roamingyak Posted February 27 Share Posted February 27 I had an interesting discussion around tyres the other day at a big dealer in Southern Africa. In short, I'm probably under inflated on tarmac. So if running a 1991 200TDIHardtop and in the 2600-2950kg range most of the time, what tyres pressures should I be running on All Terrain 235 85 R16 tyres please? I had been running 30psi front, 44 at rear as per the LR owners manual, but that is for the 7.50 R16 tyres I used to use. With the 235's being slightly bigger I should have higher pressures for tarmac use? (Save your breath if your answer is to ask the tyre company: they just refer you to the vehicle manufacturer, who refer you to the tyre company again!) Quote Link to comment Share on other sites More sharing options...
Snagger Posted February 27 Share Posted February 27 I’d add 10% for the extra width of the tyres. The best way to tell is to load it up an an even concrete or tarmac surface, make even chalk marks across the tread and then drive it a few yards and see what happens to the chalk. More brushed off the shoulders means too soft, more off the centreline is overinflated. Quote Link to comment Share on other sites More sharing options...
Arjan Posted February 27 Share Posted February 27 Chalk works. Used to run the OneTen on 2.75 bar all round Quote Link to comment Share on other sites More sharing options...
Anderzander Posted February 27 Share Posted February 27 Another vote for chalk. I think it’s all down to weight and how much suspension you want in the tyres. Quote Link to comment Share on other sites More sharing options...
Daan Posted February 27 Share Posted February 27 I'd say wider should mean less pressure, as the ground contact area has increased. But if you start with the 7.50 pressures, they should not be far off. Did the previous tyre wear evenly? that should tell you the story. 2 Quote Link to comment Share on other sites More sharing options...
Nonimouse Posted February 27 Share Posted February 27 I run the 2.3tonne Disco on 33 front and 30 back, with 235/85x16. However the tyre walls on the Falkens are stiff, so this was worked about with chalk My 110 was 33 front and 35 rear for the same size of tyre My 100" was 33 front and 30 rear Rear tyre pressures are raised for towing or max weight, but only by a few psi I've heard of some folk who run 110's at 60psi rear/ 40psi front! Quote Link to comment Share on other sites More sharing options...
Green Bob Posted February 27 Share Posted February 27 Not sure how much science is behind it but the '4 psi rule' seems to be a thing I've seen in car circles. Inflate tyres to desired pressure, drive until the tyres are warmed up and the psi should increase by 4 psi. More and the pressures are too low, less and the pressures are too high. On page 2 of this link it suggests to use 6psi for larger tyres. Quote Link to comment Share on other sites More sharing options...
Maverik Posted February 27 Share Posted February 27 47 minutes ago, Nonimouse said: I've heard of some folk who run 110's at 60psi rear/ 40psi front! This is what Land Rover recommend (for the rear) 1 Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted February 27 Share Posted February 27 I’ve gone with 32F and 34R for c. 260k miles and 4 sets of tyres, works great and never had an issue with wear. If you’re towing or have a lot of weight in the back you can increase the rears slightly. 1 Quote Link to comment Share on other sites More sharing options...
Nonimouse Posted February 27 Share Posted February 27 235/85x16 is my tyre of choice. Has been for years and 100's or 1000's of miles in various vehicles for over 30 years, always on MT's, except on Trac Edge. Probably driven on every type of surface apart from artic ice. I rarely air down, although I used to when I ran 7.50x16 XCL's or SAT's. My vehicles don't suffer from excess tyre wear Admittedly I tend to go by tyre manufacturer guidance rather than LR guidance, then do the chalk test Quote Link to comment Share on other sites More sharing options...
