What determines the mid engine adder?

[quadzjr]

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..

[ekim952522000]

I have never heard anything about a mid-engine adder?:shrug:

[Greg Amy]

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

[Andy Bettencourt]

It's a mid-rear engined adder.

[GKR_17]

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

[Andy Bettencourt]

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

[quadzjr]

Steve, it's been my presumption that the adder was more for balance than for "polar moment of inertia"

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 :)

[Knestis]

...PS: The MR2 weight is getting corrected from a calculation mistake. Read: lighter

Bag ---> Cat

:)

K

[quadzjr]

haha Now that's funny right there!:happy204:

[ekim952522000]

Is this something we really want factored into the process? I am having a hard time with this one.

[jimmyc]

Does the S2k get one of this adders?


Its engine is behind the center line of the front wheels

[ekim952522000]

Does the S2k get one of this adders?


Its engine is behind the center line of the front wheels

Currently the adder is only for mid-rear engine.

There is not a mid engine adder in ITR

[lateapex911]

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.

[ekim952522000]

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.

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

Is there a mid engine adder in ITA & ITS?

[CRallo]

It's a mid-rear engined adder.

you would say that :p



on a more serious note, why only mid-rear?

[Ed Funk]

[quote=quadzjr;289207]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:

[quadzjr]

Now, relatively speaking, the MR2 adder makes sense.

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:

[Andy Bettencourt]

I think the mid-rear advantage is under braking.

[ekim952522000]

That is what I have always heard.

[MMiskoe]

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?

[CRallo]

Where's the little icon for slipery slopes?

+1!

[Andy Bettencourt]

It's not slippery unless you make it slippery. It's not a 'balance' adder. It's a braking adder. Mid and rear engined cars are better on brakes given weight transfer. It is added in a very easy and cosnsitant way. Agree or disagree, it is not slippery.

[Greg Amy]

It's not a 'balance' adder. It's a braking adder. Mid and rear engined cars are better on brakes given weight transfer.
Whaaa...? You say it has nothing to do with balance, that it's due to braking...'cause the drivetrain's in the back...which improves braking because...there's better F/R balance.

Dee-duh-dee.


It is added in a very easy and cosnsitant way.No, it's not. It's only added to a very small group of "mid-rear engined" cars, and apparently not in ITR. And all other cars with good F/R balance - which in most cases will improve their braking (the stated reason for the adder), despite not being "mid-rear engined" - are ignored.

:shrug:

GA

[Andy Bettencourt]

Seperate braking balance and handling balance in your mind. I didn't invent it, just telling you what it is.

Mid-rear engined car will brake better and more cosistantly than the other front-engined layouts, everthing being equal. And remember, adders are applied REALATIVE to their classed counterparts so you have to look at them that way as well. The first gen MR2 is now in ITB with some pretty old tech.

If there is a contingent that feels the mid-engined, better under brakes adder of 50lbs for ITC-ITS is bogus, feel free to write in. It is applied so infrequently that it doesn't get much of a scrub-down.

[quadzjr]

so we went from blance to braking.. OK..

Braking in a straight line.. yes.. it will be more stable than a FWD or a F-R car.. but then a rear engined car would be even more stable braking in a straight line.

Do I get a break for the inability to trail brake since the rear end snap overstears and there is little chance to catch it? Or how about on long sweeping corners that the car, even in stock form, goes back and forth from understeer to oversteer back understeer in mid corner multiple times?

From the sounds of it, it is a competition adjustment that is not based on physics or empircal data, in a class (IT) that doesn't make competition adjustments.

Like I said before, I was just thinking.. It really doesn't matter.. I was just wondering..

[Chip42]

if it has to do with braking stability, why don't we just pause and note that neither the mkI MR2 nor the 914-4 have stellar braking systems.

granted, they beat many of the older (than the 2) cars in their classes, and I am certainly NOT complaining in the face of a weight break, but this wieght adder seems entirely subjective. does the 944 in ITS have this adder? (it certianly has a large amount of weight in the rear due to the transaxle) from what I gather - it wouldn't.

I understand the assertion that the mid-rear adder is consistantly applied, but I see it as being applied consistently to an inconsistant portion of the group to which it would seem to apply.

a slippert slop indeed. still, the current process is far superior to the old way of doing things. I agree that it would be very nice to see what cars recieve what handicap over and above the 25% gains and class PWR.

[quadzjr]

If there is a contingent that feels the mid-engined, better under brakes adder of 50lbs for ITC-ITS is bogus, feel free to write in. It is applied so infrequently that it doesn't get much of a scrub-down.

Just because it happens infrequntly (relatively few cars with a MR layout are legal for IT) doesn't mean it is right and can be jsut left by the way side.

