Which alternative tyre sizes will fit my DSII?

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slunnie
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Which alternative tyre sizes will fit my DSII?

Post by slunnie » Sat Mar 11, 2017 9:42 am

Duplicate Backup from Wim van Doorst
All credit to Wim for researching and compiling all of the information in this post.
http://www.clifton.nl/index.html?tyresizes.html

Because I was interested in putting alternative tyres on my Discovery Series II, either as all-day runners or as an extra set for outings, I have gathered the following information about the various tyres, availability and feasibility for my type of car. I now am the pleased owner of 245/75R16 BFG MTs on RR alloys, fitting well on the inverted spare wheel carrier. WvD
Glossary

Wheels are the metal (steel, aluminium, magnesium, or alloy) parts, and tyres are the rubber parts. Typically, there are five wheels on a DSII.
Summary

Stock tyres are 29 inch on 16 or 18 inch wheels. Obviously these fit well. Largest to fit on a stock DSII are 30.5 inch sized tyres, of which the 245/75R16 size seems to be the most often mounted. With a body lift of approximately 2 inch, 32 inch tyres may be fitted, of which the 265/75R16 are by far the most popular. Changing the spare wheel carrier is then necessary. You might fit even larger tyre sizes, but significant additional changes to your DSII will be necessary.
Effects of larger tyres than stock (width, height, wheel)

Changing the wheel diameter from 18 inch to 16 inch wheels (or going the other way around), and keeping the tyre width and the outer diameter of the tyre the same, will technically speaking not give larger tyres on the outside, but it will give you higher (or lower) tyre walls. More wall means flexibility, so that the tyre can better follow rough tracks and accommodate bumps for comfort, and get better grip. Less walls means less flexibility, therefore more direct steering. Typically, for off-road preference you choose the 16in wheels, and for on-road preference (yeah, right, in a Land Rover?) you would prefer the 18in wheels.

Increasing tyre width, keeping the rest (wheel, tyre diameter, engine, etc) the same, will give you a larger contact area (m2) between tyre and ground. As the weight of the car downwards doesn't change, the effective pressure (Nm/m2) on that contact are will then be reduced. The larger area will increase grip, which will be most noticeable on gripful ground, e.g. dry road. The reduced pressure will decrease the bite of the tyre into the ground, and make it more floating. This is positive in sand dunes, snow, deep wet mud, and other soft grounds, but detrimental in shallow mud, wet roads, and other hard grounds, where you want the tyre to bite through the upper surface down to the hard underlayer and get grip.

Increasing the tyre height, keeping the rest the same, will give you quite a few effects, some positive and some negative, depending on which way you're looking at it

First you get the higher tyre walls, similar to decreasing the wheel size, with about the same effect (see above).
The outside circumference of the wheel increases. This will make your wheel make less turns for the same speed, and make more distance per tyre revolution, leading to less engine revs at cruising speed and more mileage from your tyres. Note that in first gear, low gears, at tick-over engine speed, higher tyres will also have this effect, and make your car go faster than before. Think of that when you're just in front of the very deep precipice which you want to crawl up or down.
Thirdly the tyre radius increases, which leads to a larger arm to put the torque (=force x arm) out of the engine onto the ground: more arm, thus less force, thus less quick drive-off from stand still, and less quick overtaking, etc. Also when you want to drive up a steep incline, you may notice this reduced force.
Lastly, the entrance angle and the exit angle of the tyre will decrease, leading to a larger, longer footprint. This will increase grip and reduce the pressure, similar to wider tyres (see above), but also it will decrease the descending speed of the rubber to the ground in the revolving: the tyres are quieter.
Oops, I almost forgot :-). Larger tyres give you more underaxle clearance, with combined the increased approach and exit angles of the car. Why else are you considering larger tyres?

Obviously the aforementioned effects are proportional to the tyresize increase that you have in mind. Increases by 5% (Slightly Larger, see below) are noticeable but quite acceptable. No special adjustment are necessary. Increases by 15% (Oversized) are very pronounced, and changes to gears, diffs, etc are hardly avoidable.



