I did have a sudden blowout of the front tire of my Bike Friday when I came to a stop after a steep descent. Since then I've been careful to do more of the braking with the rear brake on substantial descents and haven't had a recurrence. But it does seem to me that this is an issue with small wheels and one that would be fixed by use of discs where the rotor size could be the same regardless of rim diameter. Another advantage of discs is that they eliminate the rim wear due to the brake pads which is also more of a problem with small wheels that have a smaller brake-track area and therefore wear out faster.