# Lost in gear ratio land....



## 29buzz (Nov 5, 2004)

Ok,so I have a Surly Krampus on the way-you know-29+ 3in tires on a 29er rim. I was going to do a 1x10 32-12/36. I started thinking about the Alfine 8. I'm very lame at math-even with a calculator....HELP! What would be the combo for this? I'm 245lb and ride tecnical in Wv....but do not need a super low-I just push 20yrds sooner on a 1x10 than with a granny. If I can get a low equal to a 30/36( or a small bit lower) i'm fine.

Thanks in advance

Bz


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## bsdc (May 1, 2006)

Without doing all the math and/or providing you links, I'll just say: I'm at the beach. I rented a fat bike with a Nexus 3 spd IGH. Make sure you get the correct chainline. This bike didn't have it. It created problems. It also didnt have a low enough gear. Slow grinding a fatty into the wind on the sand is not fun. I've got an Alfine 8 at home. I'm running it with 32/23. It's nice to have those low gears and it still leaves plenty of high gears.


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## dru (Sep 4, 2006)

The Alfine with a 20 tooth is equivalent to this: 12.4 14 16 20 23.5 27 31 38

I run a 30 tooth up front and like it for really steep stuff.

(on a 29er btw.....)

Drew


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## 29buzz (Nov 5, 2004)

Thanks for some quick responses! bsdc....not 100%sure on the chainline-but the bike I got to test was a 1x10. dru.....that sound very doable...is the 38 with the 30 up front or the 32? MRP make a 30t that fits my crank-I was considering it. But a 32/38 low would be ok.
Thanks again!


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## dru (Sep 4, 2006)

Alfine's use primary drive ratios. This is a combination of the crank ring size and the rear cog size of the Alfine. It is tricky to 'get' at fist.

My primary drive is 1.5 to 1 since I use a 30 tooth crankring and a 20 T sprocket on the Alfine.

You'll notice I listed 20 for gear # 5; that is the 1:1 gear. The hub and the sprocket rotate at the same speed in this gear. For top gear the hub turns faster and for low, the hub turns slower.

Raising or lowering the teeth count of the sprocket changes the equivalent gearing if the hub was an actual cassette.

If you are using a 18 tooth the range will be faster, probably around 34/11 and if you use a 22 tooth the range will be slower approximately 43/15 

It has no relation to what crank rings you are using, however using a smaller chainring gives lower overall speeds, and bigger rings give higher speeds.

Saying all that, a 36/24 combo is identical in range to the 30/20 I run, since the overall primary drive ratio is the same!

Drew


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## pursuiter (May 28, 2008)

I believe Krampus takes a standard 73mm bb/crankset. If that's the case, I'd start with well tested 32x22. That combo and an Alfine 8 will give a low gear of ~22x30 and a high gear of ~32x14. Staying with a 32t chainring will give you a plethora of 104 bcd crank options with cost ranging from $50 to $500.

32x22 will give you the same gears as:
Alfine___equivalent chainring x cog
eight_______32x14
seventh_____32x15.5
sixth_______32x18
fifth________32x22
fourth_______32x26
third________32x29.5
second______32x34
first_________32x42 (same as 22x29)

Later on, if you want lower or higher gear range it's easy to get different rear cogs from 16T to 24T.


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## bsdc (May 1, 2006)

Yes, but a 23T cog is one louder.


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## pursuiter (May 28, 2008)

I agree but they've been hard to find lately. I'm running an HBC 31T with a 26T in back on my Pugs, screaming :thumbsup:


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## 29buzz (Nov 5, 2004)

Ok gurus of the internal ratios...more questions! The 3sp version.....how do they hold up under big dudes---and 32 front...20 or 22 rear? The gear chart y'all gave for the 8 really helped me get a grasp of the gearing....but my feeble math skills can't get the 3 even! I was impressed with the knowledge given...so thanks and thanks in advance!

