Why the positive camber on the front wheels?

[Hugo Habicht]

Hello,

the camber on the front wheels of the G1900 is positive, about 3 degrees although it looks more.

I would like to change that but not before understanding why it was done this way. As opposed to a pretty ignorant member of this forum I do consider Japanese engineering top class in general and Kubota engineering in particular. So the engineers had a technical reason to do it this way.

Does anybody know why the positive camber?

 

[GreensvilleJay]

easier for tractor to drive in straight line.

 

[Hugo Habicht]

easier for tractor to drive in straight line.

I thought toe or more so caster angle would contribute to that, yet Kubota decided to make both zero.

 

[GeoHorn]

Positive camber accomplishes a couple of things: It allows for higher gross-weight (even with rigid suspensions). It facilitates turning-traction. It favors turn-radius.

 

[ruger1980]

In theory the camber or the vertical center axis of the front tire and the King pin axis should intersect near the center of the tire. This makes steering easier and correctly distributes the load on both items.

 

[NorthwoodsLife]

With all respect:

It is a lawn tractor. Not a race car.

Top speed might be 10 mph. Camber and castor and toe in, is set to help you drive it easily and mow grass.

That is what it does best.

I wouldn't mess with factory settings unless there is a problem with the front wheels tearing up grass, etc.

I will admit, I have a cheap Craftsman lawn tractor for finish mowing and I never checked the camber, castor, or toe in. Nor ever did I have reason to do so.

Good luck Sir.

 

[Hugo Habicht]

Positive camber accomplishes a couple of things: It allows for higher gross-weight (even with rigid suspensions).

How is that?

It favors turn-radius.

You mean tighter turning radius is possible? Have to check that.

In theory the camber or the vertical center axis of the front tire and the King pin axis should intersect near the center of the tire. This makes steering easier and correctly distributes the load on both items.

Yes, I agree. But the design does not achieve this. And the positive camber seem to move the centre of the tyre force (red) rather away from the king pin pivot point it seems (perspective a bit misleading, but picture basically correct).

 

[Hugo Habicht]

With all respect:

It is a lawn tractor. Not a race car.

You are 100% correct there

But then again, we don't know how fast we can get this machine to run and where it will be driven then But this is not my reason for asking.

I will admit, I have a cheap Craftsman lawn tractor for finish mowing and I never checked the camber, castor, or toe in. Nor ever did I have reason to do so.

Well, not much to check, it is clearly visible and I find it looks stupid. That is what is bugging me. The rear wheels (that steer as well) do not have that, their camber is zero.

 

[NorthwoodsLife]

You are 100% correct there

But then again, we don't know how fast we can get this machine to run and where it will be driven then But this is not my reason for asking.



Well, not much to check, it is clearly visible and I find it looks stupid. That is what is bugging me. The rear wheels (that steer as well) do not have that, their camber is zero.

Rear stear is cool!!!

Learn something new every day.

 

[Hugo Habicht]

Rear stear is cool!!!

Learn something new every day.

Yes, it has four wheel steering allowing for a very tight turning radius. With a 48" cutting deck it only leaves about a 20" circle uncut, very handy when cutting around trees.

I bought a 54" deck that will even make that a bit smaller again.

We agree it is not a race car, but with that steering the seat safety switch (that I joked about initially) does make sense. When going "full speed" and turning the steering wheel quickly it would throw you off the seat easily.

 

[Hugo Habicht]

Here you can see the rear wheel steering mechanism.

 

[NorthwoodsLife]

Here you can see the rear wheel steering mechanism.

That is awesome. Sorry that I called it just a lawn tractor.

A great idea but I am guessing it was destroyed by the zero turn mowers... which are just goofy.

I was in town the other day gassing up my truck at KwikTrip. A guy drives in on a zero turn mower. Goofy looking thing. He puts gas in it and then spins a 180, on a dime style, and drives to the church right next to the gas station to continue mowing.

Something inside me didn't like it. The same feeling I felt when I saw a Bobcat skid steer work for the first time, 40+ years ago. Putting me and my Kubota B7100 out of business. It was a better small space machine.

I guess, and know, that I am getting old.

Your G1900 will be a collectable. Keep it going.

 

[Hugo Habicht]

That is awesome. Sorry that I called it just a lawn tractor.

No reason to be sorry, Sir, it is a lawn tractor, not more, not less.

And I agree with the zero turn mowers. I do not like them either, despite their technical advantages. I do not even need four wheel steering, I had planned the shape of the lawn with no corners, no trees, so I have a simple straightforward cutting path.

I guess, and know, that I am getting old.

Yes, I am too, and thinking about it, everybody is, no exceptions.

Your G1900 will be a collectable. Keep it going.

Yes, that is the plan. Still doing up the tractor, cosmetics is next. Good thing is that it's design allows it to repair it yourself.

I think the older the tractor, the longer they can be used. When I looked at my friends L1421 recently (that he plans to use for the rest of his life) with a graphics LC display, CAN bus, fairly complex electronic engine and tractor controllers, I had serious doubts if he will be able to keep it running long term.

Same as with cars, it is often not the mechanics any more that ends it's useful life but the electronics. I think my friends 1960s Massey Ferguson will still be running when his 2019 Kubota is long gone.

