Ok, with all the talk about compacts, and I have read all the posts and understand them, here’s the question. I currently ride a Trek 2300 with 700c wheels, Ultegra 53/39, with a 12/27 cassette. I did a ride last year that has over 10,000 ft of climbing in a 100 miles. It’s called 6 gap century. One gap averages 7% for 7 miles, but has a couple sections that are about 12-15% for at least 1/2 miles each. You hit this at about mile 65 with about 6000 of the 10000 already in your legs. The 39/27 combo just wasn’t low enough and my cadence was around 40. I could either go with a 50/34 compact, the FSA Energy for around stay $125, or get a custom 13/30 cassette for $80 +s&h. The current 39/27 gives a gear ratio of 38.2, the 34/27=33.3, and the 39/30=34.3. Where I live and log 80% of my miles, the stock 12/25 cassette works well, but I do like to do this ride and go there occasionally to practice. So, the cassette route is cheaper and easier to change out, but the compact isn’t that much more and has more flexibility. I’m also taking it that my short cage Ulterga RD will work the 13/30. What would you do? I know, loose weight, get stronger, etc. Believe me, I’m trying, but I’m no spring chicken. Thanks for your input!!
I’ve never tried it, but can’t you get a mtb cassette and use the last gear or 3?
XXXcycles has 130bcd chainrings slightly smaller than 39.
Thanks, Tom. Yea, I could, but the 9 speed MTB cassettes run a 32 big cog, and I’m pretty sure I’d have to buy a new RD for that one. I looked at the 38 ring and it just didn’t make that much of a difference in the gearing. I’m not 100% sure my RD will handle the 30 tooth cog, but Sheldon Brown’s website says it will and I’ll take his word for it.
I would get the compact and keep your 12-27. The compact also works great with your standard 12-25 (the only difference is the two biggest cogs). If you’re going to gear down, go for some lower gears across the board. The move from a 27 to a 30 cog on a 39 ring is not worth $80. Heck, that only moves your 40 cadence up to ~44!* (at the same power/effort).
Another advantage to the compact set is the 50 ring. It’s a better big ring for us mortals in the MOP than a 53 ring.
*If I had a favorite hill that had me at 40 rpms in a 39x27, I’d be riding my 30x27 on the triple. That would allow cadence to move up into at least the low 50’s. But, a triple is a much more expensive proposition than a compact (Crankset, BB, front derr.).
I did the same ride last year. Unless you are a stud, you are kidding yourself that moving from a 27 to 30 rear cog is going to make a difference. I had a triple with a 30/27 gear. Yeah, that was way too big on Hogspen for me.
If you are serious about this ride, get a triple. I am thinking about getting a mountain bike triple next year if I do that ride. Maybe 24/27 will work. Mere mortals can’t get too small a gear for this ride.
The 39/27 combo just wasn’t low enough and my cadence was around 40.
Neither of your proposed low gear changes will drastically change your cadence on those steep grades. The 39/30 would increase it by about 11% (assuming you have the same fitness and weight) to about 44rpm and the 34/27 would increase it by about 15% to about 46rpm. If you make both changes, that’ll get the cadence up by about 27% to 51rpm.
Even a triple with a 30T inner ring with a low gear of 30/27 will only increase cadence by 30% to about 52rpm. Couple that with the cassette change and a 30/30 will get your cadence up to about 58rpm.
You could also get a triple but put a 26T granny on it (e.g. 26x42x52). A 26/27 will get your cadence up to about 60rpm.
BTW: I think you can get 12-30 cassette for much cheaper than $80. Just buy a loose 30T cog from Harris Cyclery http://harriscyclery.net/site/itemdetails.cfm?ID=800 for $10. Take the 14T and it’s loose spacer out of your 12-27, and put the 30T and the 14T cog’s spacer on the freehub body followed by the remaining 12-27 cogs.
Great idea, thats why I posted this question here. I knew you guys would come up with the best solution. So, I get the compact and then a loose 30 tooth from Harris and be all set for that bad boy come this September. Thanks a lot!!
