Tire failure on dyno

[Dick]

I've noticed that there are a number of Dyno operators on the forum and wondered if anyone has had an experience like the following. (I know this is not directly EFILive oriented, but.....)

I had a customer with a big block powered Camaro with a transbrake T400 that is only used for racing. The car usually turns in the low 10's in the quarter. Anyhow, we were doing some evaluation and had made 3 runs in high gear only, running from 3000 to 6800 RPMs. Having noted some interesting engine responses with different timing, we decided to make some quarter mile runs to identify the best setting. A run was made and completed at 122 mph when the throttle was released. About a second and a half into the deceleration, the drivers side tire had a catastrophic failure, followed by a second failure on the passenger side. The tires were brand new Goodyear wrinkle-wall slicks (exact type unknown) and had not been run since installation. Pressure had been set to 9 PSI for testing. The rear end had a spool installed, so both axels were tied together. The first tire to fail had a section about 3 foot long beating the devil out of everything in reach. Both tires and wheels were damaged beyond further use.

We go a long way to try to protect the customer from vehicle damage, but sooner or later doo-doo happens. At any rate it's pretty awkward for the Dyno shop, not to mention the customer who just lost $1000 worth of tires and wheels along with body damage to the car. While we have run many cars with slicks, this is our first such "event". My question to those of you with applicable experience; if this has happened to you, what do you now do to minimize this sort of failure?

Regards,
Dick

[GMPX]

Dick to be honest (and this is from someone who isn't a dyno operator), I have not heard of people doing 1/4mile simulated runs on a dyno, at a guess I would suggest the tires just got too hot!.
I know the times I have seen high HP cars getting beaten up on the dyno it's normally the smell of hot rubber that hits first.

Cheers,
Ross

[emarkay]

Was that a dyno run from a full stop? How hot were the tires before the pull (and the pressure before the run, was it checked?) Also not a dyno expert, but there's a potential for a much greater load on the tires on a dyno than in the 'real world',

Also being that both tires failed, is there any possibility of contact with some part of the car that could have initiated th failures?

Glad no one was hurt, that could have been much worse!

[caver]

I have had tyres seperate at speeds over 200km/h but those were road tyres that had maybe been underinflated on the road.

The only reason I can think of is that you just ran them too long and at too low a pressure.
The dyno rollers deform the tread area significantly.

I also make a point of staying under 200km/h if at all possible.

[Dick]

From GMPX:
Dick to be honest (and this is from someone who isn't a dyno operator), I have not heard of people doing 1/4mile simulated runs on a dyno, at a guess I would suggest the tires just got too hot!.



Ross, quarter mile runs on the dyno are not at all unusual. The dyno we use is a Mustang MD-1750-DE which is rated at 1750 HP and 225 MPH. The unit has 50 inch rollers to minimize tire distortion. The dual eddy current units simulate road and air drag as the vehicle accelerates. One shop, about 125 miles from us holds regular 1/4 mile competition during the winter months. That the tires got too hot is not to be discounted. We normally check tire temperatures with an infared thermometer and have never seen excessive temps. However, we are caught with our pants down on this one, as we failed to check on this car.





From emarkay:
Was that a dyno run from a full stop? How hot were the tires before the pull (and the pressure before the run, was it checked?) Also not a dyno expert, but there's a potential for a much greater load on the tires on a dyno than in the 'real world',

Also being that both tires failed, is there any possibility of contact with some part of the car that could have initiated th failures?

Glad no one was hurt, that could have been much worse!




The test that resulted in failure was a trans-break launch. As I mentioned, temperature was not checked, pressure was set to 9 PSI. Re the greater loading, I can not say as I have no real life data to support any position. Re contact with dyno parts, there are 4 rear straps securing the car with 2 on the front. The rollers are 50 inch which keeps the tires a fair distance from the plates. In addition, one person (myself in this case) monitors from the side for anomalies during the run. Nothing unusual "was seen". The pity is, there was a digital camcorder in position at the time, unfortunately it was not recording during this run. Believe it or not, the owner was thrilled that it happened on the dyno as the same failure would have put him into the wall or flipped the car had it been at the track.



From caver:
I have had tyres seperate at speeds over 200km/h but those were road tyres that had maybe been underinflated on the road.

The only reason I can think of is that you just ran them too long and at too low a pressure.
The dyno rollers deform the tread area significantly.

I also make a point of staying under 200km/h if at all possible.



These tires were brand new and had not yet seen the asphalt. Re running too long, there had been just 3 third gear power sweeps (10 seconds each) prior to the run that resulted in failure. I just checked the times of the runs and they were separated by 20 to 25 minutes each time. We had no reason to suspect high tire temperature, but as I said earlier (hanging head), we failed to actually check. We have run many cars over 150 MPH (241 KPH, had get my calculator out) without incident. We always check pressure, speed ratings and condition first.


