Stabilise your trailer by adjusting towcar tyre pressures

#towcar #tyrepressures #caravan
You want your towing rig to be stable an easy tow, right? Well there's lots of things you can do such as manage weight distribution, but something overlooked and easy to do is adjust your rear tyre pressures to suit the new load. But how much load is there, how much pressure should you add, and what's the effect if you do, or don't? All explained here.
Post questions as comments!
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[@applesbighatranch6906]

Your measurement of the longitudinal aspect of the tire contact patch... when your pieces are kept square (for greater accuracy) to adjust for load is GENIUS. So simple, and we all know the greatest things in life are indeed... simple. Thank you again, Robert! for your perspective on these matters. We are all better drivers for it.

[@craigclarke1628]

Love the simplicity of getting the increased tire pressure for towing a specific load. Can you please do a video on how to get the right starting tire pressure as tire placard and dealership difference is very large in my experience.

[@jerrymyahzcat]

The more load a tyre takes the higher the pressure has to be (up to its maximum pressure and load carrying capability) - the exact reason that you can’t just air down when your vehicle is very heavy and close to it’s maximum load carrying capacity. If you do it must be for a very minimal amount of time, at very low speeds and even then comes with risks.

[@iangoodwin345]

Tyres pressures for a "mug" like me are an interesting discussion. I have had numerous cars throughout my life and have always checked the reference labels inside the vehicle which specific the manufacturers "recommended tyre pressures". Then enter the person at the tyre replacement shop (think "tyre expert" at Bob Jane, Tax Tyres etc) and they always say to run higher pressures to ensure better tyre wear. I have been told that softer pressures suggested by manufacturers are to ensure a "softer" ride for the owner. As an example, my current Landcruiser Prado (150) has OEM tyre pressures on the door sticker suggesting around 30 psi. The tyre shop reckons the AT22 265/65/18 should be run at 40 psi to ensure optimal tyre wear and performance. That's a full 33% above OEM spec. Then, I add my 240kg caravan TBM and may need to go even further. Excellent video Robert on how to measure the change. Simple and easy to follow for the home punter like me. Question is.... how do I really "know" what the correct and optimal starting pressure is to begin with ? You run 37psi in your Ranger. Is that OEM spec or some other black magic figure? Adjusting is fine for safety and makes perfect sense, but being sure you start from the correct pressure is the mystery box for me.

[@Pat.Mustard]

I’ll second this. My Pajero runs standard highway tyres on the original 18” rims and the tyre placard in the car says to inflate them to 29/27 PSI - something like that. I’ve inflated them to 38 psi and it’s a pretty rough ride but they balloon a lot at 29. So, yeah, good question?

[@jerrymyahzcat]

Rough guide is to run them at 20% higher than placard.

[@davehoward8745]

Thanks Robert. running Khumo MT51 muddies at 48 psi with 240 kg 0n the ball. Dunno if it's too high but it tows well. Dave

[@Mouldyturnip75]

Yet so many just go 45 and 40 - for no reason than its what Bob does. Have to give it to tyres and manufacturers - they make a product capable of withstanding tremendous abuse over 100's of 1000's of cycles. Great work Robert. Such education must be part of owning and towing a trailer.

[@sydneyraj]

Eye opener on principles. Most appropriate guidance. Thanks, you have saved several thousand dollars and grief for many travellers, not only those who tow but also long distance 4wd adventure seekers carrying heavy loads.

[@user-mb1vz8yh7k]

I use a similar technique except I accurately measure how high the lowest centre line point of the rim is from the ground, next I add the load to the tow hitch & pump up the tyres until the rim height matches what Id previously measured before the extra load was added. You have now found what rear tyre pressure to use when towing. Perhaps I’ll try your technique to see if it comes up with the same tyre pressure, I think that it should do as we’re both measuring the same effect, you’re measuring along the X-axis & I’m measuring along the Y-axis!

[@L2SFBC]

Yes it's the same principle, and one method is not better than the other. Both are imprecise, but the core principle remains - more load, higher pressure.

[@BundyBearsShed]

A point of interest for me on this subject was when I bought a set of Coopers brand AT tyres they came with a card that said when driving from cold to warm say after 30 minutes of highway driving the correct tyre pressure would be 4 psi higher than from the cold setting due to the heat generated by using the tyre. e.g. if the cold tyre pressure at the start of the trip was 40psi then around 30minutes later if you checked it you should have 44psi if your tyre pressure suited the load on the tyre. If the pressure was 10psi you needed to raise the pressure if the difference was only 2psi you needed to drop a few psi. I thought you may find that interesting. P.S. Im presuming this is on the black top only but still suitable for the caravan.

