bulgie 

Hmm, I never thought of trying that. Sure would be easy to try, no welding needed. There are nice 29er tires that would fit in there, or some of the wider 700c tires could work. (You know those are the same thing right? Just different marketing terms.) If using the wider tires, best not to use the narrowest rims, though it'll probably work for a proof-of-concept test ride. Really fat tires on skinny rims have an unsettling way of flopping over to the side when cornering, especially at lower pressures.

You'd still have that horrible fork though. On our Twinn, we could get the brake to rub on both sides of the rim just by pedaling standing up. The fork was flexing side-to-side that much. Even doing a tight turn like a U-turn in the road, the fork blades would flop over enough for the brake to rub. Not confidence-inspiring!

Personally I can't see any downside to 559 26" MTB wheels, if the fork is sized for it. Yes it lowers your BB height a little, but we haven't scraped a pedal yet.

I think it all comes down to can you find a nice replacement fork with canti bosses on it already. Should be a somewhat heavy one for stiffness, with either an oversize steerer or a one-inch steerer with a heavy reinforcement in the lower part. Ours is a Tange-made Cr-Mo fork (not just Tange Tubing, but they also did the fabrication). The steerer has a heavier butt than a road single fork, plus then they also shoved a reinforcement tube up in the lower end of the steerer, so I'd expect it to be pretty bomb proof. Stronger than the Twinn fork anyway, by a mile I bet. Also (cherry on top) this fork came from a Schwinn MTB, keeping it in the family in a way, even though it was made in Japan. I don't know how difficult it is to find such a perfect fork, maybe we just got lucky, or maybe they're common as dirt.

Seattle has a shop (Recycled Cycles) that sells a lot of used bikes and parts -- got anything like that near you?

Mark B

Senior Ryder 00 

Hi,
Realizing that there is a personal attachment here, I wouldn’t go overboard with mods. First, get some decent alloy wheels & tires. If you can use the existing hubs that would be great. It looks like 700c/29ers will work. I’d also try the Tektro brakes or Mafac center pulls with aftermarket pads. Then, find a wide range FW and ride!

There are 3 or 4 co-ops in your area that my help you with this project. I volunteer at the NW Hub in Salem. We have a couple of people who like to preserve vintage bikes, if you are down our way.

My wife and I have been thru 3 tandems and several hundred miles over the years. It’s a great relationship builder.

Cheers,

Van

Jeff Wills

I was curious so I went looking. Yes, the Deluxe Twinn tandems of the late '70's had 26 x 1 3/8 S-6 Schwinn tires. Hard to find now. A 700C (aka 29-inch) rim is only 1 inch larger in diameter so a conversion to 700 x 38C tires is viable if the tires fit.

FWIW: I think the original spokes were "105 gauge" aka 12 gauge. The Twinns were heavy, awkward beasts when I moved them around the shop.

JacobLee 

Boy oh boy, so many cool ideas floating around here! Hard to keep ‘em all straight! I’ve got a couple of weird sets of 29er wheels and tires that I’ve built over the years for my Surly Karate Monkey that I can throw in there and just see if it sits right. Maybe give it a spin on flat ground with just a front brake. The rear spacing seems to be 135mm.

I was wondering about that flat blade fork. There sure are a lot of replacement forks out there, just not sure I’d want to alter the headtube in a way that I couldn’t undo. Maybe build a drum brake wheel that fits in that flat blade and see how it goes.

Yes, we’ve got some great co-op shops in Portland. I rarely buy new stuff anymore.

Thanks for the ideas and info! Much appreciated!

bulgie 

I'm sorry I even mentioned altering the head tube. It's not necessary for replacing the fork -- you can keep your existing Schwinn headset and leave the head tube alone. I only mentioned it because I sent the photo of my Twinn, which does have an altered head tube, done for reasons that probably don't apply to you. Just get a good strong MTB fork with a 1" steerer, in a suitable length for your existing head tube. For a gently ridden Twinn that stays on pavement, I think most any MTB fork will be strong enough (stronger than the existing fork).

Note, watch out for replacement forks with a loooong threaded section -- those should be illegal IMHO. They're trying to fit a wider range of frame sizes, but it's not safe having the stem expander tightening up in the threaded section, especially if it also has a slit for the headset "tongue washer", as they usually do. It's like the perforated paper on your utility bill, saying "tear here". Bad enough on a single bike, but with a tandem, not only are stresses higher, but the stakes are higher too -- two people who will go down if the steerer splits. The right amount of thread, roughly speaking, is the minimum that will work with your head tube length. It's not something with tight tolerances though; there's some wiggle room.

Let me know if you still have questions, I'd be glad to help.

Mark B

J.Higgins 

Yeah, Baby! Yeah! *channeling Austin Powers today*

I built a set of wheels using the Sturmey Archer front-dynamo/drum brake hub, and the 5-speed internal gear/drum brake rear. I was going to use them on a post-apocalyptic build over on Rat Rod Bikes, but got too busy with something else and now I'll just use them elsewhere. Thinking about making a nice winter-bike with them.

