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What makes one recumbent faster than another?

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What makes one recumbent faster than another?

Old 07-17-08, 11:10 PM
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fromabuick6
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What makes one recumbent faster than another?

Given riders of equal strength/ability, what factors make a recumbent "fast." I was looking at highracer today, a Bacchetta Corsa, and the salesman said it was faster not only because it was bit lighter, but because it was more aerodynamic than one with a small front wheel. Also it has skinny tires.

Then I was looking online at a "Gold Rush" recumbent bike, which is supposed to be fast. It's a LWB bike, and I'm guessing the fairing makes it aerodynamic--is that the main factor in speed? Again, I'm assuming the rider is a strong rider.

I'm not being sarcastic, just not sure why one bike would be faster than the next.

The Bacchetta bike is a nice looking bike, hoping to take it for a test ride, didn't have time today. Would like to try one of the LWB bikes too but they seem harder to find.
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Old 07-18-08, 02:15 AM
  #2  
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CD <- Coefficient of Drag is the name of the game on the flat. The lower the better. If a salesman says to me that bike A is faster than bike B then I would ask him/her "show me the independent wind tunnel test that determined the CD for bike+rider for each model"

When you get into the hills then it's strength/weight ration, and IMO if you can't climb on a sub 25lb bike then the limiting factor is not the bike.
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Old 07-18-08, 06:36 AM
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As far a skinny tires go i think its to do with rolling resistance. Skinny tyres have less RR than fat tires. I Think it also has to do with the "hole" you punch in the air. As you can probably tell i'm not an expert.
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Old 07-18-08, 07:27 AM
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Multipe factore. The geometry of the bike, the wheelset, the components, the wind drag (as cycloholic said - CD) and frontal wind area, thinner tires, the bike weight, how it fits you, etc.
The engine! As pointed out - not a factor with the bike itself, other than how well the energy transfer from the engine to the wheels might be.
There's lots of good fast bikes out there - try as many of them as you can. What is 'right' for one person might be not so good for another.
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Old 07-18-08, 09:19 AM
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Originally Posted by Myqul View Post
As far a skinny tires go i think its to do with rolling resistance. Skinny tyres have less RR than fat tires.
...or not. On a perferctly smooth surface that's true, but I've never had the opportunity to ride on a perfectly smooth surface. There have been "real world" comparision tests that have shown a measurable difference in rolling resistance between tires of identical construction (same brand and model), and different widths. The wider tires are faster EVERY TIME. And the rougher the surface, the greater the difference. Yeah, a 25mm Stelvio is going to be faster than a 32mm Kenda, but that's comparing apples with, um, "road apples".

The biggest factor in bike speed is aerodynamics. Period. As a rule, high- (or low-) racer is faster than a more upright SWB or unfaired LWB because the more reclined riding position gives you less frontal area. Putting a fairing and bodysock on a LWB changes everything. Frontal area becomes greater, but the CD is reduced so drastically that overall drag goes way down. This also explains why some of the fastest recumbent times in the 2007 PBP (1200k/750 miles w/33k feet of climbing) were done on (in?) velomobiles - 70lb, hard-shell faired trikes. That said, I'm sticking with my high racer for the foreseeable future. I'm just not ready to ride something as goofy-looking as a socked LWB or a velomobile.


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Old 07-18-08, 04:31 PM
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fromabuick6
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Thanks for the input. I was mostly wondering why putting a large wheel in front, as in a highracer, would account for more speed aside from the aerodynamic factor, but I guess that's it, wind resistance is the primary factor.
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Old 07-18-08, 06:09 PM
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Don't forget - and it isn't only 'skinny' tires - but, the more air pressure the tire will take (120 psi vs 50-85) makes a big difference in rolling resistance. But, with my 1.25 tires taking 120 psi, they do roll as well as the 700c x 23 on my DF. I can easily tell the difference if I forgot to check the tire pressure and it is a little low after I take off.
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Old 07-18-08, 07:14 PM
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I passed a Bacchetta carbon aero (with aero wheels) on my steel Rocket once...
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Old 07-19-08, 05:20 PM
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Test rode a few bikes today. My favorite was the Rans V3 titanium, until I found out the price -- $5200. Nice bike though. I liked it a bit better than the Corsa, seemed about as fast, and more stable. Too bad only the richest kings of Europe can afford one.
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Old 07-22-08, 06:00 PM
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Heck, I tell my upright bike riding buddies that the reasons recumbents usually have a small wheel on the front is by doing it that way you are always riding downhill, therefore faster! :>D
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Old 07-23-08, 08:34 AM
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I've got both a Tour Easy (LWB) and a Rans F5 (SWB High Racer). I'm a couple of MPH faster on the F5 due to the much better aerodynamics of the position. I know that a lot of factors enter into the equation but I've never had a bike that will carry speed over distance like the F5. The TE has me in a much more upright position, catching the wind full on my chest, but is a bit more comfortable over the long haul.

