Thursday, 9 April 2015

How to Replace a Worn Out Bicycle Rim

How to Replace a Worn Out Bicycle Rim - Intro


Many bike come with rim brakes, and whilst cycling in clean conditions will result in very long rim life, muddy or dustry conditions can lead to rims becoming worn out. Frequently off road use with rim brakes may wear out a rim in less than a year, for most though a rim will last 2 or 3 years.

Many rim nowadays have a wear indicator, a small grove or channel that run around the rim, if this is no longer visable, then chances are you will need to replace your worn out rim.

How to Replace a Worn Out Bicycle Rim - ERD


To make things easier for yourself and to avoid having to replace spokes you will need to buy a replacement rim which is the same size (or netter still buy the same rim make and model). The most important measurement is the ERD (Effective Rim Diameter). To find the ERD of you rim simple google its make and model with "ERD" after the search term. For example "Mavic EX721 ERD". And hopefully you will find out that way. Rememebr rims can come in 20", 26", 29" sizes, so be sure you are looking at the right size.

If you can not find a measurement on the web then take a tape measure and measure the maximum internal diameter of the rim and add about 4mm. This does not always give a very accurate measurement but I have done this 2 or 3 times with no problems.

So you have found your ERD, now look for a rim with a similar ERD, I replaced a factory stock alloy rim (ERD 551) with a Sun Rhyno Lite XL Rim (ERD 544), so you can go 3, 4 or 5 mm out, and still be OK.

How to Replace a Worn Out Bicycle Rim - Replace


I leant this method from a book a had a few year ago, and it a excellent way to replace a rim, as there is no need to worry about spoke lacing errors (putting spoke in the wrong hole).


First off line up the holes where the inner tube valve pokes through. Make sure to have some tape or zip ties handy.


Next fasten the rims together using some zip ties or tape. 3 points around the rim is normally enough. Then as in the above picture start to swap the spokes from the old rim to the new rim.



Take the top spoke from each crossed pair and move it upwards to the new rim, work around the wheel moving up all of the top spokes on that side on to the new rim. Do up the nipples so 3 threads are showing, you need to leave them a bit lose loose, especially on a rear wheel because other wise the "dish" will not form properly.

After you have moved all of the top spokes on one side of the rim, flip the whole lot over and do the same to the top spokes on the other side. Then repeat this process for all of the lower spokes, and hey presto, all of the spokes should be in the new rim, and you can detach the old rim.

Now go around and tighten the nipples so no threads are showing. No head for the grage and put the wheel in the bike.

How to Replace a Worn Out Bicycle Rim - Truing and Tensioning


With the wheel in the bike (vertical drop out preferable here) measure the distance from the braking surface to the bike frame, do this on both sides. You will need to keep doing this during gradually tightening the spokes to make sure the wheel is centred in the frame.

Spin the wheel in the frame it will probably wobble all over the place. At this stage you can gauge the wobble by eye. But later on you may wish to place something next to the rim (zip tie or rim brake) so as to gauge the wobble more accurately.

STEP 1 

If it wobbles to the left tighten a right hand spoke, and vis versa. Just 1/2 a turn at a time, if its a big wobble tighten 2 or 3 spokes on the same side in the area of that wobble. Do this until the wheel is fairly straight with perhaps 5mm - 10mm of wobble in either direction.

STEP 2

Then start to increase the spoke tension. Tighten ALL of the spokes half turn working around from the valve hole. You do not have to start at the valve hole, but this makes it a lot easier, as it acts as a point of reference.If at this points some spokes seem at lot tighter than other then don't tighten them.

Keep repeating the steps 1 and 2 left until the wheel  solid and all of the spokes are firmly tight. You can purchase a spoke tensioner all I have never used one.

BIG GAP ON LEFT - TIGHTEN LEFT HAND SPOKES

TOO CLOSE - TIGHTEN RIGHT HAND NIPPLE

WELL DONE ME - JUST RIGHT
It is important to realise that at any point you feel things are not going well, just slacken off all the spokes to 3 threads showing and start again. The only game killer is if you over tighten a spokes and strip the thread.

For you first go choose a strong rim, I would assume these will account for you error better than a weaker rim.

Rims vary in width up to about 30mm is OK for use with rim brakes, but you may struggle to adjust them nicely with wider rims.

Putting a little lubricant on each spoke thread prior to tensioning makes thing nicer.

Just have a go it is very satisfying, a cheap rim might only cost £10 / $20, so if you mess it up no biggy.

A failed rear wheel (never had a wheel fail on me) I would imagine would be less damaging to you body than a front one, so start on a rear wheel perhaps.

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