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Ducks
Date registered: Dec 1899
Location:
Vehicle(s):
| RE: tire pressure & tire size
Duh, I did the conversion in my head, accidentally moved a decimal place wrong and thought 300 mm = 1.18 inches. 11.8 inches makes a lot more sense. Thanks for clearing that up.  Chad
Edited by Ducks 6/8/2007 2:52 PM
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amzimmy
Elite Veteran
Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
| RE: tire pressure & tire size
Ducks - 6/7/2007 8:51 PM
Duh, I did the conversion in my head, accidentally moved a decimal place wrong and thought 300 mm = 1.18 inches. 11.8 inches makes a lot more sense. Thanks for clearing that up. Chad
Chad, I have the same problem the other way around, don't worry it happens 
amzimmy  |
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DesertStar
Expert
Date registered: Apr 2006
Location: San Diego, CA USA
Vehicle(s): 85-280GE/95-G320/08-G500
Posts: 2156
| RE: tire pressure & tire size
Harald, do you have the answer to the 'right rear flat' cause? I learned a bit in this thread, and will experiment next time out.
Since you seem to be the guru for tire pressure reduction, what tool do you use or recommend ( found to work well) to return tires to proper inflation when leaving the dirt roads and driving the tarmack on the way home? I see many compressors on Ebay and tool stores but a little leary of their performance.
Mike |
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CaptnPete
Date registered: Dec 1899
Location:
Vehicle(s):
| Re: tire pressure & tire size
I don't have the answer for the 'right rear flat' syndrome, but I read once that most debris is being thrown to the right side of the road because of the crowning of the pavenment and therefore causing more tire punctures.
Perhaps our friends who drive on the 'wrong 'side of the road can confirm this theory?
Probably worth a six pack of Dos Equis to find out. |
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Ducks
Date registered: Dec 1899
Location:
Vehicle(s):
| RE: tire pressure & tire size
DesertStar - 6/8/2007 1:46 PM what tool do you use or recommend ( found to work well) to return tires to proper inflation when leaving the dirt roads and driving the tarmack on the way home? I see many compressors on Ebay and tool stores but a little leary of their performance. Mike Hand bicycle tire pump.  |
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AlanMcR
Expert
Date registered: Apr 2006
Location: US, CA, Los Altos
Vehicle(s): G300DT E300DT 230SL
Posts: 3500
| 31" tire pressure
shakir - 6/7/2007 6:24 PM
if you dont mind me asking Alan, what pressures do you use on the road front/rear? For the 31x10.5R15
Well I've been going with a pressure between 32-35 depending on the load. The more it is loaded the higher I pump it up. For fully loaded travel I add an extra pound or two to the rear tires. (5 people, full of gear and a dog on top of the gear). So it ranges 32-F & 32-B to 34-F & 36-R.
The tires are wearing remarkably evenly and seem to last forever. Thus removing any reasonable justification for buying a new set of tires. As much as the Michelin CrossTerrain tires are mostly glorified highway tires they have done well off road. On the last jaunt in the mud the other two G's had much more agressive tires. My truck was the only one that made it through without digging in. I credit that to agressive airing down. (Aside from my near-mythic driving talent, of course :-)
Edited by AlanMcR 6/8/2007 9:15 PM
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| RE: tire pressure & tire size
Mike,
about bringing the pressure back.
If you have to do it only everyonce in a while - an upright bicycle pump works best:
http://www.4x4abc.com/ML320/ml320_puncture.html
Stay away from foot pumps - one leg gets tired much faster than your upper body.
All plug in electrical pumps are only good for ebay sellers. They have some value in an emergency one time use and small volume tires though (if you also carry a repair kit).
They will eventually fill up bigger tires (about 20 minutes for 4 x 33"). They have no lubrication and the pistons don't even have rings. They get hot fast and just seize. I find them here and there in the bushes along the trails - thrown away by frustrated owners.
Most aftermarket on-board air systems are not much better. They all lack two important things sufficient air volume and quality.
If you need to fill up big tires often, the bicycle pump won't cut it any longer.
Pretty cool is a CO2 tank ($350) which fills up tires fast (about 30 big tires). Refill about $12.
Very professional is an electrical pump that is part of the Hummer on-board air system (Thomas Industries about $600).
If you don't really need AC, you can convert your compressor to an air pump. Done that on my 300GD, works great.
Or you add a compressor to your engine like I did on one of my Toyotas:
http://www.4x4abc.com/vehicles/york.html
All these high volume air flow devices have another nice benefit - you can run air tools! Very professional.
I sometimes use the long hose with an air gun to blow fine dust off steep rock climbs (faster than winching). I still drive where others fail (dust acts like a lubricant).
