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To 275 or 255 on a 9" rim, that is the question

VB242

I.M. Weasel
Joined
Sep 21, 2011
Location
Driving the No Malarkey Bus
I just got some 17"x9" rims and I would like to put some new Falken Azenzis on them, these are going to be autocross/ track only tires. 275/40's say they'll fit on a 9" rim but that's the minimum, 255/40's are tested on a 9" rim on tire rack. Lots of anecdotal success on the internet with 275/40 on 9" , even saw 325 on a 9" rim but that really didn't look right. So anyone with direct experience?
 
A 275/40 is a tall tire. Would be close to 26" I'd think.

I have no experience with either of those sizes however. I run a 235/40 on a 9" to keep the diameter close to factory. Plenty of people run a 245/40 as well with good results.
 
rimtuck.com to check out how the fit looks, looks like there is only one car there with a 275 on a 9" rim.

I have a 265 on a 8.5. On paper it is to wide but it looks and works well enough.

Remember not all tires are created equal, some brands run wide while others run thin even being the same width.
 
I had a 275/40 on 9.5" rim and they were fairly tall. I am running a 245/45 on 9.5" rim in the rear and it's still kinda tall, but not as bad because there is a tad stretch. The 275 rubbed with my 940 56mm wheel with 38mm spacers. I did have 225's on the 9.5"s. That was some stretch fo' sho. To my surprise they held up fine for a long time. Now I have 225's on the 8.5's on the front. There is some stretch, not bad, but they lose air quickly if they get low on air in the cold temps. I drove it on the track with the 225's up front and 245's rear.
 
All the respectable tires companies post recommended rim widths for fitment. Go too wide, the bead could un-seat in a cornering situation..... too narrow and you won't like the tread wear.
 
255/40 on 9". 275 will be more weight and height and likely cost more.

These are all true, but I bought them anyway. They feel a little bouncy, but I haven't checked the pressure just whatever they put in it to mount them. Any suggestions on a starting pressure for Auto x? I'm thinking around 30-32, they are definitely more sticky and turn in a lot easier than I thought they would.
 
These are all true, but I bought them anyway. They feel a little bouncy, but I haven't checked the pressure just whatever they put in it to mount them. Any suggestions on a starting pressure for Auto x? I'm thinking around 30-32, they are definitely more sticky and turn in a lot easier than I thought they would.
How much does the wheel/tire/adapter(?) weigh? Might need a shock adjustment to control that 55lb that's trying to escape. ;-)
 
I have the koni yellows turned up, the wheels are heavy the adapter is aluminium. It didn't seem out of control, I'm pretty sure theres at least 40psi in the tires, I was whupped from replacing the stupid throttle cable after a strenuous day at work and just had enough energy to screw with the MS a little and turn the boost back up to 15psi. I have some stick epoxy to fill in the small holes that appeared in the trunk/wheel well area and some undercoating to do since I had to take out all the plastic liners in the front.
 
I liked the adjustment of the Koni yellow struts for tuning balance, but I don't know that they really did the job with just 300lb front springs on my daily driver 244.

More grip from big tires will start to uncover other weaknesses. Start saving for shocks/struts, like revalved HDs. And you can probably up the spring rate too (although, what do you run now for springs?)
 
I've run many sets of both Falken 275s and 255s on 17x9s in Lemons racing. The 275s work, but didn't get us noticeably better grip in cornering, and they do weigh more of course. 255s are the go-to now. Lighter, cheaper, and they only maybe give up a touch of grip under braking and that's it.
 
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