Recumbent - Lowracer handling

(more pictures here (http://www.flickr.com/photos/watson_house/tags/raptobike/))
Yesterday I picked up my new Raptobike and today I got to take her on her break-in ride. I rode 54 miles give or take on the Burke-Gilman. I found my raptobike handles like the performance vehicle she is. She begs to go fast through curves and rides like she is on rails. The longer wheel base and my position seems to cushion the ride, the roots and bumps on the MUP were softer than on my Corsa.

I just love how my Raptobike handles and I suppose that other lowracers have that feeling of sticking to the road as well. I could easily get addicted to lowracers, which at this point isn't so bad as more time on the raptobike is a sure bet. She is a fast steed, at the moment I am short some high-end gearing as I am waiting on the 13t cog for the Roholff and currently run a 16t cog. But even so I was able to get her up to 30 using some rolling hills and was running 18-23 on the flats while my legs held up.

Lowracers are great fun and I am glad I indulged.

I've been riding an Optima Baron lowracer for almost five years now. I know your exhilaration. Carving through turns while in full spin is something you can't do on a regular bike. The sense of speed is as though you are cornering above the asphalt in a Formula 1 racer or banking an F-18. So much fun, huh?

The lower center of gravity seems to really help carve through turns. I am having a blast with my lowracer.

Enjoy. It looks like fun. I'm starting to want one now.

Enjoy. It looks like fun. I'm starting to want one now.
I got mine as a frame kit. The shipping option for a frame kit from the netherlands was inexpensive to the US. It was $45 USD.

(TNTPackage (1x4410 grams Plus Package World Zone 5 Priority): $45.26)

I then went nuts with my plans, making this bike my dream machine. But a cheaper build would be a lot of fun - http://duncan-brain.blogspot.com/2009/02/raptobike-plans-continued.html

Arnold at Raptobike is great and will help you pick everything out. I would recommend you get his sizing chart for seats and measure rather than guess on the size. A raptobike in NZ would be fun.

Would love to know how this compares with the Performer.tw low racer, especially the one with a frame coupler.

I know someone who has a Performer lowracer, as well as a VK-2. He says the Performer is a nice bike, but somewhat flexy. And obviously heavier than a Velokraft. He is not exactly a frame-twister, so I imagine someone who was would really notice it.

The lower center of gravity seems to really help carve through turns.I don't mean to burst your bubble, but..

Low CoM is only advantages to non-tilting, multi-track vehicles. As mass is raised and the bike is leaned into a turn at speed, its tangential velocity decreases and therefore loses inertia and its resistance to straight motion. In simplified terms, the higher the laden mass (within reasonable design limits), the higher the cornering velocities achievable.

I don't mean to burst your bubble, but..

Low CoM is only advantages to non-tilting, multi-track vehicles. As mass is raised and the bike is leaned into a turn at speed, its tangential velocity decreases and therefore loses inertia and its resistance to straight motion. In simplified terms, the higher the laden mass (within reasonable design limits), the higher the cornering velocities achievable.

You're thinking it through too much! The practical result of having a lower COG is that to initiate the lean, the mass moves a shorter distance laterally. So it'll be quicker to initiate the turn.

The practical result of having a lower COG is that to initiate the lean, the mass moves a shorter distance laterally.The bike's laden mass does not move laterally during the initial stages of a turn (due to Newton's First Law of motion). The mass is simply rotated when counter-steering is initiated. Once the front tire's contact patch is laterally repositioned and no longer propping up the bike's mass, gravity kicks-in and pulls the bike's CoM downward.


So it'll be quicker to initiate the turn.Not always true, as Freddie Spencer discovered when they experimented with mounting the motorcycle's gas tank below the engine. Because counter-steering requires rotating the bike's total mass, steering becomes heavier because the bike's CoM is closer to the tire's contact patches, increasing contact patch side loading.

The bike's laden mass does not move laterally during the initial stages of a turn (due to Newton's First Law of motion). The mass is simply rotated when counter-steering is initiated. Once the front tire's contact patch is laterally repositioned and no longer propping up the bike's mass, gravity kicks-in and pulls the bike's CoM downward.

...And the acceleration due to gravity is 9.8m/sec/sec. Counter-steering is just the method of getting the fall initiated in the desired direction. The mass isn't 'rotated,' it's accelerated toward the ground; in an arc, as it happens. The higher the rider's COG, the longer the fall will take.


Not always true, as Freddie Spencer discovered when they experimented with mounting the motorcycle's gas tank below the engine. Because counter-steering requires rotating the bike's total mass, steering becomes heavier because the bike's CoM is closer to the tire's contact patches, increasing contact patch side loading.

