cassette and gear ratio help please!

[dirtybackbeat]

hi there, I'm just about to purchase some new wheels http://www.merlincycles.com/bike-sh...ory-road-wheels/mavic-aksium-wheels-pair.html

i'm looking at getting a new cassette too as my other one has seen over 3000miles now but i'm not sure about the gear ratios. at present on my bike (charge juicer 2010) it says on the spec that it has a shimano hg60 9 speed cassette. ratio is 11-25t. looking at getting a cheap cassette but the 11-25 is out of stock so it got me wondering what difference would it make to go for another ratio (12-23 or 12-25). up front i have a tiagra triple (50,39.30)

these numbers mean nothing to me unfortunately! at current i'm riding 30-50 mile rides at 18-20avg mph and if anything i could do with a harder gear. would one of the other cassettes give me this?

many thanks in advance for your help

 

[simon.r]

You can plonk the numbers into one of the many gear calculator sites to see what impact it will have.

Basically, if you want a harder gear you need either a smaller small cog at the back and /or a bigger chainring at the front. It may be an idea to spin bit faster? A 50/11 gives a speed of 33mph at a cadence of 90rpm.

 

[wheres_my_beard]

I may be teaching you to suck eggs, but as no one has responded....

Its often hard to know what the number of teeth are on the inbetween cogs on a 11-25 or 12-25 cassette, lower numbers at the backcog will produce a higher gear inch when combined with a higher number of teeth on the front cog, so a 11 (rear) x 50 (front) will be harder than 20x39, for example. Looking at this chart might help > http://www.bikecalc.com/gear_inches and this too > http://www.sheldonbrown.com/gears/

I think that the 11 tooth cog is about as small as you will get on a cassette, so you may want to opt for a larger front ring, maybe just the top one or even the middle one as well, to give you some harder gearing, and higher speeds at a sensible cadence. Changing from a 11x50 to 11x56 would mean a 4 mph gain at the same cadence (80 rpm), based on Sheldon's calculator.

Don't forget it is worth having a massive cog on the rear cog in reserve for that killer hill that might just finish you otherwise!

 

[wheres_my_beard]

I may be teaching you to suck eggs, but as no one has responded....

Its often hard to know what the number of teeth are on the inbetween cogs on a cassette, but lower numbers at the back cog will produce a higher gear inch when combined with a higher number of teeth on the front cog, so a 11 (rear) x 50 (front) will be harder than 20x39, for example. Looking at this chart might help > http://www.bikecalc.com/gear_inches and this too > http://www.sheldonbrown.com/gears/

I think that the 11 tooth cog is about as small as you will get on a cassette, so you may want to opt for a larger front ring, maybe just the top one or even the middle one as well, to give you some harder gearing, and higher speeds at a sensible cadence. Changing from a 11x50 to 11x56 would mean a 4 mph gain at the same cadence (80 rpm), based on Sheldon's calculator.

Don't forget it is worth having a massive cog on the rear cog in reserve for that killer hill that might just finish you otherwise!