Recumbent - Maximum top speed on flatground?

I have a few questions for you guys.....What kind of gearing does a bent use (I know wheels are smaller) in gear inches?

Top Speed wise.....How much faster is a bent than a upright roadie?

I have a few questions for you guys.....What kind of gearing does a bent use (I know wheels are smaller) in gear inches?

Top Speed wise.....How much faster is a bent than a upright roadie?

My fastest bent has a 120 gear inch flat-nowind-gear ratio; the top ratio for downhill and tailwind is 131 gear inches (which coincidentally is a 53/11). 90-110 is typical for top bent bike gears, a few such as Rotator have ratios in the 140's. Triikes typically slightly lower, but a few have 130 gear inch ratios in high.

Low ratios for most bent bikes are in the 20's, trikes in the teens (they don't have low speed balancing problems).

On flat pavement bents are typically 5-6 mph faster than roadies, usually slower uphill, although a few such as Lightning have seatbacks designed to let the rider push off the back with their leg and actually climb faster than uprights. The better climbing bents typically have more upright seats so they sacrifice some aerodynamic edge relative the lower seatback bents.

Greggk's site shows about a 20-25% speed advantage for unfaired recumbents over road bikes for the same amount of power.

http://www.adventuresofgreg.com/HPVMain.html

My bents all have about the same gear inches as road bikes, say 118-120 inches. Top speed is virtually the same as road bikes.

I run a 56/11 and at times a 60/11 This is on a 650c rear tubular. Top speed with the 60/11 on a flat with no wind was 45.3 mph

Depends on the motor sitting in the seat:) On the flat, owing to less wind resistance at higher speeds, a strong rider on a bent will always be faster than the same rider on a roadie.

I have a few questions for you guys.....What kind of gearing does a bent use (I know wheels are smaller) in gear inches?

My Burley Canto is 23-123 gear inches.

BTW, all bents do not have smaller wheels.


Top Speed wise.....How much faster is a bent than a upright roadie?

This is dependent on the engine and the bike too. Some bents are inherently fast due to geometry and such.

MEB- are you sure that 5 - 6 mph faster for an unfaired bent is correct? Seems like a lot to me. I'm happy to wish that as a bent owner, but it's hard to believe.

That website you referred to appears to only guess that bents are 25 to 30 percent faster, but no evidence to support that. Gregg draws his conclusion from looking at the records (which are from custom streamliners - not the bents we buy in stores).

The Mueller Fairing Folks did a study at the Wright Brothers Wind Tunnel and found that an unfaired Vision Saber (a quality hi - racer) was only 3.3 mph faster at 20mph than a roadie using his top bar. If the roadie went into his aero tuck, he was only .5 mph slower. They also tested an unfaired Vision R40 which was only .3 mph faster than a roadie on the top bar, and 1.4 mph faster with a fairing. If the roadie was in aero tuck, then the roadie was actually faster. Even if faired, the R40 was still 1.4 mph slower.

But we should be glad to know that as soon as the roadie gets tired and comes out of that aero tuck, we see our advantage realized.

This study held all of the variables constant, except for wind resistance, which is really what we're talking about here, right? The study wasn't to decide who's faster, it was looking at the effects of fairings, and that was an interesting side fact that came out. It looks like my Mueller Fairing will add 1 mph to my bent at 20 mph. I was hoping for more of a boost, but 1 is 1, and I'll take it. If you have a Saber, or some other hi-racer, it may be non-existent. Now to really get off track from this thread, I'd like to know if the additional weight (noticed when going uphill) is really worth that 1 mph boost.

If I have totally missed the mark here, somebody straighten me out! Check the study at the Mueller website. I would be GLAD to be wrong!

Glass packer, your sources sound a good bit closer to reality. The primary bent advantage is decreased wind resistance. Even the most tricked out carbon or Ti
bent is going to be 3-6# heavier at 20-24# than an equivalent ($) DF at 16-17#
and from analyticcycling.com for a given power input a lighter bike will be faster,
though the steady state difference will be less than the weight diff implies, on the flat.
Bent air resistance relates mostly to how low the bike is to the ground and the frontal area of bike and rider. The flatter the rider, more recumbent that is, the lower the
frontal cross section and hence air resistance. My Rotator Pursuit puts my legs nearly
horizontal but the seat recline is only 10-15D or so, this is only a little different than
what a svelte roady can achieve with an extreme tuck. If I were reclined to 20-30D, my cross section would be similar to what the Dutch low racers achieve. In practice
what I get with my position is equivalent to sitting in behind a DF rider which is less
than 20%. When I had the fairing on, I no longer gained ANY benefit from sitting in
behind a roady. Effort was the same beside or behind the DF rider. Never did any
deliberate coast downs on longer hills with and sans fairing but the few experiences I had suggested a 3-4% speed increase on hills of 300yd or so length and 50-80'
elevation drop with fairing. The one hill where I compared DF and bent that my record speed is 52mph on a DF, I did 51mph on the Rotator pursuit without fairing. Most of the time I do this hill on the DF and typically vary from 49 to 51mph. Steve

