Single vs Double ring piston

In all honesty claims of extra power and heat transfer are empty without tests and numbers, just people's opinions. As for KTM and most of the manufacturers they have switched from single to double, or double to single at different stages. If they can't decide with all of their research I'm sure the average Joe can't figure it out without doing multiple dyno tests and heat tests. The thing to bare in mind with a claim double rings help with heat transfer is both single and double piston rings have the same spring against the cylinder except double has 2 rings therefore you are getting twice the friction and generating more heat. I'm happy to be proven wrong with actual tests and numbers rather than my mate said so.

            Mr. Aventador… I believe you make a valid point about two rings creating more heat.

The parts catalogs have the dual rings listed and then they list the"GP PISTON" and it's the single ring version.  I do the single and add 2 1/16th holes 5mm down to lube the exhaust bridge 

Less tear downs for me....double ring

It's a matter of how hard you are running the bike and how much you want to run the risk of running an old piston when it comes to compression. If you're running a piston until the compression is so bad the bike isn't starting and running well, then you're way over the hours of the piston life. People seem to forget motocross engines are highly tuned and lightweight. So they have hours on certain parts. Drag car engines do one run with probably a minute run time and then they are rebuilt. You can run the rings until there's no compression they won't give you any issues unless your running a ported cylinder. But the piston is where the issue is. Anything over 30-40 hours on a piston in a motocross bike riding hard and you are taking a risk. Eventually the clearance will be too great and the piston slap will cause a crack and failure in the skirt, or the rings will get loose in the groove and catch a port. 

I always ran a double on my ‘01 cr250, seemed to have better compression.

I like the fact that you are still ripping on a 125.    Interesting read on this topic.  I would stick with whatever the bike came with stock.  My CR is a single ring and I run stock pistons that I change at around 40 hours.  Never had a failure with over 500 hours on the motor.

Less ring seal, so actually less horsepower. Cheaper to make though because only 1 ring groove to machine. Marketing in this sport is really out of control. Most aftermarket parts are trash in my experience comparing them to OEM. 

In theory it's logical but in reality a single ring piston gets exactly the same compression readings. If you want to gain more horsepower from compression on a 2 stroke the easiest way is to run 32:1 and the oil will help get a better seal. There was some solid research on this from Husqvarna I believe it was in the 70s and 32:1 ratio had better power and wear resistance than higher ratios.

As for OEM being better and everything else is rubbish I have to disagree. If you change pistons as per the hours in the manual, and as per the specs like clearance and ring gap - you won't get a failure from aftermarket. The KX85 was double ring until 2014 then went single ring, KTM 125 I believe was single ring then changed to double ring in 2007 untill current 23 models, while the KTM 85 is single ring.