Bigger tyres - what precautions needed? (1 Viewer)

[Etsha6]

Hi All,

I want to put some bigger tyres on my 1988 BJ74 that came with 225x80R15's.
By my calcs thats an OD of 29 inches, I want to go to about 31 inches without going wider than about 10 inches. (I also have a set of 16 inch rims.)
What is the maximum OD the BJ74 can take without having to modify, gearing, diffs whatever?
A brief explanation of the gearing/diff etc. mods required to run bigger wheels and the reasoning would also be appreciated.

Thanks
Ben

 

[crushers]

you can run 33" tires with no lift on a BJ74, 35s on it with 2 1/2 lift. no mods for either set is okay.
if you are looking for extreme articulation then a lift for 33s is a good idea and a 4" lift for 35s.
personally i like 33 skinnies with no lift...
cheers

 

[HZJ60 Guy]

Wayne is correct in that you can run up to 33's without any real trouble. You're 74 should have 4.10/4.11 ring and pinion gears that will allow those tires without the need to regear. To run larger tires you (my opinion) should set up a spring over. I would like to have a 74 with a spring over and 36" tires. Because of the over drive gear in that auto trans that comes with the 74 I could install 5.29 ring and pinion gears in that set up and still have a respectable highway RPM. It's all about engine rpm at speed. You need to choose a gear set up (and tire set up) that compliments your engine/trans capabilities.

 

[Stone]

I'm running 255/85r/16 (OD 33.3") on mine, and it's just about perfect in terms of gear ratio now. H55f with 4:11 thirds. I do have a speedo correction kit to bring my speedometer back to proper reading. Otherwise, if you have the same setup as me, you will find that your speedo will be out by around 14%.

As far as running no lift goes...my truck has the Terrain Tamer 2" lift. 31" tires will fit on the stock height for sure, but I'm not certain that the 33" tires will not rub in full flex if you don't have at least a mild lift.

 

[brownbear]

for those 16 inch rims, a 235/85 R16 is a good tire. Its a bit over 32 in size and fairly narrow(under 10 inches)

Also lots of really good tread patterns come in that size. Not so many in the 255/85R16 size.

 

[tlcruiserman]

I am running Belton suspension on my 74 with front springs turned around and I am running MTR's 35x12.50x15 also have the Auto trany and 4.11 gears. Truck wheels and runs fine. I have simular setup on my BJ70 ragtop however running truxus tires but put a little more lift in it with some longer shackles, also have 4.11 gears and turbo on the 3bii.

Me personally I do not see the need for lower than 4.11 gears if you are running up to 35" and 3b or 13bt engine. I have found 4.88 to be too low. (speaking of maining H55F tranny).

Just my 2 cents.

cheers,

Michael

 

[dieseldog]

My 70 and 73 are running 265/70/R17 tires (mounted on the newest Tundra/Sequoia rims). I have made no mods to the suspensions at all. I am considering a mild lift for the 73 though--the terrain tamer setup sounds like just the ticket.

 

[Greg_B]

I've got the Belton 50mm lift on my BJ74. No problems running 33x10 at all. The recent pic in the 7* series picture thread shows the 33x10, and some of the earlier pics show the 35 SSR's. I moved the front axle .75" forward so I could run my 35x10.5R16 SSR's. I added one leaf to the front packs on my BJ74.

You could probably run 35" tires without moving it forward...I just wanted more room. I don't like flipping the spring packs, unless you flip the military wrap and re-drill the center pin hole. I have no experience with breaking springs by flipping them, (putting the military wrap at the front) but Lowenbrau has...

Gearing is marginal with the true 35"s as the steel rims and SSR's make for a heavy combo. Does fine in most situations, however I was lugging so low in some rocks that I bumped it into reverse rotation a few times. Gearing would have helped for sure

We shipped some Beltons to Jan in Cal a short while ago, and by all reports he is very happy with them. I added one Belton leaf to the front due to his use of the truck.

Regards

gb

 

[tlcruiserman]

I've got the Belton 50mm lift on my BJ74. No problems running 33x10 at all. The recent pic in the 7* series picture thread shows the 33x10, and some of the earlier pics show the 35 SSR's. I moved the front axle .75" forward so I could run my 35x10.5R16 SSR's. I added one leaf to the front packs on my BJ74.

You could probably run 35" tires without moving it forward...I just wanted more room. I don't like flipping the spring packs, unless you flip the military wrap and re-drill the center pin hole. I have no experience with breaking springs by flipping them, (putting the military wrap at the front) but Lowenbrau has...

Gearing is marginal with the true 35"s as the steel rims and SSR's make for a heavy combo. Does fine in most situations, however I was lugging so low in some rocks that I bumped it into reverse rotation a few times. Gearing would have helped for sure

We shipped some Beltons to Jan in Cal a short while ago, and by all reports he is very happy with them. I added one Belton leaf to the front due to his use of the truck.


Regards

gb

Greg, we kept the srpings as shipped when we install them. Jan is running BFG AT 33x10.5x15 no issues. Jan is still running stock 3.70 gears Here are some pics of Jans (brown) my BJ74 with belton and BJ70RT with belton both running 35" and 4.11 gears.

Cheers,

Michael

 

[wesintl]

I've got the Belton 50mm lift on my BJ74. No problems running 33x10 at all. The recent pic in the 7* series picture thread shows the 33x10, and some of the earlier pics show the 35 SSR's.

What brand and model are those? I can't make them out in the pic posted by your SO. Thanks!

 

[Greg_B]

What brand and model are those? I can't make them out in the pic posted by your SO. Thanks!

Tires? 255/85R16 Cooper ST's. The daily drivers, and the SSR's if it goes out wheeling...though Poo may well inherit the SSR's when it get's a 13BT.

gb

 

[Greg_B]

Greg, we kept the srpings as shipped when we install them. Jan is running BFG AT 33x10.5x15 no issues. Jan is still running stock 3.70 gears Here are some pics of Jans (brown) my BJ74 with belton and BJ70RT with belton both running 35" and 4.11 gears.Cheers,Michael

Cool, thanks.

gb

 

[Etsha6]

Thanks for the good feedback gents.

Ben

 

[Tapage]

Do you plan to do a hard core off road .. ? if answer is yes, go to SO and minimun 35" MT with 4.88 Gears .. but is the answer is no, 33" with some lift with shackles or 2.5" suspension ( springs ) lift is ok for you ( with the stock gears )

 

[Jan-78FJ40]

We shipped some Beltons to Jan in Cal a short while ago, and by all reports he is very happy with them. I added one Belton leaf to the front due to his use of the truck.

Regards

gb

yes, very happy. I just came back from Baja, running some of the worst washboard roads ever, and the suspension did extremely well. I drove the same road with the same truck minus the Belton lift before, and almost got rattled into the ditch. now no problem with twice the speed
Jan