I'm not trying to rationalize, but rather answering what questions I can with the facts as I know them. I appreciate the feedback and welcome any experiences or wisdom that might be available.

Regards,
Dick

[Delco]

We do not generally run a slick tyre on the dynop for reasons such as you have experienced , even with a radial we overinflate the tyres to about 40 lb to get best traction , I would suggest with the massive loading on a very low pressure you may have got the sidewall deflecting enough to contact the roller and damage the sidewall

[MN C5]

We do not generally run a slick tyre on the dynop for reasons such as you have experienced , even with a radial we overinflate the tyres to about 40 lb to get best traction , I would suggest with the massive loading on a very low pressure you may have got the sidewall deflecting enough to contact the roller and damage the sidewall

I agree, 9lbs and hold down straps never allowed the tire to come out of its distorted shape.

[Dick]

We do not generally run a slick tyre on the dynop for reasons such as you have experienced , even with a radial we overinflate the tyres to about 40 lb to get best traction , I would suggest with the massive loading on a very low pressure you may have got the sidewall deflecting enough to contact the roller and damage the sidewall

Delco, I appreciate the input. Have you folks actually experienced a failure, or is yours a precautionary stance?

Not being a tire expert, there is a lot that I do not know about the dynamics of a racing slick. I do know that at high speeds, these tires actually go through the traps flat in the rear so that they assume a "D" shape. It is claimed about the Top Fuel cars, that at speed, 7,000 pounds of down force is exerted by the wings. If what you speculate is true, I would guess that the problem is caused by the contour of the roller rather then massive loading. I do intend to follow up with the tire company Racing Division to see what they might suggest. I sure don't have any desire for additional "experiences".

I find your comment re high pressures on radials interesting. We've been doing a bunch of tests on a radial drag tire equipped car and I had not considered using high pressure to augment traction. I will certainly explore that approach.

Regards,
Dick

[ChipsByAl]

Dick one possibility could be the brakes on the dyno. I am familar with the Mustang dyno and it can slow the car down pretty quickly. If the slicks were tied down good, that unusual braking event could have caused an internal belt failure. The tires still had a lot of inertia spinning at high speeds and were set in a forward acceleration stance. Possibly if this is tested again the car should be allowed to slow down on its own or use some vehicle braking. Just not too much to overheat the vehicles brakes.
AL

[Delco]

Delco, I appreciate the input. Have you folks actually experienced a failure, or is yours a precautionary stance?

Not being a tire expert, there is a lot that I do not know about the dynamics of a racing slick. I do know that at high speeds, these tires actually go through the traps flat in the rear so that they assume a "D" shape. It is claimed about the Top Fuel cars, that at speed, 7,000 pounds of down force is exerted by the wings. If what you speculate is true, I would guess that the problem is caused by the contour of the roller rather then massive loading. I do intend to follow up with the tire company Racing Division to see what they might suggest. I sure don't have any desire for additional "experiences".

I find your comment re high pressures on radials interesting. We've been doing a bunch of tests on a radial drag tire equipped car and I had not considered using high pressure to augment traction. I will certainly explore that approach.

Regards,
Dick

Yes I have experienced similar failure.

A racing slick expands in circumfurance as it speeds up so a top fueler is riding on a very small contact patch at the top end , also 9 psi is very low in pressure for on the dyno - at the track where you are trying to maximise contact patch it is ok but on the dyno you dont want or need the sidewall distortion as in effect you only need to get the power down not move the weight of the car.

[Dick]

Dick one possibility could be the brakes on the dyno. I am familar with the Mustang dyno and it can slow the car down pretty quickly. If the slicks were tied down good, that unusual braking event could have caused an internal belt failure. The tires still had a lot of inertia spinning at high speeds and were set in a forward acceleration stance. Possibly if this is tested again the car should be allowed to slow down on its own or use some vehicle braking. Just not too much to overheat the vehicles brakes.
AL
Al, your idea on breaking gave me something to think about. I followed up on that and talked to the folks at Mustang to see if they had tire failure and what their thoughts might be. Seems that they have had a few of these "events" themselves, most recently on their Viper which is their "dyno mule". In that case the problem was simply caused by tires which had passed end-of-life and probably should have been replaced. One of the things mentioned was the possibility of mounting the car off-axis, which could cause heating and rapid tire wear due to the knurling on the drum. That was not the problem in my case, but had been seen in the lab at Mustang. The gentleman that I talked to did not have any personal experience with slicks, but felt in general that higher pressures might be desirable.

Your thoughts re not using the dyno break has some appeal to me. The dyno break kicks in at 5 MPH less then the "end of test speed" and is not related to the highest speed seen. This is from Mustang, as I specifically asked for clarification on that. In the case of the vehicle we were testing, the "end of test" speed was 114 MPH, however the driver continued under power to 122 MPH. By definition, the dyno break would not be applied until the roll speed decreased to 109 MPH. I have not checked the data yet, but will, to see if the tire failure occurred at that speed. More to come....

