Bridgestone Adrenalin RE001 vs PP2 vs rest?

[JBT]

Where do these tyre pressure recommendations come from 36psi is more than 20% higher than that recommended by Mazda for the MX-5.

Tyre manufacturers all seem to recommend using the vehicle manufacturer's placard settings and adding up to 4psi for consistent high speed driving or towing. Typical example: http://www.bridgestone.com.au/tyres/passenger/care/pressure.aspx

I find our car becomes quite skittish at 36psi as opposed to 30-32 psi. Mazda recommends 29 psi for the NC. All pressures referred to are cold settings.

[Old Dude]

I used to run the ER30 on 36psi they were run a lot lower than that when I bought the car, and it showed on the tyres,it also used to wallow around a bit when pushed hard until I upped the air pressure.
I checked one or the PP2 and it was at 36, I will check the rest over the weekend. As far as a good alignment I got one done so will have to wait and see if its any good

Old Dude

[JBT]

So I gather from all this that:

a. the vehicle manfacturer's have no idea what they're doing, but spend considerable time and money doing it anyway; and
b. the tyre manufacturers are equally inept.

Does anyone have a science based answer (or empirical evidence) rather than opinion?

[rockitman]

So I gather from all this that:

a. the vehicle manfacturer's have no idea what they're doing, but spend considerable time and money doing it anyway; and
b. the tyre manufacturers are equally inept.

Does anyone have a science based answer (or empirical evidence) rather than opinion?

Don't have any science based evidence. (that would kill this thread anyway)

Can give you an observation.

I did a defensive driver training course last year and the instructor( Ian Luff) instructed all participants to inflate tyres to 36psi regardless of make. He seemed to think that it was quite normal to inflate above the manufacturer's recommendation.

[NMX516]

So I gather from all this that:

a. the vehicle manfacturer's have no idea what they're doing, but spend considerable time and money doing it anyway; and
b. the tyre manufacturers are equally inept.

Does anyone have a science based answer (or empirical evidence) rather than opinion?

JBT when we did our Roadcraft Advanced Driver Training course last year, the guys running that were all for higher pressures, for a number of reasons including tyre life, wet weather grip, braking efficiency, controllability and dry weather grip.

It's easier to explain with diagrams, but I'll try anyway. Firstly, if the pressures are too low, under hard braking, or when high load is placed on a tyre, such as during hard cornering, the tyre will "collapse" in the middle, reducing the contact patch and so too the grip. This is more noticeable in wet conditions when the tread blocks move in towards each other because the tyre is too pliable as a result of low pressures, thereby closing up the groves in the tread pattern which were designed for getting rid of water. If you ever have a look at a set of skid marks on the road, most of them have two narrow marks per wheel (the outer edges of the tyre), which illustrates that the pressures were too low, so the outside edges of the tyres are the only part in firm contact with the road. The more flex present in a tyre also creates more heat, and reduces tyre life. Higher pressures also keep the side walls stiffer, reducing "wallowing" during sudden direction changes. The idea of higher pressures is to maximise the stiffness of the tyre.

The Roadcraft boys have also done an experiment with tyre pressures to illustrate the correlation to tyre life. They use Camry's and Corolla's. They had always run 44psi in the tyres of those vehicles. They had a tyre rep come and try to sell them on running the manufacturers recommended pressure of 28 psi, because "they had recommended that for good reason, because manufacturers know best" Anyway, long story short, at 44 psi the tyres lasted approx 8,000kms of defensive driver training and skid pan type work. At 28 psi, the same make and model of tyre, on the same vehicles lasted barely more than 600 kms!!!

The reason 28 psi is "recommended" is because car makers don't want to upset customers with brittle bones who couldn't tolerate the ride provided at say 38 psi. And tyre manufacturers want to sell more tyres, so they recommend that they be run at a low pressure so that they don't last too long! If Roadcraft have their tyres lasting over ten times longer at higher than recommended pressures, imagine what would happen to tyre sales if everyone started doing that!! The other point to that is that tyres have a "best before" date, so if everyone even doubles their tyre life, then there will be a lot of cars on the road with rubber which has gone off and lost its grip - not a wise move. Remember kids, most people don't take too much notice/care of their cars or the tyres, so if the tread looks deep enough, they're not going to run out and get new tyres - even if they are 10 years old. Tyre manufacturers would also consider that point when recommending pressures, I would suggest.

