Help with tyre pressures

[bazzaric]

I've got 4 (surprisingly) Maxxis 205/45ZR17 84W tyres on my mini. The missus is out in it and thinks she needs to pump up the tyres. What should the PSI be for them??

[ianking]

pretty sure I put mine at 34psi

[bazzaric]

I went with 37psi!

[GCA3N]

Can't go wrong around the 34-38 psi mark. I always run around these levels.

[Big Gordy]

If you're pumpin them up to that pressure, which IMO is a tad high (I run my non-runflats at about 32psi) keep an eye on how the tread wears:Whistle: You may find it wearing more in the centre:idea:

[GCA3N]

If you're pumpin them up to that pressure, which IMO is a tad high (I run my non-runflats at about 32psi) keep an eye on how the tread wears:Whistle: You may find it wearing more in the centre:idea:


no lots of wearing on the edges still:Whistle: To be honest I normally run 34psig not too big a difference, only put them up another 2-3 when running fully loaded.

[Craig]

I run all my normal tyres at 32psi.(17"'s and 18"'s) not seen any probs with uneven wear :yes nod::yes nod:

[GCA3N]

I run all my normal tyres at 32psi.(17"'s and 18"'s) not seen any probs with uneven wear :yes nod::yes nod:


you obviously don't go round corners quick enough:Whistle:

[Forbes]

33psi for me

[doogz__]

In one thread, you slate people for driving quick, now you're telling him he doesn't drive around corners quick enough?! Bizarre!

Aside from anything else, lower tyre pressures will provide more grip. If you think he's not going round corners quick enough, and he has 32psi in his fronts, explain why the race mini's go out with 25 or so in their front tyres, and corner like they do?

On non-run flats, i'd stick with 30-32 ish, the runflats require a slightly higher pressure to fill out the centre of the tyre and stop the shoulders wearing so much, as the sidewalls are much stiffer.

38psi seems very high to me though, for a road car, that you want to grip. Must be interesting in the wet. Try loosing a few pounds out them and see what you think, they will be more compliant, the ride will be nicer too, and they will provide a bit more grip.

Our mini with it's horrible horrible run-flat 17's hovers around the 34 mark, i refuse to put them any higher, and even at that, they feel too high. If we keep it long enough, the run flats are going and i'm putting bridgestones or something decent on it.

[GCA3N]

In one thread, you slate people for driving quick, now you're telling him he doesn't drive around corners quick enough?! Bizarre!



Oh my goodness, take a chill pill dude, it was said with the :Whistle:

Do you just look for ways to get people angry or does it come natural. I know it's hard to sometimes pick up on how something is said, but I was attempting to be ironic. For me to call Craig a slow driver is ironic, I know this because I have been to a few runs, meetings, knockhill etc with him. I guess you need to know people on here before you can really understand them. Certainly judging on the NMS site comments alone is nearly impossible.

[doogz__]

Dude, i think it's you that needs to chill.

I'm well aware he's not a shy driver, i chased him back from Knockhill last time i was up in a twin turbo legacy.

I'm not trying to make you angry, you just seem to take everything i say too seriously.

Alright?

[GCA3N]

Dude, i think it's you that needs to chill.

I'm well aware he's not a shy driver, i chased him back from Knockhill last time i was up in a twin turbo legacy.

I'm not trying to make you angry, you just seem to take everything i say too seriously.

Alright?


what ever.

[RyanK]

32 at rear 30 at front for me

[GCA3N]

32 at rear 30 at front for me


Interesting Ryan, I never run that low think I will try that when I get back see what the difference is. I'm sure I have mentioned this before, but when I first got my new mini I checked the tyre pressures and they were 48-49 psi all round:eek: don't know to this date what that was all about.

[RyanK]

from my memory 32psi all round is the best combination for 17" wheels. get them deflated Greig!

[GCA3N]

from my memory 32psi all round is the best combination for 17" wheels. get them deflated Greig!


There at 34 psi now, or they were, Ben's maybe been at them lol.

[doogz__]

30 32 sounds good.

Back when i had my little saxo i used to run 30/34 but the extra in the rears were to compensate for the slightly feeble RARB and 19mm bars

[Delboy]

Does anybody actually use the tyre pressures stated in the manual :Whistle:? I'm pretty sure it states 37/38 psi for the 17" runflats on my car (which is what I've got my tryes at) but, judging from the previous comments, it sounds like I should consider reducing by at least a few psi :confused:?

I've not noticed any excessive wear on the centre of the treads (which would normally be a symptom of over-inflated tyres) and, if anything, the edges are probably more worn than the centre (cornering too hard perhaps ;)).

[Big Gordy]

I'm pretty sure it states 37/38 psi for the 17" runflats on my car

Is that not for it fully loaded with 4 passengers tho:confused:
I'll need to go out and check now:rolleyes:

[Delboy]

Is that not for it fully loaded with 4 passengers tho:confused:
I'll need to go out and check now:rolleyes:

IIRC the fully loaded number is even higher still :eek:. Also, the figures are in bar so you need to convert to psi.

