EcoModder.com

EcoModder.com (https://ecomodder.com/forum/)
-   Introductions (https://ecomodder.com/forum/introductions.html)
-   -   Tire Engineer here - concerned about hyperinflating tires (https://ecomodder.com/forum/showthread.php/tire-engineer-here-concerned-about-hyperinflating-tires-2522.html)

CapriRacer 05-24-2008 06:59 AM

Tire Engineer here - concerned about hyperinflating tires
 
I've been reading about folks inflating tires over the maximum printed on the sidewall and this is one site where this has been reported. I've joined just to add technical background as to why that is a bad idea!

trikkonceptz 05-24-2008 09:01 AM

Welcome ... and OK, where is this information, you kinda left us hanging ...

SVOboy 05-24-2008 09:10 AM

welcome to ecomodder...i dont personally inflate past the max, but i know many who do...what technical issues do you speak of?

Lazarus 05-24-2008 09:19 AM

Quote:

Originally Posted by CapriRacer (Post 28107)
I've been reading about folks inflating tires over the maximum printed on the sidewall and this is one site where this has been reported. I've joined just to add technical background as to why that is a bad idea!

Great. Welcome to the site it will be good to have some expertise on the matter. What's your background and reported by who?

Daox 05-24-2008 09:19 AM

Welcome to the site. As the others have mentioned I'd definitly like to see some testing that you have done to prove this is a bad idea. We have many people running max sidewall pressures here without any problems, perfect tire wear, and greatly increased tire life.

RH77 05-24-2008 11:28 AM

Quote:

Originally Posted by CapriRacer (Post 28107)
I've joined just to add technical background as to why that is a bad idea!

(from an old "Kids in the Hall" episode)...

...Ya lost me :confused:

Folks have to back up claims here. We crave data.

RH77

chrislk1986 05-24-2008 12:44 PM

My tires were 11psi over inflated. They're mud tires too. I took corners fast and did hard braking to test failure. No problems, but I reduced pressure by 5psi to be on the safe side. (the tires are at least 5 yrs old too, but taken care of).

Chris

Gone4 05-24-2008 02:48 PM

Perhaps we should discuss how poor the gages are on the car tire pumps. They can be off by over 10 psi in my experiences.. They always warn bicyclists not to use them for that reason. Also, they heat up a lot so you increase pressure at highway speeds if you inflate cold. I would say the concern isn't going beyond the limit of the sidewall by a few psi, but in how you do it and using what equipment, If you have other data, please enlighten us.

tasdrouille 05-24-2008 03:04 PM

Frank, I think quite a lot of threads here and on other FE forums have got to the bottom of this as far as RR is concerned. What do you believe has been left uncoverred?

The only concern I still have is related to some areas of the safety factor, as I haven't seen much data appart from annecdotal evidence.

ihatejoefitz 05-24-2008 03:24 PM

http://www.officer.com/article/artic...on=19&id=27281

This shows the relationship between temperature and tire pressure. Their test indicates that for a 20 minute drive you can expect ~+4Psi.
http://www.tirerack.com/tires/tirete...e.jsp?techid=1

Quote:

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when encountering potholes or debris in the road, as well as experience irregular tread wear. Higher inflated tires cannot isolate road irregularities as well causing the vehicle to ride harsher and transmit more noise into its interior. However, higher inflation pressures reduce rolling resistance slightly and typically provide a slight improvement in steering response and cornering stability. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures.
http://www.tirerack.com/tires/tirete...e.jsp?techid=1

-Notice, no mention of higher than normal wear, or blowouts.

tasdrouille 05-24-2008 03:37 PM

You are right about the size, I haven't seen much data either. But I was talking about the pressure relation to RR.

chrislk1986 05-24-2008 05:41 PM

I actually watched a show on the History channel about rubber or automobiles, but they had tires and showed what happens to a tire at high speed, but in slow motion. It's basically what they have on tirerack http://www.tirerack.com/tires/tirete....jsp?techid=72.

