My Yaris accelerate too slow !!! any suggestions ??

[CrankyOldMan]

If you're into math/physics, here's a brief explanation of the laws that govern acceleration of rotating bodies: http://en.wikipedia.org/wiki/Moment_...ntum.2C_torque
This really boils down to an increased moment of inertia and a fixed energy source, so the angular velocity has to decrease to keep things in equilibrium.

If you're not into the actual math, here's a brief summary:

Going to a larger diameter wheel moves more of the mass away from the axis of rotation. Rotating a mass at a farther distance requires more energy to achieve the same acceleration/angular velocity. Try sitting in an office chair and spinning around while extending/retracting your arms. Now try it with your arms extended, then try with your arms extended holding some small weights.

In the case of your wheels, you've gone to a larger diameter wheel (15" to 16") that is also likely wider than stock (5.5" to 6.5"). Your tire diameter didn't change significantly (1mm smaller) but you also added 10mm of width. Even if you kept the weight (mass) of the wheels and tires the same, you would still lose acceleration and top-end speed because you (in theory) haven't increased the power available from the engine. I know you tried a few things, but the energy required to compensate may be more than you can get from bolt-on parts.

I discovered the same thing the hard way when I replaced my winter tires (175/70R14) with sticky summer tires (205/50R15). The only mathematical solution to counter this is to go with crazy lightweight tires to reduce the moment of inertia, but that's not financially do-able for me right now.

[Jack Yak]

Originally Posted by tk-421

A wider exhaust tube will affect your top end, simply because you're losing back-pressure. Heavier/wider wheels will also affect your overall speed because of added rolling resistance.

At this point the only thing that comes to mind is to check your air filter and all related couplings. The filter should be as clean as possible, and the couplings should be very tight to make sure that there aren't any leaks adding to the problem.

You might also want to consider getting rid of any dead weight (ie try to keep your trunk empty), which actually makes a substantial difference with our cars.

Hope that helps!

i think 2" inches tube is fitting perfect ... and i thought it won't losing back-pressure !! ?

it isn't related to the cleanness of the Airfilter because i did some tests while the filter was new - after purchasing it - .. and the same result !!

Originally Posted by eTiMaGo

my question is, how long was it between you doing 180km/h and your next try that only did 160? Did you have the other mods too at that time?

long time !! .. about 9 months but i didn't change anything just the wheels and installing K&N Filter

Like tk-421 said, wheels can affect rolling resistance, your exhaust and intake might actually increase mid-range torque a little, but reduce top end power, it's hard to be sure.

I suggest you to check and clean your air filter. I let mine get real dirty over time, and it really sapped a lot of power, made a huge difference when I finally cleaned it up!

Originally Posted by Motorhead6T5

Wheels are probably taller and heavier. Making it accelerate slower and show a lower top speed on the speedo. I noticed a big difference switching from 17# 16's to 11# 15's as far as acceleration goes.

Originally Posted by CrankyOldMan

If you're into math/physics, here's a brief explanation of the laws that govern acceleration of rotating bodies: http://en.wikipedia.org/wiki/Moment_...ntum.2C_torque
This really boils down to an increased moment of inertia and a fixed energy source, so the angular velocity has to decrease to keep things in equilibrium.

If you're not into the actual math, here's a brief summary:

Going to a larger diameter wheel moves more of the mass away from the axis of rotation. Rotating a mass at a farther distance requires more energy to achieve the same acceleration/angular velocity. Try sitting in an office chair and spinning around while extending/retracting your arms. Now try it with your arms extended, then try with your arms extended holding some small weights.

In the case of your wheels, you've gone to a larger diameter wheel (15" to 16") that is also likely wider than stock (5.5" to 6.5"). Your tire diameter didn't change significantly (1mm smaller) but you also added 10mm of width. Even if you kept the weight (mass) of the wheels and tires the same, you would still lose acceleration and top-end speed because you (in theory) haven't increased the power available from the engine. I know you tried a few things, but the energy required to compensate may be more than you can get from bolt-on parts.

I discovered the same thing the hard way when I replaced my winter tires (175/70R14) with sticky summer tires (205/50R15). The only mathematical solution to counter this is to go with crazy lightweight tires to reduce the moment of inertia, but that's not financially do-able for me right now.

i know that wheel increasing the rolling resistance and causing decrease of the top speed ... but isn't it too much to decrease the top speed from 180 km/h to only 160 km/h !! ? i thought it only decrease the top speed by low rate !! ??


... btw: i did a test 2day with new stock airfilter - removed the k&N - and it only accelerate to 163 km/h