Cyclocross - Low end gearing
Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.
MTB is: Crank=22-32-42
Cas: = 11-28
Fuji will be: Crank=38-48
Cas:=11-34 (changing out the OE immediately)
Sheldon Brown's calculations tell me that the MTB LOW is a 1.5 gear ratio. The Fuji will be a 2.3 gear ratio. Using Sheldon's calcs, the 2.3 on the Fuji will be the same as a 22/18 on the MTB AND I have to struggle on the same hills with this ratio.
What do the ratios really mean? Do they really equate to effort exerted?
Right now I have to use the MTB 1.5 getting up some of the hills around home. Will the 2.3 be that more difficult?
The reason I kep bugging you guys is that I want to get this right out of the box. I tried a triple on the first Fuji I took deliver of and the shfting was awful. I really prefer keeping the double chain ring and changing the cassette to the one above. The shop is willing to do the changes initially BUT if I wait a week then its's goin to get really expensive. Now the shop guy tells me that he can get the triple adjusted so that it shifts just as good as the double. Do I believe him?
Just want to get riding and get all this fiddling over with !!!!!!!!!
Goint by Shimano's spec's the 105 rear derailler can only handle up to a 27 casette in the back so won't work with a 11-34. Atleast according to their web site, none of their road derailleurs will handle a casette that large, so you will have to go with a mountain bike derailleur not sure how well they work with STI shifters.
05-03-03, 09:04 PM
True Kev, but Sheldon had said a few times that their road deraillers are only listed up to 27 because that's what they sell. He says they have no problem with 28 or 30 teeth. 34 might be pushing your luck, however.
Regarding gears, your MTB definitely has lower gears than the Fuji. The equivalent to 22/28 would be 27/34. I.E. you would need your small chainring to be 26 or 27 teeth.
So you have three options :
- Forget about low gearing. The 38/34 "low" you are contemplating on the Fuji is equivalent to 32/28 you have on your mountain bike. In other words, think of your MTB without the small chainring and see whether or not you like it that way. BTW, don't believe sales clerks who tell you that you that the road bike will be so easy to ride that you won't need those low gears.
- Get a wide range double. I know it can be done with TA chainrings ($$) and I think also with Sugino chainrings., but I don't know the particulars. Anyway, you could get something like 28-48 or 30-48... which would mean very little overlap between both rings.
Alternately, get a double, but with smaller rings : 30-42, for example.
- Get the triple. Get the triple and make sure it is well adjusted. Adjustment of the front derailleur with STI is tricky, but it can be done. And if you really find the double quicker, nothing prevents you from "ruling out" the granny by setting the limit screw so that you can't use it, That way, you would have a "double" that would behave exactly like a double (except for 100 g extra), but you would have it in reserve for the time you need it.
05-03-03, 11:13 PM
You need a triple. You're 61 (if I recall correctly?) and you need the full range of a MTB to negotiate your current hills comfortably. Your climbing ability will probably not significantly improve.
You need the triple. Don't screw around with your knees, my friend.
My two main bikes have road triples and 12-32 or 12-34 casettes. Since I tour and commute on these bikes, and since I'm not that great a climber, I find myself using the full range quite frequently.
Having too much range won't hurt anything. Not having low enough gears could injure you.
The poor shifting on your previous bike was the result of the bike shop's incompetence and obvious lack of knowledge (thinking the 105 double FD would give you smooth shifting on a triple). Now he promises he can get it right. OK, but what happened the first time?
I'm not impressed with this shop, based on the experiences you seem to be having.
05-04-03, 05:51 AM
i'm not sure you'd really need a triple if your low gear is 38x34, no matter how old you are. it really comes down to the terrain in your area; whether you have a lot of hills to climb, or whether it's rolling or flat terrain. the truth is that, even if you're 61, the times that you would need, say, a 30x34 will be very few and far between unless you live on the side of a mountain. besides, gears that low have you pedalling at a furious pace to move at less than walking speed and barely stay upright.
05-04-03, 11:21 AM
You need a 38x78 to get walking speed at 80 rpm :)
05-04-03, 12:57 PM
Originally posted by velocipedio
[B]i'm not sure you'd really need a triple if your low gear is 38x34, B]
He says he needs and uses the 22-28 (1.5 ratio, 20 gear inches)combo he has now as his lowest ratio. That's a considerably lower ratio than a 38-34 (30 gear inches) so I don't think this is very good advice.
