dynikus

Would it be a bad idea to ride a 700c wheel on back, and a 27 1 1/4 wheel in front?
I know there's an 8mm difference in diameter, but I'm trying to make a cheap commuter that I can also train with a little. (fixed gear to practice a more round and continuous stroke)
I'll be riding this on short trips. like 5 miles at the most.
Someone's selling a 700c flip flop hub rear wheel, but no front wheel.

rpenmanparker 

Your rear brake may not work. The caliper arms may not be long enough for the pad to contact the braking surface. Also you will be changing both the seat tube angle and the head tube angle. The whole thing is likely to be a little squirrely. I would not do it, and I have ridden 700c wheels on 27" frames many times. Just always with both wheels matching. The mismatch is not a good idea.

Robert

siggy2xc

Unless you're riding really long distances, it's not a big deal. Even then it's only 8mm. Just be sure that your brakes can move low enough to hit the rim on a 700c wheel.

redcon1

Agree, not a big deal. You might need a longer reach caliper. Or, run a single brake like I did when I was poor.

halfspeed

You might even be able to nullify some of the difference with a fatter tire on the rear.

Myosmith

As you are running the bike as a fixie, you could get by with only a front brake. I'm still a believer that two brakes are a good idea anyway so hopefully you can get the rear one to reach. The 8mm difference is less than half an inch in diameter but, since it is only the radius from the axle to the ground that affects the attitude of the frame, you are talking about less than a quarter inch difference front to rear.

I'm not a fan of the idea of running a wider tire in back as there is the potential, that in a tight corner on a wet road, it could increase the chances that your front wheel will slide out first, which is a bad situation.

dynikus

Yeah, I know that I'd have to be able to adjust the calipers 4mm down. I still have to check to be sure I can do this with my brakes, or if it would require new brakes entirely.
I did see 700c wheelset a little after posting this though. It's $70, and I like the gearing on the rear wheel better. 15t freewheel, 17t fixed vs 16 freewheel and 19 fixed. The rear wheel alone was $30.
And yeah, since this is only going to be for short commutes, I didn't think it would matter much. I have a race bike if I want to go further

mihlbach

Its not ideal, but its only a 4mm difference in wheel diameter. The bike won't explode and as long as you have some sort of an operable brake, theres no additional danger.
No reason not to try it other than it might looked a bit goofy to someone with a trained eye.

Camilo

As anothr thought - assuming you don't have a problem with brake reach, Ebay or Craigslist the 27" front wheel and buy a $50 700c front wheel. You might find that 27" wheels are kind of sought after so the price differential might be very small. Again, just a thought.

halfspeed

Where did you get that idea?

Velo Dog

Nothing wrong with the idea in theory. A wider tire will have more grip, all other things being equal, than a narrow one because it puts more rubber in contact with the road. If that weren't true, Indy cars would use bicycle tires, to reduce aero drag.
Whether it's enough difference to matter, or even notice, is another issue.

halfspeed

A few points:

1) All other things aren't equal. The forces on front and rear wheels are very different. It's much harder to wash out a front wheel than a rear. It's a rather extraordinary claim that a few millimeters of width on the rear are enough to overcome that difference.
2) Indy cars aren't bicycles and have very different performance characteristics making them a bad comparison.
3) That said, Indy cars DO use rear tires that are both wider and have a larger diameter than the front.

Myosmith

Actually, the first place I heard it was right here when I was building my trail bike, which has more tire clearance in the back than in the fork so I was considering a 45mm tire in back and a 40mm in front. I was discouraged from doing it and a couple of the techs that I trust at my LBS (who are also experienced cyclocross riders and roadies) agreed. If someone has solid information to the contrary, please post it as I still have all that extra room in the back of my trail bike (used for mixed surface riding).

I absolutely agree that there are a lot of factors that influence traction including weight distribution, drive and braking forces, surface conditions, and more that I can't think of right now. I have experienced a front wheel washout, but on a bike with matching front and rear tires. Not a pleasant experience. As the consensus for my trail bike build was that wider in back could potentially increase the chances of a front end washout. I took the advice and went with matching tires.