davei1980

I am thinking about converting my commuter over to an internally-geared hub like the 5sp and 8sp hubs pictured. I am not used to how gear ratios are expressed, in the automotive world, they're quoted as ratios, not percentages.


I am currently running a 14-34T, 7speed rear cassette with a 1x crank. I usually ride on the "middle 5" cogs on my rear.


So by my math, 34T/14T = 2.42 so is my current "range" about 242%? The hubs I am looking at have ranges from 186%-325% so does that mean these hubs have BETTER range than my current 1x7 setup? Am I measuring the "range" of my current setup incorrectly?



My main question is - will I be happy with the range of an internal hub?

Is it difficult to mount on my existing rear wheel or can I buy pre-mounted?

Thoughts on vbrake/coaster brake (other than the fact that I have not ridden a coaster brake bike since my 1st BMX) ? I noticed most of the Sturmey Archer Hubs come with either option. Thanks!!!

Hoopdriver

They are expressed as a ratio with the direct drive gear as the reference. It's just reported as a percent. Using your example of a 1x7 setup. Assume that your (24t?) middle cog is the "direct drive" reference, a 28t cog would have a ratio of about 86% (-14%), for example, and your range about 70% - 170%. These numbers will change if your middle cog is not 24t. Two more things: (1) Your overall gear ratios are defined by the chain ring and cog you install. The hub specs only define the differences between the gears. (2) The Sturmey 8 speed hub uses first gear as the reference so to get a suitable low you will have to use a small chainring or big rear cog (or combination of the 2).

Sure you can mount it on your existing wheel, but it may be more efficient to just buy a new rim and spokes rather than taking the old wheel apart. If you will be paying someone to do this for you, opt for the new rim. You may be able to buy a built wheel, but it may take some effort.

You already have disc brakes on your bike. Keep them. Coaster brakes will be a big disappointment.


Good luck.

davei1980

Awesome!


So if I buy an 8 sp with 30/14/14/14/14/14/30 percent increases over the 1:1 1st gear, and I start out with a 32T front / 25T rear (similar to my lowest gear right now of 48T/34T, also all of the kits I am seeing ship with a 25T cog) then I am looking at an equivalent of 1st: 25T, 2nd 15T, 3rd 13T, 4th 11T, 5th 10T, 6th 8T, 7th 7T, 8th 5T**********


If this is the case, then my TOP gear is almost DOUBLE my current 42T/14T ratio... that's fine but I may want to start out with a smaller than 32T front ring (if they exist?)


Thanks for the info and for checking my math! I am a CPA so I am bad w/ numbers lol

acidfast7

This will help:

click here

CliffordK

Is the Fuji bike above the one you're converting?

The photo shows it in the big ring with a triple crankset (I think). You can probably use a chainring about 1/3 smaller than you normally would use. What is the rear sprocket size on the IGH hub? That will also affect your gearing calculations.

Anyway, you will need to consider chain tension adjustment. The Fuji has vertical dropouts, so you'll probably want a chain tensioner.

If you chose a frame with horizontal dropouts (opening forward or back), you wouldn't need the chain tensioner.

I don't think I've used a coaster-brake for quite some time. One advantage of normal coasting is the ability to back-pedal to get the pedals into your optimal start position. Oh, also no coaster brakes with chain tensioners.

Hoopdriver

No, I don't think your top gear will be double, but it will be higher. You may want to spend some time with Sheldon Brown's Gearing Calculator.

I printed out some example charts for you. The first below is for your current setup (I guessed at the cogs). The lower one is for the S-A 8speed using a 32x25 setup. There are other rear cogs available from S-A, but the Shimano cogs will work as well.

Hope this helps.

davei1980

I have pared down my crank and I am now only using the 48T ring. I plan on upgrading when I buy the rear hub because it's a cheapo square tapered crankset. The hubs I am looking at accept a range of cogs but most ship with a 25T.

Do you think the tensioner is optional? The simple/clean look is part of the draw of the IGH for me

CliffordK

25T puts you pretty close to the middle of the range of gearing that you are currently using which is probably good.

You may get lucky with chain length. But, as chains wear, they also stretch slightly, and thus will become loose if they had fit perfectly when new.

I'd encourage you to look for a frame with horizontal dropouts.

davei1980

This helps a ton! It definitely looks like the 8sp S-A hub has a wider "range" than my current 1x7, 14-34T setup?

