My car is slower after mods

[cleong]

I first took my car on a top speed run when it was about a year old. At that point of time, the only mods that it had were lowering springs, and aftermarket rims with 195/55/15 tires. It posted a maximum of 194kph or 120mph (GPS recorded).

Since then, I have modded the car with a DC header, and Fujitsubo axle-back exhaust. I have also switched to Iridium spark plugs, but now I'm running 195/60/15 tires. This setup was dynoed to produce 102 whp which I believe is significantly more than the stock 90-odd whp. However I was only able to post a maximum of just 181kph or 112mph, measured with the same GPS on the exact same run, and I have repeat this run a few times with the same result.

I'm wondering where the speed went. Did I get a tailwind on the first run, or did my mods actually hurt the car's overall speed? I was under the impression going to a taller tire profile would actually help the car's top speed. Keen to know what you guys think of this.