Why Wide Tyres Do Not Help In Desert Driving

[Ilya]

We are in a unique situation here, in Carnity in the UAE. We have plenty of Jeeps - stock and lifted, with 285/70 and 315/70, we have many high sand dunes - so we can run a proper set of tests and even film it  The aim of the test is ONLY to test the car's adherence to sand. It can be a dedicated drive - why not?
The disadvantages of having big tires are clear and not questioning (however, it sims that with 285/70 has nearly none of  them), people who go for big tires usually understand it and accept it as a price for a nice look

I put 315/70 on my Sahara just recently (made it for a great look only, actually wanted to go to 305/70, but it was impossible to find them in the UAE).
I had a strong feeling that the car easier drives on the sand (I am only talking about the adherence).  BUT I can't exclude the placebo effect, that's why I am open to doing a comparison

[Gaurav]

Coming back to OP of wider tyres do not help, I like to add my two cents with very basic understanding first.

I hope everyone knows that car basic HP figures as advertised by any car manufacturer is totally different than that car actual HP. Reason being that is manufacturers rate Engine with just Engine HP at the crank and when they place that engine in the vehicle there are several components that robs engine actual HP like AC, Fan, Tires, Drivetrain, 4x4, Transmission and last but not least the car total weight.

The final HP that comes to wheel for final action is called WHP (Wheel Horse Power).

https://www.mk5cortinaestate.co.uk/calculator4.php

Below example guesstimate my Pajero 225 HP at crank must be doing 168 WHP.

Now when we know how much WHP we have and what all limit this WHP, lets start talking about the number ONE factor in the "SAND" is the "power-to-weight" ratio. Lighter the car, better it will perform, just like in any street racing fundamentals.

Adding heavier bash plate, bull bar, winch on the nose of the car will seriously limit it's climbing capabilities. Before adding winch to my Pajero in 2017, I could climb Faya almost every time and now I can climb some times only. Tried in colder and summer season, day and night, cross track vs lesser cross track, result was more or less the same.

Now let's come to the final point of main concern here for wider tires.

Every increase in tire size than stock tire size will rob the WHP and eventually limit the climb capability. Having said that for offroading we do need to increase the tire size sometime to gain better ground clearance. So while doing that one should stick to as close to the stock size as possible within the bare minimum requirement of lifting vehicle by 2-4 inches max. As more you lift the vehicle more you will disturb the center gravity and roll (separate topic for another discussion).

Why to increase the bare minimum is because of below added weight that drive train will have to push.

EXAMPLES:

• Stock tire - 29 Inch - 12 Kgs
• Offroad tire - 29 Inch - 15 Kgs
• Offroad tire - 30 Inch - 20 Kgs
• Offroad tire - 31 Inch - 25 Kgs
• Offroad tire - 32 Inch - 30 Kgs
• Offroad tire - 33 Inch - 35 Kgs

So if my vehicle WHP was 168 hp with 12 kg stock tires, it will be eventually under 130 hp or lesser if I install 33's.

Above numbers are estimate only as actual numbers maybe up or down depending on tire companies and number of ply they use in their sidewall. MT tires having 10 ply sidewall for rock climbing and mountain which make them solid for rocks but results in too heavy for sand.

Few of you must have seen what many local enthusiast use here is called Sumitomo 900 (Tsamia) tires which is super light and almost bald without any treads but perform amazing in the sand. Same for Shaheen tires, but these tires are disaster on road and that's why very few daring enthusiast opt them.

In my Patrol I have tested BF Goodrich that barely used to climb half of Big red. Then switch to Cooper STT and then ATR, which was slightly lighter and reached upto 70% Big red. Then Yokohama geolander made to almost 80-90%. My Nissan Patrol SWB was flawed by bad gearing but using this as an example purely to make everyone understand that how heavier the tire will limit the climb capabilities.

On other hand I have even tried HT tires in my LC 100. With Grandtrek they were horrible to climb. When changed to Michelin LTX (in that era, discounted now) it really climbed substantially higher, because of lighter weight tires and softer sidewall - 3 ply made a day and night of a difference. @Emmanuel is still using Michelin since long time now and everyone can see his Xterra climbs really well without much of an issue.

Now coming to the last point of wider tires will not help because added width will only increase its weight and broader footprint will not help as much as longer footprint, that's what @Frederic was trying to explain. Longer footprint are easier to achieve and beneficial in getting additional height (ground clearance) at the cost of added weight, where as wider footprint will not bring anything to the table for stock vehicle. Broader tires are needed when you lift too much and add those broad tires to widen the wheelbase to lower the center of gravity. Now if you go this route then you also need good power mods to counter additional 10 kgs X 4 = 40 kgs additional stress on the drive train.

@Ilya Golubinsky you are right that we are unique at Carnity in stating the facts with expert knowledge and experience as we aren't supported by any offroad garages to sell mods. Most if not all off-road clubs in the UAE are the front-end of off-road garages or off-road products sponsors and that's why they love to sell the looks first and when customer come back to them that its not climbing enough (pet peeve), then they open the buffet of modifications - power mods, firm suspension, lift kit, re-gearing, supercharger etc.

I have spent close to 60-80k in mods on my 3 cars and still never satisfied with the stories and claims I used to get from offroad garages. And if I talk too much on logics and facts they will either ban me from the club or laugh at me to discourage such fact-finding which will eventually ruin there business model.

[Looper]

Here's a video from Cooper Tires:

https://youtu.be/q5mPgW-xRBg

[Frederic]

49 minutes ago, Goutam said:

Here's a video from Cooper Tires:

https://youtu.be/q5mPgW-xRBg

Nice, and clearly confirms our statements made.