skrotch

I recently bought a different size pinion gear for my electric Redcat and the stock pinion is a 48 pitch and has 26 teeth. I bought a 48 pitch 28T Team Losi gear and it is a tiny bit smaller ( Maybe a few 1/100th's of an inch ) than the 26T that I took off? I thought it should be a little bigger. Does anyone know why? Is this going to make the car have more top speed? I thought more teeth, higher top speed, but what if the gear is smaller in diameter. Any help would be greatly appreciated.