Obtaining tire pressure information
 

Goddamn it, why is it *so* difficult to get tyre pressure informations? I need to choose a tire that can take 51 PSI - for FE reasons, but also because my car manual also specifies a 49 PSI figure for my car. But no-one is willing to give me pressure figures - I just got off the phone from a tyre shop and they refused to quote figures, just palming me off with "40 PSI" and "You shouldn't be going over this anyway" despite me telling them that's exactly what the car manual says. Why is no-one telling me this information - it's just wasting my time and it has taken me several weeks to try and choose a damn tire, and I'm nowhere near my final decision due to the lack of information.

Sorry, I just needed to let off steam.

From my experience... just buy a tire you like. Pump it up to whatever you like and be happy. :) I run my winter tires on the Matrix (sidewall max of 35 psi) at 50 psi and have run them for two years with zero problems. I've run my 44 psi max sidewall tires on the Paseo for two years at 60 psi with zero problems too. I know people running even higher pressures with no problems. I recommend finding a good low rolling resistance tire, and pumping it up to whatever you want. I doubt you'll have problems. IMO, the sidewall rating doesn't mean a ton.

Then why do they print the figures there? They wouldn't do that if it was a complete waste of time, wouldn't they? I'm just being curious.

On my really cheap low rated tires it seems that I get sidewall rot quicker when I run a lot above the rating, not sure you can really pin it down to any one thing, every tire is different.

Also if I remember some tires don't handle as well at their rated "speed rating" if the pressure is above their sidewall rating, since you probably don't drive 120mph it probably doesn't matter on that regard either.

Otherwise I'm not sure, many of the tires I run above the rating last longer, but some others wear unevenly and end up making my car vibrate.

Again this is from 15yrs of driving I can't really pinpoint if any of the above has to do with higher than normal pressure or not.

Good Luck

Goodyear & Michelin (I assume other mfgs. as well)websites list "Max load @ PSI" for their tires. I don't know if it is "max pressure" or not.

Don

I know from personal experience that the Sumitomo brand can run 51psi max pressures.

Hi Eddles. That has to be the worlds first car manual that specified such a pressure! Is that because it's the eco model?

ollie

Correct. The non ECO4 model with the exact same tire size quotes a figure of between 28-35 PSI.

Eddles,

Read this first:

Barry's Tire Tech

What you should get out of this is that what is printed on the sidewall is relatively arbitrary - which is why the tire shop wasn't particularly interested in answering your question. They saw it as something outside their need to understand - and in a lot of respects that is true.

But allow me correct a couple of misconceptions:

Yes, they would, if it were a government regulation - which it is!

The way the regulation is worded is that the max load and the max pressure have to be listed. For some reason - and I think it is historic in nature - some folks think these 2 things are related - and most of the time they are not.

Hmm. Interesting information. The guy said massively increasing the pressure above the placard doesn't make much difference - just a couple PSI over should be fine, so I might go for the Firestone F580's which is rated at 44PSI - I'm sure it can handle a few extra PSI.

Thanks very much for your time!

You can definitely go above the rating on the max pressure. This is what they assign to achieve. . . a safe boundary between normal operation and something bizarre happening.

I know people on here are all about going 50% above max sidewall sometimes. . .but I wouldn't do it. If your car drops through some of the potholes I've accidently hit(in NC mostly) that are 3-4 inches deep(maybe more) and rock my car chassis you can very quickly achieve burst pressure. Hypothetically its a warm day you've been driving for a little while, so your pressure is substantially higher(from driving and from the heat) and you hit a big pothole, at that point you've only got to jump up about 80 PSI in local pressure somewhere in the tire to achieve burst. Its not common I admit, but running above max sidewall is not common either. Its putting alot more molecules in the tire and making it behave in funny ways.

I would go with the 44 psi tires and only inflate to 49-50 and no higher.

Blow a tire off on the highway and I promise you guys will never go over that max rating again. Its honestly like driving on a solid sheet of ice.

Sigh. Just found out from the UK's consumer report magazine and Germany's ADAC that the Firestone F590 has really high rolling resistance despite being a "fuel saver" and now I'm worried about the F580's (older version) having the same problem. So it's back to the EcoContact 3's but they are rated at 37 PSI which still worries me. The Fulda EcoControl is perfect (very good reviews, good price, fuel saver, rated at 51 PSI, everything I want) but the overall diameter is 5% smaller so the engine would spin 5% faster at the same speed, using up a little more fuel. Sigh.

One other thing to consider is raising the PSI will increase your stopping distance. Raising the PSI puts less rubber on the road, putting less potential friction on the asphalt should you need to stop. Especially in a heavy car without ABS, this can become dangerous. Nothing like trying to do an emergency stop in a 2 ton vehicle on overinflated tires to make you lose a few PSI at your first opportunity.

