What determines the mid engine adder?

Q

quadzjr

New member
I was recently thinking about the 50lb mid engine adder. I agree 100% that having the center of mass of the engine and drive train closer to the center of the chassis will enable the car to have a lower polar moment of inertia, thusly allow it to rotate easier, and change direction easier, yadda.. yadda.. yadda. IT is all physics we can't escape that.

Then I started thinking further about the MR2. The center of mass of the entire engine and drivetrain is probably a few inches in front of the rear wheels, mush like a FWD car is infront of the front wheels. Now if we look at RWD cars for the most part the center of mass of the drivetrain is probably significantly further towards the middle of the car than my "mid-engine" MR2.

Then I thought of the miata, It's entire drive train is between the axle centerlines. So by definition why is this not considered a mid engine car? and it's drive train center of mass is well within the axle centerlines.

So if we look from a pure physic's world, and the definition of mid engine. (engine center of mass between wheel centerlines). how does the MR2 and X1/9 differ from a miata?

Just thinking..
 
Steve, it's been my presumption that the adder was more for balance than for "polar moment of inertia" (PMOA is not significant at our level of technology and driving).

As such, you have a valid point, one that I've (unsuccessfully) argued in the past (as I recall, within a discussion regarding the currently-classified weight of the Mk1 MR-2 in ITB...) - GA
 
Are you sure the MR2 got that adder? It was stated the 914 got it when it was moved from ITA to ITB, but that's the only one I know of for sure. I do know the ITR Boxter did not get that adder.I've said this before -- I'd like to see it noted when cars get special penalties or breaks, since all too often it seems they're not applied uniformly.Grafton
 
The MR2 did, I do not believe the Boxster did. At the time, it was determined that chassis and brakes in ITR were advanced enough - and at those high weights - that any 50lb adders for DW or MI was negligable.

PS: The MR2 weight is getting corrected from a calculation mistake. Read: lighter
 
Greg Amy said:
Steve, it's been my presumption that the adder was more for balance than for "polar moment of inertia"
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It can't be for balance, since the miata runs a perfect 50/50 weight distribution and has an arguebaly better balance.

Not meaning to pick on the miata guys, but you have to admit it is a great chassis, just wondering why the MR2 got the adder and a car like the miata didn't. :shrug:

I am glad that it is getting re-calculated. Now I won't have to melt two buckets full of lead... just one :)
 
Think in terms of cars in the class. For example, open the hood of an Audi Coupe. You'll gasp at the weight in front of the wheels. And while it's an extreme, lots of cars in B share the issue, albeit to a lesser extent.

Now, relatively speaking, the MR2 adder makes sense.
 
lateapex911 said:
Think in terms of cars in the class. For example, open the hood of an Audi Coupe. You'll gasp at the weight in front of the wheels. And while it's an extreme, lots of cars in B share the issue, albeit to a lesser extent.

Now, relatively speaking, the MR2 adder makes sense.
Click to expand...

As long as it is applied equally to front-mid engine cars I suppose so.

Is there a mid engine adder in ITA & ITS?
 
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quadzjr said:
It can't be for balance, since the miata runs a perfect 50/50 weight distribution and has an arguebaly better balance.

Not meaning to pick on the miata guys, but you have to admit it is a great chassis, just wondering why the MR2 got the adder and a car like the miata didn't. :shrug:

:shrug:Yeah, me too!!:shrug:
Click to expand...
 
lateapex911 said:
Now, relatively speaking, the MR2 adder makes sense.
Click to expand...

There are cars in B that have a balance over a MR2 and who says that a mid rear setup requres a handicap and a mid-front does not?

I mean if we are penalizing for a great chassis, how come we don't hit the miata?

Then we can penalize for motors that loves IT mods, and add to the D series honda entrants.

Then why stop there lets start penalizing for Torque (VW's)

The people making the decision that the MR2 is well balnced car entry ever try to drive the car on a track at speed? I know I have alot to work on my driver skills but at savanna FWD civic was a breeze to drive at 80% compared to my simillarly prepped MR2.

I am not complaining.. though it can look like that. I was just thinking.. and wondering why. I don't plan on being up front, or acutally buying new tires anytime soon. "I (just) wanna go fast" -Ricky Bobby :eclipsee_steering:
 
So what about the 2nd gen RX7 in ITS? That car was promoted by Mazda as being a 'front amid-ship' motor placement. If you give the 914 and MR2 adders for having quite a bit of weight slightly ahead of the rear axle, why does the RX7 get to be the poster boy of ITS? All of the motor is behind the front axle line and unlike most cars the transmission, diff & rear suspension cradle (all in the middle) greatly outweigh the motor.

Where's the little icon for slipery slopes?
 
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