Bruce27

Hello Folks,
With the wealth of knowledge here, I hope the forum can help save me cranking time.... .
I'd like to put 700c rims on this bike as it's my planned rider for 2024...wanting greater tire options. I looked thru older threads and a person did mention the oem dia-compe cantilever brakes on this bike fitting a 700c rim.
Is that the consensus? Is it really as easy as a brake pad adjustment for these dia-compe brakes to work on a 700c?
Thanks in advance.

Kontact 

Take a look at your brakes. Does it look like the pads can be moved down 4mm?

albrt 

This is the correct answer.

RiddleOfSteel

You should be just fine with those old Dia Compe levers, or either of the Shimano MT62 or MC70 near-twins as all allow the arms to be leaned out and pads angled down to make them hit square 4mm lower. No more fidgety than any other canti adjustment. I've done it on my '84 620 with 23mm wide rims (Pacentis), and with Campy Ergos (or Tektro R200s)--ok, and new pads--the stopping power is great. It fits honest 35mm tires (these are Compass' Bon Jon Pass, bought well used) without fenders, so if you want to run some rain protection, dropping to true 32mm tires or so is a good idea. Love the ride with 35s, though. Very sweet, athletic frame with top-of-the-line manners--a baby 720 for all intents and purposes, and worthy of good rubber. If you're planning on keeping it road, then finding some used or new Compass/Rene Herse tires (Stampede Pass 32s or these Bon Jovi 35s) will be worth it. Soma Supple Vitesse EX for the next rung down in price (and often enough on sale) but still with a great ride. And of course, the workhorse Pasela for a good ride and a nice price.

Bruce27

Thanks RiddleOfSteel . Good to know you were also able to use the oem dia compe brakes going to 700c. I'll start with 32mm tires but 35mm sounds interesting.
That's a nice 620 you have.

RiddleOfSteel

Thanks! I failed to mention these are Shimano MT62 cantis, but the Dia-Compes are the exact same in architecture (triangular arm design, pivoting and articulating brake pad), so you should have zero issues setting them up. I still have the stock Dia Compe cantis, and would not shy away from running them on these 700C wheels if I wanted to.

dddd

I've done the 27-to-700c change on a 1984 720 having Shimano MC70 canti's.

What I encountered was a bit complex, and the braking leverage/power increased quite noticeably.

Rim width is a factor, as is tire width!

The rim width comes into play firstly because a narrower rim increases the pad-dive angle (which has already been increased by reducing the rim radius by those tiny 4mm).

The increased pad-dive angle reduces clearance between the edge of the brake pads and the sidewalls of the tire.
This sidewall clearance is further reduced by a wider tire jutting outward from a narrower rim. So pad geometry during setup becomes more critical (your adjustment to the pad's position/angle need to be done more precisely, to what I would call very high standards).

Due to the above considerations, I used 25mm-wide Mavic Module4 rims, even though my choice of tires was only 28mm wide.
The wider rims also moderate the increase in braking leverage caused by the lower pads, and with Aztec pads my braking is still borderline too sensitive using RSX STI levers and a shortened (from stock) straddle cable in front.

Wide rims with tall/broad brake tracks would be ideal in this case, for ease of setup and what I will call best braking.

52telecaster

I found cr18s pretty useful in these situations. Wide enough to make t a little easier. Mine was a 720 and extremely fun to ride.

Bruce27

Thanks!. This would make it easy.
I do have a set of Shimano BR-M732 cantis I've been holding for this conversion but if the dia compe work, I'll try them out first. I'd welcome a comparison between the Shimano with dia compe. I will say that the stopping power on my rear wheel right now leaves a lot to be desired.
Are you happy with the MT62's?

Bruce27

I'm going to be switching from cr18 27" to cr18 700c. Thanks for this.

Bruce27

Very good points dddd. I will be trail riding this bike so I want to put 32mm tires as a minimum. I can only fit 1-1/8" max tires on the front right now.

RiddleOfSteel

I am definitely happy with the MT62s. I have black Kool Stop pads that replaced the old stock blocks. I was using a mid-'80s Shimano SLR brake lever initially, and brake power was alright. Switching to the Ergo levers was a big improvement. Tektro R200 brake levers are essentially the same thing (profile, body shape, brake lever blade, lever ratio), so if I wasn't using a Campgnolo shifter (like if I ran down tube shifters), that's what I'd use.

Some brake systems work well together, and others look good on paper but are meh in use. Doubly so for us taller and/or heavier riders. Machined brake tracks can aid in pad bite via increased friction, but I've had (and still do have) smooth-sided rims (think Mavic MA2) that worked beautifully with Kool Stop pads to deliver as strong a stopping experience as I could dish out. All that to say, you may be fidgeting around with things to get something satisfactory, but the Shimano units are sturdy and good pads always help.

52telecaster

Cr18s grab really well too. Personally I prefer the dull silver to the polished.

polymorphself 

Really awesome rim, I’m happy to have mine. Lucked out on a pair a few years ago when they were impossible to buy, not sure what availability is like now.

52telecaster

That is a tad crowded.

polymorphself 

Ended up in some mud that was more akin to quicksand. Had to pull over and get it out with a stick. 32’s under 45mm fenders but no amount of clearance was saving me here.

Bruce27

I still need to test ride but the dia compe's work. This looks like something I should have done when I was in my 60's. Now I'm going to be tempted to try 35's someday...sooner rather than later. Thanks all.