tyre pressures with bull bar

[newby@54]

I own a MY16.5 Disco 4 fitted with an ARB steel bull bar. Its travelled about 29,000km still with the standard Goodyear Wranglers and I've just noticed that both front tyres are wearing on the outside of the tread. Apparently this is a classic sign of under inflation.

I've religiously maintained tyre pressures as per Land Rover specification i.e. 34 psi front and 37 psi rear when unloaded. But now I'm wondering with the weight of the bull bar that a higher psi is needed.

And then I got thinking about the LR specification for tyre pressures. I live in Maryborough Qld where the temperature is significantly warmer than that of Solihull UK. So when LR specify 34 psi front (and presumably this is a 'cold' temperature) what is the equivalent psi when the 'cold' ambient temperature is so much warmer than that of Solihull?

Has anyone any experience with tyre pressures with a bull bar vs the LR specified inflation pressures?

Thanks in advance

Nic

[BradC]

My local tyre guy did some measurements on my Kuhmo Solus and said they need to run up around 40 on my D3. Can't say how much of a difference it has made as they were pretty rooted when I bought the car but I haven't seen any extra significant wear. The fears have scalloped inner shoulders due to a bad alignment though.

[LGM]

Nic, I own a 2011 D4HSE and it was fitted with an ARB steel bull bar in 2012.
I have never changed the tyre pressures based upon the bull bars additional mass. In fact I never even considered it. I do adjust pressures for differing travel conditions or load but pretty much for normal driving stick with the placarded pressures. I have had Continental tyres, Cooper tyres, Pirelli Tyres and of recent times Hankook tyres (last two sets) and not had any issues or problems as you have described. :o

[4bee]

This could be worth a read.

Front Tires Wear on Outside Edge: Causes and Solutions - Tire Reviews, Buying Guide & Interesting Facts - Utires.com (https://www.utires.com/articles/front-tires-wear-outside-edge-causes-solutions/)

[SeanC]

I thought under pressure wore both inside and outside edges. Over pressure wore the centre of the tyre while just inside or outside was a wheel alignment issue.

[scarry]

I thought under pressure wore both inside and outside edges. Over pressure wore the centre of the tyre while just inside or outside was a wheel alignment issue.

Correct.

Mine has a bar,and KO2's,i run 40 PSI on black top, no worries at all,and the last set did over 60K and wore evenly.

[4bee]

Mine has a bar,

Does it also have Refrigerated Keg Storage? It never ceases to amaze me what can be fitted into a LAND ROVER.[smilebigeye]

[newby@54]

Thanks for the replies. In my initial post I meant to say that the front tyres are wearing on both shoulders or edges - so under inflation. I've pumped them to 39 and will see how they go.

Nic

[Eric SDV6SE]

I own a MY16.5 Disco 4 fitted with an ARB steel bull bar..... So when LR specify 34 psi front (and presumably this is a 'cold' temperature)

34 and 37 seems too low to me, and yes, that would be cold pressures. Allowing for ~3psi increase when hot, 37 and 40 respectively still seems low for a car running 19" rims and weighing 2.7t. The wear you are describing is definitely from under inflation. Would have been a plush ride though.

I run my current set of LT 980's at 46psi cold on the highways and byways a nbd they are wearing evenly. The previous set of Cooper Zeons the same and got 70,000kms out of them with even wear all round.

I've also got an ARB steel deluxe bull bar, but honestly have never considered the additional weight of the bar in setting tyre pressures. I just set to what I'm comfortable with ride wise and ensures even wear.
Cheers

[DiscoJeffster]

Well to be fair Eric, it is what the factory specifies so it’s not too low normally. I’ve used factory 33/36 pressures on the road and not had abnormal tyre wear aside from when my rear toe was well out. I don’t have a 100kg roo bar so maybe I’d run a couple more if so, but probably not.

The OP might be suffering under inflation however I suspect more likely worn suspension components and alignment than pressure. It’s not uncommon to get a rubbish alignment on these from a generic shop which causes more harm than it solves

[DiscoJeffster]

I should add rule of thumb is 4psi rise from cold to hot indicates the right cold starting point. The OP should be seeing far higher increases in hot if under inflation is the cause. Note also to add a few PSI to cold for high speed/country touring.

[Markus1]

17 inch ko2's. No bullbar. I generally use 43-45 for the tar. It's a big heavy car. 36 is ok , 33 is too low for fronts imo. Each to their own I suppose.

[BMKal]

I have ARB steel bar on the front plus rear wheel carrier and long range tank under the rear. I'm in Kalgoorlie - temperature is currently in low 40's. Checked TPMS this morning when I was out - all 4 are currently sitting on 40psi and spare is at 45psi. If I am heading out of town on a long run, I will pump all 4 on road tyres up to around 43 - 45psi.
Have been running Mickey Thompson STZ's up until recently (18 inch rims) and now running Toyo Open Country - would never run this vehicle at lower than about 38psi under any conditions.

[loanrangie]

Bars don't add as much weight as you think, I remember tombie saying about a 20kg difference

[worane]

I have always run 32.5 psi on my D2 td5 . It is comfortable ride and I have never had wear issues.
I think the door placard mentions something about 27 psi which seems silly.
Going above 32.5 Give a very much harsher ride to me.

