18" wheels on a '97?

[JFP in PA]

Bad idea. The 97 should not run 18" as several key suspension mounting points and the engine bulhead area are not strong enough to handle it, and modifying the car to prevent metal structure failure is very expensive. Cheaper to buy a later car...........

[Johnny Danger]

Originally Posted by JFP in PA

Bad idea. The 97 should not run 18" as several key suspension mounting points and the engine bulhead area are not strong enough to handle it, and modifying the car to prevent metal structure failure is very expensive. Cheaper to buy a later car...........

JFP,
As one of the most astute members of this forum, I value your opinion. However, it seems that the caveat for the 2.5 platform is that its suspension lay-out and structure is not designed to withstand the additional weight and load bearing that a larger diameter wheel would presumably create. What do you think of the concept of using a light weight after market wheel to reduce unsprung weight and rotational mass in order to mitigate this concern ?[/QUOTE]

Won't work on the 97 car as it is not a weight issue, but one of mechanical leverage; the body structure is not designed to deal with the mechanical leverage the large diameter wheels put on the chassis at the suspension mounting points (think of a larger diameter wheel acting like a longer breaker bar). The bigger diameter wheels also cause the car to twist more, cracking the welds in the forward bulkhead ahead of the engine. Excellence magazine did a good article on this problem not long ago if you’d like to learn more about it.[/QUOTE]

Now that makes sense to me. Thanks for the clarification. Do you mind if I post our discussion so others may understand this issue as well ?[/QUOTE]

I have no issue with you posting it, just be prepared to get into a full blown discussion of vehicle dynamics. While the weight of a wheel/tire combo does matter, even if you found an 18 inch setup that was actually lighter than the smaller wheel/tire, say the 18” Carrera ultra light five spokes and some tire, and this combination that retained a constant contact patch area (the area of the tire actually on the road), the car will still see increased torsional and leverage mechanical loads. Then you need to factor in the wheels “measured diameter” against its “effective diameter” (larger diameter tires have stiffer sidewalls, make the small increase in the measured wheel diameter seem even larger to the vehicle), and so on. Increase the measured contact patch, or use a stickier tire, and the effective diameter increases even more, increasing the loading of the chassis.

Ain’t chassis dynamics fun?[/QUOTE]

I agree that posting this discussion will likely trigger some armchair experts to espouse their view points . Still, I think that it would informative for a lot of 2.5 owners contemplating changing their wheel size .

[RandallNeighbour]

Well, I have a 97, I'm running aftermarket 18 inch Carrera lights (not nearly as light as Porsche wheels either) and my car is lowered 1.5 in the rear and 1 in the front.

I even drove the piss out of the car on a track with these rims on it and had no frame damage.

If you ask me, this was Porsche doing some serious CYA. Slauson, on the Porsche web site Q & A section, commented that he did not see it being a problem as long as the car was being flogged on a track with 18's on it.

Ooops. :dance:

I wouldn't let the fact that the car is a 97 keep you from buying it. I would, however, caution you not to buy a 97 that has not had just about every freakin' part on it replaced already with receipts to prove this fact.

The motor should not be original, nor should the coolant overflow tank, and the list goes on and on and on.

Save up and buy a newer S model. What you spend in repairs on a 97 in the first two years will be more than enough to buy a 2000 S in two years.

Seriously. Don't do what I did unless you have found a meticulously cared for 97 with a very fat folder full of receipts and the 2.5 scares the crap out of you and you would never want more HP.

[JFP in PA]

Well, perhaps you were lucky. Over the years, I've had two 97's pass thru the shop, one on 18's, one on 19's, and both with the exact chassis problems mentioned in the Excellence article, neither had ever been on a track to my knowledge. Neither was easily repairable (one I believe was eventually parted out). I would also note that there is a lot of chatter amongst the Spec Boxster crowd against buying the 97 chassis for the same reasons. Can't all be a myth................

[RandallNeighbour]

JFP, how did you know you had subframe issues on your 97's?

[JFP in PA]

From our records, “Metal fatigue type cracks or splits in the metal, some around the suspension mount areas", on the worst one "there are significant cracks in the driver’s side forward bulkhead area, near with the rear chassis meets it.”

Of all the Boxster model years, 1997 is the one we see the fewest of, probably due to age and the fact there were not that many of them to begin with. Currently, our active customer base only contains a couple of them. To see two with metal fatigue failures out of such a small "sample" has to be considered unusual.

[keithl]

18s are fine on a '99 right?