Originally Posted by
sofakng
My son is almost 4.5 years old and has only used tricycles. Somebody gave us a 12" bicycle but it's incredibly too small.
It's been my experience that kids grow out of bikes
fast until they get up to 20" (BMX-sized) bikes, which can last a while. With that in mind, I've tended to get bikes that were just a little on the big side for my kids. I also tend to buy them used since good kids' bikes can often be found cheap, even in good condition. And as long as they're not abused, you can resell them for roughly the same price you paid. (Depreciation is obviously much steeper on a new bike.)
Originally Posted by
sofakng
Our local bike shop is selling brand new (2016?) Trek 820's for $315 a piece. We are looking at one for me and one for my wife.
Lastly, I am undecided between the 16" frame and the 18" frame. I'm only 5'9" and my inseam is 30". The 16" frame felt much, much better.
Those ought to be great for cruising the neighborhood.
As for size, you and I are almost the same size. I'm just shy of 5'10" and have a 30" pants inseam*. My mountain bike's an 18" frame. I have a bike with a 16" frame as well, but it's too cramped. Frame sizing is more about the reach between the saddle and handlebar than it is about the height of the bike and unless you've got t-rex arms, I think the 18" bike will probably be the better fit. But without seeing you on the bike, I'm just guessing. Find someone you trust at a good bike shop and let them confirm in person.
* "Inseam", as you might see it in bike-sizing context, is not the same as the clothing measurement. Cycling inseam is measured from your crotch to the floor, not to the end of your pant leg.