dit

I am thinking about buying a nice used Catrike that only has a double chainwheel and where I live a Triple is needed. My knowledge on tadpoles and modern cassettes is minimal at best so I have several questions to see what it will take to do the upgrade. It currently has a 8 speed cassette.

1. Do tads use a road or mountain bike bb?
2. What length spindle will I need to install a road FSA triple? 52/42/30
3. Rear derailleur will need changed. Can I use a newer 10 speed model?
4. Will an 10speed gear changer index correctly with an 8 speed cassette?
5. Will Shram and Shimano derailleurs and gear changers interchange and index the same?
6. Will a 10 speed cassette fit on a wheel hub that currently has an 8 speed cassette?

I think that is all the info that I would need to update other than maybe where to get the needed bb spindle.

FBinNY 

1- don't know
2- check the FSA specs, and it depends on the width of your BB shell
3- most likely not, check indexing specs for "pull ratio" compatibility" But a 9s will work.
4- see no. 3
5- NO. while cassette spacing is the same, the pull ratios are different so lever and derailleur must match by brand.
6- probably not. some 9s and 10s hubs are the same, but most 8s are not.

You need to make a decision about whether to do an expensive conversion to a 3x10 system with many new parts, or keep it simple and replace only the crankset and maybe the FD to go to a 3x8 system.

HillRider

All Shimano "8-speed" freehub bodies are also 9 and 10-speed compatible as are SRAM's. Campy 8-speed bodies are not.

Unless the OP lives and rides in a quite flat area, I expect a 30T granny chainring is not going to be adequate. Trikes need VERY low low gears in hilly country.

Bill Kapaun

I agree-
It would seem to me that with a 30T small ring, the largest cog you'll find is a 36T.
That's a 5:6 ratio.
Using a "mountain" triple of say 22-32-42/4 means you could get an equally low gear with a 27T largest cog, with much closer spaced gears.
You'd also have the ability to go much lower, if needed.

dit

I sure would not have a problem doing that but I doubt that the current rear derailleur will have enough wrap to handle the added tooth difference... As far as the gear ratios are concerned it must be stressed that the drive wheel is only 20". To me it seems that the problem is getting high enough gear inches rather than getting low enough. If I remember correctly a 30 chainwheel with a 32 rear cog on a 20" wheel is around a 18 inch gear. I'll check it out but I think that is close.

A 30/36 gives a 15 inch gear and a 30/30 gives a 18" gear. That is still quite low.

FBinNY 

Thanks for that. I'm not a Shimano man, and was told that they too had a cut between 8s and 9s, same as the Campy stuff I'm more familiar with.

FBinNY 

Stupid question.

I understand why tandems have minimum climbing gear and speed requirements compared to solo bikes, but don't get why trikes would have special needs except, maybe (snark alert) for lousier engines. Without the need to maintain speed to stay upright, I'd expect that the trike's needs would be comparable to a solo road bike.

Bill Kapaun

You can get a suitable RDER for $20-30.
Shimano Altus M310 7/8 Speed Rear Der > Components > Drivetrain, Brakes and Pedals > Rear Derailleurs | Jenson USA

Shimano Acera M360 SGS Rear Derailleur > Components > Drivetrain, Brakes and Pedals > Rear Derailleurs | Jenson USA

You might specify what you have now, RE: rings & cogs and your desired gear inches.

BTW-30:30 would give you 20 GI.

dit

Good s uggestion... I have an Altus FD on my road bike with MB triple crank and it has worked great for the last 5 years and it was used when I installed it. May I ask if Shimano bar ends will work with the suggested derailleurs?

I don't have the machine at hand so I don't have many details. I am interested in getting from 18 to 80 gear inches. Rough numbers

I have researched models of this machine back to 08 and they are all triples. This machine looks new so I am curious why it has a double.

Retro Grouch 

A 50/34 compact double with a 11/34 cassette will give you a 90 to 20 gear inch range. A 52/39/30 triple will extend your gearing range on both ends.

The first thing that I would suggest would be to measure the width of your bottom bracket shell. Many of the newer cranksets are 2 piece design and are specific to either 68 mm or to 73 mm bottom brackets.

dit

Never thought of a compact double since I have none on an of my road bikes. That would be a lot cheaper option and probably acceptable to wifie. It is possible that the machine is already equipped that way. I should know more later this evening. I have asked for some more details.

HillRider

Not stupid at all. The Cat Trike is a recumbent so the rider can't stand and use his/her full weight on the pedals and they are also quite a bit heavier than most single bikes so low gears are required. It's not a stability issue, it's a force multiplication issue. Trikes can climb at 0.1 mph with out falling over if the gears will allow it.

Note to the OP: I forgot that Cat Trikes have 20" wheels so the 30T granny may indeed be adequate.

dit

No problem. I should have mentioned it in the original post.