3x7 speed conversion to 2x8 speed conversion questions

General Help
1

So, the time has come to replace my 7spd chain and cassette on the tourer. I also want low Q factor cranks as my knees hate being wide apart.
Current set-up is full deore dx 3x7spd - cranks, hubs, jis bb, deraileurs everything with matching bar end shifters.
Cranks are 172.5, 50, 40, 26
Cassette is 28-11.

I want to re-use as many parts as possible mainly due to cost and pissfartaround factor.

I understand that I can run 8 of 9 on the hub. To get the ratios I want I’s like to use a 34-12? 9spd cassette along with a compact/110 JIS square taper crank with chainrings about the 34/46 range. I will have to find a much shorter bb spindle to match, maybe around 107-113/115.

What bar end shifter Do I need? 8 or 9?
What cranks would best suit my requirements with low q? Considering sugino AT, Ritchey Pro Logic, Stronglight Impact.
Will my original derailleur work with the larger 34 tooth sprocket?

Cheers

2

First up: Gather all of the DX stuff (bar the wheels), and sell it as a group to a retrogrouch/restorer. It’s nice enough, but it’s old and worn and you’ll have a much better shifting bike if you ditch it all.

8 of 9 works on a 7sp freehub, I’ve done it. Get a basic HG50 ish 11-32/34 and ditch the 11 and use a 12T lockring from a worn out cassette (ask your LBS). Surprise! the 12T is knurled for a lockring already, lucky you!

Chainrings are often pretty pricy, save hassle and money and just buy some “CX” cranks and you’ll get exactly what you’re after. FC-CX70 for hollow arms, FX-CX50 for “C” section arms, cheaper, bit heavier. 36/46 rings on both. Easier than buying new BB & new rings.

But… BB is 68 or 73mm? If 73, buy a modern MTB double, something like deore/SLX. Or cheap out on some horrible triple square taper thing and ditch the granny and use a shorter BB. You’ll probably have to test fit a number of BBs to get the chainline / stay clearance / Q right. Or search long and hard and eventually score a 110BCD crankset and some rings to suit, then a BB to match. Ritchey Logic Compact cranksets are out there…

9sp shifters because you have 9sp spaced cassette, you just lose a click. (I may have a spare pair actually)

If your rear is an RD-M650, i.e. OG DX superlongcage, it’s rated 12-32 on the rear, 38T total capacity (i.e. (46-36 = 10) + (32-12 = 20) = 30T = OK), but let’s be honest, it’s thirty years old, it’s worn out and sloppy.

Medium cage MTB rear mech coz you don’t have a granny anymore that needs a long cage.

XT 9sp Shadow + ritchey barrel
LX/XT/Deore 9sp ‘trekking’ (but in medium, not this one, it’s long)
Shimano 105 / Ultegra (current) will only go to 30T in a medium cage, that’s no use to you.

3

Impressive amount of effort for a part worth like $10

4

$20 at least!

But yeah, hence wipe it down, sell it off, replace with new.

5

Don’t get me wrong I think it’s great to repair rather than throw away. Credit to Shimano that the part still works after 25 years. He even went to the effort of new O-rings which is impressive.

6

As stated the easiest option is a set of CX cranks.
There are options if you want to stay square taper and not cheap out.
Sugino Mighty Tour

I’ve got a set of these in the parts cupboard and a set of Stronglight 9/10 speed rings for a future project.
Very nicely finished.
Stronghlight chainring not too expensive

Bought them mainly because I could get them in 172.5mm arm length.

7

Already rebuilt mine once. Was in very good shape, as was the rest of the group and I was unemployed so had a heap of time to waste.

8

Cheers for the big effort on the reply Blakey. Due to the fact the bike is fairly retro in it’s look I reckon I’m not gonna go for any modern bb/crank combos as it will then just look like a bitsa. Stronglight Impact doubles come with rings for about $55 plus shipping from Ribble, but Q is 160 apparently. New derailleur could be a worthwhile investment especially if my long cage DX will only go to 32t.
According to Sheldonbrown a Sugino AT double is 150 Q. These could be the cranks I need.

