Author/Photographer: Don Huysmans Editor: Phil Hansford - July 7, 2001
|Yokohama Geolandar M/T tires: A few observations after the first month of use.|
First some background: I was having a rear locking differential installed in my 1987 Mitsubishi Montero/Raider/Pajero, and the existing Michelin A/T's were due for replacement soon, so it was now time to move up to a more aggressive off-road tire. But which tire? Based on comments made by users and tire dealers, the typical M/T tire has great off-road traction but tends to have poor wet pavement traction. One of the most demanding uses these new tires would face is winding paved mountain roads, in a region where it rains more than 200 days/year (or at least it feels that way). Enter the Yokohama Geolandar Mud Terrain into this equation, and all of a sudden everything seemed to fall into place. Advertised as having excellent wet traction as well as excellent off-road traction, these soft-rubber, directional, aggressive tread tires looked promising. Other users of these tires certainly seemed to support these claims. So they got the nod and 31x10.5's were installed on new 15x7 rims, and my truck had new boots! Then the trials and testing began. I wanted to see just what limits these new tires would impose on my driving style, on familiar roads and a few unfamiliar obstacles.
First off, I needed to choose a tire pressure for general road use. According to the manufacturer's specifications on the driver's door post, the stock 9" wide (P225/75 R15) tires had a recommended pressure of 26 psi (front GAWR of 2425 lbs), and 34 psi (rear GAWR of 3197lbs). The new Yokohama's were 10.5" wide, or 15% wider than stock. Being wider meant I could probably reduce the required pressure, and so I chose to reduce my tire pressure by about 15% to 22 psi. At 22 psi the tires look fully inflated on my 3290 lb curb weight truck. Next I needed to determine some useful off-road tire pressures. I aired down to different pressures from 22 psi to 6 psi (my gauge only gets down to 6 psi), and recorded how close to the ground the rim was. Then I converted these numbers to "% of rim height above the ground", or more simply: "% height", and made this chart specific to my truck, to help me in my comparisons:
Rim to Ground Measurements at Specific Tire Pressures
|Tire Pressure in PSI||Rim height above ground|
At 6 psi, 80% height, the tires looked like they were nearly as low as I should go, as their cheeks were puffed out quite well. You can also see that the greatest change in tire shape on my truck is between 12 psi and 6 psi.
|The original 225-75s alongside the Yoko 31x10.50s|
So what are the Yokohama's like to drive? Well, the first test was city and hiway, wet and dry paved roads. At 22 psi, the tires are very well mannered, braking and steering in a predictable manner with good precision. The diagonal tread blocks make some tire noise, but not really noticeable even though my truck is not too sound-proof. On the highway they were quite stable and quiet, with no steering vibration. However at speeds below 10 mph (about 15 kph), you can feel every lug hit the pavement, and the ride is a bit bumpy. The tires were originally installed at 40 psi (Why? "Because they can go to 50 psi". Duh). At 40 psi, only the middle of the tread even touched the road. I tried 25 psi, out of curiosity, and found the tires too hard, and I could feel every little bump on the road. I have also city/freeway drove the tires at 15 psi, 12 psi and 10 psi, and while the 10 psi began to feel a little too vague, the 12 psi and 15 psi still felt quite safe. At these lower tire pressures the tire noise does become more noticable. Oh yeah - Wet traction? Excellent to unbelievable. I've even tried to shake them loose, but have yet to succeed. No worries now about those ski trips, and the wet boat launch ramps!
|Offroad? Careful Adjustments Pay Dividends|
But enough of pavement. How are they off-road? Well, first I drove up the mountain road until I reached the snow. This was wet corn snow now, soft and slushy, untracked, and becoming steep quickly. I aired down to 6 psi, and was able to sit on top of the snow, and control my movement with good precision. It was possible to brake on a 5 degree down slope and stop quickly. When I tried climbing slopes above 12 degrees, the snow could no longer handle the pull of the vehicle's weight, and then the big lugs quickly dug holes, and there I stopped! At 15 psi, the tires would push into the snow, even at rest, and it was difficult to stay on top, though traction was good.
For general off-road, back roads, dirt roads, crushed rock roads, etc., 22 psi was too much and I could feel every little rock. At this pressure the tires seemed to bounce off rocks rather than grip them. This applied to 14 psi as well. Then at 12 psi the ride smoothed out, the tires really felt like they were gripping the surface, and were still able to keep the rims away from the rocks. (unlike 10 psi or lower, where the rim would get uncomfortably close to the ground at times, though the traction was still great). In general the traction was so good that I didn't need the diff lock on these roads.
|Sand Lake Oregon
Then on to the gravel and loose rocks at the beach. At 22 psi the ride was a bit rough, the tires tended to sink in a bit which increased rolling resistance, but still the wet traction was great, and the big lugs could push their way along quite well. At 22 psi the tires also seemed to pick up rocks between the tread blocks, and I had to clean them out before going back on the highway. At 10 psi all the rules changed. The tires floated on top of the gravel, and the resistance was gone. This felt effortless. Almost too easy. The truck went anywhere we pointed it.
Next up was the sand at Sand Lake in Oregon. The dune buggies, sand cars, and ATV's all use special 5 psi tires to float on the sand, so the target pressure became "as close to 5 psi as possible"! However, fearing occasional rocks, etc, I used 8 psi. What a treat! I could go many places in only 2WD! For the real challenges I used 4LOW, with the automatic transmission set on 2nd gear, and the rear differential locked. The truck did not get stuck anywhere. I could go up slopes of soft sand +20 degrees steep. Anywhere an ATV or sand car went, I could too. Anywhere. No wonder this truck likes the Dakar race! It's definitely at home on the sand, and was the only road vehicle up in the dunes. I tried a few places at 15 psi, and then I would get stuck. At that pressure I couldn't climb soft sand anymore, and the rolling resistance went way up.
|About the Author:
Don Huysmans lives in Vancouver, British Columbia, on Canada's "wet coast". Don drives an 87 2 door Raider, which he has rebadged a "Pajero". He has owned this truck since new, and now has 175 000 miles on it. He recently had an ARB locking differential installed. For more pictures of Don's rig, check out our Reader's Rides.
That left the mud of Tillamook Forest in Oregon as the next challenge. What can say. At 12 psi the tires held on to everything. Rarely did a tire spin, even when the rear was unlocked. The group I was with included another locked, Yokohama-M/T-equipped truck, as well as five other locked trucks, equipped with other M/T brands. The most telling situation occurred on a wet mud/clay-covered, bare-rock trail climb, where the two Yokohama-equipped trucks simply walked away from the others. Traction was not an issue for this tire. I didn't try any true mud-pit driving, as that's usually very high rpm, high horsepower, with a corresponding high damage risk. So no comments on ultimate mud pit performance!
On wet bare rock, which I have not had access to yet, I presume for the most part that traction would be similar to wet bare pavement, and that would be excellent.
Based on the testing so far, these are the general pressures I'll be using:
So after all these glowing reports, there's got to be something negative... Well, they look great, so appearance is a non-issue. They're a directional tire with a definite left and right, so as a spare tire it won't work as well on one side as the other, which may be an issue. They are made of a soft rubber compound, so tread life will be an issue for sure. And they are only available in a limited number of sizes, which will definitely be an issue!
Even with these negatives, it's very likely I will be replacing these tires with another set of Yokohama Geolandar M/T's - I'm that impressed!