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Unread 02-23-2014, 06:46 PM   #1
BagusJeep
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Tyres for a J20 258ci

I have had Gladys the Gladiator (yes, I know it is a J20) for a few months and after fixing a few thing slike a slipping clutch and leaky fuel tank had it out about last week to assess what needs to be done. Joonhoss asked the question the other day when I was going to be changing my big tyres. I have read through the threads on the Forum about tyre size but there is little related to my J20 with 4.88:1 gears and 258 I6.

As you can see it has an extended cab and very big 35" Mud Terrains. The wheels are 8 lug but not that wide, the 12.5" width tyres are sticking out too far, it would be more comfortable on 10.5" width ( I had the wheels apart yesterday but forgot to measure, they wheels are not very wide). The tyres rub slightly on the arches at the back.

It is going to be an expedition truck with comfortable accommodation for the 3 member family into the back country of Indonesia, which is pretty much all of the place, but lightly loaded with maybe 600lbs most of the time. The roads are abysmal and 50mph is a realistic crusing speed on the better bits, about 60mph in a drag race.

The engine is in good condition but has a Toyota carb and poorly maintained ignition system etc. I have the parts on order but the 258 is not a high horsepower or high revving unit. In my CJ7 it runs great, in the J20 it barely pulls it. It is probably putting out around 80bhp at the moment, I could coax it to 110bhp.

I fixed the speedo last week, just plugged the cable in the back, and it got to an indicated 40mph in 3rd gear on the flat, about 48mph real. It then lugged in 4th. Truth is that the gearing is not right, those big tyres are not doing me any favours in 4th gear. Even with the engine fettled I fear I will not have enough power to accelerate in 4th and climb even a moderate incline.

So with my axle ratios these are the choices of engine speed for various vehicle speeds and tyre sizes:

60 mph 50 mph 40 mph
35 2,577 2,148 1,718
33 2,733 2,278 1,822
31 2,909 2,424 1,939

Has anyone got a 258 J20 with 4.88:1 gears who could share some experience of tyre sizes? Local brand mud terrains are fairly cheap here but getting a set and finding them to be wrong would be a waste of money. My choices I think are:

33 x 10.5 x 15
31 x 10.5 x 15


Many thanks.

853129d1384841002t-comments-gladiator-sale-glad2.jpg

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1995 Cherokee 4.0 - CHEROKEE
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Unread 02-23-2014, 06:52 PM   #2
243
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No way would I put 31's on a J20, 33's on 15x8 or if you want to split the difference, 32's on 7's or 8's.

Cruising at 2700 +/- at 60 is not bad, once you are offroad your will probably be using 4-low and the 258 will be fine.
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Unread 02-23-2014, 08:51 PM   #3
BagusJeep
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Off road it is fine, low end torque and pulling at around 900-1200rpm over obstacles is fun. I am not concerned so much about 5 - 15 mph over the jungle tracks, Gladys has plenty.

I put some 31x10.5x15 on the front and they look very small but entry an dexit is easier and getting under the hood no longer requires a hop up. I am going to move them on to the rear to see the effect.
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BagusJeep lives in Bali, the Land of Temples.
With a Jeep every prayer counts.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1995 Cherokee 4.0 - CHEROKEE
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Unread 02-23-2014, 10:22 PM   #4
strvger01
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all the 8 lug wheels i've seen are 16 or 16.5 inches, not 15.
BF Goodrich AT's still come in a 32/9.50x15, iirc. so if your wheels really are 15 inch then those would do you well with your engine/gears setup.
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Unread 02-23-2014, 10:58 PM   #5
BagusJeep
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Yep, they really are 15" as I got 31x10.5x15 tyres on to two of them. This is Indonesia, for all I know they started off at 4 lug and got drilled.
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BagusJeep lives in Bali, the Land of Temples.
With a Jeep every prayer counts.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1995 Cherokee 4.0 - CHEROKEE
BagusJeep is offline   Reply With Quote




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