A few months ago, I purchased a Public bicycle. I'd always dug their bikes - the styling is cool, and the components they use are of good quality. They're good bikes, and they're set up for tooling around a city like mine (San Francisco). My bike is a V7i, with seven internal gears via a Shimano Nexus 7 hub.
Last week, I grabbed my bike to ride home from work when I discovered that my back tire was flat. Luckily, we have a small bike workshop at our office, so I threw it up on the stand and got to work figuring out how to free the wheel from the frame so I could change the tire.
Public has no information anywhere that I can find that describes this process. Even the owner's manual for the bike tells you to take the bike to a mechanic, which is just ludicrous. I found a few crappy videos around that specifically show you how to deal with this hub, but they are a little hard to follow. I've put together this guide specifically for owners of Public bikes, but if you have a bike with an internal Nexus hub, you might find it useful as well.
What you need
The tools for this are actually not that big of a deal. You need a 15mm wrench, a small pokey device (I'll elaborate in a minute), and then whatever you would normally need to replace a tube on a bicycle. Here's what I carry in my emergency kit:
This tool. It has a 15mm wrench on one end and a tire lever on the other.
A four-inch piece of wire hanger. This is the aforementioned pokey thing. Some people use part of a spoke, and others carry a 2mm allen wrench. I didn't have either of those around, but I did have a wire hanger and this thing works really well for what you need to do with it.
An inflator and a few cartridges. Ask for these at your bike shop. The inflator needs to be compatible with Shrader valves.
Some tire patches.
At home, I have a regular Blackburn pump with a head that inflates both Presta and Shrader valves, and some extra tubes. Note that if you have a Public bike, you need tubes with a longer valve, as the bike has deep rims. The tubes I use are 700x28-35, with a 48mm Shrader valve.
What to do
First, shift in to first gear. Next, turn the bike upside-down. Be careful when you do this; don't break anything off or scratch up your rear rack, fender, or gear indicator.
Now you want to disconnect the shift cable from the hub. Here's how you do it. Find a little rectangular bit with a small hole in it (see pictures). Stick your poking device in that hole and pull it forward. You should be able to crank it over about an inch and a half or so, enough to achieve a decent amount of slack in the shift cable.
The next thing you need to do is free the nut on the end of the cable from its little channel. Push down on the free end of the cable (the tiny bit that's sticking out the right side of the nut) to rotate the nut clockwise a little bit. You should be able to then slide the nut upwards and out of the channel. You might need three hands to do this. I've found that if I use my left hand to hold the pokey thing, then I can use the tire lever end of my wrench to sort of wiggle the nut out of place. You might need to mess around with yours and try different approaches, but rest assured that thing does come out one way or another, without much force.
Now you sould be able to grab the cable housing and pull it out of the little arm that's attached to the hub. Yay!
Using the 15mm wrench, loosen the nuts on either side of the wheel. Flip open your brake calipers, and the wheel should be free. In practice, it's a little hard to get it out of the frame. If the tire isn't already flat, try letting all the air out so that you can shove it against the fender a bit more and free it from the slots on the frame.
Now, change the tire as normal. Do not inflate it yet, and when you mount it, make sure you pay attention to the arrow on the sidewall that tells you the direction of rotation.
Once you've got the tire mounted, you can put it back in the frame by following everything you did in reverse order. After you reattach the shift cable, make sure both ends of the cable housing are seated properly (mine usually unseats at the handlebar end).
Flip the bike back over and put it on the kickstand. You need to adjust your shift cable. Shift in to fourth gear and then look down on the shift mechanism from above the bike. Next to where the chain wraps around the sprocket on the hub, you should see a little window. In the little window you should see two yellow vertical marks. When the cable is properly adjusted, the two marks will form a straight line. You can adjust by turning the little nut on the handlebar end of the cable housing. As you turn it, the shorter of the two lines will move. Once you get them lined up, go for a test ride, run through all your gears, and adjust as necessary.
I hope this little guide helps out someone with a Public bike who doesn't want to rely on a shop to help them with this most basic task of bicycle maintenance.