Mod
From TrialsWiki
'Mod' refers to trials bikes with 20" wheels. They are called mod bikes because originally they were made from modified BMX bikes. In contrast to stock bikes, mod bikes generally have a single gear, no seat, and a bashplate although more and more are now coming with a bashring.
[edit] Front freewheel
The front freewheel system is used on most mods. However, it is not used on the cheaper mods, and it isn’t used on some of the most expensive mods.
On all the bikes in all other bike sports the ‘freewheeling device’ is on the back wheel. A freewheeling device is what allows us to pedal our bikes, but then we can stop pedalling and the bike rolls forward without the pedals turning. To put it simply, It’s a device that rotates one way, but doesn’t the other.
But on most mod trials bikes the freewheel is screwed onto the cranks, and the hub on the rear wheel is fixed. The reason for this is because the smallest freewheel that is any good for trials is 16 tooth. This means, to keep the same gear ratio, the cog on the front would have to be 24 tooth. However, because the freewheel is located on the cranks, an 18 tooth freewheel is used on the cranks and a 12 tooth cog is screwed onto the fixed hub. This means that smaller cogs can be used, which in turn means less chain can be used and ends up being a much lighter setup. Having a front freewheel doesn’t alter the way the bike riders. However, because the freewheel is on the front, it does mean that the chain moves when you are freewheeling. Also when you pedal backwards, the chain does not move. It is very difficult to get your head around, but is much easier when you can see the setup in front of you. Long story short, it’s a setup that makes the drive much lighter. Another advantage of having a front freewheel system is that it’s a standard system with mods, not having a front freewheel system and having a 24 tooth chain ring doesn’t quite fit over some bash plates on some mod frames, making it difficult to upgrade.
Cheaper mods that don’t use the front freewheel system usually have a 16 tooth freewheel on the rear hub.
The higher end mods can come with a freewheeling system built into the rear hub, like on a standard mountain bike, but only have one small cog, instead of a range of gears.
[edit] 19" rear wheel
The majority of mods have a 19” rear wheel, which can be confusing to new riders. This is because rear tyre on these mods it a lot thicker. To compensate for the thickness of these tyres the wheel is reduced by 1”. Some cheaper bikes have a 20” rear wheel, and a thinner tyre. The main problem with this is that it makes it difficult to upgrade, because you will have to change the back wheel at the same time was the frame. Otherwise the sidewall of the rim wont line up with the rear brake.
