Cruzbike v all others

[tallaussiesje]

If MBB bents are more efficient wrt wind resistance compared to DFs, and more efficient compared to "RWD" bents for energy transfer, the cruzbike should win all around, all things being equal. Looking at the records, the cruzbikes seem to be dominating the other bents, but are getting pipped by the best riders on DFs. I ask both as a skeptical scientist, but also as someone looking to trade up to a cruzbike.

What can we take from the races and records, especially comparing Cruzbike to DFs? Is it
(a) riders
(b) DF lighter
(c) energy transfer still better on DF
(d) less wind-related cooling on Cruzbike lowering performance in heat
(e) sample size (i.e. a few people on Cruzbikes versus many on DFs).

 

[Charles.Plager]

Well...

Hi,

I think one needs to be a little careful here...

* I believe a time trial rider on a diamond frame is probably more aerodynamic than I am on my Sofrider. I don't know what happens when you compare Bradley Wiggins to Maria on her V.

* We really don't have equivalent athletes. What Maria has done is very impressive, but she doesn't get paid to do nothing but ride her bicycle (well, at least as I understand it). And there's a big selection bias. The world's best althletes who ride bicycles want to win races. All UCI races don't allow bents. So, the world's best athletes don't ride bents.

* You can't just move from a DF to 'bent and put out the same power immediately. They use different muscles. Conversely, bent riders can't move to a diamond frame if they've done their traning on a bent.

* I haven't seen anything to suggest that the energy transfer on a DF is any better than that on a Vendetta. People who have looked have found no flex in the bottom bracket when power was applied. It is hard to measure very small effects, so I don't know which way this goes. I believe (but do not have scientific evidence) that the power transfer on the Vendetta is probably better than almost all other bents.

* Yes, the Vendetta is heavier than the lightest carbon fiber bikes. If you are climbing a hill or accelerating quickly, weight does make a difference. Complete UCI-approved bikes have to weigh, I believe, at least 15 lbs. A fully equiped Vendetta, according to the Cruzbike page, is just under 22 lbs. If your skinny, 7 lbs could make a difference. (Not a problem that I have. ).

For your part (d), that's a good point. Less wind resistance means less cooling which could affect performance in the heat.

During a similar conversation on Bent riders on line, somebody complained that one shouldn't look at the records that were set on a bike to compare bikes. The response was (more or less) this: The fact that a record was set on a particular model doesn't mean that you are going to set a record when you are on that bike. But it is a very good indication that the bike didn't get in the way (through power loss, through not being (relatively) comfortable to ride during the event, etc).

For me, the most important thing is to ride. I looked at the Cruzbikes and decided they looked much more comfortable than what I was riding (ironically, a "comfort bike"). I bought a Sofrider and I haven't looked back yet. If you are looking, then I believe you'd be happy if you decided to switch.

What is best for you depends on what you want to do. If you are currently a roadie and want to continue to keep up with them (or better), get a V. If you want (fill in the blank) then (I'll give you a better answer when I see what you wrote for the last blank).

I'm now as fast on my Sofrider as I ever was on my road bike (which I didn't have very much experience on). They also have these weird geographical anomalies where I now live (I believe they are called hills ) that really mess with me (I'm from the flat part of Illinois - yes that might be a bit redundant).

Good question. Keep 'em coming.

Cheers,
Charles

p.s. You can check out my blog below for more details about my experience with the Sofrider.

 

[Hilry]

Bike type comparisons

From a scientific point of view the best tests would be the same person riding the different types in the same conditions.
I live near where Wiggo lives. When I've finished me conversion I'll pop round and get him to have a go shall I?

 

[Charles.Plager]

PLEASE get me a picture of

PLEASE get me a picture of Wiggo on a Cruzbike. ALLEZ WIGGO!



Charles

p.s. For a serious answer for anybody else reading:

If a single rider had equivalent experience with both types of bikes, then yes. What most people experience when they first move to a 'bent is that they put out significantly less power until they build up their 'bent legs. So it will take some time for new riders to be able to be "the same person" on both platforms. For what it's worth, a member on BROL has the opposite problem: his bent legs are great, he's got very little training riding a DF bicycle...

 

[Hilry]

Get a picture of

When I go flying past him on my Cruzbike I'll flag him down for a photo then!

...certainly would know the answer to the question if that wre true.

 

[leakyduck]

I found "(e) sample size (i.e. a few people on Cruzbikes versus many on DFs)." to be an interesting issue. The number of good riders on Cruzbikes is a very small number of the total bent community.

What drew my attention to the Cruzbike was the fact that Maria Parker is breaking her own records set on a different brand of recumbent. I think that is a comparison that tells something about the Vendeta.

