65LikesTune With Camber Links
10-17-2013 | 05:58 PM
#1336
Joined: Mar 2008
Posts: 5,719
From: At dirt tracks in Michigan!
Let's dissect what's happening here. I still stand by my statement about less weight increases tire efficiency. I agreed with your statement, but noted that it looked like a very simplified situation and was for onroad. Looking at the graph, both my assumptions were confirmed. On road tires have little to no profile, resulting in routhly the same contact patch regardless of the vertical load placed on them. This is not the case in offroad, where tires are designed for a certain weight to deform properly for the best contact patch.The problem with tires is they are never consist and and are always changing. From surface to contact patch to weight transfer humidity, ambient air pressure, tire air pressure, sidewall flex, ect. And will change with each tire, so the constant we have to tune for is how grip is effected by weight, and I still stand by the fact that a tire with less weight will be more efficient than a tire with more vertical load. I reiterate what I've said before. You are applying a graph for one set of conditions to a completely different set of conditions. Offroad, ESPECIALLY with any loose dirt on the surface does NOT behave this way.Now let's not confuse grip with driveability. A light car with too much grip will change directions quickly, so now let's look into the heavier buggy in your example was easier to drive and thus quicker.Never said anything about driveability. I said they handled better and in my prior example I showed how a car with a higher spring to unsprung mass ratio will be able to maintain contact with the track more often than a lighter car. For now let's assume I'm wrong and that tire grip vs weight is linear (the function might be t=w or maybe t=w/2 or possibly t=w*2 where t=traction and w=vertical load or weight. Or better yet let's just ignore traction for a minute). I never said the ratio of mass to cornering force was linear. I agreed that to a point in offroad your graph stands, but as tire conformity and surface penetration become a factor in offroad, there is a diminishing return on losing weight to the point that a lighter car will have a lower traction efficiency.Now what we want to focus on is the variables that have changed and how they have effected the buggy. Let's take three identical buggies and name them A, B, and C. Buggy a is a buggy that was built with now weight added and has a perfect l/r and f/r balance and weighs 7lbs. Buggy B is one that is identical to buggy A except for one thing, buggy B added 1lb of weight directly on the center balance point of the chassis. Now buggy C is the same as buggy B except for the .25lbs was added to each corner for a total of 1lbs. Now let's apply newtons law of motion to these buggies and compare how they act in a turn. Newtons law of motion summarized is that an object in motion stays in motion and an object at rest stays at rest unless acted upon by an outside source. So from the we can see that buggy A is the lightest buggy and will be the twitchiest of the 3 buggies, well buggy B and C weigh the same so they should act the same right? Actually no, now if we look at how the car rotates buggy C will have more body roll in the corners regardless of the weight, and it will also be the numbest car of the 3. The reason being is that the further out the weight is from the center balance point, the further the weight has to travel and more speed is required to make it change angles (think of swinging a bat with a ten pound bag on the tip of it vs a ten pound bag on the handle of the bat) what's going on in your example (more so than how tire traction is effected by the extra vertical weight) is the effects of weight transfer on these buggies, buggy C is going to push on entry more than buggy B and buggy B will do the opposite in comparison. When you change one aspect if the suspension many things are effected and that's where people get lost. Now when I said more traction does not make a car easier to drive, the best example I can think of is with onroad touring cars. If you are running a rubber tire and change to a rubber based foam tire without changing anything else, the car will be many times harder to drive with the higher traction of the foam vs the rubber. This is my take on things I'll leave it up to you to take it or leave it.
Never argued on a cars ability to rotate and know all about inertia. In my examples about the cars mass going to infinity and 0 were to show how effective a suspensions ability to keep the tire in contact with the racing surface is directly effected by the mass of the car, with a heavier car being able to maintain contact with the ground more than a lighter car. As an example, ignore cornering. Lets just do a drag run on a surface that is 'whooped out'. Assuming both cars have had their suspensions properly tuned for their respective mass and have equal amounts of unsprung mass, the heavier car's tires will be in contact with the ground a larger % of the time.
