Moving Bottom-Bracket Musings

[MrSteve]

I've read the standard logic, the, "Cool Aid" behind the MBB.
Specifically, the theory behind the idea that the climbing
prowess of the front-wheel drive MBB Cruzbike is partially
attributable to the extra input from the handlebars.

I think that's true enough, as far as that goes, but not the whole story.

My musings along this line of thought?

On a Cruzbike, the body replaces -or is a substitute for-
the frame that connects the bottom bracket to the rest of the bicycle on a
mainstream (non-MBB) bicycle.

So, with no frame to absorb flex, all pedal power is delivered to
the pavement.

This can be demonstrated by an experienced Cruzbike rider.
When the rider concentrates on maintaining a consistently
straight course, compensating for any pedal forces with appropriate
inputs from both the steering leg(s) and the handlebar, the
bicycle is much more efficient than when the rider allows the
bicycle to oscillate in time with the pedals.

So to sum up, my point is that, without a frame to absorb -and lose-
pedal-induced flex, the MBB can be more efficient.

On the other hand, until the legs learn to steer, it's more work...
since the rider is also doing the job that a frame normally does.

Yes?
No?
Maybe?


-Steve

 

[Mark B]

yakmurph wrote: Yes?
No?
Maybe?


-Steve

Maybe. In one of my earlier musings, I held the contention that you need to develop a "CruzBike Body" to be efficient on a CruzBike. What I meant by that was; you need to get your upperbody toned and conditioned to respond to your lower body input AND be mindful of what your hips are doing. It's a dance, of sorts and your body can figure it out in pretty short order as long as you keep your brain out of it. After riding a Cruzbike for awhile, you don't think the upper body input is there so much, but it is and it's a complementary force to your leg input. It doesn't wear on you, it acually spreads the workload and helps your legs endure, IMHO. If you doubt your upper body is so involved in riding a CruzBike, try switching back to a RWD bike and you will discover your body has learned a completely different dialect of body english. My experience was, the bike was totally unstable for a few miles until I readapted. It was scary, to tell the truth.

In my opinion, if you are able to ride hands free and go straight, that's a major accomplishment and testament you have your hips well under control. But, (and here's where I will probably take a real beating) I liken it to a cheap parlor trick. It's fine if you're just cruising, but I don't think you can easily power up to full running speed or climb very well in this manner. I base my opionion on the fact I can tell the difference when I just go to one hand. I feel the transfer in the one hand left on the bar; the increase of work needed to maintain my line. Try taking a hand off the bar on a climb, you'll feel the need for increased input from the other, or at least I do. Again, I don't think it's a bad thing, it's what makes the bike work and to that extent, I agree with you, Steve.

Mark

 

[Peder Torgersen]

Mark B wrote:

yakmurph wrote: Yes?
No?
Maybe?


-Steve

In my opinion, if you are able to ride hands free and go straight, that's a major accomplishment and testament you have your hips well under control. But, (and here's where I will probably take a real beating) I liken it to a cheap parlor trick. It's fine if you're just cruising, but I don't think you can easily power up to full running speed or climb very well in this manner. I base my opionion on the fact I can tell the difference when I just go to one hand. I feel the transfer in the one hand left on the bar; the increase of work needed to maintain my line. Try taking a hand off the bar on a climb, you'll feel the need for increased input from the other, or at least I do. Again, I don't think it's a bad thing, it's what makes the bike work and to that extent, I agree with you, Steve.

Mark

I also agree you need your arms when you climb. If you want to climb fast it’s a hard work out for your upper body.

Peder

 

[MrSteve]

It's funny that Mark mentioned transitioning back to a diamond-frame bike
-and those scary first few miles.

I test-rode a motorcycle for my brother-in-law last Spring, after having ridden
my Cruzbike exclusively for quite a few months.

The first few hundred yards on the motorcycle were pretty comical:
good thing the road was free of traffic!
:lol:
----

I'm training my dog to run with me on my Cruzbike
and he's doing pretty good, so far.


Add the input from a strong dog on top of the usual
low-speed MBB shenanigans....
Lots of fun!


-Steve

 

[Kamatu]

I'll note that you do get frame flex on the front triangle at least. I have a portion of the telescoping top tube that is nice and shiny to prove it when I was specifically getting my starting uphill part down. That wasn't a "it's too loose" release, it was a couple of day later "hmmm, this feels funny" feeling that a quick check showed about a half inch (1.25cm) shiny spot around the join.

OTOH, for a power climb, that force would be a downward torque around the front wheel, so, it might even be useful for keeping the front wheel on the ground.

 

[MrSteve]

Kamatu wrote: I'll note that you do get frame flex on the front triangle at least. I have a portion of the telescoping top tube that is nice and shiny to prove it when I was specifically getting my starting uphill part down. That wasn't a "it's too loose" release, it was a couple of day later "hmmm, this feels funny" feeling that a quick check showed about a half inch (1.25cm) shiny spot around the join.

OTOH, for a power climb, that force would be a downward torque around the front wheel, so, it might even be useful for keeping the front wheel on the ground.

Yes, that cam-clamp ...quick-release... whatever, the adjustable TFT must be very secure, very tight.
There is some flex in the front (only) triangle, but it's limited to the tubes themselves as the bushings in the
articulated triangle are massive overkill.
As others have pointed out, it would be nice to have a selection of solid, one-piece top-tubes available,
so that that one weak spot, the adjustable TFT, could be replaced with a one-piece tube.
...But, then again, that's a good winter project....

While I have you thinking of building custom tubes to tie the bottom bracket to the handlebar steerer tube,
why not build custom front swingarms (trailing arms), at your preferred length, to tie the bottom bracket to the front
wheel hub?
Moving the feet up a few inches would make you more aero and close up the angle between your legs and your torso
(I make more power this way).
This would make triple chainrings more practical; would require a few more links of chain and would totally
void the warranty!
-Another winter project!


-Steve