My last set of PP2's were run at 36 psi cold. They completed 8 track days, 3 or 4 skid pan days, and over 28,000kms of road use - that got them down to just on the legal limit. My wheel aligner also recommended to me that I start at 36 psi in the tyres. I take his word for it too, as he has been in the wheel alignment (specialising in race cars) game for over 30 years.

If your tyres are sliding more at higher pressures, I would suggest that it is because they are now responding better to driver input. Drive more smoothly and those problems will disappear.

[Garry]

Both of my MX5's must be freaks then because if I ran 36PSI in either of them they were very skittish however they were fine at 30-32PSI. My previous car however (fixed roof) had no trouble with 36PSI, however the manufacturers recomendation for that car was for 32PSI, not 26 like for the MX5's.

[JBT]

I was starting to worry too Garry.

When I say "skittish", I mean just that - intermittent grip over uneven/choppy surfaces which becomes particularly noticeable when cornering regardless of how smooth the inputs may be. I have dríven the same road under the same conditions at the same speeds: at 36psi (and higher) pressures the DSC/TCS is activating all over the place = no grip. However, at 30-32psi no DSC/TCS activation = grip.

I suggest that Roadcraft get more life out of their tyres at extremely high pressure because there's less tread contact with the road surface. I take the point about skid marks under braking but have you considered that the skid started because the pressures were below recommended (too low) in the first place. I've seen plenty of skid marks with full tread width too - what does that mean? 44 psi cold would be running close to the maximum pressure allowed on some tyres when the tyre gets hot.

All tyre manufacturers seem to recommend an increase of about 10% over the recommended cold pressure for high speed/high load/towing conditions. Do you really believe that car manufacturers deliberately recommend a pressure that makes the car doughy (and thus dangerous) just to make it "comfortable" to ride in and that they are colluding with tyre manufacturers in some sort of conspiracy to cause tyres to wear out earlier

As for wear: I have done a full skid pan day, three track days and 22,000km on the Bridgestones (32psi cold) and the only tyres (outside quarter) that are worn a bit too much are the ones that were on the left side (too many right turns on the tracks here) because I didn't rotate them. The others have more than half tread depth remaining - so what does that prove?

I would still like to see some empirical (rather than anectdotal) evidence on grip comparisons at different tyre pressures.

Oh, and by the way NMX516, I won't comment on your driving style if you don't comment on mine - especially given that I don't recall riding in a car with you as driver or passenger.

[NMX516]

Oh, and by the way NMX516, I won't comment on your driving style if you don't comment on mine - especially given that I don't recall riding in a car with you as driver or passenger.

Ok John, I wasn't having a go at your driving style, or even commenting on it. I apologise if it came across that way, but it wasn't my intention to do so. I made the statement that if your (being anyone reading the thread) tyres are sliding more at higher pressures (thinking in a track day situation, as we have been talking pressures for track days - note I didn't say "skittish" as is implied as a road situation) then driver input could be part of it. Our tracks are generally fairly smooth surfaces, not the sort of potholed, chopped up surface that can easily be found on the roads. That's my thinking out aloud, bouncing ideas off forumites, wondering what sensible, thoughtful responses might arise from that idea - not having a stab at anyone! I wasn't saying that anyone here is a bad driver because their car slides more with higher tyre pressures - what I was trying to say is that if they are having that problem, it might be because they are used to driving at a certain style which requires more of a heavy hand because tyre response is a little doughy. Ergo, then with tyres that respond in a sharper manner could need a softer hand to corner smoothly... The "wink" at the end of my post was in the vein of "I think that would be worth trying, and hopefully it might solve the problem" not in the vein of "I know best and your driving style is rubbish" as you seem to have taken it as being.

Further more, I'm not going to continue to debate the theory of recommended tyre pressures. From what I've seen and been told over the years, I consider that they are best for me at 36 psi, so that's what I will run. John, Doug has also told me to start out with 36 to 38 and go from there. I'm going off what guys with a lot of direct experience have told me over time. I recall Doug asking me what size tyres I had when I did ask him. Perhaps 17's can get away with lower pressures, I don't know, I've never had a car with 17's. That is my experience, that is what I am happy with running my tyres at. I suspect that different tyres would be different too. I run 34 front and 34 rear in my Pulsar... 36 is not the magical number, but that is what I'm happy running in the MX5, with PP2's on. I also run that on the RE001's.

