by "bhtooefr" (bhtooefr)
Published 09/10/2017 at 20:58
by "bhtooefr" (bhtooefr)
Published 09/10/2017 at 20:58
Tags: tourist trophy
; playstation 2
; gran turismo 4
; 2wheelsgood
; cvt
; scooters
STARS: 1
Time for another “wat r u doin, stahp” post for a mid-2000s Polyphony game! There’s a rather subtle problem with this image, that not many will get.
Here’s another image, same game, same problem (really, the only difference in this image is the name of the scooter, and the power ratings) - ignore the fact that the CVT isn’t actually where it’s drawn, on a real Skywave/Burgman 650:
So, in most scooters, the CVT is fully mechanical - it’s all weights and springs.
The rear (driven) pulley has a big spring that forces it closed, causing the belt to spread the front (driving) pulley open, giving a low gear ratio - small front, big rear means high engine RPM for low wheel RPM.
However, the front pulley has roller weights in it, that, as engine RPM increases, move out from the center of the pulley. There’s ramps machined into the pulley, that these weights push on, forcing the halves of the pulley together. The belt is pulled forward by this action, against the spring tension of the rear pulley. This is how a scooter CVT upshifts.
Tuning the shift points, therefore, consists of balancing the following attributes: weight of rollers in the front pulley, strength of spring in the rear pulley, angle and shape of ramps in the front pulley (which sets up how aggressively the front pulley upshifts), and angle and shape of helix in the rear pulley (which sets up how aggressively the rear pulley downshifts). The easiest tuning, however, is to the weights, so that’s what this game is simulating. Lighter weight in the front pulley means it won’t start upshifting until higher RPM, and therefore the scooter has faster acceleration (but, go too light, and it won’t be able to fully upshift, limiting top speed). I’m actually impressed that the game simulates things to this extent.
There’s a problem though... for every scooter in the game except for these two - the 2002 Honda Forza S (known as the Reflex in the US), the two 2005 Suzuki Skywave 250s (known as the Burgman 250 outside of Japan), the 2005 Yamaha Grand Majesty, and the 2005 Yamaha TMAX - all of this is valid, and how things actually happen in real life.
For these two scooters - the 2005 Honda Forza Z (which, as far as I’m aware, never made it out of Asian markets - lower trims of the second-gen Forza were available in European markets, though), and the 2004 Suzuki Skywave 650 (known as the Burgman 650 outside of Japan)... their CVTs don’t work like that.
These scooters have electric motors that adjust the width of the front pulley, instead of weights. This means that any possible gear ratio can be reached electronically, and optimization with weights is not actually possible, and even if it were, it’d be pointless. (In fact, both generations of Forza Z and both generations of Skywave/Burgman 650 have an optional sport mode, as well as fake gears - 6-speed for the second-gen Forza Z and the Skywave/Burgman 650s, 7-speed for the third-gen Forza Z, IIRC.)
So, yeah, why not just emulate the actual bike in sport mode? It’s not like the GT4 engine (which this is based on) couldn’t do a computer-controlled CVT - GT4 has multiple cars with either CVTs or CVT-like behavior, that behave properly.
Also, while we’re at it... the game calls itself Tourist Trophy, and doesn’t have the Snaefell Mountain Course? (Maybe that’s a licensing issue, as there was a PS2 game with it, but still.)
"Mini Guy- Now has a 4Runner" (gavinharter30)
09/10/2017 at 21:34, STARS: 0
Oh wow tourist trophy. I haven’t pulled that out in a while