As I see it there's not a very good case, if at all, for most mid engined road cars - so why bother?

The Locost concept works very well for lightweight medium powered (say 200 hp) cars, there is loads of operating experience out there to draw on and specialists abound - so why mid engined?

I agree it is different when engine power rises above 300hp, with current tyre technology the main consideration is then to get as much weight above the driven wheels and fit the widest rubber available.

But this solution has a big drawback the moment of inertia drops - great for responsiveness in turn in but the ride quality is a pile of mince and the handling's twitchy.

If you doubt me compare driving a MGF to a MX5. Which would you prefer to travel a couple of hundred miles in?

So as I see it there's no place for mid engined road cars particularaly those based on mid powered front engined drive trains. Slightly different if we are considering track day/sprint/hillclimbers but most on this forum 'aint.

Anyone think differently?

Cheers

David

Yep, I think different, my Elise was great fun to drive on the road and track.

Personal choice I guess.

I'd drive the MGF everytime, MX5 is for hairdressers only!

Rich.

[Edited on 17/2/05 by shortie]

Whilst I agree with some points, I think mid-engined is a lot of fun, I have the best of both worlds, fantastic steering due to Mini rack etc and power/weight on the rear wheels giving me better traction.

Proud Mosquito Owner (1 of 10)
Smudger
Rescued attachment Green 2.JPG

Ok I'll bite, although I can't believe this is a serious question........

Why bother building your own car at all?.......makes no sense at all when you look at it logically.

So, if you aren't particularly logical and want to do it anyway, then why not a middy?

Then the practical side of things.....over here in the US there isn't an obvious equivalent to the Escort/Cortina/Sierra....yes there are some suitable donors, but a hell of a lot more FWD donors.....

So they are my reasons....but of course I don't need to justify my decision.

I recently bought a peugeot 205 1.9gti which is rather fast, handles well, why bother building a locost when the above car only cost me £500?

It's a hobby, it's fun, you can do what you like, to your own design or otherwise, satisfying, learn/develop/hone engineering/manufacturing skills, learn about mechanics etc etc

need i go on?

mid engine is better weight distribution for better balance in a car, maybe only shown on track, but i bet a lot of finished cars onhere have/will go on a track at some point, so the benefits will be realised.

Ned.

Believe it or not your choice in engine placement all relates to your preference in women. Some men prefer a buxom woman, with the weight all up front, and some prefer a woman with a nice derriere, with, you guessed it the weight at the back. Of course almost everyone likes a well balanced woman, with some weight transfer to the front when pushed hard... But I find that a woman with a small, powerful engine placed in the back offers more performance potential in the curves...



Ok, I'll stop there! But I think my argument has more validity than the first post!

hear hear graber!!!

is this for real? ever driven a middie in anger? if well designed/set up it knocks ANY fwd car for six. why do you think all serious race cars have the motor round the back? and if you cant appreciate handling finesse even at non-racing speeds, youve got the sensitivity of a potato.

The Locost concept works very well for lightweight medium powered (say 200 hp) cars, there is loads of operating experience out there to draw on and specialists abound - so why mid engined?

I live in the U.S. Where do we locate an easy-to-find 200hp 4-cylinder engine driving the back tires?

I agree it is different when engine power rises above 300hp, with current tyre technology the main consideration is then to get as much weight above the driven wheels and fit the widest rubber available.

With 60% weight on the rear wheels, a mid-engine car will stop much faster then the equivalent front-engine version (case in point, Porsche). Light front-engine cars of even modest power easily spin their rear wheels in lower gears, mid-engine cars do not.

But this solution has a big drawback the moment of inertia drops - great for responsiveness in turn in but the ride quality is a pile of mince and the handling's twitchy.

What does moment of inertia have to do with ride quality? That's shock damping, spring rates, roll-bar stiffness, and wheelbase. If anything it'll be better because the seating position is closer to the CG giving less pitch. Handling depends on lots of things including all the above + steering sensitivity.

So as I see it there's no place for mid engined road cars particularaly those based on mid powered front engined drive trains.

Apparently a lot of people think differently; consider the Lotus Elise.

"Anyone think differently?"
An odd thing to ask considering where you are. You're making the assumption people on the mid-engine list know about as much as Locost builders when it comes to vehicle design. No - Locost builders don't design anything, they just follow instructions in a book. The people here are self-taught chassis and suspension designers who at least have a clue.