Will a 30 tooth gear work with road Shimano derailleurs? I know a 32 will not, since I tried it. Specs call for a max of 27, but I know that 28 works.
I did the same ride last year. Unless you are a stud, you are kidding yourself that moving from a 27 to 30 rear cog is going to make a difference. I had a triple with a 30/27 gear. Yeah, that was way too big on Hogspen for me.
If you are serious about this ride, get a triple. I am thinking about getting a mountain bike triple next year if I do that ride. Maybe 24/27 will work. Mere mortals can’t get too small a gear for this ride.
Art and Dirtroads,
Art, once again, I must recognize your experience and wisdom. My own experience confirms your statement above.
I am not a stud but a mere mortal. I have not done the gap century but it sounds intriguing. I have done the Assault on Mt Mitchell more than once, however. About 12,500 ft of accumulated climbing in 102 miles. The “fun” part, however, is that approx 8,000-8,500 ft of that climbing is saved for the last 27 miles.
The first year I tried it I rode a triple with a 30 tooth granny ring and a 13-26 cassette. My lowest gear was about 31 gear inches. It was murder climbing up the Asheville watershed. I tend to spin but could not on that grade. I was forced to mash and suffer. And suffer I did.
The second year I converted to Campy ten speed to get the 29 tooth cog of the 13-29 cassette, still with the triple. This gave me a low gear of about 28 gear inches. At last I could get my cadence up to 60 and slightly above. Mind you my legs/knees are not very happy when the cadence falls below 75, particularly when I am working hard. The Assault wasn’t easy by any stretch but at least it felt possible.
Dirtroads, you presently have a low gear of 38.2 gear inches. Your proposed 34/27 will give you 33.3 gear inches. You are still gong to be suffering. IMHO If you had a triple with a MTB derailleur and a MTB cassette then you could get a 30/34 combination and somewhere around 24 gear inches for a low gear. then you could climb like a mountain goat!
You would not believe the number of $3,000-$6,000+ road bikes that were on roof racks. I was always looking to see what kind of a set up riders had. At least a third of the bikes had MTB cassettes on the rear hub. The biggest cogs were 30,32 or 34 teeth. Anyone who was running such a cassette had an XT or XTR derailleur. Most of these MTB equipped road bike had double chainrings and this was before the advent of the compact crank.
I do not believe yu will be able to run a 30 tooth cog with the short cage derailleur. You will be exceeding the derailleurs capacity by a fair margin. If you can manage to get it to work I am quite sure it will not work very well.
My own recommendation, get the triple. Your legs will thank you for it. If you train yourself into a stud, just don’t use the lower gears, but it sounds to me as though you do not expect to reach that level anytime soon, if ever. In one sense it may cost more, but look at what the typical cyclist invests in some of these organized rides. Travel expenses, entry fee, lodging expenses, meals for multiple days. Then the loss of training and accompaning set back while one recovers from over doing it.
For me, it wasn’t that hard to justify the expense after taking that into consideration.
BTW, a great book that is easy to read and comprehensively covers gearing and explains capacity issues to help in determining what will work and what probably will not work is titled:
BICYCLE GEARING: A Practical Guide, by Dick Marr and published by The Mountaineers.
Good luck.
Thanks Ben for that well thought out response. Maybe I’ll just borrow my wifes slicks off her mountain bike and ride my hardtail this year. I really don’t want to spend the money to do the triple conversion for one ride/year. I did it last year with the 39/27, although it was not a ton of fun. The only one that really hurt was Hogpen gap. So, I gotta think that a 34/30 would get me by. I’m pretty sold on the compact crank anyway for us mortals. Reports were that Lance and crew did that climb last week in the Tour de Georgia with 39/25 and then went on to do the Brasstown Bald climb which is a steeper section. I can only imagine that kind of strength. I’m a good bit lighter this year, 10#'s, and just finished a marathon, so I think I’m fitter. There plenty of time between now and the 6 gap to try the compact and react accordingly. Thanks again. I want to do the Assault some day. There also a ride called “the Roan groan” up in Elizabethton, Tenn thats a good climb. I’ve done it.