QuestionQUESTION: Hello, my name is Luke,
I have low profile tires (Kumho Ecsta AST 215/35/18) on 18 inch rims on a 2006 Mitsubishi Lancer. I have had the tires for about two and a half years now and I change them for the winter and only use them from around mid March to late October. My car recommended PSI is 32 for factory tires. I have had the tires inflated at about 29-30 for the entire time I had them. Recently I went on a road trip and inflated them to about 32-33 PSI because I read they should be increased for longer road trips.
It is now about 1 week after coming back from the road trip and I have noticed lateral cracks in the front two tires (maybe 3 inch to 4 inch long) and only one on each tire. The cracks are shallow and not deep but are visible.
My Questions:
1. Is it safe to drive on these tires?
2. Did the underinflation and then the addition of the extra PSI cause these cracks?
3. What would you recommend I do?
ANSWER: Luke,
No the tires are not safe to drive on.
The 215/35R18's are way too small for your vehicle - and that's what caused the cracks. Using 29 psi when you think the tires were supposed to be 32 added to the problem, but there was never going to be enough pressure to carry the load.
First step is to look up on Tire Rack or Discount Tire what the proper size for the car should be and then replace them immediately.
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QUESTION: Just one last question then. Do you think I can have 18 inch rims on this car or not? Or was it just the tires that are too small?
ANSWER: Luke,
First let me apologize.
When I looked up your vehicle, I noticed that the minimum Load Index listed by Tire Guides was an 87. Tire Guides also said a P215/35R18 Standard Load had a Load index of 73 - and there was no way the tire was going to have enough load carrying capacity.
But when I went to Tire Rack to look up their recommendation, I noticed that there was a couple of models of 2006 Mitisubishi Lancer's that listed a tire with an 85 Load Index - and that for those models only, a 215/35R18 EXTRA LOAD would work. The other models of Lancers list a 235/40R18 as the proper fitment.
So:
1) You'll need to go to Tire Rack to search out which model you have and follow their recommendations.
2) In the cases where the list a 215/35R18 as the 18" fitment, you have to use 6 psi more than the vehicle placard - which you said was 32 psi - so you need to use 38 psi.
Altering what I told you in the first posting:
The tires were underinflated and that's why they cracked. Since you've operated the tires for 2 1/2 years that way, there is going to be some damage - and a potential for a tire failure - and those sometimes have tragic results.
So it would be best if you replaced the tires as soon as possible as they are potentially unsafe.
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QUESTION: Just wanted to say thanks for your time and answers. You are helping me alot. I have to admit I got a bit worried when you said the tires are too small for my car because when I ordered them they assured me they were ok for my car. I was just not informed enough to know about the psi and I guess that is what ended up ruining the tires.
I have the Ralliart Sedan that is listed on Tire Rack and I believe they listed that the 215/35/18 will fit my car. I will just need to get new tires now. I do have one last question, I am trying to understand the psi levels a bit more and was just wondering how you came up with the fact I should be inflating it to 6 psi more than what the car placard recommends?
Once again I thank you for your time, it is much appreciated!!
Luke
AnswerLuke,
It's about matching the original load carrying capacity.
There's a table that lists tire size and pressure and from that you look up the load carrying capacity. So the tire placard information with the original tire size and pressure, is a necessary starting point.
Once you have that, you look up the new tire size and the result is the new pressure.
The tables are not published on the internet due to copywrite laws. Besides a new table is published every year and it's 30 pages long. The organizations that publish these tables don't make anything of value except these tables, so they closely monitor for copywrite law violations. Selling the book is their only source of revenue.
I happen to have a copy and make myself available to help in these situations.
BTW, you should tell whoever it was that sold you the tires and rims, that THEY should supply inflation information when they do plus size fitments. If they don't know how, then they shouldn't be up sizing!
