Classic & Vintage - Who's good with wheel sizes/fitment?

So the bike I just built up for my girlfriend has 26x1 3/8 tires with crappy steel rims. I'm hoping to lace decent 700c rims to the hubs and put on decent tires in order to give the bike a nicer and more effortless ride. Please correct me if this won't make much difference. The space between the tire and fork crown/brake bridge measures close to 1". ...Keeping in mind I'm not trying to fit 700x23 tires. I'm looking to put something larger and "comfortable" on there more similar in width to the 26x1 3/8 on there now.

Just for the sake of possibly bringing humor to some of you, I'll let it be known that this may well end up being a cheap, heavy gas-pipe C.ITOH girls frame with 7800 Dura-Ace cranks and brakes, decent aluminum bars, decent 700c rims laced to the stock crap hubs(narrow sizing on front hub and Shimano 3sp rear), nice platform pedals, and big crappy cushy 2lb seat. Totally funny build, but she likes the ride and it gets her out on a bike with me, so that's what it shall be. :P

Hundreds of dollars worth of parts on really low end 70s frame with heavy seat - $?00
Finally finding the goofy/crappy bike your girlfriend likes and will happily ride with you - :)

Hmmm....

Going from 26" rims to 700c is actually quite a difference. Especially considering the brakes. Let's say your 26" rims have a diameter of 590mm and you switch to 700c which has a diameter of 622mm. You'd then need to move the brake pads 16mm (over half an inch) upwards, this being the difference in rim radius between the two sizes. Make sure your brake calipers are able to accomodate that.

Even if the rims and tires fit and the brakes can accommodate, you will change the gear ratios to higher (less effortless) and may lose the option of fenders.

I don't see what this change accomplishes.

The Dura-Ace brakes that I'd put on it actually don't reach the brake surface of the 26" rims. I'm sure they'd be fine with 700c rims. I'm just concerned that I might not have room for the tires. I'm hoping someone will have a good idea of the fit before I spend an hour+ re-lacing a wheel and money on tires just to see if it'll fit. The rear is spaced at 120mm or less so I can't really shove my 130mm hubs in, and the fork has a strangely narrow spacing so a front hub won't fit in either.

I think careful measuring will answer that. If it will be so tight a fit that measuring isn't good enough, then maybe that is too tight to be practical.

Or, can you remove the locknuts and spacers from some 700C wheels and thus squeeze them into the dropouts, to check?

There's nothing wrong with staying with 26" rims (new, lighter, aluminum ones). If the bike is mainly or exclusively going to be used on paved roadway, then I suggest finding tires with as little tread as possible. Specialized used to make 1.5" slicks that were really nice, but it may be that only Schwalbe (Kojak?) does now.

If you want to change to 700 rims, then measure from the centerline of axle to the brake mounting bolt location, with some precision -- like to the nearest mm. Subtract 311 mm, and that's the reach that you need. If this reach is lower than 45 or so, make sure that you have sufficient clearance for the wheel and tire at the fork crown, and rear brake bridge and chainstay bridge -- a 700 x 35C tire mounted has a diameter of about 700 mm, so 350+ mm needed, plus 10-12 mm more if you want fenders.

There's nothing wrong with high-tensile steel, but putting Dura-Ace brakes on such a frame is like lipstick on the pig, IMO.

Quick question: Why hasn't everybody switched to using ETRTO (or ISO5775) rim sizing a long time ago?

Saying a rim is 26" doesn't tell me much - there are at least four different rim diameters in 26" which need their own tire sizes. If you say "my tires are 38-584", on the other hand, I know precisely what the diameter the rims are and what tires you can use.

Actually switching to modern 26 inch rims like on most mountain bikes may be better pretty much a wheel change and with 1.0 rims and 1.5 slick tires you should come out about the same. You could run 700c's on most vintage 26 frames but it will be a tight fit and you will lose the option of fenders and may need to change brakes. I have done this on a couple of builds and it worked alright but significantly changed the handling of the bikes from laid back cruisers to much harder and twitchy bikes and they never felt quit right.

This a 26 inch wheeled Schwinn Speedster frame and the 700 wheels just bolted right in as did standard brakes. Roger

Thanks, everyone. I've got some measuring to do and I guess a couple different wheel sizes to consider.

Even if the rims and tires fit and the brakes can accommodate, you will change the gear ratios to higher (less effortless) and may lose the option of fenders.

I don't see what this change accomplishes.
I was hoping to accomplish dropping some weight from the bike, dropping rotating weight(which I've read makes the biggest difference) and getting some better riding tires on the bike. I'm Much more familiar with 700c tires than things in the 26x1 3/8 type variety. Also, adding the Dura-Ace brakes(that I already have waiting for a bike anyway) should greatly improve braking power over the cheap generic steel POS brakes the bike has now. I also have the rims. I'm just looking at buying tires and probably spokes for what I'm hoping would be a decent upgrade over stock.

Or, can you remove the locknuts and spacers from some 700C wheels and thus squeeze them into the dropouts, to check?
That's a fantastic idea! Thanks.

Sun CR-18s in 590?

Tried this! 27x1 1/4" on a Raleigh "Sport" frame (low cost, Asia-made version of the Sports). Vertical clearance was really close in the [non-matching but still 26x1 3/8] fork; I ended up moving all the parts to a more suitable frame. Would've been comfortable with 700c.

267784

On my Miyata 310; I am switching from ISO630 to ISO590 to gain some fender clearance for a bike that will be used for commuting. Going to ISO622 did not gain enough clearance. I am using a set of Suzue sealed bearing hubs 36/40, Sun CR18 rims and Wheelsmith SS14 spokes, with Kenda K40HP (90psi) 37-590 tires. I am using Tektro R559 brakes, which provide plenty of reach.

I strongly recommend against the ISO559 rims that zukhan1 suggested because you'd need to make brackets for any type of brakes to reach the rims.

Replace the steel rims with Sun CR18 rims in ISO590; available in 32h, 36h and 40h.

I put 622 wheels on a frame meant for 590s, there was room for a 23 or 25mm tire on there and no fenders... didn't really like that bike too much, I'd recommend just usnig the venerable CR-18 in 590 and buying some modern long-reach brakes to improve the stopping power.

You are assmuing she'll like the ride of 700c rims, that's a big assumption if she likes cruising on 26" wheels. When you say she likes the ride, it may be she what she like is the smaller, wider rims. I think you should reconsider a lightweight 26" wheelset and quality tires.