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GEN 1 (2010-2014) Ford SVT Raptor Forums
Ford Raptor Suspension Discussion and Modification
ICON Ford Raptor Hydraulic Bumpstop Testing + Tuning
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<blockquote data-quote="DylanICON" data-source="post: 461047" data-attributes="member: 2111"><p>The bumpstops are hydraulic and nitrogen (air). I know the common nomenclature is misleading. Technically they are hydro-pneumatic bump shocks but if we refer to them as such then they would never pop up on the Google searches.</p><p></p><p>The rebound rate is the hardest and most important part of the bumpstop tuning. If we knew that the bump occurrences were far apart we would tune the rebound to be very slow so that almost none of the impact energy would be returned to the system. The characteristic is that after impact the axle “disconnects” from the bumpstop and rebounds on the “connected” spring and shock. The other factor is that because the “spring” function of the bumpstop comes from compression of the nitrogen inside, the rate is very non linear. This is great for bottom out resistance but difficult for rebound tuning. We combat this to some extent by using a piston that is digressive on rebound. The bumpstop will rebound much faster in the first half of the extension stroke than the second however. If there are two closely spaced successive hits it is possible for the bumpstop to only rebound partially. When this happens the second hit usually has less energy because it’s not coming in with as much velocity as it would if the suspension had extended further so it does not require as much to control. If it had extended further the bumpstop would have fully extended also. Secondly the bump stop will have more residual pressure in its partially extended state and thus will have higher initial contact force to handle the situation. </p><p></p><p>When tuning a bumpstop application I do most of the nitrogen pressure, compression valving and oil fill volume determination with lots of field testing. The rebound tuneing is done with both video from the field testing and shock dyno work. On the dyno we can see how much force is being imparted to the suspension on the return stroke. We also do field data acquisition that plots the position and velocity of the suspension so we know what velocities correlate to what desired or undesirable reaction. Without the data acquisition the dyno speeds to analyze would just be a guess. </p><p></p><p>The goal is to get it to return as fast as possible but not kick back. I can usually get it to follow the suspension back out but not push it back out. The last 10-20% of the stroke is at very high pressure and usually pushes back a bit. The middle 60-70% will follow the suspension out with little force and the last 20% will disconnect and extend on its own. </p><p></p><p>The other important factor is how far the bumpstop is from contact at ride height and the percent of bumpstop travel compared to overall travel and up travel from ride height. With about 5” of total up travel and 2.5” of bumpstop travel the ratio is not what I would ideally want but convincing people that they need to stink bug their trucks even though it doesn’t look cool is not going to fly. I do have a 1.9” travel bump stop but there’s a lot of work to be done in not much room</p></blockquote><p></p>
[QUOTE="DylanICON, post: 461047, member: 2111"] The bumpstops are hydraulic and nitrogen (air). I know the common nomenclature is misleading. Technically they are hydro-pneumatic bump shocks but if we refer to them as such then they would never pop up on the Google searches. The rebound rate is the hardest and most important part of the bumpstop tuning. If we knew that the bump occurrences were far apart we would tune the rebound to be very slow so that almost none of the impact energy would be returned to the system. The characteristic is that after impact the axle “disconnects” from the bumpstop and rebounds on the “connected” spring and shock. The other factor is that because the “spring” function of the bumpstop comes from compression of the nitrogen inside, the rate is very non linear. This is great for bottom out resistance but difficult for rebound tuning. We combat this to some extent by using a piston that is digressive on rebound. The bumpstop will rebound much faster in the first half of the extension stroke than the second however. If there are two closely spaced successive hits it is possible for the bumpstop to only rebound partially. When this happens the second hit usually has less energy because it’s not coming in with as much velocity as it would if the suspension had extended further so it does not require as much to control. If it had extended further the bumpstop would have fully extended also. Secondly the bump stop will have more residual pressure in its partially extended state and thus will have higher initial contact force to handle the situation. When tuning a bumpstop application I do most of the nitrogen pressure, compression valving and oil fill volume determination with lots of field testing. The rebound tuneing is done with both video from the field testing and shock dyno work. On the dyno we can see how much force is being imparted to the suspension on the return stroke. We also do field data acquisition that plots the position and velocity of the suspension so we know what velocities correlate to what desired or undesirable reaction. Without the data acquisition the dyno speeds to analyze would just be a guess. The goal is to get it to return as fast as possible but not kick back. I can usually get it to follow the suspension back out but not push it back out. The last 10-20% of the stroke is at very high pressure and usually pushes back a bit. The middle 60-70% will follow the suspension out with little force and the last 20% will disconnect and extend on its own. The other important factor is how far the bumpstop is from contact at ride height and the percent of bumpstop travel compared to overall travel and up travel from ride height. With about 5” of total up travel and 2.5” of bumpstop travel the ratio is not what I would ideally want but convincing people that they need to stink bug their trucks even though it doesn’t look cool is not going to fly. I do have a 1.9” travel bump stop but there’s a lot of work to be done in not much room [/QUOTE]
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GEN 1 (2010-2014) Ford SVT Raptor Forums
Ford Raptor Suspension Discussion and Modification
ICON Ford Raptor Hydraulic Bumpstop Testing + Tuning
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