Climbing and Sprinting technical talk

[Jim Parker]

There has been MUCH written about the physics behind climbing on a Cruzbike vs. a fixed-boom recumbent vs. a standard DF bike. However, much of it is buried deep in long threads scattered over the blogiverse. Here is an accessible place where you can view a force vector diagram, or watch a video, which explains what may be one reason our bikes climb so well.

As many Cruzbike riders have discovered, use of the upper body is an optional way of generating extra power, especially in short segments. In a long race, with lots of climbing or sprinting sections, the ability to use both upper and lower muscle groups is a real advantage. The content below is my opinion. If you have other ideas, please share them. It's surprising to me how little we know about the biomechanics of cycling.

We understand that power, weight, and drag are the major determinants of speed at any given moment. But we don't understand the complicated dynamics of the human body as it interacts with the bicycle... especially out of the laboratory, off of the trainer, and over time. This is the frontier we are exploring here at Cruzbike. Thanks for being a part of it. What's been accomplished by Cruzbike riders/racers over the past 10 years is very promising. It's why we are still here. If we didn't believe that our bikes were revolutionary, we would have closed our doors a long time ago. People don't need another recumbent bicycle company. They need a better bicycle that can be ridden farther, faster, more safely, and more comfortably.

Jim

 

[jond]

hi jim.

i have seen steady improvement in my power figures (powertap hub) as i have gained more experience now 3500 klm on platform and arrived at a final bike fit. but i am yet to equal my DF figures. one problem is the bike is so fast and i cannot pedal all the time i am confident in time i will be able to generate equal or close to the same wattage averages. to exceed them would be nice then i would be climbing at the same or faster vertical ascent rates as my 7kg road bike df.

i have personally found that bike fit is incredibly important on my vendetta 2.0 with 1 cm boom increments making a big difference to the best most comfortable "feel" of the bike and the power i am able to generate in comparison to perception of effort.

in deed Jim the mechanism you describe is very very similar to the feel of my DF when climbing or sprinting with high exertion. the boom and drive wheel is the only thing that moves in my case with the rear planted and not moving side to side like a DF and is likely superior for this . i have observed this on 300-600 watt efforts albeit for short durations. i would say that the bio mechanics are unique to each individual rider and therefore a lot of bikefit experimentation is advised with not only the "subjective feel" being taken into account but also hard data. eg timed distance/power etc.

over time my boom has moved out by some 2 inches. this has allowed a better feel for climbing and easier for me to sit up when i feel the need to. i look forward to again repeating some long hill climbs to see how the latest adjustments have added to performance.

i remain of the opinion that the platforms potential has yet to be fully realised for myself however at this stage i would say the vendetta's weight disadvantage versus a DF is it's only drawback for climbing serious hills/mountains . of course with lower gearing you can pull a stump out of the ground but my skill level is still developing to be able to ride a smaller gear than 39-36 but a compact chainset or wolftooth in the works.

in every other respect the vendetta clearly outperforms any diamond frame. our local A grade champion could not keep up on a recent hairy chested vendetta ride. so unfair i know but i did not tell him so.

hilarious i jumped on my mates mtn bike the other day and i found it awkward as my arms wanted to tap away still with the winning vendetta rhythm. will have to see how this translates to the roadie if i ever get back on it that is.

point being it takes time to acclimate to any change in platform. in my personal case about two weeks has been my experience before previously established numbers return. so a scientific study would be possible but time consuming and subject to the machinations of the "on the day factors" and subjectivity of the rider.

 

[MrSteve]

Here's one of my more lucid explanations of how I make power happen on my 'mysterious' Sofrider -answering a sincere question posed by BROL member, 'Steamer':
-----
How?
This is how, for me, on my bike:

The right leg pushes;
-the right leg can simultaneously push to the right, offsetting its left-steering input;
-the left leg can nudge the pedal to the right, offsetting the rights' left-steering input;
-the arms can compensate;
-the shoulders can compensate;
-body-english can counter-steer/compensate for the right legs' steering input;
-all of the above, in varying degrees, at various power inputs.

Have you watched a D.F. rider sprint to the finishing line?
While watching the sprint, have you noted how the power is made?
Have you seen the bike weaving under the sprinter, compensating for the power impulses, the impulses that are also steering the bike?
Have you seen how the sprinter is off of the saddle, leaning forwards, riding
on hands and feet -or, on the front-end?
Why do sprinters sprint the way they do?
Can this power be maintained?