[Greg Amy]

Mid-rear engined car will brake better and more cosistantly than the other front-engined layouts, everthing being equal.
OK, Andy, your turn: separate in your mind where the engine is located.

You state these cars brake better and more consistently; why? Is it solely because the engine is behind the driver, or is it because they have better F/R weight balance (trust me: this isn't a trick question)? Do these cars brake better because there's an engine in back, or do they brake better because of an advantageous weight distribution?

Do these cars brake better because there's a better F/R weight distribution, or is there a better F/R weight balance because they brake better? What is the root reason here? You're tunnel-visioning on the mechanics of the result, rather than the result.

If a car had the engine behind the driver, but still had a 60F/30R weight balance, would it still get the adder? And - key point at hand here - if the car had better F/R weight distribution, but the engine was in front of the driver, would it get the adder?

Root cause -- > result.


If there is a contingent that feels the mid-engined, better under brakes adder of 50lbs for ITC-ITS is bogus, feel free to write in.Note that I am not arguing whether or not it should be applied as an adder; I'm simply arguing that it should be applied consistently and fairly using the features it's now purported to apply (despite its mis-naming): better braking, which is due to advantageous F/R weight distribution. - GA

[Andy Bettencourt]

so we went from blance to braking.. OK..

Braking in a straight line.. yes.. it will be more stable than a FWD or a F-R car.. but then a rear engined car would be even more stable braking in a straight line.

Do I get a break for the inability to trail brake since the rear end snap overstears and there is little chance to catch it? Or how about on long sweeping corners that the car, even in stock form, goes back and forth from understeer to oversteer back understeer in mid corner multiple times?

From the sounds of it, it is a competition adjustment that is not based on physics or empircal data, in a class (IT) that doesn't make competition adjustments.

Like I said before, I was just thinking.. It really doesn't matter.. I was just wondering..

Just for the record, YOU guys went from balance to braking. In my mind, this adder has always been about braking. Now like I said, love it or hate it, it is what it is and is not a slippery slope. It is applied, right or wrong, to the same cars in the same classes (S-C). If you feel it is wrong, write in and tell us why.

[Greg Amy]

Just for the record, YOU guys went from balance to braking. In my mind, this adder has always been about braking.


It's not a 'balance' adder. It's a braking adder.

Something that's always been presented as a "mid-engine adder", and all of a sudden WE are changing our tunes? Maybe it's the ITAC that needs to present its case better...?

:shrug:

[Andy Bettencourt]

OK, Andy, your turn: separate in your mind where the engine is located.

You state these cars brake better and more consistently; why? Is it solely because the engine is behind the driver, or is it because they have better F/R weight balance (trust me: this isn't a trick question)? Do these cars brake better because there's an engine in back, or do they brake better because of an advantageous weight distribution?

Do these cars brake better because there's a better F/R weight distribution, or is there a better F/R weight balance because they brake better? What is the root reason here? You're tunnel-visioning on the mechanics of the result, rather than the result.

If a car had the engine behind the driver, but still had a 60F/30R weight balance, would it still get the adder? And - key point at hand here - if the car had better F/R weight distribution, but the engine was in front of the driver, would it get the adder?

Root cause -- > result.

Note that I am not arguing whether or not it should be applied as an adder; I'm simply arguing that it should be applied consistently and fairly using the features it's now purported to apply (despite its mis-naming): better braking, which is due to advantageous F/R weight distribution. - GA

It's frustrating Greg that you argue and nit-pick and then don't take a position. All I am doing is telling you how tha adder is applied in it's most simple form because that is what has been asked - yet you inply that we don't have the brains to understand the fundamantals. Doing it or not, it's how it comes off.

I feel they brake better because that have a weight distribution that facilitates better braking. Typically a rearward bias...not a 50-50. It's about weight distribution under decelleration. I would love to see the car that had a 60-30 (60-40 or 70-30?) balance that had a mid-rear layout...and I would NOT vote for the adder. I would go on record as explaining that even though the mechanical characteristic is there, the physical characteristic we are applying for is not. We can never take 100% of subjectivity out of the process, especially when the improbable is proposed.

So in the end, there are always checks and balances and rechecks. It's why the con-calls go for 5+ hours and a straight formula isn't used.

[Andy Bettencourt]

Something that's always been presented as a "mid-engine adder", and all of a sudden WE are changing our tunes? Maybe it's the ITAC that needs to present its case better...?

:shrug:

Again, the question was 'why is mid-rear deservant of an adder'? Braking ability is the answer, not 'handling balance' like is being assumed.

[ekim952522000]

Guys instead of beating up on Andy if we don't like this, how about we put together a proposal to get it changed?

