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Mystery rubbing, need help please

Old 01-26-15, 09:41 AM
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Mystery rubbing, need help please

Hey everyone ! New user here seeking for some help. Before I describe the issue a quick word about me :
-95kg
-2m 5cm (sorry for imperial system users..
-usually use 61-62cm frames
-previous experience in a bike shop as a wrench, so presumably I know what I'm doing with my hands.
-somewhat powerful road and track racer

On to the issue :
It started a couple weeks back, on my race machine (sram set). I was freewheeling with my hands loosely on the hoods, but for some reason I squeezed them hard (don't remember why).
As soon as I did that, the bike dramatically picked up speed as if something stopped rubbing or slowing me down. At first I thought a car had nudged me from begin as the feeling was similar to when someone pushes you up a climb. But every time I squeezed the hoods the same phenomenon repeated itself ! I have absolutely no idea what could be causing this, but almost every time I squeeze the hoods it happens, and sometimes when i pull the brake levers it happens too just before the pads hit the rim.

I have noticed the same issue on my second bike (full campy), and still have no clue..
I have checked for brake pad rub, but found nothing..

Any help would be appreciated, its really annoying..
Thanks for reading
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Old 01-26-15, 10:20 AM
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Maybe when you squeeze the levers, you are also getting into a more aero position, in which case you will go a bit faster.
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Old 01-26-15, 10:31 AM
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Old 01-26-15, 10:36 AM
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Pretty much has to be in your mind.

Unless someone secretly put an electric motor in your bike, activated by hood squeeze.

If you've worked as a shop wrench, there's no way you'd miss brake rub bad enough to rob you of speed.
If there was a tire rubbing up on something hard enough to rob you of speed, the tire would have worn through and blown fairly soon.
The only possible thing I can think of otherwise is a rear hub about to seize, and when you get a bit more forward, the weight eases up, the hub spin lighter and the speed picks up.

But having that on TWO bikes pretty much indicates that it's YOU, and not the bikes.
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Old 01-26-15, 10:37 AM
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Originally Posted by Track drop out
. . . the bike dramatically picked up speed . . .
How much does your speed increase? It would have to be a few kph in order to be noticeable.
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Old 01-26-15, 10:42 AM
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Depending on the circumstances, it might be a psychological/perception effect relating to a change in expectations vs. reality. Many riders first encounter a similar effect then using rim brakes in the rain. As they apply the brakes they expect to slow down as they usually do. But there's greater delay in wet brake response, so when they don't slow down as expected, their brains register it as acceleration.

There are many examples of this where the senses send conflicting messages to the brain or when the sensory input doesn't match expectations. Sailors who've been out in rough seas will feel the land moving when they get off the boat, Some people get motion sickness when watching movies of auto races or chases that use a car mounted camera, and so on.

In your case, when you apply the brakes, the brain adjusts expectations to deceleration, and you unconsciously shift weight back, and brace arms. But the brakes haven't engaged yet, so the brain think you're accelerating.

The one thing I can say for sure, nothing magic is happening, and nothing is actually changing between when you start squeezing the lever and when the shoes start slowing the wheel.
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Old 01-26-15, 10:42 AM
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Do you squeeze the hoods like that when starting down a hill?
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Old 01-26-15, 10:47 AM
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I can not see this as a rubbing issue....in fact, it just does not make any sense to me at all...
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Old 01-26-15, 11:01 AM
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Thanks for all your answers

It doesn't make a lot of sense to me either :/ . I'm pretty sure it's not in my mind, and i'm not altering my position, just clamping down a bit harder..

I'm gonna have a look at my cables, see if there's something weird
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Old 01-26-15, 11:08 AM
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taking it at face value, what are you squeezing at the hoods under the tape? Brake cables?
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Old 01-26-15, 11:11 AM
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Originally Posted by Track drop out
Thanks for all your answers

It doesn't make a lot of sense to me either :/ . I'm pretty sure it's not in my mind, and i'm not altering my position, just clamping down a bit harder..

I'm gonna have a look at my cables, see if there's something weird
There must be a really good reason you don't want to measure it.
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Old 01-26-15, 11:30 AM
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Originally Posted by AnkleWork
There must be a really good reason you don't want to measure it.
I'm sorry ? I don't ride with a computer, but it is really noticeable
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Old 01-26-15, 11:49 AM
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Assuming your brakes aren't rubbing and your brake setup doesn't somehow backs off a bit before being applied, I have only one theory.

The first mm of brake movement before contacting the rims reduces wind resistance through decreasing your surface area and/or some sort of ground effects phenomenon between the brake pads and the rims. The fact that you would feel that difference is unlikely, but it is all I can think of that would decrease drag by applying the brakes.

Something else just occurred to me. Sometimes medical issues present themselves in unusual ways, like clubbed fingers being a sign of potential lung cancer (this is what my brother saw to lead to my uncle seeing a doctor and being diagnosed)... I don't have anything specific in mind in your case, but I do seem to recall reading something about strength in one part of the body being impacted by movement and/or pressure in another part of the body... So perhaps by squeezing the hoods you could be increasing the strength in your legs, which could be indicative of a possible medical issue. Or maybe it is activating an acupressure point... if this last point, then I see a potential to design a new brake hood shape to increase the benefit.
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Old 01-26-15, 12:05 PM
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Originally Posted by Track drop out

As soon as I did that, the bike dramatically picked up speed as if something stopped rubbing or slowing me down. At first I thought a car had nudged me from begin as the feeling was similar to when someone pushes you up a climb. ....
Let's be real.

