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Suggestions for widest ratio gearing cost effectively?

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  • Retrorockit
    replied
    I'm still thinking about how to do the 2x8 chainring. The smallest cog that I think is reasonable for a first attempt would be a 40T casette cog turned around backwards so the tooth profile will be correct as a drive gear, and the ramps on the correct side to aid an upshift. I stopped thinking about spacers because they "take up space". The world shortest 6" diameter driveshaft tube is what I have in mind.
    The thinnest 6" steel tubing I could find was 6" Dia. diesel exhaust pipe 1/16" wall So 5.875" ID. There is aluminum air intake pipe that size available too. Waterjet a 6" hole in the cog and braze the pipe in, then have a flange on the other end to attach as you please. The 6" size I arrived at from measuring the chain relief to clear the inner edge of the chain plates on a 44t=6 1/2", and a 42T=6 1/4' so 40T =6" should clear the chain. No room for fasteners or weld beads. The eutectic braze willl flow into a .001 gap and be stronger for it. It's a pretty safe assumption that it will touch at the cover over the pinion gear, but not by much.
    Replace the cover gasket with silcone sealer, and grind the casting some as needed I thnk will do oit. But it's getting into individual craftsmanship at that point.
    I noticed that the holes on the 2 different Luna 130 BCD adapters ( Aluminum CNC, and cut SS Plate) have the 5 small bolt holes clocked differnetly to the spokes. They look like thay could both be used together. 10 bolt chainring setup anyone? Anyway looking at the gear chart 50x11-40 is all I need. I just thought I'd put this out there if anyone wants to try it.

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  • Retrorockit
    commented on 's reply
    That was their default RPM. There are cadence, and gear/inch versions there also. BTW 700cx38, 27.5x2.0, and 26 x2.5 all give roughly the same speeds.
    I've observed the speeds they list in those gears, but it's not sustainable for my 65year old legs. Maybe a mile and I'm done.On some of their other calculators you can choose different cadence.

  • commuter ebikes
    commented on 's reply
    I would have chosen 90 RPM, also. Thanks for being reasonable here.

  • Retrorockit
    replied
    Here is a speed calculator I found. Just enter tires size and gear teeth and it will show speeds at 90RPM.
    Calculate cycling speeds in kilometers or miles per hour given cadence, chainring, sprocket, tire and wheel sizes.

    Low gear in the Sturmey Archer is .75 and high gear is 1.33 so a 36T chainring would model as a 48/36/27 triple crankset. I think I've got it right. Low +33% and mid +33% is what I'm using for that hub.
    I know engineeres will say I have it backward. If I was calculating torque that would be true. But I'm calculating speed and I believe this is correct. If you disagree use something else and be happy.
    Last edited by Retrorockit; 12-10-2018, 08:54 PM.

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  • Retrorockit
    replied
    A little more on the 2x 50/42 BBSHD chainring idea. Surly makes a 50T and a 42T stainless steel 130 BCD ring. Stainless steel can be silver soldered which is AKA silver brazing due to the heat involved, 70.000PSI strength is common. The spacer could be steel. stainless steel or even brass. A friction shifter should be able to shift this. I see it as a range type shift and not a shifter you would be going through the gears with.
    Last edited by Retrorockit; 12-08-2018, 07:32 AM.

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  • Retrorockit
    replied
    I spent the afternoon swapping parts. The big casette is going to need the hanger extension, and it turns out the XTR derailer is a short cage model, so I get either the 11-40 casette, OR the 50/42 chainring but not both. The casette will be tried first once I have all the parts. It's just a bolt on mod and will do everything I need. I might give the Wide-Narrow 50t ring a chance and see if it allows me to use all the cogs.
    I can't complain really. An XTR Low Normal Short Cage dearailer is quite a find for a 1x8 urban bike. I do have a long cage low normal LX derailer on my XC bike. But it makes more sense to leave it there.
    Last edited by Retrorockit; 12-08-2018, 07:29 AM.

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  • Retrorockit
    replied
    Well- welding 7075 aluminum isn't going to happen. BUT it turns out this whole mess could be soldered together on a hot plate. Maybe even with a steel spacer if I get it tinned or plated first.
    Maybe you can't teach an old dog new tricks. But there just might be some old tricks that can give the CAD/CAM boys a run for their money.

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  • Retrorockit
    replied
    I took a ride to my LBS. No not the SoFla bike boutiques in Ft Lauderdale . I rode past about 10 of those. MY LBS which is 20 miles away. Picked up a 42T chainring, and scored an XTR Rapid Rise derailer.
    So far I have a Bafang 130BCD spider adapter,a 50t "host" chainring, a 44t, or 42t to "piggyback" off of it, and derailer hanger extension in the mail. I think the LBS owner sold me the XTR because there may be some chance of it working with a 40T casette. Maybe "B Screw" length has something to do with it. Actually IDK what a B Screw is. Yet!
    This thing keeps evolving slowly in my mind. I may skip the glue amd fasteners completely and just have the whole damned thing TIG welded together. Well just the rings and spacer not the adapter!
    Oh I almost forgot. He had an old black Cannondale Headshock bike there with disc brakes. It's a 700c which bothers me not one bit since 26" wheels with 2.3" tires = 700c diameter anyway. I've run both on my 26" XC Softtail. Might be able to squeeze some 26x2.5"" Hookworms in there on my Rhynolite XT off road wheelset I never use anymore. Even without a motor I have some black Cane Creek Strados 700C disc brake rims that would "make" that bike.
    Last edited by Retrorockit; 12-07-2018, 10:13 AM.

