Safety in Numbers

[jvc88889]

I am following the guideline here "305/35-20 = 28.4" tall, 10.0-10.5 wheel" in putting 305-35-20 on 20X10" on rear.

I have measured my wheel, and it is indeed 10".

However, for their 305-35-20 PZero, Pirelli recommends rim width range of 10.5-11.5" with meas. rim width 11", sect. width 12", and tread width 12.1".

So, am I safe with my rears or not?

Michelin, Bridgestone and Goodyear all recommend a 10-12" rim width for their same size tire, 305-35-20. These brands' sect. widths are even larger than Pirelli's (12"); for example, Michelin's sect. width is 12.3".

It is true that Pirelli's tread width is larger (12.1") compared to Michelin's (11.3"), but it is difficult to compare tread width differences from one brand to another due to a tread design's rounded shoulders.

One last number: I measured my Pirelli from outer edge of bead to outer edge of bead and got 11". Does anyone have a measurement on another brand's same measurement for such a 305-35-20?

Any expert advise out there?

[PQ]

There have been a few who put 305s on he stock 9" wheel. Looks funny to me and I wouldn't trust it, but it held.

I think you'll be fine with 10" and a 305.

[SUX2BU]

You will be fine.

[jvc88889]

Originally Posted by PQ

There have been a few who put 305s on he stock 9" wheel. Looks funny to me and I wouldn't trust it, but it held.

I think you'll be fine with 10" and a 305.

I read a thread about one who put 305s on 9". It held, but after some people got on his case, he later switched to 11".

[jvc88889]

I just wonder what it is about Pirelli that they recommend only 10.5 - 11.5" for their 305s. It doesn't seem to make sense that they'd need a half-inch more wheel and a half-inch less wheel (comparing to Michelin, etc. who recommend 10 - 12" for their 305s). Only 1 inch to play with compared to 2?!

Anyway, any other opinions on Pirelli 305s on 10" even though they recommend 10.5" - 11.5"?

[Nine Ball]

How did you measure your wheel? Is this the factory rear wheel? Keep in mind that all wheels measure outer lip to lip at about 1" wider than their actual designation. So, if you measure 10" between outer lips, that is actually a 9" wheel.

The 305 tire is recommended for 10.5-11.0 wheels (measured 11.5-12.0 lip to lip). You can put them on a 10" wheel, but the tire won't handle as well in the curves. The sidewalls being pulled in are the reason, as the tire wasn't designed to handle those cornering loads with the sidewalls flexed inwards. Is it safe? Sure, it won't blow out or anything. It will just handle like a slop-box in the turns, if you drive it too aggressively.

[jvc88889]

Originally Posted by Nine Ball

The 305 tire is recommended for 10.5-11.0 wheels (measured 11.5-12.0 lip to lip). You can put them on a 10" wheel, but... will just handle like a slop-box...

Thanks for your time in sharing.

I was following the "recommended sizes for tires..." sticky that you posted, which says: "Recommended 20" tires for 2010 Camaro 305/35-20 = 28.4" tall, 10.0-10.5 wheel"

So, I got a 10" wheel and 305s. But, above, you now seem to indicate for 305s a 10.5-11.0" wheels instead.

My 10" wheel has 10" of mountable surface between the lips, and it measures 11" lip to lip (including the lips in the measurement). My Pirelli 305 measures 11" bead to bead (including the beads in the measurement).

I guess my combination is not ideal after all. I would be giving up some wear and some handling but still safe from a blowout, right?

I wonder what it is about Pirelli that they recommend 10.5-11.5" for their 305s while other brands recommend 10-12".

If I could get some measurements of other brands' 305s bead to bead (including the beads) to compare with my 11", and theirs was the same, I would feel comfortable to go ahead with installation.

Should I go ahead with the installation? Should I consider trying to return either the wheels or tires for store credit and a better match from my supplier's inventory? Really, not that much to choose from.

[CamaroDreams07]

Originally Posted by jvc88889

Thanks for your time in sharing.

I was following the "recommended sizes for tires..." sticky that you posted, which says: "Recommended 20" tires for 2010 Camaro 305/35-20 = 28.4" tall, 10.0-10.5 wheel"

So, I got a 10" wheel and 305s. But, above, you now seem to indicate for 305s a 10.5-11.0" wheels instead.

