C. Charles Hahn
CCH Auto Appearance, LLC
GanJa786 said:
That can fluctuate depending on a lot of factors, so you're not exactly choosing a foolproof standard of accuracy. Plus you're assuming the dealer uses a calibrated accurate gauge themselves.
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That can fluctuate depending on a lot of factors, so you're not exactly choosing a foolproof standard of accuracy. Plus you're assuming the dealer uses a calibrated accurate gauge themselves.
Accumulator
Well-known member
GanJa786 said:
Heh heh, my Audi dealer's gauges aren't bad these days (major Porsche/Audi dealership) but they only got decent ones recently. The other dealerships I patronize do *NOT* use accurate gauges and I don't mean they're off by a few tenths either
And that's assuming all sorts of other variables aren't factoring in. If the tires are filled with nitrogen there will be fewer of those variables, but I still wouldn't use the dealer's supposed inflation pressures as any kind of standard.
Check my earlier posts on this thread, I use ones from AccuGage (sheesh, I hate those cutesy spellings
). OK, OK...it's another one of those "how serious do you really want to get?!?" subjects, and you can do OK with a gauge that's off as long as you give it some thought..well, assuming the gauge is at least consistent.
(Oh, and off-topic, but no way would I run around with 32psi in tires! The folks at VID have repeatedly peeled tires off rims at pressures like that on all sorts of vehicles, resulting in some spectacular crashes. Guess what the real explanation for Ford Explorer roll-overs was
I consider "sidewall max minus 10%" to be an OK rule-of-thumb starting point if you don't already know what's best for the given situation.)Accumulator said:Heh heh, my Audi dealer's gauges aren't bad these days (major Porsche/Audi dealership) but they only got decent ones recently. The other dealerships I patronize do *NOT* use accurate gauges and I don't mean they're off by a few tenths either
And that's assuming all sorts of other variables aren't factoring in. If the tires are filled with nitrogen there will be fewer of those variables, but I still wouldn't use the dealer's supposed inflation pressures as any kind of standard.
Check my earlier posts on this thread, I use ones from AccuGage (sheesh, I hate those cutesy spellings
OK, OK...it's another one of those "how serious do you really want to get?!?" subjects, and you can do OK with a gauge that's off as long as you give it some thought..well, assuming the gauge is at least consistent.
(Oh, and off-topic, but no way would I run around with 32psi in tires! The folks at VID have repeatedly peeled tires off rims at pressures like that on all sorts of vehicles, resulting in some spectacular crashes. Guess what the real explanation for Ford Explorer roll-overs was
By sidewall max rule. So on my door jam it says 35Psi. So u think i need 31.5 Psi? Because whenever i go for oil change my dealer always fill up to 32 as u can see here: http://img23.imageshack.us/img23/2893/18092011081919pm.jpg.
Accumulator
Well-known member
GanJa786 said:
What's max for a tire is what's on the tire's sidewall, not the sticker in the doorjamb. Vehicle manufacturers use all sorts of criteria when determining what to put on the sticker, and many of those criteria have nothing to do with how well a vehicle handles. E.g., low inflation pressures make a vehicle have a "softer ride" which most people like.
FWIW (and maybe that's "not much" :chuckle: ) at most every driving school/track day/etc. I've ever attended the rule-of-thumb is "forty square" (meaning 40 psi in all four tires). Some people run more, but I've never had *anybody* recommend less when doing serious driving. These are situations where it's not really all about maximum handling, but also about *safety*.
Note that even tread wear, and long tire life do *not* always indicate optimal tire pressure.
I don't mean to lecture you, or to impose an opinion that others might disagree with, much less enter into some :argue but as I said, Tony Scotti and his people at the Vehicle Dynamics Institute have done an awful lot of testing in this area and their tests cofirm what I learned through trial-and-error. Generally, most tires are under-inflated, whether from people neglecting them or manufacturers/dealers recommending goofy-low pressures to make vehicles ride soft. Again, that was the real story behind all the Ford Explorer crashes (well, that and people not respectding the laws of physics).
