How to grind a rim

From TrialsWiki

Rim Grinding is done by large proportion of trials riders these days. The rim sidewall (the braking surface) is 'ground' to roughen the surface. This provides more friction which in turn gives better braking power. This is especially useful in wet weather, for example 'natural riding'.

With grinding a rim, you are removing metal from the surface of the sidewall. Depending on the type of grind it can vary by many 10ths of a millimetre. This degreases the strength of the rim which can cause buckles, flat spots, an egg, cracks or at the very worse a completely destroyed rim known as a folded rim. These cases are only likely to happen when a rim has outlived its life, meaning a rim can only take a certain amount of grinds depending on how deep the grind actually is. All rims will safely with a decent wheel build allow at least 3 medium grinds, usually it is possible to grind a rim many more times.

Different types of discs: Metal cutting disk- Used for heavy, deep grinds. Stone grinding disk- Used for Medium to light grinds.

[edit] Tools needed

Angle Grinder
Metal/Stone grinding disk
Safety goggles of some kind. Swimming goggles will do.
A vice

Rob 09

[edit] Procedure

First you need to choose what grind will be suitable for your rim and brake pads. Some brake pads are not designed for ground rims and will wear very quickly, so be careful and check first.

So, insert your wheel into your vice so the axle sits between the two vice clamps. Tighten the vice untill the wheel is safe enough to not move and is sat firmly and level. Be carefull not to over tighten the vice so that your bearings get crushed. This will allow the wheel to spin while you use the angle grinder.

Fit your prefered disk to the angle grinder. Now make sure everything is correct with the angle grinder and fit your goggles.

Stone cutting disk instructions:

Spin the wheel in the same direction you will grind the disk with (so that the disk doesn't spin against the wheel's direction).

Use the angle of the disk to allow a easy and safe grind. The angle of the disk being the edge (outer part of the disc) tilted slightly to allow the grinder to spin away from you but with the wheels direction.

Press firmly but not hard - certainly don't lean on the wheel. This will continue the wheel spinning and allow you to get an even grind. Grind the rim for around 10 seconds to allow minimum sidewall removal and damage but give you a nice flat even grind. Try to cover the whole surface of the sidewall to achieve the best results.

Turn the angle grinder off and allow the wheel to stop spinning of its own accord. Make sure not to touch the sidewall which you ground. The rim will seem rough like sand paper with a shiny raw metal colour. This is what we wanted. Repeat for the other side of the rim.

If you are using old brake pads they will require a clean to maximise performance.

Metal cutting disk instructions:

Let the air out of your tyre, lean the bike on the ground, tread on an area of the tyre to prevent it from catching on the grinder (watch your feet).

Then go round the rim in a clockwise direction whilst holding the grinder at around 80-90 degrees, do this in short bursts of about 5-6 inches at a time, try not to go over the same area twice, when going over these 5-6 inches, do them quickly for maximum roughness.

the outcome will be:

This will be a nice sharp grind and should last a fair while. This method is prefered as the grind tends to last longer.(This works for both metal and stone discs).