Can't break 40mph downhill

[wilmar13]

[iAh yes, but it's really the frontal cross-sectional surface-area which faces the wind that we're concerned with. And this frontal surface-area does increases with bigger human beings. This increases with the square^2 function of size, yet the mass will increase to the cube^3 power of size. This means that a human that's twice as big (blocking twice as much wind) will weigh four times more... So big people will go down hills faster because they have more pounds pushing each sq.in. of surface-area that's facing the wind.

Yep dead on...

Heh, heh... work out the math (it's in any high-school physics book, you don't even need to know calculus ). Going twice as fast will maybe increase rolling resistance by 2x at most, in many cases, the higher velocities across the bearing surfaces will result in less friction than before, however the frictional drag on the tires will go up linearly with speed. So overall total roling-resistance increase will be less than 2x with 2x the speed. However, the air-resistance (drag) on that object will increase by a factor of 4X and the power required to overcome that extra drag will be increase by a factor of 8X... :

Just in case it wasn't clear, not only is rolling resistance miniscule compared to air drag, and the resistance from the bearings is a tiny % of the rolling resistance (most of it is tires)... when comparing two wheels one with **** bearings and one with great bearings, as long as they are both in good shape, of this totally negligable contribution, there is no real difference % between the two in this application anyway.

Good idea!!! I plan on doing that exact mod! To go along with my turbocharged barstool and my turbo+nitrous scooter:

That is crazy, are they really yours?

 

[wilmar13]

Was putting this in laymans terms for you. Any idiot could tell you that this is not a correct stetement.

Don't worry some people like to treat what you post on a cycling forum as peer reviewed research (including me sometimes) in order to stretch thier penises a little.

 

[wilmar13]

Another way to get some more speed on the downhills is to just get more weight without increasing drag. Put a rack on the back of your bike and strap a couple hundred-pound lead-weights to it. Place the weights high so that it's flowing in wind that's already parted by your body & butt. You'd be amazed at how much faster you'll go on the downhill.... just be careful about stopping at the bottom....

Or take a spin on a tandem... without much effort you can reach some crazy scary speeds vs. a single.

 

[velomanct]

you need a steep hill, doesn't have to be a mtn at all. last week I went down the local "wall" in town. it's about 500meters long, max grade of ~17%, average around 12%. I can go from 10-45mph in 9 seconds, and I topped out at 57mph, sprinting in the saddle in my 53x12. I'm 6'1" 188lbs.

I think you need to put more effort if you want to break 40mph on a downhill. You got to sprint in the saddle.

 

[wiredued]

I just took the aerobars off and I'm debating the handlebar bag's aerodynamics maybe I'll get a bag for under the seat instead. Do you think that would help?

you need a steep hill, doesn't have to be a mtn at all. last week I went down the local "wall" in town. it's about 500meters long, max grade of ~17%, average around 12%. I can go from 10-45mph in 9 seconds, and I topped out at 57mph, sprinting in the saddle in my 53x12. I'm 6'1" 188lbs.

I think you need to put more effort if you want to break 40mph on a downhill. You got to sprint in the saddle.

 

[slickdemo]

Do you seriously have a handelbar bag, or are you making a joke? I ask that question sincerely, and maybe that alone give you your answer... at least in the U.S. most riders you'd see with handelbar bags would be either novices or "eccentrics". You may have noticed at the race you attended that nobody had a handelbar bag? I don't think that's keeping you from breaking 40mph, but it suggests what it might take is just a little more riding, getting some input on other aspects of your equipment, on your position... generally becoming a bit more "seasoned" as a rider. I'm trying not to be a snob, because it rocks that you're out there riding, going to races, and trying to break 40mph, but I can't shake the mental image that comes with a handelbar bag...

 

[wiredued]

Yes I actually have a handlebar bag it's a good place for a peanutbutter and jelly sandwich on long rides. I see alot of eccentrics on my rides I guess. I have to admit I've never been past by a bike with a handlebar bag yet but I have past a few without them it must bruise there ego a little especially when they see the rear rack and trunk bag. You've got to keep it challenging.

Do you seriously have a handelbar bag, or are you making a joke? I ask that question sincerely, and maybe that alone give you your answer... at least in the U.S. most riders you'd see with handelbar bags would be either novices or "eccentrics". You may have noticed at the race you attended that nobody had a handelbar bag? I don't think that's keeping you from breaking 40mph, but it suggests what it might take is just a little more riding, getting some input on other aspects of your equipment, on your position... generally becoming a bit more "seasoned" as a rider. I'm trying not to be a snob, because it rocks that you're out there riding, going to races, and trying to break 40mph, but I can't shake the mental image that comes with a handelbar bag...

 

[wiredued]

I just talked to a more seasoned rider he said he did 57mph downhill with a massive tail wind. Is that how most of you got high speeds on down hills using tail winds?

