Mountain Bike Reviews Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
98 Posts
Discussion Starter · #1 · (Edited)
I have a question on IGHs. I currently ride a 29er and have found what I call a "dream gear" in which I can ride all day on gentle rails to trails. I have a classic 1984 Ross Mt. Whitney (my 1st MTB) that I was thinking of converting to 5 speed IGH. Could I set the middle gear on the IGH to my "dream gear" ratio and then have 2 up and 2 down gears from there or would the difference in 26" vs. 29" wheels change things? My "dream gear" on my 29er is 44T front ring and 20 in rear. So ideally (based on my 29er rear cassette) 15,17,20,23,26 rear and 44T front handles just about ALL the riding I do long distance. Noob at bike mechanics and gear ratios btw. Thanks for any suggestions.
 

·
Registered
Joined
·
467 Posts
Probably an OK idea, so long as you limit the bike to similar "easy" terrain. I have no experience with the old Sturmey-Archer 5 speeds, but the newer ones and Shimano 5-speeds are kinda weak for harder use. If you have to buy a new hub, I would probably choose a Shimano 8....more range and seems to hold up to rougher service.

When you count teeth and figure out your gear ratioes, consider turning them into a figure you can translate across different platforms. I like "gear-inches" (each turn of the pedal equals how much distance), but your mileage may vary....

start here, then click around if you want to learn more: Gain Ratios--A New Way to Designate Bicycle Gears
 

·
Frt Range, CO
Joined
·
2,576 Posts
Your Mt Whitney is most likely 120mm rear hub spacing, all you'll find to fit is a lame-o Sturmey hub. I'd space the rear to 135mm and use an 8 speed Alfine or Nexus 8R36.
 

·
Registered
Joined
·
98 Posts
Discussion Starter · #4 ·
how do I space it? gently push the rear apart to squeeze in 135mm? I have no tools to do that.
 

·
Frt Range, CO
Joined
·
2,576 Posts
...I may try the all thread method....
Sheldon's method has the important point, each dropout must be moved independently.

The all-thread method assumes that each chainstay will deform symmetrically. Esp in the case of older frames, this isn't true. Usually the right side chainstay isn't as stiff due to the dimpling to make room for the chainring. So using the all-thread method makes the right side chainstay do most/all the movement/setting, the left side stay in place. That will cause the frame to be mis-aligned.

If I'm spacing from 120mm to 135mm I move one side 7.5mm first, then the other side. I check the dropout alignment (with h-tools) after moving one side and re-align the dropout to the un-moved side keeping the proper reference to the center of the seat tube.

To hold the frame in place, I use a bench vise and wooden blocks to hold the bottom bracket between the faces (with the frame upright). Then I can really lean into the stays and move them cleanly. I have found that adding in more than ~5mm of spacing will require the dropouts to be re-aligned with h-tools or a big wrench and a good eye.
 

·
Registered
Joined
·
98 Posts
Discussion Starter · #8 ·
Original Post #1 updated.
 

·
Frt Range, CO
Joined
·
2,576 Posts
Yes, the SA 5 speed hubs are 1:1 in third gear so 44x20 is what you want. Unfortunately, the SA 5 speed has big steps, between 25% - 37%, you'll have the equivalent of a 12, 15, 20, 25, 30 cluster.
 
1 - 9 of 9 Posts
Top