[@cameronwood1994]

I’m so glad you mentioned that the relationship between tyre pressure and tyre load is not linear. Indeed, for the European equivalent of light truck tyres, the European Tyre and Rim Technical Organisation (ETRTO) uses the formula “Reference Load = Maximum Load ÷ (Maximum Pressure ÷ Reference Pressure) ^ 0.8”. You can of course flip the formula around to “Minimum Pressure = Maximum Pressure × (Actual Load ÷ Maximum Load) ^ 1.25” - which is more practical for day-to-day use. As an aside, European light truck tyres can always be identified by the letter ‘C’ after the wheel rim diameter - e.g., 235/85R16C. It does not mean Load Range C. In fact, the letter ‘C’ derives from the word Camionnette, which is the French word for van, and in terms of the ETRTO means ‘commercial’ or ‘light truck’. They are direct equivalents to the Tyre and Rim Association (T&RA) ‘LT’ Light Truck tyres - e.g., LT235/85R16. In those cases, the letter C after the wheel rim diameter would indeed refer to Load Range C. Europe exclusively uses load indices rather than ply ratings or load ranges.

[@L2SFBC]

As always a super helpful comment, thank you Cameron!

[@Excitedtobehere]

Troubleshooting tale from the trenches. Wednesday we were towing our 3t van be behind our LC200, and normally in addition to the rear tyre pressure, I would add 9 PSI to the rear airbag bags to firm up the rear. As we only had 150km to home and were carrying 300kg less overall than normal I decided not to pump the bags. 50k up the road we encountered some severe 50-60kmh side winds which pushed the tail of the combination about ( but did not continue to oscillate)..Other half suggested we stop and put the usual PSI in the air bags and it made an immediate difference to the overall handling of the combination, kudos to her.

[@L2SFBC]

Thanks James, posted that to FB. It's a great story and the same reason why it's good to add a little pressure to the rear tyre as shown here.

[@TOYOTA.Overland]

That's in the booklet for every proper car (or a sticker on the inside of the tank door). Pressure for loading 2 people, for 5 people, for 5 people and 5 luggage, for towing a trailer, for very fast driving over 220 km/h, etc. Just need to follow it. 😉 The higher pressure is also due to dynamic stress during driving with caravan. Your static test is great, but put the camera to the rear axle on a wavy or bumpy road and do a test drive. There you might see the differences even more.

[@nicknick7052]

Yes, all true, however the TBM for the same trailer is variable as variable is the load on the rear axle (due to car load distribution) and therefore is important to remember the towing tyres pressure value is not constant.

[@MegaAnufriev]

Very useful information for towing! Thanks

[@L2SFBC]

Glad it was helpful!

[@joking7081]

Good video. I've always just done this technique just by sight. I never considered actually measuring the contact distance.

[@L2SFBC]

As long as you're accounting for the load that's the main thing 👍

[@stuartkcalvin]

That tip is very handy!

[@geofflines60]

Excellent. Thank you Dr Pepper.

[@craigtomkinson2837]

Awesome work

[@L2SFBC]

Thanks a lot 😊

[@zeushellrider27]

Great topic thank you.

[@L2SFBC]

Glad it was helpful!

[@Excitedtobehere]

Great video Robert! The simple explanation of these concepts makes them easily understood.

[@L2SFBC]

Glad it was helpful, please share!

[@michaeldallimore8590]

Very well explained thank you.

[@L2SFBC]

Glad it was helpful!

[@richardradcliffe6047]

Thanks for yet another great lesson.

[@L2SFBC]

My pleasure! Please share :-)

[@rossjohnson6509]

Really informative, simple and easy to follow.

[@L2SFBC]

Glad it was helpful!

[@rossjohnson6509]

@@L2SFBC Robert can I ask is there any logic with trailer pressures, I have a single axle camper much like in this video towed behind an Amarok. In a trip last year we snapped a leaf spring on the old camper trailer at the eye, I feel we had too high pressure still on the trailer, the exact number I can't recall but had dropped to around 20 PSI.

[@L2SFBC]

Same logic there as car tyres. More load more pressure. Exact amount dependent on volume of tyre vs weight.

[@markh6676]

if you know rear axle weight increases to 1850 isn't it easier to just calculate based on max tyre psi and max tyre load. So 925kg / max tyre load X max psi should give you towing psi. e.g., 925/1100 x 50 = 43psi Vs 800/1100 x 50 = 36psi when not towing.

[@L2SFBC]

It's not that simple an equation. What you describe is an approximation as the relationship is not linear.

[@HardstylePete]

Any tips of finding the ideal starting pressure without the trailer?

