I need some help figuring out gear ratios.

[Iron Yeti]

For 26 X 1.9 / 47-559 / MTB tire with 175 mm cranks with 7-speed Sram 12-14-16-18-21-26-32 Cassette
I used a calculator on Sheldon Brown's website and came up with this for my current setup:

For 26 X 1.9 / 47-559 / MTB tire with 175 mm cranks and 12 tooth sprocket
Now, I don't know much about gearing systems but does this new setup with a Nuvinci hub, a rear 12T sprocket and a front 44T equal my old gearing system at it's maximum highest and lowest settings? What I am trying to do is create a gearing system equal or better to my old one. I am trying to do this without a dérailleur.

Also, people are saying that I might need at least a chain tensioner, why would I need a chain tensioner with a single speed bike w/ an internally geared hub?

Thanks dudes.

 

[Sturdly]

Bikes without deraileurs normally have horizontal dropouts allowing the wheel to be moved forward or rearward to adjust chain tension. Bikes with deraileurs normally have vertical dropouts allowing for no font to rear adjustment. If you get lucky and can shorten or lengthen the chain to precisely fit then no tensioner needed. It is far easier to just get the chain length close and let the tensioner take up the slack.

As for the 12t rear freewheel I think that 13t is the smallest you will find. Staton inc recommends a 2 to 1 ratio, example 44t front with 22t rear freewheel. http://www.staton-inc.com/Details.asp?ProductID=3216

 

[Iron Yeti]

Bikes without deraileurs normally have horizontal dropouts allowing the wheel to be moved forward or rearward to adjust chain tension. Bikes with deraileurs normally have vertical dropouts allowing for no font to rear adjustment. If you get lucky and can shorten or lengthen the chain to precisely fit then no tensioner needed. It is far easier to just get the chain length close and let the tensioner take up the slack.

As for the 12t rear freewheel I think that 13t is the smallest you will find. Staton inc recommends a 2 to 1 ratio, example 44t front with 22t rear freewheel. http://www.staton-inc.com/Details.asp?ProductID=3216

I have vertical dropouts. So I don't need a chain tensioner? I mean if I got the chain to the correct length, just right, on a 1 speed setup, I wouldn't need one?

My problem with using other size gears is I want at least the same or better gearing on my new setup. With the 13/44 gearing setup I get a better setup, by those charts, right? If not what would I need to meet or exceed my current gearing setup? Or by the recommendations of the 2:1 ratio, what would give me a good setup to my old one?

 

[dogman dan]

A tensioner would be a good idea with a suspension rear. Hardtail wouldn't need it. Motorcycles of course don't use a tensioner, but the chain is much stronger and can handle a slight change in length as the rear tire goes up and down. Tighten a motorcyle chain too much and you will hear it creaking as it hit its longest point.

 

[Iron Yeti]

Alright, so can anyone help me with gear ratios?

 

[SteveMush]

A chain tensioner is always a good idea, as even in the best set up, a new chain will stretch a bit and then more as it wears over time.

 

[Lenk42602]

yeti,

I have a 12t rear, 53/34t double chainring in the front. Essentially a two speed. My bike's max speed it 40 mph on the flats, but generally i run at around 20-25 mph. I rarely drop into my small front ring 34T - this is more of a bail out gear if I ever break down somewhere. My 53t front/12t rear allows me to pedal assist the hub motor from 0-23mph. At 23 mph, i need to get my leg speed (rpms) going pretty fast.

I use a long cage rear derailluer on my single rear bmx free wheel. This is because the effective chain length changes when shifting between the two front chainrings enough that it is required. If you have an internal hub on the rear, horizontal drops, and one ring in the front, you should not need a tensioner/derailleur.

You do not have horizontal drops, so you might as well go with a double chainring setup in the front, because you most likely would need a rear derailleur(or just a tensioner and one ring up front). The only way you would not need either is if the chain length on your 13/44 set up, once installed, has the perfect tension on your chain, which is a function of your chain stay length.

BTW, if your fastest gear combo is 44t/13T, your pedal input will have an effect up to about 13-16mph give or take a few...

peace,

Len

 

[Iron Yeti]

This has nothing to do with electric motors, thus so far. I am simply talking bout trying to match up my Nuvinci hub with a set of gears to my old 21 speed.

What I am trying to do is get a similar or better gear ratio. So, are the charts I posted equal or do I need to use different sprockets?

 

[MitchJi]

Hi Kyle,

I'm still pretty weak.

Did not use the Nuvinci myself so I can't answer your question.

Maybe the information in this article will help?:
http://mitchji.home.comcast.net/~mitchji/VV29HubGearsReview.pdf

 

[voicecoils]

When using the Sheldon Brown Gear Calculator, I choose KPH @ XXX RPM from the drop down menu instead of gear inches/meters development/gain ratios. It's much easier to visualise the speed you'll be going at various gearings.

At a cadence of 60 RPM (pedaling) with your old SRAM cassette and a 44t front chainring you will be going:
27.1 km/hr in 12t
10.2 km/hr in 32t

To improve on this with the Nuvinci, using the same 44t front chainring and a 16t rear cog you will be going:
35.6 km/hr at the top end
10.2 km/hr at the bottom end.

So, the Nuvinci gives you wider gearing.

Re: singlespeed. If you have vertical drop outs you NEED a chain tensioner so your chain does not fly off as it stretches. A chain tensioner can be a singlespeed specific one or a common derailleur. There are exceptions to this rule but none apply to your situation.

 

[lawsonuw]

Huh, that gear claculator is giving odd answers.

Anywho, your old gearing gives a range of ratios from 44:12 = 3.666 to 24:32 = 0.75
to get the total percent variation (3.66-0.75)/0.75 * 100 = 388%
This is a bit more than the Nuvici hub has
To keep the same top gear with the Nuvici hub, divide your old high gear by the highest ratio of the Nuvici. 3.66/1.75 = 2.09 This is the new ratio the chain has to provide. With a 44 tooth chain ring about a 21 tooth cog is needed on the hub.

Marty

 

[GGoodrum]

The Nuvinci has ratios that range from .5:1 to 1.75:1, which is a range of 250%, which is quite a bit less than the 388% of your existing setup. You need to decide whether it is more important to have the same "top end" as before, or if you need the "granny gear"-type of low-end torque. The 44T/21T combo will match the upper end, but to match the lower, you would need something like a 34T/23T combo, I think.

-- Gary