How much does wheel width matter off roading / 4WDing

[veep]

Hi guys,

Doing some research on 4x4s at the moment and am looking between the Prado GX and GXL.

One difference is the GX has 6.5" wide rims and the GXL has 7.5" rims.

On a road where surfaces are smooth no doubt the extra 1" width makes for better traction/grip/braking.

This is the question, when you're rumbling along rough terrain or crawling over rocks is that extra 1" width going to do anything or in these situations is it more about the torque to steadily crawl over thing than the grip of the tyres?

[sbd3927]

It's the opposite. Despite urban myths, wider tyres provide less traction... IF the surface they are rolling on doesn't give way.
Have someone stand on a small piece of wood and try to pull it out from underneath, try the same with a sheet of wood, a good way to move heavy objects too.

Where the wider tyres come into play is

• on soft surfaces (less likely to sink, less of a hill formed in front of the wheel) think river sand crossings. also why you release tyre pressure to increase the contact foot print
• gravel, soil surfaces, if the surface is breaking away as you try to climb the hill, the solution is to increase the amount of surface engaged. Wider tyres or lower pressure or both. {ie the tyre/gravel interface isn't the problem, its the surface gravel/deeper gravel that's giving way, so we need to spread the load further}

So, it's offroad that extra 1" is going to make the difference, maybe between getting there, or getting stuck. Also the rim width isn't the tyre width, the difference in tyre's available may be greater.

[Chronos]

The above is spot on.

Actually the grip doesn't change. Grip is a factor of weight over surface area. Same weight but more surface area equals less weight per square inch but more area but the grip is more easily lost through changes in tyre angle or heavy steering.

Look at rally cars V road racing cars. Road cars have much wider tyres because tracks are super smooth but rally cars much narrower tyres to deal with bad tracks and even more so in winter rallies in snow and ice.

Chronos

[Oldbloke]

" Actually the grip doesn't change. Grip is a factor of weight over surface area. Same weight but more surface area equals less weight per square inch but more area " Chronos is 100% correct.

Wider tyers just means makers can charge heaps extra for no more perfornance. For more info google coeficient of friction. I did my trade as a motor mechanic and it was one of the first things we were taught.

The material type and tread can make a difference though. As this changes the grip or friction relationship to the road surface. Also chunky treads generally mace more noise at hwy speeds.
I would buy tyers that suits the majority of your driving, It is always a compromise.

[Chronos]

I should say sand driving is a different kettle of fish. You want a large contact patch and wide tyres with soft sidewalls can still bag well on low pressures.

Chronos

[veep]

Thanks for the replies guys.

Also the rim width isn't the tyre width, the difference in tyre's available may be greater.

Yeah of course, but obviously the maximum width tyre you can fit is determined by the rim. Wider rim = wider possible tyres is where I was going with that.

[veep]

Actually the grip doesn't change. Grip is a factor of weight over surface area. Same weight but more surface area equals less weight per square inch but more area but the grip is more easily lost through changes in tyre angle or heavy steering.

Got it

[FuzzyM]

If you want to fit bigger tyres the wider rims will be handy.
Also if it matters to you, skinny tyres don't look as cool as wider ones.

[Chronos]

Something that hasn't been mentioned is availability.

I realise your deciding between different spec vehicles but when it comes to the tyres them selves there's not much point choosing a fancy tyre/wheel combo that will leave you high and dry if you need a replacement in an outback or remote town. It's always better to stick to standard rim and tyre sizes if you're buying/building a touring truck. Same goes for trailer tyres.

Chronos

[Sender]

Also if it matters to you, skinny tyres don't look as cool as wider ones.

Need some fully sick mags for the prado bro!

