Cracked my PPF at the strip!
10-09-01, 09:19 AM
#1
Original Gangster/Rotary!
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Cracked my PPF at the strip!
Well, I was warned about this. Damn wheel hop. I went to the strip on Sat night two weeks ago, made 3 passes. Best was a 13.45@109, having traction issues as usual. I had my so2 pp's in the rear at 10psi (could have been too low) and my shocks on their softest setting.
I was told that the tires I'm running are not suited for dragging b/c of a stiff sidewall that doesn't give enough, therefore transmitting too much of the stress of a launch to the frame.
Well, I started noticing a bad vibrating coming from the back of the car as I revved out the lower gears. When I was at RP on Friday I took Ari for a ride and he diagnosed my problem as a cracked PPF. $600 for a new one, $450 for a Mazdaspeed one. I told him I don't have $6 to spend on a new one right now :p
Long story short, an awesome guy by the name of Dan hooked me up with an extra he had for a song. Turned a really bad day into a great one
I'll be installing the good PPF today w/my buddy Alan, wish us luck...
I was told that the tires I'm running are not suited for dragging b/c of a stiff sidewall that doesn't give enough, therefore transmitting too much of the stress of a launch to the frame.
Well, I started noticing a bad vibrating coming from the back of the car as I revved out the lower gears. When I was at RP on Friday I took Ari for a ride and he diagnosed my problem as a cracked PPF. $600 for a new one, $450 for a Mazdaspeed one. I told him I don't have $6 to spend on a new one right now :p
Long story short, an awesome guy by the name of Dan hooked me up with an extra he had for a song. Turned a really bad day into a great one
I'll be installing the good PPF today w/my buddy Alan, wish us luck...
10-09-01, 10:20 AM
#2
Super Snuggles
Another drag racing 101 tip for ya... don't air down a stock tire. It doesn't help traction, and in fact, causes the tire to "cup" (especially with low profile tires) because the sidewalls are stiffer than the tread section. Leave them at stock pressure, and don't bother with a burnout, or if you do heat them a little, avoid the water box like the plague. The tread will hold water that can pool under the tire at the starting line, even if you do a burnout.
Also, 10 psi is too low for ANY tire... even slick manufacturers don't recommend less than 15-17 psi, and they recommend the highest pressure that still affords you good traction. Things get severely unstable at the big end on a tire with pressure that low, especially a slick, and especially on an IRS car...
Also, 10 psi is too low for ANY tire... even slick manufacturers don't recommend less than 15-17 psi, and they recommend the highest pressure that still affords you good traction. Things get severely unstable at the big end on a tire with pressure that low, especially a slick, and especially on an IRS car...
10-09-01, 10:57 AM
#3
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What's a PPF?
How can I eliminate wheel hop? I have stock R1 suspension and 265/35ZR18 Bridgestone S02's. I know the wheel hop is bad, so I want to eliminate it before I break something.
How can I eliminate wheel hop? I have stock R1 suspension and 265/35ZR18 Bridgestone S02's. I know the wheel hop is bad, so I want to eliminate it before I break something.
10-09-01, 11:15 AM
#4
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PPF = Power Plant Frame. This thing that goes under your car.
And while I do agree that 10psi is way too low. It can help quite a bit to let air out of your tire, if it is inflated to help with tread wear. Most of us are going to inflate our tires for optimum grip, and not for longer/even tread life, so it's not as much of an issue.
You don't have negative camber, do you?
Sucks to break your PPF.
And while I do agree that 10psi is way too low. It can help quite a bit to let air out of your tire, if it is inflated to help with tread wear. Most of us are going to inflate our tires for optimum grip, and not for longer/even tread life, so it's not as much of an issue.
You don't have negative camber, do you?
Sucks to break your PPF.
10-09-01, 02:48 PM
#5
Super Snuggles
Every source of information I've ever seen or heard says that you do NOT air down a street radial for drag racing, since the sidewalls will not flex and and the tread will more than likely cup, reducing the contact patch, which is the exact opposite of what you want. Martini, have you ever drag raced?
Seriously, you don't air down a radial. You should be running them on the optimum rim width and near the manufacturer's maximum pressure rating on the sidewall of the tire for proper grip, tread wear and improved gas mileage. Airing down the tires will result in a softer, slushier ride, but at the expense of gas mileage, (one of the largest contributors to gas wasting is improper airing of tires) and in drag racing, at the expense of trap speed.
