If anyone is interested I have actually been doing quite alot of research and dynamic testing at work into tyre and wheel size combinations for a future model that is under devlopment and final stages of prototype testing.
Essentailly tyre stretch cause a stiffer sidewall but also speeds up the response time, for example a steering input. this is why BMW actually use a small amount of stretch on their wheels and why the S3 will have 18x8 instead of 18x7.5 pescara's on the same size tyre 225/40/18. it makes that car that little sharper as delay is reduced as well as incereasing steering feel and lowering tyre costs for customers (reducing ultimate grip levels also)
obviosuly this is all good up until a point and then performance drops off but apart from helping with clearance/looks it will effect the dynamics of a vehicle and can be used to peoples advantage if done correctly.
Nice work on the guide Jay!
I have an offset/ wheel size/ tyre calcuator in excel that i can stick up if anyone would like, usefull for when drastically changing wheel size. If I can ever help at all or go into more detail, please give me a shout. Self proclaimed dyamics geek