More hub-upright failure data

[1965Cobra427]

The past two weekends I have been running at Hallett with Dunlop slicks designed to be used on Radicals. These are the same size and type that Calscot ran during AtomFest. I have both good and bad news.
First the good. Our lap times are coming steadily down. You may remember the quickest lap during AtomFest was 1.22.4, posted late on Saturday by Tim Webb in Calscot's car. This improved upon the 1:22.6 that Joe Park ran during the "Exhibition of Speed". Joe was in my 245 Atom on BFG R1's.

This week we ran 1:22.1 on Dunlops with about 30 heat cycles on them, without wings. This only three laps into a test session last Thursday. The car has never felt so good as it does now. I am running consistent 1:25 and 1:26's much easier than my previous 1:27 and 1:28's last fall. Saturday afternoon the car ran a 1:21.8 in a 6 lap "play race" running with the open wheel racecar crowd. Shayne Stephens was doing the driving and stated that he felt there was an "easy second" to gain in the current setup.

The chassis setup: The biggest change we have made in the chassis is preload. Front springs are set to zero preload. With the front end jacked up and wheels fully extended, reduce the preload until you could easily put a .001" feeler gage between the spring and flange of the shock. We set the rear at 5 turns of preload, then upped it to 8. Ride height was adjusted using the pushrods to 4-1/2 front, 3-/12" rear, pretty much what we ran all last year. This setup with Dunlop slicks is awesome. Understeer is a thing of the past and throttle induced oversteer is easily controlled.

The bad news. Last week we were actually getting air on all four wheels coming up out of the "bitch". Looked cool, but on one lap the car came down a little crossed up and did a 360 on the asphalt. We put a bit of a twist in the driver's side upright causing the previous 1/8" toe in to become a 1/2" toe out. ---oops! In all fairness, this was with the old style mild steel upright which had been fitted briefly for convenience (kind of a long story). I replaced the upright with the correct chrome moly unit and had no additional problems with that.

Second issue- this past Friday the right rear hub failed in a way I had not seen before. The flange portion of the hub broke away from the barrel section. I have had two previous hub failures, both evidenced by the breakage of the tube section of the hub about halfway between the flange and the inner face of the tube. (It breaks just about the junction of the inner and outer bearing races.)

Parts were all replaced with no loss of track time, but this does add a bit to our group awareness of the kinds of loads that slicks and had track use can put on the upright/hub portions of the car. I'll post photos when I get the chance.

Zero loss of enthusiasm however. Fourfather and I had a GREAT time once my car was back together, completely undeterred by a few broken parts. Thanks again to Hallet for a great venue and terrific shop service.

Video of me and FF from Saturday afternoon -

http://www.youtube.com/watch?v=j6_TcGfpJ3U

[Curator]

Excellent video.Eddies pass toward the end was brilliant.I was felt the same urge to catch him as you did. Are the Dunlop slicks 15" all around?(225s?)Where are you sourcing them from? Are the Atom 3 uprights the same as the 2's? Does the factory have any plans to offer upgraded ones?I heard someone is making stronger ones.Tom is it?

[1965Cobra427]

Excellent video.Eddies pass toward the end was brilliant.I was felt the same urge to catch him as you did.

Pure fun.

Are the Dunlop slicks 15" all around?(225s?)Where are you sourcing them from?

15" fronts, 16" rears, sourced from Sasco Motorsports. http://www.sascosports.com/index.php They are headquartered at VIR, neighbors to the new TMI facility. If you call them, ask for Elton Gannaway. He knows about the Atom and was very helpful. In the video I was on tires with 4 heat cycles, Eddie on same tire with 40+ heat cycles. Remarkably similar amount of grip. At that number of heat cycles, my Hoosiers were still better than A048's but not nearly as good as the Dunlops.

Are the Atom 3 uprights the same as the 2's?

I don't know if the A3 uprights are the same as A2 units, but I'm guessing they are at least as good if not better.

Does the factory have any plans to offer upgraded ones?

All Brammo cars built after about July, 2006 have the chrome moly ones. My car was built earlier and retro-fitted

I heard someone is making stronger ones.Tom is it?

Tom told me he was working on some race-quality units.

Hub photos are coming later today.

[Curator]

Well,yes,I know it was fun However,as he passed,you can hear the determination in your shift down to persue him.

Seeing as these fit under your fenders,are they 225 wide? Are they the Radical 200/580R-15?  I am looking at an Atom2 and it has stoch tires so I will be needing better.

[DarthChicken]

Your comment about preload interests me - do you have the helper springs in place, and have lightened it that much?  Or no helper springs and just main springs?

Also, and I've never been very clear on this one - do you have to get the car realigned after touching the pushrods?  I would assume so, but  

[1965Cobra427]

Your comment about preload interests me - do you have the helper springs in place, and have lightened it that much?  Or no helper springs and just main springs?

Also, and I've never been very clear on this one - do you have to get the car realigned after touching the pushrods?  I would assume so, but  

Yes, the preload springs are in place. At full chassis extension, these are at full height. We didn't need to realign since we maintained the original ride height. If RH had changed, camber and toe would be affected and would need re-set.

Best thing about the setup is the balanced feel. Here's what Shayne had to say after a 1:21.8 run

[DarthChicken]

VERY interesting.   