Your ball.

BTW, are you, as your avatar claims, building a Midi? Regardless of the answer, you're either misrepresenting yourself, or very unhappy with what you're building!

[Edited on 2/17/05 by kb58]

I think that the V8 kid is yanking our chains. Note that he says that he's building a middy. Wither he's having a bit of fun at our expense, or he's realized that he's over his head and wants to... well I dunno, want's something.

(opening the envelope) The best response goes to....... Graber (Although I tend towwards the top heavy in my taste in women )

[Edited on 17/2/05 by kreb]

Yeah if you look at the threads he's in, it's mid-engine V8 stuff... go figure.

I think he wants to build a Middy and has the right to ask the question to see if everyone else agrees - nothing like a good debate!!!

Well, here's y tuppence worth.

I'm building a middy cos I can!! No really - a custom bodied car will usually look better if it's a middy. With a Bike engined Middy, (like mine) the weight on the rear will be very usefull considering how light the car is going to be and the porwe rgoing throught he rear wheels.

I haven't designed a chassis as such just modifying the LOCOST one and building around it. I don't have the knowledge just yet to design a whole new chassis at the mo. Driving it is going to be better than anything I've driven before HOW EVER I DO IT!!!!

quote:

---

Originally posted by chunkielad
I think he wants to build a Middy and has the right to ask the question to see if everyone else agrees

---

He posted 6 weeks too early - should have been April 1!

Following Steve Grabers train of thought....I'm building a middy AND my wife has a great arse. Consequently I am a happy bunny.

You are partly right.

For a mass produced road car it's mainly an issue of whats in the corporate parts bin and what the market will buy.

When faced with a parts bin full of transverse engines and a market that hasn't spotted the fact that no serious race car has a transverse engine then that's what you build. As soon as the budget grows car makers usually ditch transverse layouts for middy cars and go longitudinal.

For us Locosters we're faced with a rapidly diminishing supply of front engined rwd donors and a rapidly growing supply of transverse engined donors. So a big slice of the future is transverse engined middy for us.

As regards driving, acceleration, agility and braking in a straight line are better with a rear weight bias. However other aspects of handling may be worse. Middys have a reputation for being more easy to spin for example. Ride quality does suffer when polar moment of inertia goes down, that's one of the reasons why luxury cars are big!

I reckon it's still the case that a front engined home build is easier to sort out than a middy from a handling point of view. I'd be surprised if a transverse engined middy ever seriously challenged a Caterham in this respect.

Oddly, if you work through the maths of the issue front wheel drive with a rear facing longitudinal engine, as in the Citroen Traction Avant or Miller race cars of the 20s have the absolute highest cornering speeds. However they have zero adjustability at that point of maximum cornering speed so one twitch and you're off. Other layouts have lower ultimate cornering capability but much bigger (its relative!) margins at the limit so they actually go faster on a real road.

I myself am building a front engined kind of Frankenseven--long wheelbase late 1930s ish thing. I have only driven one mid or rear engined car - if you dont count the beetle. The fiero gt was a fun car to drive responsive but a bit twitchy-- but thats what made it fun. I started out in this nonscence by going to go and buy a porsche 914-- but luckily I was too big to be able to drive it. I think the choice of the front engined sevenish car is the open wheeled roadster more than anything else.
Dale

What Cymtricks said.........

When I first started talking to people about my project, several people assumed I would be doing it with a tranverse engine, and we have a race class out here that is like that. But looking at them, where does a decent length rear upper wishbone go?

Those we are building, how long have you manged to get the rear upper link, or what else have you done regarding rear suspension layout (if not retaing a McPh strut, Stratos style)

Cheers

Fred WB

When I first saw v8kid's message I wasn't going to reply as I thought he was just taking the piss. But, given the number of responses (although, notably, none from David himself), I'll throw in one of my own.

I think David's remarks suggest a somewhat narrow view of the sports car world perhaps coupled with limited actual driving experiences.

