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Old 02-02-12, 04:43 PM   #1
TomD77
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Energy and velocity lost on a rough road

There has been a 2-1/2 mile section of one of my most common routes that is (was) the absolute worst stretch of road that I've ridden. The term "rough" doesn't begin to describe it. It was rough both because of the nature of its' construction and its' condition.

The section of REALLY bad road that I would first encounter was right after what passes for a major climb around here, about 150 feet over 3/4 mile. It is a couple of hundred yards downhill at about a 2% slope and I would almost always coast down it at a gravity propelled 12 MPH. That was fine with me because to go any faster than 12 on this section of road would literally blur my vision.

It was repaved a couple of weeks ago () and I've ridden it around 5 times since. What was a 12 mph gravity only coast is now a 17 MPH gravity coast. That means that there was enough energy expended in vibrating the bike to reduce the speed by 5 MPH. I guess that if you bother to think about it, the energy necessary to rattle you about has to come from somewhere but it has to be a surprise that it has this high a velocity cost to it.
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Old 02-02-12, 05:24 PM   #2
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Hence the use of fatter, less inflated tires on crappy surfaces to keep your speed up............each individual bounce and mini-second airborne slows your speed even as you back off on pedaling to save your skeletal system. When the pavement varies repeatedly is perhaps the most pain. Living in rapidly down-and-out CA, where declining property values mean less tax monies while a greater demand is placed on public services...........means the roads that take you to the best places are the ones repaired least. In a few years I may be riding a crossbike with Jack Brown blues. And subject to vibration induced hemmorhoids (sp?).
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Old 02-02-12, 06:00 PM   #3
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Yes I found the same thing when they paved a section of roadway that went over Usery Pass. Its much easier to crest not that its smoother.
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Old 02-02-12, 06:16 PM   #4
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From experiencing many types of road surfaces in our travel, my wife and I came up with this rough approximation of the effect of road surface on speed. These are purely empirical, but we based it on a lot of miles. However, there are other variables that affect rolling resistance.

With loaded touring bikes, if we could cruise about 14 mph on relatively smooth pavement then:
Fine gravel -5 mph, cobble stones -4 mph, packed sand -4 mph, paver blocks -2mph to -3mph, rough pavement -2 mph to -3 mph. Road surface really can make a difference.
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Old 02-03-12, 07:32 AM   #5
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Pretty sure I know the stretch you are talking about Tom. I'd wager the energy expended in vector motion other than forward motion caused by the rough grounds' shaking and bouncing takes up the forward speed.

Just a hunch, you could probably figure it out with a topographic diagram in small enough scale. Or, just say the old pavement eats up your forward movement and the new smooth pavement rolls better.

Bill
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Old 02-03-12, 07:42 AM   #6
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Reminds me of that Rawhide TV song, rollin, rollin, rollin, rawhide....keep them doggies rollin
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Old 02-03-12, 08:04 AM   #7
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Pretty sure I know the stretch you are talking about Tom. I'd wager the energy expended in vector motion other than forward motion caused by the rough grounds' shaking and bouncing takes up the forward speed.

Just a hunch, you could probably figure it out with a topographic diagram in small enough scale. Or, just say the old pavement eats up your forward movement and the new smooth pavement rolls better.

Bill
I had installed an organic accelerometer on my bike (me) in an attempt to determine the frequency and amplitude of the vibration. Due to calibration problems, the accelerometer meerly yielded the information that the vibration was severe enough to Hertz.

That was near the golf course entry on the backside of NAS Whiting Field.
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Old 02-03-12, 08:20 AM   #8
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Do the same experiment with a knobby offroad tire and a slick...that IS rolling resistance weather it is the tire or the road. This is my FIRST foray into the 50+ threads...I am an official member of that set this month! I just got back into road-biking a couple years back when my 12yr old got into it. After a 25 mile ride, him on a road bike, me on a HEAVY MT Bike with big knobbies....I decided I needed a road bike again! Roll On...Get Fit!
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Old 02-03-12, 08:56 AM   #9
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Was probably too much air in the tires for the road condition. Not that you'd want to decrease the pressure unless your whole ride was on road like that.
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Old 02-03-12, 10:03 AM   #10
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Was probably too much air in the tires for the road condition. Not that you'd want to decrease the pressure unless your whole ride was on road like that.
I'd ridden this stretch so many times (100+) that I'm sure I rode it in all sorts of tire inflation states from a fresh pumped 120 to a week later 70 and it was variations of horrible. But given that it was 2.5 miles out of 25-40 miles on that route, don't think I'd allow that stretch to dictate, I just went slow.
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Old 02-03-12, 02:50 PM   #11
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One of the tricks I found when doing the Offroad Enduros I used to do--Was to find the firmer ground to get traction. Power expended on loose soil or scree was tremendous. If I could also make that soil "Smooth"- then it was a bonus.

When i rode in France it was mainly on the backroads and I looked for slopes. At the speed I went at up those slopes (Or didn't)- I never noticed any problems but as it was usually an out and back--The downslopes used to be painful. Must be the same with some of the Chip n Seal you have over there. Riding over 1" spaced out rocks must be painful- tiring and slow.
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Old 02-03-12, 03:32 PM   #12
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One of the roughest roads I ever rode, was the bike paths in the Netherlands between Vlissingen and Rotterdam. They were cobblestones. All the natives on the paths rode a little slower and had their tires deflated just a bit.
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Old 02-03-12, 03:48 PM   #13
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I'm limiting my use of the road bike with 700x24 tires to known routes that are smooth. I've started depending on my Soma Double Cross with 700x32 Vittoria Hyper slicks for pavement that should be smooth, but sometimes isn't.

Smaller road bike tires are insufficient on truly bad pavement. Larger tires are faster and safer.

I came down a hill at 45 mph and could not avoid a fry-pan sized pothole in November. With a 700x32 tire at 85 psi, it was no issue. On a smaller tire, it might have been a disaster.
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Old 02-04-12, 05:10 PM   #14
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Energy and velocity lost on a rough road? Yep. Over the last 27 years I've been consistently faster on my Alex Moulton bike.
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