Even if there was a source of drag that was removed, the bike still wouldn't pick up speed with some new input. So from a pure mechanics consideration, what the OP is feeling is impossible.

But we're dealing not with a proven acceleration, only the perception of one, so without saying "it's all in your head" that's what it is. The OP is feeling the difference between expectation and reality which is a common phenomenon.

Of course being to go faster simply by squeezing the hoods is a good thing and we all wouldn't mind the feature, but if the OP wants it fixed, the best way might to temporarilly mount a computer so he can see in black and white that nothing is changing.

BTW- let's not discount the possibility that the OP somehow got hold of one of Cancellara's bikes.
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Old 01-26-15, 12:08 PM
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Originally Posted by FBinNY
BTW- let's not discount the possibility that the OP somehow got hold of one of Cancellara's bikes.

Damn, spotted ^^

I'll try getting hold of a speedometer see how it really measures up.
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Old 01-26-15, 12:37 PM
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Let's not overlook one possibility. During the ride, use of the brakes in conjunction with some other factors such as a frayed cable or cable friction causes the brake to remain engaged. Squeezing the cable introduces a small motion of the cable housing, or change in tension, allowing the brake calipers to disengage. This sequence might not be observed on the stand.

It might not be the case, but I have found that most of the time where some odd incident is reported, something actually did occur even if it doesn't seem realistic.
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Old 01-26-15, 12:44 PM
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Originally Posted by wphamilton
Let's not overlook one possibility. During the ride, use of the brakes in conjunction with some other factors such as a frayed cable or cable friction causes the brake to remain engaged. Squeezing the cable introduces a small motion of the cable housing, or change in tension, allowing the brake calipers to disengage. This sequence might not be observed on the stand....
Yes, but the OP reports a feeling of acceleration, and removing drag wouldn't do that. Not to mention, that rubbing of brakes or tires is audible, and I can't imagine an experienced rider not hearing it.
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Old 01-26-15, 12:46 PM
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Originally Posted by Track drop out
I'm sorry ? I don't ride with a computer, but it is really noticeable
If you really wanted to know what's going on, you easily could have had someone pace you (with or without a speedometer) while you reproduced the "effect." When given the choice, human nature tends to choose something other than first hand knowledge.
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Old 01-26-15, 12:49 PM
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Originally Posted by AnkleWork
If you really wanted to know what's going on, you easily could have had someone pace you (with or without a speedometer) while you reproduced the "effect." When given the choice, human nature tends to choose something other than first hand knowledge.
Oh ! Well in that case last sunday on our club ride when engaging the brakes the sudden surge actually had me nearly collide with the rider in front. (and no he wasn't braking suddenly)
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Old 01-26-15, 12:57 PM
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Originally Posted by Track drop out
Oh ! Well in that case last sunday on our club ride when engaging the brakes the sudden surge actually had me nearly collide with the rider in front. (and no he wasn't braking suddenly)
Then it must be easily reproducible and thus measurable. Why avoid the question?
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Old 01-26-15, 12:58 PM
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hum.. i wasn't :/
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Old 01-26-15, 01:00 PM
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Originally Posted by FBinNY
Yes, but the OP reports a feeling of acceleration, and removing drag wouldn't do that. Not to mention, that rubbing of brakes or tires is audible, and I can't imagine an experienced rider not hearing it.
Two possibilities: freewheeling with his hands loosely on the hoods implies downhill, possibly a false flat. And the sudden release of a deceleration can feel like a surge.

If it also happens when he's pedaling, and a later post implied that it does, then of course he'd feel some acceleration.

I'm not near his bike and can't say whether he should hear a rub, but there have been times that I couldn't hear one. Particularly at higher speeds or with some ambient noise.

edit: let me explain a bit more. If we want to posit that something is off in perception of an issue, which is more likely? That OP imagined the whole thing, or that OP does feel something going on but misinterprets some facet of it? Or communicates it in a different manner than you'd expect? It might be nothing, but it's almost always something there.

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Old 01-26-15, 01:14 PM
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Am I the only one who's reading that the OP is squeezing the hoods, not the brake levers? Unless there's a Gruber drive power button there, squeezing the hoods cannot change anything.
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Old 01-26-15, 01:22 PM
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Originally Posted by FBinNY
Am I the only one who's reading that the OP is squeezing the hoods, not the brake levers? Unless there's a Gruber drive power button there, squeezing the hoods cannot change anything.
No, you're not the only one. That's why it makes no sense. And squeezing the brake lever is not likely to make one faster either, unless, as you suggested, it activates the secret hidden motor.
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Old 01-26-15, 02:55 PM
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OP probably forgot that there's an old-fashioned generator light on there and the wires have been run under the hoods...

of course, if true, and an old-fashioned generator can be disabled by a loose wire or two, and i'm not sure about that, it's unlikely the OP wouldn't notice it, but then again, i'm not convinced the OP isn't having a little fun at our expense either.

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