I'm about to begin my first fixed gear conversion, and I'm hoping someone can tell me if what I'm considering is a bad or good idea.

I've got an old steel frame and fork... but the "problem" is that the bike originally had 27" wheels. Yes, I'm aware that I can still buy 27" wheels, BUT the selection is limited and tire selection is even more limited.

Here's my thought... I want to put on 700c wheels, and replace the fork with a 700c fork. With wheels on the bike, the top tube is slightly sloping, about 15mm higher at the head tube than at the seat tube, so the shorter fork will "flatten" it out a bit. AND... this will allow me to run a short reach front brake.

The head tube angle is pretty relaxed, I don't THINK it will affect handling too much.

Any thoughts/comments/suggestions?

27" wheels are 630 mm in diameter and 700's are 622 mm. Leave the fork alone and just get brakes that can reach the additional 4 mm needed for the conversion. Using 700's in a 27" frame gives you the option for wider tires or full fenders which can be really nice.

Soooo... even if I have an extra carbon fork to toss on it, it's still not a good idea?

I wouldn't but that's me. Beside the oddity of having a carbon fork on a older steel frame it would change the geometry of the front end. If you want to measure what reach you need you can refer to this.

https://sheldonbrown.com/calipers.html

Scroll down to the section on reach.

You won't need to change fork to use 700c but you'll need to get long reach brake calipers. What is wrong with the slope top tube on your bike? My 78' Schwinn singlespeed has a slight slope on the top tube but that doesn't bother me.

I guess I wasn't very clear on my first post. Sorry!

The slope in the top tube doesn't bother me at all, I was just pointing it out so that all the readers would know that putting a shorter fork on the front wouldn't make the top tube run "downhill".

I've already got a threadless fork, headset, stem, and a short reach front brake that I can use. If I use the old fork, I'll have to buy a new headset, brake caliper, and quill stem.

So, I guess my question was more along the lines of: "Will this geometry change really screw with my handling?"

If you already have the parts, just do it(since you're probably going to regardless of what we say) and see how it feels.

Probably not. Some people are super sensitive about this stuff. Princess and the Pea. I would go for it. Even if you have ridden the bike as is, thus making the comparative difference more pronounced, you will likely get over it after a few miles.

It also depends on the amount of rake the new fork has but as Batty said, you most likely won't even notice a difference.

Post pics if you end up doing it. I've always been curious what that would look like.

Going from 27" to 700c wheels will also drop the bike down, placing the crankarms closer to the street and making pedal strike more likely all things being equal. A 700C fork will contribute to that as well as it will drop the front end down.

My suggestion is get some fast rolling fatter tires and brakes to reach to the 700c wheels (putting the bb roughly in the same place as with the 27" wheels) and enjoy the bike that way. You'll be able to plow right through stuff you'd have to pick your way around on 23mm tires.

The carbon fork might change the geometry slightly if it drops the front end of the bike. I say "might" because despite shorter blades for the 700C wheel, carbon forks often have taller crowns than vintage steel forks, so they might cancel out.

It can't hurt to try, if that's what floats your boat. If you don't like how it feels, you can always change it back.

That's right, so check the Axle to Crown measurement between the two forks.