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Old 2018.01.23, 02:10 PM   #1
Petercheeks
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Front end-less questions...

I've been researching front end options and I'm starting to have more questions than when I started. The one that has troubled me the most so far is how the MR-03 responds to camber curve. Is this something we actually want in our local setups?

With all the ways there is to tame the responsiveness of the front end it would seem like increasing(by increasing camber) the traction as weight is applied would result in traction rolling. It would seem too if there is any increase in camber it would create positive bumpsteer, which would increase the steering angle even further inboard, multiplying the effect to some degree. I don't know how much of a factor that really has depending on tolerances in the suspension, but it sounds like a recipe for more traction rolling.

I was talking to Mike K about his 90 and he showed me how he raised the upper control arm mount to increase the downward angle of the arm below horizontal, effectively decreasing camber as the suspension is compressed. This is the exact opposite of what all the other suspensions are designed to do. Makes sense if you're trying to limit the amount of traction during hard cornering. I'm not sure how that affected roll center, and how the combination works together or fights each other.

Outside of the MR-02 suspension there isn't any alternatives I've found that allow suspension travel without some associated CC/BS. I've tried to research it here on the forums but the threads are 1% data and the other 99% people arguing about credentials. Figured since we all race here locally you would know better than anyone what works/doesn't work in our setting.
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Old 2018.01.24, 08:36 AM   #2
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Camber gain is one of the pitfalls of the MR03 single A-Arm design. Camber gain is the increase in camber as the suspension loads. There are benefits for it when you can tune it by raising the a-arm hinge pin. This will raise roll center, but reduce camber gain.

With low traction, the camber gain can be helpful to give good initial steering with low camber, and increase as it is loaded... As traction rises, static camber (in knuckle) with less gain makes the car easier to drive.

There were aftermarket parts available to deal with these camber gain issues, that unfortunately are no longer available. Longer A-arms definitely helped give the cars a more neutral feel with static camber (used with either Reflex upper tower, or narrow hinge configuration). Now, raising the hinge location is one of the few available methods to deal with this.

I assume that traction is high where you race. What front tires do you use? Do you glue your tires? A little glue around the outside sidewall of the front tires can also help work around traction rolling issues after raising the tower bar.

I havent been racing recently, but I dont think that anything ground breaking has become available that changes much in the setup of the MR03.

Here are a couple of dated threads that may have some relevance.
http://mini-zracer.com/forums/showthread.php?t=36365
http://mini-zracer.com/forums/showthread.php?t=36225

Worth a read as well
https://docs.google.com/document/d/1...D6LrDseS4/edit
from this thread http://mini-zracer.com/forums/showthread.php?t=39289
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Old 2018.01.24, 03:43 PM   #3
Petercheeks
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Thank you for that info. Good stuff.

I'm running PN KS Mediums in the front and Pravada 5's in the rear, both taped. I haven't experienced traction rolling but I am looking to upgrade the front end. With all the options out there I was curious to learn what faults of the 02 suspension were cured with the 03, and what faults of the 03 the aftermarket was attempting to cure, and at what cost.

From my understanding between those posts and your comments the MR-03 camber gain allows you to run less static camber without the fear of digging the edge in under cornering. Essentially a compromise.

Is that correct?
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Old 2018.01.24, 07:27 PM   #4
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The negative of the mr02 front end is that it only has static camber, which means that you either have less camber than you want at corner entry to get optimum camber in the middle corner, or optimum camber at corner entry with too little in the mid corner (outside sidewall heavily loaded in mid corner).

The largest negative to the mr02 suspension is that the knuckle slides on the kingpin as suspension travels. Which can lead to slop and binding.

The mr03 suspension when oriented in a reverse kingpin layout removes vertical travel of the knuckle on the kingpin, which means a smoother suspension travel.

The negative of a reverse kingpin mr03 configuration is that tere is more unsprung mass on the front end, but my opinion is that it is worth the trade-off to gain more precision and reduce binding of the knuckle on the kingpin by only having the knuckle pivot on the kingpin rather than have the knuckle have vertical travel on the kingpin.

With camber gain that the mr03 has, it can be tuned to the conditions. Giving optimum camber at corner entry and mid corner. Adjusting the roll center, by raising the a-arm hinge along with shims above the knuckle to adjust the geometry. Combined with optional static camber of knuckles, you can really dial in the front end for maximum traction at a reduced cost compared to a double a-arm configuration that was the only real option on an mr02. Many will argue that the double a-arm on the mr03 is still the best configuration, since it has reduced camber gain compared to the single a-arm of the default mr03, with more adjustability of that camber gain with minimal part changes. I personally prefer plastic suspension parts offer aluminum. The expense of the double a-arm is also hard to swallow.

Learning when and where to adjust the camber, caster, and camber gain is important to sorting the front end. For the most part, I would have one car arranged for small track layouts or low traction with less static camber and more camber gain, and one with more static camber and less camber gain for large or high traction tacks. On race day, it is all tire prep, I would almost never adjust front suspension. Only rear suspension to adjust f/r roll rate, and tire.
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Old 2018.02.04, 11:56 PM   #5
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Lots of good stuff. The local track was just re-tiled last week so it will be interesting to see how the cars perform. Should be even more grip. Lap times will be telling.

I was wondering too how sensitive the cars are to scrub. I know with the DAA front end it effectively adds 2mm to each side, cutting the offset (in my case) down to zero. I assume this would ease up some load off the steering but not sure to what extent, or if it's even noticeable.

I was talking to another member and he mentioned the r246 cambered spindles and the plastic steering arms. You too mentioned you preferred plastic. Besides cost can you explain why?
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Old 2018.02.06, 03:34 AM   #6
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plastics are typically lighter than metals. And they rebound in impacts or break. Aluminum can bend, and you might not notice. Easier just to replace the plastic part.

plastic also needs no lubrication on moving parts like a metal to metal joint would.

Im not against metal parts, but I typically only use them when needed. The pn double a-arm typically generates the most front traction out of any setup that I have tried, but is expensive.
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