Confused about tyre pressure

[horticulturalist]

I want to keep recommended tyre pressure for my ride (vitz14).... But m confused about the calculations. I have attached the photos...
The drivers side door suggests
front tyre= 250kPa, 2.5 kg/cm² (36psi)....
Rear tyre=240kPa, 2.4kg/cm², (34psi) ....
Emergency tyre= 420kPa, 4.2kg/cm², (60psi)...
The stock tyres (165/70 R14 81S) suggest maximum pressure 300kPa, 44psi

These figures seem too much to me, as i have searched PW for the same query, all of them suggesting just 30 to 33 psi for vitz... If my calculations from kPa to psi are correct, is keeping such air pressure in the tyres safe? Will it solve the ground clearance and fuel average problem upto some extent? Which bigger size of tyres do you people suggest for the same rims?

[faizanahmad]

These figures seem too much to me, as i have searched PW for the same query, all of them suggesting just 30 to 33 psi for vitz... If my calculat

Don't go for what people say, always maintain recommended tyre pressure mentioned on door panel for better fuel economy. I keep 35PSi in my Nissan Dayz as mentioned on door panel and it gives me best fuel economy. I also experimented with 32PSI but fuel average dropped from 15KM/L to 12KM/L.
Give it a try your tyres will not explode! also fill up tires from automatic machine, manual gauges are usually faulty.

[talhamaqsoodch]

These figures seem too much to me

No, its not too much as @faizanahmad suggested , always maintain recommended tire pressure for best fuel economy. please note its inflated tire pressure, means car should have traveled less than 3KM when you check tire pressure. best time to check these pressure when your car has rested all night, in morning go straight to any pump which has digital tire pressure gauge and maintain your recommended pressure.
In Toyota Aqua i use 37 PSI front 33 PSI back.

[hash4u]

you can use these tire pressure only if u r use those thin tires (oem size)
and you drive only on well carpeted roads
@35 pounds ur front suspension will wear out twice as quick on PK roads

660 cc cars hv crap suspension in durability anyways

[saad.ikram.5688]

For perfect roads this tire pressure is ok. Our road conditions are very rough and this much high pressure will damage your suspension in the long run,
I have Alto 2015 X model and it comes with 165/55/R15 low profile tires with pressure rating 36
I keep 32-34psi and its the best. Mileage it 20-22 it goes upto 24 on 36 but it will damage the suspension in the long run

[horticulturalist]

thank you @faizanahmad @talhamaqsoodch @hash4u @saad.ikram.5688
if the OEM says 36-34, should i go for 34-32? Will that be ok for Pakistani roads? Our Peshawar roads are too bumpy these days due to BRT construction..

By the way my vitz is 1000cc, and its engine might be heavier than 660....

[hash4u]

try 32 front 34 rear. and if u feel any bump or harshness in steering while driving in broken roads further reduce pound by pound till you feel the steering and front suspension is not getting screwed

[talhamaqsoodch]

if the OEM says 36-34, should i go for 34-32? Will that be ok for Pakistani roads? Our Peshawar roads are too bumpy these days due to BRT construction..

I will again recommend to go for OEM recommended pressure. Go easy on bumps. your suspension will be fine no problem. If you feel too much vibration noise then reduce 1-2 PSI , like you said 34 front 32 rear.

try 32 front 34 rear

Always have 2-3 PSI more in front than rear

[anon35615524]

Well, here, I will suggest to slightly deviate from the specs. Instead of 34 or 36 psi, you may keep max. inflated pressure of 32-33 psi. This is not with reference to temperature here, but; road conditions! If the roads are extremely good, all the time 100% carpeted, without any "Toay Tibbay", then no problem, otherwise, better avoid.

is keeping such air pressure in the tyres safe?

For tires, it might be safe, but for suspension, it might be devastating!

Will it solve the ground clearance

Nope. I think, it will not solve the problem. Yes, you might get some marginally good fuel efficiency, but at the cost of suspension.

Which bigger size of tyres do you people suggest for the same rims?

