Tires TN75 4WD tire sizes

[RickB]

Thanks Rick, I thought that would be the case. Although I wanted 28's for the rear, none of the wreckers had anything available and new rims and centers were prohibitive for me. Although any used rims and centers seem hard to find, I ended up with a full set of New Holland 30's for the rear and 24's for the front which came off a TN75 4WD (for 16.9 x 30 and 11.2 x 24 tire sizes respectively). They are in great shape, in fact still have all the tags on them. I don't mind modifying or building new fenders as I plan to split the tractor this fall to fix the shuttle syncro and will be repainting the tractor at that time. I am lucky to have a machine shop, as I am a welder / fabricator. The rear fenders should be an easy modification. So far I really like the TN75. Although the shuttle is a bit touchy (worn), the rest of the tractor seems great. The service manual set is pretty good but you're definately right on the F series, nothing specific to the orchard tractors. I notice my front axle is different than the manual, as it articulates somewhat. I am assuming this is what is known as super steer. Very handy.

That tire combination may or may not be appropriate for the front and rear final drive ratios built into your tractor. I would check into that carefully before bolting them on.

 

[svcguy]

A good point, but one that I can't seem to find an answer to. It appears the New Holland dealers in our area either don't have the information available to them or are simply uninterested in helping. I called all over Western Canada but the best I got was a bunch of print outs showing alternate rims for the F, but none of it made much sense (to me or the dealer) and most were tagged obsolete. I did pose the question to New Holland North America, but never received an answer. I finally turned to TractorByNet and went with what other TN75's are running. If you have any suggestions on where that answer may be, I would sure appreciate it as I do understand the tires need to be matched on a 4WD.

 

[barbqranch]

Part of it comes down to how often you use 4wd, and on what type of surface. If you are like me, and only use it rarely when the tires are slipping, it might be ok. Also, you can measure the circumference of the old tires and get the ratio, and that should be approximately the same ratio of the new ones. Also, remember that it is not critical that it be exact, after all tires wear and change the ratio.

 

[svcguy]

I just got off the phone with New Holland North America and they are trying to move my request up through the system. Very nice people and seriously concerned that I couldn't find an answer quickly on this. I should have the official answer today.

My tractor is not used on the pavement, but I am planning to use it with a post driver in fairly rugged terrain which means I will be in 4WD quite a bit. While there is probably some room on the sizing issue for occasional use, I would like to get as close as possible to avoid any binding issues. I will let everyone know what New Holland comes up with.

 

[svcguy]

Rick, thanks for the heads up on checking the tire sizes. While the 16.9 x 30 / 11.2 x 24 would have been fine for the ratio, it would not work with the super steer orchard axle. The TN75F has a narrow axle (for orchard work) and limits the tire diameter possible for the front. That being said, the 14.9R28 rear and 11.2R20 front will fit and so I am trying to locate a set of those rims.

For those interested, you take the tractor ratio (in the TN75F orchard model, it's 1.278) and multiply by the rolling circumference of the front tire, then divide by the rolling circumference of the rear tire. If the answer is more than 1, then you have a positive slip and if the answer is less than 1 you have a negative slip. The TN75F orchard is supposed to have a negative slip in or around 2 to 4 %. Calculating the original tire sizes supplied by New Holland, the negative slip was about 1%, so I have been targeting that amount.

 

[SPYDERLK]

Rick, thanks for the heads up on checking the tire sizes. While the 16.9 x 30 / 11.2 x 24 would have been fine for the ratio, it would not work with the super steer orchard axle. The TN75F has a narrow axle (for orchard work) and limits the tire diameter possible for the front. That being said, the 14.9R28 rear and 11.2R20 front will fit and so I am trying to locate a set of those rims.

For those interested, you take the tractor ratio (in the TN75F orchard model, it's 1.278) and multiply by the rolling circumference of the front tire, then divide by the rolling circumference of the rear tire. If the answer is more than 1, then you have a positive slip and if the answer is less than 1 you have a negative slip. The TN75F orchard is supposed to have a negative slip in or around 2 to 4 %. Calculating the original tire sizes supplied by New Holland, the negative slip was about 1%, so I have been targeting that amount.

That looks like theyve speced it so the backs are pushing the fronts along -- skidding them in 4wd. That provides bad handling ... even dangerous. I would be interested in their rationale. I suspect they have speced to allow a non optimum situation in order to make use of tires available.
larry

 

[RickB]

That looks like theyve speced it so the backs are pushing the fronts along -- skidding them in 4wd. That provides bad handling ... even dangerous. I would be interested in their rationale. I suspect they have speced to allow a non optimum situation in order to make use of tires available.
larry

TN/F as well as TN/S (SuperSteer)tractors have a lag ratio rather than the typical lead ratio to facilitate the traction management logic of the auto 4WD function. This has been in place for 13 years without consequence that I have heard of, or design change. Certainly not typical, but it works very well. Tire life is as good as any MFD, and I have not heard any complaints about handling in any conditions traceable to a lagging front axle. Been wrenchin' on these tractors since they came out.

 

[SPYDERLK]

Thanks! I wouldnt expect tire life to be an issue with similar leads or lags - only handling. With auto 4wd i would guess it switches out when pushing becomes a problem. The problem is, for best control when times are difficult the fronts need to be pulling directionally vs being pushed. With lag I cant see how that ever happens.:confused3:
larry

 

[svcguy]

My 4WD is no longer auto, as the previous owner had trouble with the module and had the dealer install a toggle switch on the dash to engage 4WD. I am not sure how the mod was made, but am assuming that 4WD is activated by a solenoid? I would imagine the switch is delivering 12v when on, but this is conjecture on my part. How much of the TN75F is controlled by computer?

 

[RickB]

previous owner had the dealer install a toggle switch on the dash to engage 4WD. How much of the TN75F is controlled by computer?

In your case, apparently none of it.