My reasons for building mid-engined are many, most of which have already been mentioned by others. The primary one is the desire for a compact, nimble car, optimised for Sunday runs in the mountains. The second was the neccesity of using a recent drivetrain to meet emissions requirements here in Oz. The third was the "because it's different" factor - something we all should be familiar with

Re Fred's question about rear suspension. When I started out I went to-and-fro for a VERY long time about rear suspension options. As you know, true wishbones don't fit; multi-link is not much better; de Dion is a possibility; or I could retain the struts. Re-using the struts is attractive to me for a lot of reasons:
- it's cheap! Alloy sleeves to convert my struts to coil-overs cost < AU$40 each.
- it's compact. Simple packaging means simpler build.
- it's simple - in the sense of adjustments, of which there are less. Not as few as a de Dion, but less parts.
- it's cheap! (did I mention that already )

Seriously though, Lancia made it work well on the Stratos, Lamborghini made it work on the Urraco, and Toyota definitely made it work on three generations of MR2. I should be able to get tolerable behaviour for my purposes.

Dominic

Thanks for all your replies chaps I assure you I am Serious if a little frivolous to get the debate running.

I guess we are all in this because as Ned says it's our hobby/fun/learning/developing/hone skills - can't put it better myself.

The internet in general and forums like this specifically are fantastic ways to achieve these aims but the trouble is there are a lot of myths circulating which simply 'aint true.

It's so easy to get involved in the detail of "how to" in a project that we, or at least I, forget to look at what we want to achieve.

Some of those myths or partial myths are - better weight distribution, lower MOI, better traction, quicker turn in and so on.

I sprint, hillclimb and weekend drive a 25 year old v8 front engine car with 50/50 weight distribution but quite a high MOI - never used to have a problem with traction modern tyre technology and engine management systems take care of that and all the chaps I compete against have front engines/rear drive. None of them suffer these alleged problems.

The trouble is I got a new engine going from 3.6 to 5 liters and a bit wilder tuning. Now I have a serious traction problem to the extent that I'm running the old engine. - hence the midi interest.

You could say my sole interest was traction but at what price? Some tracks are bumpy, certainly here most roads are I don't want my car to be undrivable on the limit 'cos it pitches all over the place ('fraid low MOI does cause this) and if i adjust it out with dampers/springs the wheel rates will go to pot.

Also I admit I'm no Schue I need some stability at high speed another problem with midi's

At the end of the day I've no option but to go mid engined but I'd rather do it with my eyes open and I just can't see the logical case below 200- 300 hp (lightweights excepted).

Logical reasons I said, there are better reasons as others eloquently pointed out, preference for women or just 'cos you can seem like MUCH better reasons than stuffy logical reasions to me - the bugger is they dont make you go faster.

Ferrari and porsche make midis and they are designed to be very fast. Can't be that bad an idea.

Most Porsches are rear, not midengined (being pedantic)

Cheers Fred WB

quote:

---

Originally posted by Fred W B
.......Those we are building, how long have you manged to get the rear upper link, or what else have you done regarding rear suspension layout (if not retaing a McPh strut, Stratos style)

Cheers

Fred WB

---

And you can see my approach here:
http://www.kimini.com/Diaries/2004Winter/rear%20suspension.JPG
http://www.kimini.com/Diaries/2004Winter/rear%20suspension2.JPG

Interesting how we both end up with 3 brackets down each side of a vee.

Re. your second pic.

http://www.desicodesign.com/meerkat/images/020202_rear_bracing.jpg

Well huh, I hadn't seen that picture before. Doing it again I'd use a different mounting style on the lower arms. While what I have works, it's a real bitch to get at.

Thanks guys

I have been following your sites, but it was usefull to be reminded to go over them again, as a lot of things are much more relevant to me now I am actually building something.

kb58 - that is one sexy jack!

Cheers

Fred WB

The jack is the cheap aluminum one selling here for about US$89. It's not regarded well by some people as I hear it doesn't work well in the cold, and if the load isn't centered, the jacking point can break right off. But, at 35lbs, it's okay by me, for now.

Just remembered another thing. I do something that I hardly ever see, mounting the bottom of the rear shocks directly to the upright. Most people put it on the lower A-arm which puts a lot of stress on it. It remains to be seen how smart my choice was.

quote:

---

Originally posted by Fred W B
Where does a decent length rear upper wishbone go?

---

Libra Rear Suspension

quote:

---

Originally posted by Fred W B
where does a decent length rear upper wishbone go?

---

Good points, but help me understand this:
"...a front engine layout would be faster mainly due to the weight distribution and partly due to the higher centre of gravity of a transverse engine package in a middy."

