New rotaspreader arrived last week,ordered on track tread tyres,thinking they would be flotations with a track tread.Turns out they are actually remould super singles! Inflate to 6 bar,will they damage the ground more than flotations?
What does tyre pressure have to do with ground pressure?
- Thread starter stablegirl
- Start date
stablegirl
Member
- Location
- North
Upsides they are tall so long footprint.
Downsides they are narrow, squaresided, so just dig in.
Downsides they are narrow, squaresided, so just dig in.
- Location
- N.Lincs
Yep.
If you want to carry a lot of weight over soft ground you need wide, tall tyres - and you need them on your tractor too.
Been there, done that, got the T-shirt.
Over the last 10 years or so manufacturers have got away with narrow spec tyres on machines. Only with last year's wet back end (and this year's too, to some extent) has this old chestnut about ground pressure become more of an issue.
- Location
- South Devon
MS90 ? I priced one up against a Flemming 1000 with the same sized barrel
The Flemming came with 8 stud 550/60 tyres as standard whereas Marshall wanted another grand for them
I'm running the 550/60's at 1.6 bar - I think super singles will be looking pretty soft at double that.
- Location
- central scotland
Big footprint x small weight = less compaction (not no compaction)
big footprint x big weight = more compaction
small footprint x big weight = more compaction
A tyre PSI alters the size of that tyres footprint but while running the same tyre at different pressures will help ,especially the fancy Vf types it is only due to the increased contact area of the tyre just as an empty trailer leaves less ruts than a fully loaded one
big footprint x big weight = more compaction
small footprint x big weight = more compaction
A tyre PSI alters the size of that tyres footprint but while running the same tyre at different pressures will help ,especially the fancy Vf types it is only due to the increased contact area of the tyre just as an empty trailer leaves less ruts than a fully loaded one
ShooTa
Member
- Location
- Denbighshire - In the vale of Clwyd!
soo my old ford 4000 needs new rears...
Yes MS90 big wide tyres no good to me,too many side slopes I will try them at 4 bar and see how it goes,I don’t need their ultimate weight carrying ability which is nearly 5t per tyre.MS90 ? I priced one up against a Flemming 1000 with the same sized barrel
The Flemming came with 8 stud 550/60 tyres as standard whereas Marshall wanted another grand for them
I'm running the 550/60's at 1.6 bar - I think super singles will be looking pretty soft at double that.
Boohoo
Member
- Location
- Newtownabbey
800/50-34 are perfect on them...
- Location
- N.Lincs
Yeah, it's all a compromise, there's no 'one size fits all' answer. Too wide and too much flotation and you've not enough grip/traction and that can get dangerous.A wider tyre with a larger footprint will do less damage to more land
- Location
- Darlington
You want to see the damage a grey Fergie with a transport box on does delivering eheat for the syndicate. Them front tyres are like razors.
CORK
Member
- Location
- East Cork, Ireland
The old thumb rule was any more than 6tn per axle created compaction.
Wide tyres will help limit damage at the surface (or seed zone) but if the axle load is big then the compaction occurs deeper in the profile.
Wide tyres will help limit damage at the surface (or seed zone) but if the axle load is big then the compaction occurs deeper in the profile.
Deutzdx3
Member
Watched a you tube video of super singles versus flotation tyres, dug a hole and reversed trailer over the lip. Gist of it was weight spread over a larger area reduces compaction. Look at Michelin tyres, they can be run super low thus giving a much larger area for the given weight to be carried on. So reducing the tyre pressure increases the footprint so decreasing the ground pressure per square what ever you measure it in.
Arceye
Member
- Location
- South Norfolk
I thought it was more to do with the depth of ground compaction rather than the surface appearance. High pressure on a tyre will reduce the side wall flexing and concentrate the pressure in the centre of the tyre putting the compaction into a narrower line and at a greater depth. The same tyre at a lower pressure will spread the load more evenly over the whole area giving less compaction. The visual appearance may be similar but the damage varies at depth.
Exfarmer
Member
- Location
- Bury St Edmunds
The weight a tyre carries and exerts on the ground is a simple factor, weight on axle Say 10,000 pounds
divide by 2 = 5,000
area of tyre on contact with soil say 100 sq inches , thus tyre pressure on soil will be 50lbs per sq inch.
ifthe tyre is only inflated to 30psi the tyre will squab out till the area in contact is 5000 / 30 = 166 sq inches.
this will only happen if the tyres walls are flexible enough and the ground can take a force of 30psi.
if the tyre walls are not flexible, they will take as much force as is neccessary to carry the weight ( this of course is bad newsfor the tyres , but is regular in todays run flats.)
there is though another factor. How much weight can the soil carry.
if the soil will only carry 20psi then the tyre will sink in till the areain contact with the soil becomes 200 sq inches. ( 5000/ 20 )
this means that those tyres which are run at low pressure to spread the weight, do not always work as they should.
if your tyre which now has a has a contact area of 200 sq inches ( at 20 psi ) is designed to run down as low as10 psi giving a contact area of 400 sq inches
if the soil under this low pressure tyre running at say 10 psi, can only carry 8psi then the tyre may not squab and the tyre will then sink far more than expected. If it reverts to its original shape giving only 100sq inches it will need to sink until its length In the ground allows the tyre carry the weight.