Dan Burkhart 

I converted my Twinn to 559 wheels and put a roller brake on the front. Actually have roller brakes front and rear. It originally had a drum brake on the rear.

thumpism 

This is a very real consideration. I've both found these on incoming repairs and had it occur with a replacement fork I was installing.

JacobLee 

Don’t be sorry for a second for bringing up the headtube mod! I haven’t thought about those Schwinn sizing issues in years, so it was good to revisit that stuff. I appreciate it! I was more interested in the idea of fitting an 1 1/8” headset in there, but again, I’ll be as conservative with the frame and fork as I can. Thanks also for the warnings about fork threading, as it’s been a while since I monkeyed with anything threaded. So thankful you guys are willing to share the knowledge. Lots of fun!

Jeff Wills

Jacob, I have a Schwinn "mattress" saddle that I can contribute to the cause. It's missing the seatpost clamp so you'll have to go fishing at Citybikes or CCC. I live in East Vancouver but work near downtown Portland so I can drop it off when I'm running errands.

I spent 5 years as a Schwinn mechanic out of a 12-year career in the bike business. If you need help, just ask. I have a couple projects in the works- what's one more?

JacobLee 

Wow, what a nice offer! There’s been one on craigslist for a few months and I’ve considered jumping on it, but never got around to it. Maybe you’ll consider some compensation?!

JacobLee 

Oh, and I’ve been corrected on the bike’s origin. My wife bought it at a garage sale in Sonoma Ca. and gave it to me for our 5th anniversary. How do I forget these sorts of things? California School for the Blind was in Berkeley when this bike was current, so somebody probably took it home when the wheels became unrideable. The sticker is a little faded, but it came from San Francisco Cycles on Stanyan Street.

Jeff Wills

Yeah- can you clone me? My employer seems to think I can do the work of two people.

JacobLee 

Ah, I just figured out that you weren’t talking about roller-cam brakes. I was trying to figure out how on earth you would do that! Now I’m on the same page. Do those stop it well?

Dan Burkhart 

Yeah, braking is ok for the casual type of riding I do with it.
I just put on the brakes I had on the shelf at the time which were the large im70 series on the rear and the 41 series on the front. I had full intentions of upgrading the front to the larger size but didn't find it necessary.
Here is a makeover video of the bike.

And another close up look.

JacobLee 

I’ve been trying to think of a good clone/tandem joke, but nothing’s coming to me.

bulgie 

Mmm, think of the rides we could go on.


An actual Twinn! I thought about flipping the photo so the chain would be on the right, but then "Coke" would be mirrored, and of course that's what matters...
But... one bungie holding 12 glass bottles? Advertising shouldn't promote such irresponsible behavior. Better bring a broom and a dustpan with you to clean up the broken glass. Ooh don't get me started!


So cheesy! Couldn't they have found matching shoes? (Yeah uh huh, that's what's cheesy about it.)
I think that's a Columbia tandem but the gurls are blocking the view, darn it.
That photo makes me wanna... straighten that bent-in rear fender.

JacobLee 

I suppose the Doublemint twins had to appear at some point. This isn’t going to help Jeff get his work done!

billnuke1 

I’m pretty sure that the stoker seat needs to be adjusted...

Jeff Wills

Seriously, folks... quit it with the distractions. There's work to be done!

thumpism 

Adjust that stoker seat. Somebody has to do it.

JacobLee 

Where were we? Ah yes, wheels.

Did a little swapping around and had good results with a pair of 26” Rhyno Lites with big ol’ 2.35 Fat Franks.






Next, I mounted a 700x44 front and 700x42 rear on a weird set of Velocity Deep-V’s on mtb single-speed hubs. Front looked great in the fork, but rear had to be deflated, and even with the derailleur removed and the wheel all the way back in the dropouts, it still rubbed on the fender arch.






I don’t own any 650b stuff, and the 2.35’s fill things out nicely, so it seems like some polished silver Rhyno Lites might be a good fit.

bulgie 

Front and Rear wheel size don't need to match, you know. Since 700c makes the front brake situation so much better, combining that with the 26" Frank in the rear sounds pretty close to optimal. Short of replacing the fork that is, or welding on canti posts, which will ruin the paint. That front Vainqueur brake (or DC knock-off, whichever that is) looks pretty promising, but you haven't tried it yet, right? Get some Kool Stop pads for it, eh?

Mark B

Jeff Wills

The bike is missing the chain tensioner for the timing chain. There are a couple available on Ebay. It's a unique part so it might be tough to find.

I like the look of the bike with the 26" wheels and the Fat Frank tires.

JacobLee 

15.2 shiny, red pounds!



I never noticed that the fender bracket had been broken off, or that the bb shell had been forged in hell!



Bottom tube is offset, I guess so that the idler pulley lines-up? Get-er-done!



It’s always fun to notice the little details. And damn, I haven’t held a one piece crank in my hand in a long time. Makes me tired just holding those!