I power my MBB bike in sprints the same way.
I cannot maintain that level of power output for very long.
It -the bike- acts very much like a D.F. in a sprint.

Can I maintain power at cruising speeds without power loss?
Yes.
I'm acclimated to my bike.
-----

The above was posted in July, 2013 and the thread was deleted by the original poster...
possibly in a fit of snit.

Hope this helps amplify your on-point lesson on MBB/DF power, Mr. Parker.

-Steve

 

[LMT]

An interesting OP and I fully agree with the last sentence. This is my take on the whole MBB thing, in explaining it I'll at the same time also rebut some of the things that I've seen said about climbing on a MBB or fixed RWD.

All imo, and anecdotal from my own experiences riding a RWD bents and a Cruzbike plus some general thinking:-

Using the upper body when climbing would force the bike to zigzag up the road.

This may be true when you first start to use a MBB, as it was for me when I first started riding getting used to the pedal steer. But practise and refining your technique, which you only get by doing drills in the local car park and covering some miles will make sure that the upper body, legs and brain are all co-ordinated so the bike does nothing but go in a straight line.

I can climb better by bracing my back against the seat.

I've never got the reasoning behind this statement, and the reason is that Newton's third law should automatically dictate that as you put more force through the pedals there is an equal and opposite force - which means that your back is already braced against the seat. So how does bracing my back against the seat help me climb when physics makes my back being braced against the seat in the first place? Or am I missing something? I have heard of bridging (lifting your backside out of the seat) and have tried it going up a 14% hill on my Metabike, if this is what people are actually referring to then I found it harder. In that it was harder to control the bike and lifting my hips off the seat and thus supporting my weight using my abs and the support of the seat made my HR go rapidly into the red.

Pulling on the bar on a RWD bent is just as effective/the same.

It really is not, and this is down to the difference of the two systems and where your hands are placed on the RWD bent and Cruzbike. On my Cruzbike, I grab onto the bar, which in turn is attached to a two piece straight metal boom, which at the end attached to it is the BB and crankset. So when I use my upper body to move the bar, it automatically moves the BB which I counter by pedalling - the point I'm trying to make is that my upper body and legs are working as one system. On a RWD bent this is not the case at all as the drive system and you pulling on the bar are two independent systems and as such are less effective.

Also on a Cruzbike I tend to have my hands in a vertical position either holding onto the drops or wrapped over the hoods. And in this position when you pull on the bar you use the more powerful back muscles as well as bicep and tricep. In contrast on a RWD bent in the hamster position your hands are horizontal and when you pull on the bar you use more your forearms and shoulders when engaging the upper body, which are the more weaker muscles. Go out on a DF and try it, pull on the hoods and then pull on the horizontal part of the bar.




Of course there comes a point where gravity and gradient simply takes over and there is not a lot you can do to make getting up a hill any easier, except lose some weight or get fitter. However with a Cruzbike there are more options for tackling a hill. Not to mention that it is great fun knowing that at any time you can put as much through the pedals as you can by standing up over the bars sprinting on a DF.

Another big difference about a Cruzbike is that you can make it fit you better then you can any other bent. The option of a shorter or longer chainstay gives more options in terms of hip angle which if you believe the studies carried out, is directly linked to performance and able to out put more power.

Finally, a recent 600k brevet that I done, of which the last 20k is rollers in the 4-6% category, the difference between doing this on the Cruzbike compared to doing it on a Metabike which I done last year were like night and day. The Metabike being a perpetual slog and on the Cruzbike being an absolute blast, of which I had not had that much fun on a recumbent in a long time.

 

[battleaxe0]

That may be the issue with us noobs feeling wobbly going downhill - having the timing backwards increases the steering oscillation until it feels out of control?

 

[Charles.Plager]

That may be the issue with us noobs feeling wobbly going downhill - having the timing backwards increases the steering oscillation until it feels out of control?

The biggest issue I think with newbies going down hills is being tense. Being tense at high speed can introduce wobbles very quickly that can become out of control if not handled.

