Cadence, climbing, and power
I tend to charge up hills, and I know I can’t do that in at IMLP and hope to do well on the run. I also like to spin, and I’m most comfortable at 100 RPM, and really don’t like to fall below 90. My FTP currently is 230. If I try to race an IM at .70 IF and allow myself to do 105% of that on the long climbs as RnP advise, I shouldn’t exceed 169 watts on a climb.
I did some math with various gearing choices. If I stick with a 39x27 lowest gear, at 90 rpm I’ll be going 10.16 mph or 4.54 m/sec.
I went to www.analyticcycling.com to determine the maximum grade I can ride at 10.16 mph without exceeding 169 watts.
The inputs were .28 cda, air density of 1.2, weight of 85k (me plus my bike and water bottles); crr of .0045, and watts of 169.
The maximum grade I can climb with a 39x27 at 90 rpm without exceeding 169 watts is 3.6%. If I get a compact and use a 34x25, I can climb a 3.9% grade with the other parameters remaining constant.
On the other hand, at an rpm of 60 in a 39x27, my speed is 6.78 mph or 3.03 m/sec. The maximum grade at 169 watts at 60 rpm with this gear is 6.1% compared to the 3.6% at 90 rpm.
I don’t know what the maximum sustained grades are at IMLP (I hear that the hills aren’t that steep, but go on for a long time). If I don’t reign in my natural tendencies, if I hit a 6.1% hill, I know I’ll end up charging up it at 90 rpm, which results in a power requirement of 263 watts. Instead, I need to learn how to put out constant low power at a low rpm so I can pedal at 60 rpm and maintain 169 watts.
Comments
instead of changing how you ride... just look for a compact crank.
See the ironman gearing thread:
http://endurancenation.us.dnnmax.co...fault.aspx
FWIW, Everyone I knew outside of EN last year thought I was crazy for running a compact. I raced IMWI at 4.5 w/kg last year and still road a compact and I think it worked out quite well
I personally have found a 50/34 crank with a 11-25 cassette to be pretty much perfect for me for almost every HIM and IM.
I think you overlooked that I've got a 39x27 and not a 39x25.
I redid the math a bit having realized that my large cog is 27 and not 28. That doesn't change the bottom line much, though. Switching from a 39x27 to a 34x25 gets me a little bit (can climb a 3.9% hill instead of a 3.6% at 90 rpm), but the change is relatively small. There's no way I'd consider riding with a 39x25. I'm not embarrassed to show up with small gears, especially given my low power and my high cadence.
I chuckle when I see people talking about going from a 12 tooth to an 11 tooth cog or going to a 54 or 55 up front. For me, the 53x12 gets me to 34.5 mph at 100 rpm. Even on a compact, I'd be at 32.6 on a 50x12. If there's a hill that get's me going faster than that, I'm coasting. For those who prefer to pedal at 70 rpm, though, I can see the need. (70 rpm on a 50x12 only gets you to 22.8 mph.)
Riding in a 50x19 at 95 rpm is 19.55 mph and 141 watts. The next gear is the unusable 34x12 due to chain crossing. After that, the next gear is 50x17, which is 21.84 mph and 188 watts. I never thought that the wattage jump between gears at constant cadence would be 47 watts! This may not matter at IMLP where it's rarely flat, but at IMFL with those criteria, I'd be miserably hunting between gears.
Perhaps the answer is to bring my cda down to .25 from .27 and get better tires to get crr down to .004. That would put the 50x17 at 95 rpm right at 172.5 watts, a speed gain of .7 mph at the same wattage.
I'm not sure if anyone other than me finds this the least bit interesting. Oh well.
I am thinking of switching cranks anyway to go from a 175 to a 170. If I do, I'm likely to get a compact.
I did IMWis in 2008 at a much lower watt/kg than the Mighty Matt. I rode a 50/34 with 12-27 cog. I switched to a 11-26 Sram Red cassette lately and like it also. I highly recommend the compact with 12-27. I hear that Coack Dick will kick you in the nutz if you ride anything else.
Vince
Keith,
I think you're thinking too much and spending too much time with fancy calculatorthingy's. Keep it simple.
.
Your available solutions to the climbing problem are:
Possible gearing combinations are:
My recommendation, if you can spring the cash for the cranks, is 50/34 on the front, 26-11 SRAM cassette on the back. My w/kg are in the shitter right now but I did some 16-18% stuff today. Wasn't fun, but it was nice to have the 34/26. It's bought me about 10-12rpms on some long, sustained, 6% stuff like you'll see at LP.
There are no super steep hills at IMLP, just long, sustained stuff. It's not the course where you need to a 28 just to keep from falling over. And 11 or 12 cog is a non-issue, as inside EN you're coasting above about 33-34mph. In the 50/12 on my compact, I spin out at about 37-38....but I'm coasting above 34mph so who cares?