Oh, and I notice the dealer didn't check your spare. If you have run-flats (i.e., no spare) that's OK, but otherwise I'd sure ascertain that your spare tire has the recommended (max
) pressure in it. People don't think about that until they need the spare and find out it's lost air and is just as flat as the flat tire that made them get it out 
tom p.
Active member
Shiny Lil Detlr said:
Both mine have the rubber sleeve. I think it can be purchased for $3, and I do recommend using it.
The digital gauges I own have been the most inaccurate, which is quite a disappointer given the cost. Both the ones I have are off by 3 - 5psi.
Mr. Ganja, what kind of car are we working on in your example?
What does the Owner's Manual quote for recommended pressures with your normal load, probably just 1 person.
The rules (FMVSS110) in the USA say that the door pillar label shows MAX LOAD only...meaning 5 people and 5 suitcases. Great, if you're a taxi driver.
I don't think Canada has implemented this ridiculous rule, nor has the ROW. I believe your label will show different inflation pressures compared to the identical car sold in the USA.
tom p.
Active member
GanJa786 said:
OK, I assume you mean 35psi in all four tires. Nothing wrong with starting there and decide if the ride quality is good for you. (I would probably do 35Front, 32rear in an attempt to equalize the contact patch since there's not much weight on the rear wheels unless you load the car up.)
You probably have to reset (store new values) the TPMS system so you don't get warnings.
You really don't need to spend more than $15 on a good gage. Again, I'd bypass the electronic ones. The most accurate are the old $2 pencil style gages or something like the legendary AccuGage, assuming you can find it in Ca. I think Syracuse and Milton are two solid choices for a pencil style gage for a couple of dollars.
Brad B
New member
I spend a lot of time on the track where proper set up, including tire pressure management, is critical. A really accurate guage (as well as a tire heat measuring device-pyrometer, and hardness gauge-durometer) is critical. For street use, obviously this is not as necessary-but it helps. I have had a lot of experience with many different types of gauges. I have drawers full of ones I have tried and abandoned, as well as a few that I use and trust. The best ones are not cheap. Dial gauges are absolutely the best, but not all are made the same. Good ones are more accurate in all atmospheric conditions, more reliable, last longer and have pressure hold and bleed valves.
Here is a link with some useful info on what to look for in a gauge. Longacre Racing Online -- Tech Article "How to Choose Your Tire Gauge"
Longacre, Intercomp, and Moroso are a few brands I like. Personally, I find AccuGage to be junk. But that's my experience compared to others.
Here is a link with some useful info on what to look for in a gauge. Longacre Racing Online -- Tech Article "How to Choose Your Tire Gauge"
Longacre, Intercomp, and Moroso are a few brands I like. Personally, I find AccuGage to be junk. But that's my experience compared to others.
Accumulator
Well-known member
Brad B.- Since you do a lot of track days, I'm curious what psi you run and if there's a rule-of-thumb that others follow (like that "40 square" I've encountered).
Also curious about why you consider the AcuGage to be junk. Not in any way intended as an :argue or challenge, just curious.
Also curious about why you consider the AcuGage to be junk. Not in any way intended as an :argue or challenge, just curious.
Brad B
New member
Accumulator said:
The key to properly runing a tire is really built upon heat, not psi. What you want is for the heat in the tire tread to be relatively even all the way across the tread. Typically you measure in three points, inside, outside and middle. The more even it is reflects, among other things, how the contact patch is spread on the tarmac. If the temp in the middle of the tire is too high, the tire is over-inflated. If that measurement is the lowest, then it's under-inflated. If one of the outsides is over or under it reflects sidewall deflection and camber. Physically, you want the tire to be the optimum shape while in use. There are a lot of variables and each car set up as well as tire design adds to the complexity. As the tire heats up, temperatures rise, pressures rise and the target moves accordingly.
