28" or 29"

is there a big difference in between the to different sizes

No, just 1 inch… Sorry

Basically they’re the same thing. They both use a 700c rim and the only difference is the tire size:)

I’ll change my big apple to something skinnyer to save some weight… this summer, when i’m going supersonic! 60mm cranks…

There is a fundamental difference, but it’s nothing to do with the extra inch.

On rolling circumference, the difference is only 1/28 = 3.6%

On 10 mph/16kmh that would increase you to 10.35 mph/16.57 kph - hardly noticeable.

However the 29 is much better at rolling over stuff, and absorbing small changes in the road surface, the gradient, or small variations in your pedalling input. It has some of the flywheel effect of a Coker, especially if you put small cranks on.

The 28, on the other hand, is a precision tool - a delight to ride - precise, sharp, light, responsive… but twitchy and temperamental.

You will maintain a higher average speed in almost all conditions on a fat 9290 tyre than on a thin (28) tyre.

I have skinny almost slick road bike tyre on my 700c. It’s beautiful, but you need to concentrate. It’s the purest form of unicycling I’ve tried. Highly recommended by me, but most people prefer the 29.