New tyres on the back instead of the front?

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
I find it's understood easier by just describing it as an 85/15 split :p

jamesmartin said:
except for its not entirely correct ,rear wheels are mechanically driven slightly slower than fronts ,to give front wheel drive feel, vcu allows this until it starts to seize which then obviously buts a strain on the drive train (ird and rear diff),putting new tyres on rear helps to even up the drive to front and rear ,putting new on the front would make it worse
Click to expand...
 
jamesmartin said:
except for its not entirely correct ,rear wheels are mechanically driven slightly slower than fronts ,to give front wheel drive feel, vcu allows this until it starts to seize which then obviously buts a strain on the drive train (ird and rear diff),putting new tyres on rear helps to even up the drive to front and rear ,putting new on the front would make it worse
Click to expand...

This puzzles me.

If all tyres sure the same size and you are going in a straight line, how do the rear wheels get driven slower than the fronts? They are going along the road at the same speed.
 
Epicuser said:
This puzzles me.

If all tyres sure the same size and you are going in a straight line, how do the rear wheels get driven slower than the fronts? They are going along the road at the same speed.
Click to expand...

rear prop is driven by gearing ,slightly slower , viscous coupling allows the slippage (the reason why v/c is used in the first place,) if you try turning a vc you wil see theres a resistance ,the faster you try and turn v/c the stiffer it gets ,usually you can feel drag of v/c in reverse full lock or when you pull on to gravel etc where one wheel will let the wind up go ,so even on road in a straight line there is some wind up, the greater the front wheel diameter of front wheel compared to rear the greater this will be , ,rrc and p38s used a v/c instead of a difflock ,they seermed to last longer in rr but then rr is equal drive to both axles
 
And that I think would be the answer for the Freelander's woes- even out the gearing front/rear to be 50/50. Either in the diff or IRD. Gotta be a better idea than some manual connection to replace the VCU.
 
Wow I thought everyone knew this by now.
The 85/15 split means that no drive is applied to the rear wheels unless the fronts start slipping, instead they turn naturally as they are effectively towed
But if the rear wheels are smaller circumference than the front, e.g. tyres on the rear are worn more, this will cause them to turn faster in relation to the front, which causes pressure on the IRD and the VCU.
It may take a long time but eventually this can cause damage.
I always changed 2 tyres at a time on my L series because I didn't know any different. I only noticed the effects of a knackered VCU after I'd done about 80,000 miles though, so results may vary!
 
bukko said:
Wow I thought everyone knew this by now.
The 85/15 split means that no drive is applied to the rear wheels unless the fronts start slipping, instead they turn naturally as they are effectively towed
But if the rear wheels are smaller circumference than the front, e.g. tyres on the rear are worn more, this will cause them to turn faster in relation to the front, which causes pressure on the IRD and the VCU.
It may take a long time but eventually this can cause damage.
I always changed 2 tyres at a time on my L series because I didn't know any different. I only noticed the effects of a knackered VCU after I'd done about 80,000 miles though, so results may vary!
Click to expand...

think your not quite understanding how it works ,drive on some gravel after a hard surface , feel v/c
 
bukko said:
You seem to be saying the same as I said pretty much (or vice versa)
Click to expand...

not really ,back wheels are driven ,but think of it like front been on full drive with clutch fully engaged and rear with you slipping the clutch ie still got drive but different speed to what engine is
 
jamesmartin said:
not really ,back wheels are driven ,but think of it like front been on full drive with clutch fully engaged and rear with you slipping the clutch ie still got drive but different speed to what engine is
Click to expand...

So if the car is say on a lift and all wheels are in the air - all wheels would be turning but the back ones would be turning a little slower - but that dunt matter because when on an ordinary road the the rear wheels will be being pulled along by the fronts - until the fronts slip and then the vcu kicks in more and the rears then turn faster, is that about it ?
 
Brack said:
So if the car is say on a lift and all wheels are in the air - all wheels would be turning but the back ones would be turning a little slower - but that dunt matter because when on an ordinary road the the rear wheels will be being pulled along by the fronts - until the fronts slip and then the vcu kicks in more and the rears then turn faster, is that about it ?
Click to expand...

Exactly
 
Skynet said:
85% of the drive goes to the front wheels and approx 15% to the rear via the VCU. Because the front wheels are doing most of the work those tyres wear down quickest. In a straight line all wheels turn at the same rate when new.

The VCU functions by sending more force to the rear wheels if the front wheels lose traction (ie the front wheels turn faster than the rear) and a similar effect is therefore felt when front wheels are worn down more than the rear. Placing new tyres on the front only, has the effect of rear wheels turning faster and putting the VCU under strain as its trying to drive the front wheels (and engine via IRD) to move as fast as the rear wheels.

Either change all 4 tyres at once, and you WILL notice the difference in the drive when you do as it feels much smoother, or place new tyres on the rear to send differential drive in the correct direction.
Click to expand...

I've gone ahead and had the 2 new tyres put on the back and the rear ones put on the front. The 2 new tyres are General grabbers UHP but the car now feels like I'm fighting with the steering and it also keeps going 'light'. Tyre dealer reckoned it would be fine to have 'normal' tyres on the front. Are they wrong? - certainly feels like it
 
Brack said:
So if the car is say on a lift and all wheels are in the air - all wheels would be turning but the back ones would be turning a little slower - but that dunt matter because when on an ordinary road the the rear wheels will be being pulled along by the fronts - until the fronts slip and then the vcu kicks in more and the rears then turn faster, is that about it ?
Click to expand...

nearly ,vcu will lock solid when a wheel slips , but even on a straight road there is still power going to rear ,its not the same as an overrun clutch
 
Last edited:
The rear wheels are 0.8% under driven, so in most conditions the vehicle is effectively front wheel drive, with the rear wheels turnig the rear propeller shaft slightly faster than the IRD turns the front propeller shaft. Since the speed differential is low, the increase in viscosity of the silicon jelly is marginal and there is little resistance to relative rotation of the slotted discs.
When there is a significant speed differential between front and rear propeller shafts, eg the front wheels lose traction or crossing rough terrain, the viscosity and resistance to rotation of the silicon jelly increases to a level that slows or stops relative rotation of the slotted discs. With the front and rear propeller shafts locked together, drive is thus transfered from the IRD to the rear wheels.

The above is taken from the Description And Operation section of the Rave Disc for the Freelander 01>MY
If, in normal cicumstances, the rear propshaft is turning faster than the front propshaft, how can a correctly functiong VCU transfer drive to the rear wheels?
Where do these 85/15% figures come from if LR make no mention of them?
 
You must log in or register to reply here.

Similar threads

J
Back tyres matching but not with the fronts?
Replies
8
Views
986
Judd8008
J
O
Freelander 1 Tyres, coolant, filter, sunroof: Qs about the FL1, please assist!
Replies
3
Views
753
GrumpyGel
GrumpyGel
M
Freelander 1 Winter Tyres - 215/65/16 No Propshaft at the moment, Only Two?
Replies
1
Views
557
Nodge68
Nodge68
B
vibration under load.
Replies
1
Views
270
andyfreelandy
andyfreelandy
andyfreelandy
Freelander 1 Poly wishbone snubber bush squeaking
Replies
5
Views
682
kernowsvenski
kernowsvenski
Back
Top