[1965Cobra427]

Photos of broken hubs - All breakages were under extreme loads imposed by running slicks on a tight twisty racetrack. (my own doing)

Below left is a good hub. On the right is a hub broken near the point where the outer bearing race shoulders on the hub.



Here is a closer view of the broken hub. I have had 2 hubs broken in this fashion.



Here is a photo of the right hand hub which failed this past weekend. Once again a good hub is shown at left for reference.



A close up of the left hub.



When this hub failed, the flang portion wobbled on the stub (thankfully it was trapped and did not allw the wheel to come off the car). It did damage the upright however as shown here.
The hub flange scrubbed agains the upright in the bearing seal area and the wheel came into contact with the uprigght both deforming and scuffing it.



This photo shows the marks on the backside of the hub where it came into contact with the upright in the seal retaining area



Now for the useful part of this post. In each case, the first stmptom of failure is the same, regardless of the type of failure. After cornering the brakes will have too much pedal travel on initial application. They can be easily pumped up on the very next pedal stroke. The initial change in travel is a result of the brake rotor backing off the brake pad as the rotor wobbles. In these cases, we had a lap or so of the brake symptom before coming to a stop and investigating the cause. On the first hub failure, we even went to the trouble of bleeding all the brakes, searching for the cause, which ultimately turned out to be the broken hub.

The previously reported "loosening" of the rear wheel bearing/axle nut seems related to the hubs broken as shown in the top photos. I believe that if I had been more prudent in torquing the rear axle nut (each track session on slicks) these breakages may not have occured. On that subject, the nut is NOT backing off. We have paint marked the nut and axle and used a jamb nut. Something in the stack up of hub, bearing races, spacers, etc. is changing, but the nut is not backing off. We now retorque each and every session.

As to the seconf failure shown, the nuts were never found loose. I'm not sure what would have prevented this failure except not running as hard as we are on slicks. It's possible there was a metalurgical or machining fault in that hub, but the remanants don't prove that to me one way or the other. I will contact TMI and Ariel to see if they want the parts for analysis. If not, I'll need to secure a supply of these parts since I'm not planning to diminish my efforts to lower the Ariel Atom track record at my home track. So far we're nearing a one second per lap improvement since AtomFest and expect to be in the 1:20.??s before long. I'm happy to break and replace parts and report what I can in the hope that others might avoid the problems if possible. We've had great success at chassis setup and tire selection, etc. this month and are highly encouraged, not just with lower lap times and far more satisfying manners with little understeer and very managable on-throttle oversteer. It's a blast to drive!

[whooops]

Tom emailed me today.  they are still working on their prototype upright replacement designed for slicks.  He'll have some more info the closer they get to completion

[Positron]

The chassis setup: The biggest change we have made in the chassis is preload. Front springs are set to zero preload. With the front end jacked up and wheels fully extended, reduce the preload until you could easily put a .001" feeler gage between the spring and flange of the shock. We set the rear at 5 turns of preload, then upped it to 8. Ride height was adjusted using the pushrods to 4-1/2 front, 3-/12" rear, pretty much what we ran all last year. This setup with Dunlop slicks is awesome. Understeer is a thing of the past and throttle induced oversteer is easily controlled.

I'll be trying this this weekend, what should I expect for corner weighting? Front differential, bite etc? Or run with whatever it yields?

[1965Cobra427]

The chassis setup: The biggest change we have made in the chassis is preload. Front springs are set to zero preload. With the front end jacked up and wheels fully extended, reduce the preload until you could easily put a .001" feeler gage between the spring and flange of the shock. We set the rear at 5 turns of preload, then upped it to 8. Ride height was adjusted using the pushrods to 4-1/2 front, 3-/12" rear, pretty much what we ran all last year. This setup with Dunlop slicks is awesome. Understeer is a thing of the past and throttle induced oversteer is easily controlled.

I'll be trying this this weekend, what should I expect for corner weighting? Front differential, bite etc? Or run with whatever it yields?

Our corner weighting before the described adjustments was set to balance the front, side-to-side. We did not re-weigh the car after setting the preloads as described above.

[McFred]

This is a great thread, thanks for sharing your results!

[McFred]

The chassis setup: The biggest change we have made in the chassis is preload.

I'll try tinkering with this at our next local track day.  Which springs/dampers do you have?  We have the standard setup with koni's.  We noticed at hallet that the rear dampers seemed to be hitting the bump stops, so we put in a bunch more preload at the rear.  That seemed to really help on that back section with that washboard left-hander.  Since then we have discovered that the koni's are rebound adjustable.  If you take the springs off there is a button near the pushrod exit seal.  If you push that in and turn the pushrod there are 4 "click" positions.  What still confuses me is that the two rear dampers are not the same.  Using the high precision testing method of compressing the damper and counting how long it takes to extend again, one unit extends quicker with the rebound set all the way clockwise, and the other with the rebound set all the way counterclockwise  (~2 seconds to extend vs 5 seconds).  Both dampers seemed to be set for maximum rebound damping (taking the longest time to extend) which may have contributed to the damper riding the stop.  They've both been set to the other extreme and reinstalled to see if there is a noticeable difference on the next outing.

[Positron]

McFred, good stuff. I'll be adding this to things to do this weekend.

Stumbled across this.

http://www.koniracing.com/30sp8.html

http://www.koni-na.com/pdf/30series.pdf

[1965Cobra427]

As a point of reference for my posts, we are running the 2812 Konis with the race springs.