CX bike crank/cassette upgrade for road use

[Pedrosanchezo]

Hey guys,

Own a Cannondale Caadx 105 2012. Crank 46-36, cassette 12-28. Running 700x28c Panaracer pasela punture resist tires in spring/summer.
Spinning out the top end @ 34mph approx .
I use the bike lots for training and decent length road rides in summer and winter. Just change the tires to suit. My winters are a 35x700 semi slick.
Question being, what's the best way to increase top end on a cx bike?? Upgrading the chainset/crank for something bigger (like standard 53-39 or compact 50-34??) or just changing the cassette for a 11-28?? The cassette is obviously the easier and cheaper option but i wonder if the difference between the 11 and 12 would be that big. I've heard it would add 10% to the top end. This sound right?? That would be just over a 3mph in that case and would actually be pretty close to road bike pace.
Or is replacing the crank/chainset a better option and keeping the rear 12-28 cassette?? Also would the original chain (quite new on this bike) be okay to use again and would any other changes be required??

The main reason for this is i am averaging between 18-20mph on 40-50 mile rides and find myself spinning out on slight and serious downhill. I never use the lower 10 gears even on sever hills so i feel i am probably quite under geared. I never use the left paddle.

Any thoughts are very welcome and would like to thanks in advance.

Paul.

 

[simon.r]

Sheldons gear calculator will answer your questions about the differences between 11 and 12 tooth cogs.

You could just change the rings on the chainset. In theory you'll need a longer chain if you do this (it should be long enough to work on the biggest chainring / sprocket combination) but in practise if you know you'll never use that combination your existing chain should be OK.

 

[Pedrosanchezo]

Thanks for the reply Simon. So is it just a case of finding the best chainset/rings for the job then? Would the standard road set of 53-39 be okay with the 12-28 cassette or would something more compact be better suited for the cx bike?? As i say the current setup has me using the 46 all the time and only dropping on steep inclines. It's the top end that runs out too quickly.
Would you recommend a chainset?? Budget isn't too tight but i doubt if fitting a £200-£300 set would be money well spent. I am sure Shimano do decent sets around £100. Also do you mean just the rings to be changed or the set itself?? If it's just the rings could you point me in the right direction and price range for my requirements. Thanks again.

Paul.

 

[simon.r]

I'm not an expert on road bikes (most of my experience is on MTBs) so please don't spend any money based on the following! I am also typing under the influence of toothache, prescription drugs and alcohol Having said that, I think the following is right, but hopefully someone else will confirm:

Based on a quick Google I think the chainset on your bike is a FSA Gossamer BB30 Compact Road Chainset. If I'm right this has a BCD of 110mm. Just changing the outer chainring would give you a much higher gear. Stronglight do chainrings up to 53t (see here). A 53t chainring would, I think, be the cheapest and easiest option to get you a significantly higher gear. Other chainrings in this size are available.

You would need to reposition your front mech and it may mot be able to cope with the difference between 36 and 53 chainrings, so you may need to get a bigger inner chainring as well.

 

[Pedrosanchezo]

Prescription drugs and alcohol are great but not in combination with toothache. My sympathies............

All of the info you have gathered is correct regarding my bike so i will have a look at at replacing the two chainrings. Maybe a 53-39 will work. There is a lot of scope in the 12-28 cassette so i think it should be a pretty good all rounder and be capable of reasonably high speeds and steep climbs.

In summary then i am looking at 2 chainrings (prob 53-39) and a chain that fits the upgrade. I will then need to adjust the front mech. With a bit of fine tuning it will be up and running in no time.

Thanks for all your advice Simon. I will spend a short amount of time finding the desirable/correct gear and then check back here to see if any road/cx users differ in opinion. Personally though, what you say, makes sense to me. Cheers.

Paul.

 

[RecordAceFromNew]

You would need to reposition your front mech and it may mot be able to cope with the difference between 36 and 53 chainrings, so you may need to get a bigger inner chainring as well.

According to Dale's spec he has FD-5700 front mech and RD-5700 rear mech, which have capacities of 16T and 33T (even assuming it is the shorter cage version) respectively. With a 12-28 at the back that means he could safely use his existing front mech with a 52T and the existing 36T small ring. The rear mech can cope with that too, and if need be a 11-28T cassette in future.

A 52T front ring will increase all gears on that ring by 13%. A 11T rear cog itself will increase top gear by around 9%. Implementing both will yield a whopping 23%.

 

[Pedrosanchezo]

According to Dale's spec he has FD-5700 front mech and RD-5700 rear mech, which have capacities of 16T and 33T (even assuming it is the shorter cage version) respectively. With a 12-28 at the back that means he could safely use his existing front mech with a 52T and the existing 36T small ring. The rear mech can cope with that too, and if need be a 11-28T cassette in future.

A 52T front ring will increase all gears on that ring by 13%. A 11T rear cog itself will increase top gear by around 9%. Implementing both will yield a whopping 23%.

Hey thanks for the post.
So in summary you think go for the 52t big ring and try with the 12-28 and see how it feels? Would i need to change out the chain with the bigger size 52t? I assume i would have to. With this set up (52-36) i imagine it wouldn't be the smoothest of down changes? Just looking to see what the best solution is. Have you any recommendations regarding chainring type? I have looked at some stronglight, TA and shimano. Stronglight seem to be a good contender for the build versus cost. All thoughts greatly appreciated. thanks.

