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Old 01-31-2008, 02:21 AM   #1 (permalink)
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Ecomodding > Safety ?

I want to be clear before I start off any flames by accident that the following discussion is meant for educational purposes only and by no means to step on anyone's toes.

I've read on this site and other sites comments, questions and recommenations with regards to narrower tires and wheels.

Understanding the connection between tire size and friction and how it translates into FE, I see why one would think that reducing the friction from the tires would improve FE.
BUT, are those who over inflate their tires or reducing tire width (or reducing the size of the contact patch in any other way) forgetting the purposes of the tires to start with?

Being the only contact of the car with the pavement, I don't think that the tires are the right place to improve gas mileage.
Reduced contact with the pavement will hurt the performance of the braking system, the ability to corner and even the ability to accelerate sharply on some cars, all of which are needed in order to drive safely.

At what point are you allowing your MPG to take a lower priority?

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Old 01-31-2008, 03:12 AM   #2 (permalink)
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Overinflation will only reduce the contact patch on steel belted radials in extreme cases. I don't think anyone here runs enough pressure to result in a significant difference in contact patch.
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Old 01-31-2008, 05:39 PM   #3 (permalink)
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tires make such a huge difference, even in the same sizes, that the whole answer is just a grey, muddled, mess. are you really worried about safety? buy a set of high traction tires for the summer, and snow worthy tires in the winter. that way you have the highest chance of avoidance.
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Old 01-31-2008, 06:21 PM   #4 (permalink)
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Are bicycle tires unsafe?

They are very skinny and higher pressure. Not all of them though. Some comfort bikes have very wide cooshy tires, but those are not for distance or range.

I haven't heard of anyone doing anything so unusual with tires as to be dangerous.
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Old 01-31-2008, 07:06 PM   #5 (permalink)
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I'm not stepping on your toes either so don't take offense, I'm just stating my point of view.

I've seen people unintentionally under inflate their tires too much, causing them to heat up so badly that they shred apart into pieces, and I've also seen people under inflate intentionally and have the tire separate from the rim while rock crawling or off-roading.

I've also seen a person (my dad) inflate tires so much they blow up, but those were bike tires and he used the "squeeze the tire to check the pressure" gauge. That's not reliable at all

I'm not sure that over-inflating will do enough for an Ecomodder to cause them to flip or do badly enough around the turns to take effect. I take turns to where my rear suspension bottoms out (old rear shocks, front ones I replaced, waiting on funds) and I'm not near flipping.

Quote:
Reduced contact with the pavement will hurt the performance of the braking system, the ability to corner and even the ability to accelerate sharply on some cars, all of which are needed in order to drive safely.
Not to be mean, but don't most ecomodders try and use the brakes as minimal as possible? in emergency braking cases, I could understand if overinflated TOO much, but inflating to the MAX pressure on the tire sidewall shouldn't hurt it too much, and we ecomodders drive slow in the first place, and are trying to be more alert to traffic ahead to adjust for optimum fuel economy.

As for the accelerating quickly part, those vehicles are usually bad on FE to begin with, sports cars mainly. If your driving a GEO I don't think that in any way your accelerations will be very quick. at least compared to vehicles with engine's twice their size.

I understand your concern for safety over fuel economy. I don't think tires are one of the most major concerns. they safety parts come into play only when it is raining, sleeting, snowing, or hailing. but once again we econuts drive more cautiously in bad weather, I use it as an excuse to go slow and pile up traffic behind me. In my mind I see them saying oh, it's fine he's going slow because of the weather ^_^". The ones in a hurry pass me, the content ones drive behind.

Things that I do worry with safety is mirror removal, or removal of devices that make us Aware of who's around us and what's going on. these mods make us less aware in that we now have large blind spots if we're in a high traffic area. I use my drivers side mirror all the time, because I'm in the right lane (so the grass on the right of the road isn't appealing) and I don't trust the middle mirror anymore because it's always shaking and stuff from the sub's and the crappy roads. And I almost hit a fellow Jeeper because I didn't see him on my left rear fender, and attempted a left had turn. I heard the squeal of his brakes. Middle mirrors aren't too good at looking out the left windows, especially if you have other rear passengers, even if it is panoramic.

I don't remove my spare tire for fix-a-flat's either, because I know that when one of my tires do go (trust me, they've taken more abuse than any tires I've EVER seen) It'll shred into pieces, and those fix-a-flat's won't work on a non-existing tire..

