Wheel counterbalance weights

[earth]

I've had to use some valve extenders. Although they only weigh an extra 4 grams I can feel a pulsing from my wheels. What do people use to counterbalance the valve? On the rear I have the wheel magnet but nothing on the front.

 

[alicat]

If you feel it matters, could you put a spare magnet on the front as well.

 

[earth]

I can feel the pulsing mainly when breaking. The magnet does not completely counterbalance the rear wheel.

 

[amaferanga]

Are they carbon rims?

 

[earth]

They are. If the rims were heavier I don't think 4 grams would make any difference. You might say having to add weights to counterbalance a valve extender is making those light carbon rims heavy again but the extra weight of a counterbalance is still nothing compared to the weight saved from the carbon rim.

 

[goody]

I'd be really surprised if the pulsing you feel is a result of out of balance wheels. Not many people bother balancing them, I did once and didn't notice any difference, they did spin well on the stand though. I'd check for a slightly buckled or damaged rim, bulging or incorrectly seated tyre maybe the pads not aligned. When I balanced mine I used plumbers solder (wire) it only took about 2 inches wrapped around the end of the spoke then covered with black tape.

 

[Smurfy]

I can feel the pulsing mainly when breaking. The magnet does not completely counterbalance the rear wheel.

Pulsing when braking is usually due to the brake blocks grabbing at the rim. This could occur because the rim is slightly wider or out of true at one or more locations (due to manufacturing defect or damage while riding), or it could be because there is something sticky on the rim causing the brake blocks to grab at one or more points on each revolution.

 

[accountantpete]

Take the extender off and confirm that it is the culprit.

In the early days of valve extenders I used a heavy Mavic extender (20g or so) so it was a case of pump tyre up, remove extender and tighten up valve lightly with a long needle.

 

[earth]

I gave them a spin before putting the tyre on and they were perfectly balanced. As soon as I put a tyre on with an extender there is a pulse that pulls the wheel up when the valve goes through 12 o'clock and pushes it down when the valve goes through 6 o'clock. The rims don't appear to be out of true - I can see no change in the gap between pads and rim. But the tyre might not be straight on the rim. It's a tubular tyre and the first time I ever glued a pair onto rims. I'll remove the extender first to see if that makes much difference. I won't be able to ride without the extender because they are the type where you take the valve core out of the tyre value stem, connect the extender and put the core into the extender. Without the extender there is absolutely not enough stem to put a pump on. I'll have to spin them with no air in. I think I will try the plumbers wire as well.

 

[Mr Haematocrit]

I run 80mm alloy zipp valve extenders on my Zipp 808's and get no pulsing what so ever from my wheels. What are your vale extenders made from and by whom?

 

[earth]

My rims are somewhat lighter than zipp 808s. Reynolds Thirty Two tubulars. I got them for the monster hills that circle where I live. I suspect heavier rims would not be effected to such an extent as light rims. The extenders are only 20mm by Fast Foward and I weighed them at 4 grams each.

 

[Mr Haematocrit]

I also have valve extenders in Zipp 202's on my Tarmac and although the firecrest wheels are still slightly heavier than the Reynolds at 1375 grams a set compared 1040 grams a set for the Reynolds, I can't say I have ever experienced similar symptoms to what you describe.
I do not believe the firecrests 202's are a particularly heavy wheel compared to the rest of the market, as a matter of interest I also own 404 zipps which are OK also with valve extenders.

Looking into this it seems that if the dish of the wheel is not perfectly centred it can cause pulsing, but I am unable to confirm this.

I'm really interested in this as I do not believe you should need to counter balance your wheel, it just does not seem right to me, have you contacted Reynold for their thoughts on the matter?

 

[RecordAceFromNew]

I'm really interested in this as I do not believe you should need to counter balance your wheel, it just does not seem right to me

I think the centripedal force due to the 4 gram extender is equivalent to only 6 grams (under gravity) at 1 revolution per second (5 mph). I would expect such a force variation being not too noticeable (e.g. by hand holding the axle of an otherwise balanced spinning wheel) given the mass of the lightest wheel plus tub would be around 100 times that.

However any imbalance would be magnified at higher speed. At 5 revs per second (which is equivalent to 25mph), the centripedal force due to that 4g extender is equivalent to 150 grams (because said force is proportional to the square of the rev), at 5 hertz, mixed in with other disturbances if relevant of course.

 

[amaferanga]

I think you're just experiencing grabby brakes as is common with many carbon rims. The pulsing you see due to the valve extender is just a red herring IMO.

 

[earth]

Maybe it is a red herring. I can feel a pulsing when I take the wheel off the bike, hold it by the skewer ends and spin it. I can also feel it when it is mounted if I lift the front wheel off the ground and spin it while the bike is stationary. In both those examples the pulsing is very pronounced and it is not due to braking or imperfections in the truing of the rim. I can feel a pulsing under braking and it makes a pulsing sound. It may be grabby brakes but sometimes downhill I think I can feel it as well. It is not major but I thought I would see if I can sort it out. I will see what Reynolds say. ReccordAce - Do you think 150 grams at 25mph would be noticeable?