9

You can easily swap freehub body, axle and re-dish rear wheel slightly to go to 8/9 speed if you’re content with forcing the frame open a little wider.

10

I must be a retrogrouch then. Not so much because of the resistance to anything new I guess; more because I don’t like seeing usable resources binned. Yeah, quality chainrings can be pricey, but they save a lot of resources than a set of useful cranks being binned and replaced with a whole new one.

Kudos to the guy for rebuilding that DX RD. They’re good units, and that thing is still in circulation. I’d do that. If you do decide to go new, let me know. I might be keen on your DX group.

You can probably remove your granny on your DX cranks and move the chainline in with a shorter BB, replacing the other chainrings with those Stronglight Dural rings. I like Sugino AT/GT cranks by the way, but I reckon your DX ones will be pretty similar moved in. Then the 8 of 9 thing sounds like a good move. I’m friction shifting on 9sp at the moment. It’s alright. Easier with time. 8sp would be easier still. A more beardo option would be Suntour Barcons, or those Silver Shifter Bar Ends that Rivbike sell if you go for new.

11

Planet X/On one do a Square Taper CX/110bcd crankset for $70ish.

On-One Touring Crankset

CNC not forged so not ideal, but faster than waiting for some forged SQ taper 110bcd to turn up

12

It’s possibly 135mm already, but most 8+ freehubs won’t fit that hub. Been down that path.

Pete: I didn’t say bin, I said move on to someone else. If he just wanted to keep riding and lower the Q then shorten the spindle and maybe ditch the granny and get a new 7sp cassette/chain. I’m still using 7sp era XT cranks/hub & DX mech, works fine, but it was mostly NOS when I got it.

For a good working 2x8of9 system, current CX50 cranks and a 9sp rear mech is the most cost effective option with minimal pissfarting.

If you have the time and inclination, then rebuilding parts and sourcing the exact crankset etc is fine, and I’ve done that more times than I care to admit.

13

Yeah, no worries Blakey. I’m just on this try-not-to-buy-stuff and try-not-to-chuck-useful-stuff-out kick. White hipster guilt I guess. Not necessarily a bad thing, but neither is buying good new stuff.

Both options have plenty of merit.

I like those On One cranks BTW…

14

Really? I can’t see any reason a DX hub wouldn’t take a run of the mill mid 90s onward 8 speed freehub body? I’ve done it to other hubs of the same era. I mostly used 8 speed Alivio freehubs because we had a pile of them.

15

I’d say the arms are still forged, just the forged blanks have been machined to look as they do. The taper area would need the forging to withstand the pressures involved in being fitted. They look nice.

16

Assuming it fits do you need to redish-thingy the wheel?

17

Frame is already forced apart a smidge. 8 of 9 cogs on the rear will be enough, I’m not racing a 531ST (may as well stand for sherman tank) frame

18

For me at the moment I have a lot of demands on my personal finances and extravagent bike purchases just aren’t a priority. Hence re-using as much as possible. The DX group is in good nick and is even complete with the cantis and I have the original headset somewhere. Those hubs roll like nothing else I’ve ever ridden too. Have considered using the cranks with no granny but I still need a 34t, 46t or 48t ring for it, and they’re still a bit wide on the Q factor. I have a patella tracking issue which wide q exacerbates so I gotta get it as narrow as I can.

19

Yes. Its only slight, nothing extreme enough to need different spoke lengths or anything. The wheel will effectively move toward the non-drive side so it needs tweaking across to the drive side a few mm.

20

This cassette
here
appears to have knurling on the smallest 2 sprockets. Does anyone know if this is in fact the case?

Gonna pull the trigger on the stuff I need soon to make my 8 of 9.

9 spd bar end shifters are jokes, cost more than a mech.