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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / August 2006Got a question for someone who lnow about auto tires out there..
Got a question for someone who lnow about auto tires out there. I recently had to get new tires on car and when I asked the tire person about what to keep the pressure at he said 30 PSI. When I mentioned that the tires called for 44 PSI he said that you go by what the vehicle calls for which is 30 PSI rather then what the tires called for even though the tires looked soft at 30 PSI to me. Is there anyone out there that works at an auto repair or tire place that could offer me some insight here ?? At present I am about to split the difference and carry the pressure at 37 PSI. Opinion wanted. TIA > Got a question for someone who lnow about auto tires out there. > [quoted text clipped - 9 lines] > > Opinion wanted. TIA As long as the tires meet OEM specs, and the vehicle is not overloaded you should go with the manufacturer's recommended tire pressure as indicated on the decal (usually attached to the driver's door pillar  SignatureDisclaimer: Due to the nature of solving problems over the internet being mostly guesswork, please do not consider the above recommendations as the only possible solutions. -- Kevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green). >> Got a question for someone who lnow about auto tires out there. >> >> I recently had to get new tires on car and when I asked the tire >> person about what to keep the pressure at he said 30 PSI. >> When I mentioned that the tires called for 44 PSI he said that you go by what >> the vehicle calls for Refreshing! All too many tire store employees adamantly refuse to adhere to the vehicle manufacturer's specs. >> which is 30 PSI rather then what the tires >> called for even though the tires looked soft at 30 PSI to me. Radial tires often look a little soft. >> Is there anyone out there that works at an auto repair or tire place >> that could offer me some insight here ?? At present I am about to [quoted text clipped - 5 lines] >should go with the manufacturer's recommended tire pressure as indicated on >the decal (usually attached to the driver's door pillar Exactly! NOWHERE on the tire does it say what pressure is called for. If you read the entire statement it says" xxx maximum load at xxx maximum pressure. CONSULT PLACARD IN VEHICLE." Unless the vehicle manufacturer badly skimped on tire size the tire typically is not loaded anywhere close to maximum capability and does not require maximum pressure nor is maximum pressure appropriate. While under-inflation has obvious bad consequences, over-inflation is not a whole lot better. It reduces contact patch area and thus compromises handling. Over-inflated front tires can cause a vehicle to wander all over the highway as if intoxicated due to promoting oversteer. This has to do with the ratio of sidewall slip angles between the front and rear tires. The handling of a vehicle is dependent on many factors including spring rate, roll center, front/rear weight percentages etc. etc. The vehicle manufacturer's chassis engineering department knows all these things about a particular application. The tire manufacturer does not know if the tire is going on the front or the back -- often calling for different inflation pressures -- let alone what make and model vehicle it will be mounted on. Just for one example many FWD cars will be so front-heavy that they call for 32 front/26 rear. Then again, my 3/4 ton truck at maximum load -- which load is imposed primarly on the rear axle -- wants 55 front/85 rear. Rarely does a week go by where I do not succesfully address handling and ride complaints -- often with the owner gathering estimates for struts or shocks -- by setting the tires to the spec on the door pillar, glove box lid or wherever. Don www.donsautomotive.com >> Got a question for someone who lnow about auto tires out there. >> [quoted text clipped - 13 lines] > you should go with the manufacturer's recommended tire pressure as > indicated on the decal (usually attached to the driver's door pillar Isn't this exactly the sort of thing that got Ford in trouble with the Explorer a few years back? SignatureTeGGeR® >>> Got a question for someone who lnow about auto tires out there. >>> [quoted text clipped - 16 lines] >Isn't this exactly the sort of thing that got Ford in trouble with the >Explorer a few years back? What happened with the Explorer is that they were a little bit skimpy on tire capacity for the vehicle. They also had a problem with a high center of gravity due to engine placement necessary to clear the twin I-beam suspension. So they had a handling problems which they were able to mimimize with relatively low tire pressures. Unfortunately the crap Firestones couldn't take the heat. Ideal tire pressure is a compromise involving lots