Pondering front disc conversion
 

My "#1" road bike is a 2000 Litespeed Vortex that I have ridden for >100k miles. This is a great bike - fits me well, rides beautifully, and I can't see myself replacing it as long as I continue to ride on the road. A few years ago, I added a set of Campag Zonda C17 wheels. The nominally 25mm Rubino Pro tires I've always used measure out to an actual 28mm external diameter on these wheels, which makes for a comfy ride, but makes the spacing for the Ouzo Pro fork and the Chorus front rim brake very tight - 1-2mm all round. This has worked OK for the last three years, but I'm not wild about the minimal clearance. A wider fork would help with the sides, but likely not with the brake clearance at the top. Clearance on the rear tire is better and not a concern.

So, I'm thinking about a front disc conversion. I could do this with a new fork, a new front wheel and a cable-op disc caliper. The fork is easy (though not cheap) - Whiskey and Ritchey both sell 1 1/8" carbon forks with the appropriate rake and C-to-A measurement. Wheels? I've been looking in vain for a Zonda disc front wheel - I could get a full wheelset for $500 and offset the cost by reselling the rear wheel, I suppose. There are any number of flat-mount cable-op or cable/hydro hybrid calipers out there. I used to use Avid BB7s on my old MTB, and don't share many people's aversion to cable-op discs.

So, the issue is purely front tire clearance - the rim braking itself is perfectly fine as it stands. Here's the question though - I'm not going to see any change out of $1000 for what might be considered a bodge. Apart from it possibly looking funny, are there are actual downsides to a front disc/rear rim setup? Half the cars I've owned have been front disc/rear drum, given that the front bears the brunt of the braking, and it's not like the rear brake can't lock up the wheel in any case.
Any thoughts or opinions? Tx

If the bike doesn't work well enough for you as it is now with everything in proper working order. Then get another bike that will more closely fit your desires and intentions.

Maybe it's just me, but for the bikes I've "upgraded" the improvement wasn't that astounding. They pretty much were still the same bike they were originally.

Everything does work - the issue is improving the front tire clearance out of a preponderance of caution - I don't require nor expect any improvement in performance. As for getting a new bike - while a grand is a lot for converting the front braking, it certainly wouldn't cover replacing a bike of this caliber

how is the ride with a tire that nets out closer to the advertised diameter?

I really have no idea - it's been so long since I've run 23mm tires. I imagine a 23mm on the front wouldn't be quite as comfy as a 25mm masquerading as a 28mm, but is it a deal-breaker? Might be worth doing the experiment

23 is pretty skinny, i was thinking more like a 25 that doesn't measure over on your wheels. lots of 24/25/26 road tires that measure a true 25. maybe that would be enough additional clearance without losing too much cushion.

back in the day I had a 2003 gary fisher sugar 29er setup hydrualic disc front and cable v-brake rear. If you are worried about it being weird having two completely different feeling brake it never bother me, you get used to it.

What are you specifically cautious of, with regard to the minimal clearance?

It sounds like you've put many thousands of miles on the current setup, seemingly without issue. And it sounds like this bike is exclusively used on roads, with slick tires, so mud clearance does not seem to matter. Are you only concerned that the tire may rub, and damage the fork?

If that's your concern, I would just pick up a spare rim-brake fork while you still can, hide it away, and keep a close eye on the original fork for signs of rub. If you ever do develop an issue, then swap in the new fork and ride another 100k or whatever.

Maybe next time you buy tires, buy some actual 26s instead. I have a set of nominal 25s that measure 28, and a set of nominal 28s that measure 26. Both are Continental GP 5Ks, and I would be extremely hard-pressed to differentiate between them, in a blind test.

You might also find that an alternate rim-brake caliper would be slightly more compact, and increase caliper clearance by a small amount -- for a lot less money than a fork.

I would just ride it as-is. Any new fork is likely to have a different feel than the Ouzo and could make it worse even with the same measurements. The likelihood that the minimal tire clearance is going to cause issues is extremely low. Tire sizing changed a few years back as wider rims and tires became more popular the mfrs designed the carcass size to better fit them and supposedly take advantage of an aero improvement and this changed the way they fit older narrow rims. I still have the Mavic Open Pro 15mm internal width rims and noticed a few years back that most tires that used to measure a mm or several wider than labeled are now narrower and sizing seems to be even more inconsistent between brands on narrow rims than before. Check this site as they give actual widths and mounted tire diameters for most tires on the newer, wider road rim width that you have. https://www.bicyclerollingresistance.com/ I use the Conti GP5000's too and would be hard pressed to change to another tire and would just keep riding them, not worry about the clearance and save $1K.

All great commentary - thank you
Yes, I've put ~20,000 uneventful miles on this current setup. The only time there's ever been an issue was once when I rolled over a freshly asphalted road, which made the tires a little tacky. They pulled small bits of gravel up into the fork and scratched up the inner face of the fork crown. Very shallow and easy addressed with clear coat. I guess I just imagining the nightmare scenario of something larger jamming up the front wheel at speed, but I acknowledge that this is likely needless catastrophizing - 20,000 miles, after all...
I actually have a steel fork in the parts box- after I "garage doored" the original Ouzo and couldn't find an NOS replacement, I bought a Gunnar fork - don't like it as much - heavier and a harsher ride, but it works. I boxed it as soon as I found an NOS Ouzo.
The reason why I don't want to try different (possibly closer to nominal 25mm) alternative tire is completely shallow - my bike has a general yellow theme, and I get Rubino Pros in yellow - I think aesthetics matter (more than my teeth, apparently :foo:)

I think I'm talked off the disc/rim hybrid ledge for now - thanks for saving me $1000! :)

Get some Polyurethane-UV resistant (i.e. "Helicopter Tape") clear protective tape for the fork crown area. Should protect against most types of road flak. I also put some on the front and outer sides of my Ouzo fork blades to protect against chips from stones and whatnot.