On some trips in Moab I have carried a broom when in a vehicle without air. You should hear the comments when I get the broom out. But I am the last one laughing.
By the way, you don't have to air up your tires immediately when back on pavement - even with very soft tires. As long as you don't drive fast (50+ mph) or longer than 2-3 hours. Please be aware though that the car's handling changes significantly. No fast turns please. And be careful when you hit the brakes - they will be very aggressive due to the wide footprint (theoretically traction should be the same as with street pressure - but from experience, it isn't). |
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DesertStar
Expert
Date registered: Apr 2006
Location: San Diego, CA USA
Vehicle(s): 85-280GE/95-G320/08-G500
Posts: 2156
| RE: tire pressure & tire size
Thanks for the tips Harald...it really helps. I look forward to trying out the tire pressure dropping on my next outing. Apparently, I have a lot to learn rather than the old school thinking of "that's how we always did it". I never really gave it any thought and only thought it was for the 'rock crawlers' over the Sierras from me.
Regards,Mike |
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hus55
Expert
Date registered: Apr 2006
Location: north cyprus,lapta.
Vehicle(s): 300GDS, G300 LONG,300GDT CLK55 AMG CAB.
Posts: 2230
| RE: tire pressure & tire size
i will keep a broom in my cab from now on 
you wont believe the dust out in cyprus nice one harald as always! |
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| RE: tire pressure & tire size
here is the rock crawling version.
'99 TJ, 35X12.50 R 15 @ 8 psi - the tires are deflated to grab a rock almost like a hand would. Higher psi would give only a small contact patch and very little grip. Picture also shows how important high sidewalls are when it gets serious. Can't do this with 18".
 (grip.jpg)
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BusBar
Extreme Veteran
Date registered: Apr 2006
Location: UK. North West / Wales
Vehicle(s): 463 300GDL, 460 280GEL
Posts: 382
| Re: tire pressure & tire size
Very interesting thread, thanks Harald it’s certainly made me think. We are off to Morocco soon and I was planning on taking 2 spares plus an inner tube. I am however a little paranoid about weight so maybe I’ll think about cutting it down to one, given Harald’s experience with running at lower pressures. I must admit I would have only thought of doing that over soft sand etc. Traditional wisdom being that low pressures = higher temperatures which could = tire failure.
What are peoples thoughts on the emergency puncture repair cans? The ones that squirt adhesive gunk in to the tire seal the puncture and reinflate it? |
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amzimmy
Elite Veteran
Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
| RE: tire pressure & tire size
My solution to tire-pumping, it's easy, very quick, and NO hassle.........an aluminum diver bottle, a pressure reducing valve (VERY important), tyre inflation kit and voila ... you can inflate many tires!
amzimmy
 (DiverBottle (600 x 800).jpg)
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DiverBottle (600 x 800).jpg (130KB - 0 downloads)
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| Re: tire pressure & tire size
RH,
puncture repair cans are only good for passenger cars with a puncture in the tread area. Centrifugal force will keep the stuff from sealing any hole in the side wall. Besides, its awefull stuff to get out of your tire. Tire shops hate it. Its messy.
They might be OK for a 4x4 if you indeed know that the puncture is in the tread area. Its a quick emergency solution (freeway?). However, the larger volume of 4x4 tires will not completely be filled with the air supplied in the can. Never use it on tires with tubes! Duhh
Here is how I have approached the problem of tire failure.
A) Start with the must capable and durable tire on the market (BFG MT) - some old bias tires are stronger, but they don't perform.
Aa) If you can't afford a flat tire (racing, remote exploring etc) get the BFG "BAJA" tire - almost indestructable. Expensive ($350 ea) and very heavy.
B) Always keep your tire healthy, avoid hitting rocks or driving over sharp sticks.
C) Run at the right pressure. (a chapter with many variables in itself)
D) Carry the proper repair tools and a suitable pump.
To A): Best economic solution is the BFG MT. And MT even for soft sand. Yes, for soft sand. The MT tire seems to b slightly stronger than the AT. MT design does not dig you in deep - you, the driver are the one digging yourself in. At the proper size (bigger than stock) and proper deflation the MT is perfect for soft sand. http://www.4x4abc.com/jeep101/soft-sand-deflate.html
And of course you need to know all the little tricks for sand:
http://www.4x4abc.com/jeep101/soft-sand-turn-straight.html
To C): Soft tires (between 5 and 20 psi) have many advantages - however, everything has drawbacks. A softer tire has a bulging sidewall, which makes it somewhat prone to punctures. A softer tire does not like prolonged higher speeds. So, if you must drive fast on gravel (racing) you can't run soft tires.
