* * * Aerodynamics * * *

[Lowell]

I will stick with laying on my back thanks.

Me too. I hate to say this, but the whole RR/fetal position is obsolete. It is familiar to a lot of people - and has absolutely nothing else going for it.

After spending enough hours laid back with my butt a few inches off the ground at 40mph+ on a fast kart track (Calhan, CO), I have no desire to do the hobby horse bike thing ever again. Touching the seat down at 47 degrees lean angle - and pushing the front end was far safer on it than a close coupled wheelie/stoppie/highside prone high CG machine. Yes, it was weird at first - but anyone with a high performance mind should be able to adapt and perform. Or at least that's been my experience and observation.

Now here's a high performance bicycle:
http://www.challengebikes.com/html/inde ... lectie=nme

Had me going until this part... "only really suited for racing."

[rohorn]

Had me going until this part... "only really suited for racing."

There are some very enthusiastic NME street riders - but not very many! Like +20mph electric bicycles, they aren't going to be sold as street legal. What we do with them is up to us......

[rohorn]

Resting my weight on the saddle in aero position seems like it would be
uncomfortable, that's why I was thinking about the knee pads - also this is
how the gravity bikes I've seen were made. But I'm thinking shin pads would
be more practical then pegs + knee pads or such, since they could probably
be made comfortable for longer rides with no need for them to fold away.

Norton built a "Kneeler" racer - it was a great idea:

http://www.motorcycle-usa.com/Article_P ... 176&Page=1

[Lowell]

I was seeing it like this:




Resting my weight on the saddle in aero position seems like it would be
uncomfortable, that's why I was thinking about the knee pads - also this is
how the gravity bikes I've seen were made. But I'm thinking shin pads would
be more practical then pegs + knee pads or such, since they could probably
be made comfortable for longer rides with no need for them to fold away.


Note in the pic the seat is higher then what I ride with.

I almost spat my drink on my keyboard when I saw that pic. So who's going to try this out and report back with results and pictures? I wonder if the same results could be acheived with air deflectors on the down tube while simply resting your feet on the crank arms. Arms should be rested triathlon style for the best upper body aerodynamics.

On a somewhat unrelated note, has anyone ever tried measuring aero and rolling drag forces by towing a bike behind a car, with a spring scale holding the tow line? More specifically, how long would the tow line have to be so that the effects of the car (assume a low roofline sports car) would be minimal?

[safe]

I hate to say this, but the whole RR/fetal position is obsolete. It is familiar to a lot of people - and has absolutely nothing else going for it.

Well here's the problem with that theory.

On a "road racer" type setup you have the ability to "counter balance" the effect of a tire that breaks free from loss of traction. If you've ever done any off road riding you know how to do a "power slide". This same effect is used on the street only it's much more subtle and many novice riders have no clue about it, especially if they don't have a substantial dirt bike background.

"King" Kenny Roberts revolutionized the sport when he changed the way people ride (and build their bikes) so that the old "riding on the rail" philosophy that had been dominant for years before was replaced by the "flat track dirt racer" riding style adapted to the road. Modern road racers can put their bikes into a "powerslide" going into, through the middle and exiting the turn and it's all at the will of the rider. (excessive slide just wastes speed, so it's a delicate balance that is maintained)

If any of this is sounding like "familiar knowledge" then I'm puzzled why you would want to revert back to a riding style that offers no "corrective" behavior. The joke in the old days (pre-Kenny Roberts) was that "if you slide you crash". Kenny changed the sport and put the limit of performance waaaaay past the old "ride the rails" mentality. The lack of "counter measures" on a sit down bike is fine for slow speeds and non-racing situations... sort of like the difference between a "sports car" and the "family car". For "real" racing you need a riding style that allows for the tires "drifting" because at speed that's how tires behave. I slide all the time and it's normal to reach the limit of traction on anything when you go fast.

You have to be able to "powerslide" or you might as well ride the "minivan"...



http://www.motorcycle-usa.com/Article_P ... 214&Page=1

"King" Kenny, as he's been referred to since his first world championship, has an unequaled list of World Grand Prix successes as both a racer and team owner. As a racer, Roberts earned three consecutive 500cc World Championship titles, while redefining the riding style of all racers to follow. As a team owner, Roberts secured three more 500cc World Championships, along with a 250cc title with American riders, adding many more podium finishes to his successes. After taking on the unprecedented challenge of creating his own 500cc KR3 GP race bikes in 1997, followed by the 990cc MotoGP KR5, Kenny now uses Honda's new 800cc 212V motor in his KR212V MotoGP race bike, ridden by his son, and former World Champion, Kenny Roberts Jr.

[Lowell]

Somehow I doubt most e-bikers worry about being able to control slides in corners...

[safe]

I was seeing it like this:

Well it's definitely an even tighter tuck. My only concerns would be like the previous posting about "King" Kenny Roberts. Which is going to be safer at high speeds? My guess is that the knee pad approach takes away from the ability to "react" to events to a small degree.