But I have to ask is it the adder we don't like or the fact that it is only applied to mid-rear cars?

Do we agree with a weight Balance adder if it is applied to for example all cars that are 45/55 or more rear biased?

[quadzjr]

I am not beating up on Andy.. he is just the only person that has responded to my question. In all sinserity.. I appreciate his response. I had a question.. he answered it.

I believe IIRC the MK1 weight % is 44.5/55.5 +/- a perecent or so.

I think we are finally coming to some sort of a conclusion.. To re-iterate the adder is subjective based on weight distrubtion that is provided by the MR layout to provide better braking stability.

However that weight distrubtion is a hindernace on other parts on the track. If by chance that it is found that the cars really dont' have an advantage, does the adder go away? I guess that would be hard to prove, many times it has been stated on this site before that on track results are a weak excuse at best.

[ekim952522000]

Let's start by listing all of the mid-rear cars in IT factory weight balance. Let me know if I missed any. I don't know much about Porsche I may have missed a few of them.

Toyota MR-2 (90-94) ITA

Toyota MR-2 1.6L (85-89) ITB

Porsche Boxster (97-99) ITR

Porsche 914-4 1.8 (74-75) ITB

Porsche 914-4 2.0L (73-76) ITB

Porsche 914-4 1.7 (70-73) ITC

If you can find these online please post a link to the results I will look aswell.

Then after we find the weight balance for all of these we need to see if there are other cars in the same class as these that have the same, or more of a rearward weight bias.

We need to check against the rear engine cars as well.

I think that will be a good first step. Then we will have to discuss if we think it should get applied to all of these cars equally, or none of them.

[ekim952522000]

.....

I believe IIRC the MK1 weight % is 44.5/55.5 +/- a perecent or so.

....

ok are there any front or rear engined cars in ITB that have as much or more rear bias. I am asking because if it is a weight balance adder the first thing to figure out is if it is being applied equally regardless of engine location.

[quadzjr]

Fiat X1/9 roles in at 41/59 I believe.

But I am a for of getting rid of it entirely.. do to the fact that where it's weight distubtion may help in one area, it is a hinderance in another.

However it is hard to remain un-biased when I am building one currently.. But it is because of that fact that I even thought about this in the first place. another point as a continuation of the FWD adder conversation, is that if and when it is applied why is it a flat 50lbs.. when weight plays such a higher roll in slower class cars.

[ekim952522000]

I also understand the adder but do not agree with it either.

It "seems" like no one agrees with it. Is there anyone on the forum who thinks we should include weight bias in the process?

My biggest problem with it is that we remove so much stuff from the cars and then add a cage I am not sure the stock weight balance number is really a reflection of what the cars end up.

[Knestis]

Guys instead of beating up on Andy if we don't like this, how about we put together a proposal to get it changed?

But I have to ask is it the adder we don't like or the fact that it is only applied to mid-rear cars?

Do we agree with a weight Balance adder if it is applied to for example all cars that are 45/55 or more rear biased?

Since this isn't a "rule" as such, there's no formal mechanism for proposing a "change," I don't think. You could lodge your questions/concerns through letters to the Board but additional back-channel discussion can be helpful.

I'd love to hear (much like with the torque and FWD questions) options for understanding what's going on at a theoretical level. There's a tendency for folks to jump to the end of the story, staking out a position that's consistent with their interests rather than exploring the whys involved.

EDIT - For example, a case might be made that a rear-drive, rear-mid-engined platform benefits from longitudinal weight transfer in both braking AND acceleration. It also might be that the low PMOI issue described above (the snap spin behavior) is either a curse or a blessing, depending on how fast one's hands are.

And (as is typical) there's potential for a LOT of mixing of issues/influences/rationales/etc. It's very helpful - to me, anyway - if we can be as clear as possible about WHAT we're talking about. Start by explicitly defining your terms.

K

[Knestis]

... My biggest problem with it is that we remove so much stuff from the cars and then add a cage I am not sure the stock weight balance number is really a reflection of what the cars end up.

A good question. We need to remember that we start at "stock" in all instances but go from there.

On anecdote, I'd initially *think* that if anything, balance would tend to go more in whichever direction it starts. When we cleaned out the Golf shell, it ended up being a big box of air in the back. We couldn't take much at all out from the dash forward.

K

[quadzjr]

On anecdote, I'd initially *think* that if anything, balance would tend to go more in whichever direction it starts. When we cleaned out the Golf shell, it ended up being a big box of air in the back. We couldn't take much at all out from the dash forward.

K

That is pretty much I think happens to most vehicles. Having a longer wheelbase would lessen this effect a bit.

