Clydesdales/Athenas (200+ lb / 91+ kg) - Going Downhill--FAST

Hi guys,

I am a bigger person and yesterday I climbed a heinous hill. I think it may actually be a mountain but I'm not sure. Anyway, I then had to go down the hill. I was going 26mph with the brake levers cranked back almost all the way, and when I wanted to stop, it took a looong time. I had to stop a number of times to let the brakes cool off. I considered walking. It was really scary, because there is gravel and the road is really curvy. Usually I like (love) going downhill fast but this was too much. I tried braking-coasting-braking, but I couldn't keep myself at a safe speed that way.

What can I do to improve this situation?! Aside from losing weight, obviously?

I have a 2008 Jamis Aurora touring bike with "Tektro cantilevers." I got the bike a year and a half ago and maybe should get new brake pads(?).

Thanks!

Wow!
I would have been scared s*tless!
I have been thinking about crossing a bridge in my area, but have been worried about the downhill trek for this very reason.

Definitely check for brake wear. As clydes, we tend to put a little more wear and tear on the pads. Also, if they are the stock pads, those "typically" aren't very good anyway. There are some great ones out there. You can find some for disssipating heat as well as stopping power. I actually run two different pads for the front and rear.

There was a bit of sticker shock at first (I mean, come on they're only little rubber brake pads, right?) but then I realized, even the best brake pads are cheaper than a trip to the ER.

Also check your brake cable tension. After some serious downhill stops they could have stretched some and you'll need to take up the slack.

CollectiveInk, GREAT! Thanks! I was worried it might be a "time for disc brakes" situation. Haha :) I think I am going to put it in the shop for a tune-up anyway so that would be perfect. Which type do you use on the front and on the rear?

TallStevens, what is the hill like on your bridge? I think the fastest I've ever gone was around 40(?) down a hill near my house, and it was kind of scary but mostly awesome, because it was perfectly straight, no gravel, and no trees--perfect visibility. Maybe your hill is like that? (I hope!) The hill yesterday took me like an hour to go up, and I think 10 minutes to go down, not counting breaks. haha.

I wish I had that situation. I live on q gentle crest between a creek and a river. No matter where I go, homebound is uphill.

Uggh, I'm sorry. I was thinking how nice it is that wherever I get tired, all I have to do is turn around and roll. :D A lot of the people along those roads have driveways that go up or downhill in some crazy way, and I was thinking how hard it'd be to force myself to ride my bike if I lived there. I'd have to drive up to the street first.

we had the same dilema living in Littleton CO last year...
no matter which way we went... it was either uphill or downhill on the return...
same as leaving... kids were in great shape last year!

Hi guys,

I was going 26mph with the brake levers cranked back almost all the way, and when I wanted to stop, it took a looong time.

the road is really curvy. Usually I like (love) going downhill fast but this was too much. I tried braking-coasting-braking, but I couldn't keep myself at a safe speed that way.



Are your brakes adjusted close to be close to the rims? I see a lot of people that have loose brakes and I wonder how they stop just going 15mph because of how far they have to pull their levers.

Do you know how to corner? It something worth learning for those curvy descents. And feather your brakes as you go to keep the speed in check, rather than slow down - speed up - slow down - speed up.

Kool Stop pads can help. The dual-compound or the salmon compound pads wear a little faster but offer better stopping power.
Have your brakes adjusted for maximum power, which means properly adjusting straddle cables and cantilever angles (if using cantis) or pad clearance and cable travel if using calipers or V-brakes.

I'm 240 pounds and have a 2.25 mile descent on my morning commute which puts me between 45 and 50mph, and I can bring it to a stop pretty quick if I need to.

Also, for quick descending stops you need to practice shifting your weight over the back of the bike and using the front brake more than the back.

As Clydes we just have better developed descending muscles than most. :) Going fast is one thing we excell at! I've topped out at 71.4mph. Lots of fun! On the flip side it's good to be able to stop safely in a reasonable distance. There are several good suggestions above. Assuming you know the proper way to stop as clifton pointed out, I'd but them in this order and add one of my own.

First, make sure your brakes are adjusted properly. Second, Coolstops. Third, Mavic OP Ceramic wheels. With the ceramic wheels you won't have to worry about overheating your wheels/brakes and they stop just as effectively if it's raining or wet.

...What can I do to improve this situation?! Aside from losing weight, obviously?