Let me give you a short lesson on that...

The "racing posture" is to have your shoulders FLAT or at least partially IN OPPOSITION to the direction of the turn. The reason is that you can quickly "shift" your sholders and it produces a rotational torque that counters the slide of a tire. The knees (knee dragging) are also used as a sort of "balance pole" to help correct your balance when needed.

Wow, truth is that very, very few people get good enough to know proper form and so they crash for many circumstances that they could have survived.

Bottom Line: For safety reasons (being so high up) I'd "advise" the traditional "road racer" posture over the "Gravity Bike" posture. Don't forget... those guys are REALLY low to the ground.... REALLY low.... so they are dealing with different weight balance issues...

[safe]

Somehow I doubt most e-bikers worry about being able to control slides in corners...

They don't because they are too slow to have to worry about it. My point is that when you start to go faster things like "center of mass" and "riding position" can't be overlooked or you will crash and burn very quickly when you encounter your first danger...

I'm "safe" you understand... I ride like a maniac... but I do everything possible to give myself an advantage so that I don't become a victim.






http://www.norfolkarena.co.uk/powerslide/goldplus.htm

[Geebee]

Safe, if you want a real blast try a low recumbent trike around a tight corner at speed, the trick is to get your upper body over the side of the trike so that your head is almost level with the curb (to prevent it flipping and helmet please) and then if you are going fast enough you will induce a 3 wheel drift or slide, great stuff.

[safe]

Three wheeled bikes are like go-carts. They are very stable.

Comparing two wheels verses three or four is sort of the "apples verses oranges" thing though. Comparing a recumbant to a road racer style (tight tuck, not the upright bikes) is a better comparison because they both have good aerodynamics and yet they differ in handling behaviors. It seems like a two wheeled recumbant would have no "counter measures" if one of the tires started to "drift" at speed. I've never seen a recumbant "in a drift" but maybe it can be done.

Anyone ever done a "powerslide" on a recumbant?

Every 14 year old boy and his bicycle has done a "powerslide"... (or at least a looooong skid sideways with a little bit of crossup)

[rohorn]

Safe,

Actually, I find it far easier, safer, and faster to slide on a recumbent 2 wheeler than on an "upright" one. Powersliding? Piece of cake.

One thing that was weird to learn was leaning my inside leg into the corner so that my outside thigh was just about to graze the ground. It is much more comfortable and forgiving than the kneecap for obvious reasons.

A recumbent is far less pitch sensitive than an upright bike - so sliding either end is not likely to grip and fling the rider (high-side). A recumbent doesn't need the theatrics (hanging off, etc) that upright bikes need to get into and out of a corner due to the lower CG and resulting reduced polar moment about the longitudinal axis.

There also isn't a body of experience to draw on regarding recumbent stability and control in a roadracing environment. Yet. So I had to find out for myself and the results have been very satisfying.

[safe]

Actually, I find it far easier, safer, and faster to slide on a recumbent 2 wheeler than on an "upright" one. Powersliding? Piece of cake.

I've never seen a recumbant do anything serious in a performance "handling" sense. While your conjecture that a lowered center of gravity somehow makes a bike less likely to high side is "interesting" is has nothing to do with the way things really work.

A history lesson...

In the old days of motorcycles they had very "pointy" tires. The logic then was that when you leaned onto the sides the tires could stick better. The frames were actually designed to flex so that the tires NEVER broke loose. As a result, if the tire did brake loose you were almost guaranteed a crash.

The newer thinking is that you use more flat shaped tires and when you lean you ride on the edge which gives a more sensitive feedback about when the traction is getting light. The big change in frame design was to eliminate the flex out of the frame so that when the tire started to slide and then "caught" itself the frame would not hold that stress like a "spring" only to a short time later "unwind" and give you a "high side". The "high side" is really a "frame flex" issue and not a center of mass issue. (hint, hint, a "pointy" tired recumbant with a flexible frame should "high side" exactly the same way) This is when the "Delta Box" frames started showing up that really lowered the flex and thus reduced high sides significantly. (they still happen, but you really are just as likely to low side as high side these days)

When someone is in a recumbant position they lack the ability to "throw their weigh around" like you can in a jockey position. So I'm just trying to find the "magical" physics that makes your theory valid. What body part can you twist, turn or "whatever" to get rotational torque like you can with the knees and shoulders on a road racer? The head alone makes a bad "counter balance" because it messes with your inner ears sense of balance. On a motorycle you keep your head level, shoulders flat and bend everything else. Where's the "counter balance"?

I think there's a reason that you have never seen any serious "handling" performance out of recumbants. (they are not at the race tracks to my knowledge) At the level of actual competition I don't think that a recumbant would fair very well, the handling limiting the rider to well below the traction limits of the road racer. At 100 mph I would much rather be riding "on top" of something than sitting and having to pray that the tires don't let go and crash and burn.