I suspect that the TE with a fairing would give the F5 a run for the money, but that's for a future paycheck.

BTW, the new F5 is a fantastic deal for the price.

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Old 07-23-08, 10:43 AM
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I would like to try all these bikes. Unfortunately, there aren't many recumbent dealers nearby, and even if you can find one, the chances of them having a certain model in a certain size are fairly slim. And one thing I've noticed is that recumbents ride very differently from one model to the next. With a DF bike, you more or less know what you're going to get, so ordering one without a test ride isn't too big of a risk. Such is not the case with recumbents. I figure I'll just take my time and try and ride as many as possible.
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Old 07-23-08, 02:12 PM
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Originally Posted by fromabuick6 View Post
I would like to try all these bikes. Unfortunately, there aren't many recumbent dealers nearby, and even if you can find one, the chances of them having a certain model in a certain size are fairly slim. And one thing I've noticed is that recumbents ride very differently from one model to the next. With a DF bike, you more or less know what you're going to get, so ordering one without a test ride isn't too big of a risk. Such is not the case with recumbents. I figure I'll just take my time and try and ride as many as possible.
You are Absolutly right about different 'bents riding totally differently. There is FAR more difference between how my Tour Easy and the F5 handles than between any two DF bikes I've ridden. Not that one is 'better' than the other, but the F5 is much 'sharper' handling, the TE tracks better at low speeds, just a world of difference. Even my Motobecane and my LHT are kissing cousins compared to these two. I don't even want to think about trying a low-racer, I'm not sure that my reflexes are fast enough to enjoy the ride..

Best bet you've got is to talk to as many riders as you can, in person and online. Remember everybody thinks their bike is the 'best', so take what you hear with a grain of salt at times.

Except for me, I'm always 100% accurate and Unbiased

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Old 07-23-08, 02:47 PM
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There are some pretty lightweight highracers out there that approach reasonable road bike weights (Carbent Sea Dragon is around 17 pounds). I rode a 200 in the Sierras this year where for most of the ride I was accompanied by a buddy on one of those 17pound Carbents. Even at 17 pounds he lost the pack on the long climbs (this guy is fit, Furnace Creek 508 solo rider etc) but on the descents the aero advantage was incredible. On one long mountain descent on 395 there was me, him and a tandem. We were well above speeds where pedalling was possible and I managed to lose the draft of the tandem and it started to pull away. The guy on the high racer overtook me and started accelerating away like he had an engine (without pedalling) and proceeded to catch and drop the tandem.

He would probably have been faster still on a low racer recumbent.

Efficient drive train, stiff frame, aerodynamics and lightness makes some recumbents faster than others.

Last edited by rumbutter; 07-23-08 at 02:51 PM.
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Old 07-26-08, 07:19 PM
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Originally Posted by ModelT View Post
I passed a Bacchetta carbon aero (with aero wheels) on my steel Rocket once...
Did you hold onto your lead after the Carbon Aero rider got on his bike and started pedaling? I like Rockets, but I don't normally think of them as being particularly fast.

Fast attributes, not necessarily in any particular order:
1. light weight
2. stiff frame *and seat*
3. low frontal area
4. low CD
5. skinny HP tires
6. big gears
7. aero wheelset (helps with #4)

To expound a bit on some of the points: on #1, if the frame flexes, you're losing power which is not returned in a form that is usable to power the bike down the road. On #2, if you have a mesh seat, you're losing power to the mesh on every pedal stroke -- no matter how tight it is. On #5, if you have fat tires, they will be heavier (harder to spin up) and will have more frontal area than a skinny tire. And #6, a fast rider will bury a rider who runs out of gears of a downhill. Go ahead and coast, but you can't win of you don't pedal.
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