Bad dyno pull!

What do you think happened here? I have an idea but i want to hear from some of the more wiser folk out there.

http://www.youtube.com/watch?v=y3-cTjmWdXU&mode=related&search=

 

Tire shake. Big donuts do that sometimes.

 

tire blew on the other side is my guess

 

I think tire shake or failed 4 link.

 

Ya- tire shake or out of balance somewhere. The thing is, if the car is tied down correctly, this shouldn't happen. But, with big tires like that, guys often run really low tire pressures, and they can get out of shape a bit once the rpm levels get high. I'm sure you've seen dragster tires at speed- they get all out of round and are prone to tire shake.

A wise operator would have pumped up the tire pressure a bit before the dyno run to stabilize them at speed.

~Scotch~

 

Could have hit his brakes... Not supposed to do that on a dyno.

 

Looks to me like the trouble started when the throttle was closed.

 

I saw some smoke coming off the back from the start, not sure why.

 

I saw a blown big block rod with huge meats do that on a dyno once, when those big tires went out of round at 134 MPH, I left the area. I didnt want to get hit by flying parts.

 

I think something broke...

Right before the wobble started, the car lurched back on it's tie-downs...

Maybe he hit the breaks too???

 

From the looks of it, the guy tried to slow down after the runusing the brakes on the car and not the dyno brake. The reason I say this is you can see the car lurch rearward, this means the guy has let off the gas, then shortly after the car goes into really bad shake but the dyno does not slow down very much. If the dyno brake was applied instead of the rear brakes from the car you would hear the dyno drum slow down and hear a slight "whine" type of sound from the dyno brake being applied.

But, I could be 100% wrong too...

 

Don't hit the Brakes!

 

Looked like the car lurched backwards after the WOT pull was finished, upon slow-down.
Would the tires being out of round do that on deceleration, and not at the high rpm mentioned earlier?
It also looked like it was shedding parts.
-Brad

 

I say something inside the 3rd member let go.

 

Combination of underinflated tires/expansion at speed and hitting the brakes.
Watch the vid and you can see the tire(s) moving around as it speeds up. strapping it down tight while underinflated is more or less like running it overloaded while underinflated. The tread and sidewalls start to move around.

 

tires get tend to get outta round they want to get taller under sped. when he backed off the throttle and hti the brakes the tires hadn't yet started to unswell i guess you could say. more air pressure in the tires on a dyno, no brakes at the end of the pull and that wont happen. they were cutting loose mid pull as is i would have backed out of it. rad car though.

 

Those wheel speeds can get real high!!! I saw a kid in a blown BB Chevelle run 172 wheel speed on a 105 rated tire. Not safe......... Make damn sure your kid isn't standing where all the action it! those things scrare the hell outa me. You have been watching NHRA lately? Right!!!

 

My first thought is it don't have much HP or has WAAAAY too tall of gear. Reved up waay too slow!
But the shake, looks like he hit the brakes and then harmonics took over from there.

 

It'd make a great Loctite commercial

 

Well here is my guess. If you listen closely to the audio a few seconds after he hits full speed and lets off the throttle the engine dies. Now I don't know if he shut it down or it stalled, broke or what but it appears when that happened he didn't take it out of gear. I assume it has an auto in it but think about it, what happens if you're rolling along at speed and drop it into 1st? The tires start shaking as the road passing by tries to force the tires to rotate while the motor tries to stop them.

I bet that dyno was doing over 90 when the motor stalled. Even in an auto that's going to want to slow the tires down in a hurry!

 

if you look closely there is a white puff of smoke as the throttle is let off. almost as it the tires slowed quicker then the dyno and it smoked the tires (there was also a push of smoke off the engine as it was in throttle up mode..

glad it not my ride

 

When I worked at a shop with a chassie dyno the guy who ran it told me the reason not to use the brakes after a pull. The rollers are 3000 pounds and most cars will spin the dyno well over a 100 mph. Trying to stop that much weight at high speed with just rear brakes will glaze the brakes in no time.
Im suprised only one other person mentioned wheel speeds exceeding tire speed rating. I would not be suprised if that had something to do with the tire shake in the video. Tires do strange shit when you spin them to fast.

 

It also doesn't help that those M/T's (if that's what they are), could be of the "wrinklewall" variety. A tire with not much side support could start to shake alot easier than a tire with stronger sidewalls...