Lower Gearing for Suntour Sprint 9000
 

My 50 year old body does not have the stamina or leg strength to make it up some hills on my rides. The bike is running Suntour Sprint 9000 with 13-21 freewheel, and 42/53 chainrings. Looking at the RD specs, the options look pretty limited for Suntour Ultra (and NOS prices are crazy). Spec says Sprint 9000 supports up to 25T in index mode. I thought about a smaller chainring, but that would push capacity and chainring max differential is 12T according to spec. And I want to keep the 53T.
I did some gain ratio calculations to compare the Suntour to my bike running a Nexus 7 IGH. I can make it up almost any hill with the Nexus. The lowest gear on the Nexus has a 2.6 gain ratio. 28T cog on the freewheel would get me close to this gain ratio. Is it apples to apples to compare IGH gain ratio to freewheel gain ratio?

What are some other options to get lower gearing? The bike is all original Panasonic DX-6000. I would like to keep it as original as possible, but being rideable is more important.

I don't know if the the RD is indexed or not. One option is a Superbe/Cyclone/BL GT RD and a bigger cluster of the back. Or a Suntour or Shimano MTB RD from that era and bigger cluster. Another option is a 110 or 110/74 or 86 BCD crankset with a smaller inner ring. Try the FD first. If it doesn't work, get a triple FD like a Suntour Mountech.

[QUOTE=saias;22109377]My 50 year old body does not have the stamina or leg strength to make it up some hills on my rides. The bike is running Suntour Sprint 9000 with 13-21 freewheel, and 42/53 chainrings. Looking at the RD specs, the options look pretty limited for Suntour Ultra (and NOS prices are crazy). Spec says Sprint 9000 supports up to 25T in index mode. I thought about a smaller chainring, but that would push capacity and chainring max differential is 12T according to spec. And I want to keep the 53T.
I did some gain ratio calculations to compare the Suntour to my bike running a Nexus 7 IGH. I can make it up almost any hill with the Nexus. The lowest gear on the Nexus has a 2.6 gain ratio. 28T cog on the freewheel would get me close to this gain ratio. Is it apples to apples to compare IGH gain ratio to freewheel gain ratio?

Talk to Any Muzi at Yellow Jersey bike shop for AccuShift options - he's quite knowledgeable.

It is indexed.
The MTB RD is an interesting idea.

If this is set up per the '87 catalog, a new freewheel is easy to source. It came stock with a 7 speed suntour winner freewheel, 13-21. 7 speed 14-28 freewheels are not hard to find but new ones are not designed to index with Suntour. If you don't mind going friction, that isn't a problem.

The limiting factor is the rear derailleur which apparently can handle up to a 26 tooth cog in friction mode. I'd hunt around for a long cage suntour derailleur.

It won't be hard to find the parts you need if you're good with friction.

[QUOTE=tendency;22109399]Thanks for the reference. I will try to get in touch with Any Muzi.

Andy. Andy Muzi.

Six speed Accushift is easy because it shares freewheel spacing with SIS, so as long as you pair an 6 speed Accushift shifter with an Accushift derailleur and a 6 speed SIS or Accushift compatible freewheel- you're golden. So to speak.

Seven speed- I can't help you too much- but I guess I'd look for a 7 speed freewheel with your low end on it then an XC Pro or XC Comp MTB derailleur- I'd probably look for a mid cage. Sprint 9000 was just under Superbe which was top of the line. In ATB parts, XC Pro was top of the line and XC Comp was just beneath it. They're both excellent.

I run a 13 - 26 on a Univega Gran Premio with Suntour Sprint (not 9000). No problems.

I was also able to use a 13-26t on my Allez with it's Sprint accushift 6s drivetrain.

I did also use a Superbe Pro indexing RD with a 12-28t HG cassette (re-spaced to Suntour spec's), and it worked fine using Command Accu-7 levers.

Thank you for all the advice and recommendations.
Is the RD cage the only thing that determines the capacity? I was wondering if I could replace the Sprint cage with a longer cage from an MTB RD.

Go to Velobase and compare the various RDs. I tried to swap the cages on a Superbe Pro and a XC Sport? RD. The cages were the same. The bodies/mounting bolts were a little different, however. I haven't got it to work yet.

I've successfully mounted a Suntour 3 pulley cage on a 6 speed Sprint derailleur (not 9000) and it works well, no issues except it's friction. I've honestly not tried to make it index but I'd bet dimes to doughnuts it would succeed on a 6 speed standard rear freewheel/cassette. The 3 pulley cage is the same on all the different models. I've not tried to swap onto a Sprint 9000.

Yes and no... generally longer cage lengths are to be able to wrap more chain- ATB/MTBs generally have triple cranks in addition to larger rear cogs, hence the need to wrap more chain. So a MTB/ATB/Touring bike will generally have a rear derailleur with a longer cage because there's more chain in the system to wrap. So those derailleurs are designed with larger cogs in mind.

Yes you can try swapping cages- people have done such things- in some cases it's possible if you have the right parts. Keep in mind you're dealing with a 33 or so year old derailleur from a company that effectively went out of business 27 or so years ago.

If'n it were me, I'd try to find an Accushift freewheel/cassette with a 28 and see if your Sprint RD will take it (I was not able to get a Superbe Pro to work on a 28 on one of my bikes)- if your RD doesn't work, find an XC Comp or better RD.

It's never easy.

Do you really need that 53/13 high end gear?

If you can find a freewheel (not a cassette/freehub, which can definitely go down to 11 teeth) with a 12T cog, you could go with smaller rings up front. I have never owned a small cage rear derailleur that could not handle a 26T cog in back.

My suggestion: if you already have 130mm BCD cranks, go 48-38 / 12-26, which will provide you with about the same top gear and a very noticeably lower bottom gear. I just changed the 1959 Capo to 46-38/13-15-17-19-22-25, and the range suits me well, and my Campag. 980 rear derailleur handles it without complaint.

How much money are you willing to spend? Assuming that you want to keep your SunTour shifters and the indexing:

1) Smaller BCD crankset, can gain you the most advantage. Something like a 30-46T is preferred by randonneurs.

2) Larger rear Accushift compatible cogset paired with a long-cage SunTour derailleur. Some have been mentioned. Also, the X-1 was Accushift compatible, as was the Edge.

Your friend’s solution is to get a triple crankset, a mtb rear derailleur and a little wider range freewheel, like a 13-28.

Your best bet is finding a mtb triple with a 24-34-46, or something like that. My brother is running a Shimano 22-32-42 crank, (which would work with Suntour), on his road bike and doesn’t need a cassette with enormous cogs.

With a square taper BB you can fit almost anything and a mtb rear derailleur can give you the chain wrap for a triple. I put a mtb triple on my wife’s old Univega.

It will take some figuring, but your friend will end up with a bike that he can ride for decades, not just until he needs even lower gears.

John

It's certainly not easy working with Suntour. I think I will first try a freewheel with a 28 to see how the Sprint handles it. I have X1 on my Trek MTB that I can try if the Sprint can't handle it.