Even a stock road triple (52-42-30) with a big MTB cassette (12-34) yields a lowest ratio of 1.8 which is *still* not as low as what he has -- and says he needs -- now.
He already did the experiment, trying his local hills with the 30gi combo on his current bike, and he said it was a struggle.
It's not going to get any easier. He needs lower gearing.
My new 54 is on order so I have a bit of breathing room to make the gearing decision. Did return to the dealer and he said he would swap the OE 105:34/48 for an MTB LX:22/32/42. Cassette will stay OE 9S 12/26. He has done this combo before without any problems. This combo is currently on my MTB and works for me. Anxious !!!!!!!!!!!
BTW - Shimano's 105 STI is rated for double or triple.
Thanks again for your help.
05-06-03, 11:51 AM
That should work. Yes, the STI *levers* will work with either a double or a triple. You'll still need a new front derailleur, and if that's a short-cage rear derailleur on there now you'll still have to replace it because your new small chainring is so much smaller. You need a RD that can take up all that slack.
05-07-03, 05:11 AM
Why not think in terms of gear inches instead of cog ratios. This will take into account the difference in wheel diamter, and give you direct comparisons between your bikes. Use your MTB to chose the max and min gear inches you want. There is no magical difference between lightweight MTBs and CX bikes. If you need a 30" to climb on an MTB, chances are you will need the sameish on a CX.
You can setup a double with low ratios, but its difficult to make doubles work with greater than 12t difference. A 36/48 would be the lowest you would normally find on a CX type machine. A friend of mine has a Stronglight 80 double with a 28/40, but this is for cruising around a hilly town on a shopping bike.
MichaelW - Have you used Sheldon Brown's gear ratio guide? His input requires tire size AND crank length in order to perform the calculations. His guide will provide an answer in Gear Inches, Gear Ratio and MPH at any RPM. I compared the gear ratio of my MTB and tried to get close when chosing gearing for my on-order CX bike. My MTB 'low' is 20.2GI and the new setup will be 22.8GI. 'High" is 98.3 for the MTB and 94.5 for the new Fugi with the 22/32/42 MTB crankset.
The real problem with this whole thread is my inexperience. And attempting to get a bike totally to my liking off the floor the first time around. The change over is free initially BUT quickly gets in the $300 range after a week.
I have discovered one thing: Old guys gotta have low gears!!!!!!!
05-15-03, 10:11 PM
Whether or not you really need all that data on Sheldon Brown's Gear Calculator (http://www.sheldonbrown.com/gears/) depends on the type of results you want.
If you use his notion of Gain Ratio, then both figures are important. But the two other universally used numbers, gear-inches (in U.S.) and metre development (in Europe) require only wheel diametre.
Sheldon Brown is right on the money by my experiences. Today's bikes are geared with gears way too tall to be of practical use for the majority of us. It makes litle more sense to buy a bike with Lance's gears than to buy Arnold Scwarzenegger's weight set. either get the triple or find some other way., like small innner, big cog double combinations
1. Shimano 105 triple crank FC5505-L, 30-42-52 $89
2. Shimano 105, FD 5505L, 9S $22
3. Shimano 105 BB 5500, 118.5 $24
4. Shimano XT RD-M750 GS, Long cage $38
5. Shimano Cassette XT CS-M750, 11-34 $37
6. Shimano Chain CN-HG92 (Shimano specs require this chain with XT drive) $17
Total parts cost $227
Lengthen the chain to Shimano specifications
This is the combination that I will be getting on my new Fuji. Shimano says this combination will work just fine with the 105 STI shifters.
Did fine this neat site for comparison pricing
06-04-03, 09:37 AM
That's pretty much what I have on two of my bikes. I'd recommend getting a 12-34 cassette; you'll never use an 11-tooth cog with a 52-tooth ring. And personally I prefer the 12-14-16-18-20 progression on the cruising cogs vs 11-13-15-17-20. They're both XT cassettes, both the same price.
What Shimano says about chains is, of course, simply self-serving. Not that there's anything wrong with a Shimano chain, but SRAM chains work fine and have the handy Powerlink. Shimano chains require their special pins and a chain tool if you ever need to remove or repair the chain.
Thanks Rich - that's what I'll do.
Powered by vBulletin® Version 4.1.12 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.