[MalleeFarmer]

Width increases traction in most cases (except where the weight of the vehicle is insufficient to hold the extra surface area down onto the road/ground) the only exception I can think of is mud/snow where the depth of the mud or snow is shallower than the depth of the tyre a narrow tyre will cut through the soft/wet slippery surface to a hard tractable base underneath. If the snow or mud is deeper than the depth of the tyre then a wider tyre that allows the vehicle to float on top will be better. In basically all situations off-road other than the ones mentioned previously wider tyres give better traction. But They also increase driveline and steering component wear and the chances of bearing failure due to extra leverage on the vehicle from the road. I think a standard Size tyre 265/75-16 is about perfect balance between on/off road traction reliability and availability for prado/Hilux etc. if you go up to the heavier landcruiser/patrol etc. a 285/75-16 seems to work very well as an all around tyre as well. But it all depends on your situation and the roads/tracks you intend on driving. On road smaller/narrower tyres reduce driveline wear fuel consumption and driver fatigue (smaller tyres don't make the car wander as much as bigger tyres)

MF

[KWhorenet]

Added a 50mm Tough Dog lift and cranked up the Sway-Away torsion bars. I've opted for a combo of fully practical and fully sic. Stock rims and MT classic locks. The skinnier AT's are obviously better on road but for general off road they would have done the job no worries.

However when the AUD was over the USD I ordered some Mickey Thompsons from Summit cheap. 16"x8" Classic Locks.
The BFG Muddies shred off road but feel a less attached on road. Surprisingly quiet on the highway and the larger dia has acted like an overdrive gear ratio.

I like the look and stance these rims and tyres give this 'hairdresser' wagon more than anything

width difference

BFG MT vs AT.jpg (305.5 KiB) Viewed 4920 times

Feroza SXII BFG AT.jpg (530.71 KiB) Viewed 4920 times

Feroza SXII BFG MT.jpg (536.58 KiB) Viewed 4920 times

First snow trip so had to show off the bling and mud boots. Front mud flaps wouldn't hurt.

Feroza SXII Mt Hotham.jpg (621.67 KiB) Viewed 4920 times

[OODAH]

It all depends on what you plan to do,weighing up the cons n pros of tyre type and size and tyre pressures can make all the difference. The difference of 5 psi can mean getting stuck or driving straight through.

[Chronos]

Added a 50mm Tough Dog lift and cranked up the Sway-Away torsion bars. I've opted for a combo of fully practical and fully sic. Stock rims and MT classic locks. The skinnier AT's are obviously better on road but for general off road they would have done the job no worries.

However when the AUD was over the USD I ordered some Mickey Thompsons from Summit cheap. 16"x8" Classic Locks.
The BFG Muddies shred off road but feel a less attached on road. Surprisingly quiet on the highway and the larger dia has acted like an overdrive gear ratio.

I like the look and stance these rims and tyres give this 'hairdresser' wagon more than anything

BFG MT vs AT.jpg

Feroza SXII BFG AT.jpg

Feroza SXII BFG MT.jpg

Feroza SXII Mt Hotham.jpg

Awesome looking rig mate. I always thought those SWB mini trucks were great in the bush with decent tyres fitted. A little rough but will go places a patrol or land cruiser won't.

Chronos

[83neil]

It's wise to have 2 sets of wheels/ tyres so I wouldn't let wheel width decide the vehicle

[KWhorenet]

Awesome looking rig mate. I always thought those SWB mini trucks were great in the bush with decent tyres fitted. A little rough but will go places a patrol or land cruiser won't.

Chronos

Yeah not the plushness of a heavier bigger platform but nimble and able. Suspension works smoother with a bit of a load in it. Fun factor of 10 and if I have a catastrophic mishap I can repair or replace for about $500 - $3000. Fits enough gear in the back and Rottweiler in the front. Tows a tinny or loaded 7x5 trailer no worries. Have also towed grass harrows in Low 3rd before I got a tractor.

Sort of like having an off-road buggy with rego and it's not a zook
Last trip on Stockton dunes I didn't let the tyres down before Lavis Lane entry point just got past an old Patrol and VWank dual cab who tried the same on the chopped up soft s**t. pricks f***ed my line & momentum. They all thought it was funny that I got a bit crossed up to miss them & went splat. While they were getting snatched by a Cruiser we let the tyres down and drove off.

