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 | Mark E. Lamprey
Join Date: Posts: 1 
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2001-04-26 27257
The manual for my 1988 JD 950 say that it came with 5.50-16 front tires When I bought it, it had 7.50-16 tires on it. I replaced the front tires with the same size that it had on it 7.50-16. It wasn't until later that I got a manual otherwise I would have put the original size back on it. I have e mailed John Deere and asked them just what is the differance in a 5.50 to a 7.50 tire ? width, Sidewall height ??, and will it create a problem running the 7.50's. John Deere's response was, We refer all those questions to dealers, we can't help you. My dealer say's, Oh, we don't know anything about tires! Maybe one of you guys know. What is the actual differance from a 5.50-16 to a 7.50-16 tire and will that change in size create a potential problem. I don't know for how long the previous owner has run the larger size, everthing appears to be running smoothly. Although when in 4wd I do see noticable tracks in the dirt etc. from the front wheels, caused from (I will assume) the front tires pulling. Maybe that is normal Any help or knowledge would be greatly appreciated. Thanks, Mark
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| Bird Senter
Join Date: Jun 1999 Posts: 962 
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2001-04-26 27264
Mark, I would think a dealer should know something about tires, but if he doesn't, then he should be able to find out what the rolling circumference ratio is between the front and rear. Then of course, you'd need to know the rolling circumference not only of the front tires, but also the back tires. You want a very slight "lead" with the front, no "lag" and it's my understanding that you want no more than 5% lead. ....
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| Bernie Galgoci
Join Date: Posts: 1
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2001-04-26 27265
Mark. On the tires your talking about, the first number is the nominal width (the section width) in inches; the second number is the diameter (in inches) of the rim that the tire will fit on. So, a 7.50-16 tire fits on a 16 inch rim and is nominally 7.5 inches wide when mounted. A 9.50-16 tire would be nominally 2 inches wider. I keep saying nominally because actual width varies by manufacturer, inflation pressure, load, etc.. Sometimes (but not always) the height of the sidewall changes as the width changes, and changing the height of the sidewall results in a change in the rolling circumference of the tire. Unfortunately, this information isn't printed on a tire. Assuming the correct sized tires are on the rear,changing the rolling circumference on the front can result in lead/lag problems between the front and rear axles when the front wheel drive is engaged, and alot of stress on the drivetrain components. The lead/lag issue has been discussed at length on the board and it sounds like you're aware of this problem. I'm sorry the Deere dealer was no help. Since each tire manufacturer has tables available which have the information you need (i.e. the difference, if any, in the rolling circumference of the two tire sizes in question), I'd start there. Hope this helps. ....
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| scott
Join Date: Posts: 1
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2001-04-26 27270
you don't say if it's a 4x4 if not it don't realy matter. if it is then it's important to have the correct size.
scott ....
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| Fred Runzi
Join Date: Posts: 1
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2001-04-26 27273
Mark,
This page may give you some insight to your question. Fred ....
Link: Tire Center Technical Data Page
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| Mark E. Lamprey
Join Date: Posts: 1
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2001-04-26 27275
Thank you guys for all you input, it is very much appreciated. Taking into consideration what Bernie has said. If the 5.50 and the 7.50 represent the width of the tire when inflated, then theoreticly the rolling circumference wouldn't have changed all that much, if at all, (unless the height of the side walls are differant). the only thing that has changed would have been the width of the tire. The tires that were on the front were a Goodyear diamond tread R3 with a 4 ply rating in an extremely worn state. I opted for a light truck tire of the same size 7.50-16 with a very mild snow tread and a 8 ply rating. I figured the very mild snow tread would give the necessary traction when needed but didn't stray to far from Galaxy R3's on the rear. The 8 ply side walls would give all the stregnth I would ever need with the front end loader. As I said before, when in 4WD, driving accros dirt, I do see tracks being made by the front tires, I am assuming that because the front tires are pulling rather than free wheeling, there leaving tracks. Do any of you see front tire tracks from your tractors while in 4WD. I am not new to tractors, although it has been a long time and this is the first one that I personally have ever owned. I grew up on a small working farm and have been around tractors most all my life. We never had any that were 4WD so that part is very new to me. But I got to say. I am having a Blast learning and playing. Working, I meant to say Working !! Mark ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-04-28 27314
I think a detailed method for calculating lead/lag was posted on this board over a year ago--might be in the archives. You do have to know the front/rear drive ratio to use the method. Lead/lag problems are characterized by a 4wd that is hard to disengage and by power hopping. Neither was described, but it might be good to calculate the lead to see it it's in tolerance, and also to stay off hard surfaces until the actual lead is known. Actually it's not good to use 4wd on pavement anytime. If the 4wd is hard to disengage when the tractor hasn't been in a turn, and then easy if the front wheels are lifted off the ground with the loader bucket, a lead/lag problem might be suspected. I haven't completely thought it through, but I believe that being in a turn while in 4wd may cause some 'wind-up' between the drives. The front and rear wheels don't track the same distance in a turn, and tractors don't have differentials between the drives. The effect is much less than the difference in tracking between left and right wheels, but should be an effect. ....
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