I'm diggin this topic, especially since I just started looking around ebay yesterday for a good deal on a Shimano compact crank for my TriBike. I have one on my road bike and love it. I bought my TriBike last July, so this year I am going to upgrade to a compact crank. I have a question though If you don't mind me jumping in here? I am probably going to go with a 28-11 cassette as I have a lot of 8% + grades I ride. I have read that I would also need to replace the derailleur and possibly get a new chain. Does anyone know if this is true or can I just swap out the 53/39 for the 50/34?
On three different bikes I was able to just move my current front derailleur down a little and continue to use it. The only issue would be if it is already as low as it can go with the standard crank and you have no room to move it down. If that happens, just look for a 2009 SRAM Rival derailuer on closeout. Then can be found for under $40 and it has a second mounting hole specifically for compact cranks. Front shifting is friction based on bar end shifters so you can mix and match SRAM, Shimano, and Campy without any problems unless you have STI or R2C shifters.
Given my "relatively low" current FTP (2nd test next week), should I just do the compact thing instead of swapping for a 12-27 as I had planned? I've ridden the LP course a few times with 53/39 12-27, but never had to worry about running afterwards.
Why not a compact right off, you ask? I'm worried about the cadence gaps I might encounter with the compact.
If I go compact, should I stay with the 11-25 or get a12-27 or seek out an SRAM 11-26?
New bike will be a 2009 Transition Comp on closeout that my LBS is holding for me
I am only an experiment of one. That said I spent a couple of years analyzing and waffling over moving to a compact crank. I did multiple gear analyses and worried about the same concerns that you expressed. Meanwhile my method to get up hills was to grind through them and toast my legs a bit.
Then, last year I finally decided to move to a compact crank and am glad I did. I find no major candence gap issues and can spin up hills while keeping my watts within the EN prescribed ranges. (The first couple of times of use were interesting as I worked to get the hang of knowing when to shift with the big gear ranges).
I stuck with Shimano in that I have better luck using a single brand drive train (including the chain).
I ride with a 12/27 and a compact and I suppose sometimes I could use a bit more gearing when I am flying down the road, but those instances are few and far between.
I am now a compact crank believer and will never go back.
Cadence gap is a function of the cassette, not the crank. For example, on a 10spd bike:
In my opinion, it's better to have the climbing gear you need, which might give you a cadence gap, then to not the climbing gear but you don't have a cadence gap. IOW, when you're climbing a 10% grade hill with a 23t cog at 40-45rpm, you're not going to say "man, I'm soooo glad I brought this cassette cuz even though the climb and cadence are shattering my legs I know I won't have a cadence gap when I get on the flats. Yay me!"
I've pretty much decided that I'll need to go compact. Now it's just a matter of picking the right cassette(s).
I would disagree with Rich just a bit on the cadence gap subject.
The biggest thing I had to get used to when I moved to a compact crank was the dramatic change when shifting from the big ring to the small ring. The first few times I rode with the new crank found me shifting too early which generated some immediate free spinning and potential damage to my man package as I went from pushing at power to none.
However, if you do that a couple of times, you learn really quickly about the most optimum time to shift from the big ring to the small ring and the matching correct cassette gearing during this process.
Ok, I'm totally in for the compact now - nobody had previously mentioned 'potential damage to my man package' as a feature/benefit. I am so putting the order in tomorrow. Seriously though, it looks like it's gonna be the 50/34, now I just need to figure which cassette. The elsewhere linked Gear Comparison Dealio is proving to be extremely helpful in this situation.
My answer would be as simple as this:
If you're most comfortable at riding around 100rpms then you should be on a compact crank. Sure, you can achieve proper gearing with a 53-39 with the right cassette but your options are much more limited.
Thanks, Chris
I am not a bike purist or whatever and can almost never tell the difference between components etc. I also admit that the math in this thread is of no interest to me and that I have never really noticed a cadence gap in playing with different cassettes. Like Rich and Matt I am a big fan of the 50/34. My first year in LP I had a 53/39 and a 12/27. Did that work, sure I guess. The next year I had a 50/34 and an 11/26. While I have an 11-23, 12-25, 12-27 and the 11-26 I tend to always leave the 11-26 on my PT wheel and use it pretty much always. I never notice a problem where I want different gears, I just use what I have. The 50/11 is "taller" than a 53/12 and with the 34/26 I can climb a vertical wall without falling over and spin a decent cadence up anything at LP. For flatter/shorter races I never use the 26 but so what. I also never care about crossing my chain and have only ever broken a chain once which was jsut after some stoned bike shop moron put it together wrong [it was not crossed at the time]. Just don't care, have never mattered.
Some of my friends give me shit about having a compact. A few of them can pretty much make fun of anything to do with my cycling as they can crush my dreams on a bad day but it is all in good fun and they usually wait around at the finish line and have a beer waiting. The rest of them that do not understand why I would ever have a compact can generally kiss my ass but as I am a good sport I will wait around for them at the finish line and buy them a beer
In sum, stop geeking out and buy a compact!