jonalonathen

I can't post any pictures because I'm a newwbie but I fit 35c tires on my 1983 Trek 720 w/out fenders and the 27" rims. I recently converted it to 700c and have room for more rubber! Not the subject of this thread I know but the 700c conversion worked just fine with the Dia-Compe GC960 brakes that came stock on the bike. I had trouble at first but I was using a crummy set of wheels that were very narrow 19.6mm outer width. A new set of Koolstops and wider TB-14 Rims later and I've got plenty of stopping power and properly aligned brakes!

Jasongrace313

21" 1985 Trek 620 Cirrus with 700x41 Surly Knards. I have Schwalbe Marathon Supremes in 700X35 which are my favorite tire, and I just ordered some 27 1 1/4 Marathons to try as well. I have them in 26X50mm in on another bike and they have been bulletproof with good rolling capabilities and while not supple still very predictable. I'm getting the cockpit and fit figured out then I'm going to get into the brakes and drivetrain.
So far its a fun bike to ride, I haven't noticed the flex I have on my road bike under torque but I guess I'll have to pay attention to compare. My Lemond road bike seems to call my attention to its flexing.

tomtom50

I have 700c x 42 tires on a 1985 720, no fenders. About 2mm clearance at the stays and 4mm from the tread to the fork crown and rear bridge. The conversion to 700c worked with the original BR-MC70 cantilevers, no adjustment to spare.

I also have a 1983 620 running 700c x 37 with fenders. The brakes are 80's mid-reach Dia-Compe sidepulls. Newer dual pivot brakes gave way less fender clearance.

Gary12000 

I’m surprised no one has mentioned the Helicomatic rear gear cluster/hub, both mine and my wife’s 720’s came with 27 inch wheels and both had the helico hubs.. in my opinion this is the weak point of the bike, I’d be interested if others have retained the set up or converted to a different system… we kept ours, the shifting can be finicky, fortunately we are riding mostly flat ground, so we don’t shift that often…

sd5782 

I’ve got the heliocomatic covered on a Peugeot UO14 that I may part out. I was hoping to find a sad case 720 or long wheelbase 620 with a dead rear hub that someone is selling cheap that I could use it on. I guess I can dream. Actually a 728 came up a month or two ago maybe 60 miles away, but it was gone in a flash.

tomtom50

Gears are so much better now, and half the improvement comes from Hyper-drive-style shaped teeth on the cluster. No Helicomatic has shaped teeth. I suppose most people riding old Treks are retrogrouches but my grouchiness stops at the drivetrain, newer is good.

On my 720 the 700c wheels have a 10speed freehub. The derailleur is a Deore M591, the shifters are Micronew 3X10 speed integrated shifters I bought off of Aliexpress. ($60, perfectly good quality, Shimano costs a fortune). Frank Bertoesque gear range. Click shifter compatibility gets complicated, let me know if you want more details how to make it work on the cheap.

The 620 is a home conversion mid-drive ebike (TSDZ2, great unit). That means 1X shifting, the rear wheel is Shimano freehub and 11 speed 11-46 Shimano cluster. I went with Sensah for the derailleurs and integrated shifters, $110 off Aliexpress. Shifts perfectly. Amazing, really. 2nd to 1st if 37 to 46, click and it is done with never a mis-shift.

Unless you really want all-original dump the Helicomatic and go with a modern drivetrain, and convert to 700c while you are at it. 700c means lots of tire choice and more clearance for modern wide low-rolling resistance tires. They are touring bikes, give them touring tires.

Don't worry about 126mm vs. 130mm at the rear axle. 130mm fits fine into a 126mm spaced frame. It isn't worth the bother "cold-setting" the frame, although you can do that if you want.