Can we talk Tire clearance for a minute?
 

For Xmas I bought my 1983 720 a set of new wheels. Since I bought the frame only I feel I can take a little liberty in blinging it out. So my question is: what’s the biggest tire you reckon will fit comfortably and safely? Please see pics
https://cimg9.ibsrv.net/gimg/bikefor...fa4bb6ffa.jpeg
https://cimg0.ibsrv.net/gimg/bikefor...5e88bc415.jpeg
https://cimg1.ibsrv.net/gimg/bikefor...52ca61089.jpeg

First- shoot a message to Bill about getting the title changed from fire to tire.

Second... I know it's apples and oranges and stuff, but I have 700x35 tires on my 1985 720 along with SKS fenders.

How else are you planning on blinging it out?

https://www.renehersecycles.com/shop...ire-fit-gauge/

The answer to all tire sizing questions...

-Kurt

For those of us who live in California, "fire clearance" has a definite meaning.

Whooops. Mad California Love to y’all & sorry for the typo
https://cimg2.ibsrv.net/gimg/bikefor...d30c81ebff.gif

Hahn's gauge is pretty sweet. I'm tempted to order one, even though I don't have any builds/conversions on the horizon. :thumb:

In the meantime, my tried-and-true method is to throw on a tire, measure its actual width, and then use allen wrenches as feeler gauges to determine how much more room I have above and to either side of the tire. For example, if you have a 25mm tire, 5mm clearance to the chainstays, but only about 4mm clearance upward to the brake caliper, you're limited to a 28ish tire.

Thread titled fixed

...if you already know all this, I apologize, but "generally" the bigger you go in tyre size, the heavier your rotating weight gets. So there's a point at which the comfort and stability provided by a larger, fatter tyre starts to act a cross purposes to riding pleasure. For me, that's usually in the 700x28-32 range as a practical maximum, and I do have some wheels I built with newer lightweight rims that roll OK with Panaracer 27x1 1/4 tyres on them.

I have my most pleasing results with tyres like the old Rivendell Ruffy Tuffy, or some of the newer versions of them (also made by Panaracer). They're relatively puncture resistant, capable of holding high pressures with a modern hook bead rim, and mostly average in the 28-32 mm widths I prefer. they seem to do pretty well in the rolling resistance department. Anyway, this has been my experience after a lot of experimentation.

I have an '83 720, and that frame won't take much wider than 700x32 or (27x 1 1/4).

Mine has 27" rims with 1 1/4 rubber and that fits under fenders and feels very planted on crushed stone MUP paths. 28mm do a very nice job but on an all day ride I like the extra volume of a 32.

Without fenders I bet you could fit 35's without any drama, but I think that's the practical limit.

OP, Are your wheels 700 or 27"?

Is that wheel dished correctly for the spacing? Can't tell whether it's real, or if it's parallax.

It would have originally been set up for 27 z 1 1/4", the touring standard of the time. There weren't fatter tires around then, which seems to surprise people. First touring bike that I recall with slightly fatter tires was the original Specialized expedition, which came out a year or so later.

Anyway, as others have said, with fenders you're realistically looking at 1 1/4" or 32. 35mm probably possible w/ no fenders. Going to 700 may give you a bit of a hassle WRT brake adjustment, but it's usually doable in bikes of this era.

There's really no substitute for actual measurement.

Unless the wheels and tires are fancy-light, 700x32c is about the upper limit for me.... bigger than that and the rotating weight of the tires starts to feel pretty sluggish. Even then, tire choice can make a difference: I had 700x32xc Continental Gatorskins on my Centurion Semi-Pro and the bike felt _terrible_ to ride..... then I switched to 700x32c Panaracer Gravel King slicks and they feel great..... a little bit less weight, a bit more "souplesse" in the sidewall, and the feel of the ride was totally transformed.

I wonder how much of how our bikes feel really comes down to wheels and tires....

Adequate tire clearance in general terms - there is no set answer. If you keep you wheels true and are willing to replace tires sooner as they stretch, you can run them very close to hitting the chainstays, fork blades, brake caliper'brake bridge and fork fork crown. Granted, there is more risk of something sticking to your tire and hitting/wedging itself into those close spaces and possibly causing a crash. If you do not want to have to keep a close eye on your tires and/or you wnat moer security and/or you want freedom to break a spoke and still ride home, you need more clearance.

