Go Back  Bike Forums > Bike Forums > Recumbent
Reload this Page >

Help building my first recumbent

Recumbent What IS that thing?! Recumbents may be odd looking, but they have many advantages over a "wedgie" bicycle. Discuss the in's and out's recumbent lifestyle in the recumbent forum.

Help building my first recumbent

Old 02-27-19, 06:39 PM
  #26  
Ericoschmitt
Senior Member
Thread Starter
 
Join Date: Jun 2016
Location: Florianópolis, Brazil
Posts: 127
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by violini View Post
Since you mention that you also race occasionally
Oh, I meant I race the UCI rules stuff, this bike:
https://weightweenies.starbike.com/f...3156&mode=view

I don't bother racing a recumbent, there's no one to race. But I bother about going the fastest possible under my legs' power just for the fun of it, without spending a ton on carbon fiber stuff.
Ericoschmitt is offline  
Old 02-27-19, 07:15 PM
  #27  
Ericoschmitt
Senior Member
Thread Starter
 
Join Date: Jun 2016
Location: Florianópolis, Brazil
Posts: 127
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by Leisesturm View Post
I would too. That is one sweet bike. 406 rear wheel would NOT improve aero! Only if YOU weren't there, but you are, and the rear wheel is in your wind shadow so the full size rear wheel is not an issue and your gearing and tire choices improve. Where do you find oval chainrings bigger than 50T? How much do they cost? Short cranks are for if you have a problem with heel strike against the front wheel which should not be the case with a 406 front wheel. IF you shorten the cranks then you should also lower the gearing, most people don't do that. They just use 155mm cranks with the same gears that the rest of us use 170mm cranks to turn and then wonder why their knees still hurt, or why they are still so slow. BTW a standard bike can be out of UCI compliance for various reasons. A recumbent isn't UCI compliant. Period. Once you are on a recumbent you are dead to the UCI. Most of us don't care. The Stringbike drivetrain still has rotary motion of the cranks. It has all the disadvantages of being way more complex and fragile than a bicycle drivetrain needs to be, heavier too, probably. But that is just first impressions. It looks interesting. I am going to study it some more. Linear pedal motion is useful if you need your foot motion to stay inside the confines of a fairing. Consider however: year after year, the fastest recumbent in the world is what amounts to a drop dead simple Easy Racer (LWB) recumbent inside a carbon fiber shell. You wouldn't kill yourself if you tried to ride it around town but if you fell over for whatever reason getting back up again would not be quick, or easy. But have you seen a Peregrin on Birk streamliner? More information available here. I don't think there are that many on the road and they don't look cheap but the idea of a two wheel recumbent in a shell being ridden on public roads is intriguing to some.
I know a smaller rear wheel won't change much aerodynamics, but the builder said the seat is fixed to the frame at 25 degrees, so a smaller wheel lowers this angle, then making the rider more aero.

I also know that shorter cranks require a smaller chainring, in the same proportion as the cranks are shortened, so you keep the "pedal speed" the same. I actually got 120mm Sinz cranks at hand, and 38t chainring that would be equivalent to 54t on 170mm cranks. I was about to try that on a TT build, but might now save it for the recumbent. Or maybe just try before on the TT bike to decide if chainring size is right, because...

I also know that smaller wheel requires bigger chainrings, so if I go with 406 rear wheel, and if I expect my CdA to drop, and if I'm able to hold the same power... Then probably a chainring around 50t, being equivalent to 65t on 170mm cranks, would do the trick. But you can find up to 60t on aliexpress, look for "Stone 110 BCD oval chainring", the biggest one $70 shipped.

Then the UCI thing. I care about UCI for racing upright road bikes. I won't care about it while building a recumbent.

The StringBike has a bit more than only disadvantages, take a better look. I'd ride that on my upright race bike... if UCI didn't state bikes have to have a chain drive... (!!!!!!!!) I guess they made it with rotary motion just because that's what people are used too, but I intend to build something with linear motion some time. Being out of UCI anyways, that should be a recumbent too.

Then the linear pedal motion. Yes, the fastest HPV is circular motion so far. Could be for a few reasons: 1) nobody until today has trained long enough to have peak performance on a linear systems 2) Elite athletes are trained in circular motion 3) Linear drivetrains are underdeveloped. I believe all 3 play a role. Graeme Obree recently built a linear motion machine to go for HPV top speed record, but failed. His "Beastie" is backyard build with no wind tunnel data, made of cheap steel. It's fixed gear. He's now much older and less fit. He only trained a few months on it. But I still dream with linear motion. The human body is not made to pedal circles, it's that simple, we can theoretically generate more power linearly.

