What cassette should I get?

[petrolhead]

Hi Guys (and Gals don't wanna be sexist now do I?), I could really do with some advice as to what gearing to use on my Giant TCR Advanced if anyone can help? It's only a month old and is still completely stock so it still has the 52/39 chain ring and 12/25 cassette it came with but I find that I struggle badly on steeper gradient hills to the point where I have to stop as I physically can't push the pedals round anymore and getting started again is just comical what with trying to get cleats into pedals again and the like. I should probably point out that I am a relative novice and I've only been road cycling for a few months so I'm still finding my way a bit. Long drawn out climbs I can seem to manage ok albeit in 1st or 2nd gear and shorter steepish climbs are also ok as I can stand and kick up them but the steeper hills have me beat. I was considering changing the cassette for a 11/28 or a 11/27 but I'm unsure if they will fit straight on without the need to change the chain or derailleur or even if it would make that much difference, does anyone have experience of this? After giving that a try I was going to turn my attention to the chain ring and perhaps change the small ring from a 39 to either a 36 or a 34 tooth but again I'm clueless to whether this would be easily achievable? It has a full Shimano 105 groupset if that helps in anyway?

I suppose an obvious answer would be to stick to the kind of hills I can do (I live in Devon and there is plenty of both I can assure you) and keep working on the other ones a bit at a time until I can conquer them and ordinarily that's exactly what I'd do but I'm now starting to do longer rides and sportives and as such I have no control of the routes or hills that I'll come up against. Again a cheaper option would be to put on standard pedals and trainers and just jump off and push if I needed to I suppose... but it would be nice to have the option so I can swap out what I needed depending on what kind of cycling I was doing if you see what I mean?



Thanks in advance for any help or advice offered, I bow to your superior knowledge and I'm sure your name will be on the entry list in biking heaven.


Cheers
Jim

 

[R600]

hi there and welcome to the site. why not try a compact chainset, which will have 50/34 rings. this will give you a gear of 37inch instead of 42 inch. this is what i have done on my training bike and makes things just a bit more comfortale. if you then needlower gears you could look at changing the rear cassette, but (not sure of the figures)when you put bigger cogs on the back you may have to change the rear mech to a long or medium reach. If you were to keep your 39 tooth front chainring and change your cassette to a 28 tooth (about as far as you can go without mech change) this would give a low gear of about 37 inch but i prefer to have the cassette with close gearing so there are less big gaps. hope thats as clear as mud for you.

 

[Sleeper]

I've just gone over to a 105 rear mech and the max sproket on the SS version is 27. I'd recommend a compact chainset for you too, you should be able to find a 105 compact double on the bay for a good price and your groupset would still be correct (if that's important to you!)

 

[downfader]

If you're struggling with the cleats theres also no harm in switching over to flat commuter pedals for a short while. Would only cost a few quid, just keep the SPDs for later and use normal shoes.

 

[the_mikey]

Depending on which derailleur you have, you might be able to get something like a 11-27 or 12-28 on there, check out the specification of your derailleur on the shimano website, it'll tell you the maximum number of teeth your derailleur can handle.

The cassette is easy to change (with the right tools) however you may need to adjust the derailleur, if that is giving you a sense of dread then a local bike shop *Should* be able to swap the cassette and adjust the derailleur for you.

 

[RecordAceFromNew]

Fwiw changing the chainset from a 39T to a compact 34T would only be my choice if I was sure the difference is adequate for good, because firstly it is going to cost significantly more than just changing the cassette to a 28T, and secondly rear shifts are always easier, cleaner than front shifts (especially with increased front tooth difference, or under load, e.g. going uphill). I must however declare that I grew up with only 5 speeds at the back so close ratios is not a high priority to me when there are 8/9/10 speeds to play with nowadays.

But the best thing about thinking about changing the cassette, is that you are not limited to 28T if you are also prepared to consider changing the rear mech to a mountain mech (which in total can still cost less than a chainset). With that you can go up to 36T at the back - pretty much any mountain will be your oyster then!

Either change is likely to require a longer chain, unless the current chain is too long. I would suggest you use a calculator to check.

 

[2Loose]

That mech can officially handle 27t on the cassette.
I'd have gone for a compact double chainset, but would cost about 120 though.

 

[petrolhead]

Thanks for the replies so far some good suggestions there. I've looked on the Shimano website at compatibilities as was suggested but I found it pretty inconclusive really, as thought it's either a 11/27, 11/28, 12/27 or 12/28. I guess I could do that and fit a longer chain I suppose would be a lot easier than messing with the crank and chain rings? Anyone any idea what length of chain I'd need if I did that?

Cheers

 

[RecordAceFromNew]

If you are keeping the 52 up front it doesn't really matter whether the cassette is a 11 or 12, because 52x12 should be pretty high enough unless bombing down mountains at 40mph is a regular event for you. Howeve imho anybody contemplating changing chainset should always consider getting a 11T cassette because not only does it offer the option of a wider range, it can also allow one to opt for a smaller, lighter chainset to achieve the same range.

You can tell for certain whether your current rear mech/frame combination can handle a 28T by measuring the distance between the top jockey wheel and the 25T cog when you are in that gear. If the clearance is comfortably more than 6mm (due to 2mm additional radius for every tooth increase), you have no problem. Rear mech wrap capacity is not an issue for you since even a short cage Shimano mech has 29T capacity officially (52-39+28-12=29). Even if you can't get the 6mm immediately, adjusting the B screw of the rear mech will most likely give you that clearance.

You can tell what chain length is needed in your case by using the calculator I linked to previously; if the current chain is exactly right then 4 additonal teeth means 2 extra links.

For the avoidance of doubt you must get a cassette (either from Shimano or sram, road or mtb) having the same number of speeds as you have currently, otherwise your current shifter will not index properly, and similarly for the chain.