I've been looking at the Carlisle HD Field Trax tires that come on some of the X500 tractors for more traction on my GX335 when using a JB Jr. But I don't know if they come in your size. Check out the link below for some pictures and discussion.

Here is a link that might be useful: HDAP vs. turf tires

unfortunately they dont come in my size, any other suggestions.

Google the Carlisle web site for other options......there are a lot! There are other manufacturers as well.

jmeitz,
Here is a link to the Carlisle site. They have the All Trail tires in the size you need.

Here is a link that might be useful: All Trails

that is what i needed, didn't even think of looking at ATV tires. Do you think those would tear up the yard?

can one change tire themselves or is that something that a tire place needs to do?

I put the Carlisle all trails on my GT235. They really help with traction. I have not had any problems with them tearing up the lawn. I installed them myself. The only problem with changing them yourself is breaking down the existing tires.

does the x300 have tubes in the tires or is it tubeless?

Tubeless, but you can install tubes.

I put carlisle "superturf" tires on my L120. Similar tread design to a regular lawn tire, but with more coarse bars (bigger ruubber blocks, with bigger spaces in between)

I find that they give me more traction, but of course not as much as HDAP or AG tires, while not tearing up the lawn

I changed them myself.

Here is what they look like.... and fyi: I filled them with fluid for extra weight & traction....
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Put these on 2 years ago, made chains from logging shains 4 times as heavy as regular GT chains, pull wood, dirt, rocks across yard, never saw anything but impressions same as any tire will do to grass. Sure you get stuck they would uproot the grass, but the thing is, they dont spin and get stuck in the first place.

Here is a link that might be useful: Walmart tires

I sold my Carlisle Turf Savers on E-bay and went to my local Tire Shop and put Carlisle 20X10-8 Super Lugs on it.

Yeah it does show on a wet lawn, but I seldom slip traction!!! They grip and go. I love the look it created for the X300. Really Aggressive Rider.

I mow up a hill along a highway which not only is on a 30 degree slope up, but a 45 degree in some areas off the side. So, traction means safety in this area. No Problem for the Super Lugs.