Ask Bobke: Compact Drivetrain

[RADaines]

Did anyone see the Ask Bobke segment last night on Versus? He was asked whether the TdF riders use compact drivetrains for the mountain stages. His answer was "no" and the reason was something about the chain length being too short, not providing sufficient leverage. Is this true? Can someone explain this a little better than he did? Thanks.

[wasfast]

Some riders do use compacts but mostly on the ultra steep climbs (18-24%). Most are still using 39/53. When you consider the average speed yesterday was 19mph up the 12 mile Tourmalet, you don't need a "lower low" gear. That speed BTW, is downright amazing to me.

As far as the Bobke comment on the chain length, makes no sense to me. Chain length in general is all about how you setup the length in the first place.

[jblande]

Edit: my information was about the previous stage, I misread. Apologies.

[veloduffer]

Bobke's explanation sounds odd. A lot of pros turn big gears, even in the mtns.

Remember when Lance started winning and folks noticed how fast he was spinning. He was/is one of the few pros that spin small gears up the mtns. Supposedly, he and Carmichael figured it was more efficient than trying to turn a big gear slowly (like Ullrich). Similar to distance runners where small strides are more energy efficient than long ones.

[goonster]

Remember when Lance started winning and folks noticed how fast he was spinning. He was/is one of the few pros that spin small gears up the mtns. Supposedly, he and Carmichael figured it was more efficient than trying to turn a big gear slowly (like Ullrich). Similar to distance runners where small strides are more energy efficient than long ones.
According to D. Coyle's account, it was indeed the strides of Kenyan distance runners that sparked the inspiration for optimizing Lance's reduced post-cancer torque for maximum power output. However, iirc, it was Dr. Ferrari, not Carmichael, who developed the approach.

At any rate, it bears repeating that while Lance's style was very different from Ullrich's or Indurain's, the cadence was not something heretofore-unseen, and did not require anything other than the standard gearing of the era.

[srice]

I saw it too and I was scratching my head at his answer. Something about chain length and not enough leverage??? huh???? It made absolutely no sense to me.

[fiamme red]

At any rate, it bears repeating that while Lance's style was very different from Ullrich's or Indurain's, the cadence was not something heretofore-unseen, and did not require anything other than the standard gearing of the era.I heard so many times from Phil Liggett about Ullrich "turning over a massive gear," compared with LANCE's spinning up the mountains, but in practice I doubt that there was much difference between the gears the two would climb with (e.g., if Ullrich was in a 39x19, Armstrong might be in a 39x21).

[spacemen3]

According to Leonard Zinn (http://www.facebook.com/topic.php?uid=61846853456&topic=7741), Ullrich rode with longer cranks, which gave him the same efficiency benefits as Armstrong's spinning, but at a lower cadence. Apparently, it made accelerations more difficult. It's amazes me the rate those guys pedaled up the Tourmalet.

[weisan]

When I decided to switch over to compact systems five years ago, I asked my lungs, my back, my belly, and finally my legs...they all gave me the nod....I did not go askin' some back alley fortune-teller named bokke. :D

[BengeBoy]

I saw it too and I was scratching my head at his answer. Something about chain length and not enough leverage??? huh???? It made absolutely no sense to me.


This was caught my ear, as well.

I was OK w/the explanation that the pros can ride a "conventional" 52/39 or 53/39 crankset in the mountains, but the statement that a difference in chain length provides more leverage is something I've never heard before.

I wonder if he was trying to provide a quick, layperson's discussion about "chain line" not "chain leverage" ?? (although that still doesn't make sense...).

[Andreas]

I heard so many times from Phil Liggett about Ullrich "turning over a massive gear," compared with LANCE's spinning up the mountains, but in practice I doubt that there was much difference between the gears the two would climb with (e.g., if Ullrich was in a 39x19, Armstrong might be in a 39x21).

Right on.
This is one of these myths that took off due to an ill informed commentator and subsequently were passed on via the interweb - amazing.
Now it is used as an explanation why one rider could ride away from all the others for a few years - "spinning up the mountain" - right.

