I purchased a DownTube VIII H with the 8 speed SA hub and front suspension. I have seen some discussion on the forum about the high gearing. The SA8 is direct drive in the lowest gear (1) all the rest, i.e. 2-8 are overdrive. The stock crankset has a 48 tooth chainring so the gearing is way to high for all but the most aggressive hammer head–who typically don’t ride folders.
The Sheldon Brown Internal Gear Calculator (
http://sheldonbrown.com/gears/internal.html) makes it a snap to compute the ratios. For illustration I use 20 inch nominal wheel size, gear units of inches, and the stock 23 rear tooth size. I used 30, 36, 48 for the chainring sizes.
This computes some numbers that are basically meaningless to most people. The good thing about the inch gear unit is that it makes comparison between bicycles of different wheel size. In other words, a 60 inch gear will require the same pedaling effort regardless of the wheel size.
In other words your can ride a regular sized bike and get the feel of what a gear is like, tell them you want to ride a bike with a 60 inch gear.
I find that an even more useful number is to divide the inch gear by 5 to get the speed in miles per hour (mph) for a normal rider (about 68rpm) ok, ok if you spin at a bit over 80rpm divide by 4. Mph is a much more common number for the American cyclist. If you are metric and think in kph like most of the world divide by 3 and 2.5 (gotcha).
Okay to put it to the test hit the compute button and
gear 30x23 36x23 48x23
8 79.6 95.5 127.3
7 62.1 74.5 99.3
6 54.8 65.7 87.7
5 48.5 58.2 77.6
4 42.8 51.3 68.5
3 37.8 45.4 60.5
2 33.4 40.1 53.4
1 26.1 31.3 41.7
Well average rider, you do the math, how often do you ride 127/5 = 25 mph, hoe about 80/5=16 mph with a wind aided spinning 80/4 = 20 mph. Now how about climbing the local nut buster hill at 41.7/5 = 8 mph (for about 2 min or 1/4 mile for your average rider), now 26/5 = 5.2 is about all you can do on a steep hill. Put 25 pounds of baggage on that trip to your favorite hideaway and you will probably still have to walk the steep ones with the 30 or 36, but it will be a bunch better and a whole lot less often than with that 48.
You really have to look at the middle range gears 4 or 5 to investigate your average riding speed–most people can ride 12-13 mph in calm or low wind conditions without looking like they just came out of gym after trying to impress the coach on how tough they are (you know what I mean). That would be gear 3 with 48 tooth chainring ( stock) and gear 5 with the 36 tooth chainring. If you only ride downhill or with the wind stay with the stock, otherwise, change the crankset.
I see “pine cone” (p37- nice job) changed to a 39 tooth and that’s probably okay but he didn’t say anything about chainline. I have found that the SA sprocket requires the front chainring to be very close to the bottom bracket to get a straight chainline (chainring and rear sprocket are in the same plane and the chain runs straight like it should to reduce friction and wear) that looks and performs like it should. Your LBS will know what I’m talking about and your will find it in the discussions on the Sheldon Brown single speed sections. Although the SA hub provides 8 “speeds” its chain configuration is like a one speed so the chain should be straight. It is not straight with the stock 48 tooth crankset ??? How do you get what you want?
Tell your LBS you need a standard road triple with 110mm or 130mm BCD and a granny BCD of 74mm. This is very common and believe me there lots of them around, new and used. While you are at it tell them to replace the bottom bracket with a sealed unit (the best $40 you will ever spend). The 74 mm granny is the key. It provides the correct chainline and it is available in any size from 24 to 36 tooth, check the 74mm BCD page from Harris (
http://sheldonbrown.com/harris/chainrings/74.html) to see what I mean. Hey you will be glad you did if you really plan on riding this honey of a folding bike. Make the changes, get what you want and enjoy the ride. After the gears get a quality seat and start getting the pleasure you deserve. Look you will have a custom for $5-600 which is almost too good to be true.
Change the cranks. You will be glad you did.