Gear Ratios

[Toback]

Am I able to put a same speed cassette, but with a different gear ratio? for ie I have a 9 speed cassette with a (11-34) gear ratio, can I fit another 9 speed cassette with a (11-26) gear ratio? If I can, what ratio would be best for the road with a 9 speed cassette? thankyou.

[zero]

Am I able to put a same speed cassette, but with a different gear ratio? for ie I have a 9 speed cassette with a (11-34) gear ratio, can I fit another 9 speed cassette with a (11-26) gear ratio? If I can, what ratio would be best for the road with a 9 speed cassette? thankyou.

You can do that yes, changing to closer ratios usually doesn't need other parts - though a change of 8T on the largest sprocket will likely require adjustment of the angle ("B") screw on the RD when finishing the installation otherwise the top pulley sprocket will run a long way away from the cassette, which will probably make the shifting really sloppy and delayed on the easier gears. I'd recommend using a new chain unless the existing chain is only a couple of hundred km old and not measurably lengthened, (in which case, shorten it as necessary).

When you go the other way, (ie widening ratios) you need to verify that whatever derailleurs are on the bikes has sufficient teeth capacity and max Teeth for the intended cassette, and you will usually need a fresh chain for that (because it will need to be longer) though shimano derailleurs usually accept 1T larger max teeth than they specify.

The best ratios for you will depend on what the bike is - including its wheel size, how strong a rider you are, and what sort of hills you ride, and what chain rings you have - ie we don't have enough info to answer that question.

[Duck!]

Short answer: yes! Given that you're proposing changing from a wide-range cassette to a tighter one, you don't have to worry about the capacity of the derailleurs, because it will fit fine (it's entirely within the range covered by the current gear set). As zero said, just chuck a new chain on with it unless the current one is in good nick.

As for what size is best, well that's hard to judge. Given the cassette you currently have is a MTB-type, it would be reasonable to expect that the crank is probably a triple, with a big ring of 48T or less. The triple gives a good low range for hill climbing, so even an 11-23 could be considered. This gives nice slick steps across the gears, and with the 26T or smaller small ring up front, doesn't lose out too badly unless you're climbing walls. 11-25 or 26 will give a little more climbing range, but is still reasonably slick across the range.

[Toback]

Thanks for answering you guys, and yes, the crank i have at present is a tripple. 26/36/48..... I wont be doing a lot of hill climbing, I think what will be most important to me is getting the best ratio setup for going fast on flat ground.

[Duck!]

Going fast all comes down to the engine (i.e. you)

You're not actually gaining any top-end gears with the tighter cassette; what you do get is a much tighter mid-range (which is generally what you'll be using), with smaller, smoother steps betwen ratios.