This is completely a judgement call and the criteria is what is acceptable to you. I've done rides on gravel roads pushing the limit with very close clearances and brand new tires knowing full well that was not a long-term solution. I rode a couple of winters on a frame that was pure early '80s race (think very, very close) with 25c tires and cut up fenders. Got tired of that and put the parts on a Schwinn LeTour and enjoyed the huge clearance sail.

As a long term solution, I am a fan of using bikes that were designed to handle the tires I want to ride. For many years, this meant for me that my commuters were generally sport bikes designed to 27" wheels on which I would run 700c. I've had 5 frames custom built around the tires I specified.

Ben

Measure the width of the chainstays/seatstays/fork, subtract 8mm (4mm for each side), and you will have your max tire width.

No 720 however my 520 w/cantilever brakes is fitted with 700x32 (actual width measure 30mm) and mudguards. Its a tight fit.

Moi aussi, though change is to was. I don't recall how tight the fit was. I ran with SKS something-or-other P45 fenders.

A typical camera lens is a single optical opening, the camera is slightly off-center... But I would check the rear wheel with a dishing tool before any tire is mounted.

It's us with two lenses that have the problems.

This past year I ran Vittoria Zafirro 32’s on a similar vintage 620. They fit with good clearance and these are wider than you would expect for 32’s.

They provide good comfort but when riding a hilly century I noticed the extra mass. I am going to run 28’s next year.

Go to local hardware store, buy cheap plastic vernier caliper (about 5 bucks) and measure distance between stays where tire passes through them. Allow 3mm each side for tire clearance for a total of 6mm and subtract this from the caliper measurement. This will be the absolute max tire width for that frame.

I find it interesting that people bring up "sluggish" feeling wheels on a bike that was built for touring... so a 720 at a relatively weight conscious vintage touring build and still with racks... figure about 25 pounds (if not more). Add on to that the chainstays are 47cm- with a total of a 106.2 wheelbase... The extra mass of 32/35mm tires is making the bike sluggish? The bike was designed for the stock wheels to fit 27 x 1 1/4" tires- which is larger than 700c x 32 (especially as a 630mm 27" wheel is larger than a 622mm 700C wheel, and 1 1/4" is *nominally* 32mm). Wouldn't the rotational mass be more evident with an extra 4mm from the hub, and larger tires (larger circumference means more rubber, meaning more weight). Specialized's 27" touring tire offerings of the mid 80s were the Touring at 1 1/4" and the Expedition at 1 3/8" which is *nominally* 35mm.

My 1985 Trek 620 is currently wearing Sand Canyon 27 x 1 3/8" tires, but that bike doesn't have fenders. I do have plans to change this bike over to 700c x 35 tires with Honjo fenders- I'm fairly confident it'll all fit safely.

Again, my 1985 Trek 720 is currently wearing 700 x 35 Compass Bon Jon Pass tires with SKS Chromoplastic fenders.

https://live.staticflickr.com/4633/2...ecd56e20_o.jpgIMG_1724 by Dave The Golden Boy, on Flickr



Additionally, to get the full benefit of higher volume tires- one would not be riding them at high pressures- When someone suggested that I run the Compass tires at 35, I thought they were joking- or on crack. But sure enough, they rolled really nice at 35- I usually ride both the Compass and Sand Canyons somewhere south of 50PSI- and I'm more comfortable at running the Compass tires lower. This has also carried over onto the Paselas I use on my other bikes where I'm running 1 1/8" and 28mm tires- I'm cool with running them around 80 or so- whereas I used to feel I needed to be within 10PSI of the limit.

Those tires are classic

Fat tire syndrome.

https://cimg3.ibsrv.net/gimg/bikefor...1e16ec03b9.jpg
These days everyone including my pooch want big fatso tires.

With my (limited) experience with fitting much wider tyres to a 70's roadster, I'd say use the ETRTO sizes. I don't know how precise those are exactly, but they are the actual size in mm's and it corresponds with your own measurements of the frame. I went for maximum width and ended up with 1-2 mm space between the front tyre and the fender stays, which is going to be a bit of a problem if the wheel gets out of true on a long ride. Plan B was to replace the fender stays with ones that go round the outside, and plan C to return the tyres and order a size narrower. But it fits because ETRO sizes were precise enough, at leat in this case.