For the Lotus Elise 111R '04 using Praiano63's Tune with the power limiter set at 94% to get PP to comply with 500 & using a Final of 3.000 to slow things down a bit for data logging purposes, I purchased every legal tire for the SSXR track and observed these top speeds (at RedLine) for the below tires on the stock rims. CH - 285 KMH CM - 286 KMH CS - 287 KMH SH - 288 KMH SM - 290 KMH SS - 297 KMH RH - 297 KMH RM - 297 KMH RS - 297 KMH RI - 297 KMH WET- 297 KMH So the Comforts & Sports tires appear to have varying Circumferences per compound & the Racing tires appear to be identical for all compounds just different from the others. This could well speak to some of our performance experiences with Racing Tires on some models. I've seen posts querying this possibility this is to confirm those suspicions. I intend to test additional vehicles to prove what I am observing with the Lotus. EDIT: These differences for the comfort & sports tires may be due at least in part to growth due to speed like dragster drive slicks. While the Racing tires look more consistent and uniform indicating the difference is by design (greater diameter).