 

[Jim Gerwing]

V vs the world

Wind resistence increases as a square to velocity.
The largest factor to overcome as you go faster is pushing through the air.
The simplest solution for more speed (given a set amount of power) is to decrease frontal area.
Cyclists on Diamond Frame bikes achieve this by wearing tight fitting clothing, aerodymic equipment (teardrop helmets), leaning forward and tucking everything in like elbows and knees.
Another way to achieve this is to get more supine (as with the V and most recumbents that aspire to speed).
Another way to achieve this is to get more prone (see Graeme Obree's latest bike on his website where he assumes a laid out praying hamster position). You won't find too many bike like his in the world (or a rider with his ability despite his age - north of 50).
The extra feature that the Vendetta brings beyond decrease of frontal area (when compared to DF limits) is the drive mechanism which doesn't suffer from an incredibly long chain and problems of energy transmission from the point of origin (pushing on pedals) to point of application (back tire meeting the road). t
These points for me are theoretical because I have never ridden a recumbent but by the looks of things the greatest benefit of a recumbent, in particular the Vendetta, is an energy efficient body position and a drive system that appears to be at least as efficient as an upright bike (except on 'hills').
Of course, and this is proven every year at HPV meetings, if you want to go faster still (after optimising your prone or supine position without sacrificing your ability to apply an equitable force), you enclose the entire system (bike and rider) with a full aerodynamic fairing and you'll get some pretty impressive speeds (for humans).

 

[tallaussiesje]

Very interesting all around.

Very interesting all around. I wonder if there is some residual energy transfer issues with MBB vs DF because of the tendancy of the MBB to move with legs. In theory, you might be able to address this through a front wheel drive tadpole trike, or rear wheel steering/front wheel drive 2 wheel bent.

 

[Charles.Plager]

Hi,
If you're huffin' and

Hi,

If you're huffin' and puffin' on an upright, you're standing up and the bike is actually rocking side to side. (O.k. it doesn't happen when I try to ride DF fast, but when the pros do this is what happens).

When you push hard on a Cruzbike you get pedal steer. I think these two effects are morally similar and it's not obvious to me that one or the other causes bigger efficiency losses.

If I wanted to go fast, I'd ride a V. If we got enough interest, maybe we could convince Cruzbike to make a carbon fiber Vendetta.

Cheers,
Charles

 

[Jake]

high speed pedal steer


At high speed the rotating wheel itself resists pedal steer. This is the same force that helps keep a bike upright at speed. At slow speeds, pedal steer is more of an issue, as is trying to balance the bike. Spinning wheels just want to go straight.

Jake

 

[John Dorlon]

from DF to Silvio

If you want to compare DFs to Cruzbikes, I think I can offer some perspective. I started DF cycling in 2010 (at age 40) and averaged around 15.5mph on a 17lb Felt F55. I kept at it until June 2012 when I bought my Silvio, primarily caused by back pain. I had never ridden any other type of recumbent. The DF wasn't the cause of the back pain, it did make the pain more noticable. Anyway, I was averaging around 16.5 on the DF when I stopped riding it. I noticed faster speeds on the Silvio immediatly. Now, on my longish rides (60 miles) I can now average 17 mph, and my shorter rides (35 miles) I can average 18mph. There was only one ride on my DF when I went that fast, and it was because I had a good tail wind most of the way.

I definitely agree with Jake about pedal steer and speed. The only time I have to think about pedal steer is when I am pedalling hard and moving slowly - either up a hill or just starting off.

I would say choices a) and e) in your post make the most sense. As for the others:

b) I don't notice the extra weight of the Silvio except when I lift it. In fact, knowing that it is heavier but still faster makes me less concerned about weight. The aerodynamics of the Silvio allow me to gain more speed on the flats or downhills right before an uphill, and I am finding that I am able to approach hills with more momentum, so I can get over them faster.
c) I think energy transfer on my Silvio is equal to that of my DF. After all, the triangle is the same and the drivetrain parts are the same.
d) I live in Texas. It gets hot here. This hasn't been an issue for me. I will say that being in a reclined position exposes you to the sun a little more, so that makes sunscreen more important on a recumebent than a DF.

Like many others here, I bought a Cruzbike without being able to test ride, and I am completely happy with my purchase.

 

[leakyduck]

V vs All others

tallaussiesje said "Very interesting all around. I wonder if there is some residual energy transfer issues with MBB vs DF because of the tendancy of the MBB to move with legs. In theory, you might be able to address this through a front wheel drive tadpole trike, or rear wheel steering/front wheel drive 2 wheel bent."

It's been done. Called a Flevobike. Out of production. I tried to ride one once (ONCE). I did see the owner ride it, but I was not impressed.

As for power in the recumbent position. Jim Parker posted on another forum a picture of Maria on her Venteda. He used a graphic program to rotate the picture and lo and behold - Maria was in the same position as she would be on a DF, except she was reclined and thus more aero.