I did the hilly hundred last weekend and was by far the fastest bike at the event. top speed for the weekend was 55mph. Even Frankie Andrea..........riding in a pack with other fast cyclists couldn't hang with me riding solo. I was holding a 24.5 mph average for the first 30 miles on saturday. Take into account the hills on this course. Single upright bikes are no challenge whatsoever for a lowracer. Packs can be a challenge sometimes. What usually happens though is that they chase me as a pack for a few minutes then riders start dropping off ..........the pack gets smaller......... 1 lone guy who thinks he's superman........ comes off the front in a desperate attempt to close the gap......... he burns out and then I'm long gone. Passed a couple thousand riders this year. Passed them like passing fenceposts one after another. I'm sorry, but a lowracer is way faster than a DF bike. Most DF's have to draft to even go remotey fast for any given distance. 10 mile timetrials and less..........a DF can make pretty good speed but will still be dropped by a lowracer with a good engine.

http://www.biketcba.org/TRICORR/rides/hilly2004/report.html

http://groups.msn.com/BicyclingForumPicPost/trainingsetuppics.msnw?action=ShowPhoto&PhotoID=7408

http://groups.msn.com/BicyclingForumPicPost/trainingsetuppics.msnw?action=ShowPhoto&PhotoID=6996



The tailfairing gives a good 4 mph to top end and a good 2.5 additional cruise speed

I guess it also depends on the condition of the road. I've never seen bents on anything but idyllic roads. How does one "shock absorb" road imperfections?

My rear wheel is a 26x1.25. Which is a common wheel even for some wedgie bikes like womens & tandems. Because of that I am able to use standard gearing. The front chain rings are 52, 42 & I think 32. The rear cluster is a 9 speed cassette which is 11 through 24 I think, don't remember right off. I have found that this set up is common on several road bike styles. Especially touring bikes.

My flat ground top speed:
Tail wind assisted - 28 mph, sustained for about 4 miles.
Unassisted - 22 mph, sustained for about 6 miles.
The only reason I could not sustain it any longer then that is I had to start climbing hills & rises on the highway.

Lowracer1, you toad! LOL at your report. Must have been a blast riding that rig. It was a steel
version of a lowracer that first turned me on to bents in 1999. Riding with a group of DF at 23mph
about 10mi into a flat century when a lowracer went by to the L of us at 28-30mph and disappeared
down the road. "what the hell was that..." Lots of internet searching lead me to my Ti Pursuit
about a year later. You obviously have a great engine to drive that beautiful machine in your pix.
Can't get much lower wind resistance than that and NO ONE is going to sit in on the tail box. I tried once on a ride in Maryland with 7 other bents, one a tailboxed low racer. Steve

MEB- are you sure that 5 - 6 mph faster for an unfaired bent is correct? Seems like a lot to me. I'm happy to wish that as a bent owner, but it's hard to believe.

That website you referred to appears to only guess that bents are 25 to 30 percent faster, but no evidence to support that. Gregg draws his conclusion from looking at the records (which are from custom streamliners - not the bents we buy in stores).

The Mueller Fairing Folks did a study at the Wright Brothers Wind Tunnel and found that an unfaired Vision Saber (a quality hi - racer) was only 3.3 mph faster at 20mph than a roadie using his top bar. If the roadie went into his aero tuck, he was only .5 mph slower. They also tested an unfaired Vision R40 which was only .3 mph faster than a roadie on the top bar, and 1.4 mph faster with a fairing. If the roadie was in aero tuck, then the roadie was actually faster. Even if faired, the R40 was still 1.4 mph slower.

But we should be glad to know that as soon as the roadie gets tired and comes out of that aero tuck, we see our advantage realized.

This study held all of the variables constant, except for wind resistance, which is really what we're talking about here, right? The study wasn't to decide who's faster, it was looking at the effects of fairings, and that was an interesting side fact that came out. It looks like my Mueller Fairing will add 1 mph to my bent at 20 mph. I was hoping for more of a boost, but 1 is 1, and I'll take it. If you have a Saber, or some other hi-racer, it may be non-existent. Now to really get off track from this thread, I'd like to know if the additional weight (noticed when going uphill) is really worth that 1 mph boost.

If I have totally missed the mark here, somebody straighten me out! Check the study at the Mueller website. I would be GLAD to be wrong!

Aero tuck is a triathlon/time trial bike position which I do not regard as a road bike position. Aero bars are used in on time trial bikes and triathlon bikes. I’ve seen the CAD3 identified elsewhere as a triathlon bike. The drops & hoods position are what I would regard as road bike positions. TT/Triathlon bikes tend to be more aero than road bikes. I would expect a difference of less than 2 mph on level ground for triathlon/time trial bikes relative nominal bent speeds. The CAD3 was equipped with an aero fork, while the bents tested were not. And the R40 was tested with the less aero USS configuration.

