I have a savage 25 old school. Need new tires and wheels but when i find the same tire and wheel size the axle hole is 12mm, current axle size is a 5mm any suggestions on how to upgrade or fix this problem?
I'm not following your question. Pictures may help.
Are you talking about the hex size or the hole in the middle of the wheel. If it's hole in the middle it's not going to really matter unless something (like a hub) sticks out.
If I look at the HPI website, it's a 1/8 scale rig and the hex is most likely 17mm unless they did something odd. Which is entirely possible. https://www.hpiracing.com/en/kit/835
The wheels/tires tab also leads to some possible matches.