MPH

Brian1

I am toying ith the idea of fitting a 12 - 27 to get me up the slopes a bit easier.I think after looking at the gear calculator on the Tacx website that this is going to cost me about .2metres per revolution.Does anyone know what this would equate to mph on the flat.Thanks

andrewgturnbull

Hi there.

Using a 12 instead of an 11 on the flat won't cost you a thing. The 11 is for downhill or sprinting. Even for sprinting the 11 is not much use unless you've got Pettachi's lead out train.

don't even use it for time trialling on the flat.

Cheers, Andy

ps If want a proper answer you'll have to tell us what cadence you intend to ride at, and how many teeth on your front chainring.

Anonymous

a 12-27 is super duper, I use one with my standard chainset and have yet to meet a hill that defeats me with it, and that's on my 25lb monster bike!

Anonymous

For mph - try here...


http://www.sheldonbrown.com/gears/

For me, 80rpm in 39-27 is 9.3mph

overthehill

http://www.panix.com/~jbarrm/cycal/cycal.30f.html

This is my preferred gear inch calculator. Calculates either in inches or at mph for all your gears at various rpm (and prints off into a nice table).

dennisn

Brian1 wrote:

I am toying ith the idea of fitting a 12 - 27 to get me up the slopes a bit easier.I think after looking at the gear calculator on the Tacx website that this is going to cost me about .2metres per revolution.Does anyone know what this would equate to mph on the flat.Thanks

Which gear are you talking about? The 12 or the 27 or something in between. Also need to know front ring size and RPM rate. The .2 meters is not enough information. Sorry.

edhornby

http://software.bareknucklebrigade.com/ ... pplet.html

this is designed for singlespeeds but it gives you a good idea of speeds attainable

for example if you have a compact (50tooth big ring) and your 12tooth cog on 23c tyres then if you can get up to 100rpm you'll be doing about 33mph

same 100rpm on an 11t cog gets you up to 36mph, and if you can attain that on the flat then chapeau sir

Brian1

Hi Dennis what I was trying to establish is if I will lose much top end speed by changing from 12-25 to 12-27.I am riding compact chainset

Alex_Simmons/RST

Your speed will be dictated by the power you can produce and the resistance forces acting against you. Changing gears doesn't magically change the power you can produce or the resistance forces acting against you. The gearing really isn't the issue, unless you think you will spin out on the 12 cog.

If you can do that on the flat, well you don't need help, and if you do that downhill, you are probably better off getting into a tuck-coast to go faster anyway.

Where you need gearing is for the climbs.

Brian1

Thanks guys

andrewgturnbull

Brian1 wrote:

Hi Dennis what I was trying to establish is if I will lose much top end speed by changing from 12-25 to 12-27.I am riding compact chainset

See I guessed that was the question... but I assumed you were changing from a cassette where your top-end gear was an 11.

Why would you ask if you lose top-end speed changing from a 12 cog to another 12 cog?

I'm not sure that you're getting the concept here?

Cheers, Andy

cougie

Just pedal faster.....

suze

Alex_Simmons/RST wrote:

Your speed will be dictated by the power you can produce and the resistance forces acting against you. Changing gears doesn't magically change the power you can produce or the resistance forces acting against you. The gearing really isn't the issue, unless you think you will spin out on the 12 cog.

If you can do that on the flat, well you don't need help, and if you do that downhill, you are probably better off getting into a tuck-coast to go faster anyway.

Where you need gearing is for the climbs.

Ditto What he says!!!!

freehub

I'm wondering if I should put my speedo back on just for the cadence back?

suze

freehub wrote:

I'm wondering if I should put my speedo back on just for the cadence back?

This is what I do... My cadence is not so difficult to maintain (90-100+) on the flat but on climbs I tend to push a little too much rather than pedalling.
I climb better when I keep the cadence higher, doesn't bu****r my knees either . Plus , at my age I have to rely on technique a little more, than brute strength that I used to do.