Tire Pressure Manual Confusing

[Afrim]

I have 205/55R16 winter tires on right now. Trying to find the correct tire pressure but the manual is confusing. What does Type A and Type B mean exactly?

[Jas2001]

Have a look at the label on the driver's side door frame. What does that say?

[Afrim]

It only shows tire pressure for 17" wheels 😕

[Cyker]

Ah, you have the same dilemma I had when I switched to 15" rims!

I'm still not 100% sure, but the only other reference to Type A and Type B cars I could find in the manual, were Type A cars seem to be ones that do NOT have an Off mode for the headlights, only Auto, and Type B cars have an Off option on the headlights.

However, it is very possible that Type A and Type B referencing was just for the headlight stalk and do not necessarily cross over to the tyres too.

I split the difference and just inflated my 15"'s to 38 psi (i.e. midway) and that seems about right - At 36psi they sag like they're going flat, and at 41psi the ride is far too hard!

 

[TonyHSD]

Door label is clear 2.3 bar from and 2.1 bar rear. This should be about right. 
You can do slightly above 2.35 and 2.15 max. A good pressure gauge and chalk on cold is must have. Here an interesting video about tyres and pressures and why is important to have these right. 

 

[DC_Ms]

38 minutes ago, TonyHSD said:

Door label is clear 2.3 bar from and 2.1 bar rear. This should be about right. 
You can do slightly above 2.35 and 2.15 max. A good pressure gauge and chalk on cold is must have. Here an interesting video about tyres and pressures and why is important to have these right. 

 

But those numbers would be correct on a 18’’ wheel too ?

[Roy124]

Tony, fascinating how small the wheels  were.

The other thing is the tyre temperature when being checked and set.  Even quite a short distance,  say 5 miles,  is enough to raise the pressure by one psi.

It follows that those who have home tyre inflator will be inflating to the manufacturer's recommendation and those who use a filling station will be under inflating. 

Then there is the unknown of gauge accuracy. 

[Jas2001]

https://mag.toyota.co.uk/toyota-tyre-pressure-and-size-guide/ also gives some tyre pressures.

[Afrim]

Just checked the website above and it looks like the tire pressure matches the Type A in the manual. But why make it so confusing and put Type A and Type B and not be specific about what the differnce is. Anyways ill have my tire pressure set to 2.5 bar (front) and 2.4 bar (back)

[Roy124]

Thinking on about that brake video, I wonder about the Lane Tracking and centring in the event of a front wheel blowout.

The car will naturally veer, will the system try and recover that?

[Don Mac]

36 minutes ago, Roy124 said:

Thinking on about that brake video, I wonder about the Lane Tracking and centring in the event of a front wheel blowout.

The car will naturally veer, will the system try and recover that?

The steering geometry on modern cars is set up in such a way that a tyre deflating no longer causes the dramatic effect that it used to. This is possible  now that cars all have powered steering (I don't think that you can really call it "power assisted" anymore, try steering a car with the power off) so extra steering effort can be traded off against stability. When you combine the reduced imbalance that is caused by a tyre deflating with the built in self-centering action of the steering setup (castor effect) I think you'll find that the veering isn't so bad.

If the Lane Tracking was active I would expect it to cope with this situation and keep the car in its lane, but I'm not aware of anything to say it has a function that counters external steering forces on the car (which would include road camber & crosswinds as well as flat tyres) to keep it in a straight line.

[Cyker]

I'm not sure it would; The LTA and LKA (Or whatever the heck they're called - What mutant came up with such obtuse names anyway? What's wrong with anti lane-drift and auto-steer??) in mine don't try very hard, and anything resisting its steering inputs cause it to stop trying for a bit.

[FROSTYBALLS]

7 minutes ago, Cyker said:

What's wrong with auto-steer

Presumably someone, somewhere would expect the car to automatically turn corners, etc. Although could be alleviated by doing away with all bends and corners on roads ........

Reminds of some years ago when a mechanic neighbour of ours was asked to give his brother-in-law some lessons in transferring from a motor bike to a Reliant. During the first lesson, at the first corner the brother-in-law leant into the corner rather than turning the steering wheel, leading to our neighbour having to grab the wheel to execute the turn. 

Didn't give many lessons after that ....

[Cyker]

Good point... I need to be reminded common sense isn't actually very common  

[Roy124]

Interesting lane keeping this morning.  Follow the car in front quite often.  A lot of weaving trying to stay in lane.

Road was wet and driving into a low sun.  Less than ideal.

[fred88]

Must admit it can be difficult to see lane markings when it wet and sunny. Had to guess a bit the other day taking a slip off the M4.

