Pumping up to max tyre pressure

[Moya]

I'm rolling on Advan A460's (http://www.tirerack.com/tires/Spec.jsp?make=Yokohama&model=ADVAN+A460), which have a max [cold] pressure of 44 psi.

I think I filled them up to 36 psi last time.

a) Is it bad to fill them up to the full 44 psi?
b) Will I get more KM to a tank?

</noob>

[AE092]

fill it to the recommended rating

Over inflation can reduce grip and make for a bouncy ride.You don't want to under inflate either. I'm on 32psi.

[Lukey]

over or under inflating your tyres will cause uneven wear to inside or outside of the tyre (im not sure on whatside for over and whatside for under)

i'd suggest between 32 and 36 psi

[migoreng]

overinflation will wear the middle of the tyre out..

[Lukey]

ohk, my bad

[xntrik]

also
when i got my tyres fitted (re001) at bridgestone they pumped it pretty well, steering felt loose, after i reduced the psi to mid 30's steering felt more firm.

[lolwuut]

fill up to 36. see how they feel

hen go up or down from there

[panda[cRx]]

i'd suggest between 32 and 36 psi

:thumbsup::thumbsup:

[saikou27]

36 is just about right for any car. i run 38 on my falkens for a firmer ride though

[dsp26]

how are you guys justifying any of these psi's? it's dependent on profile.... 32-36psi for example is under inflation for 40 profile or less

[AE092]

32psi for 50 profile. And no more if you run that profile on Adrenalins

[Lukey]

how are you guys justifying any of these psi's? it's dependent on profile.... 32-36psi for example is under inflation for 40 profile or less

if you look on the link, the only 2 profiles are 60 and 55.

[string]

If you pump up to max pressure cold, you'll surely exceed it when warmed up. A good rule of thumb I was told was to start at 10% less than maximum (cold) and work down from there.

[panda[cRx]]

how are you guys justifying any of these psi's? it's dependent on profile.... 32-36psi for example is under inflation for 40 profile or less

he's rolling on 195/55R15 by the looks of the link

[trism]

what i do is go for a drive, hit it a litle go round some corners etc

then measure my tyres when they are hot

[e240]

Boom!

[FAT VTI]

Im on 18s with a 35 profile. Normally go to around 34-36.

[saikou27]

i read in murcotts driving manual that ALL tyres should on at least 36. car manufactures suggest lower to make the ride less harsh. anyway back to the point of this thread. no u shouldnt run it at the max psi. experiment a little but dont go near the max psi

[BiLL|z0r]

I've run 35-36 in all my cars and been good. (65 profile to 40 profile). I had the tyre shop pump em up to 44 once and it was slippery, harsh and always lost traction off the mark. Put em down a bit and was great.

[Lukey]

i run 36F and 34R on my 195/60/14 tyres

[dasicvtec]

I usually run 38 PSI on my Birdgestone adrenalines - 195/50/15.

36 psi seems to work well when taking corners though, 38 is more for economy.

[JohnL]

overinflation will wear the middle of the tyre out..

In theory yes, but in practice it takes a lot of over-inflation to do so because steel belted radials are stiff across the tread and tend to be be quite resistant to 'crowning'.

I usually run my tyres at over 40psi and they do not wear in the centre of the tread, rather they typically wear either 'flat' or with some taper wear toward the inner edge.

Having said that, all else being equal, the wider the tread the more it will tend to crown at X psi. This is because the tread has 'beam' strength from the stiff belts, and the longer the 'beam' (i.e. the wider the tread) the less 'beam' strength will exist. Quite wide treads may tend to need somewhat less psi than narrower treads to fully prevent this (but everything is relative and it does depend on the width and psi).

Cross ply tyres have relatively little stiffness in the tread, and crown easily when inflated to higher psi, and thus high psi can easily cause the centre of the tread to wear. This idea that higher psi commonly causes the centre of the tread to wear out quickly is I suspect largely an outdated idea associated with tyre case design that these days is only used with some specialised racing tyres.

[migoreng]

so if tread these days are pretty resistant to curving then overinflation will 'stretch' the sidewalls
underinflation will cause the sidewalls to 'squash?

[JohnL]

36 is just about right for any car.

That's a fairly blunt generalisation...


i run 38 on my falkens for a firmer ride though

I've had Falkens, and while they weren't the best Falkens (ziex 328), they were among the worst tyres I've ever driven on, no matter what psi I put in them...

-------

Sometimes you need to use higher psi to make up for deficiencies in the tyre. If the sidewalls are too soft (too common with shopping trolley rubber) then quite high psi may be required just to stabilise the sidewall.

