7sp freewheel - 9sp sram derailleur compatibility
- Thread starter fougio
- Start date
Chalo
100 TW
fougio said:
They're not compatible as a direct swap. At a minimum, you'll need a new 7 speed shifter that matches the pull ratio of your derailleur (SRAM makes derailleurs with two different ratios).
When you have a 7 speed shifter that works with your derailleur, you'll need to adjust the derailleur's travel limits to match the new freewheel, and adjust the cable tension to allow correct index shifting.
Chalo
100 TW
fougio said:
It depends on the shifter and the mechanical ratio built into the derailleur.
For what it's worth, Sunrace makes 9 speed freewheels especially for e-bikes, and one of those would work with the shifter and derailleur you already have. You might have to add axle spacing and widen your bike frame a bit to make one of those work, though.
hypertoric_amplituhedron
100 W
It's all about the shifter. A 9sp shifter will not be compatible with a 7sp freewheel. A 5, 6, 7, 8 spd fw is all the same cog spacing (and thus compatible), but once you hit 9, the cogs get closer together. So, the derailleur won't travel far enough between clicks.
There is no need to change derailleurs to run a 7sp chain on a 7sp freewheel. Derailleurs don't really care how many gears there are, just the cog range, cable pull ratio, and speed of the chainrings (single/double/triple).
In an apocalypse scenario, it would actually work for all but 2 or 3 of the gears (which you could adjust to be the first or last 2), which would ride a bit noisy from misalignment. It's not ideal, though.
I'd prob just go for that 9sp FW, tho. It's your cheapest possible option.
There is no need to change derailleurs to run a 7sp chain on a 7sp freewheel. Derailleurs don't really care how many gears there are, just the cog range, cable pull ratio, and speed of the chainrings (single/double/triple).
In an apocalypse scenario, it would actually work for all but 2 or 3 of the gears (which you could adjust to be the first or last 2), which would ride a bit noisy from misalignment. It's not ideal, though.
I'd prob just go for that 9sp FW, tho. It's your cheapest possible option.
Chalo
100 TW
hypertoric_amplituhedron said:
This is erroneous. 5 speed has no real spacing standard, 6 speed is usually at 5.5mm intervals, most 7 speed at 5.0mm, and most but not all 8 speed at 4.8mm. 8, 9, and 10 are all the same total width, so they clearly can't have the same spacing intervals.
http://sheldonbrown.com/cribsheet-spacing.html
This is generally true, with the caveat that both SRAM and now Shimano make rear derailleurs with two different pull ratios, and Shimano makes front derailleurs with two different pull ratios. It's not always obvious which shifter will work with which derailleur. Campagnolo only works with Campagnolo, as usual. (It's like an expensive practical joke to play on yourself.)
Some recent derailleurs are too narrow between the cage plates to behave well with 7 speed chains. The cure is to use a narrower 8 or 9 speed chain even if the cassette/freewheel is 7 speed.
spiros
10 W
You should have in mind that if you don't have to change speed frequently, if the kind of the road that you use to do it allows it, you could adjust the difference of 9speed derailleur to the 7 speed freewheel on tha way buy the adjustment screw on the top end of the cable.
Hope that I explain myself
Hope that I explain myself
So, there are 3 options as I understand. 1. Buy a 9sp freewheel and try to wide my 135mm space. 2 Use the 7sp freewheel with my 9sp derailleur and loose some of the 7speeds 3. Search for a hub motor with cassette adapter and use my 9p cassette by removing some sprockets.
Thanks everybody.
Thanks everybody.
The simplest, cheapest solution is to buy a DNP 7 speed freewheel. These have 9 speed spacing, and will work just fine with your shifter and derailleur. I just mic'ed a Shimano, and a DNP. The Shimano 7 speed is correct 7 speed spacing, and the cogs are 1.85 mm thick. The DNP cogs are only 1.68 mm thick, so work with 9 speed chain too. I would recommend running decent synthetic oil through them first. The two I bought felt like they had sand in them. I ran oil in the gaps while spinning the freewheel, until it ran out the other side. The first one is still going strong with 10K of pedaling along with the DD hub.
Warren said:
But here it says for DNP 7sp freewheel sprocket thickness 1.8mm and spacer thickness 3.1mm
https://endless-sphere.com/forums/viewtopic.php?f=2&t=18314
and here for for SRAM 9sp cassette sprocket thickness 1.8mm and spacer thickness 2.54mm
http://www.sheldonbrown.com/cribsheet-spacing.html
Is it going to work? Do you have a link for the freewheel you suggest?
There is also a 4th option. I can disassemble the 7sp Shimano freewheel that comes with the 1000w 48v hub motor kit and use custom 3d printed spacers to create the appropriate spaces for shifting.
https://www.youtube.com/watch?v=uwGCZuWPQGk
http://web.archive.org/web/20130128220005/http://blog.harriscyclery.com/customizing-shimano-7-speed-freewheels/
https://www.youtube.com/watch?v=uwGCZuWPQGk
http://web.archive.org/web/20130128220005/http://blog.harriscyclery.com/customizing-shimano-7-speed-freewheels/
I see what it says on the drawing. What I can say is, I used my micrometer to measure the two largest cogs at their thickest (non-ramp) portion, and they are 1.68 mm. It won't fit in between the others, but to my old machinist's eye, they appear the same. Except for the smallest cog, which is clearly thicker. I wrapped a new 9 speed hollow pin SRAM chain all around all the cogs, and it fits with lots of clearance. It will not hang up on the cogs, or spread the side plates. I used an aluminum Shimano 9 speed spacer as a gage, to check spacing. It is narrower than the DNP spaces. However, I use the three cog spider set, from a Shimano cassette, as a gage to line up tooth tips with any three cogs on the DNP. They are very close. It may be 8.5 speed spacing instead of 9 speed. 
All I can say for sure is that the Shimano 7 speed freewheel worked perfectly with my 8 speed shifter and derailleur, but the DNP dithered all over the place. It only worked correctly when I reduced the derailleur movement/increased the cable clamp-to-fulcrum distance on the derailleur. All the other bikes I have now are 8 speed, or 10 speed, or I would throw it on a wheel to check for you.
All I can say for sure is that the Shimano 7 speed freewheel worked perfectly with my 8 speed shifter and derailleur, but the DNP dithered all over the place. It only worked correctly when I reduced the derailleur movement/increased the cable clamp-to-fulcrum distance on the derailleur. All the other bikes I have now are 8 speed, or 10 speed, or I would throw it on a wheel to check for you.
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