 

[velomanct]

I just talked to a more seasoned rider he said he did 57mph downhill with a massive tail wind. Is that how most of you got high speeds on down hills using tail winds?

Not neccessarily. You need to find a steep hill and sprint it! None of this coasting aero tuck baloney.

 

[wilmar13]

Not neccessarily. You need to find a steep hill and sprint it! None of this coasting aero tuck baloney.

I agree... if you think it is fast, all that means is that you must live in Kansas or have never ridden down a steep mountain road. The same place where I would need to tuck and sprint to break 60, I could easily break 50 sitting upright with an unzipped jersey while feathering the brakes.

 

[BrianCRPS]

In my humble opinion breaking 40 should be relatively easy on a short steep downhill. You just need to get up to the top spped that you can in your highest gear and spin as fast as you can and when you are spun out then make sure you are in the tightest tuck you can head down and just enjoy the going fast.

Getting much higher than 50 generally takes a long hill that is steep as well. I have personally hit around 53 - 55 in a race before but again that was on a steep long hill.

What size/width of tires are you riding?

 

[wiredued]

I don't think I can spin out a 52x11 but I get close before tucking I am using 700x23 tires 130psi.

In my humble opinion breaking 40 should be relatively easy on a short steep downhill. You just need to get up to the top spped that you can in your highest gear and spin as fast as you can and when you are spun out then make sure you are in the tightest tuck you can head down and just enjoy the going fast.

Getting much higher than 50 generally takes a long hill that is steep as well. I have personally hit around 53 - 55 in a race before but again that was on a steep long hill.

What size/width of tires are you riding?

 

[slickdemo]

Maybe the problem is your speedometer. Are you sure it's calibrated right? There's little else to explain this much difficulty breaking 40. If you're even coming close to spinning out a 52-12 then you should be going nearly 35mph at that point. If you hit that point at the top of the hill then tuck and can't break 40, maybe you're handelbar bag is acting like a parachute... or maybe you black out at 39 mph and only regain consciousness when your speed drops back below 39...

 

[wiredued]

I ditched the handlebar bag and got an under the seat bag. I haven't made another downhill speed attempt yet but I did manage to hold 20mph for 20 minutes on a flat paved rail trail with no wind. I've heard that is a sign of a good recreational rider.

Maybe the problem is your speedometer. Are you sure it's calibrated right? There's little else to explain this much difficulty breaking 40. If you're even coming close to spinning out a 52-12 then you should be going nearly 35mph at that point. If you hit that point at the top of the hill then tuck and can't break 40, maybe you're handelbar bag is acting like a parachute... or maybe you black out at 39 mph and only regain consciousness when your speed drops back below 39...

 

[slickdemo]

yes, that's good, which makes it all the harder to understand why you're not breaking 40. it really could be the speedometer. you may want to check the owner's manual and make sure you've input the right # for your wheel and tire size, possibly even properly measure the wheel circumferance to be really accurate.

 

[wiredued]

The rail trail has mile markers on it and my trip meter agrees with it and back in July I went on a 93 mile ride according to www.mapsonus.com (avoid major highways option) and when I arrived at my destination the trip meter said 93 miles. I ride down the road past many radar zones with speed displays and it always matches my speedometer. I have tried to break forty on my mountain bike with slicks, aerobars and a completely different bike computer on it and only hit 39mph which is the fastest I have ever gone on a bike. On my road bike I have only hit 38mph.

yes, that's good, which makes it all the harder to understand why you're not breaking 40. it really could be the speedometer. you may want to check the owner's manual and make sure you've input the right # for your wheel and tire size, possibly even properly measure the wheel circumferance to be really accurate.

 

[Peka]

'Cause 40mph on a mountain bike would be pretty good

Actually it's not that hard. Of course, you'll need a downhill, but I can manage 40mph on mine....

 

[huhenio]

Actually it's not that hard. Of course, you'll need a downhill, but I can manage 40mph on mine....

I brake the 40 mph mark every time I go riding. The hill drops 120 feet over .7 miles. Like a 7 % or something. At the bottom of the hill I pass the 40 mph every time.

This guy needs to find longer, steeper hills.

I am 6' 1" and 200 pounds on a hybrid!!

I wonder how much faster would I do in a road bike.?

 

[Lonnie Utah]

Actually it's not that hard. Of course, you'll need a downhill, but I can manage 40mph on mine....

I had a guy (friend of a friend) tell me over the weekend that he did 52 mph on his MTB. I was thinking to myself "Well that's B.S." Not that it's not possible, but if he could really do it, he'd be riding as a NOBRA pro (which he isn't).....

L

 

[gntlmn]

I was at a race recently and couldn't believe the speeds they were traveling at, the previous year I was told the fastest riders were hitting 68mph on radar. How is this possible I can't break 40mph downhill I'm 6' 1" 195lbs isn't weight an advantage for downhill?

When in doubt, consider the simplest reason: the speedometer is not working properly. Try with someone else's bike and see if you get over 45 mph. You probably would.