And besides losing stopping power, you have decreased the cars ability to corner and, in extremely high pressure, can rattle your vehicle so badly it has the potential to cause premature wear on the body and suspension. So making your car roll easier will come at the cost of making your car stop and corner efficiently. Otherwise, we'd all be driving cars with temporary donut spares on all 4 corners.

On a front wheel drive car, I would be more willing to overinflate on the rear but not the front, since your front tires provide most of the stopping and all of the turning. To sum it up, use a bit of common sense.

Wouldn't that cause oversteer and the tendency to swap ends in a heavy stop?

Eddles -

I use tirerack.com for all my tyre info. But you're SOL if they don't carry the tire you want. When I got my Continentals ContiProContact tires, I had to tell the tire-shop dude that they existed in 51 PSI. He called the warehouse and they had them later that day.

EDIT: If you get them from a shop, try to get the better quality tire valves. Supposedly you can get valves that are designed for higher pressure.

CarloSW2

Cheers for help. Unfortunately, nearly all tires I'm looking at isn't in tirerack.com - I guess European tires isn't as common in the US.

But anyway. How do I ask for the valves? "Please fit better quality valves" is sufficient?

Thanks for your time!

Eddles -

Rats. I wish there were a "tyrerack.co.uk" for you.

I googled around, and I think the terminology would be "high pressure valve stems" :

SELECTING PROPER VALVE HARDWARE - May 6, 2002
http://www.techtirerepairs.com/tech_...0Issue%202.pdf
But, the above might not work if the *size* of the higher PSI valve stem is not compatible. I just don't know.

Let's wait for CapriRacer to chime in, he has the expert knowledge.

CarloSW2

There is. Tyretest.com ;)

Thanks again re: valve stems, I'll ask them anyway.

Would you have the numbers on that? I've been hearing this for a few years now but am finding it impossible to find data on this increased stopping distance malarkey!

ollie

Drag racers use relatively low pressures to get more grip, but there's a world of difference between wrinkle-wall drag slicks and radial car tires!

Here's the problem from my perspective:

1) If you are planing on using more than 60 psi in a passenger car tire - well, I'm already on record as recommending against this.

2) But if you are still determined to do it, then I feel obligated to give you advice to do this safely: Please use high pressure valves as indicated above. The problem will be at the retail store end.

They are going to look at you kind of cross eyed, because the valves they use are appropriate for all uses - except high pressures, which is when they'll use valves for light trucks ( meaning LT metric tires) - and they might not be the correct size.

So I would suggest you buy and mount your own valves.

First take the assembly in and have the tires dismounted. Using a knife or razorblade, cut off the old valve (if it is an all rubber valve, which you will find out very quickly!). Then replace the valve with this:

http://www.geocities.com/barrystiret...ampinvalve.jpg

You should be able to find it at any car parts place that has tire stuff. It's designed for chrome wheels and will accommodate both size valve holes. It's a screw-in, so you shouldn't have any trouble installing it.

Then return to the tire shop to mount your new tires. They won't mess with the new valves, because they'll be chrome - and of course you will have told them not to!

For those with TPMS's - and I recommend retaining the device as a good safety feature - this gets a bit more complicated - beyond my ability to know all the possibilities. Sorry.

Not going to inflate my tires to 60 PSI - that's way beyond my personal comfort zone! ;)

I've finally decided to get 44 PSI rated tires and not inflate it beyond 49 PSI maximum - I'll probably inflate it to 47 PSI which is 7% over maximum.

Thanks for your advice anyway!

try it for yourself. Inflate all your tires as much as you dare, get to a set speed, brake as hard and fast as possible, and measure your distance. Then try again with the pressure listed on the vehicle information label. Your stopping distance will be much less.

Sure it would, if you overdid it. But most front wheel drive cars are nose heavy anyway, so a bit of oversteer added to the equation might help balance things out. But it could be taken too far and like you said, cause WAY too much oversteer.

Here's the link to the wikipedia link on tires
Tire - Wikipedia, the free encyclopedia

follow the references. It is generally well known that overinflation puts less ruber on the road, hence the lower rolling resistance. But rolling resistance goes both ways. If there is less resistance in rolling, there is less resistance between the tire and the asphalt, giving your brakes less of an ability to stop the vehicle.

I know the Goodyear Assurance "Fuel Max" tires are all rated to 51 psi. Since you're in the UK I would look at the "Efficient Grip". More than likely they are too.

