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View Full Version : PSI - Go by Manual or what's on tire?


hillndale
06-01-2005, 08:09 PM
I assume you go by the Manual, but thought I'd ask -- I have a new Scag Z Cat and thought I better check the tire pressure since reading how much tire pressure effects cut and handling. Well they are set closer to what's on the tires. The manual says 12PSI in drive wheels and 25PSI in castors. On the tires it says: drive tires 24PSI max and castors say 46PSI max. So the manual is calling for roughly half what the tire manufacturer is saying. Could someone please enlighten me. Many Thanks

hillndale

Grass Masters
06-01-2005, 08:11 PM
GO by what is on the tire because the maunal was written for the tires taht was placed on any unit at the factory.

The tires you buy may or may not meet the same standards as the ones that were at the factory..

What does it say about min.

hillndale
06-01-2005, 08:27 PM
GO by what is on the tire because the maunal was written for the tires taht was placed on any unit at the factory.

The tires you buy may or may not meet the same standards as the ones that were at the factory..

What does it say about min.

It doesn't mention minimum. The tires on the machine came with the machine. Are you saying the manual isn't model specific?

LightningLawns
06-01-2005, 08:39 PM
max psi is just the maximum that the manufacturer of the tire recommends you can put as little as you want just don't exceed the max. Go with what the manual says otherwise your cut height might be off.

riches139
06-01-2005, 08:48 PM
The high pressure on the tire is to seat it to the rim during the manufacturing process.

They usually come overinflated unless the dealer did his job and adjusted them.

You'll find that 24# in rear and 46# in front will make it ride like a rock. :angry:

topsites
06-01-2005, 08:49 PM
GO by what is on the tire because the maunal was written for the tires taht was placed on any unit at the factory.

The tires you buy may or may not meet the same standards as the ones that were at the factory..

I always go by what's on the tire, too.

Far as cut-height, not only should this be influenced little to none, but I check this from time to time, in my case when the WB sits on a level surface, the blades are 4 fingers from the ground. Since both my Wb's are the same model and make, both are set to the same height - So if one should actually break down in the middle of a yard, I can come back with the other and finish it without any problems.

50 psi is what I have in the front, 30 in the rear (for my fixdeck WB). That way when I hit a bump, low tire air-pressure doesn't act like a shock absorber, causing the deck to 'sink' towards the turf and creating a nasty scalp. That, and it rules when curb-jumping.

Oldtimer
06-01-2005, 08:50 PM
Over inflate mower tires and they could be ruined. They are not belted and will stretch.

Oldtimer

hillndale
06-01-2005, 09:04 PM
Interesting and thanks -- I'm 2 for 2 -- some say follow manual and others go by what's on the tires. The drive wheels on my machine even have little stickers that say 12PSI. I'm currently at twice that.

It has just started drying out here, but my tires have been spinning a lot. I know lowering the pressure will lessen the bumpiness of the ride & I would think definatelt effect cutting heights. How does pressure effect impact on turf?

hillndale

Precision
06-01-2005, 09:24 PM
less tire pressure gives more grip

More tire pressure gives more height and more speed

Tire pressure should be run on the softer side to create less wear on the turf, less damage to the machine/driver and to create a larger contact patch.

If the manual says 12psi try it there and see how she runs. Different types of tires require different amounts of pressure. The bald from the factory castors with really thick walls typically require much less than thin treaded tires to maintain shape.

Unless you own a Ferris you tires are the only shock absorber you have.

hillndale
06-01-2005, 09:33 PM
less tire pressure gives more grip

More tire pressure gives more height and more speed

Tire pressure should be run on the softer side to create less wear on the turf, less damage to the machine/driver and to create a larger contact patch.

If the manual says 12psi try it there and see how she runs. Different types of tires require different amounts of pressure. The bald from the factory castors with really thick walls typically require much less than thin treaded tires to maintain shape.

Unless you own a Ferris you tires are the only shock absorber you have.

Thanks very much Precision -- I noticed I've been spinning my wheels (so to speak) a lot, even backing up trailer ramp. I thought something was wrong. Though you say softer tires create less wear, I would think the opposite, but I totally trust your expertise & will set the tires to the "manual specs" & see what the response is. Thanks again

hillndale

Runner
06-01-2005, 11:12 PM
What determines my exact tire pressure is whatever makes the mower go straight.

DennisF
06-02-2005, 12:25 AM
I run my Hustler Z with 15 psi in the rear tires and 20 in the front. That seems to give the best ride while keeping the cutting height accurate and no scalping.

Tire manufacturer recommendations are always maximum PSI for the tire...not the recommended PSI for the application.


Sometimes you have to experiment a little with tire/cutting blade/grass type configurations to get the best set-up for your business.

I've always found that the mower manual recommendations are the best ones to follow.

chuckers
06-02-2005, 12:33 AM
I run Scags and run 12 in the drives and 20 in the front. More psi will make you feel like you are in a rodeo.

The Captain
06-02-2005, 12:47 AM
Go by the manual, not the tire sidewall markings. The manual is the pressure the mower manufacturer designed the mower to operate at. The sidewall markings are the maximum pressure the tire can be inflated to, safely, without blowing up. The higher the pressure you run, the higher your deck will set, giving a false cutting height and a rougher ride. Why do you think auto manufactures over inflate those skinny little tires for mileage records. It sure aint for comfort.

