Wheel counterbalance weights

[goody]

Think about it another way, what is it that you feel pulsing? On a car or motorbike that has the wheels out of balance there's lots of suspension and steering joints to move around. On a bicycle there isn't much to move. The pulsing if it is happening will either be the wheel bouncing up and down, the tyre compressing then extending or the frame/forks flexing. All with the weight of the rider pushing down on those components. I did try it and although it made a huge difference to how the wheels spun with the bike on a stand I couldn't feel any difference on the road.

 

[Shaun]

Have you tried adding a temporary counter-balance and seeing if it nullifies the effect when you hold it by the skewers?

 

[Mr Haematocrit]

Just out of curiosity, Today I added three magnets used for garmin cadence meters to one of the spokes located near the valve on my zipp 202's in the attempt to replicate the symptoms you have. I was then going to see if moving the magnets around the rim balanced this out. I was not able to replicate the pulsing you mention when riding normally,the magnets did not make a noticeable difference.
Under braking carbon braking surfaces feel very different to alloy surfaces and the braking is not as smooth, if you are running aggressive pads or pads not specifically designed for carbon braking surfaces you do get a slight pulsing sensation through the brake levers, I find that cork pads are the most forgiving

 

[earth]

I think I may be overreacting. I will try a temporary counterbalance and see what difference it makes when holding the wheel and spinning it and also on the road. I mainly feel and hear a pulsing when I brake. That combined with the pulsing when the wheel is off the bike makes me think the weight of the extenders may be having an effect on the road. By that I don't mean to say I can't feel anything - I do under braking. It may be just that carbon rims have different characteristics compared to alloy and are not as smooth when braking. The pads are those supplied by Reynolds. There may be a very slight imperfection in the carbon surface but it is a fraction of a millimetre and I can run the pads much closer to the rim that I did with the alloy wheels. My rear alloy wheel is out of true by about a mil and I was unable to have it trued due to corrosion of the nipples (an ailment to be avoided at all costs). But I never felt pulsing when braking.

Again, I'll try things and say what I find. But now I am thinking that maybe I am over reacting and it is just the characteristics of carbon rims.

 

[earth]

Finally managed to try a counter balance on the front wheel. I found some thick copper wire at work and wrapped 4 grams worth around the spoke opposite the valve stem then wrapped it in electricians tape to keep it in place. I can't use that permanently but it worked for the purposes of a test. There was still a slight pulse when I held the wheel axel and span it but it was much reduced. On the bike the pulsing noise when braking was still there but I did not feel any pulsing. I will test with the counter balance a bit more then test again without.

 

[Mr Haematocrit]

Wow that's quite a bit of unnecessary rotational weight to add to the wheels.
Have you contacted the wheel manufacturer to see what they think about what your experiencing I would not be happy with adding that weight to my wheels

 

[earth]

I haven't talked to the manufacturer yet. I wanted to know what the wheels felt like with and without a counterbalance before having the conversation with them. An extra 4 grams per wheel is not ideal but also not much compared to the saving of 250 grams per wheel over the alloy ones I have.

 

[Mr Haematocrit]

My concern would be that for the wheel to be so unbalanced it would need different quantity of material either side of the wheel.... the question is does one side have 40g excess material or is one side of the wheel a little thin in material.
I see it as a matter of safety more than anything

 

[earth]

Without a tyre fitted there is no imbalance. I'm convinced it is the extra weigh of the valve stem + extender. I don't know the weight of the valve stem but the extender is 4 grams. The valve stem is a similar length to the extender so I estimate the two combined probably add up to about 10 grams. This is not much but the rims are very light. If the rims were heavier I doubt there would be so much effect.

 

[RecordAceFromNew]

Without a tyre fitted there is no imbalance. I'm convinced it is the extra weigh of the valve stem + extender. I don't know the weight of the valve stem but the extender is 4 grams. The valve stem is a similar length to the extender so I estimate the two combined probably add up to about 10 grams. This is not much but the rims are very light. If the rims were heavier I doubt there would be so much effect.

If the bearings are ok, even the missing material from a valve hole of an alloy rim (which I suspect weighs well under 4g, given 4 cc of water is 4g) would show up as static imbalance when you let a wheel (with neither tube nor tyre) idle from a spin - you will see the valve hole consistently ending up at/near 12 o'clock.

Given that is the case, if you have the time and inclination you could use the thick copper wires you have to check by iteration what the static imbalance may be with and without the tyre. There is a possibility that the figure is significantly greater than 4g in your case, e.g. due to non-uniformity in your tyre.

If the main imbalance is isolated to the tyre/valve/extender (i.e. not the wheel) then the same static counterbalance located as near to the rim as practicable should also be a reasonably effective counterbalance dynamically.

 

[earth]

I should have said earlier that if I let the wheel (front wheel) spin to idle with the bike upside down then the valve always ends up at the 6 o'clock position. This also makes me sure it is the valve stem and extender. Yes there could be an imbalance with the tyres, especially as their are glued on tubulars, but I don't want to remove them yet because it was such a chore to put the on. Plus I think the proof is in the valve stem always ending up at the bottom.

Rather than use the copper wire I would like to find a piece of lead. I'm guessing a disc about the size of a penny coin would be enough. Then I could bend it around the rim. All I would need to do is secure it with something tacky but not permanent.

 

[amaferanga]

I should have said earlier that if I let the wheel (front wheel) spin to idle with the bike upside down then the valve always ends up at the 6 o'clock position. This also makes me sure it is the valve stem and extender. Yes there could be an imbalance with the tyres, especially as their are glued on tubulars, but I don't want to remove them yet because it was such a chore to put the on. Plus I think the proof is in the valve stem always ending up at the bottom.

Rather than use the copper wire I would like to find a piece of lead. I'm guessing a disc about the size of a penny coin would be enough. Then I could bend it around the rim. All I would need to do is secure it with something tacky but not permanent.

The valve stem also ends up at the 6 o'clock position with my wheels. And if I turn the bike upside down and spin the wheel I get the same pulsing (I've had this with 50mm carbon clincher rims that weighed around 450g each and 38mm tubular rims that weigh less than 400g). This is entirely normal. This is not the cause of grabby braking with carbon rims though. You seem determined to show that it is, but I'm afraid it simply isn't.

 

[earth]

I'm sure there is an imbalance. I'm almost certain its from the valve stem. I'm not all that certain whether I can feel much of a difference when riding. There is still a fluttering sound when braking and I acknowledge this is probably due to different characteristics of carbon rims but I want to ride with a counterbalance and then without again to see if I can feel any other difference.

 

[VamP]

How good is your glue job? If the tub is not on straight, that will give you a hell of a lot more of a wobble.

 

[earth]

The glue job was the first I have ever done. It's not pretty but I think the tyre is just about straight.

I removed the weight again recently and I can't feel much difference, if any. I'm going to put it down to my obsessive curiosity.