[Tiiger]

Real good (IMO) explanation of it here I found a while ago on a physics forum.

Mehcanisms of Tire grip.

Friction
Mechanical Keying
Adhesion

As they are madr from deformable rubber, tires dont exactly follow basic friction theory. So to just say that F=mu*r is strictly wrong. Although it basically does floow this during the elastic range.

Tires only give grip when they are at the correct temperature. this is the most important thing you can remember about tires .

Now on to business.

Tires are the most important part of the suspension, either they are designed to fit it, or the suspension is designed around the tire.

People who say wider tires make more grip because ;''there is more rubber on the road' are wrong. They are both wrong that it makes mroe grip and that there is more rubber on the road.

When you make a tire wider, you alter the contact patch to be wider , but it reduces in length. So depending on sidewall stiffness, a wider tire can actually give less rubber on the road.

The main reason for tires being the size they are is actually heat management. Wider, low sidewall tires will cool better than narrow tall tires. If you can;'t get a tire up to temperatie it will give no grip, if you get it too high you will cook the rubber and ruin the set of tires.

Back to contact patch, you can safely assume that contact patch stays roughly the same area with wide or narrow tires (as long as the load stsys the same). Narroe will have longer contact patches and wide tires will have shorter.

The reason why F1 tires are wide is primarily so that they dont cook (remember they arent just wide, they are fairly high sidewalled), but they ten dto have wider contact patches because they will give better grip going round corners.

A wide tire will generate more lateral force per slip angle making cornering better. F1 cars DO NOT have wide tires for linear acceleration.

Conversely (Mike im goin to have to disagree with you here) drag racers acutally use the tires not becuase of the width, but the tallness. As we know a wider contact patch gives better cornering performance, a narrow but long contact patch is what you want for linear acceleration.

so strangely, drag racers will actually be better with narrow tires. So why do they use wide tires? (remember the most important gip aspect of tires) Temperature! They want as longer contact patch as they can get, but need the width for cooling. (eith 4000+ horsepower you do kind of build temp rather well)

But if you look at the contact patch shape between say, an F1 car or drag racer. (both are considered to use wide tires). The F1 patch will be wider and shorter for good cornering, the drag patch will be longer and narrower (relatively) for good linear acceleration.

So to sum up: Wider tires are not always better. They dont always give better traction. It depends on the car, the situation, the conditions.

Eg. Rally cars use wider tires when on tarmac rallys, and use (surprisingly) very thin tires on ice rallys.
F1 cars used to use narrow tires until aero began to be used in the 60's.
Drag racers acutally want tall tires, width is there to stop the tire being destroyed.

Reference https://www.physicsforums.com/threads/w ... te.330790/

[MalleeFarmer]

^^^ Interesting points perhaps well thought out and maybe they could back it up it makes reasonably good sensed or on road applications. but I still don't think it really applies to off-road use. Best thing for off-road traction as kwhorenet said. Tyre pressure. Aside from all the hard to prove theories from wide tyres vs narrow tyres whatever. (Although tall tyres tend to have many benefits off-road and well established evidence to say so) if you have the biggest best off-road tyres be it skinny or wide and get onto a shaley hillside and they are pumped up to 45psi you will have a lot of trouble. The next bloke might have a small set of stock 205r16s and have them at 18psi and walk straight up the same hill.

[heeple]

^^^ Interesting points perhaps well thought out and maybe they could back it up it makes reasonably good sensed or on road applications. but I still don't think it really applies to off-road use.

Theory is great but the real world is a totally different thing.

He obviously knows more than me on the subject so I'll just go with him - on a perfect surface, at the right temperature, with a tyre surface making perfect contact everything he says is surely spot on.

Types, surfaces, temperature and everything else goes completely out in reality and just comes down to picking something sensible IMO. Not the perfect theoretically best thing.

In this case I'd say a good set of A/T tyres on a Prado will get you most places whether they're on 6.5" or 7.5" rims.