I don't know much about Freddie Spencer, but it seems that moving the gas tank to the bottom of the motorcyle would require moving the engine and tranny *up* to make room. Personally, I'd think that moving everything down would be a much easier way to lower the mass than flipping the order of stuff. I would certainly expect that putting a low-mass gas tank on the bottom and a high-mass engine on top would have a derogatory effect on handling. In fact, I might go so far as to question someone's intelligence for wasting the time to design such a thing if quick handling was the goal.

I'm not sure what you're trying to say in the last sentence. The contact patch shouldn't care about how high the COG is.

Here's a thought experiment for you. Comparing a low bike to a high one for a 180 degree turn at a given speed and turn radius. On the higher bike, the rider, where most of the bike's mass resides, will follow a shorter radius circle than the the rider on the lower bike; (cosine, where the rider' angle of lean is along the hypotenuse and the turn radius is the adjacent side of the triangle, along the ground,) and thus will have to decelerate to 0 forward speed and accelerate back up to speed in the opposite direction, in less distance than the lower rider does. This means higher deceleration and acceleration rates for the higher bike. I'm not saying that the effect is noticeable, but what does Newton's first law of motion say about that?

whats new papa been missing your advice on other forum.

Nelson

The mass isn't 'rotated,' To the contrary, BlazingPedals,

Bike and rider mass is rotated during cornering, as evident by the images below. Upon initial roll, the contact patches are laterally repositioned to the outside of the bike's CoM, while all mass positioned above the CoM is rotated to the inside. (and note the word "roll" in both images)






The higher the rider's COG, the longer the fall will take.As I stated elsewhere, that is not always true. On page 107 of Vittore Cossalter's book (titled Motorcycle Dynamics), he states,

"With equal cross sections of the tires, to descride the same turn with the same forward velocity, a motorcycle with a lower center of gravity needs to be tilted more than a motorcycle with a higher center of gravity."

Furthermore; Roll response or "flickability" is far more dependent on mass centralization than its vertical position.


I don't know much about Freddie Spencer, but it seems that moving the gas tank to the bottom of the motorcyle would require moving the engine and tranny *up* to make room. Personally, I'd think that moving everything down would be a much easier way to lower the mass than flipping the order of stuff. I would certainly expect that putting a low-mass gas tank on the bottom and a high-mass engine on top would have a derogatory effect on handling. In fact, I might go so far as to question someone's intelligence for wasting the time to design such a thing if quick handling was the goal.You might consider researching Mr. Spencer before passing judgement... starting here (http://en.wikipedia.org/wiki/Freddie_Spencer)

I'm sorry, I thought this was a recumbent bicycle forum. I didn't realize it was an upright motorcycle forum.

@ Blazing: Most recumbent designers are just as concerned with dynamics as other vehicle designers, including upright bike designers. There is much to be learned from auto racing, off-road vehicles, mountain bike suspensions, F1 motorcycles, road bikes, airplanes, submarines and all other moving machines. A recumbent designer that doesn't take from these other disciplines is doing an injustice to the people that ride his vehicles.

BTW, the dynamics of a motorcycle are the same as those for a recumbent, just as they are the same for an old penny farthing. The differences in rider height, wheelbase and positioning of other components merely affects the outcome.

:)ensen.

One thing about the lowracer is that my cog is down at wheel level. In my riding position both my bike and I share the same COG, the combined COG isn't displaced like on a motorcycle or an upright.

It definitely affects handling, It might not be because it is low but how it acts in relation to the rest of the bike. The net affect is I find curves a joy on my lowracer.

One thing about the lowracer is that my cog is down at wheel level. In my riding position both my bike and I share the same COG, the combined COG isn't displaced like on a motorcycle or an upright.

It definitely affects handling, It might not be because it is low but how it acts in relation to the rest of the bike. The net affect is I find curves a joy on my lowracer.The effects you are 'feeling' are the increased, "seat of the pants", centripetal forces which are higher than that of a DF or high racer. A prime example would be riding the outside circumference of spinning merry-go-round, vs. riding closer to the merry-go-round's axis. Even though it 'feels' like you are turning the corner faster, the fact is, you are only increasing your tangental velocity, NOT increasing your angular or rotational velocity.

Your increased seat-of-the-pants feel is also telling you that your tire's lateral contact patch loading is higher than an identical bike with a higher CoM. This means that at a given speed, you are approaching the limits of tire adhesion sooner than the DF or high racer.... even though BOTH bikes are traveling at the same speed around the same corner.

Bottom line; Given two, identical bikes - one with a higher CoM and the other with a lower CoM - and piloted by seasoned professionals, the bike with higher CoM will be faster through the corners.

