I have an old FIORI byke

I would like to replace the ball in the bearing with ceramic ball

what sizze are the ball.

will it make a big difference.
Compare to my other byke it is more difficult to run

Jacques Thanks

Which bearing? Hub, bottom bracket, headset?

Why? Ceramic balls require careful maintenance, they easily disintegrate if they are not greased properly, and with the correct formula grease. Unless you are a serious racer, or a real weight weenie, they are just spending money so you can say you have ceramic bearings. Other things will bring more return for what you will spend on the ceramic items.

Besides which bearings, which bike are you doing this to (Fiori model and year,) so the correct size can be recommended.

Welcome to the Forum.

Bill

Grade 25 chrome steel ball bearings are some of the best quality and they're inexpensive.

If your bike is relatively standard then you'll likely need 50 5/32" bearings for then headset, 22 1/4" for the bottom bracket, 18 1/4" for the rear hub and 20 3/16" for the front hub.

You either have way too much experience with rebuilding bearings, or a handy copy of Sutherlands . I get to say this since mine is by my chair, and I just got through with the bearings on both bikes last week.

Bill

Hugely unlikely.
Unless your current bearings are in really, really poor condition.
In which case it's the rework as such - not the switch to ceramic - that brings the improvement.
Ceramic bearings CAN lower rolling friction with a few percent.
But rolling friction - from a good bearing - already is only a few percent of the overall resistance.
So you're looking at an improvement of a few percent of a few percent.
You do the math.
A hint: it isn't much.
The bearings are only a tiny part of the whole. You should look elsewhere. Tires, tire pressure, gearing ratio, ride position etc

Interesting thread. My first response is "Why?" Repacking bearings is worth the trouble (unless they were repacked recently). But why switch to ceramic?

I can hardly remember family birthdays and anniversaries but darn it if I will misjudge my bicycle bearing counts.