Snagger Posted February 27 Share Posted February 27 2 hours ago, Daan said: I'd say wider should mean less pressure, as the ground contact area has increased. But if you start with the 7.50 pressures, they should not be far off. Did the previous tyre wear evenly? that should tell you the story. I think it’s the opposite - the wider tyre allows more flex of the grad centre up towards the wheel, so more pressure is needed to keep the tread in even contact. Look at the pressures on low profile tyres and they are usually 40psi+. My XC90 specifies 35psi for very light loads (2 occupants) to 39psi for heavier loading, and those are 255s if I recall correctly. Quote Link to comment Share on other sites More sharing options...
elbekko Posted February 28 Share Posted February 28 Tarmac (and thus I assume higher speed?) use will probably want a bit more pressure at those weights. My Merc GLE at similar weight and on 275/55R19 likes to be around 2.5 bar (empty) to 2.8 bar (loaded), and even 3+ bar (loaded + towing). My RR, bit lighter, on 265/70R16 likes 2.3 bar (empty) to 2.5 bar (loaded), and 2.8ish bar (loaded + towing). 15 hours ago, Green Bob said: Not sure how much science is behind it but the '4 psi rule' seems to be a thing I've seen in car circles. Inflate tyres to desired pressure, drive until the tyres are warmed up and the psi should increase by 4 psi. More and the pressures are too low, less and the pressures are too high. On page 2 of this link it suggests to use 6psi for larger tyres. Even better than that is TPMS sensors with a temperature readout. 1 Quote Link to comment Share on other sites More sharing options...
Anderzander Posted February 28 Share Posted February 28 I run about 28 front and back .. I’m lagging behind ! Quote Link to comment Share on other sites More sharing options...
Nonimouse Posted February 28 Share Posted February 28 59 minutes ago, elbekko said: Tarmac (and thus I assume higher speed?) use will probably want a bit more pressure at those weights. My Merc GLE at similar weight and on 275/55R19 likes to be around 2.5 bar (empty) to 2.8 bar (loaded), and even 3+ bar (loaded + towing). My RR, bit lighter, on 265/70R16 likes 2.3 bar (empty) to 2.5 bar (loaded), and 2.8ish bar (loaded + towing). Even better than that is TPMS sensors with a temperature readout. I have TPMS sensors on my Vitara. Really good, but you can't swap wheels around or it gets upset Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 28 Share Posted February 28 7 minutes ago, Nonimouse said: I have TPMS sensors on my Vitara. Really good, but you can't swap wheels around or it gets upset Can you get the diagnostic tool for reassigning them? Don't know about Suzukis, but the tool for our Zafira was about £15 off eBay and allows you to re-calibrate and reassign the sensors (there's a menu function in the car that asks you to go round holding the tool against the sensors in turn while it records them). That said, if you don't do this all it means is that the car thinks the wheels are in different places and reports the pressures for the wrong corners (does mean if you've swapped front to back you're almost certainly going to get warnings). The Fabia doesn't even need this - just set the tyres up right and reset the sensors from the menu - but then it doesn't bother to differentiate between wheels, just tells you you've got low tyre pressure and leaves you to figure it out. The Zafira will tell you which tyre, and exactly what the pressure is in each one. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 28 Share Posted February 28 25 all round.. Or 15 off road, on 235 muds. But then LGT is not really comparable, and more air in there and he might float away 1 Quote Link to comment Share on other sites More sharing options...
Nonimouse Posted February 28 Share Posted February 28 19 minutes ago, geoffbeaumont said: Can you get the diagnostic tool for reassigning them? Don't know about Suzukis, but the tool for our Zafira was about £15 off eBay and allows you to re-calibrate and reassign the sensors (there's a menu function in the car that asks you to go round holding the tool against the sensors in turn while it records them). That said, if you don't do this all it means is that the car thinks the wheels are in different places and reports the pressures for the wrong corners (does mean if you've swapped front to back you're almost certainly going to get warnings). The Fabia doesn't even need this - just set the tyres up right and reset the sensors from the menu - but then it doesn't bother to differentiate between wheels, just tells you you've got low tyre pressure and leaves you to figure it out. The Zafira will tell you which tyre, and exactly what the pressure is in each one. Suzuki are very protective of their software. I can get the dealer to do the re-set, but that's £140 per hour Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 28 Share Posted February 28 11 minutes ago, Nonimouse said: Suzuki are very protective of their software. I can get the dealer to do the re-set, but that's £140 per hour Eek... 😲 That certainly puts me off ever owning a Suzuki! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 28 Share Posted February 28 1 minute ago, geoffbeaumont said: Eek... 😲 That certainly puts me off ever owning a Suzuki! Don't own anything German either then.... £140 is definitely not top whack for a main dealer these days. 2 Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted February 28 Share Posted February 28 1 minute ago, Bowie69 said: Don't own anything German either then.... £140 is definitely not top whack for a main dealer these days. The Fabia is just a VW Polo with worse suspension...so at least on this specific issue not so bad! Never had it near a dealer, though. Quote Link to comment Share on other sites More sharing options...