They have a lot of stuff there.

adam728 05-24-2008 08:36 PM

Quote:

Originally Posted by ihatejoefitz (Post 28164)
http://www.officer.com/article/artic...on=19&id=27281

This shows the relationship between temperature and tire pressure. Their test indicates that for a 20 minute drive you can expect ~+4Psi.
http://www.tirerack.com/tires/tirete...e.jsp?techid=1

http://www.tirerack.com/tires/tirete...e.jsp?techid=1

-Notice, no mention of higher than normal wear, or blowouts.

Right in the text you quoted it mentioned irregular tread wear.
:confused:

SVOboy 05-24-2008 08:58 PM

Yeah, irregular tread wear could be an issue, but in the people who have done it for 50k+ they haven't reported it.

cfg83 05-25-2008 01:07 AM

CapriRacer -

Quote:

Originally Posted by CapriRacer (Post 28107)
I've been reading about folks inflating tires over the maximum printed on the sidewall and this is one site where this has been reported. I've joined just to add technical background as to why that is a bad idea!

Welcome to EM! Looking forward to what you have to say.

CarloSW2

kompressor 05-25-2008 01:45 AM

I may be able to provide some useful info here as I know a ton about tires because of my racing school and driving on the track.

on the track my tires have gone up as much= as +12 psi over what i had them inflated . as an example i run my tires at 38psi front and 36 rear on the c230 for handling reasons to help curb my understeer problems and at the end of a particular 20 minute heat, on a 100 degree day my fronts were 50psi and the rear were 47psi the tires themselves were very very hot. the brakes were near 500 degrees and the tires were around 170, the fenders were over 200 degrees from the heat rolling off the wheels.

obviously noone drives like that on as street but there is a big relationship between temperature and pressure. at the track i use a tire pyrometer its like a needle you poke in the tread to measure tread tempurature. use the lazer one for the rest. also you do need a very acurate tire pressure guage being off by 1 psi on any particular tire can make handling weird, they sell em at racing supply stores. I would order the things they sell not the stuff at at pep boys or auto zone for tire monitoring duties.

at the track you measure the tempurature of the outside, middle and inside of each tire this gives you a map of how your tire pressure is working and will indicate how the tire will wear.

key: inside/middle/outside in degrees

as an example ideally on a 160 degre tire youd see 160/160/160

if a tire is overinflated you might see 145/180/145

if underinflated 155/135/155

numbers here are exaggerated for examples sake

the over inflated tire has a hump in the middle and the middle will go bald first and you will have lots of tread left on the outside.

the under inflated tire has a trough in the middle and the edges will go bald and have lots of tread left on the middle.

I am no tire engineer I do imagine that there is some over engineering, ie a tire says its max is 50 maybe you could put in 65 before it would be really dangerous but I dont know how you could tell what would be an ok amount. but thats cold and when you drive 80-100mph on the highway on a nice hot day for an hour I'd worry about explosive tire pressure loss with a blowout.

CapriRacer can most likely answer the (how much they overengineer tires) question

everyone here should get good tire pressure guages and tire pyrometers too you can better monitor your tires health that way, also keep those pieces of equipment in your car always use the tire pressure guage you own and always the same one every time, we have a gauge in each of our cars it stays with that car permanently so that tire pressures are accurate

obviously under inflated tires cost you gas mileage because they are so soft, but over inflated tires i think works because if you pump them up enough then they bulge in the middle the more the buldge the less of the tire touches the road and the less rolling resistance you have, but the bulge area will wear faster. but this is also dangerous because you really do not know how small your tires contact patch is thats all that connects your car to the road is your tires. and if you need to stop in an emergency or it rains you might be in big trouble on tires that are too over inflated think bicycle wheel instead of car tire and thats what you get out of a grossly overinflated tire.

I think it would be safer to just downsize your tire width and run near max psi you still get a smaller contact patch but you can operate the tire at a safer pressure so the contact patch stays flat which is what you want for optimal wear, and maximum traction.

ie if you have tires that are 205 width get a set of 195's or 185's that will drop your contact patch a few square inches per tire and you can then operate them at correct pressures while still achieving less rolling resistance. I always stay at least 10psi under the posted max on my tires. I do drive spirtidly quite a bit and would hate to have a tire go over max due to temperature.

tire rack is actually very helpful they will be able to tell you if say a 195mm tire will fit on your factory wheels if it wont you will need to buy a narrower set of wheels ive done that in reverse for track use gotten wider wheels than stock so that i can run 255mm tires instead of stock 225mm this also increases my contact patch and therefore increases traction.