[ekim952522000]

OK so I know some of you guys don't like LapSim but I decided to run some simulations with a 2500lb RWD car.

Here are the results.

Watching the simulation it looked like the rear weight biased cars had slightly slower mid corner speeds but later breaking and were able to get back on the gas sooner.

[Knestis]

OK so I know some of you guys don't like LapSim but I decided to run some simulations with a 2500lb RWD car.

Here are the results.

Watching the simulation it looked like the rear weight biased cars had slightly slower mid corner speeds but later breaking and were able to get back on the gas sooner.

Veddy interrrresssting.

Thanks!

K

[Andy Bettencourt]

I asked Mike to run these to see what the results were for a mid-rear bias vs. a 50-50. Seems the SIM sees value in the layout.

[quadzjr]

Watching the simulation it looked like the rear weight biased cars had slightly slower mid corner speeds but later breaking and were able to get back on the gas sooner.

Which pretty much details exactly what I have seen on track. I was able to pull up to a friends miata, mid corner I was busying tryto to catch the car he would pull me, and at corner exit I was on the throttle trying to reduce the damage. All teh advantage seemd to go out the window mid corner. Having LAPSIM with a perfect driver is one thing.. driving that car on thr ragged edge in real life is a whole other ball game.

[Chip42]

Having LAPSIM with a perfect driver is one thing.. driving that car on thr ragged edge in real life is a whole other ball game.

in all fairness, that's not the ITAC's problem.

LAPSIM is not what we base our rules on, as has been repeated countless times. it is a nice sanity check, though. as we are discussing a subjective handicap, it's as good a place to start as any.

th big standout, to me, is that the "preferred format" of the mid-rear engine,(using the 150hp example) @40/60 F/R distribution, is roughly 1s faster than the VERY common 50/50 cars, while the FWD 60/40 (or more front) car is an additional 2s slower (getting worse as % shifts forward).

again, noting that LAPSIM is simply a sanity check, it appears that we are penalizing the MR cars an equal amount as we are "helping" the FWD guys, for half the benefit. and the case is stronger in the 200hp column.

the handicap as a percentage of overall "process" weight, as discussed recently with regards to FWD and high torque is the way to go. additionally, it would appear that the MR adder should be ~half of the FWD weight break, assuming a 50/50 car as the baseline. as no one can predict with better than ±5% accuracy what the as-raced weight split will be in a given car, it's not worth the effort of trying to do so in the classification process. Noting a significant forward weight bias (FWD) or rearward weight bias (ME RWD, RE RWD) as is done now seems sensible and simple enough to use, with a determinate classified weight% adder or different IT power gain multiplier for these cars. the current process is good, but could be tweaked to be better. let's not throw the baby out with the bathwater.

[ekim952522000]

Keep in mind all the cars in this simulation were RWD.

[Chip42]

Keep in mind all the cars in this simulation were RWD.

probably for a new topic, but would you care to run 120/150/200 hp cars with the weight split 60/40 through 35/65 RWD and 70/30 through 60/40 FWD? Obviously a front-heavy RWD car would have a few traction issues thus influencing the results.

nothing but a sanity check.

[ekim952522000]

probably for a new topic, but would you care to run 120/150/200 hp cars with the weight split 60/40 through 35/65 RWD and 70/30 through 60/40 FWD? Obviously a front-heavy RWD car would have a few traction issues thus influencing the results.

nothing but a sanity check.

I did run some FWD weight balance numbers in this thread
http://www.improvedtouring.com/forum...t=25407&page=9 (http://www.improvedtouring.com/forums/showthread.php?t=25407&page=9)

Post #174 It is not the same car or track but should answer your questions.

[Chip42]

thanks mike - I knew I'd seen that before.

as a matter of lap time % difference from "ideal" 50/50, given what mike has posted now and in the past (with all of the caveats that go with it):

layout, weight\hp 150hp 200hp
FR 50/50 0% 0%
MR 40/60 -0.082% -1.35%
FWD 65/35 +1.13% +1.40%

so it appears the effect IS roughly simillar, though mid-rear engined is simulated as slightly less beneficial than FWD is detrimental. I think we tweaking of the parameters, this could be minimized on either front.

the ITR rule might need to be rethought, but the 50 lbs is likely adequate and fair given the above.

[tderonne]

Neat results with LapSim. I haven't used it. Does it assume some nominal wheel rate or something such that the "setup" changes the weight distribution? What does it use for grip/tires? More weight is going to need more tire, but we're limited by rim width. A 50:50 car has an advantage there.

And no has mentioned the Fiero. Which is an ITA car now. I think weight was added in it's transition from ITS. Are these 50 pounds in there? Or did the ITA classification come before the new process?