Edit: the reason suspension wasn't added into the tire grip equation is that no suspension is perfect and varies from car to car (including chassis from the same manufacturer, the traction numbers listed above should NEVER be used to tune you suspension rather they are there to show the relationship of grip to weight and that's what we use to tune our suspension. If you have a 4000lbs car it will never pull 1g of mechanical grip. At best you might be able to reach .75g's but again that will vary from car to car)
Again, I point to the fact that this graph is only roughly relevant to offroad racing.
Never argued on a cars ability to rotate and know all about inertia. In my examples about the cars mass going to infinity and 0 were to show how effective a suspensions ability to keep the tire in contact with the racing surface is directly effected by the mass of the car, with a heavier car being able to maintain contact with the ground more than a lighter car. As an example, ignore cornering. Lets just do a drag run on a surface that is 'whooped out'. Assuming both cars have had their suspensions properly tuned for their respective mass and have equal amounts of unsprung mass, the heavier car's tires will be in contact with the ground a larger % of the time.
Edit: the reason suspension wasn't added into the tire grip equation is that no suspension is perfect and varies from car to car (including chassis from the same manufacturer, the traction numbers listed above should NEVER be used to tune you suspension rather they are there to show the relationship of grip to weight and that's what we use to tune our suspension. If you have a 4000lbs car it will never pull 1g of mechanical grip. At best you might be able to reach .75g's but again that will vary from car to car)
Again, I point to the fact that this graph is only roughly relevant to offroad racing.
10-18-2013 | 02:51 AM
#1337
Joined: Sep 2010
Posts: 3,569
From: My house.
Maybe the current topic is not sinking in my brain cells but tire conformity phenomenon can be isolated from total vehicle weight right? The way I see,with greater weight on the vehicle the bump has to do more force to lift the buggy/shock has more work to do right? Now,the vehicle is the same but we removed 50% of weight from it. The shock is tuned to new conditions,so it still absorbs the bump. We have went down on spring rate and oil viscosity,right? So provided we tuned the shock travel,height and shock characteristics to a certain bump profile,weight isn't part of the equation.
10-18-2013 | 04:56 AM
#1338
Joined: Mar 2008
Posts: 5,719
From: At dirt tracks in Michigan!
Maybe the current topic is not sinking in my brain cells but tire conformity phenomenon can be isolated from total vehicle weight right? The way I see,with greater weight on the vehicle the bump has to do more force to lift the buggy/shock has more work to do right? Now,the vehicle is the same but we removed 50% of weight from it. The shock is tuned to new conditions,so it still absorbs the bump. We have went down on spring rate and oil viscosity,right? So provided we tuned the shock travel,height and shock characteristics to a certain bump profile,weight isn't part of the equation.
Imagine you tossed a bowling ball at two guys and they weren't expecting to catch it. One guy is 250lbs and the other is 150. Imagine the suspension is the bowling ball and the chassis is the guy. The heavier guy subles back a step or two before stepping back to his original location. The lighter guy stumbles back further, but sill returns back to where he was standing. Now, rotate this analogy 90 degrees. So that the ball is being thrown upwards. Whenever you hit a bump, the tires are given an upward velocity, thus momentum. The only boy able to push against the tire and suspension (unsprung mass) is the chassis (sprung mass). A heavier car won't be thrown as high into the air, thus will have the tires back on the ground sooner.
Please understand I'm not advocating throwing lead at your car to overcome poor handling. I'm trying to convey the idea that losing unsprung mass is a huge benefit to handling, primarily because the less work the chassis has to do on the suspension, the better your car will handle.
Forgive me if I mistyped anything...
