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Old 12-30-2010, 04:26 PM   #4
Johnny Danger
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Join Date: Nov 2008
Location: Massachusetts
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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...........
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 .
Don't worry … I've got the microfilm.

Last edited by Johnny Danger; 12-30-2010 at 04:29 PM.
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