For most of us who do not race feeling like we are going fast is enough. It is really not about the x's and the o's. Lowracers are just fun to ride.:D:D

The effects you are 'feeling' are the increased, "seat of the pants", centripetal forces which are higher than that of a DF or high racer. A prime example would be riding the outside circumference of spinning merry-go-round, vs. riding closer to the merry-go-round's axis. Even though it 'feels' like you are turning the corner faster, the fact is, you are only increasing your tangental velocity, NOT increasing your angular or rotational velocity.

Your increased seat-of-the-pants feel is also telling you that your tire's lateral contact patch loading is higher than an identical bike with a higher CoM. This means that at a given speed, you are approaching the limits of tire adhesion sooner than the DF or high racer.... even though BOTH bikes are traveling at the same speed around the same corner.

Bottom line; Given two, identical bikes - one with a higher CoM and the other with a lower CoM - and piloted by seasoned professionals, the bike with higher CoM will be faster through the corners.

You decided to ignore the other attributes of a lowracer vs an upright or hiracer in your comparison again.

Additionally I am not just talking the feel of the corner, I am talking about the measured speed. I AM taking corners faster. I AM in more control as I have to thread a manhole cover and the double yellow line in the middle of the second curve in an S that I ride every day. Now I am taking that corner at 30 mph, previously I was tapping the breaks and taking it at 24mph on my Corsa.

My lowracer has slightly wider tires, and very different attributes besides being low. Additionally the practical aspect of being low is less issues from crosswinds which do cause me concerns in my commute S Curve on occasion.

You decided to ignore the other attributes of a lowracer vs an upright or hiracer in your comparison again.No... I believe I have rigidly adhered to the Title of this thread... which you started.


Additionally I am not just talking the feel of the corner, I am talking about the measured speed. I AM taking corners faster. I AM in more control as I have to thread a manhole cover and the double yellow line in the middle of the second curve in an S that I ride every day. Now I am taking that corner at 30 mph, previously I was tapping the breaks and taking it at 24mph on my Corsa. First, you draw highly subjective comparisons between two different bikes, then leave the quantitative analysis laying on the asphalt. :notamused:

No... I believe I have rigidly adhered to the Title of this thread... which you started.

First, you draw highly subjective comparisons between two different bikes, then leave the quantitative analysis laying on the asphalt. :notamused:

Hate to rain on your parade, but results is what counts, and Dunc is experiencing significantly more secure handling on his Rapto. My guess is that vertical CoM is not the only factor. Could fore/aft weight distribution be playing a role? IME, most US-designed highracers have good balance only if you're in the middle of the height range for the bike.

My RANS F5 is exceedingly tail-heavy (60+% on the rear wheel) and has rather poor manners on bumpy pavement, around corners or at high speeds. Specifically, the front end gets very "floaty". Not at all secure. I'm currently riding a borrowed ActionBent Midracer, which most would agree is a step down the quality ladder. Funny thing is, it handles bumps and curves with much more aplomb than the F5 (haven't had the chance to do much high-speed stuff with it). The difference? The F5 is a fixed-boom design, with the seat most of the way back, and the ABMR is a fixed-seat design with the boom most of the way out. So my CoM is much more centered between the wheels on the ABMR.

Oh, and the seat on the ABMR is 6" lower. So, evidently there are other factors in play.

SP

Hate to rain on your parade, but results is what counts, and Dunc is experiencing significantly more secure handling on his Rapto. My guess is that vertical CoM is not the only factor. Could fore/aft weight distribution be playing a role? IME, most US-designed highracers have good balance only if you're in the middle of the height range for the bike.


Center of mass, horizontal distance of center of gravity from contact patches, steering geometry, diameter/cross section/pressure of tires, amount of steering "tiller"...

I'm going to have to go with PaPa on this one. I have a lowracer as well, and although it's nice to pedal through hard turns with the high bottom bracket, I feel my uprights corner faster and with greater precision. The reason, in my opinion, is exactly as PaPa says, the ability to shift weight and shift it a greater distance. Another factor in this is being able to lift myself off the seat and put my weight to one side. Sitting on the recumbent, I can't so this....

I'm going to have to go with PaPa on this one. I have a lowracer as well, and although it's nice to pedal through hard turns with the high bottom bracket, I feel my uprights corner faster and with greater precision. The reason, in my opinion, is exactly as PaPa says, the ability to shift weight and shift it a greater distance. Another factor in this is being able to lift myself off the seat and put my weight to one side. Sitting on the recumbent, I can't so this....
Too bad my comparison was with my Corsa (a hiracer) . In any case there are numerous differences between an upright and a lowracer, much more than just height.

I happen to find cornering easier on my lowracer vs an upright as well but not riding my uprights for 5 years makes that a poor comparison.

I'm going to have to go with PaPa on this one..I feel my uprights corner faster and with greater precision....

There's the key. What really matters is what you feel, all math and physics aside, unless analysis is for purposes of racing or engineering.