Run as much air in the tires as you can, and still maintain good traction. I ran 20-25 psi in my Nitto NT-555R drag radials to get good enough grip and keep trap speed up. I've heard of people running as low as 17-18 psi, but doubt that the grip gets much better, and basically, you're trying to pull a flat tire through the traps, reducing your top end speed.
For slicks, use a tube liner if the manufacturer specifies, and run as much pressure as you can and still maintain good traction. The sidewall should wrinkle, but not distort out-of-round on launch. If it does, you don't have enough pressure in the tires. Some run as low as 15 psi, but 17-20 psi is usually about right.
As with everything at the track, experimentation is the key to finding out what works best on YOUR car. But as a general rule, airing down street radials doesn't help, and can definitely hurt.
And if you want to eliminate wheel hop, do one, two, or all three of the following...
1) Unbolt your rear sway bar at the race track. The suspension will work better in a drag race application if the IRS is not tied together. Magazines commonly perform this mod to get their quarter mile times, and you should too, especially with a stock suspension.
2) If you have adjustable shocks, don't set them on a firm or stiff setting at the track. As with the sway bar, the suspension needs to be able to move freely to plant power properly, and a stiff suspension isn't requires (and actually harms performance) on the launch. You want the front end to rise quickly and plant weight on the rear tires, and you can't do that with an autocross setting. Traction will suffer accordingly.
3) Buy a set of Unobtainium (or other) bushings for the rear of the car. Rubber bushings have a lot of compliance in them, and while this reduces road noise, it doesn't force the suspension to move in a linear fashion, and allows it to deflect and distort.
What happens with wheel hop is that the differential is not stable (as many have discovered, through PPF breakage) in the chassis. Excessive movement caused by wheel hop (wheel shudder) can break the PPF (obviously), and tear the differential bushings. The first cure for the problem is to replace the differential bushings with something with less compliance for increased performance.
Secondly, the trailing links are meant to anchor the rear suspension in place, but the compliance of the rubber front bushing allows the wheel to move, skip, and then hop. Eliminating the forward bushing in the trailing link (arm) is the second step to eliminating the slop which allows wheel hop. You can replace the bushing, or replace the entire arm with a product such as the M2 Performance replacement trailing arm.
All three of the above will result in the quickest E.T. at the track. Tuning and practice will find the combination that works the best for your car.
Seriously, you don't air down a radial. You should be running them on the optimum rim width and near the manufacturer's maximum pressure rating on the sidewall of the tire for proper grip, tread wear and improved gas mileage. Airing down the tires will result in a softer, slushier ride, but at the expense of gas mileage, (one of the largest contributors to gas wasting is improper airing of tires) and in drag racing, at the expense of trap speed.
Run as much air in the tires as you can, and still maintain good traction. I ran 20-25 psi in my Nitto NT-555R drag radials to get good enough grip and keep trap speed up. I've heard of people running as low as 17-18 psi, but doubt that the grip gets much better, and basically, you're trying to pull a flat tire through the traps, reducing your top end speed.
For slicks, use a tube liner if the manufacturer specifies, and run as much pressure as you can and still maintain good traction. The sidewall should wrinkle, but not distort out-of-round on launch. If it does, you don't have enough pressure in the tires. Some run as low as 15 psi, but 17-20 psi is usually about right.
As with everything at the track, experimentation is the key to finding out what works best on YOUR car. But as a general rule, airing down street radials doesn't help, and can definitely hurt.
And if you want to eliminate wheel hop, do one, two, or all three of the following...
1) Unbolt your rear sway bar at the race track. The suspension will work better in a drag race application if the IRS is not tied together. Magazines commonly perform this mod to get their quarter mile times, and you should too, especially with a stock suspension.
2) If you have adjustable shocks, don't set them on a firm or stiff setting at the track. As with the sway bar, the suspension needs to be able to move freely to plant power properly, and a stiff suspension isn't requires (and actually harms performance) on the launch. You want the front end to rise quickly and plant weight on the rear tires, and you can't do that with an autocross setting. Traction will suffer accordingly.
3) Buy a set of Unobtainium (or other) bushings for the rear of the car. Rubber bushings have a lot of compliance in them, and while this reduces road noise, it doesn't force the suspension to move in a linear fashion, and allows it to deflect and distort.
What happens with wheel hop is that the differential is not stable (as many have discovered, through PPF breakage) in the chassis. Excessive movement caused by wheel hop (wheel shudder) can break the PPF (obviously), and tear the differential bushings. The first cure for the problem is to replace the differential bushings with something with less compliance for increased performance.
