6ul wheels

[breakaway500]

My Atom has a 4x100 BP (15x10's up front and 15x13's out back) I use Keizer wheels...very strong...very light...very expensive, but very nice.

[sbyers]

Wow 1400lbs is very light and with that power it will be amazing to drive
I will get forged wheels, I don't want to risk another failure with cast wheels.
Hopefully my hubs are strong enough
Some photos of the damage the wheel caused.

[breakaway500]

Sucks..but at least you kept it right side up...

"...it will be amazing to drive..." that is my outlook as well.....

[sbyers]

True, the damage wasn't too bad considering.
Would like to see some photos or your 4wd rocket when you've got it ready to race

Do you think going to a 17x7.5 will be better than a 15x8?
I can still use a 225 width A050 tyre with 45 profile, the only thing that concerns me is whether I can fit the extra diameter.
15 inch tyre is 587mm and 17 is 631mm, a difference of 44mm.

[breakaway500]

Extra tire diameter hurts your final drive ratio and is tougher on the brakes..but I have found,using lots of trial and error,the greater amount of tread surface around the 25" tire (631mm) benefits the overall tires performance significantly on the front of my FWD (front wheel drive). The "taller" tires have less overheating issues and a longer life in the sweet zone.So,I prefer the lower profile,but somewhat taller 17" setup. I've experimented with a lot of tires on my Focus...

You can adjust the handling with tire selection quite dramatically...for better or worse...

[sbyers]

Ok, thanks for that info
I am thinking about using a 16x8 wheel with a 225/45/16 tire. The R16 tyre diameter is 605mm, 18mm more than the R15 tyre.
I'm putting a longer gear set in the box which which should suit the torquy motor.
While what you say about the 17 inch tire seems to be good, it is just a bit too big and I'd need to do some major work to the wheel arches to get them to fit and still keep the car low. I think the 16's will be a good balance.

[paultg]

Came across another 6UL failure:
http://www.automotofoto.net/events/sigm ... k-round-1/

Scroll down. Just a reminder to check your wheels (whatever your using).

Paul G.

[WillM]

Yikes.

"The only accident (of sorts) during the day was Chris Boersma’s Civic SiR at Corner 5. The incident happened just as Boersma was making the corner and his rim with tire came off the vehicle. Thankfully, Boersma kept the car straight and safely got off the track.

The cause? His 949 Racing 6UL wheel was sheered off completely leaving the rest of the rim affixed to the hub – lug nuts and all too! The smoke that you see coming from under his wheel well is due to the high temps of the brakes and his hot engine sitting on the grass. Thankfully, there was no fire or further damage to his car other than a bent up fender and minor cosmetic damage – at least from what was known yesterday. The vehicle will be further examined and we hope to report some good news or not. The most important thing is that Boersma (the owner / driver) is safe and not injured – fenders and cars can always be replaced, not a life."

Sigma-Racing-TIme-Attack-Round-1-THUMBNAIL-10.jpg (374.17 KiB) Viewed 3349 times

"The remains of the 949 Racing 6UL wheel. As you can tell all 12-spokes were sheered off from the remaining part of the wheel still affixed to the hub. Could it be a faulty design, bad metallurgy, or just a random case? We will be investigating this issue more as we hear back from all parties especially as there have been many reports of bad products entering the market under various brands. 949 Racing has had a good reputation especially with Miata enthusiasts in North America as many run their wheels, but this incident makes one question their quality control – especially if branded as a track wheel and causing catastrophic failure on a vehicle."

Sigma-Racing-TIme-Attack-Round-1-THUMBNAIL-11.jpg (416.06 KiB) Viewed 3349 times

[horizenjob]

That's a rather alarming picture.

Does anyone have one of those style wheels and feel like measuring the cross section of those spokes?

Comparing the picture there with the wheels I have ( Minilite style ) it's obvious those wheels have much shallower spokes measured from inside to outside the wheel. The spokes on these other wheels are 1.25" deep in their middle. The stiffness change due to just a height difference goes by the cube of the ratio difference. Spokes that are 25% deeper in section would be twice as stiff. If those spokes are less then 1" deep in section, they would be a great deal more flexible.

