Tyre Pressures - 15” Wheels

[Catlover]

The User Manual tyre pressures for 15” wheels depends whether the vehicle is            
a) without a full-size spare tyre, front 36psi, rear 35psi.          
b) with a full-size spare tyre, front and rear 32psi.

then a Compact spare tyre is listed at 60psi.

I am asking, 1) why with or without a full size spare tyre means a considerable difference in tyre pressures?
Also, 2) Toyotas terminology “full-size spare tyre” and “compact spare tyre”, what is the difference?
My Prius is 15” wheels and I have what I call a Spacesaver tyre, it’s thin.              
3) Is that a “compact spare tyre? It’s pressure is 60psi and is clearly marked at that.        
I have been treating my Spacesaver tyre as a “full size spare tyre”, meaning putting a pressure of 32psi in the 4 tyres, BUT if a Spacesaver is NOT a “full size spare” then the front and rear need increasing circa 10%.

[Cyker]

I would have assumed a full-sized spare meant an actual 5th wheel that was identical to the other wheels, like you used to get in cars before space-savers (or nothing) became a thing...!

Also can't shed light on why the spare would make a difference with the tyre pressures... I have a similar quandary with the tyre chart for 15's on my Mk4 - It says type A needs 41 PSI and type B only needs 33, but I've yet to find in the manual what Type A or Type B actually means or how to tell whether my car is Type A or Type B!

 

[FROSTYBALLS]

The Yaris manual refers you to the tyre pressure label on the inside of the driver's door opening. Presumably the label will give you the correct pressure for your car (ie whether it is a Type A or Type B).

[TonyHSD]

Hi Joe, 

this perhaps has sometimes to do with weight, since full size spare tyre will have an extra kilo or two to the total weight of the car or maybe even different tyres ( different speed and load index ) used in cars with full size and cars with space savers. You can try the higher numbers then and see how it drives, if too harsh you can get slightly off course with something in between. Let see if someone from Toyota dealers knows something more about it will be interesting to learn. 👍

[Cyker]

24 minutes ago, FROSTYBALLS said:

The Yaris manual refers you to the tyre pressure label on the inside of the driver's door opening. Presumably the label will give you the correct pressure for your car (ie whether it is a Type A or Type B).

Unfortunately those list tyre pressures for the 17" rims the car came with, not the 15" rims I switched to!

 

[FROSTYBALLS]

10 minutes ago, Cyker said:

Unfortunately those list tyre pressures for the 17" rims the car came with, not the 15" rims I switched to!

Does the manual have a Type A and Type B for the 17's? If so the door label should correspond to one of the two types - and you could then assume that, for example if it is Type A, then that Type applies to your 15's.

[Cyker]

Sadly no, the 16" and 17" rims only have the one set of pressures - Only the 15" section differentiates between type A and B!!

It's a bit of a mystery, and because Toyota don't officially support 15" in the UK, despite it being in the manual, they couldn't offer any insight either...

 

[Chris Dance]

I have always kept the space saver tyre on the Prius at 60PSI. I only ever had to use the space saver once on the GEN 3. The front off side tyre went down after hitting a kerb. The AA fitted the space saver  on the front. BIG ERROR.  (It was on a busy dual carriageway). With the space saver on the front speed must be kept down to about 30MPH and it is difficult to steer. It was at night and other cars were flashing me for going slow. I did have the warning flashers on. It was a "hairy" ride. After the event the dealer advised me only to fit the space saver on the rear never on the front.  You must always keep a low speed with space saver fitted. I would rather have a proper full size spare wheel. The space saver is better than a tin of useless gunge.

[TonyHSD]

4 minutes ago, Chris Dance said:

I have always kept the space saver tyre on the Prius at 60PSI. I only ever had to use the space saver once on the GEN 3. The front off side tyre went down after hitting a kerb. The AA fitted the space saver  on the front. BIG ERROR.  (It was on a busy dual carriageway). With the space saver on the front speed must be kept down to about 30MPH and it is difficult to steer. It was at night and other cars were flashing me for going slow. I did have the warning flashers on. It was a "hairy" ride. After the event the dealer advised me only to fit the space saver on the rear never on the front.  You must always keep a low speed with space saver fitted. I would rather have a proper full size spare wheel. The space saver is better than a tin of useless gunge.

