Im looking to buy tires for the rear and i have 18x9.5inch C5Zo6 rims, and i was wondering what the widest tire i could fit on them. I know a 275 will work but will a 285 or 295 work? thanks

 

I think 275 is the best fit on a 9.5" rim. Anything wider will start to bulge.
a 275 is 10.8" wide and a 9.5" rim is 10.5" lip to lip.

 

On a 17" rim a 285 will work pretty well, but with an 18" rim your sidewall is getting pretty short. You'll hurt traction more than you'll help it if you pull the edges of the tire off the road.

What aspect ration are you running?

 

I got your best choice,,, P285/35R18. They will mount up to 9.5" wide wheels (so says my Tire & Rim book) and are 25.87" in OD,, no need to worry about the speedometer reading. Being on the back, you just need to get the right offset wheels or spacers,,, there should be plenty of clearance. I am running P295/35R18s on the back of my IROCZ.

 

I have 295's on my 18x9.5's. The slight bulge is sexy.

http://i2.photobucket.com/albums/y48...8/91z28_01.jpg

 

That 295 looks awesome, what size spacer you have with those? You guys have any pics of the 275 or 285's? I just need to get my 245's off, they look bad. Plus its kinda a waste having all that rim and then having the same width tire as I had stock.

 

im almost positive you can run 305's on a 9.5 in rim maybe even 315's

 

but why? cause it looks cool is that the only reason? It will perform like absolute crap.

I am running a 285 on a 9" rim and it performs like crap. Im running like 28psi so that i can get even tread patterns but even that didnt work. The whole inside of my tire(the only part of the tire that actually makes contact with the pavement) is worn and the outside looks almost new. They buldge too much for my liking and dont perform as well.

This is the same as putting a 295 on a 9.5" rim, ya it has a nice look but it doesnt perform as well as a 275 or a 285.

For 9.5" id go with a 285 max.

 

Iran 295/50s on my stock 16" x 8"rims, and never complained about it's lack of performance or tread pattern.

I know of a guy running the same tires right now, on his stock 16" x 8"s. No complaints there either.

Don't limit yourself to 275s/285s. A 315 should fit fine.

Keep in mind though, aspect ration will also play a role in tread patter, and performance.

 

In the rears or fronts? Usually under/over inflation presents itself with uneven wear in the center of the tread. Over inflation causing excess wear in the center and underinflation on both inner and outer edges.

Are you sure your rear-end is straight? Next time its on the alignment rack get the numbers for it...theres no built in adjustment, but some racers have been known to camber there housings...

 

Rears. You are correct about over/under inflation. It was not out of spec on the alignment rack when i had it on there about a year ago.

You said it under inflation and the outsides wear, over inflation and the inside wears down.

I was running an oversized tire on a smaller rim period. 26-28 psi was acting like it was over-inflated. Any lower and it was just stupid for handling, oversized tire on too small of a rim that was the reason for bad wearing patterns.

If i had negative/positive in the rear, id see either insides or outsides of the tires worn, not only the center section worn.

 

I have worked in Akron Ohio for 28 years in the tire industry. My latest claim to fame is the Kumho V700 DOT street legal racing tire (well that was more than 10 years ago that I started that tire line). A pretty well designed tire line that has won many SCCA national championships. Now for the technical advice.

My advice is to go no wider than a 285 tire with a rim width of 9.5". The technical reason is actually geometry,,, when you put a very wide tire on a narrow wheel, the shoulders of the tread area are pull down because you are forcing the beads to be pulled in too far which in turn pulls down the tread shoulders. That is why Stevo above wore out the centerline of the tread area. All tires are designed for a specific wheel width,,, for a P275/40R17, its a 9.5" rim width, but 9.0, 9.5, 10.0, 10.5 and 11.0 are allowed. For a P285/40R17, the design rim width is 10.0, but 9.5, 10.0, 10.5 and 11.0 are allowed. I would never put a 315 on a 9.5" rim width, as suggested somewhere above. The narrowest appropriate rim width for a 315/35R17 is 11.0"!!!!!

 

i've seen cobra guys running 315 nitto drag radials on 9.5 inch wide rims. it buldges abit but seems to work well and looks good. nitto 315's apparently run smaller than other 315 street tires so it may be like a 295 tire when its rated at 315

 

315 will work with a 9.5 inch rim.I did it on my 95 transam in the rear.It really filled up the wheel well-but thats on a 95 T/A.

