Thanks Chalo,Chalo wrote:If you have only five gears in the rear, it is not a cassette, but a freewheel. Today's multi-speed freewheels all mount on the same 1.37"-24 threads. If you have enough space for 7 speeds, use a 7-speed freewheel. If you don't have enough room for 7 speeds, you may be able to respace the axle, re-dish the wheel, and possibly spread the bike's frame to accommodate a wider cluster.
You can get a 13-28 7-speed freewheel from Shimano and an 11-28 7-speed freewheel from DNP (though the latter has made a reputation for poor durability).
You must be working with a really old bike, a really cheap bike, or perhaps both. What is it?
Sure, you can take freewheels apart and swap stuff out, if you have enough of the right ones with the right parts. They don't all have the same size body or splines/spacing/etc., so they won't all fit each other.RTIII wrote: So, I understand that you just buy a whole set of gears all at once, no making a custom stack?
The days of sprocket boards and custom freewheel stacks are past us now. The best you can do in that regard is get a couple of freewheels with different gearing but the same body, and choose whichever sprockets you like best.RTIII wrote:So, I understand that you just buy a whole set of gears all at once, no making a custom stack?
Hi Dauntless,Dauntless wrote:I'm getting a little lost in all your information, then someone wants more. All to care about is that you want to go 28mph. 1 mph for a 27" wheel is just over 12 rpm. One revolution being slightly over 7 feet, 12 revolutions topping 84 feet, etc. multiply by your 28 and you're thinking of what we'll round off to 340rpm for that wheel.
What will the rpm of the motor be? Will the sprocket be exactly the rpm of the motor or is there a reduction? If 28 teeth on the wheel are turning at 340rpm, if up front the rpm is 8 times that, then you have 8 times as many teeth up front, right? Oh, wait, that's a HUGE front sprocket, eh? If you have a 52 to turn a 28, the 52 would have to turn under 680rpm for the bike to go under 30mph. If you're using the 14 tooth in the back, you make the same calculation.
Chalo favors using quality equipment, which is great if you can afford it. Always nice to avoid the sort of 25mph faceplant that broken bikes can create. I'm always hearing people say they don't want to spend the money. So my first guess is you bought a WalMart bike at a garage sale, right? (Confirmed when my painfully slow connection today showed what else had been added.) Doesn't matter, you can make old junk work for this. If you're clumsy not even the expensive stuff will hold up.
Believe me, I know about stolen bikes. But they take the cheap junk, too. Someone I know they passed on his Dad's expensive roadbike and took his beat up old cheap mountain bike. For whatever their reasons.
This is a problem for hub motors, that have their freewheel threads attached to thin, low quality cast aluminum side covers. But it's not a problem for regular bicycle hubs. They were designed to be pedaled.amberwolf wrote:--the smaller (faster) rear sprockets are on the outer part of the freewheel (or cassette), which puts them farther from the support bearings. Not a huge deal but it means more bending loads on the axle and the hub and freewheel.
Good points of course. ...As a land-speed-record holder for some years, of course, I'm well aware of how the gearing works, but it's good to repeat for those new to gearing issues. You'll note I already put my formula on a previous post.amberwolf wrote: --the smaller the front rings are, the smaller the rear rings you have to run on for the same speed, and the higher the torque level presented to the rear would be.
--Smaller rings/sprockets also means higher wear rates.
--the smaller (faster) rear sprockets are on the outer part of the freewheel (or cassette), which puts them farther from the support bearings. Not a huge deal but it means more bending loads on the axle and the hub and freewheel. The higher the torque load the worse the bending problem is. You can add sealed bearing units that fit over the axle and just inside the outer end of the freewheel, so that the loads aren't bending.
OK... I agree about derailleurs and ebay, overall cost differential and so on. But that's NOT the question; It's a 27" X 1.25" wheel setup; are there wheels in this size with cassettes available or not? I've been looking, and so far NO LUCK AT ALL. Am I looking for a purple unicorn or what? (I've asked this question here in this thread, on other forums, etc, and nobody has yet replied with any clarity / certainty.) Your reply strongly suggests that I am NOT looking for a purple unicorn, but a lovely brown-eyed brunette - not on every corner, but out there to be found...d8veh wrote:Freewheels are not the best thing for crank-drives because the top gear hangs a long way out from the bearings. Much better would be to chuck the whole back wheel and get a used cassette (free-hub) one from E-bay. You can often get them with the cassette for about $30 -$50, or try your local bicycle recycling centre. You can also get shifters and derailleurs for not very much from Ebay if your present one is not compatible. The cost of all these things is relatively insignificant compared with the cost of the electric kit.