A further concern would be whether those failed wheels are explicitly marked for non-highway use only. Good racing wheels will say this because they do not have enough fatigue allowance to permit the number of load cycles typical road use might allow. Every rotation is considered a load cycle. Road racing would present higher loads then street so it's not completely simple. For a wheel which permits road use to fail at the track wold seem to have very low margins for fatigue and stress / strain.

It would also be interesting to put one of these wheels in a shop press and measure how much it flexes. You could block up the center and push down on the rim on opposite sides. With a dial gauge you can just measure a tiny flex and then compare to another wheel, no need to heavily stress the rim to get the measurement.

[TroyV]

Being a mechanical engineer myself for the last 20 years or so, I can tell you that there isn't enough evidence from the photos on how the failure occurred, other than the appearance that the tire and wheel did not take a violent enough hit from the side to leave some sort of visible damage to the side wall, or rim bead.

If it is stress alone that caused it, then it is very alarming indeed.

All I know is that I have literally thousands of track miles on my RPF1's, and there isn't so much as a blemish on them aside from tire boogers. AND...I got those sets of wheels from Will, who probably had thousands of his own track miles on them.

I am retiring my 6ULs from track service. I just can't drive as hard as I want to with the nugget in the back of my head of a potential failure. You Miata folks know....especially the ones in the SS and ST classes.....just to put up reasonable lap times, We need to drive at a level of desperation that most people driving other platforms do not understand. We are banging the curbs all the time, and taking turns as fast as We think We can take them, and in the process, assuming lots more risk than we probably should.

Bottom line.....I need to trust my gear to turn my fastest laps, and I can no longer trust these...regardless of how new they are or what generation they are from.

It is a shame, because as I said before, it is one of the best looking wheels on a Miata.

[breakaway500]

Being a mechanical engineer,I am sure you know everything has a threshold point of failure,and it is very possible some are pushing the 6UL wheels beyond their designed limits.Just because they fit on a car does not mean they will be "safe". High powered front wheel drive cars are extremely demanding on front wheels,especially with high offsets and track rubber.I won't run anything but a forged wheel on the Focus for this reason. If the 6UL wheels were failing with any frequency,I am pretty sure the word would be out big time. I do agree,if there is any doubt in your mind about their safety,don't use them. Especially when there are alternative wheels available with a clean track record...


"We need to drive at a level of desperation.." Love it!

[TroyV]

Not looking for the uber debate here, but I will say that if something is advertised specifically for track use, it suffices to say that would be buyers will be under the assumption that the design would exceed requirements of the track vehicles the wheels are made to fit.

...and again, we don't know the specifics of this particular failure, and I'm not sure we ever will know. All I know is that I have seen enough and experienced enough to make the call to pull mine out of service.

[breakaway500]

A track use specification does NOT mean it's indestructible,and actually more to the contrary. Most DOT rated wheels are substantially stronger than a "track" rated wheel.Sacrifices are made in weight and design for most track wheels,and so is their ultimate strength. No one needs the strength of a 1 ton dually wheel on their Miata..well..maybe you do...

[TroyV]

You can have the last word Mark...you typically do on these forums.

Something stinks here, and I choose not to smell it anymore.

[Chrispy]

I think the most significant factor is the type of testing that goes into a wheel before being put into production. Does the manufacturer simply do computer simulations of stress and fatigue or do they mechanical tests to back up their calculations? Enkei does. A small essentially one man design operation like 6UL - probably not. Enkei's own standards far exceed JWL (Japan) or DOT requirements. AFAIK 6UL doesn't publish any test data and isn't DOT, doesn't make them bad necessarily, but it is nice to know that a wheel can meet this requirement at a minimum.

Just about all the 6UL wheel failures that have been published on the web have failed in exactly the same place. This indicates a design flaw, probably a weakness that wasn't revealed in the older software simulation of the time, or a minimum stiffness threshold that wasn't met for the sake of ultimate lightness. They did revise their design so hopefully improvements were made for the 2nd generation, but without published test data you'll never know.