3 speed coaster for klunker use?

[Bicycle808]

36h has probably been the most popular drilling for 20" bikes for the past 3 decades. It's basically the "standard" rim set-up for bmx bikes. The small-diameter wheel will be fine for the hub, and will make the brake more effective, too. But, IGHs definitely last better under higher gearing, well, in the higher range of normal. 50" or more for 26"; 40" or so for a 20"...

 

[deorman]

Just to dig a little deeper, as you pointed out earlier, using a smaller wheel (20"vs 26") lowers the final drive ratio, increasing rider lever advantage, but reduces the lever advantage of the smaller wheel, whereas lowering ratio by sprocket size only increases the rider's advantage, and does not offload wheel leverage. I love old Shimano 3-pd hubs, however in my experience, a grown man can break them regardless of gear/wheel size, especially if they get dirty. With any system used off-road, I find if it has the right gearing, then I am able to make better use of inertia and therefore fewer demands on hub strength.


I miss my Mongoose.

 

[horsefarmer]

Really, what it is more than anything, is that high-torque situations will strip out the internals. The coaster brake isn't the culprit, although in some cases, the coaster can exacerbate things. What makes it different offroad is, to some degree, you're gonna be standing on the pedals and mashing to get over obstacles and up short-n-steeps, which is a lot of load.... but the other issue, the one that the folks who manufacture these things usually mention in their tech docs, is that you will kill them quick with low gears, due to increased torque. For all Sturmey-Archers (except the 8speed), Shimanos, and SRAM, the magic number is 2:1. On a 26" bike with a 3 speed, this is going to be something like a 39" low, 52" direct, and 70" overdrive (Sturmey-Archer) to a 38/52/71" (Shimano Nexus 3, most SRAM/F&S 3 speeds), which, in truth, isn't very low. Most folks riding trails will be tempted to go with a smaller ratio, and then they strip out the guts. Even Rohloff demands ratios equal to or greater than 2.4:1; Nuvinci suggests that 1.8:1 is the lowest allowable. The problems are worse in low gear, which is why there's not much concern for the Sturmey 8 speed, since 1st is direct-drive, with the other 7 gears being overdrive.... which means that a very low ratio is plum-necessary, whether you're riding trails or not.

I agree that proper set-up and state of tune are crucial for IGHs in general, but even if you have it tuned perfectly, you're probably gonna turn the guts to guacamole if you go much below the manufacturer's minimum recommended ratio. Surely, someone is gonna chime in with "I rode the Great Divide twelve times, on a 1973 Shimano 3CC, running a 36t front and a 24t rear, and had no problems".... and yeah, i guess anything is possible, but let's be realistic here.

In all honesty, i'm stoked to try the NuVinci N360 with the 1.8:1 ratio (which'd give me a range of 23.5" to 85" on a 26" wheel), but that's an expensive hub and it's got me thrown off that they don't want you to ever even service it yourself.... but, aside from that pipedream, i tend to like singlespeeds with low gearing for offroad riding, and derailer systems for those trail rides that need variable gears. Derailers are simply more robust, and far more easily maintained/serviced trailside. Rohloff hubs, apparently, can hold up to incredible abuse offroad, but they cost like $1400 these days. Gimme an old Bendix, or even the lowly cb-e110.... I can make it work on a $20 hub, no problem.

Just curious what your thoughts would be about the nexus 4 speed CB hub which I understand is a nexus 7 with the reduction gears removed. I'm running it on a 26" wheel street cruiser not a klunker at the moment, but I revised the gearing as follows:
Stock was a 46 t front sprocket and 22t rear sprocket.
1st gear (direct) 46tooth/22tooth= 2 wheel revs per crank rev x 26"= 52 gear inches
2nd gear (1.244 overdrive) 52 gear inches x 1.244 = 65 gear inches
3rd gear (1.500 overdrive) 52 gear inches x 1.500 = 78 gear inches
4th gear (1.843 overdrive) 52 gear inches x 1.843 = 96 gear inches

Revised it using 36 t front sprocket (kids 20")and 22t rear sprocket (original)
1st gear (direct) 36tooth/22tooth= 1.63 wheel revs per crank rev x 26"= 42 gear inches
2nd gear (1.244 overdrive) 42 gear inches x 1.244 = 52 gear inches
3rd gear (1.500 overdrive) 42 gear inches x 1.500 = 63 gear inches
4th gear (1.843 overdrive) 42 gear inches x 1.843 = 77 gear inches.
Is this going to shorten the life of the hub? I hope not because I like how the bike rides now.

