Drivetrain Advice Required
 

I have a Scott CX Comp bike and have been using this for over a year now. Previously I had a Diamondback Topanga which was a great old lady but getting a bit tired - like me!

I bought the Scott cyclocross bike because I thought that it would meet my increasing road cycling needs while still allowing me to take it off road occasionally. However, since I got the bike, I almost exclusively ride on the roads and have never once taken it off road. However, the bike has always frustrated me because it does not handle hills as well as my old Topanga mountain bike - understandably. But I still think that it should do better.

The drivetrain setup on the Scott is:

46/36T Shimano FC-CX50 crankset
Shimano FD-CX70 front derailleur

Shimano TIAGRA CS-4600 rear cassette - 10 speed 12-30T (12,13,14,15,17,19,21,24,27,30)
Shimano 105 RD-5700A rear derailleur

Now the things that have bothered me most about this bike are:

1. The close ratio of the front rings. The small ring does not seem great for hills. The large ring not the best for flats.

2. The range of the rear gears. The small sprockets are so close (12, 13, 14, 15) that most times I pass through 2 gears because the shift up produces too little acceleration.

3. The large end of the rear cassette also seems too low for hills.

Now what I would like to achieve is 'easier' uphill cycling. I am getting on a bit now and those hills don't get any easier. I can move up to an 11 - 32T cassette without having to change the derailleur - I think. But will the extra 2 teeth help me much? A change of cassette would certainly address the the close ratio of the small sprockets as those cassettes are 2 teeth differences with the except of 11 to 12.

I had also wondered about changing the small ring to something like a 34T but am not sure that would make much difference - without also changing the rear cassette. I also thought of going the whole hog and changing to a 48/34T set up at the front which I think the derailleur would handle, but am not sure what other issues this would give me. Apart from being a pretty expensive option.

Sooooo......... I would appreciate any advice on this one. Apart from buying a road bike! The bike was not the cheapest and I would not want to give up on it - but neither would I want to make such ambitious changes to the drivetrain as to affect the efficiency of the bike or do long term damage.

You bought a cyclocross bike and that's what you got. Those chainrings are typical of cyclocross gearing where the riders are expected to run up the steepest hills. A wider range cassette will help as will (the more expensive) crank change to a wide range double or a triple road crank.

You won't damage the bike but you will injure your wallet.

If 30T is "almost" low enough, 32T will make a difference. 1/15 or 6-2/3%.
About the same as going from a 15 to 16T cog on the back.

I LOVE close ratios.
Work out the percentages 2T at the top is mathematically about the same as 4T at the bottom.
However, it doesn't work out that way in reality, because you are moving faster and wind resistance has entered into the picture.
You should also learn your "ideal" cadence and 1T steps at the top end will make more sense.
I typically run 12-23 or 13-25 9 speed cassettes.

Many road bikes are sold with compact 50/34 cranks and 11-28 cassettes, which are good for all around usage. So the lowest gear is 34x28, which is actually slightly higher gearing ratio than your lowest 36x30 gear. If you need more climbing ability, I would definitely recommend a 11-32 or even 11-34 cassette before changing out crank sets. Wiggle has them for super cheap: wiggle.com | Shimano CS-HG500 10 Speed Cassette (11-32/11-34) | Cassettes And Freewheels

You just have to make sure your rear mech is capable of handling the upsizing from a 30t to a 32 or 34t sprocket.

Beyond that, you could switch out to a normal compact crank to get more climbing ability (34t ring) AND more flat road speed (50t ring).

Thanks for the advice guys. It may be that I try the option of changing the cassette first as it is the cheapest option to start with. Especially if you think that the difference from 30 up to 32T will make some difference. The RD will take 32 but not 34, as far as I am aware.

Hillrider, I am very aware that I bought a CX bike and was recommended to do that for the reasons I explained. Hindsight, as they say, is a great thing! As are the ever changing needs of old age!

Just one more question, please. Why are the cassette ratios so close? It kinda gives me the impression that it has been designed this way to allow for easier acceleration while going up hill. Would that be right?

