[michaelo]

Sorting out the gearing for my build.

Am going with a boone ti ring up front for sure (have them on my 960 triple and love them).

What I am is a novice at is gear selction.

a 32:16 has the same gearing as a 34:17 from what I understand. However it has a longer chain lenght. Does that mean anything? (it will be longer as it's on a 29er anyway!)

is there any benefit of one vs the other. Am i going to spin a 32 faster than a 34 at the same gearing ratio?

Any thoughts or links to other threads would be appreaciated. My search did not com eup with much.

 

[nbrennan]

The short answer is no. There will be a slight increase in rotational mass, and gross weight in general w/ a 34/ 17 set up, but the ratio/ gear inches/ etc are still the same. However, most 29ers are not geared 2:1. I don't ride a 29er, but from what i hear 32x18 is popular. Also, the more teeth you have and the more chain you have, the longer your drive train will last. Hope that helped.

 

[Glow in Dark]

There should be no difference. I run a 36X21 on my "magic gear" single speed Bridgestone MB-1 and it works great.

 

[Nat]

Okay, the logical answer is that there should be no difference, but last summer I switched from 32/18 to 34/19 and I swear it feels smoother or more responsive or something. Not dramatically, but with subtlety. I was as big of a naysayer as anyone but goddam if I don't feel it.

I've read it's because the chain wraps around more total number of teeth and therefore spreads the load out more. Maybe the metal is flexing less? Less pressure and flex per individual tooth? I've read these claims here for a few years. Sometimes you see bikes with big rings plus big cogs, and those people support this notion.

I was skeptical too! Maybe it's all in my head. I dunno, but I'll buy 34/19 again instead of 32/18.

 

[GlowBoy]

You'll be in the same effective gear. There will be very slight differences in weight (higher with 34x17), chain life (longer), and smoothness (better), but I'd be surprised if the difference is noticeable.

Most people who run 32x(whatever) do so because they have compact cranks with a 32t ring.

Most people who run 34x(whatever) do so because they have older standard cranks with a 34t. Myself included.

Are you sure you want to go 34x17 though? That is a very tall gear for real mountainbiking with 29" wheels. I run 34x22, which is at the low end of the range people run, good for lots of climbing. Racers might go as tall as 34x18, but 34x19 or even 34x20 would be plenty high for most riders in most places that have hills.

 

[Bicycle Rider]

What everyone says:

The gearing is the same, period. One full rotation of the pedals translates to two full revolutions of the wheel.

Some people say larger ring combos feel different. Smoother. I can't comment on this with any certainty, but it makes sense, since a 10t chainring engaging a 5t cog would clearly feel very notchy.

In my mind, the benefits to larger rings and cogs (regardless of what ratio you want!) are mechanical: For a small increase in weight, you get more teeth engaging the chain at any one time. You also get lower overall tension on the chain. These factors theoretically combine to extend chain life. In addition, with more teeth contacting the chain, the chain stays put better, even if run a little loose. So if your chain is wearing more slowly, and more tolerant of being out of adjustment, you can set your hub (or sliders, or EBB) once, and leave it alone for longer stretches. Nice!

Of course, the actual real-world difference between a 32 and a 34 is very little. But you can see I've thought about it, so I run a 34.

Eric.

 

[PeanutButterBreath]

A slight benefit of a 32T on a 29er is that for standard gearing, which in most cases starts at 32:18, it'll be easier to find larger cogs if needed. For steeper hills a lot of folks go to 32:20 or even higher. With a 34T you would need a 21T for a rough equivalent to 32:20, and if you wanted something bigger you are already close to the 23T ceiling for FWs.

If you are planning to run a cassette hub with Boone or Endless cogs, this is less of an issue.

 

[pvd]

larger diameter gears work more efficently, so you use less power to drive them.

smaller diameter gears make a lighter system, so you use less power to move the bike.

I would go larger. the 34 is a better choice.

see:

http://www.pvdwiki.com/index.php?title=Single_Speed_Gearing

http://www.bhpc.org.uk/HParchive/PDF/hp50-2000.pdf

 

[unit]

yes...

larger diameter gears work more efficently, so you use less power to drive them.

smaller diameter gears make a lighter system, so you use less power to move the bike.

No offence, but that seems to overstate things a bit. smaller gears do weigh a few grams less and probably will save you like...I don't know....something like 0.01% power.

I would agree that at some point you will feel the difference in smoothness, but I have a really hard time believing that anyone can quantitatively demonstrate a power savings resulting from a weight loss this small, or an efficiency gain this small. If you "feel" it.... great, but it may be merely perceptible, and it may be placebo.

