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Whats a good 4 link calculator
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<blockquote data-quote="patooyee" data-source="post: 453628" data-attributes="member: 483"><p>Here's my quick, dirty, super-over-simplified rundown of what is going on in each entry. I'm sure people are going to disagree with me, tell me I'm wrong, whatevs. Lets all learn here in that case. This is all using the 3.1d calculator that I posted:</p><p></p><p>Wheelbase = self explanatory</p><p></p><p>Tire dia. = self explanatory</p><p></p><p>Rolling Radius = Half of tire dia. for our purposes. In reality this relates to real-world tire measurements that should be made with the tire in question on the vehicle moving under power. But since we're building the suspension I'm assuming you can't drive the vehicle so just go with half of tire dia. for this. Or maybe if you know that your tire is 41" tall even though the sidewall says 44" go with half the measured height in that case. It does not greatly affect the overall numbers anyway.</p><p></p><p>CG Height = Again, since we don't know the exact height we have to approximate here. A general rule of thumb is to use the height from the ground to the top bell housing bolt of the trans. If you have really heavy axles it might be a little lower, really light axles higher.</p><p></p><p>Vehicle Mass = You're still building the suspension so you probably can't accurately weigh it. Approximate here but be realistic.</p><p></p><p>Front & Rear unsprung mass = Again, approximate. Remember, unsprung does not include the axles, tires, or wheels.</p><p></p><p>Link X dimensions = straight line distance from axle center line to link mount. Note that this is not the length of the link, it is single dimension distance as if you dropped a plum bob from the link mount and another from the axle center line and then that distance as measured on the floor between plums.</p><p></p><p>Link Y dimensions = half of the horizontal separation. So you can measure from an imaginary center line out or the total distance and divide by 2.</p><p></p><p>Link Z dimension = straight line height from floor to mount.</p><p></p><p>Static AS = the amount that the suspension will react under force / acceleration. Low numbers = not much, high numbers = a lot. AS is a matter of preference. It used to be that people liked 100%+ because they thought it would plant the tires harder but they found out that you had to tune your shocks around it to control it and it would also walk the rear axle under the rig when climbing which resulted in unpredictable hill climbs as the wheelbase rapidly got shorter. Then people started shooting for lower numbers. Now days it has almost become a moot point. People go for what they want and tune the suspension to react in accordance. I personally shoot for between 30% - 80% so that a small amount of energy goes to planting the tires but not so much as to waste it. The more energy used up in moving the suspension the less reaches the ground. Think of it as using up engine horsepower to move your suspension instead of the tires because that's exactly what it is. If you're not going to be doing a lot of suspension tuning I would think 30 - 80% would be a good range to be in anyway since it is between extremes.</p><p></p><p>Roll Center Height = the imaginary axis around which your body will roll. The higher this is the more stable your rig will be. With a 4-link it is impossible to get this higher than your center of gravity so take that into consideration when shooting for the stars. A 3-link with panhard bar is theoretically possible to get it above the CoG. In this case the body would actually roll uphill. That's just an aside though. Imagine your COG as a big huge weight sitting on top of a stick and your roll center as the point of the stick that is resting in the palm of your hand holding the big weight up. The difference between roll center and CoG is the length of the stick. Now with a big long stick when the weight on top shifts its going to be really hard for you to re-stabilize everything because the weight on top is further away from the fulcrum / the opposite end of the stick and has a longer lever arm with which to control you. Conversely, a shorter stick will be easier to control. When the weight at the top shifts it will have less power as a result of the shorter lever. This is Roll Center. When you go up an uneven hill do you want your rig standing on top of a big long stick or a short one? This is one of the most important things to get right IMO. I spend a lot of time trying to get this as high as possible / as close to the CoG as possible.</p><p></p><p>Roll Axis Angle = how much your axle will steer and which direction it will steer as it flexes. Low positive numbers here are generally better than high negative numbers. Negative numbers will result in the axle turning out of the turns causing turning radius to be reduced and causing less predictable control at speed. Positive numbers will turn INTO a turn causing tighter turning. But too high positive can cause very sensitive turns at speed. General rule of thumb here is to be in the -7* to +5* range. 