I don't know what the safe trade off is on tire width I am a big believer in having sticky enough wheels for emergency braking and rainy weather.

i think im going to go down to 195mm on the c230 first and see how that is if its too skittish and easy to have the car do a random 360 on me i will maybe go up to a 205, as I start my ecomodding process I can give my feedback on tires.

I have not even tapped the tire performance vs temperature issues yet and this is already way to long, but let me briefly say that a tire has to warm up before maximum stickyness/traction is achieved its why cars wreck while racing so much on the first lap of races because noones tires or brakes are up to tempurature so they do not have peak traction it takes a lap or 2 to get the tires good and warm. so a tire used by everday folks on the road is really not hot enough to get its best traction. that is also why they use different compounds for street tires. ones that perform better at lower temperatures.

ok I am done for now sorry that was so wordy

JohnnyGrey 05-25-2008 02:36 AM

I told you guys this was bad! Sidewall max is just that. It's not the car manufacturer recommending a comfortable number, it's max you should run them at. You guys who are overinflating are counting on margins of error and safety, thinking they don't apply to you. Tire mfg's aren't responsible for errors in crappy pressure gauges, so that's not one of the margins. One day might be significantly hotter than the next, or you might hit a pothole, or you might need to slam on your brakes. When you need your tire the most, it might blow up.

Saying I know _______ has been running his tires ___% over, doesn't say too much. If you use the same tire, the lot it came from might not be as resilient and you might end up blowing yourself up or rolling your car because of it. You'll never know how much pressure is too much until something really, really bad happens.

Overinflating has its limits, and for each psi, you get diminishing returns. How much safety do you want to forfeit for that fraction of an MPG?

trikkonceptz 05-25-2008 11:28 AM

If the underlying argument here is contact patch why not test it. Take YOUR tire down to 36 psi or whatever, lift the car, roll some water based paint over the tread and drop the car on some heavy duty paper. Then re-inflate to YOUR max psi and repeat, then measure. If the patches are the same, case closed right? This should even show weight distribution by how much of the treads are printed on the paper, to see which treads are making contact and how much.

Once that is laid to rest the next question would be side wall flexing. Now you guys keep talking about air and it varying pressure with heat. What about Nitrofill? Which has a higher balance of nitrogen than air and claims to stabilize the heat expansion in tires. Which is why aircraft and NASCAR use it.

ihatejoefitz 05-25-2008 11:40 AM

Quote:

Originally Posted by adam728 (Post 28203)
Right in the text you quoted it mentioned irregular tread wear.
:confused:

Irregular =/= higher than normal, they could just as easily mean lower than normal. Furthermore, there is a huge difference in somebody saying irregular tire wear could happen, and that it will happen. I've seen this statement posted a few time on this site with no data to support it.

JohnnyGrey 05-25-2008 11:47 AM

Quote:

If the underlying argument here is contact patch why not test it. Take YOUR tire down to 36 psi or whatever, lift the car, roll some water based paint over the tread and drop the car on some heavy duty paper. Then re-inflate to YOUR max psi and repeat, then measure. If the patches are the same, case closed right? This should even show weight distribution by how much of the treads are printed on the paper, to see which treads are making contact and how much.
I seriously doubt that the correlation between contact patch size and rolling resistance is linear. The ultimate goal is not contact patch size, but MPG. Forget intermediate details like patch size and just produce an MPG to PSI plot. You'll see the diminishing returns I'm talking about.

SVOboy 05-25-2008 11:49 AM

But there's diminishing returns for anything related to fuel economy, that's not a new idea, nor do I think it's important to the question of safety.

trikkonceptz 05-25-2008 12:19 PM

Wouldn't the optimal efficiency of a tire be contact patch size equals tire size?

