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Old 10-09-2005, 09:31 PM   #766
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There are 3 roll center blocks for the mrx4. 4.5, 5.5, and 6.5. The 4.5 block gives you the lowest roll center and 6.5 the highest. Yet 4.5 gives you less traction in the rear than the 6.5--that's what I don't understand.
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Old 10-10-2005, 05:18 AM   #767
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Quote:
Originally Posted by jeffreylin
Yet 4.5 gives you less traction in the rear than the 6.5--that's what I don't understand.

Have you tested this ,if so on what track conditions?
Also would the reverse be true to gain steering in the front
IE no shims up front on the inside upper arm = more or less traction

I raced the mrx 4 one race and was very imprresed with its handeling and corner speed


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Old 10-10-2005, 09:34 AM   #768
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Quote:
Originally Posted by jeffreylin
There are 3 roll center blocks for the mrx4. 4.5, 5.5, and 6.5. The 4.5 block gives you the lowest roll center and 6.5 the highest. Yet 4.5 gives you less traction in the rear than the 6.5--that's what I don't understand.

You have a solid rear axle. You can't compare "conventional wisdom" to how a solid axle vehicle operates. On a solid axle vehicle - you create a differential action by lifting the rear tire. So, by raising the pin, you raise the wheel later (higher roll center), creating the feeling of "more bite". Watch the rear of your car, or watch a car that is hooked up - notice when the rear tire lifts. Once you grasp the concept - you'll start going really fast. The looser the track the higher the pin - on a heavy coat of VHT use the lower the pin. The other trick is controlling the car by sway bars. Springs and shock oil are for controlling the roll rate - chassis bounce.
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Old 10-10-2005, 10:17 AM   #769
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Quote:
Originally Posted by Rich Browne
You have a solid rear axle. You can't compare "conventional wisdom" to how a solid axle vehicle operates. On a solid axle vehicle - you create a differential action by lifting the rear tire. So, by raising the pin, you raise the wheel later (higher roll center), creating the feeling of "more bite". Watch the rear of your car, or watch a car that is hooked up - notice when the rear tire lifts. Once you grasp the concept - you'll start going really fast. The looser the track the higher the pin - on a heavy coat of VHT use the lower the pin. The other trick is controlling the car by sway bars. Springs and shock oil are for controlling the roll rate - chassis bounce.
I see, thanks. Now how about the angle of the shocks? do they have the same effect as they do on sedans?
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Old 10-10-2005, 10:26 AM   #770
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Originally Posted by jeffreylin
I see, thanks. Now how about the angle of the shocks? do they have the same effect as they do on sedans?
Angle of the shocks. Once you have your base shock setup - Oil and spring combo that works: Smooth chassis movement - quick response side to side and good weight transfer/balance.

Lowering the shock creates a softer, progressive end result - raising creates a stiffer faster response.

We use the front shock position for "in the corner" tuning.

The rear shocks position is adjusted for "exit speed" and "in corner" balance.

I don't consider the chassis as a tuning segment - it should be as stiff as possible.
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Old 10-10-2005, 10:27 AM   #771
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Quote:
Originally Posted by jeffreylin
I see, thanks. Now how about the angle of the shocks? do they have the same effect as they do on sedans?
I think that you have a good setup, don't worry too much about that, just work with tires compound and with the radio settings.
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Old 10-10-2005, 10:33 AM   #772
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Originally Posted by wad
I think that you have a good setup, don't worry too much about that, just work with tires compound and with the radio settings.
Walter, you should try my car. It hooks way too much. I will be back mid-November I am sure by then you'll be an expert with 1/8 and you can help me set mine up.
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Old 10-10-2005, 10:43 AM   #773
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Originally Posted by jeffreylin
Walter, you should try my car. It hooks way too much. I will be back mid-November I am sure by then you'll be an expert with 1/8 and you can help me set mine up.
My car was doing the same thing, I just changed tires and radio setting, and no more problems
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Old 10-10-2005, 02:50 PM   #774
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Quote:
Originally Posted by Rich Browne
So, by raising the pin, you raise the wheel later (higher roll center), creating the feeling of "more bite".
If you had less Roll in the car wouldn't it lift the tire earlier? I'd think with more roll, the car would roll farther before the inside wheel lifted.

just trying to learn this car a little better.
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Old 10-10-2005, 03:18 PM   #775
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Originally Posted by cdelong
If you had less Roll in the car wouldn't it lift the tire earlier? I'd think with more roll, the car would roll farther before the inside wheel lifted.

just trying to learn this car a little better.
You are correct.

When you are on a really high bite surface - you want the car to slide (slightly) without blowing over - this is where a lower pin location would help. If the pin location is higher - your chassis would lift and then "snap" over - hard to stop a traction roll in this case.

A low bite situation is the exact opposite.