...And feather your brakes as you go to keep the speed in check, rather than slow down - speed up - slow down - speed up.+1

Make sure you don't start the descent with speed. Go slow from the get-go. It's easier then realizing, "Oh my gosh, I have to slow down" when you're already doing 30+mph.

Also, take your bike to a shop, ask them how's the wear on the pads. Tell them your concerns. Or post detailed photos for us to give some weak advice :D

I had the same problem last week at a big cancer ride. I could't hold the bike back and I had to let it go. I reached 45mph and could have gone over 50 but I tried to keep dragging the brakes. Some people recommended kool pads and 1 person said to check my brake adjustment which was off a bit do to a loaner rim.

71.4?!?! GOOD LORD! Ahaha! I just couldn't handle that.

My brakes are adjusted pretty close to the rims, but I couldn't say anything beyond that. Probably have to leave that one to the pros :)

How do I "feather" the brakes? I tried cranking on them, and it only brought me down to the top of my comfort level, and then the brakes got really noisy and didn't work that well, so I had to stop and let them have a rest. Then I tried to roll, brake, roll, brake, so things wouldn't heat up so much. But I couldn't keep my speed low enough!

How does one corner properly? I usually kind of lean away from the corner, hold the inside foot up and outside foot down, but there was gravel on the road in some places, and I didn't want to land on my face, so I wasn't comfortable leaning over at all (especially at 25mph on hairpin curves!).

Sorry if these questions are dumb or whatever. But I usually ride on flat stuff so this is mostly new to me, and I didn't like it. I want to climb to challenge myself (and not exfoliate myself on the street)!

How do I "feather" the brakes? I tried cranking on them, and it only brought me down to the top of my comfort level, and then the brakes got really noisy and didn't work that well, so I had to stop and let them have a rest. Then I tried to roll, brake, roll, brake, so things wouldn't heat up so much. But I couldn't keep my speed low enough!Lightly apply the brakes, then apply harder, then light. Same as you were doing, but the pads never leave the rim. Just degrees of how hard you brake.


How does one corner properly? Boy...there's a book right there. Best to find a group/club and ask them. Learn in person. Way too much stuff to cover online. Besides, I don't get paid for this stuff.


I usually kind of lean away from the corner, hold the inside foot up and outside foot down, This is the beginning. But, you're actually leaning "into" the corner. Away from it (outside of the corner) would put you over the edge.


but there was gravel on the road in some places, and I didn't want to land on my face, so I wasn't comfortable leaning over at all (especially at 25mph on hairpin curves!).Good reaction. Easier said than done: basically, you move your body off the bike so it's directly over the ground and the bike is upright. Then turn the front wheel into the corner. This is one of those rare moments where we actually turn the front wheel instead of just leaning into the turn. Although the bike's still leaning over significantly, here's an extreme example:

http://www.khulsey.com/motorcycles/sportbike-images/ama-superbike_ls_07_jordan-suzuki.jpeg


Sorry if these questions are dumb or whatever. But I usually ride on flat stuff so this is mostly new to me, and I didn't like it. I want to climb to challenge myself (and not exfoliate myself on the street)!Good one. :D

When you take your bike to the shop, ask to watch while they adjust your brakes and/or cables. It's a VERY important skill to know - and not just "leave it to the pros". (And it's not hard to do.)

I'm running reds on the front and blacks on the back. But I also upgraded my brakes from the tektro's that came on the Allez, to Bontrager Speed lights (got a killer deal - one I couldn't pass up) and that made a huge difference. Something about less flex, stronger clamping power. Now I can haul my 250# butt from 48mph to 0 seriously quick.

As for feathering, one technique I use, and taught my son on long descents (especially curvy ones) is to alternate front and rear brake. That way you're always braking, but they have time to cool off.

The leaning, cornering at speed uses more counter steering than physically steering. Just practice slowly, then working up to higher speeds. It takes time, practice and faith (in your tires, rims, brakes, skill level, etc.)

But I second "find a local group to ride with and ask/watch them".

