Tyre pressure T28

[dcpen43]

All the Falken table does is give you a theoretical minimum ‘safe’ pressure for a given load and tyre load rating. It does not take into account tuning tyre pressure with suspension, economy, comfort, road surface, environmental conditions etc. For my van their pressures are far too low and would result in very uneven tyre wear, poor economy and a bouncy ride from the undamped ‘suspension’ of the tyre.

isnt that the point. Your tyre will tell you your max pressure and Falken tells you a minimum and everything in between is personal preference

my 245/65R17's have a max of 50psi and load of 1090kg

falken says at 40psi a 245/65 is capable of carrying 778kg (T28 700kg)

so personal preference kicks in between 40psi and 50psi acknowledging tyre wear and ride comfort

 

[GUMY]

I have just fitted new 18" wheels with Bridgestone 255/45 R18 103Y tyres.
The tyre pressure plate on the door suggests 44-48 PSI for the front, 36-48 PSI for the rears.
On the Bridgestone tyre wall it states "never inflate over 40 PSI". Because of this, the tyre fitter said he would not inflate them over 40. He had them at 35 PSI all round, which on the short drive home felt fine.
Any thoughts / suggestions / opinions?

 

[Sasquatch]

If it drives well, the ride is confortsble, and the wear pattern is even then youre good.

 

[ginkster]

I have just fitted new 18" wheels with Bridgestone 255/45 R18 103Y tyres.
The tyre pressure plate on the door suggests 44-48 PSI for the front, 36-48 PSI for the rears.
On the Bridgestone tyre wall it states "never inflate over 40 PSI". Because of this, the tyre fitter said he would not inflate them over 40. He had them at 35 PSI all round, which on the short drive home felt fine.
Any thoughts / suggestions / opinions?

Only 40psi max! That sounds rather low, even for a laden car or SUV let alone a van. My Conti All Seasons of the same size and load rating have a max of 51psi on the side so comfortably covers the VW recommended range. Are they def 103 rated?

 

[GUMY]

Only 40psi max! That sounds rather low, even for a laden car or SUV let alone a van. My Conti All Seasons of the same size and load rating have a max of 51psi on the side so comfortably covers the VW recommended range. Are they def 103 rated?

Thanks. Yes, definitely 103Y.
Looking at it this morning, I think maybe the young lad fitting the wheels made a mistake. It actually says "never exceed 40 PSI to seat beads", but elsewhere says "max press 50 PSI". I take it this means once the tyre is "seated" on the "beads" at a max of 40 PSI, and on the vehicle, the pressure can then be increased to the manufacturer's recommended settings?

 

[Sasquatch]

I think your interpretation is right.

If the lad had any brains he wouldn't be a tyre fitter so Id be inclined not to give his word too much credence.

 

[GUMY]

He was the apprentice, and a really nice, enthusiastic chap.
Judging by how busy the place is, I don't think it's such a bad choice of career, and one that should be safe from being taken over by AI for a while yet!

 

[dcpen43]

I think your interpretation is right.

If the lad had any brains he wouldn't be a tyre fitter so Id be inclined not to give his word too much credence.

according to said AI:

So just to keep it really simple:

• 40 PSI seating limit = the mounting stage, short-term. Never go above this just to get the tyre onto the rim.
• Max cold inflation on sidewall = the in-use stage, long-term. It’s the safe maximum operating pressure, not the seating limit.

 

[Sasquatch]

He may well be a lovely fellow, and you're right - thats one job a computer wont be taking in a hurry.

Nevertheless, its not a skilled profession (being politely accurate, not derogatory - if the lad is earning his coin and is happy then fair play) and requires no technical training or specialist expertise so I wouldn't be inclined to take their advice on anything beyond getting a tyre on and off a rim.

I've been told far too much guff by tyre fitters over the years, all of it subsequently debunked be either the tyre manufacturers themselves or by proper technical experts, to believe anything they have to say.

 

[ginkster]

Thanks. Yes, definitely 103Y.
Looking at it this morning, I think maybe the young lad fitting the wheels made a mistake. It actually says "never exceed 40 PSI to seat beads", but elsewhere says "max press 50 PSI". I take it this means once the tyre is "seated" on the "beads" at a max of 40 PSI, and on the vehicle, the pressure can then be increased to the manufacturer's recommended settings?


View attachment 301236

View attachment 301237

That explains it! Yep, spot on, max 50psi now the tyres are on and seated.

 

[GUMY]

Thanks all
So, back to the question, any recommendations for pressures? I'm thinking 44 all round, then increase the rears when fully loaded with the camping gear

 

[Sasquatch]

Mine are 235/55 18, so probably a similar volume oif air. and Im 44 front and rear with a camper conversion aboard and Eibach HD rear springs. Try thjat as a starting point and fiddle from there.

 

[ginkster]

Thanks all
So, back to the question, any recommendations for pressures? I'm thinking 44 all round, then increase the rears when fully loaded with the camping gear

Have you weighed the van at all? Mine, with a full camper conversion, is about 1280kg at the front and 1000kg at the rear unladen so I have the rears a little lower day to day (2-4 psi). When loaded the front and rears end up pretty much matching. Something like 42-44 front and 38-40 rear is good unladen and 48 each end when fully laden.

 

[GUMY]

Never weighed it. Set them to 44 all round earlier and been for a good drive, mixed driving. It felt very comfortable. Also seems much more sure-footed through large roundabouts etc. than on the old skinny 205/65 16"s.

 

[jadatis]

Googled the size 255/45R18, and the loadindex 103 is an XL/ reinforced/extraload tyre.
The maxload of 875 kg is given for reference-pressure of 42 psi , and reference-speed of 160 kmph/ 99 mph.

The standard load in this size has loadindex 99= maxload 775 kg AT 36 psi upto 99 mph.
For higher speed official system is highening up reference-pressure with a system depending on speedcode.

For that the difference between max cold pressure of here 50 psi is used, wich is introduced because american DOT reqiures it .
Some give only 44 psi as maxcold, wich leaves not enaugh space on XL to highen up the 42 psi referencepressure for the max speed.

Some even give 60 psi maxcold ( Toyo) , so see the importance of this DOT requirement.

In another topic here, I give a cold pressure/ axleloadcapacity-list for the 103 loadindex in XL, with build in max reserve, at wich comfort and gripp still acceptable, you can use, once you determined the axleloads in your use 99% acurate.
Succes with that, the most tricky part .

Post 43 in this topic, and it gives for upto 160 kmph/ 99 mph , but I think you can hold yourselfes to that max speed, wich you wont go over for even a minute.
If not, write it, and I make a list for your max used speed.

I use a better system for speed, looked off from C- and truckt-tyres.
Rule of tumb , for every 10 kmph/ 6.3 mph different speed then reference, 1 loadindex step different.
Higher speed》lower loadindex
Lower speed》 higher loadindex.

Tyre Pressures 255/45/18