0* = no roll steer but that is difficult to obtain and probably not worth it anyway. Some designers actually tune roll axis based on the tracks they race.</p><p></p><p>Instant axis = I've never worried a ton about these. Maybe someone else can explain them better. I know that they are the instantaneous point around which the suspension is moving. A long x-axis will mean a longer imaginary fulcrum and more stability since forces will have further to react on the suspension? I would imagine a higher z axis means that the CoG has less leverage on the suspension to tip over also?</p><p></p><p>Travel AS = You can move the suspension around graphically by entering values in Travel Amount box. Negative values are down travel, positive are up. If you have a 16" shock and ride height is at 50% shock shaft showing then you have 8" of positive / up travel and 8" of negative / down travel, adjustable by the amount you enter. As you play with travel you'll notice that AS changes. You don't want large swings in AS, it will result in unpredictable suspensions. It's going to change some. But if at one end of travel you have 150% AS and the other you have 0% you're going to be in for one hell of a ride.</p><p></p><p>Travel roll center = how much your roll center changes throughout travel. Again, huge sweeps = not good.</p><p></p><p>Pinion change = self explanatory. This is a good tool to use to figure out before hand if your design will cause driveshaft problems though. If you're not using a CV joint then you probably want your pinion angle to change very little. If you are using a CV you probably want the pinion to continue angling upwards so that it keeps pointing at the CV joint. Conversely, if everything on your suspension is as you wish but your pinion points up through travel maybe you should think about using a CV. If it doesn't change much throughout travel maybe think about no CV.</p><p></p><p>Travel amount = see Travel AS above</p><p></p><p>Travel increment = a multiplying factor for travel amount. Enter 2 here and it will double everything you enter in travel amount. Enter 8 and it will octuple it. This was mainly put in the spreadsheet because of the two non-functioning buttons that you see below it. If you have some security features in Excel disabled and Macros enabled those buttons work and you can tap them to increase or decrease by the factors you enter. But for most people those buttons don't work and they are just a luxury when they do, not a necessity.</p><p></p><p>OK, so that's probably the quickest down and dirty on the suspension calculator possible. I'm sure I got everything wrong so let the blood bath begin.</p></blockquote><p></p>
[QUOTE="patooyee, post: 453628, member: 483"] Here's my quick, dirty, super-over-simplified rundown of what is going on in each entry. I'm sure people are going to disagree with me, tell me I'm wrong, whatevs. Lets all learn here in that case. This is all using the 3.1d calculator that I posted: Wheelbase = self explanatory Tire dia. = self explanatory Rolling Radius = Half of tire dia. for our purposes. In reality this relates to real-world tire measurements that should be made with the tire in question on the vehicle moving under power. But since we're building the suspension I'm assuming you can't drive the vehicle so just go with half of tire dia. for this. Or maybe if you know that your tire is 41" tall even though the sidewall says 44" go with half the measured height in that case. It does not greatly affect the overall numbers anyway. CG Height = Again, since we don't know the exact height we have to approximate here. A general rule of thumb is to use the height from the ground to the top bell housing bolt of the trans. If you have really heavy axles it might be a little lower, really light axles higher. Vehicle Mass = You're still building the suspension so you probably can't accurately weigh it. Approximate here but be realistic. Front & Rear unsprung mass = Again, approximate. Remember, unsprung does not include the axles, tires, or wheels. Link X dimensions = straight line distance from axle center line to link mount. Note that this is not the length of the link, it is single dimension distance as if you dropped a plum bob from the link mount and another from the axle center line and then that distance as measured on the floor between plums. Link Y dimensions = half of the horizontal separation. So you can measure from an imaginary center line out or the total distance and divide by 2. Link Z dimension = straight line height from floor to mount. Static AS = the amount that the suspension will react under force / acceleration. Low numbers = not much, high numbers = a lot. AS is a matter of preference. It used to be that people liked 100%+ because they thought it would plant the tires harder but they found out that you had to tune your shocks around it to control it and it would also walk the rear axle under the rig when climbing which resulted in unpredictable hill climbs as the wheelbase rapidly got shorter. Then people