Jim

Dale in PA
06-02-2005, 04:52 AM
Another vote for the manual. As others have stated, the sidewall markings are max safe inflation pressure, NOT a recommended operating pressure. The mower manufacturer knows what the machine weighs and calculates recommended operating pressures accordingly.

Just like the auto manufacturers.

grass_cuttin_fool
06-02-2005, 07:09 AM
I hAve a scag also and I split the difference, I run about 35 in the casters and 16-18 in the drives and it does ok. I have ran them at the max and the min and at the max they ride and bounce bad.

Charles
06-02-2005, 07:19 AM
I dont see why you would run different tire pressure for the front and back tires with a fixed deck. I go by the manuel and all the tires have the same pressure--13 psi. The heat around here causes the pressure to go up by lunchtime. So I recheck the pressure in each tire and usually have to let air back out to get it back to 13 psi

hillndale
06-02-2005, 07:30 AM
Hey, thanks so much for the answers. A huge help. I've only had this machine(scag z cat) a few weeks and running through the shakedown period has raised some concerns. (next thing I need to find out abouty is the "steering dampers"- one seems to be getting a little stiff when pulling left control arm back for reverse -- but maybe that's another thread- I gotta check into it)

Thanks again

The skies are finally blue again Maine and I'm ready to rock & roll!!!

hillndale

TLS
06-02-2005, 07:45 AM
I cant believe the spread of answers here. And the amount of incorrect information.

Run your tires at or close to what the manual says. Adjust a pound or two here or there to suit your tastes on ride.

Your max inflation is NOT what they use to seat your bead. They often go higher.

Running full sidewall pressure will wear out your body, tires, and mower much faster.

Tire pressure certainly DOES affect your cut height, and quite a bit I might add. I surely hope the guy measuring cut height by the "4 fingers to the ground" method was joking. I've never heard such a rediculously inaccurate method. A difference of just 1/8" is noticable on the grass.

I cant think of much else, but please for the sake of your mowers, drop them down close to mfr. recommendations.

chuckers
06-02-2005, 12:46 PM
(next thing I need to find out abouty is the "steering dampers"- one seems to be getting a little stiff when pulling left control arm back for reverse -- but maybe that's another thread- I gotta check into it)



There should be a spring on the lever part and a spring put Oil on it and it should fix that problem

pagefault
06-02-2005, 01:49 PM
Go with the manual. When you do the tires on your car or truck, go by the sticker on the door frame. Max PSI is the MAXIMUM that the tires are able to safely hold. That's not even what the tire manufacturer recommends.

I'm sure they put that on there for liability reasons, so that when some numbskull puts 100 psi in them and they blow up, he can't sue the manufacturer.

Your top speed is 125. That doesn't mean you're supposed to go 125.

Oldtimer
06-02-2005, 03:34 PM
The mower manufacturers don't know squat about tire pressure so put in as much air as you want. What the manufacturers don't tell you is that you can get another 3 MPH with 28 - 30 PSI in the drive wheels. Just be sure to fasten your seat belt.

More is always better.

Oldtimer
I love this site!

TLS
06-02-2005, 03:35 PM
OK..... :confused:

betterlawn
06-02-2005, 03:59 PM
OK - this speed thing has me stumped. Unless you're increasing the diameter of the tire by 10% or so by overinflating it, you're not going to get more speed out of it. Do you go faster when you overinflate your car tires? The speed is directly related to the tire circumfrence (diameter) and shaft speed.

That said, it seems pretty obvious that you should start with the manual recommendations and adjust from there. That same tire could be on 2000 other things, competely different applications. There is no reason to think you should use a sidewall pressure rating - its a max. And if you think the ride is stiff at full pressure, imagine what its doing to your mower. Its not like they put shocks on those things. :rolleyes:

RKISTNER1
06-02-2005, 04:01 PM
The Captian is right. All 6 tires on my JD were over inflated out of the crate.

TLS
06-02-2005, 04:02 PM
You'll gain a little speed, but not 3 mph.

Mainly you'll feel snappier with stiffer tires....less mushy.

I notice a difference from 12psi to 15 psi....but not 3 mph.

Precision
06-02-2005, 08:08 PM
The mower manufacturers don't know squat about tire pressure so put in as much air as you want. What the manufacturers don't tell you is that you can get another 3 MPH with 28 - 30 PSI in the drive wheels. Just be sure to fasten your seat belt.

More is always better.

Oldtimer
I love this site!


speed from over inflating a tire comes in two areas. Increased tire diameter. This creates a larger circumference so you go further per rotation.

The second is from less friction. An under inflated tire will mush and deflect with each revolution creating drag and greatly reducing the effective circumference of the tire.

Over inflation is a really bad idea. beats you up, beats up the machine, beats up the yard. Turning the mower into a pogo stick will certainly create scalps and other bad things.

dramatic underinflation is also bad. premature sidewall failure, instability of tracking and divots on turning.

Oldtimer
06-02-2005, 08:15 PM
Don't take my post about 3 MPH seriously. I wrote it as a joke.

Everyone with any experience and a lick of sense will stay with the mower manufacturer's recommendations.

Oldtimer
You cannot direct the wind but you can trim the sails!

TLS
06-02-2005, 08:23 PM
Don't take my post about 3 MPH seriously. I wrote it as a joke.

Sarcasm isn't taken well with typed responses. Sounded as if you were serious to me.

Del9175
06-02-2005, 08:37 PM
I run mine at about 15 psi. Once when doing some maintenance I put them up to the tire's recommend max and I had no traction and it was a terribly bumpy ride.