Go test some things out yourself, if you don't feel safe, DON'T GO THROUGH WITH IT. Happy ecomodding
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Old 01-31-2008, 07:42 PM   #6 (permalink)
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a lot of little things add up, high pressure in tires, trying to carry momentum around a corner to have later, disabled self adjusters on the brakes, springs between the pads to hold them away from the discs, less than normal lighting thur the plexiglass panels, low vacuum, low power steering pressure, less visiblitiy, looking at the computer, one windshield wiper. who can think of more?
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Old 01-31-2008, 09:40 PM   #7 (permalink)
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So, from what you are saying, I shouldn't have good traction at all, with snow on the ground, an ice covered driveway, and 50psi in my tires? I check my brakes and stoping distance with every change of the weather, and because I do know how good my traction is I don't have a problem taking corners fast, there are a number of nice sharp corners that I reguarly take to get to a friends house, and even with snow and ice on the roads I don't have a problem keeping traction when I see deer on the road, or some idiot pulls out in front of me.
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Old 01-31-2008, 09:50 PM   #8 (permalink)
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Quote:
Originally Posted by Blackbird View Post

Understanding the connection between tire size and friction and how it translates into FE, I see why one would think that reducing the friction from the tires would improve FE.
BUT, are those who over inflate their tires or reducing tire width (or reducing the size of the contact patch in any other way) forgetting the purposes of the tires to start with?
Not the width - that's not how modern tires work (just making sure that's clear)

Quote:
Originally Posted by Blackbird View Post
Being the only contact of the car with the pavement, I don't think that the tires are the right place to improve gas mileage.
Opinion noted. Please also be aware that tire mfr's DO think tires are a place to improve on - as do auto mfr's that want these tires on their cars....



Quote:
Originally Posted by Blackbird View Post
Reduced contact with the pavement will hurt the performance of the braking system, the ability to corner and even the ability to accelerate sharply on some cars, all of which are needed in order to drive safely.
Increased contact patch (VIA lower pressure) will reduce tire longevity and increase heat generation. Higher heat --> higher likelihood of failure. Additionally, reduced contact patch with pavement REDUCES risk of hydroplaning which, for me, is a big deal.

With respect to acceleration -- as a hypermiler, I've never put myself into a situation where I needed to accelerate out of a situation. I give myself plenty of room and plenty of space. I've also never read in any defensive driving manual (nor heard in any course) of "accelerate and steer" - I've only heard "brake and steer."


Quote:
Originally Posted by Blackbird View Post
At what point are you allowing your MPG to take a lower priority?

Moti
I'm trading my higher tire pressures for:
* weekly or more tire inspections
* increased distance between other cars in traffic
* lower speeds while cruising
* higher awareness of the mechanical state of my vehicle
* less use of cruise control (mind on CC => less alert)
* no use of cell phone

It's a more than fair trade considering fellow drivers are putting me at risk by not checking their tires for normal inflation, keep very close distances, yak yak yak on cell phones.

-------
On the subject of braking... I'm curious how pressure changes brake distance when ABS kicks on... Less traction means more pulsing (in theory - depending on ABS programming). I'll add that to my list of "eventually I'll get to that test" list
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Old 01-31-2008, 11:07 PM   #9 (permalink)
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Quote:
Originally Posted by roflwaffle
Overinflation will only reduce the contact patch on steel belted radials in extreme cases. I don't think anyone here runs enough pressure to result in a significant difference in contact patch.
Well, my guess is that you and everyone else in this thread who says that over inflating wouldn't cause any ill behavior of the car must have missed post #5 in this thread -
http://forum.ecomodder.com/showthread.php?t=764

So I guess someone DOES in fact run enough pressure that results in a significant difference of the contact patch.
Quote:
Originally Posted by jazzie604 View Post
tires make such a huge difference, even in the same sizes, that the whole answer is just a grey, muddled, mess. are you really worried about safety? buy a set of high traction tires for the summer, and snow worthy tires in the winter. that way you have the highest chance of avoidance.
I am not as worried about my safety because I will not compromise it in the way that I find that some others do.
As for me buying two sets of tires, I live in So-Cal, our seasons are summer, summer, less summer and summer .

I find that some of the advice given in this forum is perhaps improving FE but at the cost of safety.
Quote:
Originally Posted by diesel_john View Post
a lot of little things add up, high pressure in tires, trying to carry momentum around a corner to have later, disabled self adjusters on the brakes, springs between the pads to hold them away from the discs, less than normal lighting thur the plexiglass panels, low vacuum, low power steering pressure, less visiblitiy, looking at the computer, one windshield wiper. who can think of more?
And your point is?
I believe it is your question that I read about saving gas through usage of BIKE tires or space saver car tires.
A fine example of what I'm talking about.
Is your FE more important that being able to safely operate your vehicle?
A bike tire is designed to generate grip at leaning position, therefore has a rounded profile.
A space saver was designed to allow the driver to bring the car in a slower pace than usual to the next tire shop.
Unless you lean your car into corners or limit your speed to max speed that space savers are supposed to be used at, please stick to normal car tires.


I'll get to the rest of the responses tomorrow, sorry, gotta go to sleep, work starts early tomorrow...

Moti
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Old 02-01-2008, 07:17 AM   #10 (permalink)
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The post must have been erased in the crash that happened, but someone had posted this link. I think it explains it all.

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

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