To D): The most versatile repair for punctured tires are plugs. They can be inserted with a clever tool.
http://www.4x4abc.com/jeep101/plugnplay.html
http://www.4x4abc.com/jeep101/plugnplug.html
I have on-board air and a handpump as backup.
Since I started to run large tires (learned that from the Baja racers) I rarely ever have had tire failure any more. I sometimes poke a hole in my sidewall just to demonstrate how the plugs work. In some cases, driving in the desert with tires not big enough (265/75 R 16 on a ML320 - http://4x4abc.com/ML320/ml320_265_tires_baja.html), I have jumped out of the car when I heard a hissing, had the co driver put a finger on the side wall puncture while I was getting the plugs out. After plugging, the tire needed only a few pump strokes.
I have "repaired" side wall gashes of several inches in length (bailing wire and 10 plugs side by side) - not pretty but it gets you home.
On a side note.
Bead lock tires were invented for racers who wanted to keep their tires on the wheel after a 100 ft high speed jump. Took a few years until the 4WD community discovered them. Too much gas and hard steering made their tires also pop off at low pressures. They look cool, are very expensive and pretty much only mask bad driving. A must have item now (like the useless, dangerous HiLift). Good for the aftermarket industry.
I found an excellent use for bead locks (the real ones - not the fakes). If you run an expedition (or something where weight is a consideration as well as the fact that you want to drive home and when you need to patch a bad hole in the tread area or need to insert a tube when the tire is beyond repair, you no longer need to muscle tire mounting irons and other devices (besides the extar weight in the car) - if you have bead locks, you simply jack up that tire, leave it mounted on the axle, unbolt your bead lock, the tire comes right off at that side, then you reach inside and patch your hole or insert a tube, bolt the ring back on, inflate, go. Takes only a few minutes. If you have on-board air and an air wrench you'll be done a couple of minutes sooner. |
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BusBar
Extreme Veteran
Date registered: Apr 2006
Location: UK. North West / Wales
Vehicle(s): 463 300GDL, 460 280GEL
Posts: 382
| Re: tire pressure & tire size
Thanks again Harald, tire choice is already made I’m afraid. BFG AT’s 31x10.50x15’s. It’s going to be my daily driver so they seemed the best compromise.
I like the tire repair plugs, I have seen them advertised this side of the pond so I will certainly get some now that I’ve heard from someone with 1st hand knowledge. |
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| Re: tire pressure & tire size
RH,
31's are not too bad. They were the first stage modification on my 300GD.
Do the chalk line test for proper normal tire pressure once your vehicle is loaded up.
Then use 100% of that on pavement (add 30% for sustained fast speed while traveling to the loacation).
70% of normal on gravel roads if speed stays at an average of 30 mph (short sections can be driven at up to 60 mph - no longer than 20-30 minutes).
40% of normal in really soft sand (avoid sharp turns - be aware of your bulging sidewalls).
So, if 32 psi is your normal pressure:
41 psi on the freeway
22 psi on gravel roads
13 psi for soft sand |
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Boy G
Expert
Date registered: Feb 2007
Location: Bushveld, South Africa
Vehicle(s): Diesel G's: 617A and 602
Posts: 1683
| Re: tire pressure & tire size
Lovely stuff - thanks. Harald - some more please:
I have a trip planned which will involve a lot of thick and soft sand (Okavango delta). I have used BFG MT on most conditions but never in sand.
I have a choice of Bridgstone Dueler 235 85 16 or the BFG MT 235 85 16 and was going to go with the Bridgestones until I read your comments. Is the MT the right thing here?
Also I like to travel early in soft sand before it gets hot as it seems to affect traction.
I agree about softer tyres and have been doing this also ever since I got sick of changing them. |
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4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| Re: tire pressure & tire size
Andrew,
all military G built in Graz get the BFG MT - if its good for them, it might serve you well as well. Bridgestone is not a bad tire - BFG is just better. Aside from sponsoring money, there is a reason why 80% of the winners of the US off-road races use BFG.
Soft sand needs either large deflated tires (40% of normal pressure) or whatever tire you have deflated at least down to 40% (smaller tires need to be driven more carefully when deflated though - due to the smaller volume of air).
Night or early morning hours for soft sand are best. The sand particles are less stable the hotter it gets. High speed or momentum to get through soft sand should be avoided - it reduces the control you have over your vehicle and tire damage due to driver error is very likely (you might not be able to avoid that "ingrown" rock in time and get a compression cut on the tire).
Also, as mentioned before, pick lines that are as straight as possible and avoid sharp turns (resistance increases 100% in turns - 200% if you tow a trailer):
http://www.4x4abc.com/jeep101/soft-sand-turn-straight.html |
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