Ok, here's some pics of my skate wheels mod. I used 104mm 82A wheels I grabbed off teh bf's broken scooter (free) and bought 6mmx30mm screws ($0.68+tax). I would go for a longer screw if you can find it; this was the longest my local Home Despot had because they had a limited stock of metric sizes.
I cut up some old business cards to use as a shim because the screws were a wee bit too thin for the skate bearings.
It's an extremely cheap mod, and it makes the brompton roll really well. I tried rolling it once around the house (frontyard-side-backyard-and back again) and it performed beautifully. You can easily roll it across sidewalks and bus/train stations like a cart if you keep the handlebars up. No more carrying the brommie unless I really have to! Also--no heel strike! Although the skate wheels are larger in diameter than the brompton ones, they are thinner.
The only problem with this mod is that, as you can see from the pic above, the skate wheels are not worn evenly because of the braking mechanism of the scooter--one wheel is fatter and taller than the other. Because of this, on perfectly flat surfaces, the folded brommie tips over and stands on the two wheels instead of the on rollers, as shown below:
I tried moving the fatter wheel on the other side, but no cookie. The skate wheels are thinner than the original brompton rollers, and are not able to support the weight of the folded side as well, hence the tipping. It's slightly annoying, but it still stands on its own, and the annoyance is assauaged by the ease of rolling. For those attempting a similar mod, try to find skate wheels that are not so unevenly worn; maybe they will work better.