I have stock sized tyres on my CB7, and it's quite hard to find decent rubber in 195/60/15 (because it's a shopping trolley size, and the demographic wants a plush ride over handling).

Just about all the tyres I've ever had in this size have had very soft sidewalls, and I usually end up with 42 - 45psi just to get some reasonable steering response and handling stability out of them. I've found some tyres start losing some grip above 40psi, but most that I've tried are OK at 42 - 45 (if you don't mind a harsher ride).

The only tyres I've so far found in this size that have reasonably stiff sidewalls are a discontinued model of an ultra cheapy called 'Sonar SX-608' (made by Nankang), and the BF Goodrich G-Foce Sports that I've just fitted today (2 only on the front). Both of these tyres have one thing in common, a dual ply sidewall (whereas just about all others in this size only have a single ply sidewall). The BFGs also have a re-inforced fillet near the bead for additional sidewall stiffness (according to their promotional bumf), and are by far the better of these two different tyres (according to my arseometer).

So far these BFGs are very very good compared with any other tyres in this size (that I've tried). The stiffer sidewall makes them feel as if they have a substantially lower profile than they actually do, yet they aren't too harsh. At present they're at 40psi (starting point), I haven't experimented with the psi as yet. Grip seems quite good, especially compared to the middle of the road dross I've been driving on lately.

I have to say, I'm utterly chuffed to have finally found a good 195/60/15 tyre (and at a very reasonable price too!).

[JohnL]

how are you guys justifying any of these psi's? it's dependent on profile.... 32-36psi for example is under inflation for 40 profile or less

Because you need the higher psi to protect the rim, more than any other reason...

[JohnL]

If you pump up to max pressure cold, you'll surely exceed it when warmed up. A good rule of thumb I was told was to start at 10% less than maximum (cold) and work down from there.

The max reccomended psi (as marked on the sidewall) is a cold inflation pressure. The manufacturer assmes and takes into account a hot psi increase. It doesn't matter if the psi goes somewhat over the reccomended number when the tyre heats up. Don't be concerned about the tyre bursting if you go a bit over the max psi, the catastrophic failure psi will be much much much higher than that...

My understanding is that the -10% ROT is to do with finding the optimum psi for grip / handling, not to prevent the psi from rising over the reccomended max psi when the tyre warms up. As with any ROT, it's rude and crude, but in my experience with experimenting with tyre psi, surprisingly often on the money (at least it puts you in the ball park, and not too far off centre).

[Mr_will]

i run 36F and 34R on my 195/60/14 tyres


if anything, your rears should be higher to encourage less understeer.

[Lukey]

if anything, your rears should be higher to encourage less understeer.

thats what i was thinking i should start doing

[dsp26]

Because you need the higher psi to protect the rim, more than any other reason...

thats what the tyre lips are for... unless your talking about bottoming out tyres onto the rim from pottys

higher pressures on lower profile tyres is to protect the sidewall from encouraged punctures or tears as their obviously stiffer the thinner you go and don't have room for flex.

also all this theory on tyre pressures is dependent on camber...

i bet any money all the people here saying they lose traction above 36psi on their tyres have uncorrected camber (possibly combined with shit tyres like mentioned falken ziex) as a result of lowering. and roll on only ~75% tyre road contact surface area when stiffer and about ~85%+ due to flex from under inflation


***EDIT***
actually you covered it pretty well in post#22:thumbsup:

[funkdr]

As you can see in my brilliant photoshop both under and over inflating tyres reduces the surface area that the tread contacts the road.

[rambohung]

I wouldn't use the maximum pressure the tyre can handle, especially in hot summer, seen so many blow outs on the motorway. Good to start off with sightly higher psi than the car's recommedation pressure on cold tyres. Trial +1psi at a time on the cold tyres until you find the right pressure for you.

[JohnL]

As you can see in my brilliant photoshop both under and over inflating tyres reduces the surface area that the tread contacts the road.

Significant crowning from over-inflation (depicted in the upper drawing) doesn't happen all that easily with steel radial tyres, unless the pressure is substantially high and / or the tread width quite wide (it does happen easily with cross ply tyres). This is due to the stiffness of the steel belts resisting the crowning deformation. This is not to say it can't happen, especially with wide tyres at high psi.

Note that crowining is less likely with narrower treads, so (my advice, FWIW) don't be afraid of experimenting with higher psi with stock sized tyres with taller profiles and typical floppier sidewalls, it may be the only way to make them perform acceptably, and probably won't cause abnormal wear.