Don

Okay, let's look at my manual here. Feast your eyes on the unladen front tire pressures for the Y17DT engine on the leftmost column. It is all 35 PSI no matter what tire is used. The 61 PSI tire is just the "space saver" spare. Now look at Y17DT (ECO4). Now it says 41 PSI. Tell me why can't a Y17DT owner inflate his/her tire to 41 PSI? It's the exact same car. Also note the pressures for the ECO4 rear tires when fully loaded? It says 49 PSI. If it's really unsafe for me to run my tires at 49 PSI, why would a manufacturer of the 2nd most common car in the UK that weights only 2,500 lbs recommend this?

Thanks for this,

Unfortunately the Efficient Grip doesn't come in 175/80/14 - which is a fairly rare size, annoyingly enough.

I've been wanting to know the same thing. It just reinforces my thoughts on traction vs pressure and i'd like to hear a professional opinion on this.
Thanks for posting the picture of your manual Eddles.

ollie

CapriRacer -

Thank you for posting that. My information was vague. I was able to get tires rated at 51 PSI, so that's my max. Because passenger tire valve stems are rated at 65 PSI (according to that PDF I cite in my previous post), I should be fine.

For additional safety, the next time I get a set of (51 PSI rated) tires, I will make sure they install the valves you cite. If they don't have them, I will get some myself.

CarloSW2

Now, now, you have to tell the whole story!! Notice also that the 2 tires listed for the ECO4 are completely different in tire size than the others listed. Why is that?

Obviously this is a different model and the tire sizing / pressure issue is only part of the story.

Could the ECO4 tires be AA rated for traction?

ollie

The Y17DT ECO4 is exactly the same as the Y17DT but with some areodynamic bits stuck on (spoiler and underbody panels), low ratio gears, and fuel efficient tires in those sizes.

The official marketing name for "Y17DT" is:

VAUXHALL ASTRA LS DTI

The official marketing name for "Y17DT ECO4" is:

VAUXHALL ASTRA LS ECO DTI

"LS" is the trim level - the "ECO" is just a slight variant to the trim level with the changes I mentioned above. If you look at the specs in the handbook, LS DTI and LS ECO4 DTI has the exactly the same information throughout, the only difference is the tire pressures. Even the kerb weight shown in the manual is the exact same for both models. As you can see, all different trim levels/engines has different weights.

Yeah, I wouldn't put too much stock on the tire pressure listed in the book or door plaque as they are the recommendations for the stock tires. My car lists 32 PSI and the stock tires had a max sidewall rating of 35 PSI. Now I have tires that have a sidewall max of 51 PSI that I just filled up to ~50; going back to 32 PSI will reduce my FE by ~5 MPG.

Get the tires you want, fill 'em up as far as you feel comfortable. :thumbup:

This whole discussion has been a regular hoot! But in the process of researching info for making an informative reply, it seems there is a lot of grey area in this whole issue. Other discussions on this forum point out that 50 psi seems to be the happy medium between not enough braking and cornering and too little air to get good FE.

To be quite honest, I never did put much stock into the recommended psi on the placard and just filled to maximum sidewall. I've occasionally overfilled to 50, but only with a bit of trepidation. One guy I knew had a Ford F-250 Powerstroke that he managed to drive like a maniac and still get 19-20 mpg out of. And this wasn't no eco vehicle either. It had a crew cab, full length bed, 4WD, the lot. But anyway, he put his tires up to 80 psi, and he had a heckuva time stopping that thing in a timely fashion. That and it rode like it had hard rubber tires from a forklift. You hit a ant and I could tell you what it had for breakfast by listening to the ensuing rattles. I think he took it a bit far

I agree, but I'll bet for different reasons!


And this is one of MY reasons.

F-250's require the use of LT metric tires - and many of them are DESIGNED to use 80 psi - even says so on the sidewall. It is interesting that he had some issues with them at that pressure.

And just for the record, 80 psi is probably much more than what the vehicle placard calls for!

I'll bet 80 psi was way more than what was called for too.

Riding in that thing on the pavement was like riding down a dirt road in a regular car. It was just downright rough going. I'm all for saving fuel, but the damage that was possible by overworking the suspension like that would likely cancel out any fuel savings.

I am curious whether anyone has tried putting on 4 pizza cutter spare tires on their car to save gas. It would certainly offer very low rolling resistance, but wow, I'd hate to take a corner with that arrangement.

LT metric Load Range E tires are rated at 80 PSI. Load Range D is 65 PSI. Load Range C is 50 PSI. The truck was designed to handle the load the tires can take. Most people won't run them that high unless loaded. If the truck is loaded down 80 PSI doesn't ride that bad. Unloaded the contact patch gets mighty small.

Don