well the streched tire does give the feel of a stiffer sidewall because it can transfer more enegry into the ground. This will make the 215's on the 10" rim feel like stiffer tires. Also by stiffining the sidewall (effictively) you can run lower tire pressures and get a larger contact patch. The contact patch is unaffected if you only change tire size. If you upgrade from a 205 to a 235, your contact patch will be identical assumming you dont change your tire pressure. Contact patch=load+PSI. It does however change the shape of the contact patch which matters greatly. Width doesnt matter for contact patch. With overall lateral grip it does matter though. With a wider tire your spreading the load over a larger width and thus are able to run lower tire pressure and that does increase your contact patch. Running 215's on 9" wheels vs 215 on 10" wheels makes no difference in the contact patch, but it does change the overall feeling of the tire. It should give you slightly more oversteer tendencies vs having a non-streached tire. I think that all makes sense. Go here and read up if I can explain it correctally.
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