Off road mobility using terramechanics. Pt. 2b - unpowered wheels

In this series of videos we investigate off road mobility using terramechanics techniques.
Using terramechanics we can look at the factors which affect the off road performance such as soil types, wheel loads, tyre sizes and inflation pressures.
In this video we present the findings - the effects of different soils, tyre sizes and inflation pressures on off road mobility.
References used include:
Theory of Land Locomotion by M.G. Bekker, ISBN 978-0-472-75020-7
Terramechanics and Off-Road Vehicle Engineering by J.Y. Wong, ISBN 978-0-7506-8561-0

[@oldbritishmetal]

Great to see a proper analysis being applied. Your videos are superbly factual and quite frankly, a breath of fresh air. Thanks for all of your efforts!

[@defendermodsandtravels]

I realise that the technical series of videos may be hard going for some viewers however if they persevere they should end up with a better understanding of the subject. If I try to simplify them further there's a danger that I'll cut out the substance of the video and just give a very superficial coverage. I hope the current approach is good for those with a real interest in the subject.

[@Yanglopezviva]

Agree 💯 % 🔊🍻

[@mikeunsupervised9254]

For very soft sand, the 4WD mantra is always to air down. It's interesting that your analysis doesn't show that it is helpful. However, your "low pressure" is 12psi, and generally the trucks going in sand run bead lockers to allow significantly lower pressures (4-6psi). I'm curious, at what parameters (load, tire dia, tire width) would you start seeing an advantage to air down in soft sand when airing down gets you to 6psi instead of the 12psi you used.

[@mustang32758]

Very interesting video. I always thought that fish plating was the way to go over the top of a vertical welded seam, because it was supposed to be a requirement of Department of Transportation in the US. I have seen fabricated axles split vertically on welded joints but never heard if there was a finite analysis done after the fact. My assumption would be a poor weld affected the failure, then and not the design there of

[@slashsplat]

Fascinating. Have seen some testing videos that show that skinny tires are better in general for offroading, contrary to common perception.

[@Hexamin]

One should also consider that the rolling resistance of a fat tire is higher when the sinkage is equal because of the wider thread. You therefore need more traction to be able "pressing down" more soil surface or snow. This increased resistance should make fat tires even worse offroading. In my opinion the 4WD-Community is becoming aware of the issue.

[@defendermodsandtravels]

There are two counter effects here. For a given load the sinkage of a narrow tyre will be greater than a fat tyre but for a given sinkage the rolling resistance of the narrow tyre will be less. However a larger external diameter always reduces sinkage and rolling resistance. You should fit tyres which give controlled sinkage for the conditions encountered but no wider than necessary. IMO stupid wide tyres have no place.

[@philhealey449]

An interesting side point (to me anyway) for on-road aquaplaning and general adhesion I've never seen mentioned is the effect of the very significant increase in the viscosity of water at reducing temperatures towards freezing point, producing enhanced lubrication properties and greater resistance to ejection via gaps between tread blocks; both mechanisms intuitively should favour narrower tyres to avoid scary cold weather motorway moments. I'll anyway await your powered wheel analysis with interest.

[@fransubaru]

Very interesting and technical videos!! Amazing!

[@adelarsen9776]

Here's the issue Bill : People would rather believe the myth and look the part than sit and learn terramechanics, physics and demonstrated science. I've said it my whole life : Skinny tall tyres are the best. When soil type is of a certain kind no tyre will grip nor provide forward traction. The larger and heavier the tyre/rim combo mass the greater the suction. Finally, the best reason to choose skinny tyres is because you can purchase cross ply tyres which are extremely stake resistant. All the "experts" don't know this nor do they learn.

[@defendermodsandtravels]

I think skinny tyres are a good compromise for many conditions although there are situations where fat tyres perform better. However the part that I don't understand is spending a fortune to change the wheels and tyres to aftermarket fatties, not to mention the weight penalty, unless there are clear benefits across the board. There aren't. Manufacturers wouldn't fit skinny tyres (as most do) if they weren't up to the job. One caveat however. I do need to repeat this analysis for powered wheels to see if the picture changes significantly. Practical experience indicates that the picture isn't very different for powered wheels.

[@adelarsen9776]

@@defendermodsandtravels That's why HGV's, trucks and military transports all have skinny tyres. But you won't convince the "4wd brigade". The other myth of course which is perpetrated by the 4wd media and repeated by the great unwashed masses is that mud tyres are tougher and stronger when this is absolutely wrong and the opposite of truth. Mud tyres are good in mud - Not in sharp sticks, sharp rocks, heavily rooted country and stones. Of course, you can build a tough mud tyre but you won't be able to fit it to a road registered vehicle. You can fit it to a tractor or earth moving machine.

[@defendermodsandtravels]

@@adelarsen9776 You used an important word in your first post when you said "tall and skinny". A larger diameter tyre will always give less sinkage and external resistance. Larger tread width may or may not help. The Ford T had a reputation for being surprisingly capable on farm tracks for this reason.

[@adelarsen9776]

@@defendermodsandtravels Wagons Ho !!!

[@Yanglopezviva]

Excellent superb information you are the man 🔊🍻

[@gjackson123456]

Very good info. Looking forward to the powered wheel case. Cheers!

[@martingreenaway1328]

Superb content. I am glad to have come across your channel and will recommend it to my friends. This trilogy on terramechanics is similar to what I remember being covered in the early 2000s at the Defence Academy Shrivenham. I will certainly get a copy of Tatsuro Muro's book

[@defendermodsandtravels]

Thanks for the comment. There's a lot more I want to do on terramechanics which is a fascinating subject but I getting involved in too many other things at the moment.

[@airone6697]

One more time. Thanks for your job