Standard sized tyres: 29 inch

28.9in 205/80-16
29.0in 235/70-16 stock size in Europe and Oz
29.0in 255/55-18 stock size in US, optional elsewhere
29.1in 255/65-16 stock option worldwide
29.1in 235/60-18
29.3in 225/75-16
29.5in 245/70-16

Standard DSII tyre size. Obviously this size of tyres are plentiful around, and typical ones have a fairly balanced road/off-road bias, e.g., Michelin 4x4XPC, and BFGoodrich TracEdge.

The 16-inch wheels are standard issue worldwide on lower trim levels. Higher trim levels are equipped with 18-inch wheels as standard, because they give more car stability, especially in on-road situations. In the US, any model with ACE is automatically fitted with 18-inch wheels. Typical first tyre related upgrade, when supplied with 18-inch wheels, is to exchange them for 16-inch ones. The advantage is that with a particular outside wheel+tyre diameter, the 16-inch wheels have taller, and hence more flexible tyre sidewalls, and therefore offer more grip in off-road situations.

In many countries, the tyresize of a particular car is included in its homologation for that country. This results in it being illegal to mount any other tyresize (more than +1.5% or -2.0%) than originally mounted to the car. Since the DSII comes with a 29 inch tyres, the choices in those countries for alternatives are limited to the ones mentioned above.



Reasonable, slightly larger tyres: 30 inch and 31 inch

30.0in 255/70-16
30.4in 215/85-16 Popular alternatives on RRs
30.5in 245/75-16 Popular alternative on stock DSII
30.5in 265/60-18
30.6in 265/70-16 Technically the largest fit on standard DSII, but not a common tyre size
31.0in 7.50R16 Old LR style, narrow. Check for actual size
31.1in 225/85-16
31.2in 275/70-16
31.6in 265/65-18

Very reasonable alternatives. Often used on stock suspension without problems. But beware, people interested in these sizes tend to also change the suspension for lift and for improved ride.

The spare wheel carrier needs no adjustment for the 30-inch tyre sizes, but as it will be a close fit, allow for variation in Land Rover build and in practical tyre size, and measure for yourself. Wheels up to 30.5 inches may be expected to fit properly on a standard carrier (mine do fit exactly). The 31-inch tyres probably won't fit the carrier without adjustment, for which several alternatives are described below.



Rather large tyres: 32 inch

31.5in 285/60-18 Large alternative for 18in wheels
31.6in 265/75-16 Often used alternative on lifted DSIIs.
31.7in 235/85-16 stock Defender size
32.1in 275/65-18 Very wide

Rather large alternatives, and generally regarded as the largest reasonable tyre size for the DSII. It can be run on stock suspension, but expect rubbing on the radius arms on the wider ones, and even the narrow ones in off-road conditions (full lock). Also rubbing is to be expected on the inside of the wheel wells on the front wheel arch panel of the front bumper. Lift, bumper change (trimming or replacement), and adjustment of steering stops (or wheel off-set) are recommend for serious use. And note that widths larger than 267 mm (10.5 inch) will seriously rub car parts (fenders) and also extrude outside of the car body, which is illegal in many countries. On-road car handling is significantly altered.

Adjusting the spare wheel carrier is absolutely necessary for this size. Possible adjustments, all actually reported as really carried out by a DSII owner, include

