Sturmcrow

The front brake on my IRO bike has always pulsed, a lot. I tried to get it fixed under warranty, but it seems IRO has either gone out of business or is not responding to customers. I thought it was some kind of fork shimmy at first, but I eliminated that possibility by putting a rubber band around the brake lever (to keep constant tension) and pushing the bike. I could clearly feel that the amount of braking went up and down as I pushed the bike. I cleaned the brakes and rim with automotive brake cleaner, no difference. Soap and water, no difference. Pulled the pads and sanded them off, no difference. Sanded the rim itself, no difference.

I've been working on bikes for a long time. I'm pretty sure this is a defective rim. I measured the width of the rim with a set of calipers and found that it varied by 0.008 inches. That seems really small. Is it possible that only 8 thousands of an inch could cause brake pulsing? The rim itself is very true when I put it up on my truing stand.

As an aside, can anyone recommend a reasonably priced medium-V 700C silver rim? I've looked around, but don't really want to pay $75 for just a stupid rim.

bikeman715

Have you try new pads ? ,someti me changing pads will help

dsbrantjr

What type of brake do you have? Cantilever, sidepull, centerpull, V-brake, etc? If cantilever or centerpull, where is the cable stop located? Cantis with stem- or headset-mounted cable stops are prone to "brake shudder or chatter". A photo or two might be helpful.

Sturmcrow

They are dual pivot sidepulls. They are Tektro knockoffs (though they might just be rebranded). The pulsing happened from day one, so I did try upgrading to Kool-Stop salmon pads. No difference.

The bike is the IRO Phoenix. It's only a couple of years old. I did add fenders, but that should not make a difference (there is no interference between fender and brake). If I had to guess I would say the brakes are "medium reach". After feeling the pulsing, I took the front brake apart and tightened up all of the pivots to remove all play.

onespeedbiker

Have you checked the wheel for trueness?

Sturmcrow

Yep, the wheel is really true. The spokes are all nice and tight.

Bill Kapaun

After dealing with a lot of "bad" wheels on the CL bikes I flip, I can't see .008" causing a problem in itself.
Possibly if it was an "abrupt" change??

Sturmcrow

As I mentioned, the pulsating has been there since I got the bike new. I would like to emphasize that the 8 thousands is how much the width of the rim itself (with no tire) varies over its circumference. The wheel is true to within half a millimeter, which is better than most of my bikes. I've swapped in a spare front wheel and the problem disappeared. This leads me to believe the the solution is not to be found within the braking system, but the rim itself.

I would really just like to know if anyone else has a grasp on what an acceptable amount of variation in rim thickness is for a modern bike. 8 thousandths does not seem like much to me, but I know that the same variation on my car would cause major pulsation. Is that true on bikes too? This one really does pulse a lot, so much so that I've only been using the rear brake for a long time now, and that bothers me.

fietsbob

it's just text.. remote guessing is , best you get here.. did you take it to a Bike shop, already?

bnb69

Maybe your tire is out of round.

cplager

Hi,
If you swapped in a new wheel and the problem goes away, I agree it's the wheel. If it's not the rim, then I'm guessing bearings in the hub.
Cheers, Charles

Bill Kapaun

Swapping in a different rim obviously shows SOMETHING is wrong with the "problem" rim.

Trueness doesn't really have that much of an effect (within reason), since the brake set will move side to side.

Since it's a front, flip it 180 degrees and see if the problem manifests itself differently.
A "good" rim should be "smooth" in either direction.

JohnDThompson 

The tire has no effect on the braking surface.

cplager

I think he meant wheel. I could imagine if this was bad enough, it could cause the problem being described.

I'm still guessing hub...

onespeedbiker

I would beg to differ. Dual pivot brakes to not track (the pads will not follow an out of true rim), so an out of true rim could cause the sensation of pulsing as the the rim bounces back and forth on pads.

Sturmcrow

Some good ideas here. I had not thought about flipping the rim, and since I have a magnet on one side for my cyclocomputer, it is always put in in the same orientation since day one.

The hub has nice sealed cartridge bearings. They are turning oh so smooth right now, and I never feel any kind of pulsing except when braking while going over 10MPH or so. However, at 20MPH the pulsing is so bad that I fear for my safety.

I'm going to out and flip the wheel right now. I may also get out my caliper and try measuring another wheel to see how much the rim thickness varies. 8 thou doesn't seem like much, but maybe it is.

onespeedbiker

Can you get another wheel and see if it causes the brake to pulse?

Sturmcrow

I did put in a spare wheel and it eliminated the problem.

Flipping the wheel did not make any difference.

I've got a new plan to save the cost of a new rim. I'm going to swap the front and back rims. It's gonna take a couple hours, but at least it's not too hard. Its a fixed-gear bicycle, so some would say I don't even need a rear brake. Hence, if the rear is pulsating a bit, no big deal.

Chris_W

I had a Velocity Dyad rim do the same thing on the front of our tandem. It started out fine but after a few serious descents and some heating up, it always pulsated under braking. I tried a different wheel and it went away. I bought another Velocity Dyad rim so that I could reuse the same spokes. After a couple of months of using the new rim, the same thing happened. Both rims were 40 spoke, 4 cross, and as true as I could get them. The rims had definitely developed a slight bulge, and neither was at the joint.

I then gave up on Velocity rims. This was 2 or 3 years ago. I've had several different wheels on there since, all of which have had Mavic (A319 or A719) or DT Swiss (TK540) rims (mostly 36 spoke), and have had no such problems.

ThermionicScott 

Is the headset loose? That could cause the fork to judder while braking.

es1bkacsur

I bought a pair of Phonix 7-speed beach cruisers with steel rims new in box & both of them had pulsing brakes. I ended up replacing just the rim on one of the wheels, kept the original hub & spokes, and the problem cleared right up. These are just bad rims.

reptilezs

its the rim seam