This is a difficult subject to address on the internet in a chat forum. 1/8 scale cars seem to react like a racing kart. Go to a Karting site and read how they approach their setups. Keep in mind, they use the chassis as the "flex" element/suspension. They are very keen about setup and "three wheeling" corners. I hope I've helped.
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Old 10-10-2005, 07:14 PM   #776
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Rich- thanks for taking the time to reply here on this topic. It helps to know the "why's" behind the changes we make. Just a few more ??'s for clarification

Quote:
Originally Posted by Rich Browne
So, by raising the pin, you raise the wheel later (higher roll center), creating the feeling of "more bite".
the higher the pin, the higher the roll center- the less chassis roll correct? That would cause the tire to lift earlier right? kinda confused by your above statement then.

Quote:
Originally Posted by Rich Browne
The looser the track the higher the pin - on a heavy coat of VHT use the lower the pin. The other trick is controlling the car by sway bars. Springs and shock oil are for controlling the roll rate - chassis bounce.
On a loose track (not traction treated) wouldn't you want more roll (lower pin height) to give a little more weight transfer and more bite?

Thanks again for your time.

Corey
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Old 10-11-2005, 07:08 AM   #777
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Ok I am getting confused
what i am reading here is a higher roll center (distance between CG and roll center is close)is better for low bite tracks
and a low roll center (distnace between CG and roll center is greater) is better for high bite tracks

then why did mugen put out the optional rear upper arms, these arms are designed to allow the chassis to have more roll,and they state its for low bite tracks
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Old 10-11-2005, 07:48 AM   #778
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Originally Posted by look
Ok I am getting confused
what i am reading here is a higher roll center (distance between CG and roll center is close)is better for low bite tracks
and a low roll center (distnace between CG and roll center is greater) is better for high bite tracks

then why did mugen put out the optional rear upper arms, these arms are designed to allow the chassis to have more roll,and they state its for low bite tracks
Yes, the chassis having more roll is correct for low bite conditions.
You are controling a spool, no differential - creating the cornering ability by controling when you lift and drop the inside rear tire. As I said before, you can learn alot by reading how Karters approach their set-up - they, like us, run a "locked" rear end.

This is what you can learn (it does apply to 1/8th):

Physical Forces and Setup - Theory and Practice_by James Hughes

"Steering Geometry
The steering geometry can be regarded at the movement and displacement of the front wheels as the steering wheel is turned. This movement is quite complex, and involves a number of different settings. There is one thing in common though, and that is the reason why we need a complicated geometry - We MUST lift the inside wheel while cornering.
The inside wheel lift is what enables a kart to go round a corner without using a differential.
Because of this lack of a differential, a karts natural direction of travel, forwards, is very difficult to change. This is down to the differing radii of turn experienced by the inner and outer rear wheels while turning a corner. The inside wheel is actually travelling a shorter distance than the outside, so therefor is needs to take fewer revolutions to go round the corner. However, the two rear wheels are attached by a solid axle, and must therefor move together, so in order to turn, one of the wheels need to skid over the track surface. In a car, the differential will allow the wheels to turn at different rates, without this skidding action.
This skidding action, or indeed the lack of it, is what make a stationary kart so difficult to turn round - you have to overcome the grip of one of the tyres, and with the sticky tyres used in many kart classes this can expend a lot of energy.
This is the reason for lifting the inside wheel and it effectively turns the kart into a tricycle during the cornering process! The steering geometry causes the inner rear wheel to lift off the ground while cornering, which means the wheel can rotate faster than it is passing over the ground. The rear inner wheel is no longer touching the track, and we therefor no longer need to overcome the grip from that tyre in order to turn.
In fact, depending on the power of the engine, we may be able to allow some scrub. For example, while a Prokart may need to entirely lift the inner wheel, because it does not have enough power to overcome the scrub, a more powerful kart may have power to spare in the corner, meaning that the power loss to scrub can be overcome. However, any scrub will start to cause understeer when entering a corner, so even though the engine may be powerful, it may still be necessary to completely lift the inner rear to maintain decent handling."
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Old 10-11-2005, 09:29 AM   #779
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That is good Rich... I learned at an early age however, that the inside front wheel going off the ground is good when not in tantum with the inside rear wheel. lol

The response from the other person above rich... you just need to reverse what you said and your right on!
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Old 10-15-2005, 04:58 PM   #780
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Hi...

...as I am getting confused too...reading your posts about roll-center in our MRX and trying to remember my feelings when i changed RC...I decided to test these SET-UP changes at our local INDOOR track (quite funny with a 1/8scale...as it is not as tight that a 1/10scale could be faster )!!
Traction is very high there...as it's used nearly every day...

What I felt (or better saw and heard from my driver...as I am without a car this winter) was, that the car LOST traction by using the 6,5mm blocks instead of the 4,5mm ones!!
This is exactly what I expected the car to do by raising the RC...so common SET-UP theory and nothing extraordinary caused by the solid rear axle!??!

Or am I totally wrong now..??
Or are our tracks totally different from yours a few thousand miles away..??


---Martin---
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