The Mueller study shows a much smaller difference than I’d expect and smaller than persons running common courses with road vs. recumbent bikes. Mueller did qualify the data with a statement that large windtunnels designed for larger objects at higher speeds have a resolution problem with the low drag and speed of the bike, perhaps that is the source of the inconsistency.

Anyone know of a specific study conducted for resolving the bent vs. road bike aerodrag issue?

Glass packer, your sources sound a good bit closer to reality. The primary bent advantage is decreased wind resistance. Even the most tricked out carbon or Ti
bent is going to be 3-6# heavier at 20-24# than an equivalent ($) DF at 16-17#
and from analyticcycling.com for a given power input a lighter bike will be faster,
though the steady state difference will be less than the weight diff implies, on the flat.
Bent air resistance relates mostly to how low the bike is to the ground and the frontal area of bike and rider. The flatter the rider, more recumbent that is, the lower the
frontal cross section and hence air resistance. My Rotator Pursuit puts my legs nearly
horizontal but the seat recline is only 10-15D or so, this is only a little different than
what a svelte roady can achieve with an extreme tuck. If I were reclined to 20-30D, my cross section would be similar to what the Dutch low racers achieve. In practice
what I get with my position is equivalent to sitting in behind a DF rider which is less
than 20%. When I had the fairing on, I no longer gained ANY benefit from sitting in
behind a roady. Effort was the same beside or behind the DF rider. Never did any
deliberate coast downs on longer hills with and sans fairing but the few experiences I had suggested a 3-4% speed increase on hills of 300yd or so length and 50-80'
elevation drop with fairing. The one hill where I compared DF and bent that my record speed is 52mph on a DF, I did 51mph on the Rotator pursuit without fairing. Most of the time I do this hill on the DF and typically vary from 49 to 51mph. Steve

On level ground, the extra weight will show up as a component of rolling resistance, not drag.
On flat ground the vast majority of resistance is aero drag. An extra #6 on a rider bike combo of say #210 is about 3% more weight with rolling resistance being slightly less than 3 % for the extra weight. The smaller tires will also add to rolling resistance (a little harder to quantify, and varying with terrain). While a bent has more rolling resistance, it has much less aero drag.

The height of the bike & rider is a component of frontal area, not as a separate variable. The angle of rider shows up as a component of drag coefficient. Both of those are linear components along with the exponential variable air speed in the bike’s aerodrag. The rider’s reduced angle reduces his drag coefficient by channeling air over the rider rather than forcing it back forward. The recumbent & rider have both a reduced frontal area and reduced drag coefficient resulting in lower aero drag.

http://www.kreuzotter.de/english/espeed.htm


This online calculator allows you to input your specifications to compare different bike speeds and wattage inputs.

for example a tri-bike with a rider ouput of 300 watts will give a speed of 26.3mph on flat ground.

the same however with a stock lowracer with 300 watts will give a speed of 30.2mph on flat ground.


lowracer with tail fairing 31.7 mph

full fairing 46.3 mph


a tri bike coasting down a 14% grade will give max speed of 60.2mph with 157 lb rider


lowracer coasting down same 14% grade will give max speed of 84.8mph with 157lb rider


This is assuming a hill with no end. the only limiting factor being the air resistance.

Plugging in the data for the road bike on flat pavement at 300W on the calculator used by Chris one sees:

On the tops: 22.0
On the drops: 26.3

Swb recumbent (a much more prevalent bent than a lowracer) with over seat steering: 27.5.

Unfaired lowracer: 30.2

Mountain bike: 20.8

Excellent website! Thanks guys. But I have a front faired LWB, and that's not one of the options listed. Any suggestions?

That's a pretty cool calculator. I ride a Speed, but used a lowracer to get a rough idea, as geo looks pretty much the same minus a wheel. I need to lose some weight so I can go faster!

new top speed of 46.5mph

Excellent website! Thanks guys. But I have a front faired LWB, and that's not one of the options listed. Any suggestions?

The website shows the derivations on the calculations.
You could build your own in a spreadsheet using a Cw*A about 15-17% for the fairing less than the swb and add about 10 lbs, or if using uss steering just reduce the Cw*A about 15% from the lwb unfaired model.

Fastest Bicycle Speed
The highest speed ever achieved on a bicycle is 268.831 km/h (167.043 mph), by Fred Rompelberg (The Netherlands) at Bonneville Salt Flats, Utah, USA, on October 3, 1995. His record attempt was greatly assisted by the slipstream from his lead vehicle. Fred has been cycling professionally for nearly 30 years and during that time has held 11 world records.

[http://www.guinnessworldrecords.com/]