Finally, the Birk bikes. I like the Comet idea, tail fairing. I'd add a windshield at front to it. It's as close to full fairing you can get while still being able to put your feet on the ground, and getting up. Probably then you can add an stretched fabric/canvas on the sides when you wish, like the Aerowing stuff. I like their idea, looks like it helps.
Ericoschmitt is offline  
Old 02-28-19, 11:41 AM
  #28  
Leisesturm
Senior Member
 
Join Date: Jul 2005
Posts: 3,958
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 1234 Post(s)
Liked 18 Times in 17 Posts
Originally Posted by Ericoschmitt View Post
I know a smaller rear wheel won't change much aerodynamics, but the builder said the seat is fixed to the frame at 25 degrees, so a smaller wheel lowers this angle, then making the rider more aero.
I figured out that that was probably what he meant a few hours later. And, yeah, he's right, but the 700 rear wheel just 'looks right'. You obviously care about looks. I do too. Aesthetics matter almost as much as performance. And how much faster would you be with a few more degrees of recline? I also have to ask how much faster do you think you will be on a recumbent at all? I am not ANY faster on my highracer than on my roadbike. Somewhat slower actually. You are probably a lot younger than, I am with better reflexes, and will adapt to the recumbent position better than I have, but I am telling you now, unless you are on a track or some kind of closed course situation, you will likely only be as fast on a naked recumbent as you are on a standard bike.

The main reason non-competitive riders use recumbents is comfort! You said you don't care that much for comfort, you are about speed. When I want to go fast on just two wheels I ride a motorcycle. In the United States recumbent trikes outsell recumbent bikes by a HUUGE margin. Recumbent bikes fall over way too easily and older riders cannot take the risk. Competitive riders on race worthy recumbents ARE faster than roadies. They are not dramatically faster! Just a few miles per hour faster until you get out the carbon fiber and wind tunnel tested shells and and. The ultimate in linear motion is the sliding seat rowing sequence. This is impractical for a two wheel recumbent, but there are fixed and sliding seat rowing trikes (maybe bikes too, who knows). 40 ish strokes per minute is a very high stroke rate to maintain and the same is true for linear foot action. You can't do the 120 rpm craziness that you can do with pedal cranks because the pedals absorb some of the effort of decelerating your lower leg and getting it moving in the opposite direction. In rowing and linear motion, the mechanism does not help as much in returning energy for the return stroke.

The simplest linear (or rowing) action will be very much more complex than a conventional chain drivetrain. Simple works. It works very well. You have to work very, very hard to beat simple and efficient. It isn't usually worth the effort. I would have little to say about it if you were able to prove me wrong by building a prototype and putting a Youtube video of it online. If you have to sub-contract fabrication to people with specialized knowledge of welding or metalworking or framebuilding you are dead in the water. It won't be worth it. I approached a talented metalworker in my area to collaborate on an idea I had and he didn't want to have anything to do with it. Framebuilders are much braver than metalworkers. They know their creations will be used by humans in possible risky ways. I don't know how they protect themselves legally but they seem to have figured it out. In Brazil there probably aren't as many lawyers making anyone who builds something for someone else nervous about liability but you still have to weight the cost of their labor vs what you get in return. TL;DR: Buy that sweet lowracer you linked to (700C rear) learn to ride it, and enjoy riding it. Do that for as long as you possibly can.

Oh, the short cranks ... so here's the thing about that. The way you put it "when you shorten cranks you lower the gear to keep pedal speed the same" is not quite right. You don't lower the gear to keep pedal speed the same, you lower the gear to keep the perceived effort the same. Pedal speed in innate. A person's preferred cadence is like the speed they talk (or walk) at: very much built in. If you pedal 170mm cranks at 90 rpm you will pedal 120mm cranks at 90 rpm!! Well, you will want to. When you see your riding buddies disappearing in the distance you will start flailing away trying to get some road speed to catch them. If you have lowered the gears to match the percent reduction in torque of the shorter cranks you will have to speed up well past what is 'natural' to actually be fast. I wouldn't know, but I have heard that using cranks shorter than 140mm (found on bikes for children in the US) makes you feel like "your feet are tied together". That's just what I have heard. Maybe you will feel differently. Maybe you already have tried short cranks and like them. This is just what I've heard.
Leisesturm is offline  
Old 02-28-19, 12:13 PM
  #29  
Ericoschmitt
Senior Member
Thread Starter
 
Join Date: Jun 2016
Location: Florianópolis, Brazil
Posts: 127
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by Leisesturm View Post
"how much faster do you think you will be on a recumbent at all?"

