Tractor pulling and tire pressure

Pulled last night at the county fair and I got 7th out of 13.  Not a bad showing but could have been better.  I pulled my 45 diesel again, with one set of rear wheel weights and two suitcase weights stacked on the rear platform got me to the weight of 4500.   I have enough weight that I could go up to the next class but that is 6000, and 60 hp, and I think I would get run over in that class.   There isn't one in between.    Track was clay and very spongy  although not overly wet.  Eliminator rear tires were really digging down in and for the antique classes which I was in, they kept the front sled wheels down so the sled part wasn't riding on the ground and then lowered it at the 150 mark.  Most people died shortly thereafter, as it was so mushy.  My question is, is there any general rule of thumb with tire pressure and track conditions?  I lowered my tire pressure, but I think I might have went down to much.  I think I was down to 7.5 when I pulled.  The wife took part of a video and they didn't look to be bulging or torquing too bad, but she was way in front of where it started to struggle.  I guess does it get to a point where the air pressure isn't enough to provide for good traction?  I wish I would've started doing this years ago.   There's alot to learn from this sport, but it sure is fun!!

I would say that you wouldn't want to go any lower but for the 4500 class you were in the ball park. Hard to get a WD45 to do well in the 4500 class. It can be done but it will be a little heavy in the front. A tuff WD45 gas that I used to pull against in the 4500 pulled with what looked like close to 5 pounds. Tires would buckle real bad but he was always in my face against my Oliver 77.  A fellow had a WD45 diesel that looked like it just came out of the factory. He tried every thing he could think of. I don't think he ever made up to third.

You do have a beautiful tractor.  That track was real mush.  It will be interesting to see how I do at Ozaukee.  Last year, I was in fourth.  I will check the ripple next time.  Thanks for the tip Mark. 

I always pull the next weight class above what weights I have on the tractor. You'd be surprised how many of the bigger tractors you can beat. I was 600 lbs light last week, missed 3 rd place by 1 " and beat 2 JD 60, SM IH, 400 IH, Minny U or UB

I run 8.25 lbs of air in my WD 45.  I pull at 3550 lbs with 13.6 X 28's.  This pressure hooks good for me as torque tends to make the tread fold on a tight track.  When conditions are wet or when pulling on an un-prepared or sandy/gravelly track, I air down to 6 to 7 lbs. 

We found that 10 pounds worked better in the 16.9x28s on our D17. We used to run 5-8 psi and it always spun out. We talked to a guy at the pulls one day and he said that the pressure was to low and the tread was cupping in the middle. After airing up we got a lot more 2nd and 3rd, and finally won one. Now we are trying a set of 13.6x38 on it to see what it does.