[@rubberlegs]

I wonder if a tire engineer would agree that contact area is a constant, no matter the load. Perhaps it makes sense from the perspective of the tire carcass.

[@L2SFBC]

They wouldn't but it's a fairly decent rule of thumb.

[@markward38]

Hi Robert, Another great episode on caravan operation to us new caravan people. I’ve got new Toyota LC 300 (with standard tyres ) and a new 2.9ton van and I’ve had issues with uncontrolled sway and poor towing performance. I believe my rear tyre pressures could be a significant problem. How did you determine the normal vehicles rear tyre pressure on the vehicle before you added the van ,was it from the manufactures of the vehicle recommendations or was it your own interpretation by the ride of the vehicle and performance?

[@L2SFBC]

Start with the placard. Always your first point of reference.

[@L2SFBC]

However I doubt your sway problems are all pressures. See my Ways to Reduce Sway video for more.

[@erichwise7734]

Another excellent video. “Nothing good happens” such a good line. I would like to know if this is a decent rough guide to finding a good on road pressure for bigger then stock tires as well? I have been using a mathematical guide from Toyo for my tires but id feel more confident seeing how you deal with this.

[@L2SFBC]

Sort of...the way tyres work is a mixture of science, logic and black magic. Generally yes though the taller the tyre the less pressure you need in it. Going from say 31s to 37s would see you run reduced pressures for sure.

[@placestosea]

Thanks for another great video. One question, on say a prado does having the rear tyres say 5 to 8 psi higher than the front tyres,for towing , make the center diff do more work? For straight highway driving.

[@200mphgt40]

The whole idea as shown in the video is to compensate for load. So running staggered tyre pressures will better maintain effective rolling diameter when the rear is loaded much more than front. In any case, a variation in speed of the minor amounts in play here won't trouble the centre diff.

[@L2SFBC]

No it'll be fine

[@L2SFBC]

perfectly put thank you @200mphgt40! you clearly know that inflation pressure makes a tiny change to rolling radius!

[@backdoc94]

I have generally added 10 psi to my rear tyres when towing my caravan with just under 200kg tow ball weight. I need to try this method as I realise that I might be adding too much pressure.

[@ralphblundell9479]

You cannot "add too much pressure" by just adding 10 psi to the rear. Quite possibly not enough. But a good starting point. Tyres will last longer and have less chance of a high-speed failure with "too much" pressure ( within reason😉) rather than too little, due to the heat generated if tyres are too low for the job.

[@jackdawg4579]

Nice in concept, but given I actually use my Ute for what it is intended for, I have an appropriate tyre pressure to match the rated carrying capacity of the vehicle all the time. I dont notice any issues when I run it empty.

[@stevegoodwin5841]

The tyre pressures should be for actual axle loads, not their maximum potential as that is a huge variation when it comes to a ute designed for large payloads. Thus if a pressure is selected for maximum and you carry minimum you are over inflated for sure,

[@200mphgt40]

Great explanation, keeps it effective and simple. Another point to consider for trailer sway control is to check your vehicle rear suspension lateral locating link bushes for slop/play. By which i mean panhard or watts link bushes. My old commodore wagon had shot panhard bushes and you could easily wobble the car rear sideways when stationary. Easy and cheap to fix also, so well worth checking.

[@L2SFBC]

Thanks, good point!

[@SkylinersYeti]

I am assuming you are talking about tire pressure for highway speeds not trail speeds. I do like your simple approach to determining adjusted tire pressure. I am surprised how few people actually know the true weight loads of their trailer. If they know anything it is the advertised dry weights. I try to run my rig across scales not and then to check weight loads for each axle and total combined weight. I am in the USA. :)

[@L2SFBC]

Yes, highway speed...however the relative pressure front/rear of the towcar still applies even offroad.

[@stevegoodwin5841]

The recommended PSI for highway for my Toyo AT II LT245/70 R16 from Toyo Tyre tech Steve in Victoria is R 57 PSI F 50 PSI for my 3.2T tourer build Dmax Spacecab Chassis with canopy. Pressures ascertained from Steve was using actual front and rear axle weights. Not towing, but I can with GVM 3.6T and GCM 7T with the Lovells upgrade. adding 180 to 200kg on the towball will add about 250kg on rear axle and remove 50kg from front axle roughly. So following on from your vid I am going to have to add a few PSI to rear, say about 60 PSI. Sound right? (Max pressure for Max load is cold 80 PSI)

[@L2SFBC]

60 sounds about right if you're at 3.5 and then adding another 250kg on the rear axle. See how it handles, every situation is different, all I'm doing is giving the principle.