If the front-engine design achieves 50/50 weight distribution, maybe, though I think having 55-60% over the rear axle is better for traction and braking. Having larger rear tires makes a difference too regardless where the engine is.

About the center of gravity, what makes a mid-engine have a higher CG? The engines are basically the same. The transmission? The vertical placement of everything in the tranny is the same front or mid-engine. The seating position will be the same too as well as the gas tank. Givent that these four components pretty much consistute the mass of the entire vehicle, I don't see any diffference.

Help me understand.


[Edited on 2/20/05 by kb58]

quote:

---

About the center of gravity, what makes a mid-engine have a higher CG?

---

With a mass produced transverse engine the gearbox has a higher engine input shaft height than output axle height. This puts the engine well above ground level in a typical hatchback.

Move the engine into a mid engined position and typically you could lower the engine by a couple of inches, i.e. from about 6.5 to 4.5 ground clearance simply because sports cars tend to run lower and don't need to cope with being piled high with four people and their luggage. If you lower the engine you get odd drive shaft angles, tilt the engine to lower it and you make the engine bay longer and possibly mess up the sump oil level etc. So you can lower it a little bit but that's it.

Of course, kb58, you could lower it by 2 inches by using 13 inch wheels!

With a front engined car you can run both the axles and the drive shaft to the rear diff at a slight angle and still end up with a lower engine and sensible shaft angles. Some front engined sevens do run with very low engines and usually all you need to make this work is a chopped sump.

So unless you make some drastic change somewhere the front engined car has a lower CoG than a transverse engined middy just because of the mass produced parts that we have to work around.

Regarding weight distribution there is some debate about what "perfect" is. Most sources state either 50/50 or 55/45 (small rear bias). With a front engined car like a typical seven you can easily get into this range with a small engine and with the weight of a driver included. With a transverse engined middy you're probably going to end up with something closer to 60/40 by the time you've sat in it.

So for a small engined light weight car you usually get a lower CoG and a better weight distribution with a front engine.

For road cars i've heard a very convincing argument that you don't want 50/50 balance. It makes the car too twitchy. If you have 60/40 in either direction you will know what the car is going to do in a given situation and be prepared for it.

I understand now.

In our applications here though I don't think it's an issue. In my case for example, using 13" wheels and tires, axles at their proper angle, there is 4.5" under the pan. This is about as low a ground clearance as it should be for a road-going car. If I install racing slicks, there is now 3.75" under the pan. How low do you want to go?

OTOH, in the case of a true race car, yes, you are correct; we are not free to set the ground clearance to, say, 1". A FWD mid-engine cannot work. I was assuming the case of a self-built road-going car, and in that case, the CG can be just as low as any front-engine setup.

I agree that 50/50 seems logically perfect; when cornering on a skid-pad, the fastest car will be the one with equally loaded tires.

Having said that, the first strike against it is that many sports cars have larger rear tires. Now the tires aren't equally loaded the same front/back because there is a lower force/area on the larger rear tires. All things being equal, I would expect this 50/50 car to exhibit understeer on the skid pad because the fronts do not have as much traction as the rear.

If the car has 50/50 weight distribution, AND equal size tires, I'd expect oversteer because the back tires are being asked to do more then the fronts, cornering AND propulsive force, so they will break free first.

The second strick against the theory is, race tracks do not have many constant speed, constant radius turns. The car is always speeding up or slowing down; rare is the case in a turn where everything is static.

Given this, when the car is accelerating, weight transfer shifts to the rear, a good thing (for rear-drive cars.) With a greater static rear weight distribution there is even more weight on the back end, holding the rear wheels down and aiding acceleration. I will admit though that this condition can cause understeer if taken too far.

When the car is decelerating, weight shifts to the front. In a front engine car, the rear tires are practically useless now because there is no weight on them. With a mid-engine layout, the weight of the engine holds the rear tires down on the road, allowing them to add enormously to braking.

At least, that's my personal theory... for now.

kb58 - I think you nailed it. A 50/50 weight distribution is a theoretically perfect condition which only has much of a bearing on a skidpad.

I'd also take issue with the idea that you need 250 + HP before the middie is ideal. The dynamic factors that you list are weight neutral - weight transfer happens regardless of vehicle GW.

Hear Hear KB - The Lotus Elise would be a prime example of a Sub 200Hp/Sub 1000Kg transverse mid-engine car that out-handles almost every other production car known to man regardless of cost.