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  • Retrorockit
    replied
    Thanks for the reply. 153mm=6.023" So that's 6" in my book. If I have the water jet shop cut it they could probably makes 3-4 at once.
    I've got the 11-40t casette here. I was so excited to find it in 8 speed I just ordered one. It's black, and silver was $10 cheaper but I didn't ask so black it is. My chainrings are black also so I guess it's meant to be.
    What's a good source for the long derailer hanger/adapter. I see $2 ones from China. And I see Wolf makes one for road bikes. Is there one that people are having good results with?

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  • ncmired
    replied
    Originally posted by Retrorockit View Post
    Does anyone know the ID of the Luna 42T chainring assy.?
    You mean the Luna Eclipse? If so, its ID is slightly wider than my 150mm caliper, so I'd put it at a slightly fudged 153mm until/unless somebody can come up a closer measurement.

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  • Retrorockit
    replied
    I've been digging around in my parts bin and found an XT 44T chainring. And I also have a 50t shifter chainring 130bcd that fits the bafang spider. My thinking on this right now is to have a local plastic shop cut a Lexan ring the right thickness with an OD to match the 44T chain recess, and an ID to clear the BBSHD. Glue it all into one piece and reinforce it with bolts wherever there's enough overlapping metal to do so. There is a water jet cutting shop I've been meaning to visit. So metal might be an option also. So I could keep my 50x11 top gear and add a 44x40 low gear with a chainline that will allow me to use it.
    Does anyone know the ID of the Luna 42T chainring assy.?

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  • Retrorockit
    replied
    Another approach would be the Bafang 130mm spider adapter with this ramped and pinned 50T chainring (I've had this on my BBSHD) and their 38/39T version hollowed out and hung off the back with bolts and spacers using s front derailler. You could probably use a 130BCD double crank as a jig for drilling and installing spacers to build this.
    https://www.amazon.com/USA-Made-5-Bo...ainring+130bcd
    A drill press is all it would take to make the holes. Some flat head machine screws on the outside would keep the screws from moving around in the gear. Maybe thread the holes into the small gear for clearance on the back side. With a lathe you could get fancy and put a shoulder on the spacers. Leave a few bare threads sticking out the back. the last couple of threads are weaker and won't hold as well. If there's room for nuts on the back that would be best though.
    edit
    Looking at what Luna has done it seems 42t is the smallest that will fit around the Bafang gear case. Un fortunaely theres a gap in gear sizes in shiftable chainrings with 130bcd. The mid/small ring is either 38/39T Then a jump to 48/50/52t. I don't think the small gear needs the ramps to lift the chain. There are some track 42t 130bcd chainrings for 1x and they seem to be made as a solid disc solid so lots of places to drilll into them.42t is fairly common on 104bcd MTB cranksets. But it would be harder for a DIYer to index them for drilling.
    Last edited by Retrorockit; 12-02-2018, 10:32 PM.

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  • Retrorockit
    replied
    SRAM had a 3 speed IGH with casette called Dual Drive I think. Since it had an over/under gearing it came with a 32 or 38 chainring. Cannondale made some hybrids with it. 42T Luna should work fine with that.
    WideNarrow would be a mess shifting. The chain has to land odd/eve teeth every time.
    I guess they're calling it DD3 now.

    Be aware that there is a shifter housing hanging off the end of the axle. I'm not sure how rugged it is. Also i don't see a QR working with that setup either.
    Here's a photo of one. Dual drive,Headshock. If it had disc brakes it would be perfect for a BBSHD swap
    https://www.bicyclebluebook.com/sear....aspx?id=30140
    One shifter runs the whole thing. Room for a throttle.
    Guess who has it in their catalog?
    Distributors and builders of high power electric bikes and trail bikes plus parts
    Last edited by Retrorockit; 12-01-2018, 05:17 PM.

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  • ncmired
    replied
    As you know, with the 3-speed/freewheel hubs (SRAM or Sturmey Archer) you get that strong 1:1 2nd gear for "most of the time" riding, with approx 2 more gears lower and higher than whatever cassette you come up with via the 1st and 3rd gear. I'd be tempted to go for the conservative 11-40 and see if it gave you enough low gear (with the 42 Eclipse).

    I'm sitting here staring at a Luna Eclipse 42 gear piggy-backed on a 48 gear - maybe that could be made to work, although the spider would have to be spaced farther out and then might interfere with the crank arm. And, with the wide-narrow teeth, would probably resist shifting.
    Last edited by ncmired; 12-01-2018, 01:43 PM.

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  • Retrorockit
    replied
    It doesn't exist yet. But I think a 39T 50T 2 speed front derailer would be ideal. 2 chainlines. One for climbing and on for road work. The derailers 2ndary function as a chain guide doesn't hurt either. A frame mounted shifter would work since you're not likely to need both ranges at once. Everyone seems obsessed with 1x setups. I'm running 50x11 on 26x2.0 tires and it's a nice top gear. With bigger tires 48 should be OK. But for 8-9 speed I think a front derailler makes sense.

    This is all your fault. I just found a Sunrace 11-40T 8 speed casette. 11-13-15-18-22-28-34-40t. I'm always double shifting up from my 28t launch gear 28-24-21 anyway. I have some unfinished business getting a Rapid Rise/ Gripshift setup working so I can dump 5-6 gears at a stop light while standing still.
    Last edited by Retrorockit; 12-01-2018, 11:36 AM.

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