I was looking at the manual again and came across this at the end.
I already knew the 20 hp Kohler (base) model had a lower top speed of 7 vs 8 mph but now I see why. The 20 hp Kohler base model gets smaller front and rear tires!! In fact, the math works perfectly. The other machines get 26" rear tires and the 20 hp Kohler gets 23s. So 23/26*8 = 7 mph. That's where the speed difference comes from. It was kind of funny, too, because yesterday I tried out full engine speed, full hydro speed and high range and honestly it goes plenty fast. My thought was...if this is 7 mph I don't need to go 8. It would be a wild ride on anything but a smooth surface.
So why the smaller tires on the 20HP model? Not sure but I came up with two working theories: 1) The base 48" deck somehow works better with the smaller tires or 2) They used smaller tires on the base model to help get the price down perhaps on the theory that the owner may do less heavy work with it. I think the bigger tires would be better in just about every usage scenario, being taller and wider. It would be 23" vs 26" tall on the rear and 16" vs 18" tall on the front. An inch wider front and 1.5" wider rear. Seemingly the same wheels, or at least wheel diameter.
Obviously I fell into a bottomless depression on this news. But I was able to crawl to the tractor, hand over hand, just to confirm the bad news. That's when things got interesting.
First I checked the fronts.
What's this now??? The bigger size? Can't be. Let me check the other side. Yup, other side is the same. Damn.
The 64 thousand dollar question: what about the rears then?
I'll be damned! Checked the other side, too, and it's the same.
One last theory: even though the engine is a 20HP Kohler, I believe it is not original to this machine, something like ~4-6 years newer or so (I think the machine is a 2000 or 2001 and the engine a 2005 or 2006). My evidence for that:
This can't be a 2005 or 2006 because the last year for the Legacy was 2003. In 2004 they slightly refreshed the line and named it the Legacy XL. Side note, I believe all XLs came with external hydraulics (a different hydro unit), had available 4WD and typically Briggs engines (Briggs bought Simplicity around 2003). Other side note, I see the 25HP model had optional external hydraulics. Not sure how that worked but I guess they just made that standard in 2004 with the XL (all were XLs). I also think ROPS became standard around the XL model years (roll-over protective structure).
Anyway, maybe this is not the 20HP base model.
No, it is. It actually says "20 V-twin" on the rear fender and the part number matches:
Evidence of tractor age:
So that's why I've been saying 2000 or 2001 model year, assuming that was the first or second oil change. Maybe 2001 is most likely.
Anyway, back to the tire mystery. There are only a few options for how this happened.
1) It was ordered like this somehow
2) The manual is wrong
3) It was either a dealer retrofit when new or perhaps when someone outfitted the loader or something like that (or any other time after manufacture)
I don't think the manual is wrong. So I think #3 is probably most likely. I could check to see if the larger tires are specified for the loader or other attachments.