 

[battleaxe0]

Remembered this article from awhile back - the climbing part:

"Finally, there is the matter of how I passed the two Bacchettas on the Caldwell County hill. Road bikes are outstanding hill climbers because they have three ways of ascending the hill. Riders may spin, honk, or stand in turn, often passing back and forth between these options on a single long hill. Spinners just spin the cranks, bodies held more or less still. Honkers lunge back and forth on the saddles in a bigger gear, getting some of their weight on the pedals at the same time as they thrust with their legs. And standers of course just stand on the pedals, taking advantage of the wonderful free force of gravity. Recumbent bikes offer a great brace off the back of the seat for powerful spinning, but they really can only spin the hill. The Bacchetta riders, both friends of mine and at about my ability level, were spinning like mad as I came up on them on the trike, but this availed them not. I whizzed right by them, no matter that their hpv’s weighed ten pounds less than mine did.

Recumbent trikes can spin the hill of course, but they also do what might be called a “trike honk.” Trikers have a second method of hill climbing available to them based on the three-wheel stability of the trike. I learned to do this simply by trying to ride hills in higher gears and exploring how I might go about it. I was just trying to climb as easily as I could with reduced leg burn. The honking triker arches his body off the back of the seat, taking all or most of his weight off of the seat base and in effect using gravity on the pedals. On the stable platform of the trike, you can also throw your body back and forth to increase the effect, something not really possible on a recumbent bike, and you can pull as well as push on the pedals. This trike honking is less work or more work, depending on how you do it, but it is another way up the hill! I love to go up hills on my Catrike and do it well, but I don’t know how to prove that to you. We’ll have to go riding sometime. ( I suggest Easy Street Recumbents’s Catrike Rally in Austin, Texas, this April.)"

 

[Charles.Plager]

The honking triker arches his body off the back of the seat, taking all or most of his weight off of the seat base and in effect using gravity on the pedals. On the stable platform of the trike, you can also throw your body back and forth to increase the effect, something not really possible on a recumbent bike, and you can pull as well as push on the pedals.

This is commonly referred to a bridging and you can do it on many 'bents. I find it easier to do on a Cruzbike than I think I would on other 'bents because you can push against the handlebars to help get your butt out of the seat. I can only do it for a short period of time, but when I do it, I can put some serious (well, for me anyway) power out.

 

[trplay]

Help me with this if you will. I do not see Lances' and Marias bike movements being the same. The difference is the DF has a side leaning movement which keeps the front and rear tires much more in alignment than the recumbents. The recumbent is producing a lot of tire scrub. If this is correct the question would be how much power gain from the movement versus how much energy is lost via the scrub.

 

[Jim Parker]

That may be the issue with us noobs feeling wobbly going downhill - having the timing backwards increases the steering oscillation until it feels out of control?

Here's a tip for big descents. Shift into a big gear early on the descent. If you get to a speed where you no longer can or want to pedal, begin coasting. The next step is where beginners can get into trouble. Upon re-initiating pedaling, which you'll usually want to do near the bottom of the hill, initiate the power in a controlled manner. This is where it's nice to be in a big gear because the resistance of the big gear will give a sense of feedback and control. Some people have developed a habit of slamming on the power suddenly on a descent. If you do this on a Cruzbike, especially if you are in a low gear, it can cause a wobble that you won't soon forget. I add the power on a descent gradually (over 1-2 seconds) until I feel the resistance and then know I can go full-power if I want to.

 

[Jim Parker]

Help me with this if you will. I do not see Lances' and Marias bike movements being the same. The difference is the DF has a side leaning movement which keeps the front and rear tires much more in alignment than the recumbents. The recumbent is producing a lot of tire scrub. If this is correct the question would be how much power gain from the movement versus how much energy is lost via the scrub.

If you watch the video of Lance, you will see the path of the front tire is quite sinusoidal. I agree that it wouldn't seem to NEED to be so sinusoidal considering that theoretically the leaning could be accomplished while keeping the bike moving in a straight line. But in reality, every sprint or climb I've watched on TV where the DF pros are up and out of the saddle, that's just how they do it. On the other hand, on a Cruzbike, it would SEEM that the bike would take an even more exaggerated sinusoidal path (due to exactly the reasons you point out), but in reality (at least my expereince), it actually takes less. Here's my theory to explain this observation: The DF rider is actually shifting more mass side-to-side when they are out of the saddle- their ENTIRE bike is leaning and I believe their sinusoidal path somehow keeps their COG moving in a straight line. We are tilting only one wheel and the front triangle- almost no mass is moving laterally, so there is much less mass to counteract. And also keep in mind that our "steering" during these sprints is oscillating very quickly. Let's say your cadence is 80 rpm while you are sprinting up a hill. That means you are "steering" to the left for 0.375 seconds before you start "steering" to the right. That's not enough time to initiate a turn or even see any scrub visually. I'm glad you brought that up because I've wondered the same thing.