May be, 185/70/R14, but won't suggest as your vehicle has been designed and tested on 165/70/R14. Anything larger than OEM recommendation will jeopardize fuel efficiency and suspension. Handling and road grip might become better.

[jadatis]

First the 44psi(3 bar) is the maximum allowed pressure by the tyremaker, some give 51psi as maxcold.
But the pressure for wich the maxload of 462kg is allowed on tyre when driving 160km/ 99m/h , is for your standard load tyre 2.5bar/36 psi. Your small tyre can be an exeption to that rule , can be as low as 2.2bar( ? 30 psi)
Difference between 36psi ( reference-pressure) and 44 psi( maxcold) is used for higher speed then 99mh ( reference-speed) , and camber-angle more then 2 degr.

The advicepressure is nowadays calculated for max allowed axleloads, and with a formula I once got hold of from page 14 vv of standards manuall 2007 of ETRTO, I went running with it and now call myself " pigheaded Dutch selfdeclared tyrepressure-specialist" .
Can be that advice is also calculated for maximum technical carspeed, wich wont be above 180kmu, because spedcode S is max 180kmu.
The official systen then needs to highen up the reference pressure with 0.1bar , before using the formula.

From these advice pressures you could roughly calculate back the MPAW front and back.
Will so that in next post , first look back the data.

But because normal use has less then MPAW on axles, you can do savely with lower pressure.
Only then fuelconsumption is higher.

Thats the reason why electric cars have that high pressure-advice, all to give the battery higher actiradius( also for electric bikes) , that comfort is bad then you get used to walking kidneys.
Once determined that rolling resistence makes about 25% of total fuel-consumption when driving 80km/50m/h.

[horticulturalist]

thanks alot @basitali87 @jadatis

[jadatis]

Once made with use of spreadsheet a conversion list.
Here part of it . Rounded psi and bar is fatprinted.
Ths on a " nice to know basis"

Sorry, when copying the fatprint was lost, but you will work it out anyway.
Also the spacing is away.
In Holland we use a comma where England uses Dot, but also that you will work out.

1,60 Bar 23,21 PSI
1,655 Bar 24,000 PSI
1,70 Bar 24,66 PSI
1,724 Bar 25,000 PSI
1,793 Bar 26,000 PSI
1,80 Bar 26,11 PSI
1,862 Bar 27,000 PSI
1,90 Bar 27,56 PSI
1,931 Bar 28,000 PSI
1,999 Bar 29,000 PSI
2,00 Bar 29,01 PSI
2,068 Bar 30,000 PSI
2,10 Bar 30,46 PSI
2,137 Bar 31,000 PSI
2,20 Bar 31,91 PSI
2,206 Bar 32,000 PSI
2,275 Bar 33,000 PSI
2,30 Bar 33,36 PSI
2,344 Bar 34,000 PSI
2,40 Bar 34,81 PSI
2,413 Bar 35,000 PSI
2,482 Bar 36,000 PSI
2,50 Bar 36,26 PSI
2,551 Bar 37,000 PSI
2,60 Bar 37,71 PSI
2,620 Bar 38,000 PSI
2,689 Bar 39,000 PSI
2,70 Bar 39,16 PSI
2,758 Bar 40,000 PSI
2,80 Bar 40,61 PSI
2,827 Bar 41,000 PSI
2,896 Bar 42,000 PSI
2,90 Bar 42,06 PSI
2,965 Bar 43,000 PSI
3,00 Bar 43,51 PSI
3,034 Bar 44,000 PSI
3,10 Bar 44,96 PSI
3,103 Bar 45,000 PSI
3,172 Bar 46,000 PSI
3,20 Bar 46,41 PSI
3,241 Bar 47,000 PSI
3,30 Bar 47,86 PSI
3,309 Bar 48,000 PSI
3,378 Bar 49,000 PSI
3,40 Bar 49,31 PSI
3,447 Bar 50,000 PSI
3,50 Bar 50,76 PSI
3,516 Bar 51,000 PSI
3,585 Bar 52,000 PSI
3,60 Bar 52,21 PSI

[horticulturalist]