain whip tool.

Step 6: Final Touches!

Depending on your style of frame, you may have some flexibility as to the position of your rear wheel.

Our frame had vertical dropouts which means we had to buy a chain tensioner to take up the slack from the chain.

The chain tensioner is installed in the old position of the rear mech as seen in photo 1 of this step.

If your frame has horizontal or track dropouts (see photo 2 of this step) then you may not need the chain tensioner as you can change the position of your back wheel to take up the slack.

Photo 3 shows our new single speed drive train (chain ring, chain and sprocket!)

There are many variables in converting a bike to a single speed. If you have any questions or suggestions then please comment, and I will try and find answers, and I hope to learn more from other peeps' input!

ps, I am loving my single speed bike on the hills of Hastings!

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