of parameters. Unfortunately with the Explorer the parameters were unworkable. Had they gone up one tire size and used quality rubber there would have been no problem at all with the specified 26 PSI. Don www.donsautomotive.com >>Isn't this exactly the sort of thing that got Ford in trouble with the >>Explorer a few years back? [quoted text clipped - 12 lines] > Don > www.donsautomotive.com Twin I beam on an Explorer ? You have to be kidding. Anyway the problem was high center of gravity and the reaction of the lovely leaf spring rear suspension to a blow out on the rear. I would never have a leaf spring suspension - even on a go cart. Terrible compromises in the name of economy. > Twin I beam on an Explorer ? You have to be kidding. > Anyway the problem was high center of gravity and the reaction of the lovely > leaf spring rear suspension to a blow out on the rear. I would never have a > leaf spring suspension - even on a go cart. Terrible compromises in the > name of economy. Uh huh. Guess the Corvette's suspension with a transverse leaf is terrible in your eyes then. Leafs actually have advantages in certain situations. One of them is simplicity - there's no need for 4 or 6 or 14 links to control the axle movement, the leafs do it. They're also a progressive rate spring. >> Twin I beam on an Explorer ? You have to be kidding. >> Anyway the problem was high center of gravity and the reaction of the [quoted text clipped - 8 lines] > simplicity - there's no need for 4 or 6 or 14 links to control the axle > movement, the leafs do it. They're also a progressive rate spring. Coils and links always beat 'em in a conventional vehicle. Cost more - work better, much more suspension travel and better variable rate control. I don't suppose you are claiming the Explorer had the Corvette's transverse leaf and independent rear susp. ? I don't remember if my '71 Corvette had the transverse leaf (certainly it was not the plastic wonder on the latest ones). That 71 would not maintain a straight line on a slippery road with any kind of tire, or tire pressure - wandering rear end. It is unfair to mention it in the context of any modern Corvette, sorry. It was poor design in many ways and cost me plenty of time and pain to keep in on the road. That's another story - I think the tires and suspension were about the only things that did not give me trouble. > I don't suppose you are claiming the Explorer had the Corvette's transverse > leaf and independent rear susp. ? No, and you couldn't pay me to drive a Ford. You claimed: "lovely leaf spring rear suspension to a blow out on the rear. I would >> never have a leaf spring suspension - even on a go cart. Terrible >> compromises in the name of economy." I'm not saying that for most cars that leafs are inferior, but to claim that leaf springs are ALWAYS inferior is wrong. I agree that leaf springs are pretty much a nice 1800 era technology, but in certain circumstances they still work pretty darn good. Ray > >> Twin I beam on an Explorer ? You have to be kidding. > >> Anyway the problem was high center of gravity and the reaction of the [quoted text clipped - 22 lines] > and pain to keep in on the road. That's another story - I think the tires > and suspension were about the only things that did not give me trouble. Vette is still using a transverse spring in the rear and Volvo used them in the mid to late 1990's. I don't understand how those cars could be so successful and at the same time have such poor suspensions. Something is incorrect in your story.... > > >> Twin I beam on an Explorer ? You have to be kidding. > > >> Anyway the problem was high center of gravity and the reaction of the [quoted text clipped - 27 lines] > could be so successful and at the same time have such poor suspensions. > Something is incorrect in your story.... "Transverse leaf spring" is somewhat misleading, since the spring is held in place in the center, and what happens on one side does not affect the other. Also with a transverse spring, the spring is not acting like a control arm (as I recall). Most of what is 'wrong' with a leaf-spring-per-side arrangement doesn't exist for a transverse-leaf arrangement. That's the part he's missing, I think. Dave > > > >> Twin I beam on an Explorer ? You have to be kidding. > > > >> Anyway the problem was high center of gravity and the reaction of the [quoted text clipped - 31 lines] > held in place in the center, and what happens on one side does not > affect the other. Well, that's common and reasonably correct usage of the term actually. Where the transverse mounted spring is connected to the body isn't explicitly stated, but center mounting is assumed in most automotive applications. Axle design will usually determine whether one wheel is independent or dependent on the other. In fact Henry used a center mounted transverse spring in the T, but the solid axle caused one side