The Honda PCX / Forza / ADV150 / SH Forums

Yeah that's the obvious. Larger tire/wheels less rotation, lalala. How much of "that" makes a difference. It adds itself to the mix. Honda has the recipe enhancements "Little by Little by Little by Little...."
They keep us interested. Here We Are! Again

iceman wrote:

WhiteNoise wrote:Larger
100/80-14 F 120/17-14 R

Shouldn't that give a higher top speed as more ground covered for each rev (queue the 'it's not as simple as that replies')

You're right, it's not so simple to say the new tires are larger.

Old rear tire: 100/90-14, 21.1" diameter, 66.2" circumf., 956 revs/mile
New rear tire: 120/70-14, 20.6" diameter, 64.8" circumf., 978 revs/mile (-2.2%)

Old front tire: 90/90-14, 20.4" diameter, 64.0" circumf., 990 revs/mile
New front tire: 100/80-14, 20.3 diameter, 63.8" circumf., 994 revs/mile (-0.4%)

As you can see from the sizes and measurements above, while it's true the 2019 tires are wider than the older version (by 10mm in front and 20mm in back), the new tires also have a lower aspect ratio than the old tires. I plugged the old and new sizes into the Miata tire size calculator ( https://www.miata.net/garage/tirecalc.html ) and it turns out the 2019 tires actually have a smaller radius/diameter and therefore a smaller circumference than the older tires.

So even though they are wider, they actually require more revs per mile than the older tires (assuming the gearing is still the same) and would therefore result in a lower top speed. For the 2019 to be significantly faster than the old model (despite being saddled with shorter rear tires that need to rev 2.2% more per mile than the old rear tire) it must have taller gearing or more hp/higher redline, or some combination thereof.

WhiteNoise wrote:...By the Way....Hi GREG, welcome back to the fold! PCX FEVER again?

Thanks WN! Yes, I've got the fever! I bought a convertible about 9 months ago and have barely ridden my Interceptor since - it's gathering a lot of dust because I'd rather drive my vert with the wind in my hair, sound system, cup holders, etc. I think I'd get a lot more use out of a scooter now for fun little trips to the store, gym, post office, etc, places I used to take my old PCX all the time.