Fitting 235/85R16 Tyres on a Discovery

Why Fit 235/85R16 Tyres?

Well, they're about 3 inches bigger in diameter than stock, which gives you a full 1.5" extra under the differential. This is really, really great if you rock crawl or stump-avoid a lot.

They look great.

You don't have to change rims if you don't want to. A lot of folks fit 15" tyres after buying a whole set of 15" rims. 15" tyres are currently cheaper (this is changing), but the 15" rims have offsets to them which generally make it more difficult to fit as large a tyre as the 235/85R16 without many more modifications.

They come in load range "D" and "E"... which some people consider too hard a ride, but I like because they're much tougher and I get less flats out in the middle of nowhere.

Which Tires?

There's no way I'm going to tell you what tyre to buy. I have BFG AT's on one disco, BFG MT's on the other. I have tried 4 other types, and it would take a LOT of convincing to get me to change.

What to do BEFORE you take your truck to get tyres...

Springs & Shocks
If you haven't upgraded from stock springs yet, do this BEFORE you upgrade your tyres and put off your tyre purchase if you have to. The genuine springs and shocks are pretty poor, and you will be astounded at the difference in the feel of the vehicle. It will also allow you to trim less aluminum when you fit the new tyres.

Most people (myself included) are very happy with the OME springs. "Mediums" ("MDs") for the front, usually, and "mediums" or "heavys" ("HDs") for the rear. If you can tolerate a firmer ride, go for the HDs rather than the MDs in the back. An extra 1/2" of lift helps.

Ideally, do your shocks at the same time. There has been lots of debate on which type. I have OMEs and would buy them again.

If you insist on genuine springs and shocks, be prepared for much more trimming.

Rear Drop Kit
Many folks also go for the Safari Gard (SG) drop kit for your rear springs/shocks. This is a bit of a bear to put on, but it replaces the rubber bump stop that the axle bounces into at the top with a taller one, and extends the length of the shock by relocating the mounts. A few clips keep the springs safely in place. Overall, it gives you more articulation by increasing the downtravel.

Steering Stops
These are the bolts near the inside of the front wheels that limit the left-right travel of your steering (see "steerstp.jpg"). Your turn radius will suffer a bit. You will need to limit the turn radius because the larger tyres will rub against the front radius arms (see "radius.jpg").


You don't need to adjust these before fitment, as long as you be VERY careful driving home not to take a sharp turn OR you bring 2 19mm spanners with you (see below) and do it in the parking lot after they fit your tyres.

Either way, its WAY easier with 2 people. One person to crank the wheel, the other to do the adjustments.

So bring the spanners. AND bring a spare person OR a 6 foot length of house wire (14-2) that you can wrap around the steering wheel and tie it hard over in each direction.

And if you plan on getting Mud Terrains rather than All Terrains, you REALLY want to think about adjusting your steering stops before coming home. Those big lugs will really cause problems if you turn sharply and they hit your radius arm. WACK!

Front Bumper Endcaps
These need to be trimmed. If you wait until after the tyres are fitted, you will have an incredible noise and potential really trash them. The lower wheel adjacent corners of the endcaps rub. The most common (and asthetically fine) solution is to take out your dremel tool and cutoff wheel (or a really sharp knife, some caution and patience) and cut off the bottom half of each endcap. This looks good, doesn't rub, and proactively avoids a common problem on the trail: losing them the hard way. Your approach angle improves.

Note that if you have an SG front bumper, you've already tossed the endcaps.

The picture "endcap.jpg" shows a "lowprofile" endcap.

Understand that you will lose about 10-15% of your torque
The diameter of the tyre is large, so is the circumference.... this directly is a speed vs torque tradeoff. On the trail, it's not so bad. Zipping around town, you notice it. About half the folks who upgrade to 235/85's (or larger) also change their gear ratios in their differentials to 3.8:1 or 4.1 to one. Stock is around 3.5:1.

Understand that your speedometer will read ~8% slower than you are actually going
So make sure you keep the needle at or below the posted limit.... or be prepared for a ticket! You can optionally get your speedo/odo adjusted at a shop, if you really want to.

