An interesting article on air pressure & load index

[Yattokame]

I am on the same size as you and have pumped to 37psi front and back, a little more than my previous 225/50 17 recommended pressure in the manual although the pressure you mentioned is for 235/45 18.

 

However I realised most of the mid-range tyres of 245/40 18 in the market has load index around 91-95. Can't seem to find one with 98 (as recommended in manual), except Michelin Pilot Preceda.

 

So I should go for 37psi front and back? but manual says staggered pressure.

[Ftco]

So I should go for 37psi front and back? but manual says staggered pressure.

 

I find putting different pressures for front and back somewhat troublesome so I normally put equal pressure.

 

Can't go wrong following the receommendation in the manual or +-1-2 psi is ok.

[Roberttan]

BUT for MPV you got to be very careful.

this MPV could carry up to 9pax+ lagguage,so you got be very careful when you up size your tyre,1 more very important item to know is your sport rim,my advice is try not to go for those light weight rim,some of them are more suitabel for saloon car

for example 9pax x 70kg is = 630kg + 70kg = 700kg plus your MPV weight 1600kg

you better make sure your tyre and rim are strong enough to carry total weight of

2300kg (always remember to go for strong rim for MPV)

 

---

 

 

that's why I always go for reputable Jap Brand or Euro Brand aftermarket rims. Most, if not all, Jap, Phi, Thai, My, Indo, China rims have a max load of 690kg per rim. For Conti, like OZ, they are 710kg per rim.

 

I bought a used Enkei RP05 rims (this model not available here, have to indent) from an ex-Airtrex Turbo owner (hand carry back from Japan) and it has a max load of 690kg per rim.

 

 

by putting the reputable brand is still not enough, is the matching of your car weight

also by reading the load numbers on the rim you have to be careful of some have few numbers there and this depending on what pcd you are referring to

 

 

 

So my MPV is almost 1900kg, excluding any passengers, with me on board it's 1980kg, confirmed as I always sell off my old newspaper + used cardboard (mum's is doing PD at home) direct to the paper recycle factory at Defu lane (7~8mins drive from my flat in Hougang Central).

 

With 690kg x 4 = 2760kg. So I am left with 2760kg - 1900kg = 860kg of load for passenger + luggage.

 

So luckily, for my MY driving trip of 4 adult + 4 kids + luggage is defintely lesser than 860kg

I am the heaviest at 80kg, the rest of the adult - wife, maid, mum is around 50kg + -, 4 young kids are range from 10+ to 16+ kg

 

 

[Forgot2bme]

Wow interesting. Ups for the informative article!

[Grix17]

I pump 270 kPa for my 245/45R18 tyres even though they are extra load (XL) and though OE recommends 250 kPa for 215/60R17.

Comfort is quite good on CSC3 for 260-270 kPa and good for FC too.

When pressure drops to 250 kPa after 1 month without pumping air, car feels slightly sluggish (can tell with TPMS).

 

Can anyone recommend how much extra to pump if I am NOT on extra load tyres?

[Ahjun]

i pump 290 kPa for my Aveo sedan 15" x 4....

[Grix17]

i pump 290 kPa for my Aveo sedan 15" x 4....

 

Sounds pretty high. Beware that overinflation leads to premature wear of the centre tread.

I've discovered that on my tyres. Tread near shoulder has about 4-5 mm. Centre only about 2.5 to 3 mm.

Need to balance rolling resistance with even wear of the tyres.

[Mr_biscuit]

i pump 290 kPa for my Aveo sedan 15" x 4....

 

290kpa is super over-inflate your 15" wheels on Aveo.

Safety is definitely compromised and do be extra careful especially on wet road conditions.

Soon you'll realise your tyre wear is more towards the center.

 

IMHO, 240kpa (Cold Tyre Pressure) is the max you can go.

Edited March 30, 2010 by Mr_biscuit

[Babyt]

290kpa???!!! dont u feel ur car is floating and ur steering wheel is damm light until like no ground feeling?

[Chiangauto]

Thanks for sharing.good thread must always on top.

[Rtxm]

First of all, the article does not imply a "relationship between air pressure and load index" but a difference in rating(which i'll explain).

 

Secondly, both cases do not really apply to Singapore.

 

Both cases are using P metric measuresment(denoted by the P in front of the size) which is not used in singapore, singapore uses Euro metric measurements.

P metric measurement's load capacity is based on an engineering formula which takes into account their physical size (the volume of space for air inside the tire) and the amount of air pressure (how tightly the air molecules are compressed).

Hence the use of SL(standard load) based on 35psi and XL(Extra load) based on 41psi, therefore a difference in pressure.

 

The first case study which is a comparison between P225/55R17 95H and P255/35R20 93H.

The 20inch tire has a incorrect load index therefore the author suggest using Pmetric XL rated tires to correct the problem.

However there is no such division of SL and XL in Eurometric measurement(Singapore).

Eurometric is theoretically a Pmetric with only SL rating, meaning maximum load tire pressure does not change at 35psi. Therefore the only variable here is load index.

 

The second case study is a case of Pmetric or Eurometric tires being used on cars which require LTmetric rating(not used in singapore as well). The load index cannot be directly used. In simple terms, a load index of 100 for Pmetric and Eurometric is only a load index of 91 in LTmetric.

 

Summary

Tire pressure shld follow ur manufacturers recommendation(based on vehicle curb weight and load) irregardless of size as long as the load rating is correct(equal or greater then stock).

 

 

[Rtxm]

Jus to add to the summary. You can actually pump pressure proportionately lower if your new tire had a higher load index which i wouldnt recommend unless u know how to calculate.

 

for a even more in depth read on P metric or Euro metric inflation

http://marktg.toyotires.com/file/loadinflationtable.pdf

[Autom]

Hi Im sorry to have this post here as i could not start a new post...

 

Need lots of help from you guys here!

 

Looking for tyre size 185 or 175/80/r14

 

about 100 pics per month...

 

Is there any advice?

 

Please call Allan H/P: 98310824

[DeathAngel]

great info :)

[Justwe]

hm nice & thanks for the info. time to check for my air pressure.

[Doraemarc]

hi so wat determines our tyre pressure? OEM recommendation, or tyre capabalities? if my tyre max is 51psi, wouldnt pumping 32psi consider under-inflate? there r some theory abt max-10% (source: Car Bibles), so if taking acc of dat theory, shld i go for 45psi? does it matter wat car i drive?

[Zztensor]

hi so wat determines our tyre pressure? OEM recommendation, or tyre capabalities? if my tyre max is 51psi, wouldnt pumping 32psi consider under-inflate? there r some theory abt max-10% (source: Car Bibles), so if taking acc of dat theory, shld i go for 45psi? does it matter wat car i drive?

 

i think the "90% of max." or "80% of max." can be a gd rule of thumb. In ur case, it does sound a little underinflated....but if u feel tat the drive is ok (i.e. not floating, not sluggish, u ok with braking distance, decent control in wet conditions), then it's really up to u.

[Remin]

thx for the info :)

Edited December 12, 2010 by Remin