IS250 2007 Tyre Pressure Guidance Please

[Kalpesh]

Hi, apologies for whats probably a silly question.

 

I recently purchased a IS250, 2007.

It has 19inch alloys on 225 40 R19 all round.

The stock 17inch pressure recommended is 35 front and 37 rear. 

 

I currently set them to 40 PSI all round but would appreaceiate some guidance.

 

Would I be better off having 37 on the front, 39 on the back for example.  Usually there is just 2 of in the car and little weight (although the occasional long distance drive with 2 full suitcases.)

 

Im after best mileage and comfort.

 

Again apologies for the daft question.

[Linas.P]

Yeah... that will be complicated. But you can look-up cars with similar size wheels and somewhat guestimate the ballpark. I can say ~40PSI sounds about right. For example Lexus RC runs 235/40R19 in the front and 35PSI, 225 will have lower load rating, so will require few more PSI, so yes ~40PSI should do. But really one can only provide you with educated guess at best. You will need to try it yourself, see what you like (too hard or too soft), check the tyre wear, to see if they wearing more in the middle (overinflated) or both sides (under inflated) and adjust from there.

Basically, what I am saying - you can only do it by feel, trial and error. That is short answer. My guess would be something like 35-38 (front/rear).

If you actually want to calculate the load, then there is calculator, but the problem is that it doesn't give you correct ratings most of the time https://tiresize.com/pressure-calculator/ e.g. standard IS250 R17 tyres have load rating of 90, but calculator only gives rating for 91 or 94, so your calculated rating and PSI will be also wrong e.g. in this case if you choose 91, it will say you need to inflate new tyres to 40PSI or if you choose 94, then it will say correct pressure for new tyre should be 38PSI

As such you can also refer to Load inflation tables e.g. here https://www.toyotires.com/media/pxcjubjs/application_of_load_inflation_tables_20200723.pdf (p34 - it is in lbs, so divide by 2.2 for kg). To calculate the safe pressure you will need to know your tyre load rating, your car curb weight and weight distribution for your car (most of the times tyres have loads of headroom, to save you the headache, safe rating for IS250 would be 23PSI front and 22PSI rear). However, if you just want comparable pressure to OEM sizes, then you just take OEM load rating and PSI, check what it requires e.g. IS250 standard pressures for 225/45R17 is 36PSI, standard load rating is 90 and according to load table they expecting the tyre to hold 1179lbs, 225/40R19 has load rating of 93, meaning to match OEM you only need 33-34PSI. The rear is different story - IS250 has way way way overrated tyres for rear... 245/45R17 with 95 load rating and 38PSI, so if we go by what Lexus is suggesting, then you would need to match 1389lbs which would require 41PSI on 93 rated tyres.

 

[Mr Vlad]

Hi Kalpesh. How are you getting on with your new car? Simple answer for you is go for 17 inch wheels. If it's comfort you want then 17's is the way to go.

[Kalpesh]

Hi both and thank your your replies.

Part of what got me posting the question was that I got a flat last weekend, likely due to a pothole, the structure of tyre was damaged on the inside also I was hearing a mild rub/knock like sound on reversing out of the uphill drive/sometime on full lock when its cold outside, it last milliseconds. 

Tyre wear is even and I cant see anything under the arches where it mightve been catching.  I read a few other posts on the forum with similar.  I guess Im just really overly paranoid after the last lemon I had.

I havent heard it since I inflated all to 40 Psi (reversed out repeatedly trying to reproduce the noise) so am hoping it was because all the pressures were vastly different (some low 30s, one 44 prior to me getting a home inflator the other day, I literally couldnt tell the pressure was so different whilst driving it but obvoiusly not going to help) I will keep my ears open and keep a check on tyre pressure.

I did fall out with cars due my last one, but I think Im falling for her. 🙂

Such a nice drive (even with random tyre pressures!).  I dont know how Lexus managed to make such modern looking cars/interiors on cars this old.

Im hoping for some decent weather soon so I can take some pictures and post up.

Once again thank you for replies.

 

 

 

[J Henderson]

1 hour ago, Kalpesh said:

I was hearing a mild rub/knock like sound on reversing out of the uphill drive/sometime on full lock when its cold outside, it last milliseconds.

Sounds like the tyres hopping/skipping. Quite normal and nothing to worry about.

With lots of steering lock applied, the front wheels on these cars are in a positively cambered state, and effectively only using the outside edge of the tyre. Almost like the car is tiptoeing.

Cold tyres are typically not yet pliable enough to cope and tend to hop & skip when performing a full-lock manoeuvre.

This is more likely to happen with "sporty" tyres which have square-ish tread blocks on the edge. I think having larger wheels also exacerbates the issue as I suffered this a lot when I had 19" wheels.

[Kalpesh]

Hi J Hendesrson, Wow your F sport looks stunning on the original pics, only started reading up on your story just now and intend to read up with what youve done with it since youve had it, looking forward to it. 🙂

 

I heard the noise in mine again this morning reversing out of the drive, it was more of a grinding noise that lasted a few seconds till I straightended up.  I have a strong feeling that it might slightly be catching somewhere under the front driver rim somewhere when on full turn and due to the angle of the drive, as i can see a slight difference to the rim protector (Im not sure of the name but will take some close up pics).   It might just be my paranoi again though.   Im also more convinced that is more prominent when the tyres are cold so its possibly just what you said or maybe a combination of both.   For example just did some tight turns on a hilly drive and no noise at all., tyres not completely cold.

I did a 200+ mile trip in it today.   She drove like a dream. 38+mpg with a fair amount of luggage  which Im very happy with and the ride felt fine on 40psi all round.

 

 

[gji25]

[Kalpesh]

Thanks gji25,

 

I shouldve mentioned theyre 19inch wheels.  Ive had them at 40Psi for a few weeks now and happy with the ride so will stick to that for now.  Thank you for taking the time to post and reply.

 

In case it helps anyone else in future, I think I've figured out the grinding issue, Im pretty sure it was the dust guards on the brake discs, I pushed them back slightly with my hand where they felt too close to the discs and since then no grinding noise. 

 

I hope you are all well. 🙂