Edit: also what are the numbers from 1-20 in the drop menu for ?? See link for what i mean.http://www.spacycles.co.uk/products.php?plid=m2b2s149p296&i=3342

 

[RecordAceFromNew]

I would definitely change the chain if existing is too short for the new setup. If you shift into a gear where the chain is too short you could kill the rear mech, the rear wheel, the chain, the bike and land you on the tarmac. The risk is simply not worth the price of a new chain. While you might remember never to shift into such a gear, you might lend the bike to someone one day who doesn't know.

Frankly ALL front shifts are un-smooth. You mentioned that you only use the top 10 gears at present? You could possibly work out a front ring size, with a different cassette at the back, that will allow you to avoid front change altogether in the new setup. Alternatively consider this!

There are a lot of advantages in having a 11T at the back. It allows you to maximise the range of your setup (since there ain't no smaller rear cog than a 11T), it is most efficient in rear mech capacity utilisation (1T increases top gearing by 9%, achieving same in front will eat up at least 4T of capacity), allowing you to use a smaller, lighter, cheaper and stiffer front ring, and a shorter, lighter chain!

Some good discussion about chainrings here.

1-20 in spa's drop down menu is how many rings of that size you want to buy, spa suggests "hopefully".

 

[Pedrosanchezo]

I would definitely change the chain if existing is too short for the new setup. If you shift into a gear where the chain is too short you could kill the rear mech, the rear wheel, the chain, the bike and land you on the tarmac. The risk is simply not worth the price of a new chain. While you might remember never to shift into such a gear, you might lend the bike to someone one day who doesn't know.

Frankly ALL front shifts are un-smooth. You mentioned that you only use the top 10 gears at present? You could possibly work out a front ring size, with a different cassette at the back, that will allow you to avoid front change altogether in the new setup. Alternatively consider this!

There are a lot of advantages in having a 11T at the back. It allows you to maximise the range of your setup (since there ain't no smaller rear cog than a 11T), it is most efficient in rear mech capacity utilisation (1T increases top gearing by 9%, achieving same in front will eat up at least 4T of capacity), allowing you to use a smaller, lighter, cheaper and stiffer front ring, and a shorter, lighter chain!

Some good discussion about chainrings here.

1-20 in spa's drop down menu is how many rings of that size you want to buy, spa suggests "hopefully".

Okay, food for thought! What i am taking from this is that there is more than one way to the finish line. There is several.
Is there a front ring size that would not require new chain and much adjustment? I only ask as maybe something like a 48t or 50t up front with a rear cassette running 11-28 (or similar) would do the same job as a 52 ring and the original 12-28 rear?? Or possibly doing this in reverse---changing the cassette for 11-28 and seeing how that feels. From here maybe i could make an informed decision on ring size up front. What dya think??

 

[RecordAceFromNew]

Okay, food for thought! What i am taking from this is that there is more than one way to the finish line. There is several.
Is there a front ring size that would not require new chain and much adjustment? I only ask as maybe something like a 48t or 50t up front with a rear cassette running 11-28 (or similar) would do the same job as a 52 ring and the original 12-28 rear?? Or possibly doing this in reverse---changing the cassette for 11-28 and seeing how that feels. From here maybe i could make an informed decision on ring size up front. What dya think??

48x11 is higher than 52x12, although personally I am not sure if I would bother increasing front by just 2T given the faff required, so trying out a 11T at the back and see would probably be my choice but then it depends on what max speed at what cadence you are after of course.

The minimum length of the chain is determined by the large cogs front and back. You can work out what combination your existing chain allows using a calculator.

 

[Pedrosanchezo]

48x11 is higher than 52x12, although personally I am not sure if I would bother increasing front by just 2T given the faff required, so trying out a 11T at the back and see would probably be my choice but then it depends on what max speed at what cadence you are after of course.

The minimum length of the chain is determined by the large cogs front and back. You can work out what combination your existing chain allows using a calculator.

Have gone for the following: http://www.evanscycles.com/products/shimano/ultegra-6700-10-speed-cassette-ec019749
11-28.
If it turns out that i still need some top end afterward then i can look into a bigger ring. Will keep you posted once i have fitted up and had a decent outing.

Thanks very much for your help. Paul.

 

[Pedrosanchezo]

Hey guys, thanks again for the advice. Fitted the 11-28 and done 80 miles, over two outings, at the weekend. Both averaged 1mph faster so very happy with that. I find the 11 actually easier and faster on both downhill and flats. More efficient RPM.
Spinning out at (at a push) 36 so i am still left wondering if i should install a 48 or even 50 big ring. I think a 48 would be fine with the chain fitted now as there is a fair bit of flex but i'm pretty sure 50 and above would need new chain and adjustment.

Would a 48 be much of an increase including the 11 (now fitted) or a pointless exercise?? I personally like the way it rides just now but could still do with an mph or two over and above what i have just now. I also still don't use the small ring up front but i suppose that would only change if i replaced both big ring and small. At which point i would be as well replacing the chainset for something better. Lol this is the problem with bikes!! Always looking for a reason to upgrade things!! ;-)