Space savers are horrible for the transmission and specifically for differential bearings and gears, it puts so much stress on that you can pretty much damage it in a short drive. I also only used once on the front wheel for around  5 miles or less and was able to hear a whine from the diff, never again. I should just swap with the rear but wasn’t ideal place to do that 👍

[Sooty]

Could the 2 types refer to whether they are "Run Flat" or normal tyres?

[Cyker]

For my Type A and Type B thing? I wouldn't have thought so - It's more common to have runflat tyres in larger rim sizes than smaller ones!

I suspect it's some variation of the car that doesn't apply here since we don't officially get 15" rims in the UK - If anyone in Ireland or Europe who has a Mk4 Yaris on 15" rims is reading this maybe they can shed some light!  

[Sooty]

#Cyker, have a look at this link:

Toyota Yaris Review (2021) | Autocar

This may explain your question.

Also, looking at the Yaris GR it seems to have a 1.6ltr engine.

Don't know if that could be the difference. 

 

[QuantumFireball]

On 10/13/2021 at 5:56 PM, TonyHSD said:

Hi Joe, 

this perhaps has sometimes to do with weight, since full size spare tyre will have an extra kilo or two to the total weight of the car or maybe even different tyres ( different speed and load index ) used in cars with full size and cars with space savers.👍

The weight part doesn't add up - an extra adult passenger, or like a full load of shopping would make a much bigger weight difference than full-size vs. spacesaver wheel.

I imagine they're using the presence of a full-size spare to identify a substantially different car configuration, possibly one for harsher conditions like Australia where a 1,000 km car journey is considered "short" (i.e. you probably want a full-size spare!) and higher ambient temperatures would justify lower tyre pressure.

I'd say the 36/35 is the right one for this car, it's the same as my UK-spec 2012 Plug-in on 15"s.

[TonyHSD]

I found this chart of tyre pressures for Toyota cars, it might be helpful. Aaron is correct 36/35psi for Joe. 👍

https://mag.toyota.co.uk/toyota-tyre-pressure-and-size-guide/

[Chris Dance]

There seem to be lots of reasons why the space saver tyre must be 60 PSI. This has been discussed at length on Prius Chat. It is only a "get you home" wheel and is not to be used for long distance driving. I suspect the tyre material is not as good as the main wheel tyres. I would suggest to keep the space saver at 60 PSI as recommended. 

[QuantumFireball]

5 hours ago, Chris Dance said:

There seem to be lots of reasons why the space saver tyre must be 60 PSI. This has been discussed at length on Prius Chat. It is only a "get you home" wheel and is not to be used for long distance driving. I suspect the tyre material is not as good as the main wheel tyres. I would suggest to keep the space saver at 60 PSI as recommended. 

Nobody is questioning the space saver tyre pressure here...

[22926322]

Hi, I have a 17 plate Prius with 15 in wheels. The plate on the door pillar gives the tyre pressure's a at 35 psi rear and 36psi front. I have used these pressures for the past 3 years , the car runs smooth it handles well and overall gives an average MPG of over 70. I’m happy with that and that’s what I’m sticking to.

[Catlover]

Hi John, you may have looked at the original post of this thread, I was quoting from the Gen4 handbook with my car. I didn’t understand what the difference was between a) and b) as I have a space saver tyre (skinny thin), but the main tyres are 15” like yours.  Through the comments above I determined I was going to use 36F and 35R, which is different to what I was using, but it is in line with your thinking. 
Plus, over the 38k miles the car has done it has averaged just over 70mpg.

[22926322]

Hi joe,   when I purchased my car 3 years ago I thought the tyres felt a bit soft, I checked  and found the Toyota dealer I purchased it from had put the tyres at 32psi. I asked why and what difference a full size or skinny spare would make. They couldn’t answer, so I done what I thought and the door pillar said and put them up to 35/36 and have used this presure ever since (I have a skinny spare).just as a point I to have 38k on the clock to ,very pleased with this car, at 86 year old I think this car will outlast me.

[Catlover]

You doing well at that age John, the Prius is a low car, easy to fall into but not as easy to get out of. You got 12 years on, I hope I can still manage it when I am 86.