Front to Rear tire raito

[ovrszd]

I've only read the first page so far, but what am I missing? Doesn't this hold all the info you want right there? If you maintain that ratio, you will also maintain the mfr lead/lag.

Why you wanna make it so simple??? We are 50 posts in and growing!!!!

 

[Blake13]

I've only read the first page so far, but what am I missing? Doesn't this hold all the info you want right there? If you maintain that ratio, you will also maintain the mfr lead/lag.

AGREE! But each tire manufacture has slightly different RC for same sized tire. Also, when selecting new tire sizes, the decision will almost never be precisely the same ratio, having to fall slightly above or below the tractors factory tire RC ratio. In addition to this, I feel like my front assist, when engaged, winds up more than ideal. This suggests the factory tire ratio is likely on the end of the acceptable spectrum to begin with. Because of all this variance, it is easy to imagine a scenario where simply maintaining the ratio you described allows for new tires to fall outside of the acceptable lead/lag range. With all this said, it would be best to determine the gear ratio and pick alternate tires with their respective RC accordingly.

 

[Blake13]

Im leaning towards putting a 10-16.5 r4 tire on front and either a 13.6-24 r1 or 380/70r24 radial r1w on back. The 16.5" wheels are common in my front bolt pattern of 6 on 6". Rears bolt pattern is uncommon at 6.5" on 6. What I think will work well is to buy a 12x24" blank and have my stock centers welded to the blanks. This will also allow me to choose the offset.

The RC of these wheels fall within 0-5% front lead assuming my gear ratio measurement was accurate.

 

[Blake13]

A main goal of this thread was to show a simple (not taking anything apart) but accurate method for determining the gear ratio front to rear. I got some good feedback on my calculations, but I'm still hoping for more people with differential and transmission knowledge to jump in and tell me why my method works or is flawed, as it pertains to the mechanical element of the drive-train. As far as I can tell, there hasn't been much comment, aside from rScotty, on the theory behind the method I used to test the gear ratio.

 

[npalen]

I checked the gear ratio on mine several years ago by jacking up ONE SIDE of the tractor to let the front and rear turn freely. Then, with FWA engaged, simply marked and rotated the rear exactly ONE revolution. The front tire was also marked and watched the revolutions while rotating the rear. The number of turns and partial of the front is the gear ratio.

 

[dnw64]

AGREE! But each tire manufacture has slightly different RC for same sized tire. Also, when selecting new tire sizes, the decision will almost never be precisely the same ratio, having to fall slightly above or below the tractors factory tire RC ratio. In addition to this, I feel like my front assist, when engaged, winds up more than ideal. This suggests the factory tire ratio is likely on the end of the acceptable spectrum to begin with. Because of all this variance, it is easy to imagine a scenario where simply maintaining the ratio you described allows for new tires to fall outside of the acceptable lead/lag range. With all this said, it would be best to determine the gear ratio and pick alternate tires with their respective RC accordingly.

It sounds like you should start shopping jobs at tractor manufacturers, in their Rolling Gear department.

IOW, 99.99% of situations will be fine with factory supplied ratios.

If you want to start challenging the Big Boys and their lawyers, go ahead. I once observed that a local mechanic changed the tire pressure in my (current price) $100k Mercedes by more than 25% from mfr recommendation. I said - Do you want to take liability for an accident that could cost $1MM? He just said "I have years of experience, and those tire are not wearing right". I know, mfrs don't always get it right, but to unilaterally make a huge change without consulting the owner seemed very foolish to me. If you follow mfr recommendations and there's a problem you have something to fall on. They may not back it up, but really - they have millions (billions/trillions) invested, and you think you're smarter than them? You may well be, but I will take the mfr recommendation over Billy Bob 999,999 times out of 1,000,000.

 

[rScotty]

It sounds like you should start shopping jobs at tractor manufacturers, in their Rolling Gear department.

IOW, 99.99% of situations will be fine with factory supplied ratios.

If you want to start challenging the Big Boys and their lawyers, go ahead. I once observed that a local mechanic changed the tire pressure in my (current price) $100k Mercedes by more than 25% from mfr recommendation. I said - Do you want to take liability for an accident that could cost $1MM? He just said "I have years of experience, and those tire are not wearing right". I know, mfrs don't always get it right, but to unilaterally make a huge change without consulting the owner seemed very foolish to me. If you follow mfr recommendations and there's a problem you have something to fall on. They may not back it up, but really - they have millions (billions/trillions) invested, and you think you're smarter than them? You may well be, but I will take the mfr recommendation over Billy Bob 999,999 times out of 1,000,000.

They might be fine with the factory supplied ratios using the factory supplied tires, but why not make them better?

This is where us tractor owners are in luck. We don't have to be smarter than those mfrs, merely as smart. That's partly because this lead/lag ratio problem isn't a very difficult technical subject, and partly because as owners we have some big advantages that the manufacturer can't match.

One big advantage we have is that as tractor owners, our liability is limited compared to the manufacturer. We can try novel solutions while the manufacturer has to be more conservative making changes.

Another advantage owners have is that our choice in wheels and tires isn't limited to just some single manufacturing buyer's list of approved wheel and tire suppliers. Since we as owners don't mind accepting responsibility for how our own tractor works, we get to pick and choose from the whole world of wheels and tires to find exactly what we want. Mechanical designers who work for a manufacturer simply don't have that kind of freedom.

And then there is the power of being able to getting to measure things for ourself rather than depend on published specifications. We can use real world measured results to base our calculations on. That's huge. Having made the measurements ourselves, we know it is right. So we end up basing our calculations on real info instead of on some table of wishful manufacturing specifications subject to averaging, overseas manufacturing, price, and advertising hype.

Sure, the manufacturers do as good as they can and we gotta give them credit for it. Yanmar is a great example of the right way to do things. But we also understand that any mass manufacturer is going to have those limitations that owners don't.

So us owners get to fine-tune details that mass manufacturers just don't have time or resources to work on... I'd say that works out real well for both.
rScotty

 

[pmsmechanic]

They might be fine with the factory supplied ratios using the factory supplied tires, but why not make them better?

This is where us tractor owners are in luck. We don't have to be smarter than those mfrs, merely as smart. That's partly because this lead/lag ratio problem isn't a very difficult technical subject, and partly because as owners we have some big advantages that the manufacturer can't match.

One big advantage we have is that as tractor owners, our liability is limited compared to the manufacturer. We can try novel solutions while the manufacturer has to be more conservative making changes.

Another advantage owners have is that our choice in wheels and tires isn't limited to just some single manufacturing buyer's list of approved wheel and tire suppliers. Since we as owners don't mind accepting responsibility for how our own tractor works, we get to pick and choose from the whole world of wheels and tires to find exactly what we want. Mechanical designers who work for a manufacturer simply don't have that kind of freedom.

And then there is the power of being able to getting to measure things for ourself rather than depend on published specifications. We can use real world measured results to base our calculations on. That's huge. Having made the measurements ourselves, we know it is right. So we end up basing our calculations on real info instead of on some table of wishful manufacturing specifications subject to averaging, overseas manufacturing, price, and advertising hype.

Sure, the manufacturers do as good as they can and we gotta give them credit for it. Yanmar is a great example of the right way to do things. But we also understand that any mass manufacturer is going to have those limitations that owners don't.

So us owners get to fine-tune details that mass manufacturers just don't have time or resources to work on... I'd say that works out real well for both.
rScotty

I am thankful for your well thought out response! I was wanting to respond but made myself wait because I knew that what I wanted to say wasn't nearly as eloquent!