Gearing Question

The Machine

Hi all,

This might be the first silly question of 2009, if so, be nice!!

I'd like to know if it is possible to get an idea of how the gearing would feel on a single speed bike compared to that on my hybrid? If the single speed had a 42T/16 gear what gear would match that on my hybrid?

All I know about the gears on the hybrid are this:

GEARS: Shimano TX30 21 speed with STI shifters.
CRANKS: Suntour XCCT208 guarded chainset 28/38/48T.

Is this easy to figure out?

It doesn't have to be exact, I just want to make sure that the small few hills on my commute are manageable without gears....

Thomas_S_Hunterson

It would be in or around 48/18, ie your largest chainring in front and one with 18 teeth on the back if you have one?

Or alternatively the 38tooth on front and 14/15 teeth on the back.

TinyExplosions

Sheldon's gear calculator

-basically, find the gear on your bike that's the same ratio as your proposed single speed 16/42 = 8/21 etc. Roughly speaking, 48/18 is close.

It's a pretty small gear though, and you'll have no trouble around town on that

blorg

It is very easy, just divide the chainring by the cog to get the ratio. So 42/16 gives you 2.625.

With your front cogs this gives you:

28 10.7
38 14.5
48 18.3

So you need to pick a rear cog closest to one of these combos to approximate. Generally the equivalent gear on a fixie will be a little easier as it is more efficient and I think there is a bit of a flywheel effect.

This does not account for tyre size but generally that is not a big issue. If you want to account for that, you need to multiply the ratio by the wheel diameter (including tyre) in inches- this will give you the gear in "gear inches" which is generally the number used for comparisons. A rough number used for the diameter of 700c wheels is 27 inches.

Alternatively go here

stuf

Sheldon's gear calculator should help

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

42X16 corresponds to halfway between 15 and 14 on the back while using the middle ring on the front

remember that your single speed should be a bit lighter than the hybrid so should be easier to climb than the same ration on the hybrid

The Machine

Thanks guys for all the advise!

I'll check the rear cogs before I cycle home and work it out.

Cheers!

ajk24

Hi guys - I hope the OP doesn't mind me jumping in with a related question.

I have a Giant SCR4('08) which has a 36/50 front chain ring with a 12-26, 8 speed casette. I want to tackle the Sean Kelly this year and feel in need of a bit of help on the hills. I don't really want to upgrade the bike as triathlons/cycling are secondary to football/study at the moment.

I asked a more knowledgeable friend about getting a triple but he suggested that a 39/53 would be sufficient for my needs. can I get a yay or nay from you guys please. (by the way the miles of training will be done - I'm not looking to cut corners )

from sheldon's tool the results are

39 = 6.6, 5.6, 4.9, 4.4, 3.9, 3.6, 3.3, 3.0
53 = 8.9, 7.6, 6.7, 5.9, 5.3, 4.9, 4.5, 4.1

36 = 6.1, 5.2, 4.5, 4.0, 3.6, 3.3, 3.0, 2.8
50 = 8.4, 7.2, 6.3, 5.6, 5.0, 4.6, 4.2, 3.9

stuf

@ajk24

the small ring's the most relevant for climbs and the 36 will help you more than a 39 - nothing to change

DirkVoodoo

Yeah, you would want to be fairly fit and strong on the bike to use a standard double on the hills.

blorg

@ajk- you currently have a "compact" - what your friend suggests will be harder on the hills, absolutely no point doing that unless you are seriously racing. Your options to (cheaply) make things easier would include swapping the 36 front ring for a 34 (smallest you can go with a compact) and/or swapping your 12-26 for a SRAM 11-28 cassette.

Going triple is much more expensive and requires replacement of cranks, front derailleur, bottom bracket (I think) and shifters. And probably the rear derailleur too if you have a short cage.

short circuit

@akj - I have a standard double (53/39) and the bike came with a 12-26 cassette. Though I was able to use it around Wicklow .. some of the fun was lost. Hence staying with the double, I got a 11 - 30 cassette. Though I hardly use the 30 tooth cog .. its made my trips more pleasurable just knowing that I have a bail out cog. If you have a 50/36 ... I think the cheapest change you can do would be to change the cassette to a 11-28 or a 11-30 (in case you have a medium/long cage derailler - a bike shop will be able to confirm this). And if you are going to be putting in the miles before the SK tour ... you will definitely run through 1 cassette .. so you can put the expense down to regular maintenance ..

ajk24

thanks for the responses guys/girls.

given that the bike was only €540 to begin with there comes a point where trading in against something better might be more worthwhile. that point is not yet reached given that I have been nice to myself this christmas with a new pair of running shoes for my flat feet and a garmin forerunner 405 which will come in very handy for my lunch time ladder sessions - bring on the pain :mad:

blorg

Good point there from short circuit- technically what you are doing going to 11-30 is using a MTB cassette which is possible with 8 or 9 speed but not with 10 (MTB only goes to 9, while road now goes to 11 .)

xz

ajk24 wrote: »

Hi guys - I hope the OP doesn't mind me jumping in with a related question.

I have a Giant SCR4('08) which has a 36/50 front chain ring with a 12-26, 8 speed casette. I want to tackle the Sean Kelly this year and feel in need of a bit of help on the hills. I don't really want to upgrade the bike as triathlons/cycling are secondary to football/study at the moment.

I asked a more knowledgeable friend about getting a triple but he suggested that a 39/53 would be sufficient for my needs. can I get a yay or nay from you guys please. (by the way the miles of training will be done - I'm not looking to cut corners )

from sheldon's tool the results are

39 = 6.6, 5.6, 4.9, 4.4, 3.9, 3.6, 3.3, 3.0
53 = 8.9, 7.6, 6.7, 5.9, 5.3, 4.9, 4.5, 4.1

36 = 6.1, 5.2, 4.5, 4.0, 3.6, 3.3, 3.0, 2.8
50 = 8.4, 7.2, 6.3, 5.6, 5.0, 4.6, 4.2, 3.9

I have the same bike as you, and have been over the Shay Elliott (from both sides) and am 17stone, so you should have no problems. Although, just yesterday I changed it all to a 9 speed, with a 34/50 105 chainset.