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Discussion Starter · #1 ·
My front wheel on my road bike seems to have developed a weird issue when I'm applying the brakes, they seem to grab more heavily on just one small section so I can feel the pulse as the wheel rotates under braking.

The rim is true to less than a mm across its width, I've cleaned it with isopropyl alcohol, tyre doesn't look to have anything wrong.

I might try rotating the tyre next or swapping the pads, just wondered if anyone has any other suggestions?

Thanks
 

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I agree with Juan.

It sounds like you have one of two things happening.

1) you have a build up of brake pad material on the rim in one small spot. This is generally known as "transfer" and it's what makes the brakes work well in the first place. Pad material gets imbedded into the surface of the rim and that material grabs the brake pads very well and that in turn slows you down. If, for some odd reason, you have a build up in one spot it will grab and make the brakes pulse.

2) you may also have a small ding in the rim or the seam has an imperfection. Either one will make the rim slightly wider in a small area and make the brakes pulse.

If you inspect the rim braking surface very carefully I'll bet you see the spot that is causing the issue and you will know what needs to be done.

Good luck,

dave
 

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Discussion Starter · #4 ·
On my truing stand I can't see anything noticeable in the problem area, but I'll take another look and give scrubbing the rim a try.

Thanks
 

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I clean my rims pretty regularly. I also use a Scotch Brite pad with some Simple Green sprayed on the pad. They really come clean quickly. I also sand the pads lightly with 100 grit sandpaper.
 

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Discussion Starter · #7 ·
Tried all the above suggestions without success, broke out the calipers, the rim seems to be 0.4mm wider for a couple of inches, that's where I'm feeling the pulse.

I'm guessing the only solution is a new rim?
 

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Rim problem

6thElement said:
Tried all the above suggestions without success, broke out the calipers, the rim seems to be 0.4mm wider for a couple of inches, that's where I'm feeling the pulse.

I'm guessing the only solution is a new rim?
If the rim is actually deformed due to damage, then a new rim is definitely a consideration. However, there are many rims that come this way from the factory. You might want to replace such a rim if you can't stand the braking pulses, but lots of people just live with it.
 

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road bike resurrector
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also check for play in the actual brakes

I would swap pads front to rear and see if that fixes anything.

what speeds are we talking about here, 5mph or Mach 2 with your hair on fire?
 

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Discussion Starter · #11 ·
As per my previous reply it's the rim, there's a small section which is ~0.4mm wider.

I feel it at any speed, just slightly more noticeable at lower speeds.
 

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I have an rim that came from the factory with a small bump on one spot. No big deal once you get used to it....and problem will probably solve itself after few thousand miles :) Brake pads will eat that part of the rim faster till it is even. Before rims had machined brake surfaces this was common issue.
 

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I went through the same thing, tried everything I could think of -- cleaning rims, pads, new pads, check headset, brake bolts, etc... In the end, I determined my rim (Velocity Dyad p.o.s.) has the same issue with a wide spot.

I'm considering just leaving it, or putting the rim in a vise and trying to even it out. I have had blow-off problems on this rim and suspect the cause could be the same.
 

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Discussion Starter · #14 ·
smokva said:
I have an rim that came from the factory with a small bump on one spot. No big deal once you get used to it....and problem will probably solve itself after few thousand miles :) Brake pads will eat that part of the rim faster till it is even. Before rims had machined brake surfaces this was common issue.
I guess that's true, I just need to ride those wheels more :thumbsup:
 

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Cycling Dolomiti Friuli
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weltyed said:
you might also wanna sand/scuff the brake pad.
I would second that suggestion.

A few months ago I hit a rock while descending fast which blew both front/rear tubes and made a hole in each tire. The rear rim had a visible ding as well. I fixed everything but later started noticing bad brake pulsing on the front rim. I took the tire off, checked the lateral/vertical true (only a c-hair out), and put it all back together- still bad. I decided to install a new rim in case it was very slightly distorted and I just couldn't see it. The rim wasn't too expensive (€37 with shipping) so no big deal. I swapped it out and tried it- still pulsing. I (finally) looked at the brake pads and both sides had a thin line of protruding rubber from front to back about 2 mm high. The rims (Ambrosio Evolution) have a groove machined in the braking surface all the way round (I suppose to drain water). So the pads had worn everywhere but where they touch the groove. I sanded the pads flat and put the wheel on- voila', no pulsing. Meno male, I have a nice spare rim to use after my next rock-strike.
 

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Bill2 said:
The rims (Ambrosio Evolution) have a groove machined in the braking surface all the way round (I suppose to drain water). .

The groove probably is a wear indicator.
 

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I will not accept a pulse - I replace these rims. Actually, I try to repair with 2 hammers and a lot of care.

Think about going downhill in traffic and signaling a left turn while braking hard with one hand. A braking pulse in now a dangerous thing.
 

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Cycling Dolomiti Friuli
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Agreed, it's quite annoying. I do a lot of riding in the mountains with long steep descents and it's not too bad when braking hard, but when you need to feather a bit to lose some speed heading into a hairpin it disrupts your arc through the curve. Much prefer smooth deceleration. ;)
 

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Unsafe at Any Speed
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If possible (front wheel) , flip the wheel so it rotates the other way. Maybe the pads ramp up differently on the bump in the rim, that way.

I had a wheel with pulsing which was only just annoying. Flipping it reduced the perceptible effect to only just not annoying.
 
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