Ah Kevin,
A good and incisive question , and one that I have been asking myself a lot lately.... :laugh:
Actually it is a setup that was first used by Bruce on his CanAm cars. I remember reading about it in an article some time ago and liked the idea for several reasons. Basically the needle roller takes most of the radial loads, which with wide offset wheels are a lot higher than normal, and the deep groove ball on the inner controls the side thrust.
The benefits should be greater bearing longevity and this should certainly be true of the needle rollers. Because there is no preload on the bearings there should be less friction/less heat/less rolling resistance all of which are desirable attributes and of course as opposed to taper rollers there is no need to be continually adjusting them.
In fact you can't, so that is the downside. When you get a little bit of wear they must be replaced. I must admit, bearing in mind the wider tyres, greater down force, higher speeds, and length of races in the CanAm Series, I never expected to have to replace any of them after less than one hundred laps. However the article I was reading didn't go into specifics so more than likely they may have been using the much more heavy duty (and expensive) 4 point high axial thrust type as mentioned by Jac Mac.
One of the benefits of the 4 point bearing, besides taking higher loads, is that it has a split inner so it is possible for cheapskate kiwis to grind a few microns off the flat mating surfaces to take up any slight wear.......:idea:
The DL308s arrived yesterday from Singapore $20 ea, as opposed to $120 ea for the same brand to buy them here locally. Sometimes we get totally shafted on pricing in this not always idyllic paradise! Unfortunately because I wanted them quickly, fast freight was $25 ea but they still work at about 1/3 the price! The DL308s have 11 balls as opposed to the 8 in the 6308s and they are very smooth and have a really nice feel to them. These are the equivalent of the 7308Cs that Dave was talking about.
However I think the QJ308s are what I will wind up using when these new bearings are done so I will freight some in by the cheaper slow freight so I have them on hand when I need them. $70 ea in Singapore, I shudder to think what they would cost here!
So there we are, a bit of a saga along the lines of a little information can be a dangerous thing!

But like everything else, we will get on top of it (eventually!) :thumbsup:
As you suggested, I had a good reason at the time, I think the reasoning is still valid, it's just a matter of establishing the detail.
Now all I need is some smart arse to inform me that McLarens only used it for one meeting before going back to the tapers.... Jac Mac?????
I might have to have a chat to Wally Willmot at the SKOPE......