Gearing question for a GENIUS
 

I know that SoCal has it's fair share of brilliance, so I'm posing the query here as opposed to the Road Forum...At least this advice isn't quite so anonymous.

Standard Double versus Compact Double. Is there any sort of equation that proves that: a rider of a certain weight, climbing a certain hill, pedaling a certain cadence, going a certain speed...actually has to produce less wattage by using a Compact crank?

I know it's all about mechanical advantage, but I just can't get my head around it.

If a rider on a Standard is cruising up at 10 mph and is putting out 300 watts (hypothetically) isn't another rider on a Compact who's cruising up at 10 mph also putting out 300 watts, regardless of gearing? (Cadences being equal)

...I have more Standard vs. Compact questions...but I want to get this answered first. Kthx.

If two riders are going up the same hill using the same cadence at the same speed, they are using the identical gear ratio so the wattages would be identical. Whatever other gears are available do not apply to this question.

That exactly what I'm thinking...so the big argument for a Compact is "It's easier"...does that just mean slower, in most cases (pedaling a higher gear at lesser effort to scale the same grade)?

Why am I asking? I bought a Compact before thinking it through, and it's just sitting there...on my workbench...mocking me...

It gives a lower range of gears. I generally use a compact double as the lower range is more suitable for me. I spin out the top end at times but I am willing to endure that to have the low end gears available when I need them.

Since gear ratios take both sprocket sets into consideration, the original (marketing) idea was that the rear and front sprocket sets are smaller giving the same ratios but with less weight. It has evolved to just make the overall rations lower.

I am really craving a compact crank right now, since a) I am just getting back into riding for first time in almost 20 years, and b) this is the first time I have ever done hillls. That makes for a nigthmare scenario in the hills with a 53/39 + 12-25.

The past week I've been driving myself crazy trying to figure out my strategy... with the 2 primary solutions being buy compact crank or just change my cassette (from 12-25 to 13-29). I am leaning toward the cassette option, since it is cheaper (not to mention easier to swap out cassettes than cranks).

Well...here's what I did, just so's you know.

I bought and FSA MegaExo Gossamer compact.

I bought a SRAM PG-70 11/23 cassette (Gearing is close to a 53/39 with a 12/25, with a faster high speed and slower low speed)

I bought a Harris Cyclery High-n-Wide 11/28 cassette for the hills. Triple gearing, and faster than a 53/12.

I put 'em all on (the 11/23 for training...the 11/28 for climbing) and was subsequently dropped by my racing buddies, and blamed it on the compact because I'm fat and didn't want to admit that I'm just not in as good of shape as them. Swapped it all back to standard, and am now hemmin' and hawin' again.

If you go compact and run a 11-27 you will have the best of both worlds, or so I read in another article.:rolleyes:

BZZZT. This is where you look at total weight. Gear ratio doesn't matter for power output. If you have a 200lb rider going up a hill at 10mph vs a 150lb rider on the same hill at 10mph, the 200lb rider is going to be putting out more power to go the same speed. His buddies dropped him because he was probably spinning in a lower gear using less wattage than they were, therefore he was going slower. The biggest thing about climbing hills is power to weight, and there are only 2 solutions, make more power that you can maintain, or lose the weight and keep the power you have. They did an example in Buycycling once where there was a 3 mile 6% constant grade, and at 250W power output, for every 5lbs of weight it was 30 seconds longer to climb the hill. So, if you're like me at 30ish lbs overweight, and your buddies aren't, you'll take an extra 3 minutes to climb that hill if you both climbed at 250w. The reason Lance never won the tour earlier in his career was because he was carrying 15-20lbs he didn't need to carry in upper body, he lost that during cancer treatment and he became one of the best climbers in the world. The engine was always there, it was just moving more weight than it needed to, and at that level, that's a huge difference.

What are your plans for that high and wide? :)

Not in MY thread, buddy! Please, for the love of pete...it's lose. (extreme pet peeve of an anal-retentive English major)...forgive me my quirk.

Keepin' it. I'm a pack rat.

To be honest, the Compact w/ the high-n-wide was the most versatile combination I've ever ridden. I think I relied on the 34/28 far too often for my own good and sacrificed strength training for just getting up the hills without effort.

Okay, here we go... All dimensions in this discussion are unitless, so meaningless constants have been removed. Hang in there, Paul...

Energy = Mass * Vertical Gain * Gravitational Pull

Neglecting parasitic forces (wind resistance, rolling resistance, drivetrain inefficiencies, differences in pedaling efficiency, etc) makes for pretty good and pretty easy approximations on steep enough a hill. Once we make that approximation, what we find is that it takes the same amount of energy to get up that hill no matter how you go about it. After all, your mass doesn't change with how you climb, the vertical gain isn't changing, and the earth's gravity most definitely isn't affected by your climbing technique. (On the other hand, once Mars gets terriformed, climbing Olympus Mons wouldn't be nearly the challenge it would appear to be since the gravitational pull on Mars isn't as great.)

