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Discussion Starter · #1 ·
I'm riding with a beginners/intermediate group and they're scaring the hell outta me. :eek: I don't mind uphills because I do have some fitness from road riding. But going downhill sometimes scares me to death and I know I'm braking too much. I'm trying to do like it says in Mastering Mountain Bike Skills, brake good and hard to slow down and not ride the brakes, but then I start rolling again so fast. I just seem to drop like a bomb down the hill and it freaks me out, like the bike is just going to blow up on me. Does weight make you go faster? I'm 140 and the other gals are all small. I feel like a cow on wheels...is this just beginner-itis? I don't mind bombing down easier fire roads but that's about all I've ever done. I do ride above the saddle with my feet in the 3 and 9 position, probably the only thing I do right, but sometimes I find myself locking my elbows.

Will my Avid BB7 discs wear out if I overbrake? What should I be looking out for?
 

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Freshly Fujified
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You're doing fine

Each time you clear a downhill section you'll feel more confident with the next. You'll probably always feel some butterflies, and feel a sense of not being in control, but that will also help keep you in check. Keep your weight back by extending your arms and letting your backside slide off the back of the saddle, keep the feet at 3 and 9, feather the brakes and let the bike do what it was built to do. Lastly, your disc brakes will more than likely handle what you're throwing at them.

You're doing fine.....

Clyde
 

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Domestic Fowl
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Yes, this sounds like a case of "beginner-itis" and there's nothing wrong with that. You just need time to get used to going fast downhill. Things that will help are:

1) Stand on your pedals (which you are doing)
2) Shift your weight back. get behind the saddle if you need to on really steep stuff
2) Make your body loose (don't tense up) bent knees and arms. Let you arms and knees soak up the bumps. RELAX, RELAX, RELAX... BE LOOSE
3) Look ahead. Don't fixate on what's immediately in front of your tire. If you're looking there you're not preparing for the next thing that's coming. Look ahead and use peripheral vision for the up-close stuff
4) Look where you want to go. If you're fixating on something that you want to avoid, you'll probably end up hitting it.


To answer your question about weight, there's a long answer that involves some fluid dynamics, but the short answer is, yes, it does have some bearing on downhill speed.

Your brake swill be okay. ;)
 

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You'll be fine...

MTDirtGirl said:
I'm riding with a beginners/intermediate group and they're scaring the hell outta me. :eek: I don't mind uphills because I do have some fitness from road riding. But going downhill sometimes scares me to death and I know I'm braking too much. I'm trying to do like it says in Mastering Mountain Bike Skills, brake good and hard to slow down and not ride the brakes, but then I start rolling again so fast. I just seem to drop like a bomb down the hill and it freaks me out, like the bike is just going to blow up on me. Does weight make you go faster? I'm 140 and the other gals are all small. I feel like a cow on wheels...is this just beginner-itis? I don't mind bombing down easier fire roads but that's about all I've ever done. I do ride above the saddle with my feet in the 3 and 9 position, probably the only thing I do right, but sometimes I find myself locking my elbows.

Will my Avid BB7 discs wear out if I overbrake? What should I be looking out for?
Getting used to descending with speed and proper balance takes time. If it helps, a bike is more stable, the faster it goes due to the gyroscopics of the wheels. So the fast you go, the more your bike wants to stay upright.

Your brakes will be fine too for several years. You can inspect the pads visually and when they look thin, replace them. Check them right now for reference and then when they become worn thin, pop them out and put new pads in.

Ken
 

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MTDirtGirl said:
Does weight make you go faster? I'm 140 and the other gals are all small.
Remember learning in school that two objects of different weights, when dropped, fall at the same rate? Galileo dropped a cannon ball and wooden ball from the top of the Tower of Pisa and they landed together. (actually he never did it, but that's the story and the law of gravity). Unless opposed by wind resistance, weight is irrelevant.

So actually if you are "bigger" you'll have more wind resistance and go slower.
 