Meaning if your vehicle has 185 / 60 / 15 then the patch size should be 185mm. I heard a way to measure this using a simple string around the bottom of the tire and some formulas. I'll dig it up and post it to see if we can prove it true.

JohnnyGrey 05-25-2008 12:34 PM

Quote:

But there's diminishing returns for anything related to fuel economy, that's not a new idea, nor do I think it's important to the question of safety.
It is important to safety because as you start to overinflate, MPG gains level off and your safety starts to fall off rapidly to the point where you're giving up a lot of safety to secure a very small amount of economy.

Some of the guys on the Cavalier forums think I'm insane for running my 44psi max tires, at 44psi. Granted, they might be on the other extreme, but do you really want to find out how thick the margin of safety is on your tires? Remember that this margin accounts for manufacturing variances that can't easily be quantified. Just because so and so was fine running at 25% over, you might not be so lucky.

ihatejoefitz 05-25-2008 01:00 PM

Quote:

Originally Posted by JohnnyGrey (Post 28328)
It is important to safety because as you start to overinflate, MPG gains level off and your safety starts to fall off rapidly to the point where you're giving up a lot of safety to secure a very small amount of economy.

At what psi? Sources/data?

trikkonceptz 05-25-2008 01:20 PM

I came across this link: http://www.performancesimulations.co...on-tires-1.htm

It doesn't really answer our questions, but the data collected by the tire manufacturer does illustrate the varying contact patch size in relation to load and PSI.

dremd 05-25-2008 01:47 PM

Quote:

Originally Posted by CapriRacer (Post 28107)
I've been reading about folks inflating tires over the maximum printed on the sidewall and this is one site where this has been reported. I've joined just to add technical background as to why that is a bad idea!

Sweet!

Could you please provide some technical background as to why it is a bad idea?

larryn2o 05-25-2008 02:24 PM

i run 175/50r13 tires , recommended max inflation is 51 PSI . not sure if they qualify as low rolling resistance , but i like the way they look.

trikkonceptz 05-25-2008 02:39 PM

I think we were just taken for a ride folks .. funny how our "tire Engineer" hasn't been back on since the post and really didn't give us any information with his first post.

I think he wanted to spark some argument and was dissapointed when we began a rational conversation ...

Johnny Mullet 05-25-2008 04:27 PM

^ I agree!

Randy 05-25-2008 04:34 PM

Quote:

Originally Posted by trikkonceptz (Post 28348)
I think we were just taken for a ride folks .. funny how our "tire Engineer" hasn't been back on since the post and really didn't give us any information with his first post.

It's too bad really. Tires seem to be pretty complex... they aren't just balloons. I don't think we'd ever settle these arguments without some more understanding of what exactly is going on. Even simple ideas like choosing the lowest rolling resistance tires seem to be complicated by the tire size and pressure.

Lazarus 05-25-2008 04:34 PM

Quote:

Originally Posted by trikkonceptz (Post 28348)
I think we were just taken for a ride folks .. funny how our "tire Engineer" hasn't been back on since the post and really didn't give us any information with his first post.

I think he wanted to spark some argument and was dissapointed when we began a rational conversation ...

Give him time it is a long holiday weekend.

tasdrouille 05-25-2008 05:46 PM

Anyone can be a self proclaimed whatever engineer on the Internet...

This has been a hot and recurent topic for a while. I'll try to dig as much stuff as I can tomorrow when I get some time. Hopefully I'll show up with more than the "trust me, I know" and "it happenned to me" we see way too often.

Johnny Mullet 05-25-2008 07:34 PM

Well, I been a mechanic all my life and about 40% of my work involves tires. Overinflation does not cause any safety or driveability issues unless you go far beyond the suggested pressures. I am currently running 46PSI in my tires that suggest 44PSI and it's been over a month.

kompressor 05-25-2008 09:54 PM

tires really are very complex especially modern tires. from the compound to the belts, and other materials and layers within the tires. modern tires are radials so they bulge a bit at the bottom the part of the tire that hits the ground is flat for several inches front to back, so your contact patch on a tire thats 5 inches wide that has 4 inches front to back would be like 20 square inches per tire.