[@stevegoodwin5841]

@L2SFBC Thanks Robert, a lightweight 10 foot hybrid van is in our future as we get into out mid 60's. Under an ATM of 2.4T giving us a GCM of about 5.5T. I will try 60 psi cold to begin with.

[@Rawkus919]

Your Trailer stability videos are great. In response to towball weight, i wonder if you have ever weighed the rear end of a caravan for stability purposes. If 10% makes a trailer stable, how does that relate if the opposite end is say 40%? Just a thought.

[@L2SFBC]

Has a terrible effect - see my other videos for that. 10% doesn't make it stable either, lots of variables.

[@netskunk999]

Does this approach work for P-metric tires, as well? The Hankook load pressure chart only shows my tires (DynaPro AT2 275/60R 115T) inflated to 35 psi and not above. However, the max tire pressure is listed as 51 psi.

[@L2SFBC]

Works for any tyre, but never exceed the max-inflate, and in fact if you need to go that high I'd swap to a higher load-rated tyre or decrease your load.

[@gavinjewell5886]

What about when your towing off road and need to lower your tyre pressures, lets say travelling on the Gibb river road

[@L2SFBC]

Lower them. But in proportion.

[@user-bd5ni8vr5c]

@@L2SFBC lower to how much though?

[@joezephyr]

I have a box trailer, a Pod trailer. There is nothing on the trailer advising me of the correct tyre pressure.

[@gregjacques3159]

Why was there no reference to the tyre max pressure when cold written on the tyre?

[@L2SFBC]

Because it's not particularly relevant to the point being made which is towball mass = significant extra load = additional pressure.

[@gregjacques3159]

No worries excuse my ignorance, just the pressures you were mentioning sounded higher than what may be the max pressure on your Tyre. What's the story on the "max tyre pressure when cold" if you a servo for tyre inflation what then? thanks for all your info. @@L2SFBC

[@L2SFBC]

NEVER exceed the max-inflate pressure, and I wouldn't even go near it. The max-inflate pressure is the absolute maximum pressure a tyre can run at, a pressure designed for the maximum tyre load. That's not for offroad, that's onroad, so that's why for offroad I wouldn't run a vehicle which loaded its tyres to the point where you'd need max-inflate.

[@trickymon]

Maybe you could shout yourself a digital tyre inflation gauge.

[@L2SFBC]

Got one, don't like it :-)

[@trickymon]

@@L2SFBC as it’s quicker and more accurate? I don’t get it

[@glennj6465]

🤔🤔🤔👍🏻🇬🇧

[@pat9125]

Hmmm...mixed feelings on this one. I was with you when you talked about 40% more load than the TBM, you lost me after that. Tires have a max PSI weight rating. It's an easy enough exercise to determine the axle weight and your explantion works perfectly for that. After that instead of inflating and deflating tires without regard to the tire manufacturers specs why not just look up the psi for the rated load on the axel? Also why not mention to not exceed the max tire pressure. If you have to go over the max psi then you have the wrong tire, too much load or both. For example. I know that my tires have a load rating of 3750 lbs at 65psi. That is their max rated load rating. So on the rear axel I could carry 7500lbs. However the vehivle GAWR is 6800 lbs so that is my working load max for my vehicle and wheel/tire setup. If I'm loaded over 6800 then I am illegal and if i'm under 6800 I can reduce tire pressure if I need/want to based on road conditions. How much I can reduce it is based on information provided by the tire manufacturer who lists the PSI rating for various tire loads.

[@L2SFBC]

Because the tables for load/pressure aren't readily available. Because even tyre shops sometimes think max-inflate is appropriate merely heavy loads.

[@ralphblundell9479]

While your method could be viewed as correct, I believe you are starting from the wrong unladen pressure. You are treating that Ranger as if it has nothing on that rear subframe but a lightweight alloy tray. In that case, 37 psi would be a good starting point. But you've got a canopy and toolboxes on that ute--are they carrying anything? if there is anything in them at all--everything weighs something--you should be starting at a minimum of 40 psi, probably 42. Measure your contact patch at that, then repeat your procedure.

[@L2SFBC]

I'm allowing for that already

[@jefferykeeper9034]

Why is everyone spelling tire with a Y and not an I ?

[@L2SFBC]

Y not?

[@ralphblundell9479]

🤣

[@craigice9635]

Because that's English. 🙄

[@ianlloyd1182]

It’s because the English language used in the UK spells tyre with a ‘y’, the spelling used in the USA is tire. The two countries use the same language but some words are spelled differently.

[@craigclarke1628]

Love the simplicity of getting the increased tire pressure for towing a specific load. Can you please do a video on how to get the right starting tire pressure as tire placard and dealership difference is very large in my experience.

[@L2SFBC]

On the list but not near the top