The simplest linear (or rowing) action will be very much more complex than a conventional chain drivetrain. Simple works. It works very well. You have to work very, very hard to beat simple and efficient. It isn't usually worth the effort. I would have little to say about it if you were able to prove me wrong by building a prototype and putting a Youtube video of it online. If you have to sub-contract fabrication to people with specialized knowledge of welding or metalworking or framebuilding you are dead in the water. It won't be worth it. I approached a talented metalworker in my area to collaborate on an idea I had and he didn't want to have anything to do with it. Framebuilders are much braver than metalworkers. They know their creations will be used by humans in possible risky ways. I don't know how they protect themselves legally but they seem to have figured it out. In Brazil there probably aren't as many lawyers making anyone who builds something for someone else nervous about liability but you still have to weight the cost of their labor vs what you get in return. TL;DR: Buy that sweet lowracer you linked to (700C rear) learn to ride it, and enjoy riding it. Do that for as long as you possibly can.

.
Well, on an easy ride this week at 180w I did 35.5km/h avg with clip on bars on my road bike. I calculated Crr and got an avg CdA of 0.265. The recumbent builder told me most riders get a CdA of around 1.9 (with 559 rear wheel), hardly below 1.5. Not sure how he got that, but supposing he knows what he's talking about, for the same easy ride I'd be 40km/h avg and with just a few minor tweaks I'd be going faster for sure. Like both wheels discs, 3% less inclined (that's what he told me about 559 vs 406 rear wheel), narrow handlebar for tucked arms, tight lycra etc. So probably .18 or lower... Sounds good for me.

I've seen some rowing-bike systems already, they look cool but not really aero since you can't lay down!

We'll see what about those really short cranks, but I'm betting they will work well, I did my research before buying...

Liability for framebuilders around here isn't an issue, never heard about anything related. Actually for anything, liability isn't usually an issue! Plus the builder is also a friend, he'll do whatever crazy projects I ask for!
And for the custom machined parts, I'll see it, pricing etc. But as told by a biomedical and mechanical engineer friend, you just have to show up to a machining workshop with the SolidWorks file and pay for the machine time and the alloy block, that's it, they'll do it. He has done that several times for wheelchair and prosthetics parts, hand cycles and so on. Maybe sometime in 2020!?
Ericoschmitt is offline  
Old 02-28-19, 07:05 PM
  #30  
mchell
Senior Member
 
Join Date: Feb 2005
Location: Buckhorn, Ontario, Canada
Posts: 217

Bikes: Rans Screamer, Catrike Expedition, Specialized Montain Bike, Cannondale Quick SL1

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Or, if you have the money, you might try this! Mike

Overzealous XC | Trisled
mchell is offline  
Old 03-01-19, 09:33 AM
  #31  
BlazingPedals
Senior Member
 
BlazingPedals's Avatar
 
Join Date: Dec 2004
Location: Middle of da Mitten
Posts: 10,950

Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, homebuilt recumbent

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 910 Post(s)
Liked 25 Times in 20 Posts
Originally Posted by Ericoschmitt View Post

Then the linear pedal motion. Yes, the fastest HPV is circular motion so far. Could be for a few reasons: 1) nobody until today has trained long enough to have peak performance on a linear systems 2) Elite athletes are trained in circular motion 3) Linear drivetrains are underdeveloped. I believe all 3 play a role. Graeme Obree recently built a linear motion machine to go for HPV top speed record, but failed. His "Beastie" is backyard build with no wind tunnel data, made of cheap steel. It's fixed gear. He's now much older and less fit. He only trained a few months on it. But I still dream with linear motion. The human body is not made to pedal circles, it's that simple, we can theoretically generate more power linearly.
Graeme wasn't competitive at Battle Mountain because he failed to learn from history and went with old discredited modes; specifically linear drive and the prone position; both of which were disproven decades ago.
BlazingPedals is offline  
Old 03-03-19, 01:25 PM
  #32  
Ericoschmitt
Senior Member
Thread Starter
 
Join Date: Jun 2016
Location: Florianópolis, Brazil
Posts: 127
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by BlazingPedals View Post
Graeme wasn't competitive at Battle Mountain because he failed to learn from history and went with old discredited modes; specifically linear drive and the prone position; both of which were disproven decades ago.
How exactly was linear motion disproven? Is there any study comparing the efficiency of linear leg motion on oxygen consumption vs power output on athletes well trained on both systems or is that an anedoctal case of underdeveloped drivetrain and untrained athletes on a linear system?
Just because the record beating machines are circular that doesn't mean linear couldn't possibly beat if better developed.
Thats not stopping me from trying, certainly...
But now I'm excited about having found that low racer manufactured nearby
Ericoschmitt is offline  
Old 03-04-19, 08:36 PM
  #33  
BlazingPedals
Senior Member
 
BlazingPedals's Avatar
 
Join Date: Dec 2004
Location: Middle of da Mitten
Posts: 10,950

Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, homebuilt recumbent

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 910 Post(s)
Liked 25 Times in 20 Posts
I don't know if there is any study that I could find to post. It was a LOOOONG time ago.

