|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
quantifying design criteria
So I'm beginning an experiment with designing a recumbent. I'm also a
complete bent newbie but I do have some metalworking/composites experience and a lot of upright wrenching experience so I figure it's worth giving it a go. Having said that I'm trying to pin down what the bent community means when they say a bike is "fast" or "slow". I mean it's obviously related to seat angle and BB height. a Tour easy is a differnt beast than a bacchetta aero. But how about the different between something like the aforementioned aero and a street machine. BROL describes the aero as fast and the street machine as being kind of slow. But the riding positions are similar. (particurlarly on the 26/20 version of the aero) A quick analysis of the side pics of both bikes suggests that with a similar seat angle the frontal area would be quite similar. Is weight the major player in this comparision then? Or is it a more amorphus "this bike feels fast" kind of judgement. My goal is a high-racer/fast touring style of bike. Challenge serian or similar. I haven't yet sold myself on teh 26 front wheel tho. I've never ridden a bike witha seat that high and I was wondering how it might fare in stop and go traffic. The extra visibility would be nice, but I'm worried about getting a foot down. I have a 35 mi rt commute of which approx 5 mi each way is in traffic with a lot of stoplights. Thoughts? Cheers and thanks for helping a newbie out. -Tim |
Ads |
#2
|
|||
|
|||
quantifying design criteria
"buckyllama" wrote
So I'm beginning an experiment with designing a recumbent. [...] My goal is a high-racer/fast touring style of bike. Challenge serian or similar. I haven't yet sold myself on teh 26 front wheel tho. I have a Volae Sport (650/650) that probably meets that description. You can find high-racers used for perhaps not a lot more than you could build one yourself, -- though rolling your own may have certain rewards. I'd still suggest that you ride as many types as you can before you finalize your design and begin to build it. I've never ridden a bike witha seat that high and I was wondering how it might fare in stop and go traffic. I've only been riding my Volae for about 5 months. Getting feet down to stop hasn't been a problem. Getting them back up to start is only rarely a problem. %^P The extra visibility would be nice, Between my two more upright seating recumbents (Tour Easy and BikeE) and the Volae, I don't know that I feel much extra visibility. Head height is not really that different. I will say it's easier for me to look behind on the Tour Easy or BikeE than on the Volae because of head/neck angle. I have mirrors on all my bikes, but still like to glance back. The more horizontal the neck angle the less you can easily see by looking over my shoulder. Because of this, I feel that in traffic, the more upright seating is slight advantage. Bottom bracket height is not really an issue. The Volae is definitely faster/easier, but with narrow (650x23) tires it is not much fun on bumpy/rough surfaces. If I were commuting on it I would probably get another wheelset and beefier tires. But that's why I have and ride three different style recumbents... I broke a spoke on the Volae last weekend, luckily only about three blocks from home. I rolled the bike back home, took off the wheel, strapped it behind the seat on my Tour Easy and rode to the local bike shop to leave it for repair. A person I know was shopping at the LBS when I got there and I related my story. When I said I'd "gone home and changed bikes", she commented that I'd said that like someone else might say they had "gone home and changed clothes". I told he she was right. %^) Perhaps you may want to design and build several different bikes! Good luck, Jon Meinecke |
#3
|
|||
|
|||
quantifying design criteria
buckyllama wrote: ... Having said that I'm trying to pin down what the bent community means when they say a bike is "fast" or "slow". I mean it's obviously related to seat angle and BB height. a Tour easy is a differnt beast than a bacchetta aero. But how about the different between something like the aforementioned aero and a street machine. BROL describes the aero as fast and the street machine as being kind of slow. But the riding positions are similar. (particurlarly on the 26/20 version of the aero) A quick analysis of the side pics of both bikes suggests that with a similar seat angle the frontal area would be quite similar. Is weight the major player in this comparision then? Or is it a more amorphus "this bike feels fast" kind of judgement.... While frontal area is an important factor as it largely determines aerodynamic drag, there are other issues in seating position. Combining a reclined seat with a relatively low bottom bracket (BB) will reduce the amount of power the rider can generate for acceleration and climbing. A seat with variable recline [1] could be used, but would add weight and mechanical complexity. Another issue is rider comfort. A rider will generally be faster overall if he/she is comfortable on the bicycle, even if there is an objective performance tradeoff to gain that comfort. Leave riding fast in pain to the UCI professionals. To state the obvious, rolling resistance and drivetrain friction will also affect performance, but to a lesser extent than aerodynamics except for low speed climbing. [1] Here is one of the very few bicycles with variable seat recline http://www.fortebikes.com/images/gallery/SEAN2.JPG. -- Tom Sherman - Fox River Valley "Abnormal would be a mountain lion speaking English." - M.V. |
#4
|
|||
|
|||
quantifying design criteria
I'm not sure what you mean by variable seat recline. I'm planning on
making the seat adjustable within a reasonable range (approx 30 +/-5 deg abovr horiz for the hip-shoulder section of the seat, upcurved top to limit neck/upper shoulder strain) using a similar system to a t-bone. My current drawing puts the BB center at about the same level as my hip joint when seated (a few inches above the seat base). Speed at all costs is not my primary goal but the thing needs to be fairly fast and also climb reasonably well. This is more fast tourer than racer. My primary design consideration is to optimize this bike for my commute. It need to handle traffic adequately when needed. It needs to be fast on the flats and it needs to climb reasonably well. My morning commute consists of a long gradual downhill which I usually maintain about 25-30 on on the road bike. followed by a streatch through town which is all stop and go. Then a ~10 mile streatch of flat to rolling hills which I maintain about 20 on the road bike, then a 3 mile climb (2 - 10%) , a 2 mile downhill and a 1/2 mile climb (4 - 15%). Avg speed on the computer is usually a hair over 16mph avg. at the end. If I can match that rolling avg on the bent with a bit of practice, I'll be happy. I'd rather gain a bit of speed on the flats in exchange for a little climbing ability since the flat roads are heavily travelled and the faster I am, the safer I am. -Tim |