to be affected by the other. > Also with a transverse spring, the spring is not acting like a control > arm (as I recall). Most of what is 'wrong' with a leaf-spring-per-side > arrangement doesn't exist for a transverse-leaf arrangement. That's the > part he's missing, I think. > > Dave voter <w3cyykcv7q8gjpv@jetable.org> wrote in article <JpednXQEmZVduEvZnZ2dnUVZ_s2dnZ2d@comcast.com>... > I would never have a > leaf spring suspension - even on a go cart. Terrible compromises in the > name of economy. Yeah ! The highways are littered with the early, parallel-leaf-spring-equipped Mustangs and Camaros that flipped over for no reason whatsoever...... > voter <w3cyykcv7q8gjpv@jetable.org> wrote in article > <JpednXQEmZVduEvZnZ2dnUVZ_s2dnZ2d@comcast.com>... [quoted text clipped - 7 lines] > no > reason whatsoever...... Yes indeed - the Mustangs were very much like the Explorer, including the I-beam front suspension and high center of gravity, and overloaded tires. God - why do I waste my time on these newsgroups ? They only exist for people to make stuff up and spout it to other idiots like me. voter <w3cyykcv7q8gjpv@jetable.org> wrote in article <qvSdnfcuJeqsZ0rZnZ2dnUVZ_oudnZ2d@comcast.com>... > > voter <w3cyykcv7q8gjpv@jetable.org> wrote in article > > <JpednXQEmZVduEvZnZ2dnUVZ_s2dnZ2d@comcast.com>... [quoted text clipped - 9 lines] > > > Yes indeed - the Mustangs were very much like the Explorer, including the > I-beam front suspension and high center of gravity, and overloaded tires. > > God - why do I waste my time on these newsgroups ? They only exist for > people to make stuff up and spout it to other idiots like me. Look at your own statement, a.shole !!!! > >> I would never have a > >> leaf spring suspension - even on a go cart. You were speaking about leaf spring suspensions in general - NOT being Explorer-specific........... The part about you being an idiot, however, was DEAD-ON !!!!! > voter <w3cyykcv7q8gjpv@jetable.org> wrote in article > <qvSdnfcuJeqsZ0rZnZ2dnUVZ_oudnZ2d@comcast.com>... [quoted text clipped - 29 lines] > > The part about you being an idiot, however, was DEAD-ON !!!!! DEAD-ON is right - I'm an idiot for wasting time jaw'ing with nit wits. >Got a question for someone who lnow about auto tires out there. > [quoted text clipped - 9 lines] > >Opinion wanted. TIA You don't say what kind of vehicle you have. If it is a truck and you change the load range rating, you may need to use a different pressure. If you installed the original spec tire that came on the vehicle, you need to follow the vehicle manufacturer's recommendation unless you have good reason not to do this that may include other vehicle modifications. Once you leave the OEM tire specs, you are on your own to figure out the best pressure or foillow someonelse's recommendation assuming they have any basis for their recommendation. Lugnut >>Got a question for someone who lnow about auto tires out there. >> [quoted text clipped - 20 lines] >someonelse's recommendation assuming they have any basis for >their recommendation. Most often they do not! don] www.donsautomotive.com >Lugnut Hey Don, what kind of tire pressure do you suggest for radials on dirt? All the books and all the recommendations I get are for guys running bias ply race tires. They're BFG Radial TA's on a heavy Camaro. Been running around 20psi, thinking of going down to 16-18 because that's what everyone says but wondering if that's too low - and like I said, they're all running bias ply tires in different classes than I am. Ray > Hey Don, what kind of tire pressure do you suggest for radials on dirt? > All the books and all the recommendations I get are for guys running [quoted text clipped - 6 lines] > > Ray always listen to what the manufacturer gave specs. for. >>Hey Don, what kind of tire pressure do you suggest for radials on dirt? >>All the books and all the recommendations I get are for guys running [quoted text clipped - 8 lines] > > always listen to what the manufacturer gave specs. for. <sigh> It's a race car. An oval track dirt track race car. >Hey Don, what kind of tire pressure do you suggest for radials on dirt? I have no clue, I have never done it. What about stagger? Can you run different size tires on the back? I assume you are allowed a locked rear end. Do you have a stagger gauge or can you borrow one? I suspect -- but do not know for a fact -- that it would be harder to adjust radial tires for stagger through air pressure. With bias ply tires on dirt we work with what we feel is a fairly large "window" of acceptable pressures in regard to traction and use pressures of the rear tires to fine-tune stagger which we consider the most critical. Front wheel stagger pretty much doesn't make a rat's a.s! Don www.donsautomotive.com >All the books and all the recommendations I get are for guys running >bias ply race tires. > >They're BFG Radial TA's on a heavy Camaro. Been