BTW, Patrick, I had seen that cassette on ChainReaction earlier at £1 dearer! Although, I did think that the extra few quid for a lighter cassette may have been worth paying.

http://www.chainreactioncycles.com/s...e/rp-prod52312

eh, weight savings at the center of the wheel won't really make much difference except on the weight-weenie scale. :P

Very true! A bit anorexic, I suppose! :)

Oh another thing while I am in thinking mode. For the increase of 2 teeth on the cassette, is it likely that I will need to replace the chain?

Put it in the large ring/large cog combo, and see how the RD looks. Grab the chain near the bottom of the large ring (or hold the crank in place), and see if you can pull the chain and rear mech cage forward by another 2 chain links (1 inch) without binding the rear mech.

Many thanks, Patrick, I'll check that in the morning.

I don't understand why you think that converting the front to a 48/34 or even a 48/32 would be such an expensive option. It looks to me like it would only involve replacing the two front chainrings. Depending on how your chain was sized originally you MIGHT need a little longer chain. that would give you both an easier hill climb gear and a little faster flat road gear.

What's your favorite flat road gear with no wind? If I could duplicate that with a 48/15 to 48/19, that's what I would definitely do.

I reckon that to change the 2 rings would cost around £85. I think it would probably need a new chain at about £15 and also probably a front derailleur at around £30. I have not checked those costs properly - or even confirmed the need for the derailleur - but I don't think it would be far off that cost.

On this bike, my favourite gearing is the 46 x 13. I have not checked out a road bike.

I'd like to recommend a different option for you to consider:

11-36 cassette
Shimano M592 RD
new KMC chain - leave it a bit long so that you could change your big ring to 50T in the future, the M592 will handle it.

Many thanks. Do you think that the existing FD will handle the 50T ring?

+1. I think the FD should be ok jumping from 46-50, you will need to raise it a hair.

I'm like you, I have 9sp 11-32 on my commuter, which most people would consider fairly wide spacing, and I usually shift two at a time. I might as well have only 5 gears back there, because I only ever use the odd ones! If you feel that your current cassette is spaced too closely, so that shifting doesn't make enough of a difference, AND you want a lower bottom end, you will love a larger cassette like 11-36.

Yep, I feel like I have a 7 speed cassette, or something like that, on the back. I would need to change the RD to go up as high as 36. The max mine can handle is 32T. I was planning on trying that, but may now have a look at the cost of a new RD.

I noticed on eBay today while looking at rings that someone is selling off a 34T front ring. I am thinking of trying this - and the 11 - 32T cassette - if I can buy it cheaply enough. If it does not work, then I won't have lost too much money on it.

RD capacity estimates are always conservative, you can stretch them. The two limitations are chainwrap (tooth difference between big-big and small-small) and whether the upper pulley will be bumping against the big cog. You can try to correct the latter using the B-screw, or getting a longer screw with the same threading from any hardware store. I suspect you'd be able to get your current RD off of an 11-36, but whether your current RD (mid-length cage?) can handle (46-36=10) + (36-11=25) = 35 tooth chainwrap, I don't think so. You'll almost certainly need a long cage RD for that, which means mountain, and in the 10sp era, you gotta worry about whether mountain derailleurs are compatible with road shifters in terms of cable pull.

dont 'feel', count.. 7 speed has 7 cogs .. a shimano K cassettes 13_34t are 7 good ratios

combined with a 50-40-24t triple crank I toured for 10 years on just that ,minus 1 ,(it was 6 speeds)

9 speed MTB RD work with 10 speed road shifters in Shimano's world. But not the other way around. The M592 can be found for less than $50- almost anywhere. It is reliable and rugged.

Thanks for the advice, Rube. The RD is a Shimano 105 RD-5700A which is a short cage derailleur. I had wondered if I could push it to 34T, but was not wanting to take a risk with it. I don't know. I suppose if I could get a cheapo somewhere, I would take a chance and if it did not work, then settle for a 11 - 32T cassette.

I have bought a 34T ring for the crank on eBay. It is a Stronglight ring - not Shimano - but thought it may allow me to try out the size to assess it. It was not expensive, so nothing much wasted if it does not turn out right. Other than effort, time, etc, etc, etc! :)

Shinano Tiagra 4700
50/34T crank
11-34T cogset

If You want even smaller ratios, you'll need to use MTB components.

Tanks, Abu. I will try the 11 - 32T cassette and smaller chainring and see how things are. But it will probably come down to either settling with what I have got, or changing the entire drivetrain similar to what you are suggesting.