 

[Bicycle808]

Well, my initial thoughts were that you'd probably be alright, b/c the Shimano 4speeds are 1 direct/3 over. The way that low gear ratios kill IGHs is that a low primary gear becomes stupid-low once you dip into the underdrive gears, and the planets strip out. Without underdrive gears on a Nexus 4, you ought to be safe....or, so i thought.

But, then I thought to myself: "yeah, that's a sound theory, but you've never tried out a Nexus 4 at all, let alone with low gears!" I love theorizing about bikes, but i don't like talking straight out my butt, so i searched a bit. Did some research. Found this Shimano tech doc: http://web.archive.org/web/20131126...SG_4R35/SI-4R35A-EN_v1_m56577569830613248.pdf
The cool part, from the top left of the page: "The CJ-NX10 cassette joint can be used with sprockets from 15T to 23T. However, it is recommended that you use it in combination with sprockets from 20T to 23T and front chainrings from 31T to 33T..." So, it looks like you're in the clear....

....and, it looks like my hunch was spot on, too.

 

[LukeTheJoker]

Well, my initial thoughts were that you'd probably be alright, b/c the Shimano 4speeds are 1 direct/3 over. The way that low gear ratios kill IGHs is that a low primary gear becomes stupid-low once you dip into the underdrive gears, and the planets strip out. Without underdrive gears on a Nexus 4, you ought to be safe....or, so i thought.

But, then I thought to myself: "yeah, that's a sound theory, but you've never tried out a Nexus 4 at all, let alone with low gears!" I love theorizing about bikes, but i don't like talking straight out my butt, so i searched a bit. Did some research. Found this Shimano tech doc: http://web.archive.org/web/20131126...SG_4R35/SI-4R35A-EN_v1_m56577569830613248.pdf
The cool part, from the top left of the page: "The CJ-NX10 cassette joint can be used with sprockets from 15T to 23T. However, it is recommended that you use it in combination with sprockets from 20T to 23T and front chainrings from 31T to 33T..." So, it looks like you're in the clear....

....and, it looks like my hunch was spot on, too.

That is some good info there! Hopefully someone will try it out!

Luke.

 

[horsefarmer]

Cool info 808,
I'm happy with the hub and the bike it's on. From what I read the Schwinn cruiser four was not popular when new probably because it was too tall geared.

 

[Raoul Dude]

Just curious what your thoughts would be about the nexus 4 speed CB hub which I understand is a nexus 7 with the reduction gears removed. I'm running it on a 26" wheel street cruiser not a klunker at the moment, but I revised the gearing as follows:

Awesome timing on this part of the thread -- I bought a Classic Four on craigslist last August and started turning it into another "muscle bike." After I got it home and started reading the same thing about the gearing, I changed it to a 39 tooth chainring and am a lot happier with it now!

This week I'm hoping to paint the frame metallic blue and call it "finished" -- but I seem to have a nasty habit of going back and adding to bikes I thought I was finished with.

 

[Bicycle808]

@Raoul Dude , i'd be tempted to put a 23t or 24t on the back of that t'ing, see how that flies with the 39t front. I'm assuming you got a 22t out back right now?

 

[horsefarmer]

Awesome bike Raoul Dude!
Here is a pic of mine - def a rat in primer brown and black...

One of my favorite bikes.

 

[Raoul Dude]

@Raoul Dude , i'd be tempted to put a 23t or 24t on the back of that t'ing, see how that flies with the 39t front. I'm assuming you got a 22t out back right now?

Funny that you should ask....

I haven't actually counted it, but between @horsefarmer and what two random bicycle websites claim came on it, I'm sure it's the "stock" 22t.

That 39 x 22 gearing was just about perfect last September, after a spring and summer of riding a bike as often as I could, and I spent most of my time on this one in 2nd and 3rd gears and only using "low" for hills.