Viich

I agree - look for a frame with either track forks or forward exiting horizontal dropouts. Your current frame looks to have vertical dropouts, as most modern derailleur bikes do. This will make your single speed chain very difficult to tension - there's no rear derailleur to take up the tension. You can use your derailleur or a purpose built chain tensioner with a vertical dropout frame. As was previously mentioned, coaster brakes won't work with this type of setup.

Pictures from Sheldon Brown to explain what we're talking about: (From this page: https://www.sheldonbrown.com/gloss_dr-z.html


Horizontal Dropout

Vertical Dropout

Track Fork

davei1980

Ok thanks-- do you know if the purpose-built tensioners use the same derailleur hanger or mount to frame? Part of what got me on this kick is my derailleur is a pos and I think the hanger is bent. I like this bike and got it for cheap but the components are poor quality so I am slowly replacing

corrado33

Going IGH is a bit extreme for a simple bent derailleur hanger....

Don't try to go IGH on a vertical dropout bike without a tensioner or eccentric bottom bracket. It won't work.

Yes, some tensioners use the same mount as the derailleur. Some don't. Some bolt directly to the chainstay or downtube... I think.

acidfast7

Agree. This thread sounds like a recipe for disaster and a lot of subsequent complaints about how IGH are crappy.

corrado33

Yep. Queue the "it's SO heavy, the shifting slips, the chain comes off the cog, I still have to use a tensioner" comments.

davei1980

Thanks for the advice/info. Sounds like I have some soul-searching to do - if I want to continue down this path on my commuter/MTB conversion or just spend the $500 and get an 8sp IGH /Belt drive. I think the cost is about the same!


I may just put down the wrenches and take it in for a good tune up this winter then hit the bike swap in town in the spring

fietsbob

Know where the 1:1 gear is , typically in the Middle reduction gear and overdrive on either side..

My Sram I 9 its 5th, on my SA 3 speed its second..

on sturmey archers new 8 speed , is all overdrive gears, 1:1 is 1st

Rohloff only 3 are overdrive , the rest reduction gears, double reduction for 1~7..


read the manuals, they are on line..





....

davei1980

Awesome! yeah the S-A stuff is all 1st gear 1:1 unless it's the 3 or 5sp. The Shimano is a different story but they also recommend you don't "pedal hard" with their hub so I am like


I will be in your neck of the woods next week BTW!

CliffordK

It is easy enough to straighten a bent derailleur hanger. I built a tool to do it with a tape measure. Your local bike shop or bike co-op should have the proper tools.

Or you can straighten it with an adjustable end wrench and eyeballing it. If your bike has removable hangers, you can often find a replacement for a couple of bucks.

If the hanger moves when you tighten the wheel, then remove it, and do some touch-ups with a file to get it to sit flat.

You can find a moderate quality used rear derailleur for a lot less than you'll invest in the IGH.

As far as the horizontal dropouts, you can find them in most bikes from the 1980's or earlier.

I don't believe you need a lot of adjustment if you select the right size of sprockets and perhaps use a half-link. So, add a short horizontal dropout to the above list.

davei1980

Yeah it's like $10 for a new hanger ... My goal is to swap out all the crappy components 1 component at a time on this frame but the IGH may be a stretch because, and not limited to, the complications with building out the wheel.

davei1980

I think you guys have convinced me to make my winter project a single speed frame/IGH build.


Any ideas on what's best? Track frame? There's one on Amazon for $100 with built in chain tensioners and good reviews/come with a fork.

Viich

They will work fine for a winter build. Check tire clearance before you buy, and figure out how you're going to run the cables. I often use electrical tape if I don't have cable stops, eyelets, etc.

davei1980

Good call. I think S A makes a pulley that clamps to the seat stay so that's good. I think I am gonna go coaster to eliminate one more cable

Viich

Also, I went back to the Amazon you posted - make sure you comparison shop with Niagara cycles- they have some good prices on SA hubs.

NormanF

That's no longer true... if you're going to run an IGN on a VD bike, then install an eccentric bottom bracket. It will allow you to use an IGH with the proper chainline tension with a VD bike.

acidfast7

It depends ... some colleagues with Rohloff and the EBB have issues with the clamping mechanism holding the EBB in place loosening over time.