I posted this in the Mechanic forum too, but figured you guys have run into this more regularily. Can I put new 700C wheel set on my 1980 Nishiki that currently has 27" rims and tires? I just bought a set of Suntour Superbe Pro Short reach calipers and I have to place the brake blocks to the lowest adjustment to get them to contact the rim.

You may need long-reach calipers -- particularly in back -- but that's the only issue.

( Dumb Question ) Are 700C rims a smaller diameter than 27"?

yup

What is the advantage of 700C wheels versus the old 27"?

More choice in tires. Slightly smaller diameter makes for a slightly stronger wheel.

700c rims are approx. 8mm smaller in diameter than 27" rims, or more importantly they have a 4mm shorter radius, which is the distance between the center of the hub and the outer edge of the rim. Some of the older road brakes will reach, some won't. If you're already maxed out at the adjustment slot on the brakes with the 27" rims, those brakes aren't going to work with 700c rims. On an older bike I recently changed from 27" to 700c, I had to use BMX brakes on the rear to get the necessary reach. The old front brake worked, but barely. The BMX brakes I used are of the same basic design as a dual-pivot road brake, they're just a much larger version. I was able to pick them up at a local BMX shop for little to nothing, and they work just fine. I believe Harris Cyclery sells some BMX brakes they recommend for extremely long reach applications on older bikes..........The reason I went to the 700c rims is that I was looking for an economical, pre-built wheelset with a modern freehub that would accept an eight or nine speed cassette, and also I wanted to have a good selection of tires to choose from. So my advice would be if you're not upgrading to a modern drivetrain and you're happy with the 27" tires you can get, there would be no reason to change. If you're upgrading to an eight speed cassette or more, or you want the selection of tires available in 700c, then the change would be worth it.

Thanks for the excellent explanation. I think I'm going to stay with the 27s for now.

One other thing, if you go to 700c rims you'll probably need to cold set your frame so that it has rear dropout spacing to match a modern road hub (130mm). That's also going to mean a lot of changes to your drivetrain. That is, unless you can find a 700c wheelset with a hub to match the existing spacing on your frame. Or you could always build your own wheels, or have them built, using a hub to match your frame's dropout spacing and whatever 700c rims you choose. Problems, problems.....

Which uses slightly less material to make, but costs slightly more, so you're getting slightly screwed in exchange for the slight convenience of the metric system. I don't know about you, but I feel slighted...

It isn't that hard to find older 700c wheelsets all ready for 120mm or 126mm spacing. Even if that isn't desireable, all one needs to do is change the axle.

USAZorro, you're saying use a 126mm or 120mm axle in a hub body and freehub that's designed for 130mm spacing?

You can easily shift spacers in an older six speed hub, but I'd imagine the body of the cassette on a modern 130 ten speed freehub would simply be too wide to do this. Anyone who has actually done this can feel free to correct me. It's never even occured to me, actually, until this conversation. None of my bikes are at 130, even the mountain bike. You can still find freehubs at 126, for six/seven speeds, if you vastly prefer a freehub. In general, I'd just find a decent old freewheel and go with a freewheel hub. These can quite easily be respaced, provided you have a stock of hub spacers. The wheel may need a re-dishing. Not that hard, at least not with a dish tool and a truing stand.

700 wheelsets for older frames (read: narrower rear spacing) are not that unusual. Most tubular wheels were that size, and many older frames/brakes have both the clearance and the caliper reach to accomodate both sizes.

I personally would not cold set a frame from 120 to 130mm. Might go about 4-5mm tops.

There are lots of older brakesets with a decent reach; modern frame design seems to tend towards less clearance between the frame and wheel, hence the shorter reach brakes.

Freehub - never mind. I missed that detail.