tire pressures with a 300 TDi - Defender Source
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  #1  
Old May 27th, 2007, 07:10 PM
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Clark Bowen
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tire pressures with a 300 TDi

I was checking the tire air pressures and bringing them to NAS factory settings when I realized that my front tire pressures are probably too low for the highway with a 300 TDi, winch and heavy bumper. Book says 28 lbs. I run 30. I figure I have about 350 more lbs on the front end than a stock D 90 now.
Any thoughts?
Also I applied the QuietCar coating and re-installed the bonnet. I'll post pictures and comments after it has fully cured (7 days).

Clark
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  #2  
Old May 27th, 2007, 08:21 PM
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I just look at the max pressure on the tire and go with that for road use..
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  #3  
Old May 27th, 2007, 09:58 PM
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Jim C.
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Ouch!
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  #4  
Old May 27th, 2007, 10:24 PM
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Quote:
Originally Posted by Cirbo
Ouch!
X2, thats about the worst possible way to figure correct tire pressure. Must ride like you have square wheels too.
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  #5  
Old May 27th, 2007, 11:54 PM
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Julien Dalbin
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Quote:
Originally Posted by cdb
I was checking the tire air pressures and bringing them to NAS factory settings when I realized that my front tire pressures are probably too low for the highway with a 300 TDi, winch and heavy bumper. Book says 28 lbs. I run 30. I figure I have about 350 more lbs on the front end than a stock D 90 now.
Any thoughts?
Also I applied the QuietCar coating and re-installed the bonnet. I'll post pictures and comments after it has fully cured (7 days).

Clark
What pressure are you using on rear axle ?
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Old May 28th, 2007, 12:06 AM
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Clark Bowen
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38 lbs
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  #7  
Old May 28th, 2007, 08:54 AM
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Julien Dalbin
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I run 28 all round with 265 BFG AT.
I'm one of the guy that still don't get why
you need a greater pressure in the rear ...
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  #8  
Old May 28th, 2007, 11:51 AM
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Clark Bowen
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300 TDi tire pressures

JFD wrote:
"I run 28 all round with 265 BFG AT.
I'm one of the guy that still don't get why
you need a greater pressure in the rear"

Actually, I wonder why too. How does it handle on the road versus the stock pressures? How about tire wear? Are you running a diesel?

Clark
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  #9  
Old May 28th, 2007, 11:55 AM
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I ran 65psi most of my recent 4000+ mile trip, when I lowered it to 35psi for a smoother ride off road and did not put it back to 65psi my fuel mileage slipped almost 1.5 mpg. I drive a 300 tdi diesel with just about all the accessories you can have so it it pretty heavy, plus all my gear. Ride was really good on the hwy, but rather harsh off road. To each his own I guess.
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  #10  
Old May 28th, 2007, 02:10 PM
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Julien Dalbin
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Quote:
Originally Posted by lrnasd90
I ran 65psi most of my recent 4000+ mile trip
Damned, that's a lot of pressure , 65 psi....

Clark, I do run a Tdi also.
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  #11  
Old May 29th, 2007, 07:42 AM
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I think pressure is different on each setup and tire combo. YOu should really be checking your pressure by chalking a tire and running it.. THen seeing if its over or under inflated for your rig.. I usually run 35-45lbs in mine
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  #12  
Old May 29th, 2007, 08:17 AM
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28lbs front and rear, 10lbs off road
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  #13  
Old May 29th, 2007, 10:22 AM
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7lb front, 5lb rear.
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  #14  
Old May 29th, 2007, 05:00 PM
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Julien Dalbin
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Quote:
Originally Posted by Buckon37s
7lb front, 5lb rear.
right pressure for post climbing ???
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  #15  
Old May 29th, 2007, 10:12 PM
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Different tires sizes and load ranges require different pressures.
28psi IMHO is much to low for the street on a D90
For your tires Clark I think 40-45 front and ~35 rear.
You can do the chalk thing too ,but I don't think it will give a true estimate because your tires may be too wide for your wheels.
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  #16  
Old May 29th, 2007, 11:21 PM
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Clark Bowen
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tire pressures on 300 TDi

Thanks Shane.
I'm astonished at the range of pressures various people run on the street.
Tire companies are always saying that 10% under or over inflation leads to multiple heat and wear problems, so that would indicate there is a near ideal for my motor/winch configuration and tire size. Makes me wonder how LR come up with 28/38.
A brake shop I used in Eureka insisted upon very different pressures and they were like your numbers. He got it from some chart - I think.
So I'll give those numbers a try and see what happens. It does feel like I'm getting some tire "roll" on sharp turns at my current pressures - 30/38 - but it feels more like it is the rear that is buckling under a bit.

Clark
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  #17  
Old May 30th, 2007, 01:39 AM
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Chris Davis
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Mine is always a balance between rough ride and bad handling. My D90 is pretty fully loaded weight wise and running the 255/85's I run 30 all around, ish.
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  #18  
Old May 30th, 2007, 03:38 AM
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I Run around 35 psi front & read on my 200 tdi with 7.50 16 radials but it really does depend on load & tyre size
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  #19  
Old May 30th, 2007, 09:58 AM
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Several combinations work well in the 30-40 psi range. Larger tires need less pressure to support an equal load as stock tire. Heavier loads require increased pressure for any size tire. Chalking is good but actually measuring the tread depth (outer, middle , and inner) @ X psi and checking at the next oil change is the best way to monitor tire wear for driving in individual conditions. Having said that I run 30/30 in my stock tire D90, and 25/25 oversize Series III. FYI when acquiring the Series III it had 85psi, 85! because that was max listed on the Load range E side wall. Brought that down to 25 and drives like a different truck.

Why +psi in the rear? For year manufactures have suggested increase pressure in the rear for most all vehicles. Increased pressure provides increased stability, to a point, which makes the rear of the vehicle more stable. MFGs like stable vehicles (just ask Chevy about the corvair)! This pressure offset enhances the understeer charachteristics of the vehicle, again which MFGs and their legal counsel like. Squaring up the pressures (same f/r) usually makes for a better handling vehicle and better tire wear.
Jim
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  #20  
Old May 31st, 2007, 01:46 PM
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I dare say there is some sort of graph for trye pressure against load but whether it's a straight line form 0 load/0 pressure up to max load and max pressure is beyond me
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