I heard that T.A. made 72 tooth chain rings. I'm curious if anyone can confirm this (or better yet has a picture). I've seen plenty of one-off pictures, but do 60+ tooth chain rings ever some up for sale?

For kicks I worked out the gear inches of my Mercian... fourteen tooth rear, 60 tooth front, on 27s. That's about 116 gear inches... would be a kick to get a 72 (since I have a pretty strong stoker!).

Anyone have one kicking around?

I guess the small-wheel bike market has kept big chain rings in production!

I was able to find this 62 tooth chain ring. Not sure if it will fit on a standard spider though.

https://www.racermateinc.com/product...th-chain-ring/

and Bike Friday has chainrings up to 60 tooth

https://store.bikefriday.com/index.php?cPath=67

Small wheeled folding bikes will usually have larger chainrings to compensate for the small wheel size.

EDIT:

Or you can get really stupid (65T to 90T):

https://trisled.com.au/product-catego...uards-rollers/

Hey, can I ask a total n00b question, and one that's off topic as well?

I can understand brake levers on the rear handlebars for a "hoods" hand position, but what does that brake cable on the rear handlebars do on that Mercian tandem?

Thanks.

Could be a rear hub brake? The non-drive side of the rear hub is massive and it looks like the cable runs down there.

The fat rear hub could be one of several multi-speed hubs. The grand daddy of them all is the Rohloff which costs about a grand. There's also Nuvinci and Shimano Alfine and Nexus hubs.

I have a 65 tooth chainring on Schlumpf Mountain Drive on a recumbent trike. I was going to replace it after 27K miles on it but the price at a recumbent shop was $170 so I figured it would do as is.

Looks like a drum brake on the rear, popular with tandems before hydraulic discs made their debut.

The bike has three brakes: front and rear cantilevers, and a rear disk brake, and is set up so there's a lever for each brake.

TA chainrings

they made 68T for sure

Apparently for the equivalent 49D, 53T was the largest Stronglight made
https://www.classicrendezvous.com/Fra...loy_cranks.htm

Oh, have fun with your TA chainrings.

Here is the cheapest 70T ring that I've found.
Bikingreen 70T BCD130 Recumbent Chainring CNC 7075 Road Fixie black TT Track | eBay

Both Driveline and Vuelta make a 60T ring for a reasonable price.
mr_ride DRIVELINE 10,11 speed, Road Bike - Racing Chainring 60T BCD 130MM BLACK | eBay

VUELTA SE 110mm 60T SLV | eBay
Vuelta SE Flat 130mm BCD 5-arm Road Chainring | eBay

Here is a mixed 110/130 bcd, 60T
Brompton BCD 110+130 60T Chainring also fits Schlumpf Speed/Mountain Drive (ATS) | eBay

For the TA,
54T
TA Chainring 54 Specialites Criterion Vintage NOS | eBay

57T
RARE VINTAGE TA 57T 3/32nd ALLOY CHAINRING IN GOOD CONDITION FOR MOULTON or TT

You could ask Biking Green if they could make a ring without machining the spider (or machine a custom bolt pattern). I believe the rings are hollowed a bit on the back side... solid might be better.

You may also be able to make a custom spider to fit from your TA to a 110BCD or 130BCD ring.

I have also seen large steel exercise bike chainrings on occasion, often as a solid plate that could be drilled/machined to fit your TA.

I do have fun with my TA chainrings, and have for years.

FWIW, my 1984 Gitane tandem came with a 54T Stronglight 99 large ring. And the cranks Stronglight made for BioCam came with a 60T ring.

Also consider changing out your freewheel or cassette.

For a 54T chainring:
14T Freewheel 3.86:1
12T Freewheel 4.5:1
11T Freewheel 4.9:1
10T Cassette: 5.4:1
9T Cassette: 6:1

For a 60T chainring:
14T Freewheel 4.28:1
12T Freewheel 5:1
11T Freewheel 5.45:1
10T Cassette: 6:1
9T Cassette: 6.67:1

For 70T chainring:
14T Freewheel 5:1
12T Freewheel 5.83:1
11T Freewheel 6.36:1
10T Cassette: 7:1
9T Cassette: 7.78:1

So, if you have a 60T chainring with a 11T freewheel or cassette, you will get higher gearing that your 70T chainring with a 14T freewheel. Even the 54x11 is almost the same as 70x14.