 

[Abbott Smith]

Muscle groups, power train and the abilty to vary technique.

I came to my Vendetta V20 after years of riding DFs and then two RWD bents.

I loved my earlier bents. But they afforded one climbing option that I refer to as the Diesel Engine Spin. As a big rider I have more in common with Jan Ullrich than a Pantanni or Armstrong. Ullrich had to spin rather than dance. Same for me. And I learned to push back into the seat when I climbed on a RWD bent rather than fold forward. The back of the seat was what you push off to gain power. No problem on flats but counterintuitive for many riders on hills. Hence why it becomes a mantra for climbing a RWD bent.

The V20 is different in three key ways for me as a recreational cyclist.

1. The power transfer is more efficient. This is huge. I'm not losing power to a chain the length of a football field and a series of idler arms. This is enhanced by the stiffness of the V20 frame. It allows me to quickly change tempo and maintain momentum on climbs with varying pitch. Both types of recumbents handle steady moderate grades well, but in varying terrain the power transfer of the V20 dominates.

2. The direct connection between the handlebars and the bottom bracket engages both my core muscles and arms as well as my legs. I rode 30 miles last night with 1800' of climbing. Today my legs, arms and abdomen all have that recovery day feeling. I'm using all of them riding this bike.

3. The geometry of the V20 also allows me to vary my riding style within a climb. I can spin. I can power honk as described above and I can pull up into an upright position to 'stand'.

My instinct is that the physics are slightly different than a DF. But here's the thing. I don't care. I won't ride a DF. My V20 isn't a DF & it gives me three different climbing options. There were multiple times last night where being able to take a break from one position and go to another made the difference in my ability to get up the hills without stopping.

This bike allows me to better enjoy riding in the hilly terrain around my home. I don't ride to race. But this bike is still the right bike for me.

My set up is 50/34 with an 11-42t cassette. I have Wolftooth 16 and 42t aftermarket cogs.

 

[Robert Holler]

Jim has hit all the nails on the heads here in this thread. I will also add that these things develop with time and are skills that one has to put the time in to master. That is not to say they are difficult - they just need to be mastered.

Particularly the V20 and also the S30 - these bikes are faster than the rider - they need to be mastered. Kind of like sliding into the cockpit of a formula one car - you have to learn the nuance before mashing the gas pedal down.

 

[battleaxe0]

Here's a tip for big descents. Shift into a big gear early on the descent. If you get to a speed where you no longer can or want to pedal, begin coasting. The next step is where beginners can get into trouble. Upon re-initiating pedaling, which you'll usually want to do near the bottom of the hill, initiate the power in a controlled manner. This is where it's nice to be in a big gear because the resistance of the big gear will give a sense of feedback and control. Some people have developed a habit of slamming on the power suddenly on a descent. If you do this on a Cruzbike, especially if you are in a low gear, it can cause a wobble that you won't soon forget. I add the power on a descent gradually (over 1-2 seconds) until I feel the resistance and then know I can go full-power if I want to.

Point taken.

Unfortunately, we don't have anything ya'll would consider big. The spot I'm referring to is about a 15 foot drop over 800 foot run. I mash the heck out of it to get to the drop as fast as I can go and try to use the drop to put me over the 30mph speed limit sign at the bottom. I haven't beat it yet on any bike, but I've gotten close. Unfortunately, it's bumpy, so mashing the Silvio at that speed down this drop I get squirrely. On my latest attempt that point was around 27mph. That's up from 22 so I'm learning I think the bigger gear idea may help, because the lower cadence means fewer moments of steering input.

 

[ratz]

Pulling from the past BROL conversation where this exact conversation got diverted.... I want to add some of my muscle engagement observations.

