Mkskid

Hey guys!! Need some Help with the gearing on my trike. Here it is I have a problem with finding the right gears. I have a Sturmey Archer SRF5(w) hub with a 22T trike gear on it. Next the front gear where you pedal from is a 36T it runs the removable gear on the hub that is a 14T gear. Than the gear on the back is a freewheel 18T. I thought I could put a blind fold on and throw a dart at a Chart of something and come up with a Winning Combination. That didn't work out to well for me. So, after all most three month of Changing,Throwing,and @#$%^#@ at these gears I am here to kiss the ring.

You guy's are good so be kind and Gentle!! There is going to be alot of ?'s I'm ready. I will try to answer all the ?'s to the best of my knowledge which isn't much about this subject.

A little back round on me: The last 4 years of my career I built titanium rotary racing motors for Mazda Racing Division. That totaled 7 World Championships in a row. So, I know which end of the wrench does what, but this trike is Killing Me.

Help Please for my Wife's Sake!!

Jeff Wills

OK- bike/trike people call the gear up front a "chainring" and the gear on the rear hub a "cog". It's a little confusing when you say you have a 22-tooth cog on rear hub then you say you have a 14-tooth cog on it. Which is it?

Another thing that makes a difference is the rear wheel size- is it 20-inch? 26-inch? Is it a homebuilt trike? A commercial trike? What brand?

Here's a good primer for figuring out your trike's gears and a calculator to figure out the different gear ratios:
https://www.sheldonbrown.com/gears.html
https://www.sheldonbrown.com/gear-calc.html
(Yes, the gear calculator will do the ratios for your SRF-5 hub.)

It's not really all that different from figuring out the gear ratios for a car on different race tracks.

My career(s) started in the bicycle business as a mechanic and parts finder. I also built recumbent trikes nearly 40 years ago. I had my fun but now I have a "real" job. This is where I started:



As to rotaries... a while back I ran across a JDM Mazda Cosmo with a 20R engine at the local Starbucks. I had to wipe the drool off my chin.

VegasTriker

Am I correct on figuring out that you tried the trike with three different cogs on the SA hub? The problem may not be in just choosing which cog is satisfactory but that the SRF5(w) hub may not be suitable for your trike due to the wide gap between gears delivered by the hub. Few trikes, with the exception of some low end, entry level trikes, have such small chainrings and the result is a very limited gear range. You can post the results from using one of the gear charts to make answering your question easier. Jeff Wills is right in saying that without knowing the diameter of the rear wheel, it is impossible to even guess at a gear range..


From a discussion at the SA website about this hub: "does the (w) version have 33% steps between gears, and the non-(w) version have 25% steps" The answer was "yes" so you have a hub with large changes as you shift, making it hard to find a comfortable cadence.

Mkskid

Morning Guys!! I will try to explain the transmission the best can. I don't know all the phases and meanings so bear with me. The system has 2 chains and 4 gears. The first chain has a 36t chainring then goes to the hub SRF5(w) to a 14t cog that is changeable. The second chain starts on the hub with a 22t fix gear and goes to the rear axle at the rear axle is a 18t freewheel. How do I get all that into a gear calculator if I even can. If I can what do I do with what comes out?
Some have asked the size of the rear wheels 24inx2.10. The whole problem is the gearing is WAY to low. 1st gear great 2nd gear great all the way through. 3rd gear about half way through gets hard to pedal. 4th gear after about 58 seconds I have to pull over and take a Nap. 5th gear "forget about it" as my Italian friends would say. All I need is three gears I can put on this thing, One I can't change so I can enjoy the 5 gears I paid for. I don't need a PHD in trike I just want to ride my trike down to the beach to check the new swimsuit fashions so I can go home and tell my wife about them. She loves that "LOL" and I do too. Any ?'s. This is the first big mistake I've made the trike's gearing is WAY WAY to High not low. I'm totally new at this so be kind. I'm also a big boy and you can beat me up a little.
This is very frustrating Now I don't know To High To low upside downside. The thing that pisses me off the most is I can't explain it to you guys the right way. With my background and knowledge I have no clue it's very humbling. My wife says after everything I have built blown up or people wanting to buy whatever it is I'm working on it's always seems to work up just the way I wanted it to. Maybe I should just keep my head and get on with it and stop crying. The way I wrote the gears is what it's doing. High or Low I don't know.

Jeff Wills

OK: 36 tooth (front) ÷ 14 tooth (mid hub input) x 22 tooth (output) ÷ 18 tooth (cog) x 24" (-ish) diameter wheel yields these gear inch numbers:

1st: 47.0
2nd: 56.5
3rd: 75.3
4th: 100.3
5th: 120.4

As you've found, these are very, very high gears, suitable for a running a streamliner at Bonneville but not much else. A typical trike would have a low gear around 30 gear inches and a high of 80 gear inches. To do this I would change the cog on the SRF5(W) hub to something much larger, around 22 teeth. That gives you this:
36 tooth (front) ÷ 22 tooth (mid hub input) x 22 tooth (output) ÷ 18 tooth (cog) x 24" diameter wheel yielding these gear inch numbers:

1st: 29.9
2nd: 35.9
3rd: 47.9
4th: 63.9
5th: 76.6

In order to get the chain to work you'll probably have to add a couple links to it or replace it entirely. "Cutting" a bike chain to length is pretty easy- there's probably thousands of YouTube videos on how to do it.

This should suit you unless you're climbing steep hills. If you're climbing hills and you're a "big boy", you should look into a trike with more gears, like a 24 or 27 speed.

You're asking the right questions... keep going!

Leisesturm

It sure would be interesting to find out what kind of trike this is. Doesn't sound like one of the typical commercial offerings. Was it intended to have an e-assist (electric motor) as well? I don't think anything can be done to make this drivetrain practical. A 30" 1st gear is still way too high IMO. If brought down to something better like ~15" then the high gear will really suffer. More speeds like the earlier poster suggested ... absolutely. But how to get them? If we knew more about the trike it might guide our thinking. I mean ... the mid-drive might be a good place to put another freewheel and get more gears. Or not. Without seeing the trike we can't say. A triple crankset might be another but it might present too much of a torque load to the IGH (rear hub). TL;DR more information is still needed on this trike.

BlazingPedals

Good info from Jeff. Is it possible/economical to convert this trike to a standard derailleur system, whether or not you keep the mid-drive?