 

[PaulL]

I guess, and know, that I am getting old.

Yes, I am too, and thinking about it, everybody is, no exceptions.

The old fella down the road always says to me "getting old really sucks." My stock answer is "it's better than the alternative."

 

[GeoHorn]

….
Your G1900 will be a collectable. Keep it going.

If it remains original.

 

[Hugo Habicht]

If it remains original.

It is and it isn't. I am not making a museum piece out of it, I want it fully functional, paintwork flawless but it has to do work. And every tractor here in the forum I have seen has been modified as per requirements of the owner. Are they original?

Also when I did repairs and noted weaknesses of the original design (weaknesses that showed after over 30 years of hard work) or flaws in the original design I modified it. For example:

- combination box is now contactless, shows error codes, has status LEDs for quick fault finding and an override function that allows the tractor to be started despite faulty safety switches

- instrument cluster now has proper dials for temperature and tank and added instruments for engine oil pressure and an engine rev counter that can be switched to hydraulic pressure and driving speed

- extra seals on the front wheels that prevent corrosion

- front axle modified to remove steering play

- steering box modified to achieve play free steering

- radiator plug that does not brake off any more

- coolant drain valve that does not brake off when you touch it

and plenty more. The work I did so far is described in Reviving a G1900

Decide for yourself if original or not. Every modification I did can be easily brought back to factory condition. So if you want back 2 inches play in the steering, no problem.

 

[lugbolt]

reduces steering effort. That is the only purpose.

these were available as 2ws and 4ws. The 4ws models were easier to steer than the 2ws. I have had both and can speak from experience. The front axle is the same between the two. Mass production, why make two different front axles, right? So on the 2ws version, they had a bit more effort to turn, so positive camber was incorporated into the spindles to reduce the steering effort a little.

that info came directly from Kubota-not a rep, but one of the japanese engineers (had to be translated), from way back in the 1990's when the dealer I was working for took on Kubota. Should have been about 1992 or 1993. Kubota reps bought out some of the engineers to explain a few things about their brand. Wasn't the first time I spoke with them. Later on in about 06-ish (RTV gas) and then in about 2010 or so, then in 2012 I think when they came in asking questions about what equipment needed what updates or changes. Translators worked for Kubota. Since we had kubota AND kawasaki, they were trying to compete with the Mule 600/610 series, so they built the RTV with a little single cyl gas engine and they brought them to us to compare. Watching the Japanese engineers drag race the Mule vs RTV across the parking lot was hilarious. Their prototype eventually became the RTV 400 which was mostly a flop.

Anyway, that is the only purpose of positive camber in this application. It can lead to excessive wear on the tires if used on hard pack and/or paved surfaces. Reducing positive camber will increase steering effort. Probably quite a bit. May not be a problem if the unit has power steering, and G1800/1900 does not. But it can, but will require some work to make the motor assembly fit under the dash. The 200w ATV EPS should work just fine with some general fabrication work.

Handling is of no issue although if you max out the HST pedal stop, they will run about 10-11 mph, and if you turn the governor up a little they'll get up around 13. but the engine is screaming pretty good (closer to 4000 RPM). On the 4ws model, that's just too fast due to the rear caster, they kind of get squirrelly and hard to keep a straight line. I have not tried it on the 2ws--that one is my mom's and she does NOT need to be able to go that fast, period. I did it on my 4ws though and generally don't recommend it on them because of what I learned.

Good luck.

 

[Hugo Habicht]

@lugbolt : thank you very much for the detailed information !

The 4WS getting squirrely at high speed: is that due to the smaller steering radius compared to the 2WS or maybe also due to the play in the steering box (which I eliminated completely)?

I thought the caster helps to keep the vehicle running straight, but that information belongs to front axle only steering.

Also the rear king pin bushings on mine were completely worn; I think this would contribute significantly to that too. I had considered adding grease nipples there. Do you think this would be a good idea?

 

[pigdoc]

Seems like there is positive camber on the front wheels of many farm tractors...
One thing to realize is that we rarely drive our Gs on flat ground! So, perhaps the camber improves front traction on uneven ground.

Hugo, one upgrade I did on my G1800S is to install a couple of handles on the fender pan. I liked the handle on the fender of my L2500, so I bought two of those for the G1800 (one for each side). PN is 34670-29440. Cast aluminum, $34 each is a bit spendy, but they are very robust and comfortable. I also bought the nuts for those handles because I didn't want to have to hunt up nuts that would fit (02174-50140).

Gives me a handhold to stay in the seat when I'm on a sidehill. You do NOT want to wrap your fingers around the (sharp) edge of the fender pan itself! You just might lose those fingers if an axle happens to fail!

My G1800S came with a spinner knob on the steering wheel. Very nice when making sharp turns as we tend to do with 4-wheel steering!

-Paul

 

[lugbolt]

with rear steering there will always be some tolerance stack up. .001 here .002 there, it all adds up. Combine that with a steering geometry that is solely designed to be easy to steer, and it'll get sorta squirrelly with more speed. One could change the camber of the king pins and caster, but honestly it's not worth the effort. It would be a lot of effort on this machine for little gain.