27 inch wheels went out of production for new bikes at around the same time cassettes became the industry standard. So there never were any OEM bikes that came with 27" cassette rear wheels. 27" is still supported, kinda, but it's supported with cheap old fashioned parts for old bikes.RTIII wrote:It's a 27" X 1.25" wheel setup; are there wheels in this size with cassettes available or not? I've been looking, and so far NO LUCK AT ALL. Am I looking for a purple unicorn or what?
THANK YOU, CHALO! This is exactly the kind of thing I needed to know!Chalo wrote:27 inch wheels went out of production for new bikes at around the same time cassettes became the industry standard. So there never were any OEM bikes that came with 27" cassette rear wheels. 27" is still supported, kinda, but it's supported with cheap old fashioned parts for old bikes.RTIII wrote:It's a 27" X 1.25" wheel setup; are there wheels in this size with cassettes available or not? I've been looking, and so far NO LUCK AT ALL. Am I looking for a purple unicorn or what?
If you can slide your brake pads down 4mm, you can fit a 700c wheel in the same bike with no other modifications. (You might need to spread the rear spacing for a wider hub, and reset the derailleur limits.).
I do 700c conversions of 27" bikes all the time. I also fit 27" bikes with new 27" wheels pretty frequently. What I don't do is build up new 27" wheels on cassette hubs, because a custom build like that is sightly more expensive than even a new stock 700c wheel plus a new longer reach brake. And then you don't get the benefit of the hugely improved tire selection in 700c.
If your bike has a steel rear rim, just forget it and convert at least the rear wheel to 700c. Steel rims are weaker than aluminum, and heavier, and they don't brake nearly as well-- especially when wet. If it has an aluminum rim in good condition, you can choose to try it as is, or lace it over to a cassette hub (which is a lot of exacting work), or replace it with 700c anyway because that's easiest. But you probably will not find a 27 inch replacement wheel with a cassette hub anywhere.
For this application, since there is no existing 34T that is deeply offset (of which I am aware), no adapter is necessary! You can use the stock spider with a "dual chainring" mounting. This may end up with a chainline that's just too far outboard, even with the longest available chainring bolts (16mm, I think) and longest spacers you can get away with. So, instead, you could make a simpler adapter using the same basic idea and mount it to the INSIDE face of the spider then have a second set of mounting holes and mount even further inboard from there. Your challenge will be getting your new chainring as deeply toward the motor as possible without rubbing. You probably can't match the factory's work in this regard, but you can probably come close. You'll have to work out the spacing inward yourself. However, the basic ring is simple enough - sorry, can't do an engineering diagram, but you should be able to follow this:What a great adapter you have made for 110 bcd !!! I want to put 34t 44t on it! Please, please give me a sketch or a drawing, that I could do it! Thank you very much!
Maybe they're forgetting that sometimes your battery is flat and you have to do all the work with pedal power! IMNSHO, they're being silly in omitting workable gears for the poor soul whose stuck in a pedals-only condition!Norton wrote:Yeah, that is a beautiful piece of work. It will be great to see how the 2 chainring set-up works.
Is it just me, but that stock chain ring looks different than a typical bicycle chain ring. The teeth seem a lot taller than typical bike components.
This is part of the new SRAM ebike mid-drive specific drive train they recently released.
This bad boy is a 11-42 tooth 8 spd steel cassette. They have a derailleur and a chain to handle it.
Only it's $390, so I'm out.
The idea is to give you a large gear range without all the small steps a regular bike rider needs.
Maybe someday.....https://www.sram.com/sram/mountain/fami ... 1vma70wya0
Mathematically this is still a big top to bottom range of gears. (I hate the work HUGE these days...)RTIII wrote:..Maybe they're forgetting that sometimes your battery is flat and you have to do all the work with pedal power! IMNSHO, they're being silly in omitting workable gears for the poor soul whose stuck in a pedals-only condition!