Inverting the carrier, which will raise the wheel by 3 to 4 cm (approx 1.5 inches). Downside is that it will also shift the wheel more to the left, and thus put more leverage on the door hinges plus obscure a larger part of your rear view. For this option you will have to remove the interior trim of the door, undo the six carrier bolts, re-use the four upper/lower fixing holes, and with the metal fixer as a template drill two new middle holes in the door, and re-attach the carrier. Also this option will need adjusting the rear wiper arm to allow full travel: undo bolt/screw, pull out, readjust on the spline, reattach. An afternoon of home-mechanic work, but it will give you a stable spare wheel carrier, allowing for all practical tyre sizes, up to and including 33-inch tyres.
A reasonable alternative adjustment is drilling mounting holes lower down (20 mm, or 3/4 inch) in the carrier, which needs removal of the interior trim, flattening the pressed rib on the bottom of the mount, and some accurate drilling, and has a very stable result. Obviously, for this the interior trim has to be removed first, and put back on afterwards. A raise of approx. 2 cm (0.75 inch) seems achievable with this alternative, allowing for all tyres up to 32 inch as listed above.
A next alternative is to wing it: just put on the larger wheel on the carrier and slam the door. You can help the bumper down a bit by loosening the two bolts which hold the bumper on the frame, and then slam the door and re-tighten the bolts. Effectively the bumper will be pushed down a bit. If you can live with the rubbing this is an easy way out, but only applicable for the tyre sizes between 30.5 and 31.5 inches.
Lastly, you can put the wheel way higher up on the stock spare wheel carrier, using merely two bolts instead of the default three. The attached wheel will slightly tilt forward towards the rear window. Downside of this option is that the spare wheel will be attached to merely two bolts, both on the same off-centre (bottom) side of the wheel, causing leverage, with questionable stability. Obviously, you can make any tyre size fit.

The 32-inch tyres are the stock size for Defenders, and therefore there are plenty examples about, e.g., BFGoodrich AT or MT, Rover MT/R, Yoko Geolanders, and many others.



Oversized tyres: 33 inch and larger

32.6in 285/65-18 Not common, but they exist
32.7in 265/80-16
32.8in 267/80-16 (actually 10.5in wide)
32.8in 285/75-16
32.8in 305/70-16
32.9in 32x9.5x16 Simex is slightly off in its designations
33.0in 33x10.5 Simex too
33.1in 255/85-16 Several people reported to have this on their DSII.
33.4in 295/75-16 Too wide. No reports
Things may seem scary below this line. That is only natural: they are scary! You're out of bounds here
34 in 8.25x16 Michelins (way off in its designation)
34.5in 315/70-17 Chevrolet Camaro wheels with practically an exact fit for DSIIs, daily driver, by Greg
35in 35x10.50x16 Yes, Greg made these Swampers SSR Radials 'fit'. Merely had to remove some loose sheet metal that was in the way.
35in 35x12.5x18 Nothing serious here, just adding some data for the 18in wheelers
36in 9.00x16 Michelin XL: trial fit made Greg chicken out. No other serious attempts reported
36.5in 9.00x16 Unbelievable: Greg fitted these too, and did the Globe tour with it. Note: Michelin XZL is way off with its designation here.

Oversized alternatives. Lift absolutely needed. When going for these sizes, expect also to do some serious bumper manicure (trimming or completely replacing). Not only are these diameters too large to fit without major adjustments, also widths larger than 267 mm (10.5 inch) will seriously rub car parts (fenders) and also protrude outside of the car body, which is illegal in many countries.

Furthermore, engine performance and braking effectivity will significantly deteriorate. Expect therefore to change gear ratios, and to upgrade brakes to heavy duty substitutes. Additional alterations required include the obvious body lift, spare wheel carrier adjustment, bumper manicure, etc. And expect to often replace broken half-shafts, drive shafts, hub assemblies and diffs. Finally there is a higher pliable tyre sidewall, increasing the left-right tilting potential of the DSII. Retaining sway bars, and ACE is reported to have sufficient good (on-road) stabilizing effect. Interestingly, fuel consumption has been reported to be not increased for these tyresizes, but contrarily seems to be stable or even better.

Overall, these oversized tyres, are only for the brave of heart, but necessarily in combination with a substantial body lift, you get an enormous under-diff clearance! Not many reports that people have actually fit these sizes, though.

The people wishing to fit these tyres are the more adventerous types, so won't fit road-biased ones. In this size, many very potent, and therefore attractive tyres come available, such as Simex Extreme Trekkers, Interco Super Swampers, and numerous big MTs of various makes. It is also estimated that off-road capabilities of wheels already increase with merely size, so that even All-Terrain tyres in 33 inch tyre size will provide enhanced off-road performance.



Other information

With special thanks to Bryan McGlade, Greg Bright, Greg Hren, Greg Davis and Simon Lun for the sound advice with respect to 33 inch or larger, oversized tyres on a DSII (don't).

This Howto is maintained by Wim van Dorst. Last update: 26 December 2004
Cheers
Slunnie


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