The tractive force required to drag this tyre through the ground is massively increased as dragging the tyre will then increase its squab causing a bulldozer effect.
it is critical to get the right flotation tyres!
divide by 2 = 5,000
area of tyre on contact with soil say 100 sq inches , thus tyre pressure on soil will be 50lbs per sq inch.
ifthe tyre is only inflated to 30psi the tyre will squab out till the area in contact is 5000 / 30 = 166 sq inches.
this will only happen if the tyres walls are flexible enough and the ground can take a force of 30psi.
if the tyre walls are not flexible, they will take as much force as is neccessary to carry the weight ( this of course is bad newsfor the tyres , but is regular in todays run flats.)
there is though another factor. How much weight can the soil carry.
if the soil will only carry 20psi then the tyre will sink in till the areain contact with the soil becomes 200 sq inches. ( 5000/ 20 )
this means that those tyres which are run at low pressure to spread the weight, do not always work as they should.
if your tyre which now has a has a contact area of 200 sq inches ( at 20 psi ) is designed to run down as low as10 psi giving a contact area of 400 sq inches
if the soil under this low pressure tyre running at say 10 psi, can only carry 8psi then the tyre may not squab and the tyre will then sink far more than expected. If it reverts to its original shape giving only 100sq inches it will need to sink until its length In the ground allows the tyre carry the weight.
The tractive force required to drag this tyre through the ground is massively increased as dragging the tyre will then increase its squab causing a bulldozer effect.
it is critical to get the right flotation tyres!
yellow belly
Member
- Location
- south west lincolnshire
a cross ply tyre exerts much higher pressure than a radial tyre at the same pressure because the tyre wall on a crosply is very stif f
most radials tractor tyres ground pressure is couple of psi above tyre pressure
i found that radial tyres at the correct tyre pressure for the speed and load do a lot less soil damage than if they are 10 psi higher set for road speeds
our sprayer on wide wheels at 20 psi can make a rut but at 10 psi at field speed pressure it leaves little mark in ploughed seed beds
you do have to hold back on the forward speed to reduce the wheel slip
Define ground pressure? More rubber on the ground for a given weight = less ground pressure and less shallow damage, hence Terra Tyres making less of a mess on soft cultivated ground. Modern tyres with increased flexion tyres allow the compromise of narrower widths, bigger foot prints, faster road speeds and the ability to transmit torque.
Nescient
Member
Your brother is spot on. It's YOUR argument that's poppycock. This is easily proven by a children’s experiment.A 1 foot wide tyre at 30psi will exert a hell of a lot more ground pressure per square inch than a 10 ft wide tyre at the same pressure bearing the same weight. My older brother would insist that a tyre exerted the same pressure per square inch as the tyre pressur, poppycock.
As for the lady with the syleto`s on,depends if I had the right glasses on
A party balloon inflated to pressure ‘P’ and then weighed and found to have a mass of ‘W’, will flatten slightly if put on the ground, typically creating a circular or egg-shaped contact area of ‘A’. (The balloon distorts until its internal pressure is spread over a large enough area to transfer the balloon’s weight to the ground, at which point the flattening stops.) Measurement of A and calculation will show that P x A = W, proving that the balloon’s internal pressure supports the balloon’s weight. Since the ground and balloon are in equilibrium (neither is shooting off in opposite directions) it follows that the upward force the ground is exerting on the balloon is equal to the weight of the balloon, and since both forces are acting on the same (contact) area, the balloon’s internal pressure and that the ground bearing pressure must be equal.
If one then takes a smaller balloon and inflates it to the same pressure P, and (keeping that pressure constant) adds weight to the balloon to bring its mass up to W, one will find that when placed on the ground the smaller balloon’s contact area will be exactly the same as that of the larger balloon.
The mathematical proof of this is simple. Pressure = load/area. (P = W/A)
Transposing this formula gives A = W/P. I trust you can see that if you fix W and P (as you have), A will always be the same – with no involvement of tyre widths or anything else.
This means that ANY number of inflated flexible objects, regardless of their size, shape, material of construction or substance of inflation, will create the same size contact area with a supporting surface, so long as the objects’ masses and inflation pressures remain constant across the group.
So... a 1ft wide tyre and a 10ft wide tyre, each at 30psi and each carrying, say, a 2880 lb wheel load, would each create a contact area with the ground of 2880/30 = 96 square inches. The only difference would be that the footprint of the 1 ft wide tyre would be 12 x 8 inches, while that of the 10ft wide tyre would be 120 x 0.8 inches.
To close, I have two further comments. Firstly, ‘pressure’ means ‘load per unit area’, so ‘pressure per square inch’ means ‘load per unit area per unit area’ – which is of course nonsense. Secondly, the UK has been metric for over half a century, so why are you still living in the pounds, feet and inches Middle Ages? ;-)