Change of Cassette.

Notnormal

Not stricly an MTB question but couldn't find an equivilent forum on the road section. I have a hybrid bike which I use for commuting (Scott Sub 30). Please excuse my lack of technical terms etc as I'm a bit of a novice.

Basically on anything more that a gradual downhill theres no point in pedalling as even in top gear I'm not adding any drive. I want to replace the cassette to change the gears so I can still add drive when going downhill. I've read up online on how to change a cassette over but as long as I get one with the same number of gears will I need to adjust the gears and or change the length of the chain as well? I'm keen to have a crack at doing this myself and don't want to end up taking a load of bits into my LBS and asking them to save me!

nicklouse

well the smallest cog on the rear is an 11T. what is your current small cog on the cassette? Also how many gears has it got? total and rear.

Notnormal

After looking up what 11T means!!! The smallest sprocket on the rear wheel has 11 teeth, there are 8 different sprockets on the rear cassette and three on the one by the pedals. Making a total of 24 gears. I'm grateful o any help!

Captain Turok

Hi I'm not v clever when it comes to these things, but you may find that the issue is to do with the the 42 teeth on the big ring of the chainset.

I think you'll find its already got 11 teeth on the smallest cog of the cassette

I only mention because I had the same issue with mine. Love the bike though.

nicklouse

Notnormal wrote:

After looking up what 11T means!!! The smallest sprocket on the rear wheel has 11 teeth, there are 8 different sprockets on the rear cassette and three on the one by the pedals. Making a total of 24 gears. I'm grateful o any help!

Ok then changing the cassette will do nothing. you will have to look at chainring of the crankset and go bigger.

not as simple as you will need to lengthen the chain (new chain) and then move the front mech and reset the cable tension.

so at a guess, as mentioned, 42T on your big ring? look to go to 44 or a bit bigger.

I would discuss this with your LBS (Local Bike Shop).

Notnormal

Thanks for the replies, I will be speaking to my LBS as it now seems beyond my bike mechanic abilities. Does anyone know roughly how much the parts and labour should cost for a job like this? Appreciate it will be a rough guess only.

Captain Turok

Can't (don't want to!) remember what it cost, sorry.

But for what its worth, I went for XT as it came with a 48T chainring, as I remember it the Deore or LX didn't (?).

It was complicated by needing a different bottom bracket as well. But got an additional discount by going for the previous years specification.

But pricing up the options at your LBS is the best place to start.

supersonic

How fast are you turning the pedals when in top gear? 42/11 will get a reasonable top whack when turned at 120 rpm!

Captain Turok

I fixed a cordless Cat Eye computer thingy to mine, with the 42/11 (as originally supplied on the old Scott Sub).

It (or I) seemed to max out at only 27mph*, but going down hill (as Notnormal mentions in his first post) it was a case of not being able to spin my legs fast enough!, rather than a power issue.

* I should add that I had to enter the circumferance of the tyre manually, an a 'user error' may have occurred..

ride_whenever

I'm with super, you need to crank the pedals faster, it is better for you.

Notnormal

Mine only has MTB (26" I think) size wheels on as well which probably doesn't help the problem?

supersonic

No, doesnt help, as you need a larger chainwheel to get the same gear inch. You can work it out: taking a nominal circumferance of 2000mm, the 42/11 gear will move the bike 7.64 metres per full crank revolution.

At 100rpm this is 764m per minute.

= 45.8km per hour

= 28.6 mph.

120 rpm is generally the max cadence you see riders using, and the tyre circumferance may differ slightly from the one I suggest depending on the tyre.

coll_coll

..uncanny... I have a Scott Reflex 30 ('06) and decided on Saturday I need a new chain.. which may also mean a new cassette... and in turn as I do many more road miles than off (saving for a 'proper' road bike), I worked a mental route all the way to asking if I can just change the 42T for a 44T....and then found this thread.

So pedal faster ... mmm... whirling dirvish image of 16st at 120 rpm...

I'd be interested to know the outcome and the ease of swapping a 42 for 44 at the same time as a chain change...

TiA

Craig

(Added-thinking of changing to Shimano XT M760 Outer Ring; existing spec Shimano FC-M410 with 24x34x42 )

supersonic

Should be east to swap. Again, you can work the difference out fairly easily - you will increase your top gear by 44/42 = 4.76%


Need to make sure the new ring has the right bolt holes and sizes for your crank. I am not sure whether the crank you have is a true 8spd chainset.

Notnormal

Local shop was closed today for the bank holiday but I'll take it in tomorrow and see what they say. Not sure what increments they go up in but might go bigger than 44T if it all fits and the price is right. I'll post my results here........

supersonic

Some front mechs can only handle 44t largest cog, and jumps of 12t

Notnormal

If anyone was following this unfortunately its not viable for me to change the chainset. Basically if I go larger on the chainset it means it would catch on the frame of the bike where the rear wheel is. I could increase the width of the axle that the chainset is mounted on but it starts to get a bit more expensive. Thanks to all who posted here,