'94 Trek 520, tires?
 

I picked up a second hand 1994 trek 520 several months ago and have been using it as a commuter as is. I am starting to plan for some weekend touring (mostly pavement with some light gravel) and want to replace the tires as they are pretty old and showing significant wear. Everything on the bike is original, including (i suspect) the 700x28 tires. The rims are original mavic, inner diameter around 14mm according to my ruler.

Any suggestions for tire and tire size?

For a tire size I'd suggest sticking with the 700 x 28 size if it hasn't caused you any problems up to now. If you're not too heavy and you won't be carrying a lot of gear then that size should work. MY bike and me weigh in at 220lbs and I've ridden 28 tires with no issues, and at times I've had 10 more lbs of gear with me. I have a touring bike and currently use 700x35's on it carrying 15-25 lbs (credit card touring). A Trek 520 should be able to easily take wider tires than 28's if you want to go with a larger size tire.

Tire type. Not sure about gravel riding, someone else can chime in on that, but for road riding I've been using Vittoria Randonneur tires - easy to get on and off the rim, puncture resistant, and has a little bit of tread for wet surfaces. Others here will recommend Schwable tires, I tried them but they were tough to get on and off the rim, so I returned them to the LBS. They are expensive, too.

If you want convenient and inexpensive, those Blackburn 700x35 tires from Walmart are a pretty good deal. $25 and they last forever.

Big fan of Continental Gatorskins here, and I like the 28 width. Even on my 1983 Trek 520.

I could not find any specs on the rim width for that bike online. If your rims are indeed 14mm inner width, 28mm is the largest recommend tire.

I am a big fan of schwalbe marathon plus tires. Only one sidewall puncture in 8 years and many miles of commuting and touring. They are stiff and difficult to mount, but not crazy difficult. Expensive? Not bad if you get them from "across the pond." Chain reaction cycle has them for $35/ea albeit with a $100 min to qualify for free shipping.

The OP's rims are regular old 15C. He should be able to run up to 35s with no problem. In today's fat tire world that old 2x rule has been ignored and debunked a gazillion times.

I like the plain Schwalbe Marathons (with Green Guard) for pavement touring. Roll well, not too expensive and good puncture protection. I have the 28mm version on my road bike front wheel and rode 36 miles yesterday. I bought them in that width to replace my road bike tires when the original tires wore out. I have done loaded touring on the 40mm wide Marathons on one of my touring bikes.

I do not use the Plus variety.

A number of different Schwalbe tires have the word Marathon in the model name, thus I cited my version have Green Guard to differentiate them.

x2 for Schwalbe Marathons (with Green Guard). I have a '95 Trek 520 and am running those in 35mm. Fast rolling and very comfortable with or without a load.

Trek 520 tires
 

I have a '94 Trek 520 that I bought new. I currently run with 700x38 Schwalbe Marathons on Rhyno Lite Sunrim wheels. If the 700 x 28s are working out ok for you on the roads you ride, then stay with what works, but around here on our not so great road surfaces the 28s probably wouldn't hold up very well. That would be especially true carrying a heavy load of panniers etc. '35s would probably be fine too.

If your rim inner width is 14mm, I would stay with 28s.

I am a little surprised at all the recommends for 28mm. People acted like I was weird when I put 28mm on my Windsor Touring way back when. Also, didn't the 520 come with 32s and many (most ) touring riders fitted wider tires? I'd have expected most folks to have suggested 35s. They seem to be the norm to me.

Did a LOT of research on this problem a couple of weeks ago and ended up ordering Schwalbe Marathon Evolution Supremes. They just came yesterday so I haven't tried them yet, but all roads seemed to end up there for touring tires. I picked Supremes because they have the best rolling resistance, I ride smooth pavement and don't tend towards getting flats. Different criteria would have led to a different conclusion.

The OP wants to use this for commuting and weekend longer rides on mixed surfaces.

There is 0 reason to use 28mm tires. That rim width can handle wider and quality wider tires will roll fast and be comfortable.
0 upside for a 28mm tire.

Generically for touring, I agree, but for his rims I think 28s look better.

Earlier I tried to look up his bike on Bikepedia, but I got a security warning on that site so did not open it. Now as I type this, I have not looked at the vintage trek site for years, so took a glace to see what that says on a 1994 520. That bike came with 28s. It does not say how big a tire the frame or fork will fit with or without fenders, so that is a question mark. But the 94 has canti brakes so it likely has more room in the frame than a road bike. That said, I am still focused on the rim inner width for my thoughts on which tire for his bike.
http://www.vintage-trek.com/images/trek/94/Trek94.pdf

My light touring bike is 700c, has 37mm tires. Medium touring bike is 26 inch, 40mm for mostly paved routes but rail trails warrant 50mm tires. My heavy touring bike is 26 inch and use 57mm tires. That said, my road bike is shod with 28mm and rando bike with 32mm tires.

https://velobase.com/ViewComponent.a...e9ff1&Enum=107

The stock rims have a 22mm outer, so most likely a 16mm or 16.5mm inner width. Throwing a 40mm tire on that would be perfectly fine, so a 37mm or so would obviously also work without any issue or even concern.

Continental Grand Prix Urban is tested for very low rolling resistance for a tire of its size. That's probably what I'd get today if I was shopping for a commuter tire. Apart from the low rolling resistance, they are nothing special. But hey, it feels good to go fast.

https://www.rei.com/product/152159/c...E&gclsrc=aw.ds