[Big Gordy]

OK I'm quoting straight out of the Haynes manual here:thumbs up:

175/65 R15 84H, 195/55 R16 87H, 205/45 R17 84V
Normal load ...... Front 2.1bar (31psi) Rear 2.1bar (31psi)
Full load........... Front 2.4bar (35psi) Rear 2.4bar (35psi)

205/40 R18 82W, 175/60 R16 82Q,T,HM+S, 175/65 R15 84Q,T,HM+S, 195/55 R16 87Q,T,HM+S, 205/45 R17 84Q,T,HM+S
Normal load ...... Front 2.3bar (33psi) Rear 2.3bar (33psi)
Full load........... Front 2.6bar (38psi) Rear 2.6bar (38psi)

T115/70 R15 90M......4.2bar (61psi)

Lesson over for today kids:idea::bigwave:

[Gismo]

T115/70 R15 90M......4.2bar (61psi):eek: i wouldn't want to be near that when pumping it up :frown:

[Delboy]

Just to back-up my previous post, I've just checked the manufacturer's sticker on my car that gives the tyre pressures (inside the drivers door or, in my case, the suicide door ;)) and for the 205/45 R17 84V tyre with the car normally loaded it states 2.6 bar all round (37.7psi) and with the car fully loaded it states 2.8 bar front (40.6psi) and 3.0 bar rear (43.4psi).

Surely, the tyres should be inflated as per the manufacturer's guidelines, which I assume must be optimal for traction and wear?

[Forbes]

The pump at Tesco is set up for 28psi as standard.

[doogz__]

43.4PSI is ridiculous imo. I'd never have any tyre pressures set that high on a road car.

As a very rough rule of thumb, and at that, one that doesn't really apply to run-flats, with their stiff sidewalls, the mass of the car in pounds, divided by the average tyre pressure, in PSI, is the area of the contact patch (in sq.in). So dividing this by 4, then again by the width of your tyre should yield the length of contact patch on the ground.

So it's easy to see, the higher the pressure, the less rubber is on the ground, although like i said, this doesn't really apply very well to runflats, and only makes any sense at reasonable working pressures where the tyre stiffness doesn't have much noticeable effect.

I'd be interested to see what the reason for pressures that high is.

[ianking]

T115/70 R15 90M......4.2bar (61psi)





:eek: i wouldn't want to be near that when pumping it up :frown:

That will be for the cars with the space saver spare wheel option. Space savers seem to get super hard pressure to make up for the tiny profile.

[doogz__]

Yup.

Mass is constant, area is small, therefore pressure has to go up to compensate.

[Delboy]

I'd be interested to see what the reason for pressures that high is.

Me too - I was quite surprised to see such high recommended pressures. I have been assuming that it is a run-flat thing since I've never had them before but I'm no expert :confused:.

[doogz__]

Random fact:

Apparently run flat tyres, depending on size and make, carry a 15-27% weight penalty over non run-flat tyres.

That's a lot of unsprung weight!

[Delboy]

Apparently run flat tyres, depending on size and make, carry a 15-27% weight penalty over non run-flat tyres.

That's a lot of unsprung weight!

Thank goodness you don't need to carry a spare :rolleyes: !

[doogz__]

True, but a spare wheel would be sprung weight.

Unsprung weight is bad news. That's why race cars, and some road cars (E-type for example) had inboard brakes, to reduce unsprung mass.

Run-flats have a higher rotational inertia as well, adversely affecting braking and acceleration.

Can you tell i really don't like them? lol

[Delboy]

True, but a spare wheel would be sprung weight.

Unsprung weight is bad news. That's why race cars, and some road cars (E-type for example) had inboard brakes, to reduce unsprung mass.

Run-flats have a higher rotational inertia as well, adversely affecting braking and acceleration.

Can you tell i really don't like them? lol

Yeah, that was beginning to come across...............doesn't make you a bad person though :lol:

[binnie]

The pump at Tesco is set up for 28psi as standard.

you do know the arrow buttons will adjust this figure yeah? :p




Interesting Ryan, I never run that low think I will try that when I get back see what the difference is. I'm sure I have mentioned this before, but when I first got my new mini I checked the tyre pressures and they were 48-49 psi all round:eek: don't know to this date what that was all about.


thats normally delivery pressure, in theory the car can sit around in an airfeild for months without the tyre deformingsounds like it wasn't PDI'd properly :frown:

[Stewart]

Bought a Michalin twin foot pump a few years back, I hate those petrol Garage ones. Got my RF 195/55/R16 87H set to 2.2 Bar or 32 Psi as the sticker in the door suggests.

[GCA3N]

Went into 3 different Tyre places today (long story short two of them would not do a puncture repair on a run flat) Anyway I asked them what they suggested I should run the tryes at pressure wise.

They gave me a print out and according to their computers, the 205/45/17 runflats (one, cooper and S) should be 36psi (front and back), and 39psi loaded. The JCW Cooper S can't remember the tyre is 39psi and 41 loaded. This is all very strange.

[Big Gordy]

I should have said the figures I quoted were for the R50/53:blush: The R56 must be different:Whistle:

[GCA3N]

I should have said the figures I quoted were for the R50/53:blush: The R56 must be different:Whistle:

Ah that's the reason for the discrepency.