Fitting road cassette on MTB

[Cyclist33]

Hmm, that's odd; the top gear on the front cassette I'm running is absolutely enormous compared to my older one.

Can we start using the right terminology so we don't get confusing? The "front cassette" is called the chainset or crankset (and includes the crank arms themselves, incidentally).

As is often the case with these threads, you do need to do a wee bit of homework for yourself. It's to do with the ratio of teeth between the chainset rings and the cassette rings. Many chainsets will have the teeth quantity printed on them, should look something like "48-36-26". You can count the teeth yourself too, it goes "1, 2, 3, 4... "!!

In theory (I think), the same gear is achieved if you had a 48 tooth ring upfront and a 12 tooth cassette, as if you had 44/11, because the ratio of front to rear is 4.0 in both cases. This statement "Most road cassettes seem to have a 12 tooth top gear, whereas most MTB cassettes have an 11 tooth top. In other words, your top speed will be lower with the road cassette. " is only half true because even if the road cassette has a toothier smallest cog, its top gear will be greater if the largest front ring is sufficiently toothy also so as to make its ratio higher than the mtb's highest

 

[Drago]

My commuter is a Hopped up Carrera MTB and at 30 MPH it still hadn't run out of gears on the original 42t chainring and rear cassette. We were heading that way, but werent there yet.

Our OP must ride like Roger Ramjet to need a bit extra.

 

[fossyant]

Popping hybrid tyres on will give you a good increase in speed. A road cassette will mean the steps between each gear is less, so you'll have less of a 'jump' between gear ratios - this means it's better for the road.

 

[SomethingLikeThat]

Our OP must ride like Roger Ramjet to need a bit extra.

Heh I'm not really anything special. I just wanted to make it a bit more suitable for the road without buying a whole new bike.

 

[mcshroom]

I'd practice spinning and fit a cassette with an 11 tooth small cog (and a new chain). For tyres have a look at something like Schwalbe Marathons or City Jets - you will be amazed how much easier it is to ride with slick tyres on the bike.

Even with a 42t big ring at the front, that gives you a gear of 110.7" 95" with 26x1.5" tyres. With that you would be able to go at 30mph if you are spinning at 100 rpm (which is quick, but not ridiculously so).

I ride a tourer with a 42t large chainring and an 11-32 cassette (700x32c tyres) and it's very rare I would like more gears, at which point it's usually time to tuck in and enjoy the decent

 

[PpPete]

I'd practice spinning and fit a cassette with an 11 tooth small cog (and a new chain). For tyres have a look at something like Schwalbe Marathons or City Jets - you will be amazed how much easier it is to ride with slick tyres on the bike.

Even with a 42t big ring at the front, that gives you a gear of 110.7" with 26x1.5" tyres. With that you would be able to go at 30mph if you are spinning at 100 rpm (which is quick, but not ridiculously so).

I ride a tourer with a 42t large chainring and an 11-32 cassette (700x32c tyres) and it's very rare I would like more gears, at which point it's usually time to tuck in and enjoy the decent

I make it 94" but 30 mph at 100 rpm is right
The other points are valid too.
It does take time to get used to spinning, feels quite un-natural at first, but do persevere, it is worth it, not only for the extra speed you get, but also because it massively increases your endurance.

 

[mcshroom]

Hmm, machars.net gives the 110.7", Sheldon gives 95"

 

[Rickshaw Phil]

Hmm, machars.net gives the 110.7", Sheldon gives 95"

I'd agree with Sheldon. A road type tyre on a 559 rim will give a rolling diameter of around 25" ish in my experience.

95 gear inches should still be good for sprightly performance.

 

[mrandmrspoves]

Mountain bikes are geared with a bias towards going up mountains, I think. So basically if you use a road cassette, you get much bigger gears. The front cassette of my bike is a road cassette, and its smallest gear is the same as my bike's old second gear - middle is very close to my old third, and then the outer is just brilliant going downhill. I don't miss my old smallest gear, never used it anyway. I recommend it.

Mountain bikes are not only geared for going up mountains......when they get to the top what do you think they do next?
Hence mountain bikes have wide ratio gears (as do touring bikes) so they can go up steep hills - travel at reasonable speeds on the flat (but not at 40mph!!!) and go at a fair old pace downhill.