[thwart]

Compacts were really big in the last week of the Giro this year... almost everyone was on 'em.

http://velonews.competitor.com/2010/05/road/gearing-for-monte-zoncolan_118163

Does that mean the Giro d' Italia is tougher... ?

[bzbvh5]

Does that mean the Giro d' Italia is tougher... ?
That's what I thought. Other forumites explained to me the Giro is not tougher because only Liquigas brought their A Team to the Giro. The Tour has all A Teamers.

But I do remember a comentator talking about the use of compact cranks on one stage of the Giro.

[goonster]

Does that mean the Giro d' Italia is tougher... ?
I believe the Giro often has steeper max. grades than the TdF. That doesn't mean it is "tougher". After all, it's not so much the route rather than the level of competition that makes the TdF the toughest of the grand tours.

[BengeBoy]

Compacts were really big in the last week of the Giro this year... almost everyone was on 'em.

http://velonews.competitor.com/2010/05/road/gearing-for-monte-zoncolan_118163

Does that mean the Giro d' Italia is tougher... ?

Also I thought there was some PR about someone (Vino?) using one of the new SRAM Apex rear derailleurs with a 12-32 cassette on one of the big mountain stages of the Giro. With a compact crank as well, as I recall.

[McQueen]

According to Leonard Zinn (http://www.facebook.com/topic.php?uid=61846853456&topic=7741), Ullrich rode with longer cranks, which gave him the same efficiency benefits as Armstrong's spinning, but at a lower cadence. Apparently, it made accelerations more difficult. It's amazes me the rate those guys pedaled up the Tourmalet.


Lennard Zinn may be a master of most things mechanical, but his theories on long crank arms are one area that I think he is off the mark.

[ClutchCargo]

Some riders do use compacts but mostly on the ultra steep climbs (18-24%). Most are still using 39/53. When you consider the average speed yesterday was 19mph up the 12 mile Tourmalet, you don't need a "lower low" gear. That speed BTW, is downright amazing to me.

As far as the Bobke comment on the chain length, makes no sense to me. Chain length in general is all about how you setup the length in the first place.

Where did you get the 19mph average from?
Horner did shared his power meter data with SRM and they reported that he did the climb in 52:22. I believe the climb is 11.532 miles (18.6km) long. by my math, that results in an average of a little over 13 mph. :confused:

[McQueen]

I thought I smelled a lot of bs in Bobke's response.. But let me ask this hypothetical...

If you have the exact same gear length, and you have two different setups producing it.. One being a 42-14 and the other being a 39-13.. Both are 81" (and assume they are for the sake of argument.)

Would leverage play into it at all, say because the distance between the center of the spider and the outside teeth of the chainring is longer, creating more leverage with each downstroke.. Or is it completely negated by the lesser amount of leverage in the rear. Just trying to think through his explanation for any soundness to the theory?

[jvp]

I think the 19mph ave was for the entire stage. Still pretty impressive considering the last ~12 miles were climbing the tourmalet.

[Richard]

I believe the lever arm is the crank to bb distance, not the bb to chainwheel distance. The longer the crankarm, the longer the lever. The size of the chainwheel and cog should be immaterial.

[Onno]

Could it be that Bobke simply misunderstood what a compact crank is--thinking it refers to short crank arms, rather than smaller rings? That's the only way I can make sense of what is reported he said.

[John M]

Or is it completely negated by the lesser amount of leverage in the rear.

Yes.

His jabbering is just that. The actual differences in friction caused by differences in chain tension that result from chain length or cog size discrepancies would be negligible compared to that required to overcome resistance to air (wind) and road friction. A properly maintained modern chain-drive derailleur-equipped bike is highly efficient.

[ping771]

Also I thought there was some PR about someone (Vino?) using one of the new SRAM Apex rear derailleurs with a 12-32 cassette on one of the big mountain stages of the Giro. With a compact crank as well, as I recall.

