The creator of GTR explains how the GTR is so heavy
 

From the designer drawing board itself. Not all aftermarket like 600hp stripped GTR(lighter) can do a better time than the stock GTR in the nurburgring. That wt has a purpose. A 600hp GTR will be faster in straight line but in Nur time might be different. It is a better package car. If you want a dragster make it 800hp good for straight line but not for Q day use.

NISSAN GT-R: KAZUTOSHI MIZUNO INTERVIEW
Part I of PH's exclusive video interview with the Nissan GT-R program chief

Last month PistonHeads was invited to visit Nissan's Nurburgring Technical Centre for an exclusive interview with the 'father of the GT-R', the car's program manager and chief engineer Kazutoshi Mizuno.

PH Editor Chris-R posed questions based on suggestions from the PH forums, and we captured Mizuno san's answers on camera. Check out the film clips below, for some fascinating insights into the mind of this famously single-minded chief engineer, and his philosophy about the GT-R project.

The fount of all GT-R knowledge very kindly answered all our questions in English, making frequent use of the office whiteboard to illustrate various points.

Without blowing the PH trumpet too loudly, we're forced to say that GT-R 'geekery' doesn't get much better than this. So pay attention class, and take it away Mizuno san..

Q1) For such a high performance machine, the GT-R is a big car and heavy one. Tell us why that is?

http://www.youtube.com/watch?v=8nGiZ...layer_embedded


Q2) So what is the best way to reduce weight from the R35 to make it perform better?

http://www.youtube.com/watch?v=x1izu...layer_embedded

Q3) In your previous answer, you seemed to be telling us the parameters of 1700kgs weight and 485hp were set from the beginning of the project, is that correct

http://www.youtube.com/watch?v=eXtOY...layer_embedded

Q4) Why did you opt for a V6 engine, instead of an engine with more cylinders?

http://www.youtube.com/watch?v=Nf8rA...layer_embedded

Q5) What about the transaxle - some competitors have seven or eight speeds, so why does the GT-R have only six?

http://www.youtube.com/watch?v=bc5wI...layer_embedded

Q6) The R34 had the HICAS rear wheel steering system. Why didn't that make it onto the latest GT-R?

http://www.youtube.com/watch?v=gil9U...layer_embedded

very good videos and informative

cliffs?

Great post

was hard catching all of it when he described the reasoning behind the v6. basically balance?

Wow... nice videos!

cant really understand his english 100% but oh well



so basically he is saying light weight is good, he understands that..ok...

light weight better for acceleration and breaking, but you want heavier weight for cornering speed?

Mechanical grip through deadweight?

FYI, if the F1 teams were allowed, by regulation, to run lighter than 600kg, they would.

He's saying you can't get the same downforce as F1 cars or any racing spec cars. So they substituted extreme aerodynamics with actual weight so when you corner there's more grip on all 4 corners of the car by having the weight with the added downforce. That in turns create a similar weight acting upon the car as an actual race car. Something like that...

That was interesting to watch. It feels like they are trying to make the new gtr too balanced by trying to make it able to do everything. I don't think a car that is too balanced and tries to do everything can be a real sports car.

I agree, the whole dead weight argument seems to be the only explanation? he never mentioned how you could get more cornering grip through aerodynamics. which is exactly how F1 cars achieve their cornering grip.

I would have liked it on how the body is reinforced and put together. that there, is probably another big part on the great chassis of the R35.

He says in the clip that they're making a normal roadcar. They had no intention of trying to generate that kind of force through aerodynamics on a regular car.

very interesting video to see what design constraints the R35 was built around. The PH questions were centered around the assumption that the R35 could be so much better and faster if it was lighter and had more power (typical go-fast mods people do to the car).

But from the point of the designer, the application of the car being:
-non-professional drivers
-not high-speed where down-force is a major factor in contributing to the grip of the car
-varied driving conditions: snow-covered road vs dry track conditions vs rainy highway

And the design starting point was the contact patch of the tire, assuming a 20" tire. The car was built around the contact patch --> goal of 50/50 weight --> engine choice --> transaxle complexity --> etc....