-sent from my iPhone on the way to the ER
10-18-2013 | 08:55 AM
#1339
Joined: Mar 2011
Posts: 2,766
From: Houston
Fred, I was thinking about weight bias and weight transfer on mid motor cars vs rear motor cars and I realized that the rear motor car will have less weight upfront and thus more front end grip. Well with a mid motor car it's going to be closer to a 50/50 weight balance and that means that the front end will have less grip, so what if you run a 4wd front tire on it to increase grip at the front end? I don't own a mid motor buggy so if you feel like being generous would you mind seeing if there's a difference on your mid motor car, or anyone else out there? I do think that the car will need to be retuned but I don't think that you will have to rebalance your springs but the car will have to be tuned for the extra front end grip. Just curious
For a clue, look at the wording under the Figure 1-1 in that book. This is where it gets confusing. Pay attention to the middle section of the paragraph.
"As weight is increased, the traction also increases." Now lets look at the following sentence. "The important thing that must be recognized however, is that the increase in traction becomes less and less as weight is increased." They sound contradictory but they aren't.
Take a look at the extreme left side of that graph. With zero weight, we have zero traction. That seems logical. If the tire can't touch the ground it certainly can't grip it in any direction. As the graph progresses to the right, notice that as weight goes up, traction still goes up. As the second sentence I am quoting states, at a certain point, in the case of this graph around the 1000 lb vertical loading point, each additional pound of vertical weight does not give a full pound of lateral grip although it is increasing. Below that point each pound in vertical weight increase gave more than a pound of lateral traction. That was the tipping point.
RC cars are very light. So light in fact that they are effectively always on the left side of this curve. This is why adding weight increases traction to the point that it can increase total cornering ability at a higher g level. As with everything it is only to a point as this graph shows since too much weight will start to hurt performance. Weight has other side effects though with a big one being that it is more kinetic energy to dissipate in a wreck which results in more broken parts.
The thing to realize about weight distribution is that more weight forwards results in less yaw torque leverage that can be applied to the chassis from the wheels that are steering. This assumes of course that the front wheels are what are steering. Weight shifted rearwards allows more yaw torque leverage (please don't nitpick over that chosen term!) to be applied to the chassis by the wheels that are steering. As easier way to state this is more weight forwards equals more tendency to understeer and more weight rearwards equals more tendency to oversteer. Some people add weight up front and actually gain steering though. Ignoring the other things affected by a weight shift such as spring rate balance and relative roll stiffness changes, part of this is due to the fact that we are on the left half of that graph and that the added weight just gives the tires more traction. It is all about balance and not going too far though.
10-18-2013 | 10:05 AM
#1340
Tech Apprentice
iTrader: (5)
Joined: Jan 2013
Posts: 59
From: Dahlonega,ga
I can absolutely assure you that a rear motor car with less weight on the front wheels does not have more front traction due to less weight. I think there is a bit of a misinterpretation being made from that book as it is a bit confusing to explain clearly in less than a book page.
For a clue, look at the wording under the Figure 1-1 in that book. This is where it gets confusing. Pay attention to the middle section of the paragraph.
"As weight is increased, the traction also increases." Now lets look at the following sentence. "The important thing that must be recognized however, is that the increase in traction becomes less and less as weight is increased." They sound contradictory but they aren't.
Take a look at the extreme left side of that graph. With zero weight, we have zero traction. That seems logical. If the tire can't touch the ground it certainly can't grip it in any direction. As the graph progresses to the right, notice that as weight goes up, traction still goes up. As the second sentence I am quoting states, at a certain point, in the case of this graph around the 1000 lb vertical loading point, each additional pound of vertical weight does not give a full pound of lateral grip although it is increasing. Below that point each pound in vertical weight increase gave more than a pound of lateral traction. That was the tipping point.
RC cars are very light. So light in fact that they are effectively always on the left side of this curve. This is why adding weight increases traction to the point that it can increase total cornering ability at a higher g level. As with everything it is only to a point as this graph shows since too much weight will start to hurt performance. Weight has other side effects though with a big one being that it is more kinetic energy to dissipate in a wreck which results in more broken parts.
