Converting Suburban 5-speed to 10-speed

[Passaloutre]

I've got a late 70s Schwinn Suburban that I've been riding for a couple years now. I bought it cheap, fixed it up, and ride it for leisure. Therefore I'm not looking to spend a lot of money or buy a different bike. It's not pretty enough to be a restoration piece. I've attached a photo of the as-bought condition.

It is currently a 5 speed with Positron Rear Derailleur and Shimano Front Freewheel, and I'd like to upgrade it to 10 speed for some of the hills I have to deal with along my route. In order to make this change I believe I will need the following, but feel free to offer your opinions and tell me if I'm wrong. You'll notice a common theme of sticking with vintage parts or upgrading to more modern standards, which I think it something we all feel. I'm kinda leaning towards modernization, as I've already switched to new dual-pivot brakes and alloy wheels, and I really like what they've done for the bike.

- New crankset: well this is obvious. I need one with two chainwheels instead of one. I'm conflicted because part of me actually likes the front freewheel system (being able to change gears while coasting in anticipation of a hill for example), but part of me wants to move to more modern, lighter, reliable components. There are old two-speed front freewheel systems available on ebay, so I could switch to that pretty easily, or do I just bite the bullet and go with the more standard fixed crankset?

- Front derailleur: well I'll need something to switch between the two chainrings right? Any reason I shouldn't just go with the $10 "Schwinn Approved" GT-250 that would have come on this bike in the first place? What advantages would be offered by a more up-to-date front derailleur? And what shifter would I need? The bike currently has a single front stem shifter lever, do I just get a dual stem shifter, or move to thumb shifters on the handlebars. Using flat, not drop bars on this one.

- Rear derailleur: I kinda like the positron rear derailleur, but if I'm upgrading everything else, should I swap this in the process? If I stick with it I keep my indexed shifting, but have the issue of difficult to find shift cables. Swapping to anything *else* of a similar vintage seems like a downgrade. So it's either keep the positron or modernize: any opinions there? If I modernize the rear derailleur I might as well modernize the front one too...

- Rear freewheel: if I get rid of the front freewheel, then I have to put one on the rear. I think this will work fine: https://www.amazon.com/gp/product/B000AYB57S/ref=ppx_yo_dt_b_asin_title_o03_s01

Anything else I should be concerned about? What would you do here?

 

[AndyA]

If you need a lower gear for hills, a 10-speed isn't necessarily going to help. You need to figure out your current gear ratios by counting the teeth on your chainring and on the five cogs. The lowest gear ratio you have will be the number of teeth on your chainring divided by the number of teeth on your biggest cog. If you want to make it easier to climb hills, you need a lower ratio than you have. The most straightforward way to accomplish that is to replace your chainring with a smaller one (fewer teeth) or replace your cogs with bigger ones (more teeth). If you want to switch to a 10-speed setup, you need to check if that will actually provide a lower gear. With my 10-speed bikes, I almost never use the big chainring, but stay on the small chainring (aka the granny wheel). So, these are, for practical purposes, 5-speed bikes.
Have fun!

 

[Passaloutre]

Thank you Andy, that is a great point. The existing chainring has 45 teeth. The 10-speed cranksets I'm looking at have two chainrings with 39 and 52 teeth, so they would indeed get me a "lower" gear for hills.

 

[AndyA]

Yes, the 39-tooth ring would give you a lower ratio. You could try 1) replacing your 45-tooth with the 39-tooth on the existing crank, if the parts fit, 2) removing the 52-tooth ring from the new crank and put that on your bike, or 3) putting the new crank with both rings on your bike. Option 3 might be a good experiment; it's easy to do and the extraneous chainring won't get in the way of anything. In any case, you need to look at the alignment of the chainrings with the cogs and derailleur. Try to duplicate the current alignment with the single ring by adding or removing spacers, as needed.

 

[Passaloutre]

Yeah I suppose there's no harm in trying the other chainrings without a derailleur just to see if I like the new ratios. Still, if I'm going to stick with it, I'd like some advice about what derailleur to use.

 

[AndyA]

For me, I wouldn't bother with the two front rings and front derailleur. I would adjust the ring or the cogs on your 5-speed setup to get the gear ratios that suit your hill-climbing.

As I mentioned, I don't use the big rings on my 10-speeds and 12-speeds. There is a neat website where you can calculate everything you need to know, that is BikeCalc.com. You can plug in info on any combination of wheel size, chain rings, and cogs and see how fast you'll go when you're peddling a certain cadence. For example, one of my 12-speeds has chain rings of 52 and 40 teeth. The cogs are 14, 16, 18, 21, 24, and 28 teeth. So at 40X14 (the highest ratio for the granny ring), BikeCalc tells me that I can go 18.6 mph when peddling 80 rpm. I can only pedal at that rate downhill. I might go a little faster than that going down a big hill, but at that point, I'm not peddling, just enjoying the ride. Therefore, I don't have any need for the big ring.

 

[Passaloutre]

Yes I think you're right. Looking at my available gearing, the lowest ratio I currently have is a 46:32, or 1.4. If I swap to the double chainring, I get a 39 tooth ring, but then I have to install a new freewheel (because my existing freewheel is the FFS system). All of the new threaded 5 speed freewheels I can find have a largest rear sprocket of 28. 39:28 is also 1.4, so that doesn't get me any lower than my existing setup. I could seek out a vintage freewheel that has up to 34 teeth, but then I might have to swap out my rear derailleur, and so on.

I think I'll stick with what I've got and work on my endurance

 

[Sven]

Like, @AndyA suggest, stay with the five. I personally like the Front Freewheel System. Its the precursor to index shifting.

 

[Passaloutre]

Yes I do like the Front Freewheel. It's nice to be able to change gears while coasting, in anticipation of a hill. And the indexing works nicely.