Amazing to see the engineering thought process that guy goes through!

Obviously, if you want the car to go faster for a specific application, then you sacrifice one of the other design values.... For racing (especially WRC), teams can afford multiple setups (and cars) to customize for each race environment... but for most owners where the car is also their daily driver, then this car appears to have been well thought out... whether people like it is another thing....

Well, if it's a "regular car", why would it need a fast time on the Nurburgring?

I wonder, with that much weight torturing the tires through the corners, how consistent are GTR-R35's laptimes on the Nurburgring on like a 5-lap stint compared to a 1-lap flyer?

Can an engineer on here explain to us, assuming that the GTR-R35 has x unit of grip, if a lighter car needs more or less than x unit of grip to enter, go through, and exit the corner at the same rate of speed?

lighter is always better. the reason is when you go through a corner you have lateral load.

if you have a 2000 lb car vs a 3000 lb car with the same tire contact patch, the lighter car will corner faster because there is less weight in the lateral load.

his argument is that more weight is better in all conditions (dry, rain, snow), and of course he's trying to make it look good (its his baby).

I'm afraid all the gtr fan bois are going to think heavy cars are better.

the weight of the gtr is a side effect of the awd system. Anybody who preps are gtr for racing will strip it out to "add lightness".

good info!

I remember there is a part where he mentioned that lighter cars ARE faster, but they are harder to maneuver? Perhaps its more twitchy?

His arguments make absolutely no sense. His comparison of the F1 and GTR free body diagram may make sense, but when you try to do it on the lateral axis, it all falls apart.

F=ma (force = mass times acceleration)
In our case, acceleration is the centripetal acceleration, mass is mass of the car, force is lateral force from the tire. If an F1 and the GTR goes through the corner at the same speed, they have the same centripetal acceleration, so to answer your questions, the light car needs less lateral force from the tire. If the gtr is 3 times heavier, it will need 3 times as much lateral force(ignoring aero effects). Of course, that was all simplified to highschool physics, there are much more going on, but even the gtr can't defy the laws of physics.

The other point he made about the tire contact patch area is true, but it is a fact that lateral force does not increase linearly with increasing load. ie if the gtr is 3 times heavier than an F1, and they have the same tires, and ignore all aero effects, the gtr does not have 3 tires more grip.

It's been years since engineering school, and I'm no longer doing engineering as a professsion... but from what I recall (perhaps someone else here is more knowledgeable)...

Part of the Engineering discipline is breaking down a number of complex interactions into tangible elements. The Chief Engineer (CE) for the R35 broke down some of the "priority" elements in the videos. He started at friction of the contact patch.

traction = friction = coefficient of friction (a property of the materials in contact) x downward force (aka weight).

So based on that equation, maximum friction comes with greatest downforce (weight) multiplied by the friction coefficient of the tire. Hence, his argument that greater weight is better for traction. He did say lighter weight is better for acceleration and braking(I think?)...

However, the CE simplified the model by only working in 2D (front and rear axles). In a turn, you have the side-to-side forces at work as well (outside-wheel vs inside wheel). A lighter car (as well as location of center of gravity - CG, and suspension design, etc.) will affect how much weight shifts from inner to outer tires. Once this downward force on the tire exceeds the coefficient of friction limits of the tire, then you get slip.

But think about it, tires have to handle a lot. (If you took a motorcycle riding course, they actually explain it pretty well). But for a car, in a turn, your outer tires have to handle: 1) acceleration/deceleration forces, ie. force in line with the direction of rotation of the tire, 2) side-to-side forces, ie. the tendence of the car's CG laterally on the tire, and 3) The front-rear shift in weight on the tire. and 4) the increased downward load from the side-to-side weight shift from inner tires to outer tires.