If I'm not mistaken, Contador used a 11-32 cassette made by SRAM that had in the 2008 Giro, which was one of the motivating factors in the development of the Apex. The following is a quote from BikeRadar.com on the Apex: "At the launch of the Apex groupset in Mallorca, Spain on Tuesday, SRAM explained that the idea for the 11-32 cassette was born directly from Contador's triumph on stage 16 mountain time trial to KronPlatz at the 2008 Giro d'Italia, a result that helped secure his hold on the maglia rosa."

[Ralph]

I thought I smelled a lot of bs in Bobke's response.. But let me ask this hypothetical...

If you have the exact same gear length, and you have two different setups producing it.. One being a 42-14 and the other being a 39-13.. Both are 81" (and assume they are for the sake of argument.)

Would leverage play into it at all, say because the distance between the center of the spider and the outside teeth of the chainring is longer, creating more leverage with each downstroke.. Or is it completely negated by the lesser amount of leverage in the rear. Just trying to think through his explanation for any soundness to the theory?

81" gear is a 81" gear. Front cog divided by rear cog X wheel size. There are several combinations that can give this. It can't matter as long as it's a decent chain line.

[RADaines]

Here's the actual video. Very funny.

http://www.youtube.com/watch?v=Sfv9Z3kKbgs

[palincss]

81" gear is a 81" gear. Front cog divided by rear cog X wheel size. There are several combinations that can give this. It can't matter as long as it's a decent chain line.

It can't matter all else being equal. But if you got your 81" gear with 16" wheels and a 50 x 10 tooth rear sprocket your drive train will be much less efficient than if you were using a 50 x 16 tooth rear sprocket and 700x23 tires and you might very well notice that.

[learlove]

I think Bobke has been drinking alittle too much vino.

Maybe he should just concentrate on the number of times he can mention "Lance Armstrong" in a broadcast so he can get his $$$ up before Lance goes bye bye and with it super expanded coverage of bike racing and the tour. I bet next year, sans Lance, it will just be Phil, Paul and Bob commentating. No Chris, Frankie and others ect. and Bob will have to do Frankie's job in teh field not sit at the table with Paul and Phil.

[Chief]

The posed question is: "Is it acceptable for them (pros) to use a compact crank geared 50/34 with a 12/25 or 12/27 cassette." Forgetting the BS about chain length for now, Bobke makes the point that the 12/25 or 12/27 cassette is used with 53/39 and 53/42, but the 50/34 is not used by the pros with these cassettes because they don't provide enough torque (leverage). One could argue that with the same cassette greater torque is provided with the larger chain rings which, with everything else being fixed, requires a longer chain--clearly a rather convoluted argument. If greater torque is required, then a 11/23 or 11/21 cassette could be used with a 50/34 crank. As I interpret his response it has to do with 12/25 or 12/27 cassettes being used.

[CaptStash]

It can't matter all else being equal. But if you got your 81" gear with 16" wheels and a 50 x 10 tooth rear sprocket your drive train will be much less efficient than if you were using a 50 x 16 tooth rear sprocket and 700x23 tires and you might very well notice that.

Why? You still have the same mechanical advantage. The exact same force would be required to turn the wheel. This of course assumes you could make a chain bend around a 10 tooth cog. Remember that when we use tooth counts it's only shorthand for diameter. If you could use less force with one way to get a certain mechanical advantage over another you would be violating the second law of thermodynamics. And we wouldn't want that now would we?

CaptStash... (the physics police)

[wc1934]

would someone please pass Bobke another beer

[PacNW2Ford]

Why? You still have the same mechanical advantage. The exact same force would be required to turn the wheel. This of course assumes you could make a chain bend around a 10 tooth cog. Remember that when we use tooth counts it's only shorthand for diameter. If you could use less force with one way to get a certain mechanical advantage over another you would be violating the second law of thermodynamics. And we wouldn't want that now would we?

CaptStash... (the physics police)

Time to turn in your badge - the "2nd Law of Thermodynamics"?????? Entropy? Whaaaa????

