L110CDL wrote:

As a couple of you have mentioned that 265/75/16 BFG's are no good for the real world driving and only for fast cars, i would have to disagree with you there and your saying that the 235/85/16 will do the job as good or better than the 265/75/16 ?

Please enlighten me on these comments

Sadly my normal go to web links with people that are better at explaining things than me seem to no longer exist. The link I'd love to share is this: http://www.expeditionswest.com/research/wh..._rev1.html

Tall, narrow tyres have a lower rolling resistance. That's why bicyles with taller tyres are easier to pedal. In off road driving in soft conditions, a wider tyre needs to move more goop out of the way to make progress. This is the first factor.

Second factor is that traction corresponds with the length of the contact patch. For a given pressure the narrow tyre will have a longer contact patch. Letting air out of a tyre does little to the width (unless you're going round corners which we'll come to later) but primarily makes the patch longer which is one reason why letting air out of a tyre inproves traction (and that's something that's done by drag racers on hard concrete too). The other reason you want to run at reduced pressures is so that the tyre can flex around the terrain, a tyre that's wrapped around a rock will grip it much better than one that's perched on top of a rock. That conformability is something that's completely irrelevant to drag racing

If you are just running at standard pressures on the road then the skinny tyre still has benefits. The maximum force through friction that a tyre can support is calculated with the formula F=μR, with F being the friction force, μ being the coefficient of friction (defined by the stickiness of the rubber and deteriorating with age which is another reason to change your tyres regularly) and R being the force pushing the tyre in to the ground - i.e. the tyre pressure. Skinny tyres run at higher pressures than wider tyres so up until the limits of the rubber disintegrating they will stick better.

Finally, a skinny tyre is lighter so less rotating mass which is easier to start and stop, less unspring weight so the suspension can do a better job, less load put on all the vehicle components. This is also a good reason to use alloy wheels which should be lighter than the steel equivalent.

The advantages are more surface friction, lower rolling resistance and a longer contact patch for a given ground pressure. And because the tyre is narrower you get a better turning circle and less mud up the sides of your car which for most people are good things.

For an off road vehicle you want a lot of sidewall because it means you can lower the tyre pressures more, it protects the wheel and provides more comfort (the tyre is springier).

Now, there are disadvantages to skinny, high profile tyres.

In the same way that the long front to back contact patch gives you front to back traction, a wide contact patch gives you side to side traction. For the same pressure you can't have both long and wide. When you go round a corner, the side wall flexes and picks the inside edge of the tyre up. Effectively, this reduces your tyre width. To limit the effect you need a wide tyre with a short sidewall running at a high pressure.

Where you are seriously at risk of sinking without trace you need a lower ground pressure. You can usually go lower with a wider tyre before you can problems with running out of sidewall or loosing a bead. This is why you see arctic vehicles with balloon tyres and beadlock wheels.

Look at military and commercial off road vehicles (e.g tractors), they are almost all running things with a long and narrow contact patch. The exceptions are things that need flotation without much in the way of traction like crop sprayers which usually have wide tyres unless working between rows. Tesla, interestingly, give their vehicles equiped with 19" wheels a longer range than the ones with 21" wheels.

There are reasons to run wide tyres but none that are relevant to what I use my Defender for and what a Defender is really good at.

shropshiredefender wrote:

What I said was "Just had a new set of 235/85/16 BFG AT fitted as the wider 265/75's have no obvious benefit in real world driving" ie there is no difference other than looks - and that's a matter of personal choice.

No worries  1996 Golf Blue 300Tdi 110 Pick up. Keeper.


Clayton.

Cupboard wrote:

L110CDL wrote:

As a couple of you have mentioned that 265/75/16 BFG's are no good for the real world driving and only for fast cars, i would have to disagree with you there and your saying that the 235/85/16 will do the job as good or better than the 265/75/16 ?

Please enlighten me on these comments

Sadly my normal go to web links with people that are better at explaining things than me seem to no longer exist. The link I'd love to share is this: http://www.expeditionswest.com/research/wh..._rev1.html

Tall, narrow tyres have a lower rolling resistance. That's why bicyles with taller tyres are easier to pedal. In off road driving in soft conditions, a wider tyre needs to move more goop out of the way to make progress. This is the first factor.

Second factor is that traction corresponds with the length of the contact patch. For a given pressure the narrow tyre will have a longer contact patch. Letting air out of a tyre does little to the width (unless you're going round corners which we'll come to later) but primarily makes the patch longer which is one reason why letting air out of a tyre inproves traction (and that's something that's done by drag racers on hard concrete too). The other reason you want to run at reduced pressures is so that the tyre can flex around the terrain, a tyre that's wrapped around a rock will grip it much better than one that's perched on top of a rock. That conformability is something that's completely irrelevant to drag racing

If you are just running at standard pressures on the road then the skinny tyre still has benefits. The maximum force through friction that a tyre can support is calculated with the formula F=μR, with F being the friction force, μ being the coefficient of friction (defined by the stickiness of the rubber and deteriorating with age which is another reason to change your tyres regularly) and R being the force pushing the tyre in to the ground - i.e. the tyre pressure. Skinny tyres run at higher pressures than wider tyres so up until the limits of the rubber disintegrating they will stick better.

Finally, a skinny tyre is lighter so less rotating mass which is easier to start and stop, less unspring weight so the suspension can do a better job, less load put on all the vehicle components. This is also a good reason to use alloy wheels which should be lighter than the steel equivalent.

The advantages are more surface friction, lower rolling resistance and a longer contact patch for a given ground pressure. And because the tyre is narrower you get a better turning circle and less mud up the sides of your car which for most people are good things.

For an off road vehicle you want a lot of sidewall because it means you can lower the tyre pressures more, it protects the wheel and provides more comfort (the tyre is springier).

Now, there are disadvantages to skinny, high profile tyres.

In the same way that the long front to back contact patch gives you front to back traction, a wide contact patch gives you side to side traction. For the same pressure you can't have both long and wide. When you go round a corner, the side wall flexes and picks the inside edge of the tyre up. Effectively, this reduces your tyre width. To limit the effect you need a wide tyre with a short sidewall running at a high pressure.

Where you are seriously at risk of sinking without trace you need a lower ground pressure. You can usually go lower with a wider tyre before you can problems with running out of sidewall or loosing a bead. This is why you see arctic vehicles with balloon tyres and beadlock wheels.

Look at military and commercial off road vehicles (e.g tractors), they are almost all running things with a long and narrow contact patch. The exceptions are things that need flotation without much in the way of traction like crop sprayers which usually have wide tyres unless working between rows. Tesla, interestingly, give their vehicles equiped with 19" wheels a longer range than the ones with 21" wheels.

There are reasons to run wide tyres but none that are relevant to what I use my Defender for and what a Defender is really good at.