I have everything in the car. I actually have extra weight. I'm guessing that with driver at the track I'm around 3480-3500 lbs.

3400 curb weight - 15 gallons of gas = 3295+155 for me and clothes + about 40 lbs of stereo crap I'm too lazy to remove.

Thats right in my guess range.



And it depends on the tire. If you have a soft sidewalled Khumo it will make a world of difference, if you have a stiff sidewalled potenza, T1R, etc. its going to do much less for you.

I've never benefitted from it (aka had it help with wheel hop) nor does the physics make sense. You want the "air" to carry as much of the load as possible, the tread needs to lay flat, if you let the sidewall carry more you are losing grip because the sidewall is like a spring, it will hold more and more weight without sagging (to a point) as you unload the rest of the tire.

http://www.fhwa.dot.gov/pavement/utwweb/facilit.cfm

The machine they show tests the impacts of Radial tires vs. bias ply tires on pavement. Bias ply tires having continuous bandings throughout gave a more even loading on the pavement (as the pavement sees it) and the peak loading was generally in the center of the tire (like a balloon would produce). This meant that there was one peak pressure applied to the pavement and it decreased going towards the sides.

The federal DOT (FHWA) noticed that after they solved the severe rutting issues by implementing the super-pave mix design, the use of radial tires on trucks had seemed to increase the wear on the roadways. Testing shows that radial tires produce a pair of HIGHER pressure areas on the shoulder of the tire, and have a low pressure point in the center. This causes two cracking surfaces, and because of the shear levels of having the high pressure point on the edge of the tire instead of in the center, it causes the roads to "crack" or rut more than was predicted.

^^ this all makes sense given the experience I've had at the drag strip, practicing launches on a backroad with lowered tire pressure (to notice 2 skinny lines with a gap instead of 1 solid line).

Some tires it helps, I'm not denying that, some tires it makes a huge difference on, and some cars don't respond the same, on a FWD car you are unloading the tire, so I don't know the best procedure to launch - I just know what has consistently worked for me in the past, what works for the other drivers posting the top 1/4 mile times, and what I've concluded from thinking about the physics of it.

If it works for you.....great. I'll respectfully disagree until someone posts a better 60' WITH a better 330' as well (as compared with me/Veetec/warmmilk etc.) using lowered tire pressures. I still think its placebo - if you make a change to the car, and launch even slgihtly better, and there isn't wheel hop, it makes you feel like you improved something. I don't think it means you improved the car though - I've gained .2 in the last 2 months just learning to drive my car better. I don't change anything because I'm just now getting out of it what its able to make.

 

Thanks for the info Peak. I haven't taken my Nismo to the track yet, been waiting for the cooler weather here in Texas to come. But also afraid of the clutch issue that could start.

Back in the day, I was one of the fastest 2001 Maximas 5mt to run a 14.8 bone stock. Most couldn't get near that. But that was by lowering the tire psi about 5 psi and doing similar to what you said, but a lot more feathering of the clutch and gas due to fwd.

 

feather the gas of take off and when you feel the tires grab floor it.

 

Yeah, I was asking a Cobalt owner how he was launching. Hes got the smallest pulley GM has, a custom tune, etc. etc. and was running low 14's, but I couldn't imagine getting any grip off the line in that thing. Theres not a lot of weight and it all transfers to your wheels that do nothing for you.

And don't worry too much about the clutch stuff - just don't slip it too long. The only REALLY consistent thing I've heard is that it seems to be load/RPM related, and it seems to be heat related. Both of those make me (personal un-educated opinion) its something more than just one issue, that when combined makes a bigger problem. Like the slave being prone to overheating and boiling fluid, and a weaker pressure plate than should have been used. Meaning the clutch has too little grip and is prone to not being able to even provide that because of overheating issues.

Mine seems completely heat related - I don't have issues if I launch hard but get the clutch out fast, its only if I try to drag it out and keep the RPM's from falling at all. Thats when the 60' times look great and the car runs a 17 at 75 because I have to give up the run and just get off the track.

 

I am positive i could of gotten a better 1/4 time with more practice with launching ...plus the strong *** winds didnt help.

 

What the difference between a 1.5 and 2.0 way differential?


Also what is breakway TQ?

 

1.5 way / 2 way refers to lockup on accel/decel/etc. 1.5 way doesn't lockup on deceleration (lets the car rotate into a corner) and 2 way does (makes the car tend to push into the corner.

Breakaway torque has to do with the lockup rate.

 

cool cool


Thanks for the info

 

go buy an evo/sti. rev to redline and drop the clutch and let the TCS do all the work for you. I remembered the first time i heard my 2nd cousin say this(right after his mommy bought his evo for him) i was just like. .................... *sigh*

 

With an evo or STI redline launches are not a good idea, the AWD differentials have a tendency to grenade under those circumstances. My freind has learned that the hard way with his STI.

 

I think I'll stick to the z

 

i've heard rx8's and s2000's, need near redline launches for any respectable 1/4 mile times. Can those cars easily handle launches like that? and if it can is it cause of a stronger transmission or because they're low torque 4 cylin?

 

I launced at 3500/4000RPM with my wrx ..scary stuff lol

 

Wheel hop in most cases, FWD or RWD, are most likely the cause of a very soft supension and as you have already mentioned, psi. . . on my 93 prelude (196,000) miles with stock suspension i was running 15.3 in the quarter and when i went to a stiffer suspension, still stock motor at same psi as factory suspension, i ran 14.5. . .not bad for nearly 200k miles on a stock H22A1 motor. . .even though the suspension on our 07 Z's are new they still seem soft to me and have too much play, but as was mentioned before, it is good for autocross. . .my first time at the track was 13.9 with wheel hop in my Z. . .

 

Wheel hop in most cases, FWD or RWD, are most likely the cause of a very soft supension and as you have already mentioned, psi. . . on my 93 prelude (196,000) miles with stock suspension i was running 15.3 in the quarter and when i went to a stiffer suspension, still stock motor at same psi as factory suspension, i ran 14.5. . .not bad for nearly 200k miles on a stock H22A1 motor. . .even though the suspension on our 07 Z's are new they still seem soft to me and have too much play, but as was mentioned before, it is good for autocross. . .my first time at the track was 13.9 with wheel hop in my Z. . .
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star light star bright, my Z is the first star in the sky at night, wish you may wish you might but you still won't beat my Z tonight. . .










I lowered my car so I know that I don't have soft suspension. Nice job on the 13.9 I think I just need to learn how to drive on the track and try the tire pressure thing.

 

Wheel hop I was told is mostly caused by weak motor mounts. If you put stronger ones in, it usually solves the problem. It helped my 91 SE-R when I did it. Obviously this is for fwd cars.