Linear drives have the disadvantage of the rider's legs completely stopping and then reversing direction twice for every power stroke. Lots of wasted energy, big dead spots in the stroke. There have been some schemes to make the pedal cycle more ellipsoid, and they can increase the length of the main power stroke, but only at the expense of magnifying the dead spot at the top and bottom. (There's that stopping and reversing direction thing.)
BlazingPedals is offline  
Old 03-11-19, 12:30 PM
  #34  
Ericoschmitt
Senior Member
Thread Starter
 
Join Date: Jun 2016
Location: Florianópolis, Brazil
Posts: 127
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by BlazingPedals View Post
I don't know if there is any study that I could find to post. It was a LOOOONG time ago.

Linear drives have the disadvantage of the rider's legs completely stopping and then reversing direction twice for every power stroke. Lots of wasted energy, big dead spots in the stroke. There have been some schemes to make the pedal cycle more ellipsoid, and they can increase the length of the main power stroke, but only at the expense of magnifying the dead spot at the top and bottom. (There's that stopping and reversing direction thing.)
Could be... Or maybe people in the past missed some outside the box thinking to make the drivetrain work better.
BTW indoor rowing is linear, and they also have power meters indoors. As far as I've checked (quite a long time ago) they managed to put equivalent power figures to cyclists when comparing HR and oxygen consumption. I also remember a guy mentioning he did both sports and his FTP, maxHR, and VO2 were about the same when tested indoors for both sports. Not a scientific comment at all, I wont bother researching that all over again, but if you are curious...
Ericoschmitt is offline  
Old 03-16-19, 04:42 PM
  #35  
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 3,562
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 184 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Looking at the https://ce.olx.com.br/fortaleza-e-re...leta-585063383 bicycle, a 406 wheel would probably not
work with the brakes, they are enough smaller diameter for this to be problematic.
It is also not clear how the bike is adjusted for rider size, possibly a telescoping boom? If you are too far in height from the
seller that may be a problem.
sch is offline  
Old 03-21-19, 11:44 PM
  #36  
Cycle Tourist
Senior Member
 
Join Date: Jan 2017
Posts: 225
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 61 Post(s)
Likes: 0
Liked 8 Times in 8 Posts
Easy Racer

I built a long wheelbase recumbent several years ago. High quality 20" bmx wheels and tires are easily available. They can be smooth high pressure tires that allow high speeds. My rear wheel was originally a 27" aluminum job but I changed to a 26" wheel when I turned it into a touring machine. I tried a fairing but found it too heavy to be useful. The low slung position gives you a nice aerodynamic advantage over any upright bike on flat roads. As a hill climber the design is pretty slow. I commuted to work on flat smooth roads and managed a 25mph average including a few traffic lights. My freewheel was 13-32 and I found a triple that accommodated a 54-44-26. Even with a long cage derailleur you had to be careful about not crossing gears too radically. A barend shifter did the shifting. I felt like I was on a motorcycle and pedestrians had a tendency to missjudge the speed when crossing streets resulting in some close calls. I built it from two fairly decent old English donor bikes. The two extra tubes needed to complete the build came from some cheaper cro-moly bikes. I'm not sure if the plans are still available but it was pretty straightforward and I needed only a hacksaw, a single file and the cheapest oxygen/propane or mapp fuel braizing set. The welder cost all of thirty dollars and if you take your time and file everything to fit tightly your frame will be unbreakable. I braized part of a derailleur cage to support the long chain about half way between the chainwheel and the freewheel. I cut and braised some tall handlebars rather than complicate things with more traditional under the seat steering. The seat was thin plywood, foam rubber and denim material stapeled over the whole thing. The thing was maybe 35 lbs and looked a little like a lowered chopper but it really flew. As a touring cycle it was great tearing along flat roads but grinding up hills was no picnic and not being able to stand while pedaling was often literally a real pain in the butt.
Cycle Tourist is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
2wheels4ever
Electronics, Lighting, & Gadgets
4
02-14-17 10:15 PM
heckler
Clydesdales/Athenas (200+ lb / 91+ kg)
21
03-15-08 09:50 PM
jerrymcdougal
Classic & Vintage
11
08-10-07 09:47 AM
Second Mouse
Road Cycling
7
04-11-06 04:09 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.