 

Properly fitting tires to wheels is really an engineering decision, in which subjective or emotional reasons should play a very small role as tie-breakers among otherwise equal choices.

Doc probably has more specific information to work with, but the more uniform you can get the loading over the contact patch the better your grip will be. In that respect, the measuring rim width (or design rim width if actually known) should give you better results for any given tire size than you'd get with a narrower wheel, with better stability at the big end being a side benefit. This is not to say that a 295 on a 9.5" wheel might not give a tiny bit better straight line traction than a 275 on the same 9.5" wheel - just that it won't be as good as it (the 295) could be on a rim of more proper width.

Just because you can physically mount a tire up on a too-narrow rim and get it to hold air isn't a good enough reason to do so. Certainly not for sustained street duty. Sidewall flexing and the related heat generation are increased by a too-narrow wheel fitment, and IIRC the point of greatest flexing moves to a different location along the sidewall (that may not be as well suited to coping with it).

The lower pressure that you'd end up running in order to keep the tread centers from wearing out prematurely (which adds further to the flexing and heat issues) *might* be something you can get away with at the dragstrip. That's because you don't drive more than about a mile at a time from when you pull to the line to your return to the pits or staging. Only about half of that driving is at much of any speed, so there isn't nearly as much heat added as there would be in more normal usage.

I realize that some of the subscribers to this thread may not be particularly interested in cornering. But there's a separate thought that's related to the lateral stuff, and that's the stability of the car in the event of tire failure. When you mount a tire on a too-narrow wheel, you give away some of this stability, especially when it's the rear wheels/tires. The flip side is that if you can mount your tires on relatively wide rims - up around the tabulated maximum wheel width for any given tire - you improve things tremendously. We all hit things in the road once in a while (even me), and if something cuts a tire down at speed it's a little too late to wish you'd chosen a different wheel width/tire size combination.


Norm

 

Running too wide a tire is a bad idea. Everyone here that detests against it is absolutely right. I have 335s on my 11" rear rims right now. They bulge like crazy . I am getting some Nitto 555Rs in a few weeks to fix the problem. Only reason I was running the 335s, is cuz the tires were practiaclly given to me from a guy with a Viper.

 

I have also been told that if the tire is too wide or narrow for the rim it is mounted on, the bead in its seated position is not on the rim correctly and could cause a bead failure. So if that is correct then there could be a possible safety issue as well.

Maybe Doc can verify if that is true or not.

 

without sounding dumb, what size tire would you run on a 8-8.5-9 inch wide rim then?

using a 60 series sidewall..

I have a set of 255/60/15s and am limited in wheel well area..

This is a NON-thirdgen question.. its for my other car..

 

well i dont run 60 side wall but do run a 50, and 255 is all the bigger i'd go. thats what i want to run on my 16x8 irocz wheels

i've heard of ppl running 275's on 17x8's. but the optimal size is 9 inches or so.

my slicks are 26x11.50x16 ET streets mounted to my extra irocz wheels. they fit good and look great too. not sure how wide they are. they say 11.50 but its probly like 10.8 tire contact patch/sectional width. they are just abit wider than my 245's

 

255 is good on 8.5 and 9" wide.

 

well said, Norm.

bims01: Yes, the bead seat is very important. When mounting wide tires to narrow wheels, the bead will rotate, putting alot more stress on the inside bead wires. The toe of the bead area may not even touch the rim any longer. This can lead to bead wire fatigue & failure. I have modelled this exact situation on FEA (Finite Element Analysis).

 

I changed my mind. I'm not going to post. No matter how many times you tell people the right thing to do. People still put a 295 tire on a 7 inch rim, etc.

Idiots.

 

i believe BFG recommends an 8" rim for their 275 / 60 / 15 drag radials, but i'll double check
Eric B

 

The Design Rim Width for a P275/60R15 is 8.0"...

The proper design rim width depends not only on the section width but also the aspect ratio. 70 and higher aspect ratio tires will be on rim widths that are 70% of the section width,,, 65 and 60 series tires are best on rims that are 75% of the section width,,, while 40 series tires are best on rim widths that are 85% of the section width. The rim widths that are calculated are rounded to the nearest 1/2" width. Or 1.0" for very wide tires.