Wheels

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Amended 27/10/18

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User avatar
munga
Posts: 38
Joined: Thu Jul 08, 2010 9:18 pm
Location: Bristol

Wheels

Post by munga » Wed Oct 26, 2011 9:19 pm

I have a 780 selectomatic which has had the rear wheel centres turned around so the tyre valves are on the inside of the wheels. Is this done just to make the wheel base wider or is there other reasons.
Also if i wanted to turn them around can i turn the centres with the tyres on or do i have to remove the tyres first ?

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calvin
Posts: 490
Joined: Sun Apr 04, 2010 10:41 pm
Location: ireland / northern ireland

RE: Wheels

Post by calvin » Wed Oct 26, 2011 9:25 pm

im pritty sure you do not have to take the wheels off the tyre but if your cutting the old bolts off i would not recomend it ) does turning the centres around not shortin the wheel base ?
3 pot , 4 pot and the MIGHTY 6 POTT!

Eric_T
Posts: 1408
Joined: Sat Dec 31, 2005 11:57 am
Location: North Wales

RE: Wheels

Post by Eric_T » Wed Oct 26, 2011 9:31 pm

There are 8 combinations as to where the centre can be in relation to the rim, the sole reason for this was to increase or decrease the track width of the tractor (David Brown tractors were the first to do this) It does not affect wheel base.

If you change the wheel width, make sure that the 'vee' of the tyre tread is pointing forward, or upward when viewing the tractor from the back.

:)

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calvin
Posts: 490
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Location: ireland / northern ireland

RE: Wheels

Post by calvin » Wed Oct 26, 2011 9:45 pm

sorry i ment width not wheel base
3 pot , 4 pot and the MIGHTY 6 POTT!

Guest

RE: Wheels

Post by Guest » Wed Oct 26, 2011 10:20 pm

Turning the centres around increases the centre opf gravity making it lower and obviously more stable on steep gradients as it also increases the width between the wheels, this however is not advisable as you weaken the points of contact of the wheel centre on the nuts and studs and also put more strain on the hub bearings. As Eric T says, ajust the track or width by moving the centres to either the inside of the rim lugs to widen the track or outside to decrease it as the wheel rims are. If you wish to increase or decrease the width further you have to reverse the rims and also turn the tyres in order that the cleats are facing the correct direction. If you have one, look at the handbook for the tractor, all this will be explained there including the front axle track width settings. Prolonged use with the dish centres turned inside out will cause problems.

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jimc1390
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Location: cornwall

RE: Wheels

Post by jimc1390 » Wed Oct 26, 2011 10:24 pm

really? seen sprayer tractors spend there lives out there
db 990 selectamatic
case ih 1594 com ed
db 1390 gd90 loader

Guest

RE: Wheels

Post by Guest » Wed Oct 26, 2011 10:39 pm

Probably because they think it makes them more stable Jim, which it will, guess they've just been lucky. Ask any car pimper what reverse rim wide wheels will eventually do to suspension components and bearings, plays havock with the geometry.

Eric_T
Posts: 1408
Joined: Sat Dec 31, 2005 11:57 am
Location: North Wales

RE: Wheels

Post by Eric_T » Wed Oct 26, 2011 10:55 pm

Front wheels should not be reversed, as this causes poor steering geometry.

As for reversing the dish on the rear wheels, at a guess they were designed to withstand long hours of work at wider track settings. Thinking about it, the relatively short change in bending moment, the distance from the outer bearing of the reduction unit to the centreline of the rear tyre changes by approx 6 ins? So the damage might not be as great as we think?

Guest

RE: Wheels

Post by Guest » Wed Oct 26, 2011 11:15 pm

I've seen some tractors with the centres reversed plus the rims turned so that the inside from the lug only the outer edge of the rim to the bead is taking all the weight on the lugs, now that is asking for trouble.

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munga
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Location: Bristol

Post by munga » Wed Oct 26, 2011 11:39 pm

I meant width of the tractor not wheel base but i think you all knew what i was trying to say !
Can i swap the centres around with out removing the tyres or letting down the tyre pressures as i dont want the wheel rims to buckle when i undo the bolts !!!!

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tdickson
Posts: 85
Joined: Thu Oct 29, 2009 3:57 am
Location: Wyee, New South Wales, Australia

Post by tdickson » Thu Oct 27, 2011 1:49 am

An interesting question. According to the David Brown Instruction Books for 780 & 880 it details 8 different combinations for various orientations of wheel centre, rim and lugs. Why would David Brown publish this if it was not advisable to do so???

Here's a snippet from the 850/880/990 Drivers Guide which is also reproduced in the 780 & 880 Instruction Book. Perhaps it something to do with the desired application/use.
1967 David Brown 880A / 540113
1968 David Brown 880A / 550795

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wheeler
Posts: 249
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Location: USA
Contact:

Post by wheeler » Thu Oct 27, 2011 5:50 am

Dish in or dish out is just how you attain the desired track width of the rear tires. does not hurt a thing whichever way. You can move them around however you like with out removeing the tires. You may have to switch sides to keep tread pattern corect with some changes. I would not reverse the front wheels though. There is plenty of adjustment in the front axle.

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erkki
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Location: North Finland

Post by erkki » Thu Oct 27, 2011 6:01 am

I can not see any problem in turning the wheels. I have made that a couple of times for special purposes and also changed the wheel from left to right to get the arrow pattern flow on correct direction. Turning the front wheel hub is more complicated question because theoretically steering is quite ok when the front wheel contacts ground on the same spot as an theoretical extension of the king pin. If there is big difference, the steering wheel is very eager to knock on fingers on an uneven field.

RGDS
Last edited by erkki on Thu Oct 27, 2011 4:07 pm, edited 1 time in total.

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jimc1390
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Location: cornwall

Post by jimc1390 » Thu Oct 27, 2011 11:01 am

i thought it was strange, everything down here is on 72" for spuds and veg, not just sprayers but harvester tractors etc
db 990 selectamatic
case ih 1594 com ed
db 1390 gd90 loader

Guest

Post by Guest » Thu Oct 27, 2011 9:35 pm

Where I worked every tractor we ever had spent its life at 72" spacings which I believe was the second widest spacing available. Tramlines were 72" and potato rows were 36". Never had any problems.

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