[TonyHSD]

I had once tyre blown up after hitting a large gap opening between bridges on M1 and M25 , front right tyre lost all pressure in a split of a second and there were no steering issues. I did not use the brakes though until almost stopped completely as the flat tyre and regen braking did it all for me.
The car has no safety futures, can’t comment on that. 

[Rhymes with Paris]

Re Frosty's comment on transferring motorcycle to car driving skills.

As all bike riders will know, leaning into the corner, and indeed counter steering becomes second nature.

A few friends of mine in the early 2000s came to grief when the fashion for on road quads became more common.

Used to steering by leaning, and two wheels, neither of which was likely to clip a kerb on the nearside, they found themselves upside down, wondering what happened.

Luckily none of the ones I knew were seriously hurt.

Same with new trike riders, that nearside rear wheel, when forgotten about, soon tips 'em over.

[Dylanfan]

With a front wheel blowout, the car moves sideways because the centre point of the steering is not through the centre of the wheel. Citroen built a number of cars where the centre was through the wheel and even had adverts showing a car having a blowout at speed, the car was fully controllable and didn’t pull to the side (GS) They also had fully powered steering that did the same (CX, Ltd XM).

 I don’t think that the modern electric assisted system can cope in the same way.

[Paul john]

26 minutes ago, Dylanfan said:

 I don’t think that the modern electric assisted system can cope in the same way.

I have had a blowout on the front in my Prius due to an idiot in a highway maintenance lorry spraying the road with nails.

 
at 50mph it was no fun but im still alive. 

[Cyker]

Ack, glad you're okay. It's this sort of thing which is why these stupid smart motorway laybys are utterly useless - It's not like you have any choice to have an incident in range of one or not! The people who forced this scheme through should be forced to drive on them and have their wheels randomly blow up and see how they feel about it when they're stranded in the left live lane with a fully freighted artic bearing down on them!

 

[Don Mac]

4 hours ago, Dylanfan said:

With a front wheel blowout, the car moves sideways because the centre point of the steering is not through the centre of the wheel. Citroen built a number of cars where the centre was through the wheel and even had adverts showing a car having a blowout at speed, the car was fully controllable and didn’t pull to the side (GS) They also had fully powered steering that did the same (CX, Ltd XM).

 I don’t think that the modern electric assisted system can cope in the same way.

I don't think that you understand what Citroen did if you think that their system was doing something which electric power assistance can't.

The force exerted on the steering changes when a tyre deflates mainly because the wheel drops, thus altering the angle of the steering axis and the scrub radius (the distance between where the steering axis intersects the road and the contact patch of the car). In the old days cars were often set up with a positive scrub radius (intersection point inboard of contact patch) because this made the steering lighter, the downside was that they didn't deal with uneven braking from side to side or tyre deflation so well.

Modern cars, which don't rely on the driver's muscles, tend to have a negative scrub radius which has pretty much the opposite properties.

It's not the easiest thing to grasp (or explain...), but you'll find loads of material on the web (with some good diagrams). There's a reasonably simple starter on Wikipedia - https://en.wikipedia.org/wiki/Scrub_radius#:~:text=An advantage of a negative,steering control in this emergency.

My point is that having power assisted steering allows manufacturers to make cars with inherently stable steering geometry without requiring huge efforts from the driver. Compare some of the anecdotes above with what used to happen (I had a puncture once in a 1980 Vauxhall, I did not stay on the road).

There are, of course, other factors at play. Modern tyres tend to be lower profile, so the change of the steering axis' angle will be less, and more resistant to shredding when deflated. Car manufacturers have the advantage of computer modelling and decades of experience in setting up suspension sytems to behave the way that they want.

 

I'll shut up now....

[Dylanfan]

I never said Citroen used electrics, the CX, SM and LHD XMs used hydraulics where there was no physical connection between the steering wheel and road wheels. It doesn’t matter what happens at the wheels, the hydraulics always keeps the wheels pointing where you are steering.
The GS and some other models had the wheel steering axis through the centre of the wheel, because of this, whatever happens to a tyre it is fully controllable as there is no sideways pull because the pivot point it still central.

[Extreme_One]

On 11/5/2023 at 2:17 PM, FROSTYBALLS said:

On 11/5/2023 at 2:11 PM, Cyker said:

What's wrong with auto-steer

Presumably someone, somewhere would expect the car to automatically turn corners

Hmmmm. Are you saying yours doesn't?

Mine does. If I were to take my hand off the wheel for a moment, say if I were to give my glasses a quick clean, the car definitely steers round corners.

The old MY21 didn't do that, but this MY23 definitely can.

It's a certainly a surprise to a passenger the first time they see it! 😆

[FROSTYBALLS]

7 minutes ago, Extreme_One said:

Are you saying yours doesn't?

No, our Aygo doesn't