Just keep trying. :D

The biggest thing you can do is look where you want to go! Ignore the dirt (as hard as that sounds). The bike will go where you are looking. So, if you have a path through or around the gravel patches that is where you should be looking. If you fixate on the gravel in the road you will ride right through it. Leaning away from the corner is not good you want to lean into the corner if you are not neutral on the bike. Your foot position is fine. Finally, get your braking done before you enter a corner (you're not racing). :) As Mkadam68 mentioned, you could (and people have) written books on the subject of cornering.

btw 71.4 wasn't so bad. I didn't even know I went that fast (because it was dark) until my support vehicle pulled up next to me later on and asked if I knew how fast I was going. I didn't believe them until I looked at the max speed on my own speedo. The key to speed is to only go as fast as you are comfortable. If you start getting uncomfortable you are going too fast and should slow down and get back in your comfort zone. Getting out of your confort zone is a recipe for disaster.

By the way, as you get more confident, you'll start dropping hills faster. eventually, you'll hit a "Death Wobble". It's a torsional vibration from harmonic frequency differences between the balancing of the front and rear wheel. It's scary as hell, but easy to fix. Just tuck a knee into the top tube and don't stiffen or tighten the upper body. It'll stabilize. My Allez has a death wobble right around 45-48 MPH, and then it stabilizes.

and learn how to brake with the front as previously mentioned...
75% of your stopping power is up there!
but you have to learn how to use it or "endo time" it might be!
.
on my Harley I replace front pads more often than rear...

Are your brakes adjusted close to be close to the rims? I see a lot of people that have loose brakes and I wonder how they stop just going 15mph because of how far they have to pull their levers.

This is wild animals' main problem...and the problem many people have with brakes! Disc work so well because the travel from full off to full on is a matter of millimeters. Rim brakes can't be set that close but they can be set much closer than his are. My brakes engage within the first 1/8 of travel and a fully locked before half travel.


Do you know how to corner? It something worth learning for those curvy descents. And feather your brakes as you go to keep the speed in check, rather than slow down - speed up - slow down - speed up.

Sorry but this is the wrong way to go. Constant feathering of the brakes, or even riding them, doesn't lead to better control. Constant friction will only lead to overheated wheels. Brake hard before the corners and ease off in the corner. Control speed by braking hard when needed but don't drag the brakes all the time.

Also, for quick descending stops you need to practice shifting your weight over the back of the bike and using the front brake more than the back.

Shifting your weight back is important but it's not so that you use the front brake more than the back. Most of your stopping power comes from the front to begin with. Moving your weight rearward and down makes the small amount that the rear wheel contributes more effective. The added benefit is that it's harder to pivot around the front hub, i.e. endo, with a lower center of gravity.

Shifting weight to the rear also keeps the rear wheel from sliding. A rotating tire will stop you faster than a sliding one.



and learn how to brake with the front as previously mentioned...
75% of your stopping power is up there!
but you have to learn how to use it or "endo time" it might be!


Actually about 90% of the stopping power comes from the front brake. There are some people arguing that you should only use your front brake because of this. However, what they are failing to realize is that the maximum deceleration of about 0.5g using front brake only can only be attained by lifting the rear wheel off the ground. Until rear wheel lift occurs, the rear wheel and brake contributes to the over all deceleration of the bicycle.

How fast could you safely negotiate the turns on this decent? I have found that terminal velocity for most bikes in most situations is somewhere 45-50 mphs.

Let me clear up a common misconception. Being a clyde does not make you descend faster than the stick people!! On a descent, there is one and only one force that acts on all of us that is responsible for picking up speed: gravity. The acceleration of gravity is constant regardless of your mass (weight). If you remember back to 6th grade science class, this is why a bowling ball and a ping pong ball would fall at the same speed dropped from a building (ignoring air resistance).

But speaking of wind resistance, this is the major force that acts on us when riding. There is also wheel friction, but on a fast descent, this becomes negligible in the face of wind resistance. Unlike gravity, the wind's force is different for all of us. The force of the wind resistance acting on us depends on our aerodynamic shape. The bigger the shape, the larger the surface area for the wind resistance to act on. So us clydes have bigger "billboard" for the wind to act on. And though it doesn't make much difference, the heavier clyde rider will have more rolling resistance (friction) from tire contact with the ground.

Terminal velocity is the point at which the force acting to speed you up (gravity) and the force acting to slow you down (wind resistance) are equal to each other. This is possible because wind resistance increased exponentially with your speed. This means that if your speed doubles, the force of the wind acting against you quadruples. At some point, the resistance forces acting on you equal the force of gravity trying to pull you faster. My personal experience with terminal velocity on my bike is as mentioned above, about 46 mph. No matter how steep the descent, I can't seem to break 46 mph. I actually have a stick buddy who has never broken the 50 mph mark either, so I doubt you will find that you are able to go much faster than this no matter the descent.

