Bearonabike

I bought a Nishiki Prestige for $40 at a local pawn shop. It looked a wreck but I have rebuilt a few Treks and 3 or 4 S-10-S bikes and I had some suspicion that the awful appearance was just surface crud. I nailed that one, the bike is in really good shape but it does have some miles. I have to replace the freewheel and intend to buy a 5 speed with a very low (Megarange) gear if I can find one. I also have to replace the chain rings. They are razor sharp little buggers that want nothing more than to spill my blood as I work around them.

The crank is a Suntour a-5000 and I have the chain rings off so they are no longer dangerous but do not know if chain rings are all the same bolt pattern or if there are differences. If there are, how do I find ones that will match my cranks?

HillRider

I couldn't find any useful info on that bike or crank but I'll assume it has a 5-bolt 110 mm bolt circle diameter for the chainrings. Chainrings in that pattern are very common and any bike shop will have them.

FBinNY 

Assuming that they have a 5 bolt pattern, you can measure the on-center distance between two bolts and multiply to get the bolt circle.

Keep in mind that they have to conform to an existing number so if small measuring errors have you come up with something like 111 or 109mm you can be pretty sure you need a 110mm ring.

If not sure what's real or not, you can find a list of existing patterns at the Sheldon Brown site.

dsbrantjr

Bolt circle diameter calculator; Bolt Circle Diameter Calculator

Ironfish653

A 5-speed Megarange might be hard to find, if such a thing exists. You can find 14-24s and 14-28s all day, but to get the 34 tooth cog, you might have to stuff a 6-speed in there.
Since you are replacing chainrings, try finding a smaller set of rings; if you have a 52/42, try fitting a 48/38 or even a 42/32, depending on how low you want your gearing.

bulldog1935

why do you want 5-speed megarange in FL? I would think a 13-28t would do anything you'd ever want to do (any wind), and you might like narrower gear steps better.

Make sure you replace the chain.

Suntour made a CW-1000 Superbe crank, which was 144mm bcd. (Campy Strada) - if that's the correct size, you can get TA chainrings in UK, and they're very good - 41T is the smallest and only TA makes that. You could use a 46T large and have half-steps that split the steps between your freewheel steps. Look at this link, and see if this is it:
VeloBase.com - Component: SunTour CW-1000, Superbe
https://velobase.com/ListComponents.a...b-dac2d4abd9e6
is this the bike - it may be a Strada-clone crank - 1987 catalog


here we go, Sugino A-5000 crank


Found a Sugino RD5000 crank, which is 130mm bcd - this would allow a small chainring of 38T
VeloBase.com - Component: Sugino RD5000
https://velobase.com/ListComponents.a...5-f608b2c7f6de

Make sure you get bolt circle diameter correct before you order chainrings.

SJS cycles and Spa cycles in UK are great for ordering TA chainrings.

bulldog1935

I have some nice parts around here.
I have a TA 144 bcd 46T outer chainring in good shape.
A Suntour Ultra-6 freewheel (should fit in the same space as a 5-sp freewheel) in very good shape.
I have an IRD 5-speed freewheel, 13-28t hyperglide with 20 miles on it.
With either of these I can provide the matching freewheel socket.
If any of these parts interest you, send me a pm...

Bearonabike

Thanks!

Bearonabike

Thanks, much help and much appreciated. In past rebuilds, I have replaced the whole crank assesmbly. THese cranks are in too good a shape to trash.

bulldog1935

my buddy hauled one daughter as stoker on their tandem, and younger daughter on a trailer bike - he was hauling two girls - and I doubt if he never went to those little gears on his triple.
You'd never need a gear smaller than 35 inches, which would be 42T small chainring and 32t big cog

IRD makes these:



half-steps would be a big bonus with such wide rear cogs
Here's my old Raleigh when it was wearing 46/41T half steps (144 bcd)



Sugino GP 130 = 130mm bcd

With a 38T inner chainring, 28t rear cog would give you a 36" low gear - probably the lowest gear you would ever want.
A 41T or 42T outer ring would give you perfect half steps (and a 44T would blow it and overlap everything)


this is about as nice as you can make 10 gears - narrow steps, no overlaps, perfect range for touring gears

here's the full gear analysis

Bearonabike

Will keep this in mind, thanks!

bulldog1935

look back at my last post - ran a gear chart for you on the IRD freewheel with 38T inner and 42T outer chainrings, scanned it and edited into post.

Bearonabike

I have it on my desktop. I have to measure the bolt pattern but this is what I want to go for. Thanks again.

bulldog1935

you're welcome

ps, you have a lot of choices in 130 bcd chainrings - Sugino, SRAM, FSA, Stronglight

found a 42T Stronglight on ebay, and 38T inners are everywhere...

bulldog1935

I plugged the 13-32t IRD into Mike's gear analysis

It would get you down to a 31" gear which could spin-climb a 12% grade without your daughter in tow.
All the gear steps are under 10", which is what you want, though the semi-log graph shows they're not quite as evenly spaced below 40" as the 13-28t 5-sp
you could also hunt around for other freewheel options, plug them into Mike's calculator and see what you get.

The way you ride half-steps is make your first shift up or down on the crank, next shift in the rear, and if you need trim again, back to the front. If possible, spend most of your time on the big ring, so you can grab that half-step down for a shallow grade.
I love them on an older bike with wide freewheel. The 3rd rebuilt of my Raleigh, I went to a cyclotouriste triple half-steps, and a granny ring to get me up the 400' climb and 14% grades to reach my house at the end of a long ride.
But this is a big undertaking, needing a 122mm asymmetric bottom bracket.