JBT you will run your tyres at 32 psi, and that's probably never going to change because I doubt anyone will be able to ever produce to you some empirical evidence as to why you might be better served with higher pressures. None of the manufacturers will ever do so, and looking at skid marks on the road will always draw the response of "but yesterday I saw some that were...". As far as I know, none of us here are forensic crash investigators, so no matter what any of us say, it's probably all just crap anyway.

Edit: oh, and while I think of it, I run my semi slicks at 28 psi cold. That is what has been recommended to me by various people with a lot of experience with those tyres. As I understand it, the reason is because the tyre is a stiffer construction than a normal road tyre, and so doesn't require as much air pressure to keep it in shape.

[Old Dude]

I know by looking at my OEM tyres ER30 being run at 30psi were wearing out on the edges, so obviously not enought air ,

since I upped it to 36psi on both them and now the 16 inch PP2 the car doesn't wallow, and I must admit the PP2 do give a comfortable ride, I just have to wear them in a bit and see what happens.

I got the wheel alignment when I put them on, and they put 36psi in them, as previously stated my only concern was that I had to turn the steering wheel more to get the same directional responce with these new tyres, and are waiting to see how they go once all the mould goo wears off.

Anyone know a good wheel aligner on the Gold Coast or Brisbane who specialises in our stuff.

Old Dude

[AJ]

Fulcrum Suspension is a Club sponsor Old Dude, & have done a lot of MX5's

[JBT]

Doug has also told me to start out with 36 to 38 and go from there. I'm going off what guys with a lot of direct experience have told me over time.

My points of discussion are related to everyday road use and not track. However, for every race experienced person that has recommended high pressures I've had another say the very opposite. I haven't been able to find any authoritative source (car or tyre manufacturer, motoring body etc.) that recommends anything more than about 10% above manufacturer's placard settings and then only for high load/speed conditions.

I'm surprised no forum contributors (so far) have any enlightening data that they can share.

[Old Dude]

Thanks AJ
I will see how this one goes and will try them if its no good

[marcusus]

All tyre manufacturers seem to recommend an increase of about 10% over the recommended cold pressure for high speed/high load/towing conditions. Do you really believe that car manufacturers deliberately recommend a pressure that makes the car doughy (and thus dangerous) just to make it "comfortable" to ride in and that they are colluding with tyre manufacturers in some sort of conspiracy to cause tyres to wear out earlier

Yes! I would hazard a guess that right comfort gets them more sales than a "minor" safety increase. You can't really gauge safety by driving a car (in fact you can only really gauge it if you have a crash), but comfort is very easy to gauge.

With regards to your DSC activating, it'll all depend on the algorithm Mazda uses to activate it in the computer programming, but there could be situations where it activates without needing to activate and vice versa. For example, if the algorithm specifically detects on the amount of verticle angle (aka camber) a wheel changes, then having a lower pressure will cause less camber because of the increased "grip" the two outer edges of the tyre will have. This doesn't necessarily mean that you actually have more grip, because the contact patch could possibly be much less based on how low the pressure is. Remember though, that this is only an example and quite possibly is not how Mazda does it. It just serves as an example to illustrate that even though lower pressures might not activate your DSC, it may not necessarily equate to more grip.

[Guran]

Tyre pressures affect so many aspects of a car that no one recommendation is going to suit everyone. In the grand scheme of things, most people rarely drive their cars beyond 5/10ths, let alone 8/10ths. The first sign of tyre squeal and they get all panicky! For the majority, they're more concerned about tyre wear life and ride comfort, not on limit grip and steering feel. That is why the recommended tyre pressures are so low - they favour ride comfort mostly and possibly tyre life (but only if you're pottering around), which suits 99.9% of kms dríven. If you drive beyond 5/10ths and want to experience the limits of the car without them being dulled by doughy tyres then it's best to up pressures beyond the placard recoomendations. You will get much less tyre roll in hard corners (hard cornered low pressure tyres don't grip too well if they roll off and the rims contact the road!), lighter steering, improved fuel economy, shorter stopping distances (especially in the wet), and better wear patterns. This is why the advanced driving schools recommend higher pressures: because they frequently drive and instruct thier students to experience driving well beyond 5/10ths.

As for the science, perhaps John Cadogan should look into this next time he does the tyre testing for Wheels magazine.

[JBT]

I'm surprised no forum contributors (so far) have any enlightening data that they can share.

Maybe I should have made that "enlightening factual data".