Landing hard, should I worry about foot pegs?

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#1
Hello everyone, Lately I've been trying to jump a 75-85ft. tabletop, Of course my goal is to clear it but for now I'm trying to build up enough courage to do so. Right now I land on the last 3/4 of the jump. I'm about 210 and ride a YZ400 with the stock suspention. Sometimes when I land I land the bike on both wheels at the same time and bottom out. I try to avoid this by bringing my front end up. but sometimes I fail to do this and land wrong. Now here is my question... Like I said before I'm 210lbs. and I'm worried that I might be putting to much stress on my foot pegs when I land. How much pressure can these things take? Are they likely to break? Yesterday, all I did was try to practice this jump and the bike took it's fair share of abuse. How much can these bikes take? What about the metal that holds the foot pegs in place? Are these easy to break?
 
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#2
The footpegs are probably not the first thing to worry about. If a guy your size gets big air, one should probably consider some suspension modifications, stiffer springs come to mind.
 

blackhawk468

President of Bling
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#3
Make sure you are on the gas when you land. It will help dampen the supspension or something like that and make for a smoother landing.
 

RM_guy

Scared of DirtWeek<BR>Club *********
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#4
I’ve often wondered the same thing. I’m 210 when naked (sorry for the visual :eek: ) and have had my share of hard landings, not necessarily from 85’ doubles though.

The shear stress of the pin that the peg pivots on is probably the weakest link and all foot peg designs are not equal but a ball park stress value for the pin with a 4G load (4 times your body weight) from a 200 lb rider is roughly 25,000 psi. with a 3/8 dia pin. That may sound high but I assumed all the load was taken by one peg and I don’t know if 4Gs is realistic.

The shear strength for the pin is the question. I don’t know what material they use but shear is generally half the yield strength . For, let’s say a hot drawn 1050 steel, which has a yield of 49,000 psi, the shear would be roughly 25,000 psi. That means that with a 4g hit on one peg by a 200 lb rider, the pin would start to yield (permanently deform). A weaker material, like a grade 5 bolt, would probably break.

Bottom line is you’re probably safe so long as the pin, foot peg, and frame are in good shape. When you replace he pin, make sure its an OEM part and not some bolt you find laying around. As the pin wears, the cross section is reduced and the overall strength is compromised so make sure it’s OK.

Disclaimer: The numbers above were quickly calculated and I won’t swear to their accuracy but they are in the ball park. I just don’t want to get blasted for any liberties that I may have taken. If anyone does know the typical g-force from a landing and the actual material that is used for the peg pivot pin, I can do a more complete analysis.
 

smb_racing

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#5
I would check the welds at the frame brackets for signs of stress failure before attempting the jump each time. Stress failures are indicated by light spots in the metal (if metal is visible) and/or splintering paint. Cracking of the mount might also be a problem but for the pegs themselves I'd say they're pretty tough.
 
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#6
Originally posted by smb_racing
I would check the welds at the frame brackets for signs of stress failure before attempting the jump each time.

That would work GREAT in racing ! :confused: Maybe not EVERY time you jump, although maybe after hard landings and at the beggining and end of each ride. :cool:
 

High Lord Gomer

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#7
I have bent (and eventually broken) footpegs before, but it has been the result of *lots* of hard landings. They all showed signs of drooping before breaking, though.

As mentioned, a properly setup suspension for us beefy riders (I'm 230+ in my bare glory) will prevent the rest of the bike (and our bodies) from taking sych a beating by not bottoming out as harshly or as often.