started shooting for lower numbers. Now days it has almost become a moot point. People go for what they want and tune the suspension to react in accordance. I personally shoot for between 30% - 80% so that a small amount of energy goes to planting the tires but not so much as to waste it. The more energy used up in moving the suspension the less reaches the ground. Think of it as using up engine horsepower to move your suspension instead of the tires because that's exactly what it is. If you're not going to be doing a lot of suspension tuning I would think 30 - 80% would be a good range to be in anyway since it is between extremes. Roll Center Height = the imaginary axis around which your body will roll. The higher this is the more stable your rig will be. With a 4-link it is impossible to get this higher than your center of gravity so take that into consideration when shooting for the stars. A 3-link with panhard bar is theoretically possible to get it above the CoG. In this case the body would actually roll uphill. That's just an aside though. Imagine your COG as a big huge weight sitting on top of a stick and your roll center as the point of the stick that is resting in the palm of your hand holding the big weight up. The difference between roll center and CoG is the length of the stick. Now with a big long stick when the weight on top shifts its going to be really hard for you to re-stabilize everything because the weight on top is further away from the fulcrum / the opposite end of the stick and has a longer lever arm with which to control you. Conversely, a shorter stick will be easier to control. When the weight at the top shifts it will have less power as a result of the shorter lever. This is Roll Center. When you go up an uneven hill do you want your rig standing on top of a big long stick or a short one? This is one of the most important things to get right IMO. I spend a lot of time trying to get this as high as possible / as close to the CoG as possible. Roll Axis Angle = how much your axle will steer and which direction it will steer as it flexes. Low positive numbers here are generally better than high negative numbers. Negative numbers will result in the axle turning out of the turns causing turning radius to be reduced and causing less predictable control at speed. Positive numbers will turn INTO a turn causing tighter turning. But too high positive can cause very sensitive turns at speed. General rule of thumb here is to be in the -7* to +5* range. 0* = no roll steer but that is difficult to obtain and probably not worth it anyway. Some designers actually tune roll axis based on the tracks they race. Instant axis = I've never worried a ton about these. Maybe someone else can explain them better. I know that they are the instantaneous point around which the suspension is moving. A long x-axis will mean a longer imaginary fulcrum and more stability since forces will have further to react on the suspension? I would imagine a higher z axis means that the CoG has less leverage on the suspension to tip over also? Travel AS = You can move the suspension around graphically by entering values in Travel Amount box. Negative values are down travel, positive are up. If you have a 16" shock and ride height is at 50% shock shaft showing then you have 8" of positive / up travel and 8" of negative / down travel, adjustable by the amount you enter. As you play with travel you'll notice that AS changes. You don't want large swings in AS, it will result in unpredictable suspensions. It's going to change some. But if at one end of travel you have 150% AS and the other you have 0% you're going to be in for one hell of a ride. Travel roll center = how much your roll center changes throughout travel. Again, huge sweeps = not good. Pinion change = self explanatory. This is a good tool to use to figure out before hand if your design will cause driveshaft problems though. If you're not using a CV joint then you probably want your pinion angle to change very little. If you are using a CV you probably want the pinion to continue angling upwards so that it keeps pointing at the CV joint. Conversely, if everything on your suspension is as you wish but your pinion points up through travel maybe you should think about using a CV. If it doesn't change much throughout travel maybe think about no CV. Travel amount = see Travel AS above Travel increment = a multiplying factor for travel amount. Enter 2 here and it will double everything you enter in travel amount. Enter 8 and it will octuple it. This was mainly put in the spreadsheet because of the two non-functioning buttons that you see below it. If you have some security features in Excel disabled and Macros enabled those buttons work and you can tap them to increase or decrease by the factors you enter. But for most people those buttons don't work and they are just a luxury when they do, not a necessity. OK, so that's probably the quickest down and dirty on the suspension calculator possible. I'm sure I got everything wrong so let the blood bath begin. [/QUOTE]
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