Page created: 25-Nov-03

Re-published: 1-Nov-09



Technical: Discovery I
Wheels & Tyres

From the outset, it was always my intention to fit bigger tyres with a more off-road bias. On a Discovery however, anything larger than the stock size of 235/70 x 16 will foul on the rear wheel arches at full axle articulation. After a bit of research I quickly discovered that trimming back the rear corners of the wheel arches is a relatively straightforward task and quite unobtrusive, and this significantly increases the range of tyre sizes that will fit.

Other things to consider however, are the gearing, suspension set-up and the steering. To accommodate 235/85 x 16 tyres for example, as commonly fitted to Land Rover 90ís and 110ís, itís necessary to raise the suspension by two inches (50mm). Once again itís the rear wheel arches that are the limiting factor, as they were never designed with tyres of this size in mind. This size tyre would also raise the overall gearing by about 10 percent. As the Discovery is already fitted with the highest ratio standard transfer gears, this can have a significant detrimental effect on the vehiclesí performance. Larger tyres can also foul on the front radius arms on full lock although, as long as you can live with a wider turning circle, adjusting the steering lock stops can compensate this for.

As Iíd already decided that I wanted to retain standard height suspension, it soon became apparent that the most suitable tyre size would be 245/75 x 16. These provide a useful 20mm extra ground clearance whilst only needing relatively minor trimming of the rear wheel arches. Gearing is raised by approximately 6 percent, which is not too much of an extra burden on the engine and transmission.

A less obvious benefit of this tyre size is that the speedo also now reads accurately. It turns out that the Discovery speedo is designed to read approximately 6 percent over actual road speed, which is comfortably in the middle of the zero to 10 percent over range that they must register in by law. The downside is that the change also affects the odometer, which makes fuel consumption figures look worse, albeit more accurate.

Trac Edge is a genuine 50/50 on/off road tyreWhen deciding on tyre make and pattern I had a number of factors to consider. I wanted a tyre that would provide more off-road capability than the stock tyres offered, but not be so aggressive that handling might be unduly compromised when heavily loaded or when towing. I also wanted something that had good wear characteristics. It took no time at all to settle on the BFG Trac Edge. They have an excellent reputation as an all round 50/50 on-road/off-road tyre and should be good for 50 000 miles. They were also something of a known quantity as Iíd had them fitted on my previous Land Rover. They've since proven to be an excellent choice and have performed well on the Discovery over a wide variety of terrain. The only downside is a distinctive hum at around 40mph which wasnít noticeable in my much noisier Land Rover.

Unfortunately, BFG have now discontinued the Trac Edge and replaced it with the All Terrain Traction Advantage.

Alloys wheels just too nice to take offWith regard to wheels, it was my original intention to swap the alloys that were on the vehicle when I bought it for some Discovery steel rims. These are both less susceptible to damage and more easily repairable in the field if they do take a knock, which was a serious consideration given the imminent trip to Morocco that I had planned at the time. I even went as far as buying the rims ready to swap over. However, when I eventually collected the vehicle I decided that the alloys were just too nice to part with. I convinced myself that it was a small compromise that I could live with as I planned to take a second spare wheel (which would be a steel rim) to anywhere really remote. I havenít regretted it yetÖÖ.