In my personal experience The upper body stuff comes into play when I want it to; I can bridge on my Silvio and Vendetta just like I could on my Trike and any other stick bikes I've tried. But if I grab those handle bars, pull hard and sit up just a bit; I can accelerate very very fast on a MBB. If I then pump and rock the nose rhythmically with my pedaling ala a DF I go even faster (up hill or on the flat). Last night I did just that goofing around a local 1 mile Strava sprint segment; I finish with the KOM by 20 seconds beating out some guys from a pace line; watching the KOM comparative replay I beat them on the final climb where I was full body attacking. I also did it at 11pm in the dark; add some light and I would have gonna a lot harder in on the down hill part. Winning via the uphill demonstrates something is up.

When doing that rhythmic pumping, it's not the same as a DF, I know what wheel bending,deflecting power and scub feels like on my old carbon wonderbike I did that for years; it's not that; there is no scrub on the Vendetta So what is it?

BTW, I think I am going to start callnig the Vendetta my Aluminum wonderbike; it's only fair after-all.

I think there is a component here that is analogous to "Free weights" in the gym that applies. Body builders lift free weights because all of the stabilizing muscle come into play; more stuff working and stress means better muscle development throughout the limb being used. You just can't get that on a ridge, fixed position, weight machine. MBB feels like that.

So my current Postulate is that most bents and trikes are very static machines; that force you into very fixed position and encourage the human to produce a machine like consistent power stroke that uses a fix and finite set of muscles. That consistence is not what the human body really excels at and fatigue is quick to prove it to the doubters (yes you can train to be really good at that; but that's the 1% elites that do). This static application of power is why on a tradition bent (is there such a thing?) bridging works, heart rates stay down, why fatigue seems to limit the high end exertion, and lastly why it can really stress the knees (just like pedals without float).

Meanwhile on the MBB the front is moving and as a result there is no true fixed leg motion; it's not locked it a single plane; it moves around; and you have to bring an the extra micro muscles into play to stabilize everything; and those non perfectly aligned muscles can contribute to the effort and allow for a more distributed load, yield more power for longer.

I don't really think my arm pulling back on the handbar is putting power to the pedal but it's allowing me to use additional leg muscle to contribute to the push; and giving me a slight bonus of the "leveler" that is the boom changing the angle through the power stroke.

The challenge I present people who don't believe the MBB potential is this:

Go ride 6 pieces of machinery:

1) Stationary Upright Computer Cycle (heath club life cycle)
2) Stationary Recumbent Computer Cycle
3) a Recumbent Trike
4) a Recumbent Stick bike
5) any MBB bike
6) any DF Race Bike

1-4 ride very much the same and the exertions feel the same. They all have very very stable, solid and predictable riding positions and it's hard NOT to ride them locked in smooth and even.

5-6 can be ridden on demand in a very destabilized manner with lateral body motions; and they ride very much the same in that they feel looser, lighter, faster; and undeniably they accelerate at rates unmatched by 1-4. The exception to that would be to go out on a Fast light RWD Bent like a CA2 and Bridge and really lay into it; by adding a bunch of unnecessary left and right hip wiggle. I bet you find you can go just a bit faster. Actually I know you will because I do. Or perhaps you already done that and you know it works.

 

[Abbott Smith]

Ratz's post prompted me to remember another difference on the V20. When I change positions I change my breathing. This is particularly true in the upright sitting position. Changing my breathing changes the power demands my heart is placing on my system during a climb.

Popping my heart rate is a critcal component in the MBB climbing equation. If I get too far into the red, my labored breathing makes it impossible to maintain my balance or line. My riding becomes unstable and unsafe. This is why I am still struggling as a novice MBB rider with the steeper grades in excess of 15% that are embedded in some of my longer climbs. I can attack short isolated steeps but the embedded ones are still beyond my current fitness.

Sitting up during a climb changes the demand I'm putting on my diaphragm and I notice that difference because I can get my breathing into a better rhythm.

It's another piece of what Ratz is describing relative to micro muscle groups. Using different positions expands the variety of ways I task my muscles to breathe.

 

[Abbott Smith]

Jim has hit all the nails on the heads here in this thread. I will also add that these things develop with time and are skills that one has to put the time in to master. That is not to say they are difficult - they just need to be mastered.