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Hey MTDirtGirl, no need to worry, everyone has been in the same boat at one time or another! :)
The most important thing to remember is to stay loose and not panic!! Try your best not to freak out and keep in mind that one day soon it will be awesome fun instead of scary like it is now. A helpful mindset to use is that thousands upon thousands of people have overcome the fear up until now so it isn't impossible! :)
Always try not to lock your elbows because they will help act as suspension for your upper body. If your elbows are locked then it could also mean that your grip is too tight as well, which in turn makes riding down hill at speed hard.
Stay loose, that is the key. Don't worry too much if you feel a little out of control, as long as you are pointed in the right direction more often than not you will be fine. Let the bike move under you if needed, just keep your body weight balanced with that loose feeling.
And stand up on your pedals, this will help you shift your body weight much easier whenever necessary. Like when the going gets really steep it will help you get your weight over the rear wheel when you lean as far back as you can.
But always keep your body from tensing up, it won't help at all especially if you crash!! :eek:
Finally, just enjoy it!!!! :)
 

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Discussion Starter · #7 ·
tlg said:
Remember learning in school that two objects of different weights, when dropped, fall at the same rate? Galileo dropped a cannon ball and wooden ball from the top of the Tower of Pisa and they landed together. (actually he never did it, but that's the story and the law of gravity). Unless opposed by wind resistance, weight is irrelevant.

.
That's what I thought, but I feel like the cannon ball.

I have a new FS with 4 inches of travel front and back. Maybe it's because I'm used to my old cheap hardtail which would have bucked me all over the place at these speeds...need to trust the new bike more I guess, also learn where the rebound damping should be.

Also, I have trouble staying in the tracks. THAT is hard, and when I wander up on the sides it feels like I'm going to lose it...okay so I'm new at this. :eek:
 

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Good advice from everyone here, no need for me to repeat it.

I will add that you should focus on what they say, but also take an opportunity to take an "even more beginner" out, and then slow down to their pace. You'll feel a LOT more comfy at that pace, so take the opportunity to focus on your ride, to focus on hitting your marks, to focus on doing all the things everyone here said to do.

If you make this style of ride a regular part of your regimine, along with riding with more advanced riders, and riding with similar skilled as yourself riders, it will really help.

To me, I need to push myself, but it also helps to take a step back every once in a while and focus on the fundamentals (which is easier to do when you are the strong rider in the pack). In addition, it is a cool thing to share what you've learned with others....

Good luck, it sounds like you are on the right track (pun intended...)
 

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Beg to differ

tlg said:
Remember learning in school that two objects of different weights, when dropped, fall at the same rate? Galileo dropped a cannon ball and wooden ball from the top of the Tower of Pisa and they landed together. (actually he never did it, but that's the story and the law of gravity). Unless opposed by wind resistance, weight is irrelevant.

So actually if you are "bigger" you'll have more wind resistance and go slower.
Not to dispute Gallileo because this is an entirely different set of circumstances.

Source: http://www.sportsci.org/jour/9804/dps.html

During descents, the negative slope of the hill in the power equation reflects the addition of gravitational potential energy to the power generated by the cyclist. In a freewheel (passive) descent, the cyclist's speed will be determined by the balance of the air resistance force and the gravitational force. As the cyclist accelerates, sv2 increases. Once kaAsv2 (plus the negligible power term associated with rolling resistance) increases to match giMs, the cyclist will reach terminal velocity. Any further increase in speed must be achieved by adding energy through pedaling. However, on steep hills, terminal velocities may reach 70 km·hr-1. At such high associated values of sv2, even the application of VO2max would result in only a minimal increase in speed.

Terminal velocity can be solved for in the cycling equation above by setting power at 0. If one assumes the rolling resistance term is also 0, and that there is no wind blowing (v = s), then the equation becomes:

kaAs3 = -giMs
or s = (-giM/kaA)1/2
Thus, the terminal velocity is roughly proportional to the square root of the ratio of M/A. Scaling reveals that larger cyclists have a greater ratio of mass to frontal area. They therefore descend hills faster as a consequence of purely physical, not physiological, laws. Since the larger cyclist has a greater mass, gravity acts on him or her with a greater force than it does on a smaller cyclist. (Note: A common misconception is to note the equal acceleration of two different sized objects in free fall in a vacuum, and assume that the force of gravity on both is equal. The force on the more massive object is greater, being exactly proportional to mass, which is why the more massive object is accelerated at the same rate as the less massive one.) While the larger cyclist also has a greater absolute frontal area than the smaller cyclist, the difference is not as great as that for their masses. Thus, the larger cyclist will attain a greater s3 before a balance of forces results in terminal velocity.

With lighter cyclists climbing hills faster due to their greater relative VO2max, and heavier cyclists descending faster due to their greater M/A ratio, one might assume that equal performances would occur in races involving equal up and down segments. However, ascents take longer than descents, so a speed advantage to small cyclists on the acsents produces a greater time advantage than large cyclists obtain on the descents. For this reason, smaller cyclists are generally superior competitors on hilly road races.

-------------------------------------------------------------

My personal experience tends to agree with this.

That being said, don't worry about your brakes. Maintain them regularly and ride with confidence. Ride as slow as you feel comfortable and have fun doing it.
 