Bz


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## 29buzz (Nov 5, 2004)

Ok....after reading lots of posts-and thanks to whoever it was-I forgot to write it down...I have a chart now! But still the question remains.....big guys 250lb and up.....give me any negatives. How low is to low for the ratio before I crush its insides? I have built one for a 170lb guy...all is good 6 months and counting. I have seen some big dudes on them...but looking for long term. Also-anyone turn the lil gearbox thing so the cable runs up the chainstay? Thanks again and Happy Thanksgiving!!


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## bsdc (May 1, 2006)

If you want long term durability and gear ratio galore, go with a Rohloff. Everything else is a compromise. Often it's not a bad compromise. Sometimes it is. Weight is just one factor. Pedaling style, terrain, frequency of riding, lucky choice of hubs, etc. I've heard of little dudes breaking Shimano IGHs. Big guys often sit and spin more, and walk more hills. Little guys stand and hammer. Who knows?


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## 29buzz (Nov 5, 2004)

Thanks,butRohloff is out of the question....I dont need all the gears and can get 10 3sp for the price of one Rohloff. I can re-lace a hub-about 20-30min. So a season or more is fine. I crush a lot of cass. bodies and hubs anyway. I stand-you have to in our terrain. So any one who is brutal on equipment have any feedback?


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## iperov (Sep 9, 2012)

I use only three front gears xD
enough for me,
better concentrate mind on your legs muscules to produce more power, than concentrate "what rear speed better now?"


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## jrm (Jan 12, 2004)

*Have you tried Sheldons Gear Calculator?*

It really is great..

Sheldon Brown's Bicycle Gear Calculator


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## rifraf (Dec 22, 2012)

29buzz said:


> Thanks,butRohloff is out of the question....I dont need all the gears and can get 10 3sp for the price of one Rohloff. I can re-lace a hub-about 20-30min. So a season or more is fine. I crush a lot of cass. bodies and hubs anyway. I stand-you have to in our terrain. So any one who is brutal on equipment have any feedback?


Hi 29buzz,
what sprocket do you run on your hub and what combo do you use up front on your cranks?
Tell us about the kind of terrain your riding. Your being satisfied with the three speed sounds interesting.
If its a matter of not wanting or being able to use a front derailleur have you considered a Sram Dualdrive? 
Cheers

Just spotted you run a 32 up front. I tried Sheldons calculator.
Using a dualdrive and your 32t front ring and a 10 speed cassette with 13-36T you would get a gear inch range of 18.9 to 97.2. 
The dualdrive from memory gives 35% approx between the 3 speed ratios, with gear 2 of the IGH being 1:1.
I've read but not confirmed that the Dualdrive can handle a 10speed cassette.
Hope this helps


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## NYrr496 (Sep 10, 2008)

jrm said:


> It really is great..
> 
> Sheldon Brown's Bicycle Gear Calculator


Cool.


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## vikb (Sep 7, 2008)

29buzz said:


> Ok,so I have a Surly Krampus on the way-you know-29+ 3in tires on a 29er rim. I was going to do a 1x10 32-12/36. I started thinking about the Alfine 8. I'm very lame at math-even with a calculator....HELP! What would be the combo for this? I'm 245lb and ride tecnical in Wv....but do not need a super low-I just push 20yrds sooner on a 1x10 than with a granny. If I can get a low equal to a 30/36( or a small bit lower) i'm fine.
> 
> Thanks in advance
> 
> Bz












I had an Alfine 11 in my Krampus for several months and in a 29er hardtail the year previousI I was running a 32 x 23T setup and found it to work well for techy trail riding and bikepacking. I walked some on the steepest climb bikepacking, but I would on any bike at some point on these rides.

The A11 has the same low gears as the A8.










I have 2 Pugsleys that have been running A8's [32 x 23T] for 5yrs. Including some loaded touring in the mountains. The A8's have held up to sand, snow, salt and dirt with no issues.

I haven't worked out the gear inches for each setup, but they are more than adequate for riding with big wheels in the mountains with some camping gear as well as unloaded techy riding. I prefer to not have too low a gear in the tech otherwise I apply too much torque and spin the rear wheel - plus I don't get enough distance covered in my 2-3 power strokes to get over the crux.

If you do not need a crazy low granny gear you will be fine. :thumbsup:


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