wheel sizes, gear ratios, and bucking trannies
Thread Starter
Registered User
Joined: Feb 2003
Posts: 361
From: ghettos of malibu, yo
wheel sizes, gear ratios, and bucking trannies
Ive got 18" wheels on my wrx...how does this affect all the gearing in the car? What I mean is, will my top speed in x gear be significantly different? What are the top speeds for each gear, stock?
Also, is the speedo affected? I feel like when I drive the speed limit, everyone is driving faster...but it seems like with the larger diameter the speedo would register and slower speed (since the wheel turns less for a given speed).
Also, just out of curiosity, what causes the bucking when you're in a low gear and your foot is off the clutch pedal, but not on the throttle? Like when youre in first cruising around the parking lot, and it bucks if you aren't using one of the two pedals. Is this just friction? But if it is, why the 'bucking'...why doesn't is just slow down?
Also, is the speedo affected? I feel like when I drive the speed limit, everyone is driving faster...but it seems like with the larger diameter the speedo would register and slower speed (since the wheel turns less for a given speed).
Also, just out of curiosity, what causes the bucking when you're in a low gear and your foot is off the clutch pedal, but not on the throttle? Like when youre in first cruising around the parking lot, and it bucks if you aren't using one of the two pedals. Is this just friction? But if it is, why the 'bucking'...why doesn't is just slow down?
Registered User
iTrader: (7)
Joined: Dec 2002
Posts: 10,029
From: Sacramento CA
Car Info: 02 Impreza WRX sedan
It's the overall diameter of the tire that determines compatability with the stock speed sensor. For an increase in wheel diameter, the aspect ratio of the tire must be decreased numerically to maintain a similar overall wheel/tire height and diameter.
https://www.i-club.com/forums/showth...eet#post411480
--
0==WW==0
"…axles of evil…" - george w. bush
https://www.i-club.com/forums/showth...eet#post411480
--
0==WW==0
"…axles of evil…" - george w. bush
Registered User
iTrader: (7)
Joined: Dec 2002
Posts: 10,029
From: Sacramento CA
Car Info: 02 Impreza WRX sedan
Origami posted by dorrington
Also, just out of curiosity, what causes the bucking when you're in a low gear and your foot is off the clutch pedal, but not on the throttle? Like when youre in first cruising around the parking lot, and it bucks if you aren't using one of the two pedals. Is this just friction?
Also, just out of curiosity, what causes the bucking when you're in a low gear and your foot is off the clutch pedal, but not on the throttle? Like when youre in first cruising around the parking lot, and it bucks if you aren't using one of the two pedals. Is this just friction?
--
0==WW==0
"…axles of evil…" - george w. bush
Thread Starter
Registered User
Joined: Feb 2003
Posts: 361
From: ghettos of malibu, yo
hmm..interesting...
but it occurs between 2 and 3 thousand rpm i feel, and thats about cruising rpm. basically you're saying that the engine doesn't "like" to be at that low end?
but it occurs between 2 and 3 thousand rpm i feel, and thats about cruising rpm. basically you're saying that the engine doesn't "like" to be at that low end?
Guest
Posts: n/a
Ahh sooo!
You get bucking at 2k to 3k rpm when driving in a parking lot? This suggests you are letting your foot off the throttle from time to time and you get a sudden loss of speed. Is that right?
If that's what you are talking about, you are experiencing the effect of engine compression braking coupled with short gears (I'm assuming first gear). The engine braking is the same as other gears. However, with other gears you are moving much faster and the momentum of the car overcomes the engine compression. Additionally, the rpm impact on will be less severe when you are in a higher gear (taller gear, lower gear ratio). For each rotation of the wheels you are pushing the engine at greater rpm (lower gear equals less wheel rotation for greater rpm - think backwards). So it's doubly easy to use engine braking smoothly at higher gears, but not first gear.
You really want to avoid jerking your car like this. It's hard on the driveline. Metal bits get slammed around. Try being smooth. Don't be afraid to slip the clutch a bit. In the long run it's probably easier on the clutch to slip rather than jerk around.
MadRich
If that's what you are talking about, you are experiencing the effect of engine compression braking coupled with short gears (I'm assuming first gear). The engine braking is the same as other gears. However, with other gears you are moving much faster and the momentum of the car overcomes the engine compression. Additionally, the rpm impact on will be less severe when you are in a higher gear (taller gear, lower gear ratio). For each rotation of the wheels you are pushing the engine at greater rpm (lower gear equals less wheel rotation for greater rpm - think backwards). So it's doubly easy to use engine braking smoothly at higher gears, but not first gear.
You really want to avoid jerking your car like this. It's hard on the driveline. Metal bits get slammed around. Try being smooth. Don't be afraid to slip the clutch a bit. In the long run it's probably easier on the clutch to slip rather than jerk around.
MadRich
Thread Starter
Registered User
Joined: Feb 2003
Posts: 361
From: ghettos of malibu, yo
oh yeah...i DO keep it smooth, but I was curious to know what it was that caused it to buck...I figured it was engine braking, but I didnt know why it jerks
its done it on every car I've owned if you dont use the clutch enough. usually if you keep your foot on the throttle just a bit, it stays smooth but you slow down...or you could just shift to 2nd...
its done it on every car I've owned if you dont use the clutch enough. usually if you keep your foot on the throttle just a bit, it stays smooth but you slow down...or you could just shift to 2nd...
Thread
Thread Starter
Forum
Replies
Last Post