Gu 4.2 wheels/tyres/power

Submitted: Sunday, Jan 13, 2008 at 15:23
ThreadID: 53435 Views:2013 Replies:8 FollowUps:1
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Gday all been looking at some exhaust turbo mods for the gu 4.2tdi as she lacks power on take off and struggles big time in the sand even with lower tyre pressures
However it seems the problem got worse with the fat tyres fitted
Had 750r16 tyres with standard split rims which looked like cheesecutters after 2" lift kit so in went the 2657516 tyres with 7"rims looks great goes crap
My thoughts are as the 4.2tdi likes the revs the fats cant push the sand out without thrashing her and the skinnys didnt req the same force to get movin
Anyone had similar problems ??
and what sort of rim/tyre set up are you using
Cheers Barn
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Reply By: Member - Roachie (SA) - Sunday, Jan 13, 2008 at 15:43

Sunday, Jan 13, 2008 at 15:43
Depends what sort of pressures you're going down to when in sand and how soft the sand is and how much weight you're carrying etc.

My last rig was a 4.2TD and it didn't like dry sand unless I went down to around 15psi.......
AnswerID: 281392

Reply By: Dave(NSW) - Sunday, Jan 13, 2008 at 15:47

Sunday, Jan 13, 2008 at 15:47
Barney Rubble
Do exhaust & dump pipe mods it will make a big difference I am running 285x75 x16 MTZ's and found if I drop tyre pressures to 20psi I have no trouble.
Cheers Dave...

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AnswerID: 281393

Reply By: David from David and Justine Olsen's 4WD Tag-Along - Sunday, Jan 13, 2008 at 17:25

Sunday, Jan 13, 2008 at 17:25
I have a 4.2TDi and I run 267/75/16. I have no problems in the driest loosest sand running 15 to 18 psi
AnswerID: 281415

Reply By: Trevor R (QLD) - Sunday, Jan 13, 2008 at 21:55

Sunday, Jan 13, 2008 at 21:55
Hi Barn,

Sounds like the tyres are not low enough.

As an alternative: cause I know most of us don't think outside the square. Instead of Turbo mods have you thought of lower ratio transfer gear. I have both turbo mods and the lower transfer gear and I reckon the transfer gear is one of the best things I have added to the truck (if not the best). Transfer Gear will set you back $1250 plus a bit more for fitment. Turbo mods will set you back anything up to $2500 depending on what you get done, even dump pipe and exhaust will be more than a grand. Marks Adapters is the mob I used but there is others, Mark's has two ratios for the GU to choose from so go as low as you like. The 3.7 ratio gives 80 odd percent reduction (this was my choice) but there is another 2.8 ratio (or there abouts) giving much less reduction but still add heaps to offroad ability of your truck.

I was backing the loud pedal off all the way to the top of Big red via main pass and chicken track (Simpson Desrt) in third low just doodling up, No doubt I would have been more than 3 tonne here as even empty I am 2960kg no passengers or fuel. One pass of this dune (the hardest way to the top) was third low giving it heaps but other cars failed even in first and second low of thier trucks, did not see anyone else get up this pass and tracks were well and truly sand blown suggesting not many try.

Just an alternative that you may not have thought of????

Cheers, Trevor.
AnswerID: 281475

Follow Up By: Member - Barney Rubble - Monday, Jan 14, 2008 at 00:24

Monday, Jan 14, 2008 at 00:24
Thanks trevor sure sounds worth a look at the transfer mods
good to see someone thinking outside the square
In general i could learn to live with the truck on the road but off road ability seems to be where she lacks Thanks again Barn
FollowupID: 545813

Reply By: Truckster (Vic) - Sunday, Jan 13, 2008 at 22:09

Sunday, Jan 13, 2008 at 22:09
like others, I had no problems at Robe, less problems than some of the others... Im only running 285's, but will go to 305/315's next.
AnswerID: 281479

Reply By: desert - Monday, Jan 14, 2008 at 10:31

Monday, Jan 14, 2008 at 10:31
G'day Barney, As you know doubt know, the rolling diameter of 750x16 vs 265/75 is bugger all. Depending on your actual ply rating of the fats, you will need to experiment with inflation pressures, all very much depending on load carried. In the Gibson on the last crossing, I found that I could only go as low as 30 psi in the rear as I was topping 3.6 Tonne, but even at this level, the bagging was such that I had no trouble on any of the big dunes.
AnswerID: 281531

Reply By: Robin Miller - Monday, Jan 14, 2008 at 21:34

Monday, Jan 14, 2008 at 21:34
Hi Barney

There certainly is an optimum tyre size / power available equation and generally speaking I believe most cars are over tyred.

Going from 750 to the smaller diameter but wider 265 certainly makes the car harder to get going in most but not all situations.

I run several sets of tyre combinations mostly on 7 inch rims on my Patrol, but even though my car has the power
(slightly warm 4800 GU) I believe that the 235/85 and 255/85/16 both of which have about the same cross section
of tread are about right for Patrols.

The equation does shift though and when I next hit dessert in a couple of weeks I will run 265/75 BFG AT as I plan to pull a trailer and in this case I feel that trading off wheel height for torque
will be worth it.

I agree with other comments expressed here in that once you have decided on a tyre then some work needs to be done to work out your optimum pressure.

Robin Miller
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AnswerID: 281646

Reply By: Member - JohnR (Vic)&Kath - Tuesday, Jan 15, 2008 at 08:20

Tuesday, Jan 15, 2008 at 08:20
Barn, the exhaust and dump pipe mods have all been mentioned but I was pulling others off the beach with 285/75x16 tyres on soft SA beach sand last summer. I was able to drive right through where they were bogging. Tyre pressures at low levels and large radius tyres do it well every time.
AnswerID: 281700

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