As for the cooling issue. We ride in the high desert (100+ temps) and have never had a problem overheating. You are still getting air flow and thus cooling.

 

[Jim Gerwing]

I don't have a Vendetta but...

Check out the website 'analytic cycling'. There is a feature that allows you to predict speed based on a number of variables that affect the production of velocity such as: frontal area exposed to the atmosphere, aerodynamic drag, air density, system mass, rolling resistance, slope and wattage.
I played with these factors, changing one at a time to see the effects on speed. I ignored some factors because they are less of a concern to me but visit the site and have a go yourself if interested.
I found that, for my parameters, changing the mass of the system (bike plus rider weight) by -10% resulted in a 0.7% increase in speed.
Changing air density (which factors in temp., humidity, air pressure and altitude) by -10% resulted in an increase of speed by3.4%.
Changing frontal area by -10% resulted in an increase of speed by 7.2%
Changing slope by 10% down to even ground resulted in an increase of 72%. (Hills, ie working against gravity, is a significant chore)

I have a Vendetta on order.
If I can hit the right day (meterological conditions) on the right course (flat) in good shape (a few pounds lighter) able to produce a decent wattage combined with cycling skill (say 1/3 of a horsepower~250 watts average input) on a Vendetta (as opposed to my DF) which will give me a decrease of frontal area of, I'm estimating, 10% THEN I should be able to perform a significant personal best. 7.2% seems a lot to hope for but that's the calculation.
We'll see.

 

[Charles.Plager]

Hi Jim,
I'm assuming you are

Hi Jim,

I'm assuming you are talking about http://www.analyticcycling.com/ and this page in particular. Quite cool.

At higher speeds, air resistance is pretty much everything (which is quite consistent with what your numbers above showed).

I guess the next interesting thin will be a Vendetta with a fairing, followed by a Vendetta with a fairing and a full wrap.

(Could you imagine one of those going down a 10% slope? As George Takai would say: Oh my! )

Cheers,
Charles

 

[Jim Gerwing]

Good Guesses

Heh Charles:
I haven't bothered to figure out how to paste a link knowing that Google can take care of the extra step in e-navigation.
You got me thinking about gravity as a hinderance to forward progress. This is where the DF has an advantage because one may pull down on bars as well as push down on the pedals whereas on a recumbent one can pull back on the bars and merely push out on the pedals(no assistance from gravity). In fact the steeper the grade, the worse the condition becomes where one is actually needing to push up on the pedals to a degree. But I am not concerned being a flat lander.
As for fairing, you are reading my mind. If I am faster on a recumbent (and I do have a v on order) my next step will be to put a full fairing on it and see what we can do.
As to your parenthetical note: have you checked out 'gravity bikes'? Scarey fast but not my cup of tea.
Regards,
Jim

 

[John Tolhurst]

"You got me thinking about

"You got me thinking about gravity as a hinderance to forward progress. This is where the DF has an advantage because one may pull down on bars as well as push down on the pedals whereas on a recumbent one can pull back on the bars and merely push out on the pedals(no assistance from gravity). In fact the steeper the grade, the worse the condition becomes where one is actually needing to push up on the pedals to a degree."

I don't subscribe to this analysis. To my mind, the body is able to put out its power regardless of its particular orientation to gravity, as long as its weight is supported adequately. Prone, upright or recumbent.

 

[tallaussiesje]

Interesting with the

Interesting with the Flevobike.

re fairings, I understand the advantage of fairings. Being encased is especially important for maximum speed or for keeping dry, but for long distance races it would appear that the extra weight is a disadvantage. Thoughts?

 

[leakyduck]

Fairings

Farings are relitivly light, but the areo advantage is major.

After the elections are over in Nov I was planning in harvesting some Coroplast and having a go at a free fairing.

If I do it, I will post the results here

 

[John Tolhurst]

Go ask Tom

http://traylor_fwd.home.mindspring.com/critical_mass.html

Tom Traylor's site has changed very little if at all since 2005 when I started designing these kinds of bikes. Its very difficult to go somewhere in a design and research sense and not find Tom there waiting for you.

 

[Charles.Plager]

Hi,
@tallaussiesje:  Weight

Hi,

@tallaussiesje: Weight only matters for climbing and acceleration. Air resistance matters for everything. This is why velomobiles (which are usually twice as heavy as regular recumbents) do so well as far as average speed over a given course.

@Jim: On most recumbents, you can brace yourself against the back of the seat and put out more force than if your just using gravity (a la DF). On Cruzbikes (but not most other recumbents), you can pull against the handle bars as well (just like on DFs).

I really want to see a Vendetta with a fairing and a windwrap...

Cheers,
Charles