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RC8.2 Rear End Changes Analyzed: Book Setup -> Maifield 2012 Nats

RC8.2 Rear End Changes Analyzed: Book Setup -> Maifield 2012 Nats

Old 07-22-2012, 10:50 PM
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Default RC8.2 Rear End Changes Analyzed: Book Setup -> Maifield 2012 Nats

Like many out there who built the custom 'worlds' car last year, let alone people brand new to the platform, when I got the 8.2 and threw the stock setup on I was quite disappointed to say the least--the car rolled all over the place in the corners and the rear washed out constantly. My first reaction was to throw my old rc8b w/ worlds setup on it--this gave me my old car back, basically, but I really wanted to understand what was going on with the direction the team had taken and what things like the lower d-plate and custom holes Maifield drilled in his shock tower were doing. After all, they're running a "lower d-plate" to "lower the roll center", but then they raise it more than they lower it by going down to a custom hole on the tower, so the explanation of "it lowers the roll center, this equals more traction" just wasn't making sense.

Over the past month, I've done a lot of track testing and analysis of what the new direction the team has taken with the rear, specifically Maifield's setup changes from the neobuggy article about his nats car that many of us had been doing for a while. In addition, I measured the heck out of the car with a pair of calipers and then plugged everything into Performance Trends Suspension Analyzer, examined the roll center changes and the changes to camber rise when the car is squatted and rolled. This helped me understand what had caused the changes I had experienced on the track. It also made it quite obvious that there is some misconception about what is actually causing the "more traction" in the rear of the car with the changes the team has done -- that's not to say the team doesn't know what they're doing, I wholeheartedly believe that they do, but what is said on the internet and what works its way back to the club racers isn't always 100% accurate.

Let's compare the book setup geometry to to Maifield's nats geometry. The main differences in play here are inside hole on the aluminum rear hubs, the custom "one lower" drilled camber hole on the tower, and the lower d-plate that lowers the rear hing pins down 1mm. Note that Maifield ran his car at 30mm, but in order to compare just the changes and make roll centers come out comparable, I had to set both cars to 29mm in the rear. Also note that I had to multiply all figures by 10 to get the software to take them since it was designed to get angry if you put numbers in that were out of range and the software was designed for full size cars.

Stock


Maifield 2012 Nats


The first thing you should notice is that Maifield's roll center is HIGHER than the book setup, even with the lower d-plate mod. This is due to the inner camber link mount being lowered. This means that his setup, even with the lower d-plate, has less roll than a stock setup. If you only get the d-plate mod, then you're going the OPPOSITE direction that Maifield is going in terms of ROLL CENTER. This is the danger of following trends.

Now lets look at what happens when both of these setups go into a corner.

Stock


Maifield 2012 Nats


What should be abundantly obvious now is that Maifield's setup has much more camber gain. How much? Maifield has 2.17 degrees more camber gain in the example chassis roll above, giving his outside tire more contact patch in this specific situation (note that his outside tire is more straight up and down.) It is my belief that this camber gain is the key to keeping the rear in play in corners--after going to the drilled hole on the tower, I noticed a dramatic increase in my ability to power through the apex and corner exit where I previously rotated and waited for the rear to hook back up to put the power down. It showed up in my lap times as well.

Summary
The book setup has a lower roll center than Maifield's setup, even though Maifield has a lower d-plate. Obviously just going for the lowest roll center isn't the ticket. Maifield's setup has WAY more camber gain. My thoughts on this, having come from building the "worlds rc8b" last year, is that they have moved from the lower hole on the hub to the upper hole, and down on the tower (two holes) for the camber link in order to sweep the upper/lower control arms upwards towards the wheels, putting the suspension further into the "camber rise" curve when at normal ride height, causing more camber gain in the corners. In their latest mod, you will find the front caster blocks have their mounting hole for the lower arm moved upwards (so I hear, I have not measured myself,) perhaps continuing this trend in the front of the car--only time will tell.

Lower D-Plate Mod
As far as the d-plate is concerned, I don't run the lower d-plate mod. There's two reasons: I don't feel my roll center needs to be any lower--I feel that I need to run at least the 2.6 sway bar. If I was hanging around the 2.5 all the time and still couldn't get enough chassis roll, then I might. The other reason is that using the stock d-plate gives LESS camber gain on squat, yet provides MORE camber gain on roll. It's not much of a difference, to roll center or camber gain--the 1mm difference is pretty small, smaller than any other adjustment done to the rear. I'm not a fan of it, but to each his own. Maifield runs it, and he could easily run circles around me. I can't explain it. Do what ya like