#5
|
|||
|
|||
quantifying design criteria
"Sunset Lowracer [TM] Fanatic" wrote in message oups.com... buckyllama wrote: ... Having said that I'm trying to pin down what the bent community means when they say a bike is "fast" or "slow". I mean it's obviously related to seat angle and BB height. a Tour easy is a differnt beast than a bacchetta aero. But how about the different between something like the aforementioned aero and a street machine. BROL describes the aero as fast and the street machine as being kind of slow. But the riding positions are similar. (particurlarly on the 26/20 version of the aero) A quick analysis of the side pics of both bikes suggests that with a similar seat angle the frontal area would be quite similar. Is weight the major player in this comparision then? Or is it a more amorphus "this bike feels fast" kind of judgement.... While frontal area is an important factor as it largely determines aerodynamic drag, there are other issues in seating position. Combining a reclined seat with a relatively low bottom bracket (BB) will reduce the amount of power the rider can generate for acceleration and climbing. A seat with variable recline [1] could be used, but would add weight and mechanical complexity. Another issue is rider comfort. A rider will generally be faster overall if he/she is comfortable on the bicycle, even if there is an objective performance tradeoff to gain that comfort. Leave riding fast in pain to the UCI professionals. To state the obvious, rolling resistance and drivetrain friction will also affect performance, but to a lesser extent than aerodynamics except for low speed climbing. The only thing I would add to Tom's excellent message on recumbent bike design is to be aware of high bottom brackets. Very many of us will get numb feet if the BB gets much above the seat. A high BB will also affect handling to some extent. Hence, the reason why so many recumbents have a low BB. It is the classic design and for good reason. I have always thought that the Tour Easy could have a slightly higher BB in order to ensure more rider comfort. But the BB cannot be higher than the seat or I will get numb feet. I think this may be more of a factor as you age, but I am not sure about that. I have also known a few young riders who cannot take a high BB. -- Ed Dolan the Great - Minnesota aka Saint Edward the Great - Order of the Perpetual Sorrows - Minnesota |
#6
|
|||
|
|||
quantifying design criteria
buckyllama wrote:
I'm not sure what you mean by variable seat recline. I'm planning on making the seat adjustable within a reasonable range (approx 30 +/-5 deg abovr horiz for the hip-shoulder section of the seat, upcurved top to limit neck/upper shoulder strain) using a similar system to a t-bone. My current drawing puts the BB center at about the same level as my hip joint when seated (a few inches above the seat base).... By variable seat recline I mean a seat where the angle of the seat back can be changed while riding. This is complicated by needing to have the seat base move forward to keep the rider's leg extension constant while pedaling. The Forte lowracer I posted a link too is one example of such a bike. [1] The variable seat recline allows for an upright seat back for more sprinting and climbing power, and a reclined seat back angle for minimizing frontal area on flat and downhill sections. Further testing is needed, but variable seat recline could potentially improve overall climbing ability of recumbent bicycles by allowing changes in position. [2] [1] The only other I am aware of is the one ridden (and built?) by John "Rocketman" Williams which reportedly has a seat recline angle adjustment from 10 to 40 degrees from the horizontal. [3] [2] Studies have shown the fastest way to climb longer grades on an upright bicycle is to alternate between sitting and standing. [3] By convention, recumbent seat back angles are measured from the horizontal. -- Tom Sherman - Fox River Valley "Abnormal would be a mountain lion speaking English." - M.V. |
#7
|
|||
|
|||
quantifying design criteria
ah, the variable seat position is a very neat idea. A bit out of the
scope for this project but maybe someday.... hmmm. I can envision a 3 part seat so that the base, back, and shoulder sections move relative to one another so that each position is comfortable and effective. |
#8
|
|||
|
|||
quantifying design criteria
Edward Dolan was on topic when he wrote: ... The only thing I would add to Tom's excellent message on recumbent bike design is to be aware of high bottom brackets. Very many of us will get numb feet if the BB gets much above the seat.... Back in the ancient past when I owned a 20/20 Wishbone RT [1] with a 13-inch/33 cm seat height and 26-inch/66 cm bottom bracket height, I would suffer from foot pain unless I wore shoes with proper fit and very stiff soles (i.e. SiDi Dominator II Mega). The SiDi shoes also offered the advantage of being black, as a rider's feet will be in his/her vision on a bike with a high bottom bracket. Brightly colored shoes would be an annoying distraction. [1] See http://www.ihpva.org/incoming/2001/wbone2.jpg. -- Tom Sherman - Fox River Valley "We are discussing whether humans as prey are 'natural'. Clearly, they are, or that mountain lion wouldn't have been trying to eat a human." - M.V. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Design News article about bikes | [email protected] | Techniques | 8 | January 14th 05 01:07 PM |
[AD] Free web design | Richard Quick | UK | 6 | August 22nd 04 09:43 PM |
"Actually you are the first person to bring up this issue" | James Annan | Techniques | 848 | April 6th 04 08:49 PM |
London design Standards for Cycling | Jeremy Parker | UK | 3 | February 3rd 04 06:19 PM |
Does the world have room for another full suspension design? | Simon Brooke | Techniques | 31 | January 5th 04 04:21 PM |