when we talk of car platforms, and also how sometimes multiple models are based on the same platform, what are we talking about?

what is a 'platform'? how much must it be changed to not longer be the same platform?

why can't manufacturers have one platform of various sizes?

i'm sure on this last question at least, target vehicles have different needs, perhaps towing or cargo capacity, vs. being light and stiff for a sportier ride.

but it seems these days talk about platforms is very loose and unspecific.

but on a small sedan and a bigger sedan supposedly sharing a platform, e.g., lexus IS and GS or 5 series and 7 series - why is a shortened version of a bigger car platform a bad thing?

 

In most cases, the term "platform" describes the frame/chassis/unibody underpinnings that engineers use as the start for everything else they design around it, or add to it. Common sense, of course, when designing a vehicle, dictates that a lot of time, money, and effort can be saved if an existing platform is used as a base instead of an all-new one. But, of course, the flip-side of that coin is that all-new platforms can take advantage of new-technology and advancements like higher-strength metal-alloys, better aerodynamics, space-efficiency, adaptability to newer and more efficient drivetrains, etc.... that an existing platform may not do.

This works, of course, for more things than just automobiles. Different types of Navy ships, for example, often share the same underlying keel/hull, which can be adapted for different purposes.

 

lol that's funny paul, i was actually thinking about the same thing when i was driving to work today, after talking about e coupe based on c platform, 5 being on shortened 7 platform, is based on gs platform, rx on camry platform, etc...

i also wonder what exactly defines a platform then? how to say one is new independent platform and what defines one being a derivative of another? shape? weight? strength?

for for example the 5 with shortened 7 platform, what's the pros and cons? price? structure? weight? strength?

 

ok, with that, i am starting to question some of the things said (even by me).

for example, the e coupe is based on the c platform. everyone says it's bad and make the car cheap. why? it's not as strong? or is it just because it says c and not e?

5 based on the 7, people say it's bad. why? coz' it's just heavier by default (and why)? does that mean if they make an independent platform for the 5 it will be lighter?

and then we move to 2is based on 3gs platform (thanks mike for correcting me), interesting enough i remember reading people say it's good because that means 2is is "just as strong". what do we say about that then?

 

Good question and many different answers.

The easiest one is platform sharing simply cuts costs as you have multiple vehicles based on a similar basic structure that can be modified to suit different vehicle needs without needing to construct a completely new platform. Platforms are expensive to design and build by themselves if it is only for one vehicle.

I think one of the most well know examples is the Nissan FM platform. Before the FM, Nissan literally had 20+platforms/engines etc. With the FM, I think it went down to 6-8 platforms but they sold more vehicles and variants. The platform is flexible to support a tiny 2 seat 370Z all the way to a huge Nissan Fuga/Infinti M37/56. It saves a TON of R&D and in costs. Most people don't care about platform and today engineers are so good they drive good in any vehicle.

The negatives are weight. Since it is not vehicle specific the platform is usually beefed up. So smaller cars gain more weight than if they had their own platform. We are talking a couple of hundred lbs at least.

Also since its not specific to a car there is so much R&D you can do to make it specific to the car. If one of the cars rides harsh, the others have a much higher chance of riding harsh even if they are bigger. If one of the cars isn't that sporty, it will be harder to make the others sporty.

Lets look at the E60 vs F10 5 series. The E60 cost much more to product, it had some aluminum chassis parts and had its own platform. It was one of the lightest cars in class and the sport champ. BMW figured out though what most of us already knew, most people don't care, don't buy or track them. So they used an existing platform, the 7 series, shortened it and blam, came with the 5 series. Well now it drives like a SWB 7, its at least 500lbs heavier and there is no getting around the fact the platform was designed for a bigger, cushier car.

Looking at sales, most people don't care.

The engineers behind the FT-86 insisted on a new platform which will cost more and be hard to make a profit since it will be a small volume 25k or so car. He pretty much said "platform sharing sucks". That said it allows the engineers to design everything around this platform without having to worry a sedan or SUV or something will be used from it. Thus the car has a super low center of gravity, will weigh under 3000lbs and drive like a bat out of hell.

Lets look at the 3GS platform which was made to share with the 2IS. This helped with profits. It also means the 3GS and 2IS are very close in weight, which hurts the 2IS.

