Question regarding the comparing of gear ratios
 

I was wondering how the gear ratios would be in comparing my new Dahon Curve D3 with a typical 6 or 7 speed derailleur system? One of the staff where I purchased the D3 mentioned that the gearing on the 1st gear of the Curve would be compared to the 1st gear on a derailleur - 2nd gear to a mid gear on a derailleur, and the 3rd gear to the top gear on a derailleur. Is this about right? If that's the case, I don't think my wife will be pushing 3rd gear then.

Thanks
Wayne

It's a rough guide,about right.
Depends on the driller set up you are comparing it to.
Basically take the front chainwheel tooth count d3 equals 52 ish and divide by the back cog. This gives you the wheels revs per pedal. Then times by the wheel diameter.

Ok that gives you the gear in mm or inches. you can compair that to a 28 to 112 figure for a standard bike.
However for an internal gear you need to take in to account underdrive and overdrive. Of the top of my head it's about 40 percent decreased on the sa r speed and a simular overdrive figures.

Get the figures and put it through seldon brown gear calculate to be precise.
Hope this helps.
Ps it's a cheap and simple job to alter the rear cog size if you find its an issue.

Well the range the person at the shop quote is correct in a very general sence but I highly doubt that the top gear is going to be very tall. From a quick look at the specs for the curve d3 I found it shows a 46t chain ring up front and at best it might have a 16t in back coupled with the 16" wheels and the 3 speed hub you would get a 34 to 61 gear inch range so this baby would not exactly be built for speed. Most of the 6 or 7 speed derailleur systems I have seen have 14-28t freewheels out back which are usually coupled with a 52t chainring and on a 20" wheeled bike that yeilds a 37 to 74 gear inch range. Now I have made a number of assumptions and I would need more information from which bike you were directly comparing them to but my conclusions would be this:

A. The Curve D3 is geared pretty low so it would be suited to climb hills but in the flat anyone would probably be in the highest gear.

B. It is very comparable to a 7 speed system but it appears to be slightly lower gearing.

C. With a 34 to 60 gear inch range this bike is not at all comparable to a typical road bike gearing range which is in the 28 to 120 gear inch range.

Side note: not sure if you know but the smaller the gear inch number the easier the gear.

Interesting info guys. My wife and I just came in from our ride, and the gearing of the D3 is perfect for her. 2nd gear is a good gear for just riding around the streets - 3rd gear is just a small step up, and definitely nowhere near high gear on a 6 or 7 speed derailleur. All in all, I would say that my wife doesn't need any more gears than the 3 she has. Before our ride this morning, I was envisioning my wife pumping her tush off trying to use 3rd gear, but fortunately its not the case.

The math is all done for you here Sheldon Brown's Bicycle Gear Calculator

the epicyclic internal gear is a % above or below the direct gear *, in a 3 speed that typically is the middle, 2nd one..

that gear is the chain ring teeth count turning the wheel cog tooth count ratio, ,'X' times .. multilied by diameter or circumference of the wheel.

*AW3 its 25% down, 33% up.. 3/4, 1, 4/3 ..

I like that website. My hub is a SRAM i-motion 3, which is not on his website - yet. Apparently from what I was reading earlier, its a fairly new hub, so perhaps in time, he will update his list.

Probably unchanged from the Sachs .. they shipped all the German production machines to Taiwan when the took the company over .

try 0.73, 1, 1.36.. all the Sachs Sram 3 speeds on the chart are the same.

It will be a lot slower top end than your brommie six speed. Down hill you can overtake her. She have to improve her tucking in position and slipstream your back wheel....

It was on there,I used it on my old Swobo Otis when I got it. You can just use the Shimano Nexus Inter-3,it has the same spacing as the i-Motion. BTW,my Otis was an '06,so that hub has been around awhile. I do think they're putting out a newer version,however.