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Old 10-07-2005, 07:39 PM   #751
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Quote:
Originally Posted by cdelong
Mike- could you explain the physics of your last reply on my question regarding high traction situations where the inside rear wheel may be lifting briefly entering a turn (nearly traction rolling). You had me removing a shim from the rear upright and standing the shock up one hole.

Am I trying to eliminate chassis roll (and bite) or increase the roll to absorb the lateral momentum. Standing the shocks up I understand, but not removing the shim. Does removing the shim have a larger impact on the camber gain than the roll center position?

I guess what I'm asking is if I encounter high traction am I trying to get, or get rid of chassis roll to correct the problem?

Sorry for all the questions, but about the only thing I can't get a grasp on is my above question. There seems to be more than one way to skin a cat.
Yes I to am interested in this answer

thx
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Old 10-07-2005, 09:03 PM   #752
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I spoke to Mike and he told me that the Mugen cars seem to work opposite to conventional wisdom when it comes to roll center. Effectively, if you raise the roll center in the rear you increase bite and lowering it you decrease bite. Thus, by removing the shim you are lowering the roll center and you decrease side bite and reduce the tendency to traction roll.

I don't know why this is the case but testing on the track confirms what Mike said. I am just guess but perhaps it has to do with the relative position of roll center and center of gravity? If someone know the reason please share. Thanks.
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Old 10-07-2005, 10:13 PM   #753
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From what I understand, if you work on the hubs, you are working on camber change but if you work on the bulkhead you are working on the roll center.
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Old 10-08-2005, 11:02 AM   #754
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When I raced full size cars the higher roll center increase traction ( to a point) as well. The higher roll center means when entering a turn more weight will be transferred on the outside tire creating more bite and traction. Lower roll centers develope less weight transfer and obviously less bite (traction). Too much roll on one side or another can create less traction because the tire will break loose. So there is a sweet spot in between.
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Old 10-08-2005, 11:36 AM   #755
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Quote:
Originally Posted by sfelish
When I raced full size cars the higher roll center increase traction ( to a point) as well. The higher roll center means when entering a turn more weight will be transferred on the outside tire creating more bite and traction. Lower roll centers develope less weight transfer and obviously less bite (traction). Too much roll on one side or another can create less traction because the tire will break loose. So there is a sweet spot in between.
Is that roll center or center of gravity you are referring to? Roll center is the pivot point of chassis roll. I can see how raising the center of gravity will increase traction i.e. more weight transferred to the outer wheels when cornering. But if roll center is underneath the center of gravity shouldn't lowering the roll center do the same as raising the centering of gravity in this respect?
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Old 10-08-2005, 05:54 PM   #756
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I was just looking at some pics from the worlds and noticed several mrx4's running yellow rims. Where are they getting them and what brand are they?

Anyone know where besides rc mushroom you can purchase the aluminum upper a-arms supports?
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Old 10-08-2005, 06:08 PM   #757
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Those yellow rims were the new GRPs. I'm not sure if they are coming here. Fast Tires have the new GRP rubber with a different rim...more like the 1/10 scale BBS style.
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Old 10-08-2005, 11:08 PM   #758
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actually it is lowering the roll center, makes the center of gravity higher than the roll center. when you make the roll center higher than you are closer to the center of gravity and then obviously less roll. Making the Upper A arm pivot point higher makes the roll center lower and this makes the center of gravity higher in regards to roll center... therefore car will lean more to the opposite of the turn. Lowering this pivot point... smaller mm of spacers, raisinesthe roll center, makes it closer to cneter of gravity of car and thus creates less body roll... less bite than the above .... gets confusing but good to know when the car needs more or less bite.
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Old 10-09-2005, 07:12 AM   #759
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Quote:
Originally Posted by sohlman
Those yellow rims were the new GRPs. I'm not sure if they are coming here. Fast Tires have the new GRP rubber with a different rim...more like the 1/10 scale BBS style.
Where is a good online store overseas to order these type of parts besides rc-mushroom?
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Old 10-09-2005, 08:51 AM   #760
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Quote:
Originally Posted by sfelish
Making the Upper A arm pivot point higher makes the roll center lower and this makes the center of gravity higher in regards to roll center... therefore car will lean more to the opposite of the turn. Lowering this pivot point... smaller mm of spacers, raisines the roll center, makes it closer to center of gravity of car and thus creates less body roll... less bite than the above.
here is a paint diagram I drew up. It's pretty much the same way XXX-Main setup guide explains things. If you remove the shims, the IC is farther out and the RC will be lower.
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Old 10-09-2005, 07:02 PM   #761
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your right the xxx main shows it well...if you drop the shims... the rc raises closer to cg and less roll.... good drawing... can put on the other lines to show.... another good example is in book also...if rc is higher than cg, then it is like a motorcyle, car would lean in direction of corner...rc below cg , car leans away from turn direction... how much roll it has is dependent where you set your rc.
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Old 10-09-2005, 07:07 PM   #762
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I don't think we'd ever see the case that the CG is below the RC in these cars. The engine sits so high and a good portion of the sprung weight is above what the RC would be.

It's possible, but I would not know how to figure it out??
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Old 10-09-2005, 07:21 PM   #763
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you are right... impossible or if specially built... just trying to get an image across
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Old 10-09-2005, 09:10 PM   #764
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Well, this is what I could not figure out about this car. Raising the roll center increases traction in the rear and lowing decreases traction--completely opposite to conventional wisdom.
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Old 10-09-2005, 09:23 PM   #765
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I believe your stating it wrong.... when you lower the Roll center point... in regards to the center of gravity...thus larger distance between center of gravity and roll center you increase traction by creating more roll to the outside wheel of turn. When you raise the center of gravity... taking shims out... you make the roll center closer to the center of gravity point and then less roll less traction, looser car. It follows the norm. Take the lines fromthe graph given.... take the last red line and extend it... lesser angle than the line above.. the IC is further out... but the line that is for the roll center now goes up to intersect...thus the roll center point is higher... closer to the center of gravity...less roll...less traction.... this makes me grab books and read also.... but the cause and effect and the mechanics of these is what is needed to better your car. I have seen you drive jeffrey... this shouldn't bother you, your to good!!!!
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