Ramp

Ugh. I appreciate all responses and points of view and have no desire for a "best oil" thread - lol.

My reaction not to pick these rims up were based on the initial thought that for basic street driving and occasional twisties that 9" front's may be to big. That seemed to be confirmed by some, although most agree that they will "squeeze" in. While price is important, I'm not looking for the cheapest and definitely do not want to affect handling negatively by having the wrong combo up front nor have limited tire choices or have to worry if a 235 may fit but a 255 won't. On the other hand, I don't want to have a set up that simply looks wrong, so aesthetics does matter in that regard.

Based on the annual miles I'm likely to put on them, they will age out before wear out.

So, could there be a consensus on the most appropriate available tires at tirerack/etc (such as the Sumitomo), in the right combo that will provide appropriate street handling, comfort and the right look, fit and feel ? Plug and play is best for me.

I know, a lot to ask for.

R

hacker-pschorr

It's not the width of the front wheels we are concerned about, it's the offset. If these were ET65 - ET70 wheels that would be a different story. That extra 13mm makes things just a tad bit tighter which makes some of us a bit nervous about fender clearances.

$800 though, that's cheap if they are in good shape. If they were local to me I'd buy them and start hitting up shops for used tires in whatever size I'd like to run and do a test fit. Yes I've done that before.

docmirror

Hacker is exactly correct. I have the 18x9 wheel with Hankook Ventus ECO 235/40x18. It is very, very close to hitting on the left front liner. In fact, it may scuff just a tiny bit. With almost any tire, it will be trial and error. Don't forget the front settles a bit after driving. Tire dia is 25.2" inflated of course.

docmirror

As for a tire recommendation, that's almost as fractious as an oil recommendation. I can tell you what I've had trouble with before, but leery about posting any recommendation.

My VW GTI came with Kuhmo on it, and I didn't like them. However, when I had to replace a front, did both front tires. I went back with Kuhmo Ecasta and they were absolute junk. I had a set of Firestone tires on my 968, and they were only fair. They gave off some road noise, and seemed to tramline on concrete more than other brands. Replaced them with Sumitomo HTR II and that provided good stick, but not very good wear. Lots of choices in 235/40x18 tires from $84 all the way to $300. I would prolly do the Pirelli P-zero for summer only, or the Sumitomo HTR A/S for all season. Do NOT use summer rated tires below ~36F.

YMMV, objects in mirror, contents have settled, celebrity actor not real doctor, and may cause **** leakage.

SwayBar

Yes, it's all about offsets. I am currently running with no fender-rolling or rubbing:

O9.5 x 18 x 68mm, 265 tire
10.5 x 18 x 59mm, 295 tire

I can probably get a 305 in the rear no problem.

Sumitomo HTR Z III's, excellent tire for the street. If you have the bucks, get the Michelin Pilot Sport 4S, arguably the best ultra-performance tire for the street.

docmirror

I will opine that an offset greater than ~65 on the front is concerning. I drove one with a rather large offset, and it was no picnic.

YMMV

FredR

Did you ever find out what the problem was?

docmirror

The design of the front suspension and steering is not made for that great of offset. If one draws a vector from the upper ball joint through the lower ball joint which pivots for steering, the vector will strike the ground somewhere near the inside/center of the contact or pressure patch of the tire. Much design work is done to insure that the pivot vector is well placed so that the steering will have a positive correction for angular momentum when the wheel is turned(wheel will return to center under movement). Having a significantly larger offset changes the geometry of the contact point on the tire, and can defeat this safe margin for steering correction.

FredR

The offset is a means to an end - that end being the NSR-[negative scrub radius] and the 928 suspension design requires an offset of 65mm to achieve the design NSR of -10mm. The debate about scrub radius is interesting in that a positive scrub radius can improve braking, zero scrub radius tends to induce "squirm" and a negative scrub radius improves stability in the event of brake system problems or if one side of the car runs into ponded water creating a yaw effect. The Porsche engineers decided the NSR approach was best. This is why I smile somewhat ironically when folks deploy wheels with ET55 and think it is a "good thing".

The question most punters ask regarding wheels is whether they will fit whereas what they should ask is whether they will work- as Porsche intended and to do that they need an offset of 65mm. The thing is that once one understands the design and why it is the way it is, less diligent owners are oblivious to the fact there is something lacking. Most will probably never see an event where they actually need such until the day they do - not a good time to find out when going sideways into a wall at 100 mph. I am all for trying to improve upon what Porsche gave us but fitting kit that is less than what Porsche produced is just abject stupidity in my opinion but each to his own of course. .

DR

Doc obviously forgot to put the proper wider wheels on the rear, I have no doubt it was a handful with just the larger wheels/tires on the front......beyond that I can't see any other reason.

I guess me ,Dave C, Roger T, Jim Mayzerk, Mark A, Marc W, Tom F, Greg S, Mark K, Swaybar. and on and on and on, must be some bada$$ drivers (well we already know Mark A and Tom F are) to have been driving our 928s for the last decade or 2 with 9"+ and 65mm and higher offsets. Oh, lets not forget the Factory 928 Cup Racer program with their Factory 9.5" 68mm offset Front Wheels..



Cheers,

Dave

Speedtoys

I wont disagree with you.

Other than state that its a skill to "drive what you got, including the build in negatives" well, and then even competitively, if you dont have that skill set, or DO but dont get to develop it (track days)...then sometimes an unoptimal setup needs a heads up to some people.

Then, they know that theyre "about to learn something important"...sometimes by surprise.

hacker-pschorr

I thought they were talking about wheels with offsets under 65, since most wheels that "fit" the 928 that are "affordable" are ET57 on down....and the lower the number the more you adversely effect the handling.

Cannot say I've felt anything unsafe with my cars wearing et57's, et55's or even et52's up front, I do understand the theory behind the talk and the concerns about running such wheels.

SwayBar

Doc, my car drives perfectly, and has for years. So maybe something else was wrong with that car.

hacker-pschorr

"Larger" offset as Doc is putting it is actually a lower number..... ET45 is technically a larger offset than ET65....these are negative offsets.

This would all be a lot easier if we used backspacing instead of offset.

Jebus....buy a lottery ticket. Doc and I agreeing with each other in multiple posts

FredR

This is getting Trumpesque

Quote: ET German translation = 'Einpresstiefe' which translates as 'insertion depth'. The 60 is the measurement in 'mm' from the centre line of the wheels. Generally when you see 'ET60', 'ET45' the measurement is a 'positive offset'.