06SuperWhite_SoCal_tC

I'm pretty sure you can rule out the Wheels... Think of it this way... If the speedo is only reading 118mph than the ECU only thinks the car is going 118mph. Therefore Maybe the Wheels are throwing off his actual speed, but it wouldnt show on the ODO, only in what his car is actually doing vs. what the Speedo says he's doing.

Jan06xB

How fast do you think they spin when they balance them? How fast do they spin when you are driving down the road at 120mph? If they are balanced properly you should be able to spin them up and spin them down in a few seconds - not like the car is going to fall off the blocks and take off into a wall - that only happens in the movies just like explosive decompression in the movies with people getting blown around and sucked out the window . . . only in the movies! In real life your ears pop and a puff a wind blows by for a few seconds. Just make sure you spin both tires together or else one will spin at twice the speed if the other is stopped.

torqueTc

iTrader: (11)

Kydog, were cool man, dont worry! you can read my thread!!

turbogsxr750

i really hope you are joking. running a car up to 120 mph on a jack stand is no where near safe. you think that a just a tire or axle vibration can make it come off of the stand? Anything can go wrong while doing that. Have you not seen dyno runs were a car has come of due to some malfunction. They have safety precautions in place for these resaons and things still go wrong. That is also like saying that since i have a jack under the car that i can go under there and the jack will protect me. How many times has that been a persons last thought? you ask how fast do you think they spin when driving down the road at 120..... probably 120 considering the sensor is usually on the inside of the wheel. What you may not realize is the wheel of a car only touches the ground every 8 feet or so at 120 MPH due to variations in the texture of the road.

let me guess you are one of those guys that thinks a guy smoking while filling up his gas tank at a gas station is going to catch on fire.

Jan06xB

Block of wood or cement under the suspension and if it is vibrating then get the wheels balanced. If you want to be even safer then take the wheels off and just spin the rotors. Geez you sure you have worked on cars before? Guess you shouldn't rev the engine in neutral to red line in case it jumps into gear and takes off into a wall either huh?

aen

im not sure about you but if i were to do that and the wheel ONLY vibrates at 120 mph. i wouldn't be TOO concerned.....

in fact if i were to do that i don't think id have hte guts to push it that fast to see if it even vibrates.

Resu

I've got to complament you on using your head while testing the car.

Jan06xB

Guys Guys it will be like throwing a rev and with the wheels off it will rev up and back down in a couple of seconds. It is NOT like running a dyno where you are at full throttle and pumping out max horse power with the chassis chained down to the ground so it will not take off and all sorts of torque being generated to the wheels and the dyno drums. Just don't slamming on the brakes all of a sudden while in gear at high RPM because that is going to put a lot of strain on the gearbox and clutch assembly.

deathbyc4

come on, this is an easy one. Seafoam your engine, take out your interior, get a 5 angle kanooter valve job, re-grease your seat lugs, change the air filter in your radio, and you will get you top speed back.




Honestly, probably the wheels or the ecu if the wheels are real close to the same diameter as the stock ones, which i doubt. of course, the ecu is not as acurate at cutting off either, lots of variables.

engifineer

The needle isnt off by a percentage if the needle is installed incorrectly. It is off by a certain amount all the time. So if it was reading 118 at 127, it would be reading 1 when he was running 10mph, so that would be pretty noticeable.

boostaddict

jan06xb im going to agree with everyone sayin that its not safe. a block of wood? are u serious dude the tie downs that they use sometimes arent much of a help. picture 1 jack stand fallin while the front wheels are spinning at 90mph(ok even 30) that car is going to hope all over the place and the pretty block of wood will be in the same spot. let alone even perfectly balanced front wheels at 90 will prolly cause such a vibration it will fall off the jack stand. u might as will just set the cruise at 90 and go out for lunch. srry im not going to flame you but i will ask did u graduate high school because that was the dumbest thing i have ever heard..you can do that for ur XB and make sure no one is around but no one else try that. id rather take my chances sky diving without a chute!

Jan06xB

I can see that you have not tried it. When the wheels are balanced on a tire balancing machine they are spun at about 80-90 mph and are balanced to within a quarter ounce if the tire guy knows what he is doing. Second the energy stored in a 26-30 lbs spinning tire is not going to do much to a 3600 lbs car if it did touch the ground. Third it will not vibrate off the block of wood unless you are using a piece of 2x3 on end - I am talking a 6x6 a few feet long under the suspension spring and the weight of the car is going to be holding it down on the wood so figure about 1000 lbs of weight on each block of wood being shaken off by an ounce of imbalance?? Not going to happen. Fourth I said if you want to just take the tires off and then it really will not go anywhere and you get rid of the spinning weight. Remember you don't have the entire mass of the car moving at 120 mph you have only the tire moving at that speed and a quick tap of the brakes will stop it in an instant plus you can just push in the clutch. Believe me if you get vibration at any speed while on the block you will have that same vibration on the road and you should not, so that is no problem. Like I said my friend did it with his Toyota last month with the tires off and with his wife on the gas pedal while he looked under the car on blocks and that was the only way he could have found out about the CV Joint boot getting out of balance by a big blob of grease inside it causing it to vibrate over 60 mph. It ended up damaging the differential and transmission seals requiring a $1500 rebuild of the tranny which was done BEFORE he jacked it up and found the boot bad AFTER the tranny work had been done! Don't put the body up on blocks because you will have the axles hanging at the wrong angle - you have to block up the suspension under the springs is best. I am an engineer and have been working on cars for about 35 years and my brother has worked on cars of all types, motorcycles and jet engines in planes and helicopters and balances tires for motorcycles that go 180 mph. I know what I am talking about.

engifineer

.

The rotational inertia of a car wheel will not make it tear through a shop UNLESS you are still on the throttle and just hold it down.. but it will do a lot of tire smoking in the process. If you dont want to take someones word for it, mythbusters even proved this by trying the old driving onto a moving trailer myth. When hitting the ramp, the tire treads are moving at 60mph in relation to the ramp, but conservation of momentum does its job and keeps the car from launching into the truck.

But again, I am leary to hear of a bunch of kids setting their car on a set of cheapo jack stands and running it up to speed as well

olaHalo

^^good ol mythbusters
love that ____

Jan06xB

So I guess you don't want to hear how I turned my brake rotor while jacked up with the engine running in gear with one tire on the ground.
Yeah that sudden change in speed will definately make for a little smoking tire action just like when an airplane lands - those skid marks at the end of the runway are the tires spinning up to 120 mph as they touch down.

monkeysauce

a ScangaugeII will allow you to input your tire size to get an accuate speedo reading. Some GPS units can also calculate your actual speed.

HunterGreene

Bringing it back to the top speed issue (ok, it wasnt that far off), I thought that the car was gear-limited at 127, not a fuel cutoff, like a rev above redline.

Dumb question, but how much gas was in the tank? Sloshing around due to accel. could cause a cutoff

Jan06xB

I think they have a speed limiter which works on the speed sensors in the wheels in addition to the rev limiter on the engine so that you don't go TOO fast. I think the xB may have a speed limiter also - guys with turbos should chime in on this one..

engifineer

The tC has both a rev and speed limiter. Without the speed limiter it would be gear limited at somewhere around 135 or so.. if it isnt power limited before that. I would guess reaching the gear limit on stock power would be pretty tough with 160hp.

joonsmart

yeah..i tried mine last week on my at tc when raced with moded up 350z, we started around 60mph and i topped up at around 120mph and wouldn't go any furthur and that the time that 350z cut me off...i wonder what the top speed of 350z can go...60-120mph i got no problem with 350z..only 0-60mph and 120mph up.... hehe