So anyway, my whole point is that if you can safely learn to descend at or near your terminal velocity, you can work with nature instead of against it, save a lot of break pads, and have a lot more fun. But, many would argue that 45-50 mph is never safe on a bike, no matter your skills or the road.

But, aren't we harder to stop, because we're bigger? That's the part I was worried about. I wish I'd taken pictures of the down part of the ride, so you could see what I was dealing with. I only got a couple of the trip up, and they don't do it justice anyway.


Thanks for all the advice, everybody! I always use both brakes, and on this hill I used them as hard as I could, but I will try moving my weight around on the bike and see what happens (down hills and around corners).

Hopefully sometime soon I can get my bike in the shop to get the pads changed, brakes adjusted (with me watching).

Also, I am a lady :)

Thanks again!

How fast could you safely negotiate the turns on this decent? I have found that terminal velocity for most bikes in most situations is somewhere 45-50 mphs.

Terminal velocity???? I regularly exceed those speed in corners...I think I mentioned above that I hit 71.4mph on my single bike (verified by my chase vehicle) during RAAM a couple years ago. I've been over 60mph so many times I don't even try and keep count. A gentleman went over 100mph on his bicycle down the side of a mountain a couple years ago.


Let me clear up a common misconception. Being a clyde does not make you descend faster than the stick people!! On a descent, there is one and only one force that acts on all of us that is responsible for picking up speed: gravity. The acceleration of gravity is constant regardless of your mass (weight). If you remember back to 6th grade science class, this is why a bowling ball and a ping pong ball would fall at the same speed dropped from a building (ignoring air resistance).

But speaking of wind resistance, this is the major force that acts on us when riding. There is also wheel friction, but on a fast descent, this becomes negligible in the face of wind resistance. Unlike gravity, the wind's force is different for all of us. The force of the wind resistance acting on us depends on our aerodynamic shape. The bigger the shape, the larger the surface area for the wind resistance to act on. So us clydes have bigger "billboard" for the wind to act on. And though it doesn't make much difference, the heavier clyde rider will have more rolling resistance (friction) from tire contact with the ground.

It's not that simple. We don't live in a vacuum. Since we're in 6th grade, go to your nearest cub scout pine wood derby race and try to win with an un weighted car. I ride with little racer boys and easily smoke them on descents. By your understanding of physics, greater wind resistance, greater rolling resistance etc., they should drop me like a rock on the descents just like they do on the climbs! Man, that'd suck!!!



Terminal velocity is the point at which the force acting to speed you up (gravity) and the force acting to slow you down (wind resistance) are equal to each other. This is possible because wind resistance increased exponentially with your speed. This means that if your speed doubles, the force of the wind acting against you quadruples. At some point, the resistance forces acting on you equal the force of gravity trying to pull you faster. My personal experience with terminal velocity on my bike is as mentioned above, about 46 mph. No matter how steep the descent, I can't seem to break 46 mph. I actually have a stick buddy who has never broken the 50 mph mark either, so I doubt you will find that you are able to go much faster than this no matter the descent.

So anyway, my whole point is that if you can safely learn to descend at or near your terminal velocity, you can work with nature instead of against it, save a lot of break pads, and have a lot more fun. But, many would argue that 45-50 mph is never safe on a bike, no matter your skills or the road.

Maybe if you took your hands off the brakes you'd go faster? 46mph? I'm still pedaling at 46mph!

Terminal velocity???? I regularly exceed those speed in corners...I think I mentioned above that I hit 71.4mph on my single bike (verified by my chase vehicle) during RAAM a couple years ago. I've been over 60mph so many times I don't even try and keep count. A gentleman went over 100mph on his bicycle down the side of a mountain a couple years ago.

Sorry, that's BS. Check your units. 71.4 km/h maybe


It's not that simple. We don't live in a vacuum. Since we're in 6th grade, go to your nearest cub scout pine wood derby race and try to win with an un weighted car. I ride with little racer boys and easily smoke them on descents. By your understanding of physics, greater wind resistance, greater rolling resistance etc., they should drop me like a rock on the descents just like they do on the climbs! Man, that'd suck!!!

