Pulsating when braking on front wheel

BigPoser · Jul 29, 2015

On one of my wheelsets, the front wheel pulsates when braking. It doesn't matter which bike I run the wheels on, it still does it. The wheel itself appears to be very true visually when spinning it on the bike.

What causes the pulsation? Is it the way that I have the pads set up on the braking surface?

I'm at a loss.

Thanks in advance.

Brandon

craiger_ny · Jul 29, 2015

Could be a number of things. What is your wheelset? My first suspicion is usually the seam, how is your rim joined? Has it always been this way or did it start after some time of ownership? Have you checked the rim surface for anomalies or buildup? Bulge in sidewall?

BigPoser · Jul 29, 2015

craiger_ny said:
Could be a number of things. What is your wheelset? My first suspicion is usually the seam, how is your rim joined? Has it always been this way or did it start after some time of ownership? Have you checked the rim surface for anomalies or buildup? Bulge in sidewall?

My hoops are Kinlin XR19's with Sapim Laser spokes. Originally I had these wheels on my 31 year old steel frame, but I had thought it was a loose or bad headset. Recently switched them to my Focus, and it still does it, which means that they've always done it. They are about a year old at this point. I have looked at the rim and haven't noticed any kind of build up on them at all. Sidewalls look good on both sets of tires that have been mounted.

Mike T. · Jul 29, 2015

BigPoser said:
My hoops are Kinlin XR19's with Sapim Laser spokes. Originally I had these wheels on my 31 year old steel frame, but I had thought it was a loose or bad headset. Recently switched them to my Focus, and it still does it, which means that they've always done it. They are about a year old at this point. I have looked at the rim and haven't noticed any kind of build up on them at all. Sidewalls look good on both sets of tires that have been mounted.

Kinlin have a sleeved (or pinned; it doesn't matter) joint, as different from a welded (and ground smooth) joint. On some pinned (or sleeved) joints there is a slight miss-match of the joint ends, which catches the pads every revolution. Have you checked the joint?

duriel · Jul 29, 2015

turn the wheel around so it rotates the other way, it may help with your problem enough to forget about it.

BigPoser · Jul 29, 2015

Mike T. said:
Kinlin have a sleeved (or pinned; it doesn't matter) joint, as different from a welded (and ground smooth) joint. On some pinned (or sleeved) joints there is a slight miss-match of the joint ends, which catches the pads every revolution. Have you checked the joint?

I will now.

duriel said:
turn the wheel around so it rotates the other way, it may help with your problem enough to forget about it.

I'll try that out as well.

Kerry Irons · Jul 29, 2015

BigPoser said:
What causes the pulsation? Is it the way that I have the pads set up on the braking surface?

As others have explained it is most likely the rim joint. Try taking a sanding block to the rim sidewall at the joint (on both sides) to smooth out the bump. Another possibility is that the rim took a hit and bulged the sidewall someplace else.

BigPoser · Jul 29, 2015

Kerry Irons said:
As others have explained it is most likely the rim joint. Try taking a sanding block to the rim sidewall at the joint (on both sides) to smooth out the bump. Another possibility is that the rim took a hit and bulged the sidewall someplace else.

Just so it's clear to me, where on the rim exactly is the joint?

Mike T. · Jul 30, 2015

BigPoser said:
Just so it's clear to me, where on the rim exactly is the joint?

Exactly opposite the valve. You'll find the valve opposite the joint

Peter P. · Jul 30, 2015

Kerry Irons said:
As others have explained it is most likely the rim joint. Try taking a sanding block to the rim sidewall at the joint (on both sides) to smooth out the bump. Another possibility is that the rim took a hit and bulged the sidewall someplace else.

This.

If you take the tire off, you can pinch the sidewalls between your thumb and forefinger while rotating the rim. You might be able to feel the spot where the rim might have hit something, causing the sidewalls to either narrow or widen.

Same if you run your finger along the circumference of the rim. Do both sides. You may feel the flat spot.

A bad seam is less likely but still quite possible. Check this after checking the others I mentioned.

looigi · Jul 30, 2015

IDK if it's been mentioned, but sometimes the brake track gets contaminated in a way that causes pulsing. Cleaning the track with a green scotchbrite pad and some soapy water can remove the contamination and restore smooth braking.

November Dave · Jul 30, 2015

+1 to looigi's suggestion. We include alcohol pads for an initial cleaning on new builds (grease/oil used in assembly will seep out during shipping), but a clean rim is a happy rim.

BigPoser · Jul 30, 2015

Thanks all! I didn't have time to take the tire off as of yet, but did flip the wheel around this morning before a quick ride and it did make it better. Still a slight pulse, but better. I'll work on getting the tire off and inspecting the rim a bit more closely this weekend.

Mike T. · Jul 30, 2015

BigPoser said:
Thanks all! I didn't have time to take the tire off as of yet, but did flip the wheel around this morning before a quick ride and it did make it better. Still a slight pulse, but better. I'll work on getting the tire off and inspecting the rim a bit more closely this weekend.

Did you physically feel and/or for a miss-aligned joint?

Here is my website fix for a bad joint -

Rim Joint Fix.

ericm979 · Jul 30, 2015

Rim widths often vary around the wheel. If the variation is more than about .1mm, it causes the brakes to pulse noticeably.

It's easy to measure with a set of digital calipers. The tire must be removed. A quick way to check for width variation is to set the calipers at the valve hole then rotate the rim with the calipers in place. You'll see if the rim varies. Then to measure the variation, take measurements at every spoke or every other spoke.

Some rims have non parallel brake tracks. Those are not as easy to measure.

Pulsating when braking on front wheel

BigPoser

craiger_ny

BigPoser

Mike T.

duriel

BigPoser

Kerry Irons

BigPoser

Mike T.

Peter P.

looigi

November Dave

BigPoser

Mike T.

ericm979

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