My 10" wheel has 10" of mountable surface between the lips, and it measures 11" lip to lip (including the lips in the measurement). My Pirelli 305 measures 11" bead to bead (including the beads in the measurement).

I guess my combination is not ideal after all. I would be giving up some wear and some handling but still safe from a blowout, right?

I wonder what it is about Pirelli that they recommend 10.5-11.5" for their 305s while other brands recommend 10-12".

If I could get some measurements of other brands' 305s bead to bead (including the beads) to compare with my 11", and theirs was the same, I would feel comfortable to go ahead with installation.

Should I go ahead with the installation? Should I consider trying to return either the wheels or tires for store credit and a better match from my supplier's inventory? Really, not that much to choose from.

You're right...the sticky does indicate 10-10.5. My guess is you will be fine with the 305 on the 10'', so long as you do not do a lot of track driving. People are running them on stock 9'' wheels and not having catastrophic problems, so I think 10'' would be ok.

But I think we do need some clarification on the discrepancy between the sticky and this...

[Nine Ball]

Many of my customers run the 305 on the 10.0 wheel, without issue. The wheel is on the narrow end of the spectrum, but still works. Just be certain your wheel offset is correct, or the tires may stick out. When you order a 10.0 wheel with intentions to fit a 305 tire, you have to actually spec out the wheel based on a 10.5 wheel offset, so that the tire still tucks correctly. This keeps the centerline of the tire the same, regardless of the wheel being 10.0 or 10.5 wide. The tire is more critical to fit than the wheel.

Tony

[jvc88889]

I am hoping not to experience the 10" "slop box" and hoping to experience the 10" "without issue".

Some have said that the tire design varies from manufacturer to manufacturer. So, my Pirelli 305 may be slightly different than a Michelin 305. Pirelli recommends at least 10.5" while Michelin recommends at least 10".

Does anyone know why Pirelli appears to be more conservative?

I am leaning towards going ahead with the install even though its out of the manufacturer's recommendation. I don't do track driving and would get used to the feel of the combination. I was thinking of upgrading the suspension at some point anyway.

I believe the stock offset is 40mm and my new wheel's is 45mm, so that should help somewhat with the fit. I guess I won't really know until the wheel is test fit prior to mounting.

So, maybe the sticky should be changed to 10.5 - 11" for 305s instead, then. Also, I believe the 295s are at 28.1", but that is not within .5" of stock 28.7", so maybe 295s should not be recommended.

[flht99b]

I have a brand new set of Pirelli P Zero 305/35/20 sitting in my basement waiting for my 20x11 Forgestar CF5's. The Pirelli P Zero is WIDE, over 12 inches wide. My tires free standing measure 11" across at the bead. I'm sure a 10.5" wheel will work fine, a 10" is probably as narrow a rim you'd want to use with these tires. My opinion only, the Pirelli P Zero 305/35/20 looks to be made specifically for a 11" wheel. It is an OEM size tire on certain Ferrari's and I believe they use an 11" wheel width ( between the bead section ).
Ed M.

[Nine Ball]

Correct, the Pirelli 305 tires are wider than other brands. I'd compare the Pirelli 305 tire to most 315 tires from other brands. They have a sidewall that protrudes quite a bit, whereas most other brand have flatter looking sidewall profiles.

[jvc88889]

For what it's worth...

My Pirelli 305s also measure 11" across the bead. I believe the tread width is about 12" and a comparable Michelin 305 at about 11". However, the "section widths" are 12.1" and 12.3" respectively. These numbers from specs. at tirerack.com.

I called Pirelli today regarding their recommended wheel range for their 305-35-20. Tire Rack had it on their website at 10.5-11.5", but Pirelli told me the range is actually 10-12". So, Tire Rack and Pirelli are giving different wheel ranges for the Pirelli 305.

Trusting in Pirelli that they have the most current data, this was a relief since I have already received my 305s and my 10" wheels. It would be better to have a wider wheel, but at least I am comfortable that it will fit and not blow out. I would probably be upgrading suspension for handling at some point in the future anyway.