SRAM makes several 10T MTB cassettes. And the Capreo (and derivatives) are 9T cassettes.

DNP Epoch makes a 7spd (& greater), 11T freewheel.
12T freewheels are relatively easy to find on E-Bay depending on gearing you choose.

Anyway, after you get up to 60T, at least drop down to 11T on the rear... if not smaller before hunting for a larger chainring.

very good - I was scanning history sites, so 53 was the largest listed on a site for prewar 49 and postwar 49D.

and the 99 is not 50mm bcd outer...the others are

And here it is, removed from service as 54T is not compatible with my elderly decrepitude:

it's still classy

I live in monster hills, and go as fast as I need on 46T/12t.



but really big chainrings do make sense on tandems (130"). My buddy's Santana has a 53T/11t combo for tall gear.
On long descents, tandems can easily hit 50 mph, and with with their long wheelbase are stable at that speed.
A good drag brake is also a tandem requirement - rear rim brake on a tandem can easily overheat the tire.
And it looks like on the gorgeous Merc in the OP photo, the stoker gets the drag brake control.
My buddy's Santana has canti rim brakes and a disc drag brake but the captain controls it all.

The original pic looks like a drum brake. Note the torque arm on that chainstay. A disc drag brake for a tandem would have a really big rotor -- much bigger than in the pic. I think giving the stoker control of the drag brake is the most common setup.

Big chainrings are slightly more common among recumbents, due to smaller wheels. One of my lowracers has a 26" rear wheel, and I routinely use a 56T chainring. I've used a 58T before, but stretching the front derailleur between a 30T granny and a 58T big gear requires perfect setup. Some 'bents with 20" drive wheels come with 62 and 63T rings, but due to derailleur capacities they're limited to 39T granny rings. It's almost impossible to find big rings that are pinned, so shifting will be balky. If you're running a 14T in back, changing the freewheel will be a much more economical and better-working solution.

My buddy's Santana also had a drum drag brake, and he modified it for a disc.

Thanks for the third brake information and your patience with my brief thread hijack.

On topic: My first recumbent had dual 20"/406 wheels and came with a 63t ring. I replaced that, first with a 60t and then with a 56t.

Off topic: A disc brake makes a really lousy tandem drag brake, as it can't be engaged all the way down a long descent without the likelihood of overheating and loss of function.
If a disc brake is used as an auxiliary rear brake and is used for periods of slowing alternating with cool-down time, then that can work. Our tandem came with V-brakes plus a rear disc. I removed the rear V-brake and set up the disc (with 203mm rotor) as the primary rear brake. If we ever need more stopping power - for loaded mountain touring, etc. - I'll add the V-brake back as the extra brake for use by stoker.

Now with 11t cassetes, the higher gear ratio can be made with a little smaller chainring than when freewheels were 13 or 14t.

IN That era The Other brake on the Rear Hub was an Arai Drum (Drag) brake , It looks even bigger because of it's Large amount of Heat Sink.




...

Florian Schlumpf , in Switzerland , who also makes the Mountain Drive crank has Chainrings, for my Brompton I use a 130bcd 54t..

Hostel Shoppe sells Vuelta rings that go up to 60 or 62 IIRC.

And at the same seller--there is a couple others from single recumbent companies that are 72t and 80t I think.
Some company made a recumbent trike once that used 305mm wheels, but was intended as a "racing" trike and was geared pretty tall.
...
These trikes didn't use a front derailleur, do note. They were either compound-geared or just 1x8 or whatever.

I've experimented a bit on my Bike Friday.



That is the Bikingreen 70T listed above.

I've had troubles getting a front derailleur fitted, so currently "greasy fingers shifting", to maybe a 52T or so???

Rear end has a Sachs 3x7 dual drive (9 to 8 cassette).

I liked running the dual drive in direct drive mode (I thought it was most efficient that way). I would occasionally shift the dual drive, but rarely needed to drop the front chainring.