That has nothing to do with air drag. The heavier cars win because they weigh more and have greater inertia, so they go farther before stopping on the flat part of the track below the ramp.

Just like the pinewoord car, heavier riders are indeed harder to stop (to answer OP's question). That is why the point of my post was to learn to deal with the speed instead of fighting it.


Maybe if you took your hands off the brakes you'd go faster? 46mph? I'm still pedaling at 46mph!

More BS.

Sorry, that's BS. Check your units. 71.4 km/h maybe

I've done more than 50 mph on a single and more than 55 mph on a tandem. I've also know other people who have done much faster on a tandem. Terminal velocity on a bike would be close to terminal velocity in free fall...around 125 mph. The fastest downhill speed is currently 130 mph (http://www.mtbontv.com/2007/09/130-mph-downhill-speed-record/)...on snow:eek:


More BS.

Depends on gearing. With a rear cog of 11 teeth and a front ring of anything above 48 teeth (48, 50, 52, 53), I can be pedaling at over 46 mph. I'm not sure that even I have the guts to go fast enough to spin out a 53/11 gear. At 50 mph that gear is still feeling like it has another 50 or 60 rpm before you'd be spinning too fast.

Sorry, that's BS. Check your units. 71.4 km/h maybe...

...More BS.

I don't question it. I question the sanity of it (but I also question the sanity of UMCA racers in general... Coming from an RUSA rider, that's saying a lot!)

The first hill on my morning commute is 2.25 mile long with a couple of 10% drops on it. I routinely hit 46 - 48mph coming down that road without even pedalling. If I had a gear high enough, I could put more speed on it; but I max out at a 48/11 which only takes me up to 48 - 49mph if I spin it out at 145rpm.

Altitude and air temperature play a role in terminal velocity. "Thinner" or less-dense air will not produce the same aerodynamic drag as the air that is denser at sea level and on cold weather days.

Warm air and higher altitudes produce higher speeds.

Also bear in mnd the UMCA cyclists are generall down on aerobars, as well and very aerodynamic. I crewed RAAM for Rob Lucas and he topped 70 dropping down into Monument Valley, for example, and also topped 70 dropping down Wolf Creek Pass in Colorado. I was driving the chase vehicle in both instances.

Wildanimals, I think you really need to look at your whole braking system. I would not feel at all comfortable going down a hill on which I was unable to stop easily. You never know what's around the next corner; one day I was bowling along about 30mph on a nice little side street that usually sees no traffic... and found, around a corner, a whole bunch of bicyclists coming up, all over the road. I was really glad for disc brakes and confidence in stopping.

One thing to be aware of, that hasn't been mentioned, is that braking heats the rim, tire, and the air inside. If it gets hot enough the tires will blow off the rims. This happened to a friend of mine on a ride we were doing in the mountains. Fortunately he didn't crash.

So, make sure you have strong brakes, adjusted well. If your rims aren't straight enough to allow the brake pads to be close, then get the wheels trued. Make sure the cables move easily in the casing. If not, squirt some lubricant in there and work the brakes.

Then go out and practice. Find out what the limits of the system are, on a short hill. Find out what at what gradient you can stop easily.

People talk a lot about going fast--I've had bikes up to 50MPH when I had a good view ahead--but rarely about how quickly you can get into big trouble. Is the thrill of the hill worth the risk of serious damage if something around the curve isn't what you expect?

tail winds could also accel your downhill experience, no matterr 50mph on a bike with gravel is really freking scary!

tail winds could also accel your downhill experience, no matterr 50mph on a bike with gravel is really freking scary!

50 - 51mph is my official white-knuckle death grip, chamois-staining speed. I did 54.something last summer and that was just too danged scary for me.

Also alternate between front and back brake, on long descents you can overheat your pads. Alternating gives them a chance to cool off and they will then work more effectively.

By the way, as you get more confident, you'll start dropping hills faster. eventually, you'll hit a "Death Wobble". It's a torsional vibration from harmonic frequency differences between the balancing of the front and rear wheel. It's scary as hell, but easy to fix. Just tuck a knee into the top tube and don't stiffen or tighten the upper body. It'll stabilize. My Allez has a death wobble right around 45-48 MPH, and then it stabilizes.

Ha, that reminds me that around 85-90 on my motorcycle, everything got super smooth. Stayed that way up to the century mark. It was all in the harmonics...

