Bicycle Mechanics - Trike woes

I ride a TerraTrike with a Sturmey Archer 8-speed hub. Love the thing, when the hub's working. Hoping for help here (and general discussion) so I can keep the wheels turning. I have the Sturmey
Archer X-RF8 eight speed hub (second one in 3 years and less than 2K miles). They both malfunctioned in the same manner.
Riding along at a moderate pace when the pedals lock up in 3rd gear. A back rotation releases the pedals movement, but then the only gears that engage are 2, 5, 6, and 8. Everything is correctly adjusted per factory specs.
So, can this hub be fixed or am I out for a new one? If a new one is in order any one have recommendations not Sturmey Archer?
The first Hub on the trike was replaced under warranty since it had fewer that 100 miles on it. Second probably has 1200 miles.
HALP!

I've never opened up that particular model hub, but suspect that it's an internal clearance issue, which cannot be fixed. IGH hubs have various units geared to each other and rotating at different speeds at all times. You shift by a sliding clutch which engages one or another ring. If the clutch should engage two rings simultaneously the hub locks up.

Usually the design prevents lock up with a dead zone between where the clutch leaves one ring and picks up the other. If for some reason this is too narrow, or the clutch off kilter a bit, it'll hit both at once and lock. There may be some corrective repair that can be done in the shop (I've never opened this model), but likely it calls for a new hub.

The SA 8-speed works by having three sequential planet gear "modules". The sun gear for each one can be locked to the axle, in which case the module gears up, or free to rotate about the axle, in which case it passes drive directly to the next module. By combining different modules gearing up or passing direct drive, you can get 8 gears. I suspect you've had a failure of one module. It may be possible to replace the failed part, as it's possible to buy parts for the 8-speed here in the UK. Where are you located, OP?

I'm in scenic Arkansas, USA. Not may Sturmey Archer folks around. I've researched best I can and am seriously considering converting it to a Shimano Allfine 8-speed hub.
Anybody had experiences or opinions about this hub.
I might mention that I stand 6'9" tall and tip the scales at 275 lbs., so I think that just too much of a load for the Sturmey.

I'm in scenic Arkansas, USA. Not may Sturmey Archer folks around. I've researched best I can and am seriously considering converting it to a Shimano Allfine 8-speed hub.
Anybody had experiences or opinions about this hub.
I might mention that I stand 6'9" tall and tip the scales at 275 lbs., so I think that just too much of a load for the Sturmey.

All IG hubs have upper end driving torque limits that are lower than most derailleur systems. Combining your weight with Ozarks climbs seems likely to push those limits regardless of the brand. Especially if you use a lower primary drive ratio (smaller front and/or bigger rear sprocket.

I don't know what gearing you use, but if it's near the upper limit of the hub's specs. I suspect that the Alfine won't be much better. IME the simpler 3 and 5 speed hubs tend to be more bulletproof than those with more gearing, so if you can live with 5s that may be a better bet for you.

There's another alternative that might make sense depending on the trike's design. Often these trikes have the hub installed as a mid-point transmission, with a final drive chain from the hub to rear axle. If yours if of that type, try for a lower final drive ratio, ie larger axle sprocket, and a correspondingly higher primary drive ratio. This will have the hub running at lower torque loads while maintaining the same gear range.

That's kinda depressing, I guess. Although I don't know why more gears is necessarily better. Since I tended to use the middle 3 or 4 gears on my 8 speed, three might do. Any one have an opinion on the Sturmey Archer 3 speed in this application? I know where I can get a "deal".
:thumb:

Before abandoning your 8s concept, check the specs. Just about all IGH hubs specify a maximum drive ratio (drive sprocket/chainring) compare that to what you have, and make some kind of adjustment for your weight and terrain. In your shoes, I'd assume the max was based on a 200# rider, so if the hub says nothing bigger than 1:2 (18 back/ 36 front) than I'd limit myself to something more like a 18 back/44 front.

If that's workable (you'll compensate by riding the lower end gears for the hub) you're good to go. It'll take a bit of math shifting the hubs output ratios to find comparable final drive ratios that match what you're actually using now. But if you're not currently using the lower gears you might be able to get the hub torques down to an acceptable range.

As I said, if this is a mid drive transmission (small loop of chain from hub shell to drive axle) as is very common on trikes you can (hopefully) change the axle gear to lower the torque on the hub and have all fall within spec.

I suspect that the Alfine won't be much better.

I'd say there's a good chance the Shimano unit is designed and/or made to higher standards; they're a huge company that has been responsible for many, many refinements.

Thanks. It's not a midhub drive, so I guess I'll have to sharpen up my calculator and do some teeth counting. Stay tuned. I know I'm needing advice.

Thanks. It's not a midhub drive, so I guess I'll have to sharpen up my calculator and do some teeth counting. Stay tuned. I know I'm needing advice.

Regardless of the brand or type of hub, there are three elements to consider. The issue is input drive torque, so it's the input gear ratio, your weight and the terrain. I don't suspect you're planning a crash diet, so it might turn on the terrain. If you don't climb steep hills or accelerate hard you'll have greater margin of error but, given your weight, I still don't think you can run these hubs near their max input gear ratio. Good luck with the calculations.

The trike currently has a front sprocket with 46 teeth and 25 (do they make a 25 or can I not count?) on the defunct SA hub. So if I'm anywhere with my calculations (serious doubts here), the new hub sprocket should be 16 or 18 teeth. Any truth in that?

The trike currently has a front sprocket with 46 teeth and 25 (do they make a 25 or can I not count?) on the defunct SA hub. So if I'm anywhere with my calculations (serious doubts here), the new hub sprocket should be 16 or 18 teeth. Any truth in that?

Based on offsetting the gear range for your weight vs. 200# your on target. But understand that this will shift the gear range to high by 25-33%. Make sure that you'll have a low enough gear for your needs when you're done. The other way would be to calculate what you need to keep as a low gear, then calculate what the smallest sprocket will give it to you. IMO it's better to have a bike that has the gearing you need even if it's pushing the limits of the hub, then to protect the hub by limiting torque but not having a bike you can enjoy riding. If you now have a 25T on there, maybe a 20 or 22t may be enough to make the difference.

You might also call the maker, discuss your weight and get a recommendation of maximum sprocket size. If you're buying new, call both Shimano, and SA and factor their advice into your buying decision, especially if one offers a guarranty.

Sturmey- (sun race) Archer USA is in Northern California...
Rohloff USA is also in Northern California.

I think Shimano's US offices are in SoCal., Sram in Chicago.

AFAIK the 8 speed cog is different from all other SA hubs, no smaller than 19t, [23 & 25]

Welp, after a bunch of consulting, I think I'm gonna give the Shimano Alfine 8-speed with a 20 tooth sprocket a go. Not sure, but it seems to be a consensus. Keeping my toes crossed. :thumb:

Sounds reasonable. Hopefully you'll have good luck with the combo, and it doesn't matter whether it's the hub or gear ratio change that solves the problem as long is it stays solved.

Welp, went with the Shimano Alfine with 20 tooth sprocket. Gonna have to shorten chain. Any advice on going from a 24 tooth to a 20 tooth?

Welp, went with the Shimano Alfine with 20 tooth sprocket. Gonna have to shorten chain. Any advice on going from a 24 tooth to a 20 tooth?

With a typical arrangement, where the chain wraps 1/2 the sprocket, you'd remove 1" or 1pr links to correspond to the two teeth fewer being wrapped.