Quote:

trikkonceptz ;If the underlying argument here is contact patch why not test it. Take YOUR tire down to 36 psi or whatever, lift the car, roll some water based paint over the tread and drop the car on some heavy duty paper. Then re-inflate to YOUR max psi and repeat, then measure. If the patches are the same, case closed right? This should even show weight distribution by how much of the treads are printed on the paper, to see which treads are making contact and how much.
the static contact patch is different from the dynamic contact patch ie when you go around turns and accelerate and brake the load changes on the tire and the sidewalls flex quite a bit in a hard corner with the right pressure your tire will actually use some of its sidewall thats why the treads curve over the edge a bit and are not just on the bottom of the tire. if your over inflated you might get scalloping or the center might wear down etc... I am not saying i know exactly the type of negative tire wear that will happen.

and its all relative 5psi over max maybe theres no difference 20psi over max i bet you see something.

also thats why I brought up taking your tires temperatures before I do it for racing its a very valuable tool for figuring out how your using your tires.

also as your car leans into a turn your suspension flexes the inside wheel gets positive camber and the outside wheel negative caber so the car leans out and the tires rubber actually flexes the whole tire sort of moves left and right on the actual wheel, if your tires are too hard I don't know what that might do to cornering ability I will try to contribute actual numbers on tire temperatures vs pressure when I have a free day. I can take some readings under inflated , inflated properly, and over inflated. that will at least provide some data to back up what im trying to express however poorly in text.

tasdrouille 05-26-2008 03:57 PM

Rolling resistance coefficient (RRC) literature review:

At moderate speed, 90%-95% of the tire RRC is due to material hysteresis, 2%-10% is due to surface friction or micro-slip and 1%-3% is caused by air friction.

Tire inflation pressure is the main factor affecting hysteresis.

Warm tires have lower RRC than cold tires not only due to increased pressure, but also because the internal damping of rubber decreases when its temperature increases.

Given equal pressure, the initial RRC of a tire at -20 C can be more than twice as at 40 C.

The RRC is almost the same from 0 up to 55 mph, when it starts to increase rapidly. At 80 mph, it is roughly twice as much as 55 mph.

Worn out tires can have a RRC up to 20% lower than new tires as a significant part of the hysteresis happen in the thread which is not so much affected by inflation pressure.

The relation between tire pressure and RRC is almost linear, and is still significant in excess of 100 psi.

As a side note, it is interesting to note that fuel consumption can vary by more than 10% depending on the smoothness of the pavement.

Effect of width, aspect ratio and diameter on RRC:

Note: This applies to RRC only, not rolling resistance in terms of force, which is more important than RRC in stop and go driving.

This aspect of RR is very hard to tackle as there are multiple variables working in opposite directions. Nonetheless, by looking at the variation in RRC of the same tire when one variable is modified at a time, and by looking at average RRC for each tire size, we can conclude that generally, all other things being equal:

- Larger diameter tires have a lower RRC than smaller ones.
- The lowest RRC tire width is the closest one to the tire diameter times 14 (ignoring units of measure). (At max sidewall pressure and max load)
- The lowest RRC aspect ratio is lower as tire diameter gets larger. It appears as the the lowest RRC Diameter/Aspect ratio are: 13/80, 14/75, 15/70. (At max sidewall pressure and max load).

Overinflated tires will wear more in the middle than optimally inflated tires. However, optimal inflation varies with load and tire size.

Blowout risks related to sudden pressure rises in overinflated tires are non existent as radial tires will not unbed under 150 psi.

Overinflated tires have higher risks of cuts, but reduced risks of rim damage.

The temperature increase delta decreases as initial cold pressure increases.