After ordering the last of the parts this winter, I took it out for a (longish) first ride of the spring and was amazed and depressed at how even 2nd was geared too high for sustained pedaling after a couple of miles. "Either my legs are out of shape after a winter of being lazy, OR I need to find a bigger sprocket for the rear end, OR I should look around during my next visit to the bike co-op for a smaller chainring. I can at least get my legs back into shape soon, but I STILL might look for new parts!"

Edit: as it turns out, I WASN'T quite as out of shape as I'd originally thought! I had tried to "fine tune" the shifter cable before the first ride this spring, and had apparently tightened too much. It would only go into 2nd, 3rd, and 4th gears, and was riding around in 2nd THINKING it was 1st. Ooops.

 

[Raoul Dude]

Awesome bike Raoul Dude!
Here is a pic of mine - def a rat in primer brown and black...

One of my favorite bikes.

Yours looks awesome too, horsefarmer!

Mine had the same huge chrome fenders, which is where I first got the idea to make an adult sized Stingray out of it -- but I was a little worried that I'd mess up if I tried to cut the fenders down.

That's a GREAT chainguard as well -- is that "stock" from a different year Classic Four, or is it from another bike?

 

[horsefarmer]

Thanks! The chainguard is a $1 swap meet special - it says "three speed" on it - but it's pretty well worn off.

 

[user 15387]

If you do this, buy a modern internal gear hub with a coaster brake. I suggest the Sturmey SRC3. The AWC is also not bad. I don't care for the Shimano Nexus quite as much. Avoid the old Sturmey coasters for klunking. They're fine for general utility use, but the brakes are small and weak. The TCW is especially to be avoided for stressful use.

If you're putting much stress on the brake/hub, go modern and preferably new. Internal gear coaster brake hubs can work, but they're cylinders of suffering when stuff starts to go wrong/break on them, so avoid anything with signs of heavy use/abuse. Always use a front brake with them when possible.

 

[horsefarmer]

Here is a shot from before I mounted the chain guard to my Nexus 4 speed. That sprocket setup sure looks klunkerish.

And for reference I got the front sprocket off a Girls China Schwinn 20" bike like this that I picked up at St Vinnies for $5.

A plus is it's got the proper Schwinn hole pattern!

 

[SILVERKINGPC]

Sachs Dreigang-ers are way cool, and out-perform any IGH IMO. Older sturmey archer 3SC's hold up pretty well too, but run sensitive parts. Above is a recently-purchased low-mileage and just-cleaned German-made 515, my favorite 3-spd hub. Good luck finding the 10.5mm axle nuts though. skpc

 

[horsefarmer]

Wow! Sachs Torpedo Model 515 3-Speed look really cool inside.

Looks like it's a sliding gear automotive type transmission.

 

[SILVERKINGPC]

Not sure what the above axle is from HF, but it looks like a two speed in the 1936 diagram. (pre-war) An earlier version of the 515 was the 3111, similar in design and toughness, but slightly different internals. The diagram above looks like a cable-actuated two speed, or maybe an early 3 spd of some sort. Never seen it before. Most internal trannies for bikes have a sliding driver on the axle like that. Very cool diagram. The materials in the 515's are clearly high-carbon and precision hand made, something that today is missing in new products.
515 & earlier 3111 below.

 

[horsefarmer]

Ha, you are right different guts. Still really heavy duty construction throughout.

 

[Bicycle808]

I agree that the older F&S hubs were the best of the multi-gear coasters, hands-down. But, reasons related to pats availability and accessibility, plus the chances your shop will be able to work on one, lead me to pick the AWC as my go-to hub. ANY part is still available new, as are the complete hubs. Several shifter designs to choose from, too. They also make an aluminum shell version, the s-rc3, which is extremely similar on the inside....

But those F&S hubs, man.... they look like a vintage soup-can, but the metal itself and the worksmanship of each component are just incredibly nice. Built to last, for sure...

 

[SILVERKINGPC]

I totally agree. I do not run the old planetaries on anything but the road. I have tried a little dirt with them in the past, but because of the horrible braking power and sensitivity to abuse, I won't ride them in the dirt when the bomber & proven multi-speed w/discs is still around. As B808 well knows, the AWC is sweet for general use, so long as you "mullet" it with a front brake of some sort. It was so well designed with parts available to boot. I have a hard time even seeing them anymore. Maybe B808 is hoarding them.. The new Sturmey Archer planetary with the disc setup would be cool to try out on a road Rat with matching front disc.