[safe]

At the wikipedia website they have a very favorable opinion of the recumbant trike:

"Three remarkable characteristics of recumbent trikes include: 1) the fact that the rider does not need to disengage from the pedals when stopped; 2) the trike can be geared very low to enable mountain climbing while heavily loaded and at a slow speed, without losing stability; and 3) trikes are capable of turning sharply without leaning, producing lateral "g forces" similar to sports cars. Recumbent trikes may also be more suitable for people with balance or limb disabilities."

...but they seem less enamored with the performance of the two wheeled recumbant:

"Balance. Balance is easier to effect with a higher centre of gravity, because of the "pendulum effect" (it is easier to minutely change the angle at which ordinary bicycles lean).[2] The lower center of gravity makes two-wheeled recumbents harder to balance, especially when moving slowly or on unstable surfaces. If a wheel slides, the bike will typically go down very fast. Where one can change one's weight from the seat to the pedals on an ordinary bicycle, one's weight is only on the seat while riding a recumbent. This ability to shift one's weight and place weight on one's feet is an important part of the difference in balancing an ordinary bicycle and balancing a recumbent. Maneuverability. Recumbents have usually a larger turning radius. Also, it's impossible to jerk the front wheel up curbs. Since the front wheel is usually small, driving up unlowered curbs is very risky even with suspension."

http://en.wikipedia.org/wiki/Recumbent_bicycle

A comment on this, on my lead acid bike I placed the batteries very high up in the air, but the effect is that it makes the steering LIGHTER than if I had placed them down low. A bike steers about the center of mass and so the FURTHER the tires are from the center of mass the MORE responsive it is. (more torque to rotate the mass) I know, it sounds "crazy" but that's how bikes actually steer... weird huh?

The irony is that people think that a lowered center of mass is "good" when in reality it's the opposite... one gets the best handling with a center of mass that is higher... it's just the weird physics of bicycles... (that's why those scooters with the low mass handle so bad... it's for the same reason... kind of reminds me of the old "bikers" verses the "mods" debates back in the 60's)

The recumbant trike looks like the winner... (if I had to pick)

[rohorn]

I used to do lots of sportriding - and spent a day at was once called Sears Point. I've owned and built a number of sport bikes. And enjoyed them a lot. There are some great roads near Cloudcroft, New Mexico, near where I used to live. Heck, here's my old RZ between Cloudcroft and Ruidoso:

http://i19.photobucket.com/albums/b157/rohorn/rz350.jpg

That you haven't seen or experienced anything regarding the performance potential of the recumbent configuration is the result of your lack of knowledge on the subject. I've BUILT some motorized recumbent racetrack bikes - they work. They are far less sensitive to tire profiles. I've done a lot of testing.

As far as crashing and safety goes, virtually all the injuries come from the initial impact with the ground - something speed has nothing to do with. But losing control with your butt 2 inches off the ground is downright comfortable compared to being flicked off of a 30" high seat. I've done both.....

The whole throwing the body or body parts to control a road bike was pure BS in my opinion - and has been proven:
http://www.superbikeschool.com/machiner ... achine.php

Current racing design is about selling what's in the showroom this year - and going with what is familiar to the tuners and riders. Kenny Roberts is a legend - one who I admire a lot (as one should be able to discern from the above picture), but his old racing style is very much obsolete. You don't see too many flattrackers making it into GP anymore - there's a reason for that. There's also a reason why laptimes have pretty much stagnated for the last 20~ years with only microincremental improvements (due to tires and engine management) - the dynamics of the basic roadrace bike design has resulted in a developmental dead end.

Which is why I'm messing with recumbents. I'd rather develop what's next than consume what's yesterday. In the mean time, a lowracer recumbent is the fastest configuration for a low powered electric bike - arguing otherwise is just so much grumpy old man BS.

NOBODY is powersliding a 1000 watt bike at 100 mph and highsiding it anyway.

[rohorn]

The irony is that people think that a lowered center of mass is "good" when in reality it's the opposite... one gets the best handling with a center of mass that is higher... it's just the weird physics of bicycles...

There's a big difference between what makes a bike easier to ride at low speed and what makes one faster on a racetrack. Scooters and motorcycles have vastly different high speed characteristics as a result of the different wheel sizes and wheelbase, not to mention terrible suspension. Build a motorcycle with scooter wheels, wheelbase (but with a motorcycle CG) and nasty suspension and you'll still have a squirly motorcycle.

The higher the CG, the more the front tire has to steer to deviate the path of contact to attain the desired lean angle. Or it attains the desired lean angle later with the same steering angle. And at high speed, the limiting factor to corner entry and exit is the ability of the rider to steer into and out of the corner. Such vehicle behavior is desirable in low performance riding, such as the kind referred to in the Wiki page (a reference notoriously bad for its errors and bad information, by the way), but isn't how one goes about developing a high performance bike on which one aspires to corner with any degree of speed.