Understand that you will have to trim the aluminum at the rear of the rear wheel wells
Don't do it if you aren't prepared to take a hammer and saw to your pristine aluminum. Proper body work tools work best, but patience and care are more important. A dremel tool with a cutoff wheel makes the finished job neater. You can do this at home after you get home, as long as you don't have to drive major off road to get home, and don't insist on doing articulation calesthetics on the way home.

Make sure your rear trailing arm bushings are in good shape
A common problem of more rubbing on the rear than you expect is due to worn trailing arm bushings. This is the bar that goes from the frame to the axle... at one end it is shaped like a "T", the other is a threaded bar that goes through 2 rubber pucks that sandwich a bracket. Some guys replace the rubbers 3 times a year (heavy off road use) and insist that rubber feels the best. Others (like me) do enough work on our trucks to strain our marriage, so I put in some soft poly bushings and will never have to replace them.

In case you haven't thought about it...the spare tyre JUST fits on the carrier
... had a last minute panic at the shop when I wondered if the spare tyre would clear the back stock bumper... it does.

If you made it to here and are still convinced....
..that you want some awesome tyres that look great and give you 1.5" more clearance under your diff.... ..put on an old shirt, grab those 19mm spanners and a friend, and a fist full of cash, and away you go!

OK, you're at the tire shop

They'll ask you about 4 times "are you sure these will fit???" You'll learn some more 4 letter words as they try and mount these tyres on rims... They'll ask you again "are you sure these will fit???" They'll watch you drive out to see if they actually do fit, and shake their heads at your insanity.

OK, You are parked in the tyre shop parking lot admiring your new look

Time to adjust your steering stops
Now, hopefully if you intended on doing them here, you brought those spanners and the person or wire. Save yourself some time... note that when you turn the wheel to the right (driver view), you will be rubbing on the right, and you will be adjusting on the LEFT. Don't spend 5 minutes adjusting the side that rubs only to find out that you adjust the opposite bolt from the rub site. Voice of experience.

It's pretty obvious how the steering stop bolts work...there's a lock nut on the back side, and the bolt just moves in and out to set the limit.

And home you zoom, proudly parading your newfound vertical loftiness ... and avoiding any big bumps!

Back at the Ranch

Rear Wheel Well Trimming
I told you that you would have to...

Best if you access to a ramp, but if you don't then you have to do it by guessing. You'll need trimming on the back of the well from 1" at the bottom back corner of the well, and tapering out at about 9 o'clock (looking at the right back tyre).

I ended up trimming TOO much... thinking that rubbing was happening at the back of the well. You should be able to do it carefully and make it look pretty good. One trick is to cut horizontally every 2" and bend each section back individually... don't try and stretch the aluminum.. it will split. Then use a dremel cutoff tool to carefully trim so that the folded flap looks regular and isnt 1.5" long.

If you plan on getting a rear bumper, the SG rear bumper requires you to trim that same part of bottom off the back panels, so no trimming of the arch would be required. Darrell Murrey (AZ LRO pres) got tired of bashing his back panels, so he just chopped them off below the trim line and replaced that with a rubber flap!

Trying them out
I really like the 235/85s... lots of rock crawling in Arizona, and the extra clearance is really nice.

Be CAREFUL your first trip... when you crawl over obstacles, have someone outside the truck watch that back tyre when it comes way up for rubbing. You can really slice your lugs if you didn't trim enough.

That's about it.

Congratulations! Wow your friends! Awe your fellow stock rover-ites! Attach a rope ladder to the side of your truck so that you can still climb in and out!

comments and suggestions on this to terry@westkeep.com. If you do all this and are pissed off at me because you didn't like the outcome can take a flying leap: it's your truck, it's your decision. Go back and read the disclaimer at the top.

Terry West
Arizona Land Rover Owners
95 Disco SE7 ("Polar Bear")
96 Disco XD BC Eco Challenge ("Yellow Jacket")