Lionelhutz, I suggest you do the same. Drop your pressures to 24psi front/20 psi rear and drive it for an entire month then get back to us. I guarantee you will be really happy with the reduced harshness while still retaining the "sports car" visual appeal.

 

To satisfy my own curiosity, I ran some calculations of the total internal volume of air within all of the tires discussed in this thread.

I apologize ahead for the simplistic nature of my calculations. They are rudimentary in that they assume the section width continues the entire way to the rim, but this will only help INCREASE the volume of the higher profile tires since the calculations assumes that, in the case of the 255 section tire, the torus shape is 10 inches wide from tread to rim, as an example.

Approximate tire volumes:
--225/70/15 - 1,560 cubic inches
--255/60/15 - 1,710 cubic inches
--275/40/17 - 1,410 cubic inches
--345/30/19 - 1,828 cubic inches

For as flawed as these approximate volumes are, the message is clear: There is a less than 30% difference in air volume between VERY disparate tire sizes. And the lowest PROFILE tire...which you say should hold MORE air...has the GREATEST volume.

So...um...OK. That's one thing.

Wow.

Really SHOULD be running 17 PSI, but that seems just a little TOO low?

In response to your asking me to run my tires at 20/24 for a month, all I can do is offer my absolute most sincere answer: No.

I say this with my hand over my heart and all the respect in the world. All of the previous discussion aside, I simply do not feel safe driving my car in this condition.

ALL of the statements made in the above quote ARE SYMPTOMS OF TIRE UNDER-INFLATION. To a point, the tire is part of the 'suspension system', but to deflate the tire to the point of having it be a squishy balloon is just wrong. As in 'not right'. As in 'negligent'.

When making the choice between the two, I would HAPPILY sacrifice tread wear for safety. There is no question on that point. Call me a sucker.

Wow, again.

I have no interest in retaining visual appeal. I DO have an interest in retaining the SPORTS CAR appeal that is also safe.

To the point, my car rides great.

 

Suit yourself but you're really missing out on a great ride with hardly any negative side effects.

In my previous thread titled "Tire Bulging At Low Pressures" I found there was no significant bulging until the pressure dropped below 5 psi. Something to think about.

 

No, won't happen. I actually want my car to drive like a sports car, not just look like one...

 

If you were to take a nationwide poll you'd discover the average owner NEVER checks their tire pressures as they leave that up to the dealer that does all of their maintenance. With oil changes now extended to 10,000 miles or more a tire can be dangerously low for months at a time while the ignorant driver (or drivers) don't know they're driving an accident waiting to happen. Over the years I have seen a number of cars motoring down the freeway at 70 mph with a tire so low the rim is almost touching the pavement but yet the driver doesn't know his tire is about to shred itself.

Knowing they will be taken to court and sued over anything the world's automobile manufacturers are taking the only route they can; recommending maximum pressures be used regardless of how harsh the ride is or how quickly the tires wear out from over inflation.

 

I only used that size tire on my 79 when it was still new. I went to wider rims and 45/50 series tires. Back then I was doing auto cross events and they would set up a skid pan with timers. You put white shoe polish on the inside and outside of you tires to measure tire roll under while doing a series of CW and CCW laps.

Watching roll under and lap times you could adjust the air pressure to get the best before your turn on the solo laps. It was not done with the low pressures suggested here on some posts

You really have to keep up on your alignment and tire pressures to end up with perfectly worn flat across the tread face when it is time to replace the tires.

I went away from 15 inch because they quit making them with any AA A traction and temp and very low speed ratings. The highest used be something like V speed rated. I'd rather spend $500-600 on a tire and replace them every year to be safe. They are gone in about 5000 miles. They ware perfectly with over 40 psi 335/35/17 on 12 inch rear rims

http://www.tirerack.com/tires/TireSe...r=17&zip-code=

 

Very interesting!

 

I know you won't listen to this, but for the sake of everyone else reading I have to ask the question...

What happens under braking, cornering or both?

Your simple equation is for a static car sitting on level ground. I assume you drive your Corvette right?

When you brake, that 900lb front tire loading might increase to 1100-1200 per corner. If you factor a hard cornering manouver in there (to avoid an obstacle or perhaps just for fun), the outside front tire might see as much as 1300-1500lb of load.

Using your assumption of a linear relationship of pressure to max load, you would need 28psi in the front at 1500lbs of load. This is what people were trying to show you with the cornering videos earlier.

Not to mention low pressure tires typically having longer stopping distances than higher (or correctly) inflated tyres.

