wondering why a lot of the engines only have a rear ceramic bearing, what's the problem with running a front one too

there is no benefit to running a front ceramic, so its simply a cost thing....

Wouldnt it reduce the rotating mass and free it up more though? Or not enough to notice?

probably has more to do with the bearing being smaller ànd its weight is closer to the center of the bearing. a rear bearing is much bigger and heavier so the lighter balls make a bigger difference as they are farther from the center. the front bearing also has 5 or six smaller balls instead of 9-11 much larger balls so there is less surface area to create drag on the front bearing so tbe low drag ceramic balls dont have as much effect.

Even with the main bearing the difference is hard to notice. People just want to have performance parts.....

ok cool...thanks

I agree with this completely.
Personally when I replace standard size main bearings I use a steel bearing, and I always make sure to purchase a 9-ball bearing. 9-ball bearings use bigger balls, while 11-ball bearings use smaller balls which are prone to failure at about 2 to 2.5 gallons of use. So when it comes to bearings, the size of your balls is what matters.

As for third party ceramic bearings I do not trust them. I bought five of a certain brand and three of them were "notchy" when new. Now some people will say that will wear in and such, but I have seen ceramic bearing failure on cheap ceramics, and it totally destroys your engine. So I simply stay away from them.

I thought that the ceramics last longer, do they?

Not particularly.

The thing to note is that for MOST average users, they last a little longer since the ceramic balls don't rust.

Yes, what we use are ceramic-hybrid with a steel cage, but minor surface rust that would usually destroy an all steel a ceramic hybrid does a little better.

As to why not use them in the front...1) no real performance benefit (2) dirt intrustion... a steel ball will 'eat' some amount of dirt coming past the seal without issue over it's service life. Ceramic balls DO NOT tolerate any dirt.

Basically this.

When using quality bearings, there is really nominal performance difference until higher RPM where the ceramic will show itself being more stable.

this 9 vs 11 ball bearing is interesting and something I didn't know

Depends the quality of the bearing. And because no RC bearing comes with a detailed specsheet you can not compare the (written) quality.

Yes displaced-balls are actually a thing. Lol.

The goal is to keep them from skating (from being crowded together under a load) or very fast acceleration. Want them to always roll.

Ceramic bearings in the front for offroad use is risky.

There’s a lot of stress on the front of the engine. I once chipped a tooth on a brand new CB from flat-landing a few too many times. Ceramic is like glass and shouldn’t be used there when the advantage is so minimal and the risk is so high.

From what I understand, on-road racers do F&R ceramics on their engines because for on-road, it really makes that much of a difference with as fast as they go. For them, it’s probably maybe 1/10 of a second or something but a front ceramic bearing is just one more way for them to cut lap times and the road is smooth so there’s no risk.

When I first learned how to and started changing my engine bearings, I did ceramics for both front and main on 2 of my engines not knowing any better but both of those engines are still running strong. One of them, my Beat 5, now has 7 gallons through it. I put those bearings in around 4 gallons but when I change them again, I’m doing steel front, ceramic main but only cause I know better now. All my other engines I’ve done correctly since then.

Cost difference isn’t all that much of a big deal to me but the risk/benefit factor is.

I havn't seen a real test by running an engine on ceramics and by replacing the bearings running that same engine on steel bearings. Only then you can determ the difference.
Believe me with all I have seen on tolerances and fooling customers by giving them different timings and/or other piston material it is hard to say that 2 engines -one ceramics and one steel- are exactly the same to give a reliable test.