[Rick Fischer]

Here's another two bob's worth (shillings) for millenium members :0)

Low pressure wear is on both shoulders not just one. Too high pressure is in the centre. Tyre wear (note tyre not tire) on one side (shoulder) is normally an alignment problem. Scolloping is shockies.

Vehicle manufacturers always set up a vehicle's tyre pressures to give "understeer", not for optimum tyre wear or vehicle "control". Why understeer.............and very simply: If average punter is going too fast into a corner natural reaction is to take foot off. Doing so will cause the nose to tuck in and go around. In front wheel drive vehicles understeer can get to a point where it is referred to as "terminal understeer".

Increasing pressure increases grip, lowers rolling resistance.

Suggest you use either 4psi or 6psi test for correct tyre pressure. 2psi rule/test is for "P" tyres and 4 for LTs.

Ergo: check/set tyre pressure cold, run until tyre is hot say 30km (with an appropriate load) and check pressure.

if the pressure has risen less than 2psi for Ps or 4psi for LTs the tyre pressure is too high, if it has exceeded 2psi for Ps or 4 for LTs then the original/set pressure is too low. Uhhhh! Yep! Contra-indicated.

If pressure rise is too low tyre is running "cool" too much air. If pressure rise is too high, tyre is underinflated and running too hot (excessive deflection)

Running cool not a real problem, better grip less rolling resistance better fuel economy but centres wear.

Hot running is a disaster. Heat kills tyres, caused by excessive "deflection". Heat will cause hidden delamination inside the carcass. The tyre will not necessarily fail at the time but at the later "Mystery" blow out, tread separation. Most punters blame the "crappy" brand, not the long time ago or continual excessive deflection of the tyre.

Cheers

RF

[Rick Fischer]

Another thought:

If tyres are found with outside shoulder wear, it is obvious that those tyres will have been running underinflated/over deflected for a considerable period of time. The tyre carcass will be damaged with invisible internal delamination. My advise would be to replace those tyres.

Cheers

RF

[glttce]

When I took delivery of my 5th Disco (1 Series 2 TD5, 2 x Series 3 TD2.7, & 2 x Series 4 SDV6) just before the Series 5 disaster hit the market, the salesman gave me two excellent pieces of advice based on his extensive experience in the Land Rover service area. The first was to use sport mode for improved fuel economy (and that works by about 1.0l/100km), but the second was to always run the tyres at 40PSI all round. In the Series 3's and the first Series 4 the original factory rags never lastedmore than 40K. These ones look likely to exceed 50K. I have always run with an alloy bull bar, fridge and rear cabinet work, and I am not hard on tyres, having got in excess of 80k on General Grabber replacement tyres and similar on brake pads. It seems that the slight increase in harshness is more than offset by the improved tyre wear.

[Barraman]

I have a 2015 Disco fitted with an East Coast heavy duty alloy bullbar. I run tyre pressures by the book. I only got 40,000 km out of the original Goodyear Wranglers but the wore out evenly after being rotated every 10,000 km or so.

I am about to replace my Pirelli Scorpian ATs that are just nudging 80,000 km (also evenly worn out) with Scorpian AT Pluses which certainly look the goods!

About half of my mileage is towing a 6.5M boat!

[discojools]

I have a 2010 D4 2.7, with bars, winch and long-range fuel tank etc.,now done 180000k. Have always run at placard pressures or maybe up 2 psi. Tyre wear has not been a problem. Had 2 very scary incidents where after service pressures were set at over 40 (42 front and 45 back) psi all round. One incident was in the dry and the other wet. Both showed a up lack of grip to what I was used to... so I am not sure that increasing tyre pressures increases grip. I maybe wrong bit certainly not from the experiences I have had. Never had that type of incident running placard pressures. I strikes me that manufactures would set up the suspension with those recommended pressures for maximum grip handling and ride quality. I know that in the UK tyre retailers and garages have to set pressures at the manufacturers recommended pressure. In fact I seem to remember at every garage tyre pump there was a table of cars and the tyre pressures for each make and model.

[Slunnie]

Thanks for the replies. In my initial post I meant to say that the front tyres are wearing on both shoulders or edges - so under inflation. I've pumped them to 39 and will see how they go.

Nic

I'm not sure what wheel size ou run, but from what I can gather, the lower the profiile the higher the pressure you need to run. I would expect the higher the weight the higher the pressure also.

On my Audi when it was on 19's it wore the front tyres on both edges really badly despite being at the recommended pressure, and with the cost of 255/40-21 Pirellis now I did a bit of research to stop this from happening. The recommendation from people who run the same tyre/car was that they needed to be at 42psi for them to wear properly. I also chatted to the tyre mechanic who checked the wheel alignment and he recommended 40psi (and said 42psi was even better). He was saying that the lower profile tyres generate a lot of force through the sidewalls (edges) and as you corner it rolls the corners down and it unloads the middle of the tyre which makes them wear on both sides and the increase in pressure is to make the tyre retain its shape (and retain traction) when cornering. My D2 on 285/75-16 with its big sidewalls wear perfectly flat irrespective of if I run 32 or 42psi but has lost a bit of traction at the recommended 28psi.