Nonimouse Posted February 28 Share Posted February 28 1 hour ago, geoffbeaumont said: The Fabia is just a VW Polo with worse suspension...so at least on this specific issue not so bad! Never had it near a dealer, though. The Vitara has been particularly reliable and all the basic service software is ok on a basic Garage reader. I have to take the car into the main dealer to re-set an SRS warning light. I fitted a new sensor, all works fine, but I can't wipe the light with a standard reader, it comes back on after 20 mins.... Quote Link to comment Share on other sites More sharing options...
Snagger Posted February 28 Share Posted February 28 4 hours ago, elbekko said: Tarmac (and thus I assume higher speed?) use will probably want a bit more pressure at those weights. My Merc GLE at similar weight and on 275/55R19 likes to be around 2.5 bar (empty) to 2.8 bar (loaded), and even 3+ bar (loaded + towing). My RR, bit lighter, on 265/70R16 likes 2.3 bar (empty) to 2.5 bar (loaded), and 2.8ish bar (loaded + towing). Even better than that is TPMS sensors with a temperature readout. I had a TPMS set on my Volvo here in DXB. Cost a lot when I bought it on recommendation several years ago. Nothing but trouble - some sensors failed, they used to leak air from the valves (the sensors were serviced with new seals and the bad reading units replaced under warranty) and then the screen failed, so it got binned. If you do get TPMS, get the type with the sensor inside the rim - the types with sensing valve caps keep the Schroeder valve open, so any small defect results in slow leaks. Their downside is battery replacement, though. I did have the cheap valve caps with clear tube and spring loaded colour bar, factory set to specific pressures. I had very good experience with those in the UK, but they kept cracking or spitting out the injection moulding pip in the end and leaking in DXB. Could be the brand sold here, could be the heat and UV. But they have the same vulnerability as the electronic valve cap TPMS systems - they have to keep the valve open to sense pressure and they are bigger than the standard valve cap, so more exposed to impact. Quote Link to comment Share on other sites More sharing options...
Eightpot Posted February 28 Share Posted February 28 From memory, the MoD tyre pressures stenciled on 110s were 28/48 for 7.50s. On 235s I've always gone a little higher at the front, around 30-32 and 45-48 at the back which works well. Tyre wear has always been consistent and even, it helps with mpg and I like the stability on gravel and it works fine on sand till you get to the real flumpy stuff. 1 1 Quote Link to comment Share on other sites More sharing options...
roamingyak Posted March 10 Author Share Posted March 10 (edited) OK, thanks for all of the helpful thoughts... I'll go for 32 and 48 when on asphalt, the rear needs a bit more than the 44 I have been using. Edited March 10 by roamingyak 2 Quote Link to comment Share on other sites More sharing options...
SPendrey Posted March 24 Share Posted March 24 On 2/28/2024 at 10:20 AM, Bowie69 said: Don't own anything German either then.... £140 is definitely not top whack for a main dealer these days. Yep, recently had an MOT failure on the family E Class. Mercedes want £174 just to "look at the car" to determine if they would like to replace the rear subframe or not. I chose to do privately. 1 Quote Link to comment Share on other sites More sharing options...
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