Then lets look at the IS F. That is why they had to work so damn hard on the chassis and it was the most track tested car in Toyota history until the LFA. They had to work with a platform that;
1. Began life with the GS
2. Was shortened for the IS
3. Never was built or intended for a V-8 or F model

In contrast BMW knows from day one any platform with the 3 series WILL have a M3.

 

lets just say that the C was based on the E coupe does that make it more okay to everyone?

 

do we know that for a fact? if that's true that means bmw has larger margin on f10 than e60?

 

and now with what mike said, why and how do we justify that the e coupe basing off the c platform (RXSF you are mean ) is a "bad" thing? like i said, it doesn't sound good, but seems like that means the e coupe is probably lighter. what's so bad about it then?

 

great posts / discussion. thanks all.

cliff notes:
- a smaller car using a bigger car's platform will be heavier than it would be if it had its own platform
- the e coupe is bad because it uses the c class platform

not really sure i buy any of this. because adapting any platform to different models can mean any number of changes. i could see a huge reason TO share platforms is compliance with regulations. plus, if a car maker has platforms A, B, C, how are we to really know if they're 3 entirely different platforms, or 3 with 10%, 30%, or 90% overlap in design?

and the c-class platform for example must be pretty stout because they have a rocket c63 model! so i see nothing wrong at all with using it for an e coupe which is probably shorter than an e sedan i'm guessing?

excellent post.

wouldn't ride harshness be more a factor of the suspension, or is the suspension considered part of the 'platform'?

according to motortrend:
so it's 400lbs heavier, bigger with more goodies, so i don't think we can really say it's heavier simply because it leveraged a bigger car's platform.

qft!

the ft-86 is unlike ANYTHING in toyota's range, so it obviously has to have a new platform.

if it's based on the GS then it was intended to have a V-8.

i don't think lexus worked that hard on the IS-F. as we know it was a skunk works project that got the green light for production. no doubt they then had to do a lot to make it comply with regs and be reliable/serviceable/etc. but the car feels seriously front heavy and still like a 'bolt-on' job.

which as we know is a win. in fact, it's a huge win because even the basic bmw's often feel nicely balanced and great to drive, being lighter than their more loaded fancier models.

 

very true, what makes two "different" platforms? i am sure there are stuff that are "common" or relatively similar between platforms, how do we differentiates?

and you bring up a good question paul. i don't think the c platform is by any means weak. it can handle the c63, that's something. of course question remain is whether it's weaker (on paper) compared to e platform, which supports the e63 with even more power and weight?

weight with platform is also another thing i have been asking for a long time and no one can give me an answer. f10 is based f01 platform, and it's 400lb heavier than e60, but what makes one say it's all because of the platform? i will agree if using the f01 platform allows bmw to put more stuff on the car making it heavier, but the platform itself isn't necessarily the weight.

one example is between the es350 and the rx350. both are based on the camry platform (i hope i got that one right!). es350 is 3580lb, rx350 is 4178lb, whopping 700lb difference. granted one is passenger car and one is "suv", but you get my point. i don't think anyone can blame the added weight on the platform.

i don't think we can blame the isf on the platform by saying it's not for v8. like paul pointed point the gs platform was designed with v8 in mind. but i will take that if they say they never designed that platform to handle the kind of power and performance in the 400+hp track performance. that will indeed give the isf a very bad starting point.

 

The suspension, or at least parts of it by design, is generally considered part of the platform. But even the chassis alone affects handling. Every twist and bend in the chassis effects the flex and twist and energy absorption.

 

I'm no engineer, but I would assume that in order to support and weight and stresses of the larger F01 (especially in LWB) some things have to be beefed up which I think is where the weight comes from. Including the chassis itself, welds, rivets, braces, supports, etc.

 

the new 5 may use the 7 series platform, but regardless the new 5 is simply BIGGER, with more stuff (features) than the old 5, so that alone most likely accounts for most of the weight gain.

since the new 4GS is apparently pretty much the same length and wheelbase as the 3GS, i doubt it will be significantly different in weight (probably some weight savings, offset by some more stuff), and the 4GS is likely to be smaller than the new 5.

 

of course, i am not saying bigger platform isn't heavier. i think likely it's the case. but just to say that the f10 uses f01 platform and that's why it's so heavy (or that it's automatically a bad thing) i don't know what's there to support the claim

 

i believe in 4gs thread they say the 4gs is lighter than the 3gs.