Obviously tire manufacturers have done their R&D and suggest optimum results when their tires reach a certain recommended pressure. On track tires, let's say Toyo RA-1, for instance, the sweet spot is about 42lbs for Cayman S. (Mid engine, RWD, 3500lbs) At the start of a track session I might fill at 32-34lbs to compensate for the upcoming heat build and pressure build. Adjustments are made frequently. Toyo says this is the best for max adhesion. (They also suggest min and max heat ranges) From there I make adjustments for suspension mods and driving style. I may end up with 38F and 42R. Actually, because of the differences in the track, (number of righthand corners vs lefthand corners, speed and braking needs) each tire will have different pressures. That's why you get more finite adjustments by reading with a pyrometer after every run. Every car is different. And different tires have different sweet spots of adhesion.
Street driving is less critical but the same principals apply. And the net result is better mileage, better handling and grip, longer wear. The same things you want on the track. I make temperature readings on all my street cars so I know, in return, what psi to run them at. Anal retentive? Yes. But then why not as much with this as we are with detailing. :0
Not sure I answered your question in my ramblings. And you surely knew this already.
As for AccuGage, I have probably had 5-6 of them over the years (dial and digital) and while half of them just crapped out from bad seals, others have proven innacurate/inconsistant when compared with a test of multiple others. You know, take 4 guages and see what reading you get. Odd man out gets the heave ho. They don't seem to be very reliable either in the rigors of track day use where you may use it 50 times a day. That's been my luck with them, anyway. The best ones, IME, have been Longacre. Those have been with me the longest.
Accumulator
Well-known member
Brad B.- You take the temp/inflation to a much higer level than I do :bow
Interesting that your "start low and let it build" as opposed to "starting high and bleeding off", but again you're being much more meticulous about it.
On street driven vehicles, do you find that the pressures optimal/preferred for handling always go hand-in-hand with longer treadlife? It simply never works that way for me on our current vehicles and while I decided to quit worrying about it long ago (eh, so I replace tires more often, not the primary concern in my case) it does still make me wonder at times.
Sorta a case of chasing a moving target- what will be the optimal inflation for any given moment? In an emergent situation that couldn't be predicted....tires cold/hot, vehicle heavily loaded/not, what's the setting that's most likely to average out if you know what I mean.
I keep one of my calibrated/matched AccuGages unused as a control and my "regular use" one still agrees with it. Heh heh, now you have me all paranoid and I'll sure keep the Longacre brandname in mind
Eh, you have me thinking how I haven't done any track days (well, with my own vehicles ) since forever and I really oughta do that some time...
Interesting that your "start low and let it build" as opposed to "starting high and bleeding off", but again you're being much more meticulous about it.
On street driven vehicles, do you find that the pressures optimal/preferred for handling always go hand-in-hand with longer treadlife? It simply never works that way for me on our current vehicles and while I decided to quit worrying about it long ago (eh, so I replace tires more often, not the primary concern in my case) it does still make me wonder at times.
Sorta a case of chasing a moving target- what will be the optimal inflation for any given moment? In an emergent situation that couldn't be predicted....tires cold/hot, vehicle heavily loaded/not, what's the setting that's most likely to average out if you know what I mean.
I keep one of my calibrated/matched AccuGages unused as a control and my "regular use" one still agrees with it. Heh heh, now you have me all paranoid and I'll sure keep the Longacre brandname in mind
Eh, you have me thinking how I haven't done any track days (well, with my own vehicles
) since forever and I really oughta do that some time...
Brad B
New member
You generally start low on the track because cold, overinflated tires are very slippery. Low pressures give more flex at the start but that flex generates heat and within a couple laps things start improving.
Tire wear in the real world happens so slowly that it's hard to say if all the anal retentive stuff is worthwhile. Probably not. but on the track tire wear is like 100 times greater. (I go through 2-3 sets of tires a season.) So I just assume the benefits I see there will translate.
Yea, pressures are a moving target. But it keeps geeks like me busy.
Tire wear in the real world happens so slowly that it's hard to say if all the anal retentive stuff is worthwhile. Probably not.
but on the track tire wear is like 100 times greater. (I go through 2-3 sets of tires a season.) So I just assume the benefits I see there will translate. Yea, pressures are a moving target. But it keeps geeks like me busy.