CV versus Tripods

[Jim Garry]

I'm putting together a Formula F for autocross. It needs CVs. There's already one Tripod style on each half shaft, but no housings (the expensive part).

But expenses aside, the big question is will one type hold up better to abusive autocross standing starts with low gears and soft slicks?

Will the Tripods hold up to that stress as well as the Lobro style CVs?

Usual wear is not at issue here.

All thoughts welcome!

[Daryl DeArman]

on edit. Sorry got ahead of myself focussing on the title. I'll let somebody with more first hand knowledge in your specific application respond.

[RussMcB]

I'm not super knowledgeable, but,

When I consulted recently with someone with a respected reputation, they indicated the Lobro CV joints were generally stronger.

One aspect I like regarding CJ joints is you don't need to worry about plungers and springs.

[DaveW]

That's interesting. I always assumed (as I've said before, assuming anything is a bad idea, so that's my fault) the tripods were less likely to fail during clutchless shifting than Lobro CV's since almost everyone uses them and most shift clutchless. I actually broke a Lobro CV on an early attempt to shift my Staffs w/o the clutch. Of course, maybe it had been previously compromised by a wreck or something and I hadn't noticed that it was damaged.

I have never used the tripod joints, so no experience there.

[Jim Garry]

Dave, I understand you've never use tripods but from your engineering perspective do you have thoughts about standing start issues?

[DaveW]

Without a serious stress analysis, I have no real data to support an opinion. A brief Google search on the subject of strength gave me no useful info other than when they were invented and their use characteristics.

However, having said that, the weak component in Lobro CV's has always been the ball separator (the thin steel component with the guide holes). These tend to crack when the joint is subjected to an excessive angle or stress, such as in a wreck. The other components can wear, but this is a longer progressive process that doesn't usually cause failure.

OE (Lobro CV) ball separators usually tended towards being too hard in order to slow the wear process, and so were subject to cracking instead of just yielding when overstressed.

Two other facts differentiating these are that 1) Lobro CV's have a larger angle capability than tripod joints, but that's not relevant for non-steering axles, and 2) tripods are slightly more efficient (less friction), but that's also not relevant when the angularity is very small.

So, you'll have to rely on someone else for their actual use experiences.

[Roux]

The Royale RP31 has the standard CV joints on most cars from the 80's. I never had one fail

For my Wyvern one-of-a kind I went with the small Trilobes from Taylor that they call out for D Sports racers and formulaSAE. Lowish cost, low mass, lots of length options on the shafts. If I posted the number of spares I carry and the amount of time spent regreasing and replacing worn out parts almost everyone would conclude that I have made a bad design choice. This winter I made modifications to the system to make it easier to get in and grease them, and I have also designed a captive plunger that will avoid having the flying plunger and spring syndrome when taking the outboard joint apart. The failure I have seen is the needle bearing fails in one of the wheels. Hard to tell if the ring holding the needles on one of the three axles pops off or if one or more of the needles crush and then mayhem ensues. Have never had the tiny little axles shear off of the hub or any of that. When it fails you finish the race but with some vibration and some cleanup to do. Those needles go into everything.

Torque is from a Honda Fit with the restrictor although we did run it without the restrictor in some Limerock autocrosses with shared drivers so the car barely stood still, however those autocrosses don't have a standing start but a lot of full throttle first gear stuff. The failures were always at roadraces and mostly when I had neglected greasing the wheels, like for most of the season. With the new design greasing will be easy and each side will get a refresh every other weekend

Steve

[Jim Garry]

Thank you Dave.

[EACIII]

My Lola 644 had CV joints and I used to break the metal cages all the time. Wish I could have bought replacement cages. The Bowman has Tripods and have never broken one of those. But have broken axles a few times. I now carry complete axles with Tripod joints installed as spares so it is a quick swap if I break one.

Ed

[Daryl DeArman]

The import drag racers are running 8 second 1/4 miles, with 1000hp launches using quality tripod joints at inner end and 930CV's at outer end. So, appropriately sized/spec'd they are both up to much, much more stress than anything a little formula car is going to throw at them.

I would utilize the tripod only design on the rear of a IRS car simply because I don't want the additional complexity/mass of a joint designed to allow a wheel to steer that doesn't need to.

[Rick Kirchner]

on the lobro cages take a cartridge roll and polish all the edges to prevent cracking.

[DaveW]

on the lobro cages take a cartridge roll and polish all the edges to prevent cracking.

I did that on mine - it did not prevent the occasional failure. Of course, having corners torn off occasionally didn't help...

[Neil_Roberts]

Either will work fine for CM autocross. Tripods have the potential to be a bit lighter because you have the option of buying aluminum housings that have steel race inserts.

Here is what I think about tripods and CVs for high power applications.

[Jim Garry]

Neil I miss your blog posts. Thanks for the link.