The thing to realize about weight distribution is that more weight forwards results in less yaw torque leverage that can be applied to the chassis from the wheels that are steering. This assumes of course that the front wheels are what are steering. Weight shifted rearwards allows more yaw torque leverage (please don't nitpick over that chosen term!) to be applied to the chassis by the wheels that are steering. As easier way to state this is more weight forwards equals more tendency to understeer and more weight rearwards equals more tendency to oversteer. Some people add weight up front and actually gain steering though. Ignoring the other things affected by a weight shift such as spring rate balance and relative roll stiffness changes, part of this is due to the fact that we are on the left half of that graph and that the added weight just gives the tires more traction. It is all about balance and not going too far though.
For a clue, look at the wording under the Figure 1-1 in that book. This is where it gets confusing. Pay attention to the middle section of the paragraph.
"As weight is increased, the traction also increases." Now lets look at the following sentence. "The important thing that must be recognized however, is that the increase in traction becomes less and less as weight is increased." They sound contradictory but they aren't.
Take a look at the extreme left side of that graph. With zero weight, we have zero traction. That seems logical. If the tire can't touch the ground it certainly can't grip it in any direction. As the graph progresses to the right, notice that as weight goes up, traction still goes up. As the second sentence I am quoting states, at a certain point, in the case of this graph around the 1000 lb vertical loading point, each additional pound of vertical weight does not give a full pound of lateral grip although it is increasing. Below that point each pound in vertical weight increase gave more than a pound of lateral traction. That was the tipping point.
RC cars are very light. So light in fact that they are effectively always on the left side of this curve. This is why adding weight increases traction to the point that it can increase total cornering ability at a higher g level. As with everything it is only to a point as this graph shows since too much weight will start to hurt performance. Weight has other side effects though with a big one being that it is more kinetic energy to dissipate in a wreck which results in more broken parts.
The thing to realize about weight distribution is that more weight forwards results in less yaw torque leverage that can be applied to the chassis from the wheels that are steering. This assumes of course that the front wheels are what are steering. Weight shifted rearwards allows more yaw torque leverage (please don't nitpick over that chosen term!) to be applied to the chassis by the wheels that are steering. As easier way to state this is more weight forwards equals more tendency to understeer and more weight rearwards equals more tendency to oversteer. Some people add weight up front and actually gain steering though. Ignoring the other things affected by a weight shift such as spring rate balance and relative roll stiffness changes, part of this is due to the fact that we are on the left half of that graph and that the added weight just gives the tires more traction. It is all about balance and not going too far though.
10-18-2013 | 11:14 AM
#1341
Joined: Mar 2011
Posts: 2,766
From: Houston
The important thing to remember is that the traction aspect is theoretical. Nowhere does that graph take factor of adhesion into account. It is easy to assume that adhesion is the same as traction. I can tell you that calculating tractive effort on trains, factor of adhesion and tractive effort are not the same. The tractive effort in that case is the amount of torque directly applied to the rails whereas the factor of adhesion is the amount of available grip. Traction on a tire can be thought of in a similar manner since it is still a wheel on a surface.
We can clearly tell that the same amount of weight and same tire area applied to a vehicle on concrete will have a very different level of adhesion than the same vehicle on ice. The overall trend may be the same in regards to weight vs traction but the actual curve will be located at a far different weight number.
We can clearly tell that the same amount of weight and same tire area applied to a vehicle on concrete will have a very different level of adhesion than the same vehicle on ice. The overall trend may be the same in regards to weight vs traction but the actual curve will be located at a far different weight number.
10-18-2013 | 12:23 PM
#1343
Tech Apprentice
iTrader: (5)
Joined: Jan 2013
Posts: 59
From: Dahlonega,ga
I'll be using a kyosho zx-5, you can adjust the rake by placing shims on top of the hinge pin holder to decrease rake (increase anti dive)the hinge pin holder mounts to the bottom of the front diff.