With under-inflation (lower drawing), the centre of the tread is lightly loaded (compared to the edges) because the air presssure is too low to support the weight across the full width of the contact patch and sidewall stiffness is supporting much of the car's weight, i.e. at low psi it's the sidewalls themselves (the section of sidewall that is between the road and the rim) that is carrying a lot of weight, thus loading the edges of the contact patch more than the centre.

Note that at 'normal' inflation pressures the section of sidewall that is between the road and rim carries very little of the car's weight because weight 'hangs' of the rest of the sidewall in much the same way as a bicycle wheel carries weight, i.e. by the weight 'hanging' off the upper spokes that are in tension (not resting on the lower spokes that are in compression (or 'side spokes' that are in bend)). The great majority of the car's weight is supported in the sidewall by forces acting in tension and shear (top and sides of the sidewall), not compression (bottom of sidewall), which is because the sidewall has limited stiffness in compression.

As psi comes down, less weight is carried in the middle of the tread and more is carried on the bottom section of the sidewall, which is why it becomes obviously deformed at lower psi (because it's not very good at carrying load in compression), and the tread will start to wear more at the edges than the centre. The stiffer the sidewall the more load it will be able to carry in compression, and the more pronounced this wear will be, but the less under-inflated the tyre will visually appear to be...

[JohnL]

I wouldn't use the maximum pressure the tyre can handle, especially in hot summer, seen so many blow outs on the motorway.

The vast majority of catastrophic tyre failures are caused by overheating due to under-inflation. The rest would be caused by tyre defects, and probably close to none due to over-inflation.

Keep in mind that (with a non defective tyre) what causes failure is overheating, which causes the seperate components of the tyre to come apart. What causes heat build up in tyres is the continual 'rolling deformation' as the tyre rolls under load over time. What causes higher rolling deformation is lower tyre pressure, so lower pressure = a hotter tyre = more likely failure. Higher psi creates an effectively stiffer tyre that deforms less, and therefore runs at a lower temperature, and therefore less likely to fail...

Very over inflated tyres may run on a substantially smaller section of the tread (especially at large camber angles), which could cause localised overheating in part of the tread...


Good to start off with sightly higher psi than the car's recommedation pressure on cold tyres. Trial +1psi at a time on the cold tyres until you find the right pressure for you.

I don't really disagree with this, but don't be afraid of the max pressure written on the sidewall. You could just as easily start there and come down until you find a pressuere that works for you.

[JohnL]

if anything, your rears should be higher to encourage less understeer.

Depending on the tyre, the initial psi, the increased psi, the suspension geometry (etc), increasing rear psi may decrease or increase understeer.

[FAT VTI]

I still think alot of the tyres ****ing up and blowing is mainly due to people not checking their tyre pressure enough. Especially when they have -2.5 + camber and 18s, 19s or 20s.

[JohnL]

unless your talking about bottoming out tyres onto the rim from pottys

That's what I mean. If sidewall height is minimal, then the sidewall is more fragile (less flexure) and the rim more exposed to damage. Increasing psi will alleviate the problem, but not cure it.


higher pressures on lower profile tyres is to protect the sidewall from encouraged punctures or tears as their obviously stiffer the thinner you go and don't have room for flex.

If the psi is too low then the sidewall can get crushed between the rim and whatever it's impacting. Psi should be set according to what psi gives the preffered driving (and wear) characteristics, not what merely allows them to survive every day occurances in the real world.

I'm very anti ultra low profile tyres on huge diameter rims, they just don't work well (in fact can be quite dangerous), are totally impractical and look like an absurd characature of what a purposeful wheel / tyre combination does look like.

Nothing screams 'wanker' like mirror polished 20" rims wrapped with rubber bands...


i bet any money all the people here saying they lose traction above 36psi on their tyres have uncorrected camber (possibly combined with shit tyres like mentioned falken ziex) as a result of lowering. and roll on only ~75% tyre road contact surface area when stiffer and about ~85%+ due to flex from under inflation

Quite possibly. I'll also suggest that ultra low profile tyres have way too little sidewall compliance as it is, let alone at the 'recommended' higher psi, and this is contributing to decreasing grip at higher psi, especially at exaggerated camber angles.

Sidewall compliance is one of those things where too much is bad, but too little is even worse...

[JohnL]

I still think alot of the tyres ****ing up and blowing is mainly due to people not checking their tyre pressure enough. Especially when they have -2.5 + camber and 18s, 19s or 20s.

Yes, under-inflation...

Excessive camber and stupid tyre sizes wouldn't help...

