sillygolem

What derailleurs can handle a 38t rear sprocket?

I'm x-posting this with the Bike Mechanics forum b/c I'm pretty sure only Suntour used a rear sprocket this size, but I haven't seen anything matching up this crazy-big freewheel with a derailleur to handle it.

Jeff Wills

Suntour made an AG-Tech derailleur to go with the AG-tech freewheel: https://www.disraeligears.co.uk/Site/...erailleur.html . I'd bet that one of the newer derailleurs for 36-tooth cogs could make that shift.

DMNHCAGrandPrix

The Huret Duopar had a large range, certainly up to 36 teeth, but don't know about 38.
https://velobase.com/ViewComponent.as...m=108&AbsPos=4

sillygolem

Who makes a 36t cog derailleur outside of the higher-end SRAM X series? I need something designed for a small number (5-7) gears so I can use a 3/32 chain to fit the cog and chainwheel teeth.

nlerner

I was thinking Shimano Mega-range variants, but looks like that's designed to handle up to 34t.

Neal

sillygolem

I think this might be worth looking into: While their rated as 34t max, they seem to work on 36t just fine. I may be able to get a Tourney Mega-Range to fit over a 38t by replacing its giant pulleys with something normal-size.

Spookeay Bird

I guess this could. It's what I put on my 27 speed Cannondale.
Derailleur

Sixty Fiver

Capacity of a rear derailleur will be affected by the hangar length and bikes designed for wider range touring gearing or off roading have hangars that maximize the possible range of the derailleur.

The Suntour AG (Alpine Gear) and Huret Duopar have massive capacity and the new XT has a rated capacity of 36 and would probably handle 38.

Most long cage mountain derailleurs will handle 34 teeth as will many older GT models like the Cyclone and VX... but only if they have the right hangar.

sillygolem

This is going on a frame that uses a claw derailleur, so distance would be determined by what's on the derailleur, or if it's bolt-on the size of the claw adapter I put with it. Range won't be an issue as I intend to run this with a single chainwheel (34-14 = 20t range.)

I would probably have problems with the XT because it's for a 9-speed: I probably couldn't limit the the movement enough on the high end and it wouldn't work with a wide enough chain to fit the cogs.

Sixty Fiver

What are you building that needs a 38 tooth cog in the rear ?

Pulling stumps ?

sillygolem

Yes.

I live in the Ozark Mountains, which has exactly two directions: Up and down. I've found I either need a granny gear or a high gear to ride around here, and the Suntour freewheel fit the bill while letting me go to a single chain wheel up front instead of using three wheels as I thought I'd need to originally.

jonwvara 

I use a Duopar with the same 38-tooth Suntour setup and it shifts very well--no problems. I've got a 45-40 in front for a super-wide-range double. Not much of a high gear, but I don't need one.

ColonelJLloyd 

I'm curious why you need a 38t rear cog.

pastorbobnlnh 

Sometimes you just can't get low enough.

nlerner

That's the great-granny gear.

Neal

sillygolem

After putting different keywords in from this thread (yes, some of us do use search,) I uncovered this:
https://www.bikeforums.net/showthread...-5sp-freewheel

So, a Tourney would work as I thought, but it doesn't need smaller pulleys, it needs an extra spring to get it into place. Bonus for being readily available and cheap, rather than requiring me to hunt eBay.

zandoval 

I hang out on my 34t gear more than I would like to admit so I can see where you are coming from on needing 38t - Consider welding a hangar onto your dropout and make a little lower to give you more room for your large gears - Then you could possibly use a regular long or medium cage dérailleur... Its a thought...

jonwvara 

Get old and go live in some mountains and it will become clear to you, I think.

Spookeay Bird

he's going to start a pulp wood company using skidded bicycles to pull the logs out of the woods.

sillygolem

As a matter of fact the closest thing to me is a sawmill. While you city slickers complain about unaware drivers, my only cause for concern is logging trucks and the occasional doofus hunter of a 4x4.

ColonelJLloyd 

I understand the need for low gearing. A 38t rear cog is not how I'd go about getting it.

Really? I mean, if your gear is much less than 1:1 you can walk the bike up the hill about as fast as you can ride it, correct?

Sixty Fiver

Just threw a 26 tooth granny into my Trek to go with the 30 in the rear but plan to swap out the 11-30 cassette for an 11-34 to give me a 20 gear inch low for some mountainous touring.

For a single bike the only time I would need that is when I am mountain biking and my mtb has a 22/34 low gear (16 gear inches) and will go straight up walls with that gearing.

Conversely... I can climb pretty much anything on my road bike that has a 40 gear inch low but it only weighs a spec over 20 pounds, carries nothing, and does not see such extreme grades.

Should I mention that I don't have 100% use of my left leg and have to be able to sit and spin up any climb as I cannot stand and hammer the pedals like I should.

There was a time I could go up most things with a 1:1 gearing.

sillygolem

Went to pick up the freewheel from my friend, pulled it out of the (rather large) box...28t max.

I've started my search for alternatives. Does anyone know when/why Shimano made freewheels with what appear to be skipchain cogs for the highest two cogs? Is there any reason to avoid Maillard aside from the odd-sized freewheel splines?

Or is it just time to cold-set the frame to 6-speed spacing and be done with it?

I have a mountain bike with 1:1 gearing and the limiting factor is how long I can spin: On some dirt roads even a brief pause would find me rolling back down the hill. It's still about running pace, which wouldn't be all that realistic on a steep hill anyway.

ColonelJLloyd 

Perhaps you could search eBay or post a WTB in the sales forum for a freewheel. I know Suntour made a 14-34t 5 speed freewheel. I have one, but it's earmarked for a friends 1x5 city bike build.

Jeff Wills

The Shimano "skip-tooth" freewheels were from the late '70's. The top cogs' missing teeth were a shifting aid. This was superseded by Uniglide and then Hyperglide, both of which shift far better than old square-tooth cogs and any iteration of Maillard.

IRD offers a 5-speed 13-32 freewheel: https://store.interlocracing.com/fr76and5sp.html . Not particularly cheap, but probably better than a 30-year-old parts bin denizen.