Double classing on different brands

I would think within a lap or less he’ll adapt just fine.

An 85 will have 100% different ergonomics anyway, even same brand. Just get the bike you want/he wants.

I agree with this !

All kids are different. We went from YZ65 last season to KTM65 this season, my son was significantly faster the first day on the KTM. Picked up n 85sx to get started on and he was expectedly timid at first but he was only riding on occasion to get used to the difference. Sitting on the two they feel nothing like each other and when the 65 had a transmission failure in May I had no choice but to put him on the 85 until the 65 was back in action. After two practice days he was ripping it like his 65 and when the 65 was running again he could not get comfortable with how small, twitchy, and slow it felt.

He's 10yrs, 4' 7", and 100% full time on the 85 now

While I cannot comment on how your kid reacts to bike changes, I have no problem going back and forth from my crf450 to a yz250f, which of course could not be more different. The key is to have him ride both often and he’ll be used to both

Yeah with mini bikes their so different at each displacement, even the same oem that it really doesn't matter. An kids adapt usually alot faster then we do anyways.

With big bikes it can be different though for some people because each 125/250 or 250f/450f are based on very similar chassis, suspension ect for each oem. That being said I didn't have a hard time hopping from a yz250F to a husky 450 and back all day and it doesn't get much different then those 2 bike. Aer, kyb, steel, aluminum. A motor with a lot of bottom vs the husky that just felt so smooth that you don't even realize how fast your going.

Kids learn and adapt insanely fast, as you're no doubt aware having a little ripper, I wouldn't sweat it and Falcons point hits the nail on the head. Enjoy yourselves dude 👍

That will be fine, a 65 is different from an 85 no matter what. Switching brands won't hurt a thing. I used to run a YZ125 in the 125 class, a KX250 in the 250 class, and a Husky 250 in hare scramble with no issues.

Back in the 80s. I rode a PW50 and a KX60 at the same time, then a KX 60 and a CR 80 at the same time. It was no big deal. You figure it out.

I did it with a YZ250 and CRF450 about a decade ago. It’s an adjustment for half a lap then you’re golden if you set them up reasonably similarly control wise.

That being said, it’s a 65 and 85 so it’s gonna be a significant change even within the same brand so I don’t know that I’d worry about it all that much.

Way back in the day I used to race a YZ125 and a YZ400, if the open race was after the 125 race the first few corners were kind of crazy as I would ride the 400 like a 125 but then I would settle down and be fine. The 125 felt slow so it was pinned all the time.