So taking the model to the extreme... Forces 3 and 4 above add to traction of the tire, while 1 and 2 fight against it. When F1 and F2 > F3 and F4, you lose traction... Now that's on one tire. So if you took the extreme case, where you were accelerating to lift the front wheels (pitch) and turning to lift the inner wheels (roll) so that all the cars weight was on the rear, outer tire, you would reach the maximum traction of the car on that tire. If F1 and F2 were less than this, then you would maintain traction. But those aren't the only forces in play because we've got four corners on the car... You also have the car's rotation to account for as well (yaw), which adds twisting force on that tire.

In any case, what I think I'm trying to say is that analyzing the handling of the car is complex. I think he simplied his explanation greatly for the purposes of the questioning. He wasn't dealing with engineers and car designers... Did you see the interviewer roll his eyes when the CE went into explaining reasoning for not using super-hicas? The CE started at a simply "priority" in his design and built out from there to answer all of PH's questions.

Yah, thats where he mentioned the part with professional drivers and the amateur drivers the GT-R is meant for.

"Iz berry impotant, ok?"

He said that every other line.

I think I know what you are saying, but again it's reflective of oversimplification of the dynamics involved in car design.

Yes lighter can be better, when designed well within the overall constrainst of the car and what you're trying to achieve. eg. you prep a car differently for short auto-x runs on dry asphalt vs high-speed and endurance lemans race vs driving in the snow-covered country road to visit your uncle's hunting cabin.

If you only focus on lightening the car and cramming a v10 into the engine bay, without considering your spring-rates, dampening, even gear ratios, you likely will have a poorer-performing car because the car will sit higher and bounce around on the bumps --> lose traction (his starting point).

Actually, using your 2000 lb vs 3000 lb example, theoretically, and making the following assumptions:
-equal driver input
-ignoring aero-loads
-equal ratios of weight shift between front-rear (pitch), side-side (roll), rotation (yaw) - these are dependent on suspension design and weight distribution of the major components and chassis
-equal contact patch distribution amongst 4 wheels (suspension and chassis design)
-equal power to weight-ratio (engine selection)
-equal power band of the engine (gearing selection and engine design)
-same tires
.... the two cars should have same speed through the turn and reach max traction at the same time.

What the CE kept saying was "the package" of the car. there are so many constraints in the design of a vehicle and depending one what is a priority, you build around that priority and try to stick within the constraints you set out with. If he was looking to build a competitor to the Lotus Elise or MRS spyder, I'm sure the car would have looked a lot different.

I am by no means a fanboi.... I just appreciate solid engineering design

thats exactly the point.... who doesn't know lighter cars are faster. thats if the average driver could control it in the first place. Light cars aren't exactly easy to drive.

they are making a street car, not a dedicated race car for pro-drivers

I'm not a big gt-r fan myself. But I have to say the designer has it's own concept for designing a fast car and it worked. Proved that heavy cars can corner faster if it's done correctly. Obviously it's not like if you put 200kg on your front tires on your Toyota Yaris, it's going to make it corner faster. It's all about the engineering.

I don't agree, read the book "how to make your car handle"

http://www.amazon.com/How-Make-Your-.../dp/0912656468

I even got some pages on this subject for you:

http://northwestmr2.com/incoming/dutch/pictures/1.gif
http://northwestmr2.com/incoming/dutch/pictures/2.gif

I agree they built one hell of a car. But he's selling the cars weight as a good thing. The car is actually very heavy by many peoples standards, including Nissan.

Thats why they are building the vspec which will apparently be 150kg lighter.

This is what makes the GT-R unique, along with Evos and STIs. Fast on any surface in any condition.

the Vspec is already on the market and it's only down by 60kg due to the ceramic brakes and the TE37 Spec II on the car.

Vspec is supposed to be more of a track day toy than the regular GTR though, which means less weight IS better.

I can understand where he came from, he puts on all this dead weight because GTR is a "multi-performance super car" it's meant to be driven 365 days a year be it rain or snow. Hence at lower speeds and traction conditions this car has to work without downforce. Like someone said, this car has to work like a WRC car without actually getting its settings changed around with the environment....so a massive car is easier for the drivers to handle in those situations.