Low PSI, undersized, wrong tires? - Fuelly Forums

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Old 09-11-2008, 09:19 PM   #1
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Low PSI, undersized, wrong tires?

First I would like to startoff with my confusion about newer tires having a "max psi" rating of only 35psi. I've noticed recently an infusion of tires into the market that have a "max PSI" rating of 35psi and I'm wondering if the tire manufacturer's have changed anything about these tires or if they're "cracking down" on hypermilers who utilize the higher sidewall ratings of the tires. Secondly I'd like to discuss a problem that a friend has with his 2003 dodge grand caravan.

He clearly got new rims for this vehicle with them being 16" and shorter tire than oem. When he was parked today, I saw that the sidewalls of the tires were flexed a lot, it was almost as if the tire was inflated to 10psi. I first inspected the tire to see what its sidewall rating was and it said only 35psi. So I checked the PSI of the tire and was astonished to see it was at 35psi. The tire was really really flexing, if the actual tire was 3 inches tall from the rim to the end of the tire, this tire had the effective height of only 1.5" because the sidewall was flexed (bulging) so much. I noted down the load rating and a few other ratings in my head then went home.

My guess was that these tires are really meant for a car but then I went on tirerack.com and it found it managed to pull up tires with the same load index rating and that's when I decided to post here.


The tire seriously looked like the second tire in that image.

What is with the paultry 35psi rating? What were the original load rating for the tires that came with this vehicle? I'm hoping someone could clarify what is going on with this vehicle.
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Old 09-12-2008, 01:50 AM   #2
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I think I know what the problem is. I forgot to mention the guy said he got wider tires (say from 215 to 235) and that is what is causing it to bulge and be "overloaded' like I've described.
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Old 09-12-2008, 04:29 AM   #3
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I think I know what the problem is. I forgot to mention the guy said he got wider tires (say from 215 to 235) and that is what is causing it to bulge and be "overloaded' like I've described.
The tires are probably literally overloaded. Every tire has a "load rating", and you should NEVER buy a tire with a lower load rating than the one that came on your car. PSI ratings are often (if not always) directly related to load rating. 35 PSI tires will have a much lower load rating than 44 PSI tires, and 44 PSI tires will have a lower load rating than 52 PSI tires.

I thought 16" wheels were standard on a Grand Caravan... not that you couldn't get new rims in the same size as the originals.

Check the load rating. It is often unsafe to run a lower load rating than stock, even if you don't technically exceed the lighter load.
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Old 09-12-2008, 07:38 AM   #4
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As you said, the sidewall is only 3" and it is properly inflated, so maybe that short sidewall is making the bulge look bigger??

One thing to check is the sticker on the inside of the door that will tell the original factory tire size and recommended tire pressure and load ratings. That will at least give you a comparison of what was originally on it/and what is on it now.
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Old 09-12-2008, 10:59 AM   #5
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it's probably because of the wider tires. They stick out more and some of the height is lost because the tire has to now bend in to meet the rim.
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Old 09-12-2008, 11:22 AM   #6
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it's probably because of the wider tires. They stick out more and some of the height is lost because the tire has to now bend in to meet the rim.
Yeah, plus after reading the article below, it would seem that it'd be even better for sidewall stiffness if you bought tires that were much narrower than your rims.
http://www.mazda6tech.com/index.php?...d=20&Itemid=50
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