I needed some new front tires for the Elantra N for the second half of the autocross season. OEM tire size is 245/35-19, I run a lighter 18" wheel with a 245/40-18 to keep the outer diameter the same. When ordering from the Tire Rack, a pop-up screen informed me of a big discount on the tire I wanted, yeah!
When I got the tires, I realized there was also a change to the size: 245/45. It was right there on the screen, I just didn't notice it. I didn't have time to swap them out so I mounted them for the fall. Now, the past three events have been some of my best finishes ever. Huh....
The tire is 1" taller than I usually run. Could the change in sidewall really make a difference? Or is it just fresh tires and more experience? Weird.
It would be like changing gear ratios. Are you in a lower gear and able to keep up due to the taller tire? Lower effective ratio? A bigger sidewall will give more compliance and is effectively lowering your spring rate. That should transfer balance forward slightly. Could it make a difference, sure. I'd bet more on that the old tires were heat cycled and fresh rubber is the biggest difference.
This reminds me of those old spark plug test ads.
"We replaced these OE plugs with our super-trick, quadruple prong, unobtanium tipped, double-the-price, space age plugs and found 2 horsepower on the dyno"
Failing to mention that the OE plugs had been in the vehicle for 100k miles and the gap was all wrong.
To the OP...most likely just new versus old...but the gearing mentioned elsewhere might also factor in.
I intentionally run a "wrong" size tire on my 03 Merc, since I haven't had to opportunity to do a gear change. China Mart and Sam's will not mount them.
Might not really be related to your racing, but I do get better MPG with this combo (including after correction facto) and other minor benefits.
I would assume your difference is in the effective gear ratio change.
In reply to Andy Hollis :
Hahaha, yep! Like the old tests you used to see in Super Street and the like.
"This header makes 23whp!" Please ignore this was compared to a stock header on an engine with headwork and cams, so the aftermarket header actually did something.