PS - The comparison of pinewood derby cars to bikes is apples to oranges. In pinewood derbies, the primary resistance force is friction, not air drag.

Anyway, I don't know what the actual terminal velocity of a bike is on a given descent or at free fall, etc. I was merely offering up the fact that both myself and a skinny friend of mine seem to max out somewhere just under 50 mph. Just a personal experience...if someone else is able to go a lot faster on a different hill, my "terminal velocity" is by no means backed by calculations of scientific evidence.

Pfft! Work hard going up, then who cares about your downhill speed!:D...Take your time and be safe!:thumb:

I think its more about balance and picking good lines. I rarely use my brakes on a mtn descent. Maybe lite feather of the breaks before hitting a sharp switchback. I dont brake in a turn or I lose the smooth turning effect.

I rarely pedal on a downhill mtn descent. So I find it funny that on the same ride, I hit 45 max and all my friends hit 55 but I'm usually the first one down!:roflmao2:

Lance didn't win the TDF going dowhill!:p

I was merely offering up the fact that both myself and a skinny friend of mine seem to max out somewhere just under 50 mph. Just a personal experience...if someone else is able to go a lot faster on a different hill, my "terminal velocity" is by no means backed by calculations of scientific evidence.
Are you coasting or pedaling? I think most other clydes have a different experience. Personally I seem to out coast lighter folks on the downhills. I often have to apply brakes to keep from running them down, it's kind of annoying.

The science explanation lies in the square/cube law. An object that is doubled in all dimensions has eight times the volume and mass (the cube) but only four times the surface area (the square). So for increasing sizes the mass goes up faster than the surface area, which leads to a higher terminal velocity even with greater drag.

With gravel, I don't like to go much over 25 mph either. There is just no way to stop fast while going downhill on gravel. I would have stopped as well.

On pavement, there are a lot of hills around here where I hit at least 45 mph on a regular basis. I've hit 55-57 mph a few times. I don't feel safe spinning my pedals over about 95 rpm when I'm going over 40 mph down a hill, so all of the top speeds are with me coasting downhill in a tucked position (butt off the back of the saddle, feet at 3-o-clock and 9-o-clock, collar-bones hovering over the handlebar, hands in the drops, with a flat-back). My top speed so far is 57-58 mph. I could have gone faster on a straighter section of road, but I usually wimp out and apply the brakes on the roads that I've gone that fast on. I find even shallow curves intimidating at that speed. The prospect of running off the road, or crossing the lane and slamming into oncoming traffic is not worth the risk to me.

With gravel, I don't like to go much over 25 mph either. There is just no way to stop fast while going downhill on gravel. I would have stopped as well.




I hear ya. It's not so much a fear thing as an "Is it worth it" moment. Above 30, I start considering what happens if I fall. I can handle road rash, but cycling is supposed to be fun.

After 50, discretion is the better part of valor

Altitude and air temperature play a role in terminal velocity. "Thinner" or less-dense air will not produce the same aerodynamic drag as the air that is denser at sea level and on cold weather days.

Warm air and higher altitudes produce higher speeds.

Those are certainly factors, however, they'll only cause minor changes around the terminal velocity. Terminal velocity is going to be a lot higher than 46mph:thumb:

Those are certainly factors, however, they'll only cause minor changes around the terminal velocity. Terminal velocity is going to be a lot higher than 46mph:thumb:

http://www.denysschen.com/catalogue/density.asp

Sea level @ 30F = 0.080 Lbs/Ft^3
7000 feet @ 90F = 0.055 Lbs/Ft^3

http://www.denysschen.com/catalogue/density.asp

Sea level @ 30F = 0.080 Lbs/Ft^3
7000 feet @ 90F = 0.055 Lbs/Ft^3
So how does that affect terminal velocity? Since drag varies as the square of velocity a 45% change in density would give a 20% change in terminal velocity. That does seem like more than a minor difference.

But I think the real reason you hit higher descent speeds at high altitudes is because or the dearth of long steep downhill grades starting at sea level. :lol:

I hear about guys that don't apply brakes regularly hit 60-65 mph, going down the back-side of the local Rist Canyon loop (from the top of Rist Canyon, going down towards Stove Prairie: near Fort Collins, Colorado). Those guys are NUTS! Little dips in the road make both of my tires leave the ground on that road when I'm going over 50 mph, and you can't see around those shallow curves...its not safe.