Wayne
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Old 07-23-2012, 01:06 AM
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Thanks for the input Wayne. I have just installed the LRC c and d plates into my rc8.2. Based on your insight should I be modding my rear tower for the lower camber option to get the full benefits of the LRC c and d plates?
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Old 07-23-2012, 02:01 AM
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I was struggling for rear grip and had tried a couple of different things set up wise which did help but still did not fix the rear end of the car.Car was drivable with a steady hand on new tyres but as soon as the edge wore of the tyres it was a handfull to drive. Reading the 8.2 thread about the extra hole in the rear tower I drilled mine and reset my rear camber to 2/3 Deg. Running the same tyres that were on the car it handled like I thought the car should have from new. I was able to push he car hard over everything from grass covered switch back corners to high speed rough sweeping corners the rear of the car stayed planted. When it started to step out instead of spinning out the rear of the car drifted out a bit but stayed online. Very impressed with the cars handling
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Old 07-23-2012, 02:39 AM
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Originally Posted by prowlag View Post
Thanks for the input Wayne. I have just installed the LRC c and d plates into my rc8.2. Based on your insight should I be modding my rear tower for the lower camber option to get the full benefits of the LRC c and d plates?
IMHO, the drilled lower hole is a must if you run the hub in the top hole (stock and maifield nats setup) where it meets the lower arm, regardless of your C and D plate, otherwise the roll center is practically sitting on the ground, and even worse if you run a lower d-plate.
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Old 07-23-2012, 03:53 AM
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Originally Posted by Razathorn View Post
IMHO, the drilled lower hole is a must if you run the hub in the top hole (stock and maifield nats setup) where it meets the lower arm, regardless of your C and D plate, otherwise the roll center is practically sitting on the ground, and even worse if you run a lower d-plate.
Thanks for the advice. Looks like I'll be getting the drill out tonight! What size drill bit do you recommend?
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Old 07-23-2012, 05:47 AM
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I drilled the "0" hole in the tower but havn't used it yet. Tried out the Avid 1 dot -1mm pills this weekend along with 7K, 7K, 3K in the diffs and lowered the front roll center by going 2 up in tower and 1 in plate. These changes along with a new lay out at my local track and I ABSOLUTLY LOVED the car this weekend. for the first time since the worlds kits came out I am not chasing a set up. IT let me drive it hard, break traction in a sweeper if needed but get on it hard in switch backs and 180 turns.
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Old 07-23-2012, 09:21 AM
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Originally Posted by prowlag View Post
Thanks for the advice. Looks like I'll be getting the drill out tonight! What size drill bit do you recommend?
Biggest one you have that still fits in the existing holes?
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Old 07-23-2012, 10:13 AM
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Razathorn you are my hero. Ive been following along in all the threads related to the RC8 and RC8T hoping to come across info like this.

I dont have the aluminum rear hubs so obviously cant run the 3rd hole and therefore havent modded my tower for the new camber link either. I did however install the Avid -1mm pills in both front and rear of my truggy before the last race and it felt like the best change Ive ever made. However I lowered all the pills and the upper camber link too so I dont think I actually changed the roll center based on your pictures. I installed Avid pills in B and D plate and 1 dot lower in the A and C also 1 dot lower in both front upper arm pills and 1 hole lower on the rear tower camber link. I know it felt good but have no idea what Ive actually done.

If you have the time could you plug in the numbers for the Avid inserts and see what actually happens when using them. I feel like they are a great middle ground between the low B plate and original one and obviously a much cheaper way to lower the rear rather then buying the Ghea plates. Plus I felt like it was more even rather then running the really low B plate and only 2mm down in the D plate.
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Old 07-23-2012, 11:01 AM
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Originally Posted by PTP Racing View Post
Razathorn you are my hero. Ive been following along in all the threads related to the RC8 and RC8T hoping to come across info like this.

I dont have the aluminum rear hubs so obviously cant run the 3rd hole and therefore havent modded my tower for the new camber link either. I did however install the Avid -1mm pills in both front and rear of my truggy before the last race and it felt like the best change Ive ever made. However I lowered all the pills and the upper camber link too so I dont think I actually changed the roll center based on your pictures. I installed Avid pills in B and D plate and 1 dot lower in the A and C also 1 dot lower in both front upper arm pills and 1 hole lower on the rear tower camber link. I know it felt good but have no idea what Ive actually done.

If you have the time could you plug in the numbers for the Avid inserts and see what actually happens when using them. I feel like they are a great middle ground between the low B plate and original one and obviously a much cheaper way to lower the rear rather then buying the Ghea plates. Plus I felt like it was more even rather then running the really low B plate and only 2mm down in the D plate.
The change to your truggy probably raised your roll center because lowering the rear camber link is around a .2" change in the opposite direction of the .04" (1mm) d-plate change. What you most certainly did was increase camber gain, as will the alu hubs with 3rd hole -- the alu 3rd hole is something I consider to be a requirement for any setup on the buggy. I think the camber gain change is what made your setup feel better.