running around 20psi, >thinking of going down to 16-18 because that's what everyone says but >wondering if that's too low I typically run 8-10 on my left rear! > - and like I said, they're all running bias >ply tires in different classes than I am. > >Ray Don <don@NO-SPAMdonsautomotive.com> wrote in article <lu8bd2ljtcsm2c06ljdahmr1shhvo4ru8u@4ax.com>... > >Hey Don, what kind of tire pressure do you suggest for radials on dirt? > [quoted text clipped - 24 lines] > > > >Ray If you run two tires with exactly equal circumferences, but the LR has that circumference @ 15 p.s.i. and the RR has it @ 30 p.s.i., you will have a difference in loaded radius when the tires are on the car and the car is on the ground. THAT is stagger. The wheels are turning about the loaded radii. . >Don <don@NO-SPAMdonsautomotive.com> wrote in article ><lu8bd2ljtcsm2c06ljdahmr1shhvo4ru8u@4ax.com>... [quoted text clipped - 34 lines] > >The wheels are turning about the loaded radii. Understood. Therefore the stagger gauge does not tell the whole story. To complicate things further, true stagger will change with weight transfer when cornering. I have been meaning to mark some tires, put them on the front of my racecar and roll it forward measuring the turns and come up with a rought formula for the inflation factor. Don www.donsautomotive.com Don <don@NO-SPAMdonsautomotive.com> wrote in article <c65cd2pjufsrbphntl1ptf3ajtduuh53sa@4ax.com>... > >Don <don@NO-SPAMdonsautomotive.com> wrote in article > ><lu8bd2ljtcsm2c06ljdahmr1shhvo4ru8u@4ax.com>... [quoted text clipped - 19 lines] > >> >They're BFG Radial TA's on a heavy Camaro. Been running around 20psi, > >> >thinking of going down to 16-18 because that's what everyone says but > >> >wondering if that's too low > >> [quoted text clipped - 21 lines] > Don > www.donsautomotive.com I built a loaded radius tester - it looks a LOT like a spring rater - and do ALL my tires according to corner weights and loaded radii. You can take two tires with circumferential measurements of, let's say, 84-inches. If one tire needs 30 p.s.i. to reach that 84-inches, and the other tire needs 28 p.s.i. to reach the same 84-inches, then you're going to have two VERY different tires with two different loaded radii and two different contact patches when one is exchanged for another - even though they both read 84-inches in circumference OFF the car. When my driver wants a certain change on a pit stop, I can give it to him, exactly - because I know the weight of the corner, and I know the loaded radius of the current tire.. I can also give him the exact, same loaded radius as the current tire. All I need to know is the corner weight where the tire will be mounted, and the loaded radius of the tire that is currently on the car - which I probably already measured and recorded anyway. NASCAR would not allow one of my customers who runs with them to use this setup after I built one for him and they saw it, so he just mounts the tire on the corner of the car where it will be run, then measures it with the car's weight sitting on it. A little more labor-intensive, but he has a bit more tire information than the measuring tape and stagger-stick guys. Of course, he plays around on the tester with the tires he takes home - just to learn a little more about them for the next time. What you COULD do, would be to mount the tire on the car in whatever position it will run, set the car down on a level floor, then measure from the floor to the edge of the rim. Once the chassis feels neutral, THAT would be the base you look for. You could also add/remove tire pressure to see what sort of changes it makes in the loaded radius. While you could use a tire tape to the sixteenth-of-an-inch, I use a vernier height guage to the thousandth. >>Hey Don, what kind of tire pressure do you suggest for radials on dirt? > [quoted text clipped - 10 lines] > Don > www.donsautomotive.com Was running a 235/60 LR and a 235/70 RR - about 1.5" taller. The rear end is welded solid. I'm switching to 275/60's on the front and RR because the rules allow it and I needed tires anyway. I just keep getting wildly different #'s for pressures, and I'm going lower, but like I said, everyone I ask seems to run bias plys and in different classes. :) >>>Got a question for someone who lnow about auto tires out there. >>> [quoted text clipped - 27 lines] > >>Lugnut EXACTLY!! Lugnut > Got a question for someone who lnow about auto tires out there. > [quoted text clipped - 9 lines] > > Opinion wanted. TIA Your car should have a sticker that shows the minimum and maximum pressures front and rear. The minimum is probably around 30psi or lower and the max is probably close to 40psi. I've always run tires to the high side of the recommended range and gotten good tire and gasoline milage without having the car ride like a lumber truck. |
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