FullaBulla

Howdy Y'all,

Thanks for letting me join this resource. I'm looking forward to all the knowledge I can gain from the folks here. I'll admit, I'm no bike mechanic, but have a desire to learn the workings of my bike and being able to maintain, repair and update myself as needed moving forward. Please excuse my lack of knowledge in nomenclature/terminology. I've got a 1984 KHS Montana rigid frame MTB I would like to upgrade with different gear ratios to help with touring and climbing the steeper terrain here in Western North Carolina (I'm a flatlander and these climbs are really something). The current drivetrain is stock (except for the shifters) with a triple chainring/crankset (36/40/48) and a 5 speed cassette (14/32). My initial thought is the possibility of replacing the chainring/crankset with smaller chainrings to help with climbing this steeper terrain and leaving the 5 speed cassette as is. Is this possible and what concerns or issues should I consider moving forward? It wouldn't let me add any pics as this is my first post.

Thanks for your guidance, any resources and advice!

Charlie

Tourist in MSN

It should be possible to buy different chainrings.

Park Tools is one of the best resources on bike repair and maintenance on youtube.
https://www.youtube.com/@parktool

There are people on youtube that post videos that can give false information on bikes, usually it is ignorance by the presenter. I try to only use videos from sources that are known to be good. Park has great reliable videos. Arts does too.
https://www.youtube.com/@artscyclery875

There are lots of different chainring standards. In the 1980s, most or perhaps all were symmetric. You want to buy ones that fit.
https://www.sheldonbrown.com/cribsheet-bcd.html

The Sheldon Brown website is also a great resource for general information, although a lot of it is dated, but so is your bike.

I do not know if your bike has indexed shifting or if it is friction. If it is indexed, you probably do not want to change the derailleurs or shifters. If friction, then a different rear derailleur shifter could be an option with a longer cage that could take up more slack chain. The reason I say that is that right now the front has a difference of 12 teeth between biggest and smallest chainrings, the freewheel is 14 teeth, total of 26. Your derailleur might not be able to take up more than 26. That could mean that you do not want to have a bigger difference in front chainrings than the existing 12.

NOTE: Corrected a word in above paragraph later.

If you use smaller chainrings, your chain will be too long.

You have some studying and research to do to get smart on bike mechanical stuff.

You would need some tools. And probably would need a square taper crank arm puller.

FullaBulla

Thanks Tourist in MSN for the info and resources. I go to Parks quite a bit on Youtube. I'll definitely check out the others. I ordered a crank arm puller last night. I'm running friction shifters so thanks for the tip on the rear shifter.

saddlesores

Considering the age of the bike, and not knowing the maintenance history, I'd assume there would be a fair amount of wear on all the components.

In that case, if you change out the cranks/rings, then you'll likely need a new freewheel and chain. (I'm guessing it's a freewheel and not a cassette.) May also need to switch out the derailleur pulleys.

Your rear dropouts (I think) are 120mm, don't think you'll be able to use a 7- or 8-speed. 5-speed NOS available on ebay.

https://www.ebay.com/itm/296009315759 suntour 5spd 14-34 freewheel for $35

5/6-speed chains also available.

But the question is.........what if you replace the crank/rings?. Someone more knowledgeable (cycocommute!) can tell you whether 7,8,9 speed rings will work with 5-speed chains and cogs.

What is the make/model of your rear derailleur? Google the specs for capacity.
If you have freewheel, and not cassette, do you have a freewheel tool?

abdon 

Chances are you have a standard (old school standard) triple crankset with five bolts holding the rings. If so the Bolt Circle Diameter (BCD) is 110mm for the large and medium rings, 74mm for the smaller ring. If so, the smallest you can go on the small ring (the 74 BCD one) is a 24t ring. Even replacing that 36 ring with a 28 ring should net you a significant bump on the granny gear department.