[Mr_will]

Depending on the tyre, the initial psi, the increased psi, the suspension geometry (etc), increasing rear psi may decrease or increase understeer.


not really, for a given suspension setup, all other things being equal, a higher pressure in the rear will promote (not create) less understeer

of course the effect will vary depending on suspension setup but as a general rule what I said is correct

[JohnL]

not really, for a given suspension setup, all other things being equal, a higher pressure in the rear will promote (not create) less understeer

In other words, to paraphrase; 'a higher pressure in the rear will create more oversteer'.

In general I don't agree. IMO (and in my personal experience) increasing rear tyre pressure will tend to decrease oversteer because the higher rear psi will decrease the slip angles of the rear tyres relative to the slip angles of the front tyres.

Of course there will be exceptions, e.g. if the increase in rear psi causes the tyre's contact patch to become smaller, or effectively smaller (as happens if the loading across the contact patch face becomes more uneven).

A lot depends on just what the starting psi may be, and at what psi the particular tyre fitted to a particular car (and which end of the car) gives it's best lateral grip (i.e. the exact psi above or below which the grip falls away).

Check this page:
http://www.rogerkraustires.com/TechSheets/overunder.shtml

But I'm sure you'll be able to find others that state the opposite...

[jks24]

i hav advanti 17s and i whack 34 in them and they feel good

[string]

In general I don't agree. IMO (and in my personal experience) increasing rear tyre pressure will tend to decrease oversteer because the higher rear psi will decrease the slip angles of the rear tyres relative to the slip angles of the front tyres.


Exactly my thoughts. To "promote" oversteer you need to greatly increase the torque the rear axle applies around the CoG. Lower tyre pressures allow for higher slip angles (but probably at the cost of maximum lateral grip* [not that it matters when the balance is far towards understeer]).

If you want more rotation for free, dial in some rear-toe out (or get rid of your toe-in). Or alternately add more rear roll resistance to build up slip angles in the outer rear tyre quicker (i.e. what a rear-swaybar does).

[JohnL]

Exactly my thoughts. To "promote" oversteer you need to greatly increase the torque the rear axle applies around the CoG.

I'm not sure I follow your meaning, but I suspect I don't really agree, or at least don't agree with how you (might be) thinking about it....

One way to increase oversteer / decrease understeer is to increase lateral weight transfer at the rear (relative to the front) by increasing rear roll stiffness (springs, ARBs, damper rates, to a limited degree - tyre vertical stiffness), or decreasing front roll stiffness.

When cornering this means that the OR becomes more loaded and the IR becomes less loaded, and because the increase in a tyre's grip with any increase in weight is not linear (i.e. contact patch grip increases with increasing weight, but at a diminishing rate, i.e. to gain max grip we want to spread X weight over as much area of rubber as possible, as evenly as possible), this results in less grip at the rear axle line.

This method of lessening rear grip will tend to increase front grip because increasing weight transfer at one end of the car reduces weight transfer at the other end, so at the rear we get X- grip and X+ at the front.

Another way would be to either raise or lower the rear tyre psi above or below the exact psi that gives the greatest lateral rear grip (which will tend to be the psi that gives the largest / most evenly loaded contact patch, at a given camber angle). This would cause less even loading across the contact patch area which creates less grip from that tyre because the more unevenly loaded the contact patch is the less grip it produces (even if it's nominal area remains the same, or even a bit larger).

Low psi might cause a somewhat larger contact patch, but with higher loadings at the edges and less at the centre. This could mean less grip despite the larger area (with some of the extra area only being very lightly loaded, and maybe only the edges heavily loaded...).

Higher psi may create a somewhat smaller contact patch, but it's likely to be more evenly loaded and still grip well, unless the camber of the wheel causes the contact patch to become too small (tyres at higher psi, or with stiffer casings / sidewalls, tend to be somewhat more sensitive to correct dynamic camber angle than tyres at lower psi).

This method of lessening rear grip will tend to leave front grip unaffected because it doesn't affect weight transfer at either end of the car, simply loses grip at the rear. So, we get X grip at the front (unchanged), but X- at the rear.

As such, raising / lowering psi above / below the 'ideal' psi isn't as good as a means to adjust understeer / oversteer as altering front / rear roll stiffness, but still useful to gain the required balance (which will still tend to result in a faster car, even if overall grip has been lessened somewhat).


Lower tyre pressures allow for higher slip angles (but probably at the cost of maximum lateral grip* [not that it matters when the balance is far towards understeer]).

If you want more rotation for free, dial in some rear-toe out (or get rid of your toe-in). Or alternately add more rear roll resistance to build up slip angles in the outer rear tyre quicker (i.e. what a rear-swaybar does).

See above...

(trouble with toe is that it can be less than great for tyre wear...)

Have a read of this discussion:

http://www.eng-tips.com/viewthread.cfm?qid=220757&page=1