Energy = Power * Time = Power / Speed

The first part is simple physics. The second part is pretty obvious since time and speed are inversely related. The faster you climb, the more power you need. Climbing 50% faster takes 50% more power. Plain and simple. But notice that climbing 50% faster gets you up there 50% faster, so your total energy expenditure stays the same. This is why the mountains are where huge time gaps are made.

Power = Torque * Cadence = Pedaling Force * Crank Length * Cadence

Here is why gearing matters. For the same speed, you can do it in different gears, resulting in different cadences. Your cardiovascular system (again neglecting parasitic forces) doesn't care because the same amount of power is needed at that speed no matter how you go at it. (In reality, higher cadences have slightly higher parasitic forces.) But your leg muscles may care, because you can only pedal so hard without getting tired really fast.

To be continued...

Here's a Lance question; Carmichael and Ferrari re-trained Lance to climb (and bike, basically) at a higher cadence than everyone else. What gearing was he using? I though he was pretty much climbing those monsters with a 39/25, but if he was pedaling at 110 rpm and his rivals were in the same gear but pedaling at 80-90, how come they always seemed neck-and-neck (until LA's ultimate superhuman breakaway)?

Im thinking they had different gearing. Im not a spinner like Lance unfortunatly(sp), Im more of a mid range guy like Ulrich. I doubt the two of them were using the same gearing.

Thanks, Jason.

Gee guys, since Mo'Phat was talking about himself in the original question and really comparing a compact vs. a standard double, mass does not apply. (at least that is how I interpretted it). I mean, does one really believe I didn't realize that the more mass to move against gravity, the more power will be required.

Serves me right for getting involved in this type of question. So, you guys are right...I will keep quiet now.

So,,,BZZZZTTT over and out

Gearing choice. Assuming the same rear cassette, a 50/34 gives a 15% lower low gear than a 53/39. That means that assuming you're in your low gear (otherwise, it doesn't matter since you can adjust your cog selection accordingly) you can go 15% slower while going at the same cadence. Alternatively, you can achieve a 15% higher cadence while going at the same speed.

Picking artificially higher gearing will make one's legs stronger over time, but it does not ensure faster performance. If you are sufficiently overgeared that your legs' ability to generate force/torque becomes the limiting factor, then you would be faster going with a lower gear. Because long distance climbing on a bike is ultimately a cardiovascular exercise, fatigue notwithstanding, you are ultimately about the same speed no matter what your cadence as long as your cadence is reasonable. But your legs probably can go at it longer in the high end of the cadence range since they are being asked to put out much lower forces. ("Reasonable" and "high end" being relative to one's personal efficient cadence range.) But on the really low cadence regime, you can only pedal so hard. You become torque limited, and power becomes essentially proportional to cadence.

When pushed for an answer, Terry Morse guestimated this low cadence regime to end at about 50 RPM. My own experiences would put my estimate of this low end somewhere in the 40-60 RPM range, too. Below 40 RPM, I clearly am torque limited, and getting my speed up with a temporary burst of power allows me to maintain that speed afterward because my power rises as my cadence rises. In the 40-60 RPM regime, it's probably not a 1:1 correlation anymore, but bringing my cadence up still definitely helps. Above 60 RPM, my climbing speed basically is determined by cardiovascular limits. Though as I tire, my leg strength goes before my lungs, and very late in a long ride (or late in a hard ride), my preferred minimum cadence keeps going up.

This is what I have on my new bike! Am I in trouble??? http://server12.ipslink.com/~wwwmama...ult/nerves.gif

You're right. It only appears as an incidental term (along with gravitational pull) in the first equation to first establish that parasitic forces aside, energy = vertical gain. Simple physics equation. After that, discussion of mass and gravitational pull falls to the wayside because those are being assumed constant.

Sorry... the future science professor in me likes to start from well established points and work a discussion from there.

No, you could change the rear cassette to a 13x29 and be fine. I have found that I can climb with what I have. Gears often times make me lazy. Meaning Ill shift to an easier gear just because I think I should, not really because I need too. It may take you 3 to 4 weeks to get used to it depending on how much you ride. I think you'll be fine, and you will get faster. The body adapts better then the mind.:p

Climb with it and find out! :D

:p That's the only way to find out, I guess. :)

Sean, that's true... but I don't want to have to turn back on a ride because I can't handle it! That would bum me out.

Sorry for the hijack, Mo'Phat http://purplepixelations.com/karensemotes/hijacked.gif

If you decide to go with a compact crank, there are options that start as low as $140. Or you could just get a different cassette in the back to start.

Better give that bike to me! :D Just kidding...

With existing gearing, you may be more limited in terms of what you can climb. It's equivalent to losing your two lowest gears on your Trek. But happily, gearing can be changed.

the purpose for compact gearing is to get lower gearing with a closer group of gears. if their cadence is equal their gear inches will be equal, if the compact rider is in a 34x17 and at 90rpm and the standard rider is in a 40x20 at 90rpm they are both in a 54 inch gear (front/backx27=gear inches). theoretically the compact uses less energy as there is slightly less friction on the smaller gears (unless go go too small like an 11 tooth where the severe chain angle wrapping around the cog adds more friction) but this is too hard to measure in the real world. so the answer is NO the wattage will be the same for both riders.