Front to Rear tire raito

[PILOON]

I have 'played' the tire change game as well.
Got lucky I guess as I found a pair of mounted rear rider mower tires on EBay that matched my factory Mitsu fronts.
Made a whole world of difference with FEL work especially on snow and muddy surfaces as they were much wider.
Problem then was Armstrong steering.

 

[Blake13]

Your method seems accurate for determining the gear ratio but there are other variables in determining lead/lag.

What other variables would really matter? All it would take is gear ratio and front and rear tire rolling circumference like I used. With new tires, the literature values should be just fine for rolling circumference (no tread lost). That said, it does help to not be backwards in my thinking like you pointed out to me bellow! :laughing:

If I understand correctly, you are saying that the smaller REAR tire is leading. It would actually be lagging with its smaller diameter and the FRONT tires would be leading. Right?

Good catch! I had the concept in my head flipped. As you point out, the smaller the tire's diameter the more it will lag not lead. This correction should get the numbers closer to what would be expected. I am going to edit the first post to correct my error. Thanks!

 

[chriswheeler]

I never liked driving any 4wd on a hard dry surface because you can directly feel the miss match in your seat. I have a set of newer Carlise Farm Specialist 7-16 R1 fronts I bought couple of years back to replace the factory Titan brand of the same size. The work well, but when working on snow or ice they work fairly well without chains. If it is like any other 4wd pulling from the front is a good thing. Same raito will cause a slip or a stick sooner. Same time we don't want the gears to work against each other causing excess ware. I was not able to measure the new Titan tires against the new Carlise tires side by side to match the factory specs. Sticking to the same size marking on the new tires I'm counting on the manufacture for the same size and load rating. Stick to the factory recomemded tires for your tractor, or better.
chris

 

[Blake13]

I may well have misunderstood what you wrote, but as I read, you lacked about 85% of the 28th revolution of the front tire. But then you used 85% in your calculations. If I understood correctly, you should have used 15% in those calculations.
Additionally, I believe you have skewed your revolution counts by have unloaded/no resistance on your tires.

Ill try to explain it better. Using the 17 lugs as a scale, the last revolution of the front tire was 16/17 plus an estimation of a percent of the last 1/17th. The 85% was my estimation of the last lug gap, not the entire revolution. In my calculation I worked backwards which was confusing. Working forwards, the last revolution would be:
(16/17) + (.15(1/17)) = .95 revolutions
.95 revs + 27 revs = 27.95 revs total for front. You can see this matches the original calcs.

The tire size, loaded nor unloaded, does not matter for revolutions. 360 degrees is 360 degrees. Only revs matter for the gear ratio and that was what i was attempting to measure. Loaded vs unloaded DOES matter for distance the tire travels per rev, which is why I used the rolling circumference value published by the manufacturer for any lead/lag calculation. I don't need to measured the lag/lead. That can be calculated with rolling circumference and the correct gear ratio.

 

[California]

I think you need to paint a stripe across the tires then roll forward in 2wd, and measure the paint imprints on the asphalt.

Then select tires that will let the front lead the back. I think the recommended lead is 5% but research that.

 

[rScotty]

Actually I never used the diameter or radius of the tire for any calculations. Every time I used the tire size, I used rolling circumference. This number was always taken from the manufacture's literature.

Blake13, I haven't gone through your arithmetic yet....will later today. When I first started doing & reporting that measurement on the old Yanmar forum - about 1995/6 - I used the same technique of jacking up one side of the tractor, making marks on the tires, putting it in 4wd, and rotating the one while counting the other. Repeated it several times. I was able to calculate reliable measurements for the gearing which I later confirmed in the Yanmar shop manuals. BTW, when doing these long rotations, boredom is a real problem! I found that I wasn't sure I could trust my keep count mentally, so made marks on a piece of paper..... Sounds like you found the same thing.

You and I have done a couple of things differently.