[palincss]

Why? You still have the same mechanical advantage. The exact same force would be required to turn the wheel. This of course assumes you could make a chain bend around a 10 tooth cog. Remember that when we use tooth counts it's only shorthand for diameter. If you could use less force with one way to get a certain mechanical advantage over another you would be violating the second law of thermodynamics. And we wouldn't want that now would we?

CaptStash... (the physics police)

As a physics polizei you should remember that the efficiency of a chain driven by a 9 or 10 tooth sprocket is dramatically worse than the efficiency of that same chain driven by a 15 or 16 tooth sprocket. You would notice that loss of efficiency, I think.

As for "assuming you could make a chain bend around a 9 tooth sprocket", they're in common use every day on folders and small wheelers using the Shimano Capreo group. Also, back when the AM series Moulton came out, it used a special 9-10-11 tooth cog set on a specially modified Sun Tour freewheel.

[CaptStash]

Time to turn in your badge - the "2nd Law of Thermodynamics"?????? Entropy? Whaaaa????

You are correct sir. I take of the badge. Throw it on the ground and stand on it. Bad badge.

CaptStash.... (Disgraced policeman)

PS: I meant the first law.

[PacNW2Ford]

I shot the sheriff...

Have a good weekend

[johnnymossville]

Longer is better. That's what she says.

[Elefantino]

Who still watches Bobke, let alone asks him something?

I have successfully navigated my second straight Tour without having watched Mssrs. Roll and Hummer. In the morning, it's strictly Harmon and Kelly, and when my wife watches at night it's the two-hour replay of Phil and Paul.

Bobke?

Meh.

[johnnymossville]

Who still watches Bobke, let alone asks him something?

I have successfully navigated my second straight Tour without having watched Mssrs. Roll and Hummer. In the morning, it's strictly Harmon and Kelly, and when my wife watches at night it's the two-hour replay of Phil and Paul.

Bobke?

Meh.

I think Bobke is on something. possibly a prescription.

[mgm777]

I think Bobke is on something. possibly a prescription.

Quite possible. He shattered his femur and tore his femoral artery this past winter in a skiing accident near Durango. I saw him in April and he was still hobbling around on crutches. I think he rode up Tourmalet during the rest day. Bobke has an eccentric personality and is tough as nails.

[oldpotatoe]

Also I thought there was some PR about someone (Vino?) using one of the new SRAM Apex rear derailleurs with a 12-32 cassette on one of the big mountain stages of the Giro. With a compact crank as well, as I recall.

sram MTB RDers are compatible with sram road levers. So he could use a XX RD and a MTB 10s cogset. sram made a touring group when they made XX w/o even knowing it. Barends, XX RD, 12-32 10s cogset..etc.

[wasfast]

Where did you get the 19mph average from?
Horner did shared his power meter data with SRM and they reported that he did the climb in 52:22. I believe the climb is 11.532 miles (18.6km) long. by my math, that results in an average of a little over 13 mph. :confused:

Phil gave the average speed as 19.1mph. I may be incorrect between the climb and the entire stage. I didn't have any data, just a TV commentator and I believe EVERYTHING I hear/see on TV:_)

Even so, 13mph average doesn't need a compact crank (34/50 or so)

[victoryfactory]

Maybe what Bobke was trying to say was that a pro
racer still wants that 53 even in a
mountain stage for the flats and down
hills?
He would fall behind pretty quick
with a 50 big ring on the flat bits.
He is an ex pro after all. The problem
is he tries to make up for his
inarticulate comments with his nutty
guy act. (maybe it's not an act)
He knows what he is talking about, but
we don't. For the 99% of viewers who aren't bike geeks, It doesn't matter.

Like Shatner said to the Trekies... get a life.

VF

[BengeBoy]

He knows what he is talking about, but
we don't

VF

I think that's the problem; he's now getting paid to be a TV commentator, explaining cycling to a mix of real enthusiasts and folks who might tune in only once a year. *If* he knows what he's talking about, he should explain it differently.

I re-watched this segment again last night. His comments about "chain leverage" make no sense to me.

[victoryfactory]

Ex athletes don't always make the best broadcasters.
Good sports analysts are very rare. In any sport.

VF