Regards,
Dick

[Dick]

Yes I have experienced similar failure.

A racing slick expands in circumfurance as it speeds up so a top fueler is riding on a very small contact patch at the top end , also 9 psi is very low in pressure for on the dyno - at the track where you are trying to maximise contact patch it is ok but on the dyno you dont want or need the sidewall distortion as in effect you only need to get the power down not move the weight of the car.
Exciting ain't it!

The issue of pressure seems to be dominant in most of the conversations I have had. Nobody "really knows", but the universal feeling seems to be that more is better. As I said in a previous reply, we have run a number of cars with slicks and some with lower pressure then this one and have had no problems. Perhaps if you do enough, it will catch up with you (us). I think I mentioned that we employ hold-down straps that pull straight down on the axel. What we do is set tension until sidewall distortion is just visible and then back of slightly. I mention this so that you would not get the false impression that we pull them down until they look low on air.

Need more air.......

Regards,
Dick

[Dick]

It seems that Goodyear has 6 Racing Tire Distribution Centers in the U.S. and one of them is located 14 miles from us at the Michigan International Speedway. We made a trip there to see if they could provide any help or insights with an eye to preventing tire failure during tests at our facility.

We were given a tour of the facility and shown a their huge selection of Racing Tires. There we also scores of Simi-trailers being loaded with tires destined for various races. The tires we saw varied from Jr. Dragster tires, all the way up to the 2024 used by Top Fuel dragsters. By the way, we were awed by how lightweight the sidewalls of the 2024 tires were. They are 2 ply woven and flimsy even compared to the wrinkle wall tires used by Pro-Modified cars. A real eyebrow raiser! Another thing we saw that was very interesting, was fellow mounting slicks on a special test fixture. He would inflate them to 20 PSI, reduce the pressure to 6 PSI and then measure the circumference (rollout) at working pressure. They would then match tires into pairs for final delivery to customers. Now that's very cool!

We were then introduced to a gentleman that travels with the trucks and Represents Goodyear at major races. In this case, he was the person who doing the follow-up on the tire that blew on Brandon Bernstein's car. At that point, we commenced discussion on dyno testing cars with slicks. They did say that they personally did not have experience with testing on a dyno, but were happy to help based on the experience they have with tires in normal applications. In discussing strapping to the dyno and in particular pull-down straps, they were NOT at all concerned. They were quick to point out that even a pro-stock car will have 2500-3000 pounds of down force at speed in addition to its own weight. When we rephrased the question and asked again, they repeated that it was not a problem. Going on, what did concern them was the possibility of a tread wave building on the front of the tire. They felt strongly that tests should be conducted with higher levels of air pressure. While they were reluctant to offer a specific number, what seemed to be implied was something in the 15ish area. The recommended pressure for bead setting is 20-25 PSI and they felt something slightly lower would be appropriate. Curse the lawyers, keeps folks from saying what they really think! The last suggestion they made, and it was strongly emphasized, check both sides of each tire for proper bead seating.

Dyno testing with Slicks, summation:
1. Don't fret too much about down force.
2. Use lots of tire pressure (i.e. 15 PSI).
3. Check for proper bead seating.
4. If used, check for proper bead screw installation.

It seems that they were in possession of the tire and wheel that failed on our dyno. While they do not "know" what caused the failure, they are of the "opinion" that it was caused by improper tire installation. First, it is critical that the beads be properly seated prior to deflation to operating pressure. Second, it is critical that if used, bead screws must be installed properly using the procedures recommended by Goodyear. In this case, bead screws were only used on the outside bead of the tires. In addition, the screws were of the wrong type and did not actually penetrate the bead. Lastly, in not penetrating the bead, the screws actually pushed the bead away from the rim. In their "opinion", during the run, the bead seal was compromised resulting in instant tire deflation. There was no evidence of tire failure, the damage to the tire and wheel appeared to be the result of the run down. The tire and wheel are being forwarded to the Racing Division engineering department, and if there is a definitive answer, it will come from there.

Regards,
Dick

P.S. Even though the Distribution Center felt the tires were not defective, they did do a courtesy replacement. That's 500 bucks worth of tires. Pretty decent of them, I think.

[Brains]

I would start looking for issues with tire GROWTH and contact with the body of the car. That is typically the problem with tire failure when it affects both, and happens at high speeds. Seen it happen several times. Speed the car up, tire contacts the fender, and starts cutting. Couple seconds later --BOOM--

[Dick]

I would start looking for issues with tire GROWTH and contact with the body of the car. That is typically the problem with tire failure when it affects both, and happens at high speeds. Seen it happen several times. Speed the car up, tire contacts the fender, and starts cutting. Couple seconds later --BOOM--
Good point, but that was not the problem in this particular case. This car had been run for several years without any problems. We are putting together a check list and will add this for new set-ups.

Regards,
Dick