Every other time that I'm up there, I see things in the downhill lane like slow-moving tractors, stopped vehicles (usually construction/utility or ranchers stopping to fix fences, phone lines, signs or reflector posts, etc.), deer eating the salty grass near the edge of the road, small groups of cattle that got out of the fence, etc. Not safe. Not safe at all.

So how does that affect terminal velocity? Since drag varies as the square of velocity a 45% change in density would give a 20% change in terminal velocity.

Check your math, the change in resistance is not linier. 20% is not correct, even if it was, it would be significant.

Michael

Here's the hill! http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=scappoose,+or&sll=37.0625,-95.677068&sspn=45.467317,78.837891&ie=UTF8&ll=45.755787,-122.903452&spn=0.019672,0.038495&t=p&z=15

It's JP West Rd. It doesn't look as curvy from space, but much* of the time you can't see what's coming up. You guys would probably think it is baby stuff! But I found it harrowing. haha. :(

I think my brakes are okay. They aren't in a state of disrepair or anything. They are very close to the rims, I have the levers adjusted so I don't have to pull them too far to get the brakes fully engaged, and the pads are older but not worn down to a fraction of a mm or whatever. My wheels are true! It was just so steep. I'd get myself down to 3mph by not-quite-fully engaging the brakes, and when I'd let go again, I'd be going 30 in like 5 seconds (please don't do the math on this), without pedaling. Out of control! I'm going to try again and see what happens, but I'm too busy for the next couple days :/

The science explanation lies in the square/cube law. An object that is doubled in all dimensions has eight times the volume and mass (the cube) but only four times the surface area (the square). So for increasing sizes the mass goes up faster than the surface area, which leads to a higher terminal velocity even with greater drag.

+1.

This is why the big guy leads the train downhill.

Check your math, the change in resistance is not linier. 20% is not correct, even if it was, it would be significant.

Michael

OK then, lets walk through the math. I'm sure it will be riveting.

0.080 / 0.055 = 1.4545 i.e. a 45% difference in density.

square root of 1.4545 = 1.2060

You got me, I should have rounded that to a 21% increase in terminal velocity given a non linear squared drag function. Why did you think I was talking linear? A 20% increase is the difference between 40 and 48 MPH, that sounds significant.

Do you have a different answer for the increase in terminal velocity based on the density changes you mentioned? You seem certain 20% is wrong. I'm not trying to be argumentative, nor am I in a huff at having my math skills questioned (well, maybe a little), just wondering.

It's too late in the day, but I still don't buy the 20% is insignificant.

Here's the hill! http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=scappoose,+or&sll=37.0625,-95.677068&sspn=45.467317,78.837891&ie=UTF8&ll=45.755787,-122.903452&spn=0.019672,0.038495&t=p&z=15

It's JP West Rd. It doesn't look as curvy from space, but much* of the time you can't see what's coming up. You guys would probably think it is baby stuff! But I found it harrowing. haha. :(



That is no small hill there young lady. If you climbed that, I am quite impressed. I mapped the hill and it looks like about 2 mile with about 900 feet of decent. :twitchy: Parts of it are showing a 19 percent grade, so it is indeed steep and cause you to gain speed quickly.(The mapping site may not be totally correct, but it does give a general idea of what the hill is like) I have a similar hill down here that I ride the brakes on.

On a side note, we are doing a Clyde/ Athena ride down in Albany on September 5th if you would like to join us.:) It will be a 40-50 mile no drop ride, just so you know.

I'd get myself down to 3mph by not-quite-fully engaging the brakes, and when I'd let go again, I'd be going 30 in like 5 seconds (please don't do the math on this), without pedaling.

Spoil sport.

Oh what the heck. 30 MPH in 5 seconds is an accelleration of 8.8 ft/sec, which is about one quarter gravity. It's probably not a simple as that implying a 25% grade, but might not be far off.

From that terrain map it looks like the steep section drops 320 feet in altitude in about 2500 feet of road. That computes as a 12.8% grade if I read the map correctly. While that's not insane it's pretty steep. My claim to fame is once climbing 400 feet in a mile even. That 7.6% average grade was plenty enough to give me a bad case of the willies going back down. But I have a problem with heights and the descent set off my acrophobia.

To the OP if you want to stop fast the easiest way is to shift wieght to the back of your seat or even better get off seat and have wieght over the rear wheel and then brake, you will stop in a hurry.