Need a diagram of the wiring for a Derbi Cross City

SOURCE: i need to tighten the chain on my derbi cross city 125

looks like you have a nut at the rear of thr swing arm, one on each side, these are the rear wheel/chain adjusters. slacken the wheel nut and then adjust the nuts, there should be some kind of markings on the swingarm so you can get both sides the same. when done tighten the wheel nut and you are done

SOURCE: Hi i have a derbi cross city 125 back wheel problem

You can get new wheels on ebay, or at your local motorcycle dealer, and it does not have to be the exact same tyre, but it does have to be the same hight, i would reccomend bridgestone tyres as they last a hell of a lot longer than the stock, well worth your money

SOURCE: where can i buy a

Try ebay.
Hope that helps