But hey, you keep assuming the 40 year old placade is the best advice. I'm sure that'll keep your safe.

You know, come to think of it, my convertible didn't come with a shoulder strap seat belt - that must be the safest option for these cars, because that's what the engineers decided on back then.

 

Now I see, if you drive your Vette like a 60's station wagon and never go fast around corners or in a straight line then possibly you could get a smoother ride.

However a Corvette was not meant to be driven like my grandmother drives to the grocery store. Try some high speed cornering and let us know if the tires don't roll off the rims. In a straight line at 40mph you are probably getting a comfortable ride.

 

No...he's stated that he occasionally goes in a straight line at 120 mph.

If that doesn't make you feel warm and fuzzy about 20 PSI, I don't know what would...

 

Tires are not constructed the same today as they were 40 years ago. Most folks know this and it's already been mentioned. TBTR knows this but he gets his kicks out of folks disagreeing with him. I'm not about to reduce the tire pressure in my CTS-V to anything under the recommended pressure of 32 PSI for a 4200 lb vehicle nor reduce the pressure in my Civic to anything below 33 PSI in a 2800 lb vehicle. Anyone who suggests doing so is an idiot.

Moving along, tires today require more pressure to reduce rolling resistance in order to improve fuel economy. Every little bit helps including engines shutting down a couple cylinders at highway speed. Making cars lighter and smaller. More contoured shapes to lower the drag coefficient. 40 years ago, tire pressure recommendations were usually below 30 psi. Today they can be as high as 35 psi or 44 psi if the car will be used at sustained speeds over say 100 mph. For best fuel economy, tire wear and overall safety for the vehicle, the vehicle manufacturer recommends the tire pressure. To compare any tire made back in the 70's or earlier and the recommended tire pressure back then with today's tires and pressures, is comparing apples to oranges - they're both round but that's as far as it goes. TBTR can play his little game with tire pressures, carburetors, etc but again, knowledgeable folks won't listen to his BS and worse, follow what he recommends. He is not what he represents himself to be but that's just all part of public forums and anonymity.

 

The tires that came on a '74 Vette and to what the door jam plate PSI relates to were Firestone steel radial 500, GR70-15. Once you deviate from that tire you can't safely assume that 20psi is good for any other type or size of tire.

 

YEP...warm and fuzzy and sipping on a cup of hot cocoa.

All I can write is that I AM GLAD that I live where I do so I do not have to worry about being on the same road. AND all I hope for is that those people who read this stuff...realize as it has been stated.....comparing tires of 40 years ago to current tires is pointless.

I am officially pulling myself out of this 'black hole' of a thread.

DUB

 

I'll solve the problem this spring. I'll drive my vette down to texas and you sign a waver about your tires and rims and see if they are OKAY after a 15 minutes of my vette driving or an industrial area on a weekend.

 

Yes, but those are momentary loadings; not sustained loadings and its the sustained loadings that destroy tires. In the 20+ years I have been running 24/20 psi I have encountered every driving condition possible; rain, sleet, snow, 115 degree summers @ 75 mph for hours at a time, bumps, ruts, sideways drifting, panic stops, and you name it.

Think what you want but the big 255X60R15's don't require 30+ psi when mounted on a C3 because they're rated for twice the C3's weight.

 

OK guys I'm not a mechanic, and engineer, and I don't math. I skipped ahead from page 4 because I now have a headache. I'm putting 30-32 PSI in my tires, because that's what I've done all my life with every car I've ever had. I'm going to keep an eye on them, and I believe I will find that the tires will wear evenly, barring a mechanical issue, just like they always have.


I do appreciate the passion and tenacity that you all bring to the discussion, but you left my dumb a** in the dust pages ago.

 

Please define "big".

And please describe the difference between the "bigness" of a 255 section tire versus a 225 section tire (60 or 70 series...your choice) given that their weight ratings are essentially identical.

And please identify the differences between the 255 section tire and the "bigness" of the afore mentioned 345/30-R19 Viper tire.

This is all related somehow...I'd like to understand your words as to how.

 

And that's where the problem lies as people put 30-32 psi in their tires out of sheer habit with no valid reason WHY they do. Would you feel it would be necessary to put 30-32 psi in the big 255X60R15's if they were mounted on a VW bug? Or a Datsun B-210? Or roller skates?

 

You don't want to do that. Midland, Tx is a town best seen from your rear view mirror.

 

DO NOT listen to toobroke. He still lives in the 70's and cannot grasp new technology and he preaches to folks like yourself who come here to get sane advice. That said, put 30-32 psi in your tires and check for abnormal tire wear patterns regularly.