I actually did plug in the numbers for the -1mm d-plate (avid pills for example) already, I just didn't post them up to spare confusion in the original post. The lower d-plate lowers the roll center, but not by much, and it increases camber gain on squat and decreases gain camber on roll--you may not be able to see it in the pictures, it was very minimal and only obvious when looking at the program's output screen that isn't pictured here. I'm of the opinion that minor roll center changes on cars that use sway bars is sorta silly when you're not at the extremes of your sway bar selection, but that's not to say the d-plate mod isn't doing something else not yet identified.

Here's my car vs Maifield's, the only difference in the geometry being that I do not have the lower d-plate.

Mine (no lower d-plate)


Maifield's (lower d-plate)



Mine (no lower d-plate) Squatted


Maifield's (lower d-plate) Squatted


Mine (no lower d-plate) Rolled


Maifield's (lower d-plate) Rolled


The biggest change with the lower d-plate is the roll center. You can't even see the camber gain differences with your eyes, but the roll center is obviously lower with the d-plate. Now, do you want this? Up to you. Keep in mind that the team guys have been using very tight machined pistons (such as the GHEA ones) and I've noticed what I think to be a trend that they are using damping pack to control over-rolling on corner entry to gain roll ability mid to corner exit. What I'm trying to say here is that their roll profiles may not work with a car that isn't running the same damping setup -- this includes the fancy tight pistons, so keep this in mind.
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Old 07-23-2012, 11:57 AM
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Originally Posted by Razathorn View Post
The change to your truggy probably raised your roll center because lowering the rear camber link is around a .2" change in the opposite direction of the .04" (1mm) d-plate change. What you most certainly did was increase camber gain, as will the alu hubs with 3rd hole -- the alu 3rd hole is something I consider to be a requirement for any setup on the buggy. I think the camber gain change is what made your setup feel better.

I actually did plug in the numbers for the -1mm d-plate (avid pills for example) already, I just didn't post them up to spare confusion in the original post. The lower d-plate lowers the roll center, but not by much, and it increases camber gain on squat and decreases gain camber on roll--you may not be able to see it in the pictures, it was very minimal and only obvious when looking at the program's output screen that isn't pictured here. I'm of the opinion that minor roll center changes on cars that use sway bars is sorta silly when you're not at the extremes of your sway bar selection, but that's not to say the d-plate mod isn't doing something else not yet identified.

Here's my car vs Maifield's, the only difference in the geometry being that I do not have the lower d-plate.

Mine (no lower d-plate)


Maifield's (lower d-plate)



Mine (no lower d-plate) Squatted


Maifield's (lower d-plate) Squatted


Mine (no lower d-plate) Rolled


Maifield's (lower d-plate) Rolled


The biggest change with the lower d-plate is the roll center. You can't even see the camber gain differences with your eyes, but the roll center is obviously lower with the d-plate. Now, do you want this? Up to you. Keep in mind that the team guys have been using very tight machined pistons (such as the GHEA ones) and I've noticed what I think to be a trend that they are using damping pack to control over-rolling on corner entry to gain roll ability mid to corner exit. What I'm trying to say here is that their roll profiles may not work with a car that isn't running the same damping setup -- this includes the fancy tight pistons, so keep this in mind.
What program are you using to calculate all those things?
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Old 07-23-2012, 12:34 PM
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Originally Posted by putte_Rolf View Post
What program are you using to calculate all those things?
Performance Trends Suspension Analyzer. Designed for full size cars, but has support for ours if you multiply the numbers by 10. Should be by 8, but that's too much work when x10 is just moving a decimal point after measuring. Note that I didn't put in anti squat in on any of these.
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Old 07-23-2012, 12:36 PM
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As a techie kind of guy, I love actually seeing the math and reasoning behind set-up changes. Thanks for this one!
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Old 07-23-2012, 12:59 PM
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Scroll the page down from top to bottom and it looks animated...

I am easily entertained, sorry.
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Old 07-23-2012, 01:39 PM
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Any chance you played with moving the rear wheel hub in the lower position on the software?
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Old 07-23-2012, 01:51 PM
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Originally Posted by aaronmn View Post
Any chance you played with moving the rear wheel hub in the lower position on the software?
Yes. It raises the roll center to run the lower hole, as you would expect. I used to run this hole exclusively before drilling the custom camber hole. In order to sweep the camber link upwards towards the wheels at ride height and gain negative camber, you have to counter by going up on the hub to lower the roll center or else the roll center will become too high.
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