Something else to consider....if you are using Boone front and rear (you didn't specify a rear), you might want to consider a larger ring and cog (even larger than a 34x17)....For that sort of money, I would want rings and cogs large enough that I can see them and appreciate the beauty (a 17 tooth cog doesn't show like a 22 will when it comes to Boone's design).

Just my thoughts....The larger Boones look WAY nicer than the smaller ones, and at some point most of us buy things because of how they look.

 

[SyT]

This is an interesting topic. I'm about to replace my 36:21 al. cogs and ring with 32:18 all stainless.
My reasoning was for a longer lasting drivetrain (mainly the front ring) and more rock/log clearance, getting rid of the bashgaurd with the 36 (Bike is 29r, fyi) I will pay particluar attention to the sensations others believe they're feeling

 

[unit]

This is an interesting topic. I'm about to replace my 36:21 al. cogs and ring with 32:18 all stainless.
My reasoning was for a longer lasting drivetrain (mainly the front ring) and more rock/log clearance, getting rid of the bashgaurd with the 36 (Bike is 29r, fyi) I will pay particluar attention to the sensations others believe they're feeling

I would also be interested in knowing the difference in diameter of the 32 vs the 36. I don't expect there will be a very large difference in ground clearance. There may be a appreciable difference between the 32 and the bash guard however....?

 

[shiggy]

Okay, the logical answer is that there should be no difference, but last summer I switched from 32/18 to 34/19 and I swear it feels smoother or more responsive or something. Not dramatically, but with subtlety. I was as big of a naysayer as anyone but goddam if I don't feel it.

I've read it's because the chain wraps around more total number of teeth and therefore spreads the load out more. Maybe the metal is flexing less? Less pressure and flex per individual tooth? I've read these claims here for a few years. Sometimes you see bikes with big rings plus big cogs, and those people support this notion.

I was skeptical too! Maybe it's all in my head. I dunno, but I'll buy 34/19 again instead of 32/18.

That has long been my position: bigger ring/cog = smoother feel.

What I never understand is why some think a bigger ring/cog with the same ratio will change your cadence and/or wheel speed.

In any case I think you are going to find a 2:1 ratio on a 29er to be WAY hard in Colorado.

 

[Enoch]

Where does that leave me? I'm running a 30 tooth ring and I absolutely love it. My ratios are a tick smaller, seems to wind up quicker on my 29. more clearance, I also get a little less chain deflection under hard choppy efforts

 

[GlowBoy]

I would also be interested in knowing the difference in diameter of the 32 vs the 36. I don't expect there will be a very large difference in ground clearance. There may be a appreciable difference between the 32 and the bash guard however....?

I don't think most people would notice a 2 tooth difference, but a 4 tooth difference is fairly visible even from a distance. I would think if you're sensitive to ground clearance, you might notice 36.

 

[SyT]

I would also be interested in knowing the difference in diameter of the 32 vs the 36. I don't expect there will be a very large difference in ground clearance. There may be a appreciable difference between the 32 and the bash guard however....?

36 t bashguard is 6.5" o.d., 32t ring is 5.25"o.d., so I will gain .625" in ground clearence assuming I run the ebb at about the same position

 

[rensho]

Smaller makes it less likely to hit a log/rock. Smaller makes it more likely to chain slap.

I run a 29t, and would go larger next time.

 

[roadiegonebad]

Smaller makes it more likely to chain slap.

chain slap? I guess if you are using a tensioner

 

[rensho]

chain slap? I guess if you are using a tensioner

Nope. This is SS with a SIR9.

 

[G-reg]

A few have already hit on durability, and I'd agree. An 18t cog is going to have a longer life than a 16t. On the bigger cog you have more teeth/chain engagement, and the chain makes a bigger radius turn around the cog. And on a 29er where you may want run a smaller cog than a 2:1 set up it will be more worthwhile to get a 34. So I'd recommend a 34 if you are starting from scratch. But if you’re doing a budget conversion and the crank you have is a 32, ride it for a while and you'll probably never know the difference.

 

[pinkdirt]

Why is that?

What I never understand is why some think a bigger ring/cog with the same ratio will change your cadence and/or wheel speed.

.

Okay, I just had this exact question the other day while riding.
I run a 33/19 (1.74 ratio) and rider B runs a 32/18 (1.78)
She flies up hills faster than I do because I feel like I can't turn the gears at a certain point and feel like I am pushing way hard which ends up slowing me down considerably on long climbs.
However, when we are on flats, I can pedal with a really high cadence and can get up to much faster speeds easily, without spinning out.
Is this just a coincindence based on each riders strong point, (stronger climber vs. spinner) or does it actually have to do with the gearing being bigger in the front for me?