References:

TYRE ROLLING RESISTANCE ON ROAD

Passenger Tire Rolling Resistance

Rolling Resistance Testing: California Energy Commission’s Fuel Efficient Tire Program

vtec-e 05-27-2008 04:42 AM

My first post here other than my intro and i'm in the thick of it!! I have pics of my tires with 105,000km on them at sidewall pressure(44psi, recently upped to 50) but don't know how to upload them here. When i do, the bulge in the middle theory should bugger off! On the other hand, i am still, like everyone here, looking for DEFINITIVE data on braking distance versus tire pressure. I know cars weigh differently and therefore have differing loads on the ground but you get the point. Every time i used to go for a new tire, (which was a long time ago) it was pumped to 32 psi. A month ago i had to get a new tire for my 4 month old kia. The guy put on a new tire and pumped it to 32psi without even asking was it going on the front or back, what kind of car was it (i was in my civic); heavy or light. Nothing, just put 32psi in there, no questions. When i got the car first, it had 32 front and rear and i was afraid to corner in it. It's a diesel and is heavy on the front and i can tell you this, it looked like it was flat on the front and that the tires might pull off the rim at any moment. I suppose my main question is this: If the tire pressure is so bloody important then why dont the tire manufacturers supply us with a grip v pressure graph with every tire. I've seen a LITTLE bit but the data only covered one or two tires and only up to this magical figure of 32psi!! I reckon grip goes up as pressure goes up for an awful lot more than they would have us believe. And of course tire life is extended dramatically. Ok, rant over. Now i want DATA from somebody before i go crazy!! I'm "tired" of this argument. It will stop when i get my data. I promise. But if anybody brings it up after that, i'll give them a serious dose of "copy and paste" Ok, rant over this time. Sorry, i'm sleep deprived, need to go to bed. I work nights.....zzzzzzzz....zzzzzz

ollie

vtec-e 05-27-2008 05:50 AM

http://ecomodder.com/forum/picture.p...3&pictureid=11
105,000km at 44psi. Actually i only went up from 44 to 50psi a month ago.
No uneven wear and hit the odd pothole too. No tire damage. So, as far as i'm concerned, the only argument left here is braking distance. Does anyone here have datalogging equipment? Microwave ground speed sensors? Thats what we need to finish this argument off. Personally i've braked hard at 50psi and noticed no difference, wet or dry. But personal feeling doesn't count does it!! Later lads.

ollie

CapriRacer 05-27-2008 08:21 AM

Sorry, guys. Holiday weekend.

Plus I didn't know where to start - but I certainly don't think the "Introduction" forum was the place. I'm glad - and surprised - that this generated such a lively discussion.

But I suggest we move it to some place more appropriate. How about this:

http://www.ecomodder.com/forum/showt...8793#post28793

whitevette 08-09-2008 08:43 PM

Quote:

Originally Posted by vtec-e (Post 28790)
http://ecomodder.com/forum/picture.p...3&pictureid=11
105,000km at 44psi. Actually i only went up from 44 to 50psi a month ago.
No uneven wear and hit the odd pothole too. No tire damage. So, as far as i'm concerned, the only argument left here is braking distance. Does anyone here have datalogging equipment? Microwave ground speed sensors? Thats what we need to finish this argument off. Personally i've braked hard at 50psi and noticed no difference, wet or dry. But personal feeling doesn't count does it!! Later lads.

ollie

Great pic, Ollie!
Those "wear in the middle with anything over sidewall recommended P." people just can't see for looking. There is a (steel?) belt in todays radial tires...it wraps around the circumference of the carcass, very much like a tank tread. Higher P. won't bulge through this belt. Bias plies, yes ; radial plies, no. Bias ply tires are gone (except for some trailers and specialty tires).Good riddance!
There has not been a word about "tread squirm" on these posts. This "squirm" is the wear mechanism for the tire tread; as the tread squirms it acts like a pencil eraser...wearing away against the pavement and heating the tread.. IMSA race cars had their street tire ( rules) treads ground half-way down...to reduce this additional mass from pulling the tire apart at speed and to give the tire better lateral response.

CapriRacer 08-10-2008 07:55 AM

Whitevette,

As I indicated in the post right above yours, this is the "Introduction" forum, and not the place to have a technical discussion - so we've moved this discussion to:

Edit: The link doesn't take you to the followup thread. Here is a new link:


http://ecomodder.com/forum/showthrea...ires-2582.html

Nevertheless, your post has a couple of fallacies in it, so I think you would benefit from the discussion.


All times are GMT -4. The time now is 05:28 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com