Particularly the V20 and also the S30 - these bikes are faster than the rider - they need to be mastered. Kind of like sliding into the cockpit of a formula one car - you have to learn the nuance before mashing the gas pedal down.

Expanding on this idea, reaction time and the decision making process are part of riding.

My wife is learning to ride a bike again. At this point her biggest challenge is the decision making process. When do I shift? Where do I start setting up my line for the curve that is coming? Who has the right of way as I come up to these pedestrians on the trail? What is the turning radius of this bike? Riding any bike is a cascade of decisions.

Within the first few weeks of riding my V20 I saw an average speed increase of 3-4 mph. At that relative speed change, every decision has to change. Throw in the center of gravity changes, the Dynamic Boom and full body integration and you quickly become aware that all of your decisions need to be altered.

I ride with DFs. I've needed to relearn how to space myself on climbs, descents and rollers. My tempo on climbs is different than the DFs. At times I blow by them and at others they pass me. I'm learning to really watch my spacing when conditions call for me to accelerate during a climb. More than once I've had to scrub off all of my momentum just short of the apogee of a climb because I've come up on the wheel of a friend without the space to pass them. In many cases these are much stronger riders than me.

It's a weird experience. At times I feel like I'm riding in molasses compared to them and others I pass them like they're traffic cones. All while maintaing a climbing rhythm that feels appropriate for the V20.

Then there are the rollers and descents. They know to get out of the way on long descents. One friend described Sigr-D as a torpedo on Wednesday's ride. And in hills where conserved momentum carries up the far side of a roller, I have to coast and periodically sit up. The V20 rolls so efficiently through this terrain that I become a guided missle. It's incredible. On a DF or RWD bent I'm a 12-13 mph rider. On Sigr-D I'm a 16-18 mph rider on level terrain. But in the rollers I find myself in the rarified air of 21-26 mph sustained riding with top speeds in the high 30's and climbing at 16 mph. Believe me when I say that requires rewiring the whole motherboard of my riding decision tree.

 

[Jim Parker]

This graphic is not meant to be modern art. It's a bird's eye sketch of the relationship between the hips and pedals when the boom is in neutral vs angled left (red) and angled right (green). If you are ready for some seriously geeky analysis, keep reading below.



I wanted to quantify the change in distance between the hips and pedals that comes from the upper body angling the boom. I turned our kitchen table into a drafting table, and set up a scale drawing based on 24 inches from the steerer (head tube) axis of rotation to the middle of the BB axle. For calculation purposes, I used 2 inches of lateral movement of the BB axle, which corresponds to 4.76 degrees left and 4.76 degrees right angling. I used a distance of 12 inches for the center-to-center distance of the human hips....




Next I used a "stance width" of 268 mm for a typical road bike crankset, from this excellent article.

Next, I calculated the total change in distance from the hip to the ipsilateral (same side) pedal with boom angling, when the pedal is straight up or down, which is 1.125 inches or 2.86 cm.

Next I calculated the average speed of the fore/aft movement of the pedals at a cadence of 80 rpm, calculating that to be 76.2 mm/sec.
Then using a little calculus, estimated the peak speed of the pedal to be 120mm/sec (0.12 m/s).



So now, in the Force diagram below, I inserted an approximate speed for the BB-end of the crank. Now I am not sure how to calculate the effect of that motion on torque. I'll sleep on it tonight, but let me know if you have any insights.

Jim

 

[Bentas]

Some great action of French mbb rider Olivier Pitchoun ,not to shabby speed wise for a steel homebuilt!
The interesting thing is you can hear his breathing at different speeds ,during the climbing near the end especially.

 

[Bentas]

You get a good idea of what Jim was talking about in an earlier post ,stopping pedalling/coasting and resuming again at high speed, I first read of Oliviers build report for this bike in 2010, this vid was created a few weeks ago, it's great to see how much control at speed can be gained after 5 years and many thousands of klms on fwd mbb format.
His camera is mounted so that you get a good view of more of the bike ,bars even hands at times which I feel puts you right in the drivers seat ,great stuff .
I just realised ,you get this view because his bars are mounted half way down the boom.
His gearing is compact 50 x34 and 28x11 , 11 speed cassette ,still pedalling at 70 klms hr at one point ,impressive!
You can see more of Oliver's vids on his sight Pitchoun en bent