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tlg said:
...So actually if you are "bigger" you'll have more wind resistance and go slower.
Back to my comment about fluid dynamics...

There's a little more to the problem than just size. Since we're talking about downhill, the forward driving force(or a portiion of it) is due to gravity. Force is the product of mass x acceleration, the mass being the combined mass of the system(bike+gear+person) and the acceleration due to gravitational attraction is equal to the sine of the angle of the slope x gravity.

Wind drag is proportional to frontal area, coefficient of drag, viscosity of the air, and the square of the velocity. Until velocity has reached a point where wind drag force is equal to the forwared drving force caused by gravity(equilibrium), the rider will tend to accelerate.

So writing the equilibrium eqation we get the following:

v = viscosity
c = coefficient of drag
A = frontal area
V = velocity
M = mass
g = acceleration of gravity (~9.81m/s^2)
i = angle of incline where 0 degrees <= i <= 90 degrees

drag force = v x c x A x V^2
force due to gravity = M x g x sine(i)

At equilibrium drag force = force due to gravity

v x c x A x V^2 = M x g x sine(i) --- equilibrium equation

V = sqare root( (M x g x sine(i))/(v x c x A) ) --- velocity equation derived from above

From the above velocity equation we can plainly see that a larger mass will have a higher velocity for a given frontal area. We can also see that increasing surface area for a given mass decreases velocity.

For the ratio of mass to frontal area(M/A) for humans in riding position, in general, mass increases more quickly than frontal area. Therefore, a larger person tends to have a higher velocity at equilibrium assuming a similar riding position.

One can also derive from this that a rider can change their equilibrium velocity by changing their frontal area(e.g. getting into a tuck position, or sitting up more).

Its that simple. ;)

Dang, TLG. Now look what you made me do. I got all scientifical and stuff. :eek:
 

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jeffj said:
Not to dispute Gallileo because this is an entirely different set of circumstances.
Good call Jeff. I was going to go physicist on this thread when i read that post. Fat guys roll faster- i'm proof.
 

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I am also a beginner at mountain biking, and am having the same type of problems as you are. I have noticed that I have improved in controling the bike, and my speed increases with my confidence. This seems like a challenge all beginners go through, so I am not worried about it, and am just having fun. One of the biggest problems I am having is trusting the tires grip when I lean into a fast corner. I sometimes go a little wide of the singletrack on high speed corners, but I stay loose, gently go onto the brakes and wind up fine.

Just keep riding, and I am sure you will soon improve.
 

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Go to school on them

I mean follow a faster rider and watch how they do it. This has worked for me in carts, boats, dirt bikes and MTB. It's easier to have some confidence when you can copy the guy in front of you and watch how they set themselves up and flow through turns, jumps, rough stuff, whatever. I figure if they can do it, so can I.
 

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Riding the brakes

I'm not sure if you're reading that right, but I believe it's aimed at braking before entering a corner, so you don't skid during the turn. Just as you ride the car brakes on say a looooooooooooooongggggggggggg DH descent in a Mtn pass on a highway, you do the same on a bike. You don't wait until the bottom and then hit the binders (at 200 mph).

It's fine to ride the brakes to scrub speed or have a reduced velocity when descending. and like other posters say, it's about fun, comfort, learning over time, and the control of the bike allowing you to achieve those things.

Maybe I'm wrong, but I nearly always have a finger on, or close, to a brake lever so as to get the bike to react to trail needs and directions.

Good luck, Jim
 

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tlg said:
Remember learning in school that two objects of different weights, when dropped, fall at the same rate? Galileo dropped a cannon ball and wooden ball from the top of the Tower of Pisa and they landed together. (actually he never did it, but that's the story and the law of gravity). Unless opposed by wind resistance, weight is irrelevant.

So actually if you are "bigger" you'll have more wind resistance and go slower.
Not quite. Unless opposed by FRICTION, weight is irrelevant. In this case you have to overcome:
1. Air resistance
2. Friction between your tires and the trail
3. Friction between your bearings and the wheel

While it's true you have slightly more air resistance due to your size, the force generated by your mass times gravity more than compensates for this....unless your deploying a drag chute. :)
 

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I honestly don't know what is too fast vs not fast enough, but I think that you should go as fast as you are comfortable going. This may vary depending on terrain, pads you might be wearing, your familiarity with the trail,etc.
 

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Shouldn't be a problem...

I weigh about 210 and have been using the same brakes as you for the last 3 years. I've never broken anything and they've never failed me...I trust 'em like an old friend.

Just keep an eye on your pad wear and you'l be fine.
 
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