this is how dennis jean and i finished in the 1949 RZR. we had no idea that all the bolts broke. we got really lucky to say the least just finishing. we pulled out a third overall and a second place finish in the pro class.
2012 BITD Parker 250 Pics & Results by UTVUnderground.com
- Thread starter JoeyD23
- Start date
Don’t mean to turn this is to a structures redesign thread, but if it draws more ppl to this site then good, since this site does provide the most accurate tech info on the net.
Most rule books I have read limit relocating suspension hole centerlines, but do allow gusset kits, not sure about splicing upper lugs with billet I suggested. I’m no UTV racer check your series.
Disclaimer: This below gets pretty complicated…..
Here the lower lug design looks good, too large a hole/arm without enough surrounding material is what failed the upper lugs. Ideally if you put a bolt through a hole, or in this case an arm tube which I suspect failed first, you want a minimum of 2x the diameter of the bolt (or tube) edge distance(ED). ED is the distance from the center-line of the bolt (or arm tube) to any edge (chassis, etc), or lug edge in this case. Do the math, if that tube were 1” in diameter there s/b a min of 2” ED, or 1.5 lug tab material tab sticking outboard past the arm tube, looks more like .25-.5 but I can't tell from the photo.
Besides ED other considerations are bearing area (area the bolt bears up against the lug based on thickness and diameter, the materials ability to transfer load to the bolt), shear and tensile stress capability of the bolt. Gets complicated I won’t go into depth.
That’s why I said if you’re in this situation, to get the tabs right a machined detail w/all four lugs machine in, splice it into the chassis with the proper ED and pitch on fasteners. Pitch is the distance between fasters, 4D for metal design, 6D for composite. This fitting could be billet aluminum 7050-T6 if the plate is less than 3” deep w/ stainless bushings.
Racing or running these tabs is risky and unsafe, I’ve been trying to explain in other threads lately….The 900XP has similar issues Dragonfire racing helped here w/a bolt on.
Axles: Where and how can lead to why. 900XP has some issues there too.
Nice race pics BTW.
The bolt(probably 8) didn’t fail bud I am gathering from the pic the chassis/arm did. I think what you are thinking (correct me if I am wrong) is a larger diameter 7/16 bolt will produce more bolt bearing area against the chassis lug and shear capability, and you’re correct if there is edge distance, which there was not enough to begin with for the smaller probably 5/8 bolt. But that’s only part of it, if the structure (chassis lug) is too thin and can’t make the stress transfer to the bolt chassis fails, there is not enough material to resist shear. Hence, you’ve heard the ol adage bigger/stronger better but what fails next? = The chassis/arm but sooner.
I don’t know why some of these UTV companies put tortilla chips chassis lugs that probably caused the arm to fail here. Maybe the gusset after market race companies give them a kick back because it is very apparent they defy all the basic stock rules of structural design, even in their latest sports model the XP900. Just weak points I guess all UTV’s have them, but the things that make ya go hmmmm!
I don’t know why some of these UTV companies put tortilla chips chassis lugs that probably caused the arm to fail here. Maybe the gusset after market race companies give them a kick back because it is very apparent they defy all the basic stock rules of structural design, even in their latest sports model the XP900. Just weak points I guess all UTV’s have them, but the things that make ya go hmmmm!
This is the first time we have had an issue with the A-arm bolts on this car and this is the 3rd season for this car. Bolts are Grade 8 and axles are 300M. Car is at XMF as we speak getting looked at. As stated above there is a trade off with UTV's, you can strenghten one spot BUT the stress still will be transfered to another spot. Basically the bolts sheared at the nuts. good news is only 2 out of 3 bolts sheared on that side. Even better news is the race was over when we discovered it!
Hey pal the bolts either broke or came lose the frame and both A arms are not damaged.The bolt(probably 8) didn’t fail bud I am gathering from the pic the chassis/arm did. I think what you are thinking (correct me if I am wrong) is a larger diameter 7/16 bolt will produce more bolt bearing area against the chassis lug and shear capability, and you’re correct if there is edge distance, which there was not enough to begin with for the smaller probably 5/8 bolt. But that’s only part of it, if the structure (chassis lug) is too thin and can’t make the stress transfer to the bolt chassis fails, there is not enough material to resist shear. Hence, you’ve heard the ol adage bigger/stronger better but what fails next? = The chassis/arm but sooner.
I don’t know why some of these UTV companies put tortilla chips chassis lugs that probably caused the arm to fail here. Maybe the gusset after market race companies give them a kick back because it is very apparent they defy all the basic stock rules of structural design, even in their latest sports model the XP900. Just weak points I guess all UTV’s have them, but the things that make ya go hmmmm!
I’m misreading the pic then, and I’m not familiar with this model, looks like a weak chassis. Bolts very rarely fail in 100% shear; it’s more than likely tension (a pulling action on the surface that propagates a crack from bending). Unless it’s a nail or rivet bolts are rated in tension. The bolt went into tension failure from bending probably from worn arm bushing’s, torque, etc, and/or as a result of reaching its fatigue life.Hey pal the bolts either broke or came lose the frame and both A arms are not damaged.
Just a friendly word of caution, consider yourselves lucky! If the chassis was put in service at the same time it’s probably next then you'll have a mess on hand. You may want to consider a gusset kit, replacing the bolt, bushing, etc, more often. A larger bolt and/or more chassis will improve reliability(make it more fail safe from worn bushing's, torque, etc) and fatigue life per the guidelines stated above.
Good luck, keep it safe!
They put a huge 1/2 page picture of our car on the front page of the paper version of that article. We were pretty stoked! Thank you to everyone that came to Parker and made this event such a success!