10-18-2013 | 12:51 PM
#1344
gotcha, I switched from the zx5 to an xb4. I was wondering because most of our cars don't have an upper control arm or adjustment more like a real car and the more common term I hear for that in rc cars is "kick". We also don't hear "rake" a lot. Just trying have a clear understanding.
You guys make such huge posts with so many big words.....
You guys make such huge posts with so many big words.....
10-18-2013 | 12:52 PM
#1345
Just to muddy the conversation...
Anti-squat is a big factor in traction, but even more in feel and conditions effect it greatly.
When the rear suspension rises, during squat, that is chassis weight that is NOT being transferred to the tires!
Where it gets confusing is conditions will effect feel, or how traction breaks when and if it does. Less anti-squat will break loose less violently, but generally gives less traction under power and more does the opposite.
Basically on very loose tracks, aggressive anti-squat will help with rotation(unloading off power) and on power traction.
On higher bite tracks less anti-squat will feel more consistent.
This is "usually" how it is used.
Anti-squat is a big factor in traction, but even more in feel and conditions effect it greatly.
When the rear suspension rises, during squat, that is chassis weight that is NOT being transferred to the tires!
Where it gets confusing is conditions will effect feel, or how traction breaks when and if it does. Less anti-squat will break loose less violently, but generally gives less traction under power and more does the opposite.
Basically on very loose tracks, aggressive anti-squat will help with rotation(unloading off power) and on power traction.
On higher bite tracks less anti-squat will feel more consistent.
This is "usually" how it is used.
10-18-2013 | 12:55 PM
#1346
gotcha, I switched from the zx5 to an xb4. I was wondering because most of our cars don't have an upper control arm or adjustment more like a real car and the more common term I hear for that in rc cars is "kick". We also don't hear "rake" a lot. Just trying have a clear understanding.
You guys make such huge posts with so many big words.....
You guys make such huge posts with so many big words.....
Next I hope we will discuss toe in at the rear hubs vs the arm mounts or maybe roll center migration.
10-18-2013 | 02:59 PM
#1348
Joined: Sep 2010
Posts: 3,569
From: My house.
*snip*
Imagine you tossed a bowling ball at two guys and they weren't expecting to catch it. One guy is 250lbs and the other is 150. Imagine the suspension is the bowling ball and the chassis is the guy. The heavier guy subles back a step or two before stepping back to his original location. The lighter guy stumbles back further, but sill returns back to where he was standing. Now, rotate this analogy 90 degrees. So that the ball is being thrown upwards. Whenever you hit a bump, the tires are given an upward velocity, thus momentum. The only boy able to push against the tire and suspension (unsprung mass) is the chassis (sprung mass). A heavier car won't be thrown as high into the air, thus will have the tires back on the ground sooner. *snip*
Imagine you tossed a bowling ball at two guys and they weren't expecting to catch it. One guy is 250lbs and the other is 150. Imagine the suspension is the bowling ball and the chassis is the guy. The heavier guy subles back a step or two before stepping back to his original location. The lighter guy stumbles back further, but sill returns back to where he was standing. Now, rotate this analogy 90 degrees. So that the ball is being thrown upwards. Whenever you hit a bump, the tires are given an upward velocity, thus momentum. The only boy able to push against the tire and suspension (unsprung mass) is the chassis (sprung mass). A heavier car won't be thrown as high into the air, thus will have the tires back on the ground sooner. *snip*
10-18-2013 | 05:28 PM
#1350
Tech Apprentice
iTrader: (5)
Joined: Jan 2013
Posts: 59
From: Dahlonega,ga
gotcha, I switched from the zx5 to an xb4. I was wondering because most of our cars don't have an upper control arm or adjustment more like a real car and the more common term I hear for that in rc cars is "kick". We also don't hear "rake" a lot. Just trying have a clear understanding.
You guys make such huge posts with so many big words.....
You guys make such huge posts with so many big words.....
