Does it matter if a wheel is 2mm 'not round'?

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swee'pea99

Squire
Thinking of getting a used wheel, which I've been told is a couple of mil off perfectly round. I've never had any great success with correcting 'ovalness', as against the usual trueing - does it actually matter? Would I notice any difference in the ride (assuming I couldn't fix it)? Would it get worse over time?
 
I reckon you would feel it.2mm might not seem like a big deal,but in wheels it's a lot.
Eventually it would weaken and become a lot more.
It wouldn't take a lot of time or money to get it trued though
 
Location
Loch side.
Thinking of getting a used wheel, which I've been told is a couple of mil off perfectly round. I've never had any great success with correcting 'ovalness', as against the usual trueing - does it actually matter? Would I notice any difference in the ride (assuming I couldn't fix it)? Would it get worse over time?
You will feel 2mm if you glide along on a very smooth surface like a perfect garage floor or down a supermarket aisle. This is unlikely to happen so, you won't really feel it. However, you will always know it and see it. That's worse than feeling it if you are anywhere near (ab)normal like the rest of us.

Here is your chance to develop a new skill. Buy the wheel and fix it by trial and error. Here's how:
1) See the bump as a mathematical normal curve. You know, one of those symmetrical bell curves.
2) Identify the centre point of the curve i.e. the highest point of the bump.
3) Identify the two outliers.
4) Mark these three points with something on the rim - a permanent marker is good.
5) Count the number of spokes inside the curve. It could be an even or uneven number, it doesn't matter, as long as you stick with your number.
6) Measure the size of the bump at the highest point. In your case that is 2mm. Do some maths. There are 56 threads per inch on a spoke. That's 2.3 threads per millimeter. If you have a 2mm bump, you have to turn the (centre) nipple 2 x 2.3 times to advance the nipple 2mm down the spoke. This is a crude calculation because a) the spoke will stretch and therefore you will have to turn the nipple a bit more and b) the spoke follows a triangular line from rim to hub and you have to "trig" a bit of extra turn to compensate for the extra length. Make a decision and come to a conclusion that you want the spoke to travel 2.5mm, not 2. Redo your math and go 2.5 x 2.3 = 5.75 turns.
7) Now draw your normal curve on a piece of paper, draw your "involved" spoke in and assign numbers to each spoke according to the above calculation. The centre spoke/2 spokes will get the brunt of the 5.7 turns but as you move away from that spoke/s on either side you taper down. Work from the centre and turn the nipples as planned and keep your wits about you. You don't have to make all the turns in one bold move. Start small but keep account of how much.
8) If this was a front wheel on a road bike, if your measurements were accurate to start with and if you kept your head with the numbers, your wheel is now true. Obviously it won't, a bit of fine-tuning and you are there.
9) However, if it were a back wheel or a disc brake front wheel, all things are not equal. The spoke angles are not the same on the left and on the right. Those at a slacker angle will need more turns to travel the extra distance and those on the side with the straighter angles will stretch more. Conundrum and calculus!
Keep calm, proceed as above for a symmetrical wheel and afterwards simply do a lateral true. In summary for this wheel, you do the match, turn the spokes and then true laterally.

There is only one rule: Don't loosen spokes, just tighten them. Because the bump is smaller than the normal area of the wheel, you have to pull it in, not relax the entire wheel to bump level.

Off you go. Report back here how it went.
 

Dogtrousers

Kilometre nibbler
I've been told is a couple of mil off perfectly round.
A "couple of mil" may not actually be 2mm. Using the term "couple" sounds pretty imprecise to me. It may be less than 1mm. It may be 4mm. I imagine those two extremes are significantly different.

Just a thought.
 

Haitch

Flim Flormally
Location
Netherlands
A "couple of mil" may not actually be 2mm. Using the term "couple" sounds pretty imprecise to me. It may be less than 1mm. It may be 4mm. I imagine those two extremes are significantly different.

Just a thought.

The guy was selling a wonky wheel, it could be two inches.
 

Kajjal

Guru
Location
Wheely World
Thinking of getting a used wheel, which I've been told is a couple of mil off perfectly round. I've never had any great success with correcting 'ovalness', as against the usual trueing - does it actually matter? Would I notice any difference in the ride (assuming I couldn't fix it)? Would it get worse over time?

It depends on the overall condition and trueness of the wheel and also if it is going to be used heavily e.g. mountain biking. Few wheels are prefect but as long as they are well made and in good condition it doesn't matter. If it was a long way off true that suggests a problem.
 

Spoked Wheels

Legendary Member
Location
Bournemouth
Thinking of getting a used wheel, which I've been told is a couple of mil off perfectly round. I've never had any great success with correcting 'ovalness', as against the usual trueing - does it actually matter? Would I notice any difference in the ride (assuming I couldn't fix it)? Would it get worse over time?

"does it actually matter?" As it has already been said, on the road, hardly noticeable.If the brake track is narrow, like the second generation of Pacenti rims then it would matter.

"Would I notice any difference in the ride (assuming I couldn't fix it)?" As above.

"Would it get worse over time?" I don't see how it would deteriorate differently to being round to 0.5 of a millimeter

" I've never had any great success with correcting 'ovalness', as against the usual trueing "

I don't think I'm very good at explaining techniques :blush: but I'll give it a shot ^_^

To simplify things, let's assume the wheel has a bump in the middle of three spokes. You are trying to eliminate the bump and yet maintain the lateral trueness, bearing that in mind, you would try to replicate what you do on one side, on the other side. Lets assume that turning the spoke directly below the bump one full turn is enough. You would also need to turn the spokes either side 1/2 turn. So, if the spoke you turned one full turn is pulling the rim to the right then turning the two spokes either side by half a turn, would actually turn the rim to the left by one full turn too. In practice, you need to bear in mind that you are not introducing spoke twisting but that is another topic :smile:. This is a very simplistic view to make the technique easier to understand.

Now, there is a good chance that the extra tension created another issue somewhere else, so you fix that and so on until you are happy BUT you will not achieve a perfectly round wheel.
 
Location
Loch side.
2mm sounds a lot to me,and the pressure of doing quite a few miles on it would surely flatten it over time.
Just what I think.
It doesn't work like that. Elastic materials - spokes, rims, tennis raquets etc, don't deform from repetitive strain below the yield point. To use an analogy that you may understand; repeatedly hitting a tennis ball with your racquet will neither make a dent in the tennis racquet nor create a flat spot on the ball. The same goes for a hump on a bicycle wheel.
 
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