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Different wheels on the front and back

Sid

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great_britain
Hi all
Im thinking about putting smaller wheels on the front of my landcruiser 120, something like 285/50/20 and on the rear 305/50/20. Its an lc4 series so has the atrac and centre diff lock. The thing that puzzles is that its permanent 4wd with a 40-60 torque split front to back. If i dont press the button to engage the centre diff lock, is the centre diff effectively an open differential? If so then im thinking i should be able to put different size tyres on the front and back. I can always change back when off roading but the jeep does spend most of its time on the road lol. Your thoughts on this would be appreciated.
 

David

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1st question is why would you want to do that, 2nd question why 20" rims
 
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David

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I will answer your question width is not so important but they need to be the same height
 

Chris

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Well you did end by asking for our thoughts. And I am with David. Why on earth would you even entertain something as stupid as this? Frankly since the days of setting this forum up, it's one of the most ridiculous suggestions I've ever heard. For the life of me I can't see what potential advantage this would give you other than to make your 120 look like a beach buggy.

I know you won't like this answer, but we're just trying to save you from yourself. And please don't call it a Jeep.
 
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Shayne

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They are saying you will regret it . It's permanent 4x4 and knowing myself how skittish at speed my truck was with worn panhard/control arm bushes i'm inclined to say the road holding ability of even a Cruiser is a finely balanced affair . When we go up with a suspension lift we are forced to correct caster in order to retain the trucks original footprint or its handling suffers .
 

Juddian

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Looks wise, odd is about the kindest term i can think of.

Just run those two through a tyre size calculator calculator, according to which the 305's will be revolving 16 times fewer than the 285's every mile driven.
Off road this wouldn't matter, not as those tyres will be worth a damn off road, but on dry roads your centre diff will be working constantly to compensate, how much long term excess wear damage could be caused is debatable.
Ride quality will be utterly ruined.

What i don't get is why would someone wish to do this, i've seen picks ups shod on 20" wheels and they look, well, stupid, a 120 possibly even worse.

Maybe a RR Sport Aldi A8 or Porsche badged VW Toerag with darkened windows all round and 4 in your face drain pipe exhausts sticking out the back would be a more suitable subject?
 

Sid

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putting different sizes on the front and back, wheels will obviously spin at different speeds. on an open differential, this would not be an issue. I'm thrown off by the 40-60 torque split. when the car runs its an open centre differential unless you decide to lock. the torque split on the 120 is not variable, it's a permanent 40-60 split. on the newer model the torque is variable. putting a slightly smaller tyres on the front would effectively give the front more torque despite it being a permanent torque split of 40-60 because small tyres require less torque to rotate. therefore you would effectively end up with a 50-50 split. my question was regarding the engineering aspect of the transfer box and centre differential. the design will have a tolerance - I'm asking buy doing what I suggest is it with this tolerance?
 

Shayne

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Tyre sizes are never what they claim but from experience i can say a 305/70 on a 10" wide rim is slightly smaller than a 285/75 on an 8" wide rim , but then they were different brand names . If you had a whole warehouse of the sizes you want from every different manufacturer i'm reasonably sure you could get a diameter match but then you end up with the wider tyres wanting to lock up long before the front so your brakes would be crap thanks to ABS .
 

Sid

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Tyre sizes are never what they claim but from experience i can say a 305/70 on a 10" wide rim is slightly smaller than a 285/75 on an 8" wide rim , but then they were different brand names . If you had a whole warehouse of the sizes you want from every different manufacturer i'm reasonably sure you could get a diameter match but then you end up with the wider tyres wanting to lock up long before the front so your brakes would be crap thanks to ABS .
this is scientifically incorrect, if the weight is constant .
 

chadr

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....I'm thrown off by the 40-60 torque split. when the car runs its an open centre differential unless you decide to lock. the torque split on the 120 is not variable, it's a permanent 40-60 split. on the newer model the torque is variable. putting a slightly smaller tyres on the front would effectively give the front more torque despite it being a permanent torque split of 40-60 because small tyres require less torque to rotate. therefore you would effectively end up with a 50-50 split...

Sorry for more questions than answers....but why are you against a permanent 40/60 front/rear torque spilt and what do you hope to gain by moving to 50/50 split? What would be the gains?

(Not that I think your method will achieve that without some serious downsides both in terms of mechanical reliability of the drivetrain and overall drivability and safety of the vehicle.)
 

David

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Toyota spend millions in R&D getting it right most of the time, and you think running odd wheel size will make it better. Be interesting to see how you would get on at MOT time lol
 

Shayne

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Go ahead ain't nothing a bit of polishing won't fix

 

uHu

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Im thinking about putting smaller wheels on the front of my landcruiser 120, something like 285/50/20 and on the rear 305/50/20. Its an lc4 series so has the atrac and centre diff lock. The thing that puzzles is that its permanent 4wd with a 40-60 torque split front to back. If i dont press the button to engage the centre diff lock, is the centre diff effectively an open differential? If so then im thinking i should be able to put different size tyres on the front and back. I can always change back when off roading but the jeep does spend most of its time on the road lol. Your thoughts on this would be appreciated.
Different wheel sizes of this magnitude would give you problems with atrac and abs, and the centre diff would not enjoy working overtime.
If you were to engage CDL, you would not be able to disengage it at all, without some advanced acrobatic moves on a loose surface.

If the Jeep spends most of its time on the road, why don't you keep the Cruiser for more suitable work.;)
 

wobbly

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I have 5mm overall height difference caused by new tyres on front, worn on rear, and it winds up when reversing really badly, yours will do the same.

I run rears at 40psi and fronts at 35psi to compensate, but even then its knocks if I reverse around a corner.

Still, horses for courses, give it a go and let us know how it goes.
 

AndyCook

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I wonder what your insurance company would say about different tyre sizes and would they honour a claim
 
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