One is that I did NOT lock the differential....simply went very slowly and carefully when rotating the "drive" tire. Not sure if I rotated front or back tire as my drive tire - I think it was the front. I'll check my old notes & post later.
Secondly, the marks on front and rear tires ALMOST lined up several times as I rotated, but when they finally did line up it was EXACT. So much so that I was surprised. Not off by a lug or a little, but exact.

Third, for the rolling circumference I had on at the time slightly worn original R1 Ag tires on the factory rims. I used wet white paint dots on the tires, drove on an asphalt road in 2WD. and measured between paint spotches on the road.
I was surprised at the variation in the measurements I got. Even though I took care several times to use a straight section and not move the steering wheel my measurements over about ten tire revolutions varied by several inches. In the end I averaged that measurements. I think I remember that my measurements were fairly close to the manufacturer's numbers for RC, but definitely different. I'm guessing the difference was due to my preferring low tire pressure and having some tire wear on a fairly light wt tractor - a YM336D. I don't know what the manufacturer used for tire pressure or for tractor weight..
Anyway, I saw enough of a difference to make me glad I'd measured mine.
I later tried to measure the rolling circumference on dirt and got even more variation - too much to be useful. In soft ground or snow it's probably not going to work at all.

I did all the work because I was going to buy 4 new wheels and tires so I could shift from R1s to turf tires. I did so, and of course had to rely on the manufacturer's RC numbers when ordering the turfs.
When I got the tires and wheels changed and everything mounted up new I measured again and found that I had accidently nailed it. The front to rear lead/lag was essentially zero. Might have been a tiny, tiny bit of front wheel lead because steering was still fine, no pushing on turns. However, I could shift between 2 and 4wd at any speed in any gear just by tapping the lever. In the end, I had to put a positive lock on the 4wd selector lever to prevent vibration from constantly shifting in and out of 4wd.

rScotty

 

[California]

Blake listen to rScotty, he's the one here who has researched issues in near everything with the rigor of a scientist.

Just thinking out loud here - maybe near zero lead/lag is best for working in a straight line - discing, pushing snow, anything where you need maximum pulling force. On the other hand my own application in the orchard is that I need the front axle to pull the nose around in a tighter turn than I could make in 2wd. In turns the front takes a longer path than the rear, so some lead is preferable to reduce the effect of the rear shoving the front forward.

I stay in 4wd because I'm always on a loose (disced) or muddy surface. (recent pic). But as rScotty noted the few feet I travel on concrete within the parking stall just to get clear of the opening, feels like it is stressing the gear train and scrubbing the tires. I sometimes shift to 2wd before going in - and should do that every time.

 

[npalen]

I've found that different brands of the same tire size can vary a lot in rolling circumference or radius. I replaced the original Bridgestone 13.6-16 rears on my B9200 Kubota a couple years ago and found that the new 13.6's were a couple inches larger diameter at recommended inflation pressure. That was alarming so I played with reducing the air pressure to under 10 PSI and that got the rolling radius down to match the original reasonably close. Turns out that was probably a good move in that it rides much smoother also.
Incidentally, my understanding is that rolling circumference is not necessarily rolling radius times 2 PI in reality. There are variables affecting the two measurements.

https://www.tractorbynet.com/forums/tires/371468-tires-why-rolling-circumference-loaded.html
This is a 2016 thread discussing rolling radius etc.

 

[pmsmechanic]

I changed the front tires on my 4410. Factory was 27 x 8.50 x 15 turf. I switched to 26 x 12 x 12 turf. If I was careful what brand of tire I bought they were the same height when stood side x side. What I hadn't counted on was the increased squat of the 12" tires vs the 15" tires when the loader was full of dirt etc. because of the wider sidewall. My "cure" was to increase front tire pressure during sustained front end loader work and to disengage the front wheels during any transport of dirt on harder surfaces. It works but not ideally. I sure like the increased flotation of the wider tires though.

 

[Blake13]

What I hadn't counted on was the increased squat of the 12" tires vs the 15" tires when the loader was full of dirt etc. because of the wider sidewall.

Good tip, I hadn't thought of that either!