Ratios ,

[ozboz]

i have seen something that tells us what ratio pedals to wheels are
Ie , 1 rotation of the Chainwheel
=. So many rotation of the wheels
What I am trying to learn is what the ratios are for a 34 chainring to a 34 cog on the cassette ,
Any one help ?

 

[Sharky]

1
Bikecalc.com

 

[smutchin]

34/34 = 1

Assuming a 700c wheel with 25c tyre, that's a wheel circumference of 2.1m, so for each full turn of the pedals you will travel 2.1m forwards (1 x 2.1m).

At the top end, if you have a 50 tooth large chainring and 11 tooth sprocket, the ratio will be:

50/11 = 4.55

So for each turn of the pedals you will travel 9.6m forwards (4.55 x 2.1m).

 

[raleighnut]

This is the resource I use, just enter the info into the boxes,

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjy0tG_qu7RAhXKCcAKHXlMA8QQFggcMAA&url=http://www.sheldonbrown.com/gear-calc.html&usg=AFQjCNH9MBGQOcyOZk6qZTEeJyBgtLvKlg

EDIT I find cadence in RPM to speed in MPH the most useful, especially for SS setups

 

[Ajax Bay]

I find this gear calculator is excellent. This can be customised ad infinitum and also allows consideration of any cassette, any chainring combinations, tyre size, cadence, chain angle exclusions, and you can compare two setups. I commend it to you all.

 

[Dogtrousers]

This is quite a messy subject.

Traditionally, in the UK, gears are expressed in "gear inches", which is the wheel size of an equivalent "ordinary" (penny farthing) bike. Typically around 30" is a low gear, and over 100" are high gears.
Traditionally, on the continent, gears are expressed as "développement" which is the distance in metres that the bike will travel for one rotation of the pedals.
Ratio is less useful, because the actual "highness" or "lowness" of the gear is dependent on both the ratio and the wheel size. So a given ratio on a road bike would be a totally different gear on a Brompton. But both of the above (inches and développement) would be the same on both.

Sheldon Brown writing on the subject here. A good explanation of existing systems and a quixotic proposal for a new one.

It doesn't really matter what system you use as long as other people understand you. On the fixed gear forum people happily discuss riding a (say) 64" gear and understand each other. I doubt any of them has any idea, or cares, what a 64" penny farthing would look or feel like.

I've never seen the gear calculator that @Ajax Bay referenced, and it looks great. Almost, (but not quite ), as good as my venerable gear calculating spreadsheet.

 

[MichaelW2]

You can look at gear ration from front chain ring to rear sprocket, but you can also factor in the circumference/ diameter of the tyre to give travelling distance per rotation and you can factor in the length of the crank. Sheldon Brown website is informative.

 

[ozboz]

Thanks for replies , some interesting and informative replies
I am checking this out as I have just started riding a road bike with a compact 50-34 , 10 speed 11-25 , so , I have been riding bikes with tripples , actually had a tripple fitted on my Surley , story is , these 64 yo legs need help !
especially as one of them is not firing properly , on my first ride on my roadie Sunday I didn't take on any inclines and I do not think I will manage them with the present setup , so Checked out the net and I can get an 11-34 , 10 speed cassette , this will help tremendously ! Well I hope it will !!

 

[gazza1286]

You may need to swap your RD to a long cage to cope with the larger cassette. Obviously a longer chain too.

 

[ChrisEyles]

34/25 is quite a tough gear to push up a steep hill. Swapping the cassette for an 11-34 will help enormously. For the way a lot of us use our bikes (exploring, long rides, steep hills) I think a triple crankset and something around 11-32 on the back is pretty much optimal.

 

[Aravis]

34/25 is quite a tough gear to push up a steep hill. Swapping the cassette for an 11-34 will help enormously. For the way a lot of us use our bikes (exploring, long rides, steep hills) I think a triple crankset and something around 11-32 on the back is pretty much optimal.

I largely agree, but I do think the almost universal inclusion of an 11-tooth on cassettes is unhelpful, especially when there's a 12 there as well, as seems normal.

On my regular bike I have 48/38/28 chainrings, and the supplied cassette was 11-12-14-16-18-21-24-30. When the cassette needed to be replaced a couple of years ago, I saw two problems. Firstly, the 11 was a waste of space, quite literally. Secondly, although the 30 probably did give me a low enough bottom gear, the jump from 24 to 30 was uncomfortably big and I often wanted something in between.

I replaced it with 12-14-16-18-21-24-28-32 (Shimano HG200 Tourney - incredibly good value). A small but subtly significant change. The problems described above are solved, and because everything is effectively shunted outwards one position, I soon found that the combinations I use most often are in the optimal position for each chainring.

To be honest, with a 48 on the front I don't have much use for the 12-ring either. When I finally need to replace the chainset, I'm seriously considering using something like 40/30/22, which should mean I can get what I need from a 12-25 cassette or similar, with the benefit of smaller gaps in the middle.

 

[si_c]

The bike I'm looking at has a subcompact chainset (48-32) with a wide range cassette (11 / 13 / 15 / 17 / 20 / 23 / 26 / 30 / 34) which I think is fine for me. I'm much happier spinning up a hill than grinding and given that I live in a flat area, I don't get much practice with hills so low is good.

 

[smutchin]

I do think the almost universal inclusion of an 11-tooth on cassettes is unhelpful,

This is a long-term gripe of mine. I'm convinced most people don't need anything smaller than a 14, even with a 50t chainring.

That said, the rising popularity of 1x groupsets makes more sense of wide-range cassettes - I've seen a Tripster set up as a 1x with an 11-40 cassette. I get this. Just as most people don't need very high gears, they don't need small gaps between gears either.

 

[Dogtrousers]

Thanks for replies , some interesting and informative replies
I am checking this out as I have just started riding a road bike with a compact 50-34 , 10 speed 11-25 , so , I have been riding bikes with tripples , actually had a tripple fitted on my Surley , story is , these 64 yo legs need help !
especially as one of them is not firing properly , on my first ride on my roadie Sunday I didn't take on any inclines and I do not think I will manage them with the present setup , so Checked out the net and I can get an 11-34 , 10 speed cassette , this will help tremendously ! Well I hope it will !!

I'm sure it will.

You just need to find the tech documents to check what the capacity and max sprocket size of your rear mech is. 11-34 would need a capacity of 39 teeth (50+34 - 34+11), and a max sprocket of 34 teeth (obvs). Ask on here and you'll probably find people who have successfully pushed derailleurs beyond their stated limits.

Regarding the pointless little 11T sprocket. No, I don't need it. But when it's there, I do use it quite a bit.

 

[ozboz]

Once again , many thanks, a tripple would be the go , but I do not know if I could get one in there ,
The Surley accomodated it , but this carbon BH looks an unlikely candidate for one , so max-ing out the rear sprockets is my only choice , and changing rear d'lr and chain etc , as mentioned in thread