Steve

I was thinking a bit more about this. When a mid-engine car has wider rear tires, it's an even further improvement. Dynamically the car now approaches the advantage of 50/50 weight distribution because traction can be identical front to back. AND it still retains the mid-engine advantages of better traction under acceleration, and better braking due to the rear weight bias.

What's we need are two Locosts using the same engine, one front engine and one mid, then compare performance under all conditions. Easy to say...

[Edited on 2/22/05 by kb58]

I've never heard of a 250bhp limit at which a mid engine becomes better than a front engine but it's probably a result of the issues I mentioned above.

Smaller volume cars need to rely heavily on mass produced parts. The Elise, MGF, MR2 etc had their layouts determined by what was available in the mass produced parts bin. That ment fwd drivetrains. To get rwd the drivetrains were moved to the back giving a transverse middy layout.

250bhp is very roughly at the point where mass produced engines give way to purpose designed ones. It also corresponds roughly with the point at which the mass produced and small cars give way to more exotic, lower volume stuff. The truth behind this limit is probably that it represents the limitations of a typical corporate parts bin to provide a ready made fwd drivetrain ready to be moved rearwards.

For our kind of cars, a light weight mass produced engine gives slightly worse CoG and arguably worse weight distribution if you choose a fwd package as I pointed out above. With a traditional Seven layout you can lower the CoG and get better weight distribution due to not being stuck with the relative heights of the axle and engine crankshaft of a typical fwd layout. Of course the Polar moment of inertia is worse with the front engine so it isn't entirely clear which layout wins out overall.

As the engine gets bigger the effect on polar moment gets worse for a front engined layout and the benefits of shifting the engine to the middle become more marked. Also the market for bigger engined cars will justify designing a special driveline. I would guess that once you move from the smaller V6s to big V6s or V8s then middy is best just on the basis of polar moment. Thinking about it this point isn't far off that 250bhp limit.

Just a final thought. The MGF and MR2 have slogged it out with the MX5/Miata for years and judging by the road test reports it's hard to find a clear winner. Likewise has anyone put an Elise up againt a Caterham with a similar power to weight ratio? Was there a clear winner?

From what I've seen the Elise will kick most 7's tails with a comparable power-to-weight ratio. The more extreme 7s will win by virtue of superior output.

On the Middie versus frontie debate- my experience is that it's easier for a mediocre driver (such as myself) to get the most from a neutrally distributed car. A superior driver will be able to wring more from the middie despite it's more extreme tendencies towards overster, due to the superior traction and braking.

Depends how well sorted the middie is.

It took the Stig on Top Gear a whold morning to get a fast clean spinless run in the Porsche GT, but only a couple of attempts in the Merc McLaren Slur

Got to disagree with you chaps - no suprise there then!! - 50/50 is a myth.

50/50 is a lousy combination for the average sporting driver and car and its just not far enough for racing.

Here's my tortured reasoning - Just observe what your car does when coasting round a corner - the blessed thing slows down! Yup the combination of aero, rolling and scrub losses slows the dashed thing down significantly. To keep our constant speed (another myth but anyhow) we need to apply throttle. Observe yourself at speed and it is suprising just how much throttle is required. Well I was amazed when I first twigged it anyhow.

Now with 50/50 weight distribution the cenrtifugal force is going to make both tyres break away at the same time- so where is our traction force coming from? Yup it's stolen from the rear wheels (assuming RWD) reducing the rears ability to hold the road.

Hmm - terminal oversteer - dangerous can't have that so the designer has to incline the roll axis, or whatever, to make the front break away at the same lower limit. i.e. add understeer

Answer is to put more weight on the front wheels so there is spare tractive capacity at the rear wheels to maintain constant cornering speed. Say 55/45.

All the above only applies if all the wheels are the same size which is the case for most road cars (apart from ferrarri et al).

Make the rear wheels bigger and its a whole new ball game - now we can load up the rear to get traction without loosing out on cornering.

Still I would never choose 50/50 though if you are prepared to do without a spare or an ineffective spare at best its a no brainer to go the whole hog.

Cheers

David

PS Centrifugal force is another myth!!

Huh?

Well it's nice to know that nose-heavy pigs are great handler's after all. Well I guess you showed all those dummy engineers at Porsche, Mazda and BMW. Good on you!

Now if you'll pardon me, I'm heading off to the garage to add some balast to my front end.