Secondly, the trailing links are meant to anchor the rear suspension in place, but the compliance of the rubber front bushing allows the wheel to move, skip, and then hop. Eliminating the forward bushing in the trailing link (arm) is the second step to eliminating the slop which allows wheel hop. You can replace the bushing, or replace the entire arm with a product such as the M2 Performance replacement trailing arm.
All three of the above will result in the quickest E.T. at the track. Tuning and practice will find the combination that works the best for your car.
10-09-01, 07:31 PM
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Originally posted by martini
And while I do agree that 10psi is way too low. It can help quite a bit to let air out of your tire, if it is inflated to help with tread wear. Most of us are going to inflate our tires for optimum grip, and not for longer/even tread life, so it's not as much of an issue.
And while I do agree that 10psi is way too low. It can help quite a bit to let air out of your tire, if it is inflated to help with tread wear. Most of us are going to inflate our tires for optimum grip, and not for longer/even tread life, so it's not as much of an issue.
Is that not correct? If you have your tires inflated to the manufacture's specs, it should have even wear all the way across the tread, yielding the longest tread life.
correct me if I'm wrong.
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10-09-01, 11:19 PM
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Originally posted by BrianK
Wait a second... how does lowering the presure in your tire increase tread life?
Wait a second... how does lowering the presure in your tire increase tread life?
I still maintain that a lower than street pressure will give you better grip upon launch. I will agree that it will slow your trap speed.
Yes, Jim, I have.
I will admit I'm more of an autocrosser than drag racer at heart, launches are still an integral part of autocrossing, though we don't exactly set our tire pressure for a better launch, but rather, for the corners. :P
10-10-01, 04:03 AM
#9
Yellow Dragon is no more
RP reinforced Pluto's PPF several times with repeated failures after welding, etc. He has Mazdaspeed and has no problems. I have the Mazdaspeed PPF as well ... no problems. It would really suck to keep pulling everything just because you didn't want to fix it right the first time.
Also if you want to drag race ... get a drag launch kit and save yourself the head ache. You'll get better times too.
Also if you want to drag race ... get a drag launch kit and save yourself the head ache. You'll get better times too.
10-10-01, 10:44 AM
#10
Original Gangster/Rotary!
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Update!
I'm sure you've all been anxiously awaiting the results of my PPF transplant 
Alan and I both had to work late and got to the shop at alomst 7. The bastards close at 8 (I thought 9) so we resolved to put the car up on the lift and perform a recon of sorts.
Well, the PPF is definitely screwed. I big crack toward the rear (right underneath a crossbrace) and you can see where the crossbrace has been worn down by the PPF rubbing it. There's also a bigger crack right in the middle off the PPF which extends upward at least 2 inches. This one has me worried.
When I back out of the garage in the morning I can hear the damn thing creaking; makes me nervous driving my FD. I've been keeping the revs below 3 whenever possible and below 4 all the time. I also have the profec b off so I'm seeing minimal boost.
Alan and I are going back to the shop earlier tonight to finish the job.
You guys might want to put your FD up on a lift to check the condition of your ppf. I'm pretty sure both cracks on mine are from a recent trip to the strip. Very audible vibration (that increased w/revs) is what tipped me off. I would think that if you have a problem, you'll probably hear it. But better safe then sorry .
Btw, on a positive note, I'm getting awesome gas mileage
Rich
150 rwhp below 4k :p
Alan and I both had to work late and got to the shop at alomst 7. The bastards close at 8 (I thought 9) so we resolved to put the car up on the lift and perform a recon of sorts
.Well, the PPF is definitely screwed. I big crack toward the rear (right underneath a crossbrace) and you can see where the crossbrace has been worn down by the PPF rubbing it. There's also a bigger crack right in the middle off the PPF which extends upward at least 2 inches. This one has me worried.
When I back out of the garage in the morning I can hear the damn thing creaking; makes me nervous driving my FD. I've been keeping the revs below 3 whenever possible and below 4 all the time. I also have the profec b off so I'm seeing minimal boost.
Alan and I are going back to the shop earlier tonight to finish the job.
You guys might want to put your FD up on a lift to check the condition of your ppf. I'm pretty sure both cracks on mine are from a recent trip to the strip. Very audible vibration (that increased w/revs) is what tipped me off. I would think that if you have a problem, you'll probably hear it. But better safe then sorry .
Btw, on a positive note, I'm getting awesome gas mileage
Rich
150 rwhp below 4k :p
10-10-01, 02:41 PM
#12
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I think I'll check mine this weekend... ive done a couple launches with horrendous wheel hop and have heard some clunking in the rear when driving , or when i brake... i always figured it was just worn out bushings. Take pics!
