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Old 2nd December 2012, 22:44   #31
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Default Re: Monocoque SUVs : Advantages and Disadvantages

I don't know whether it is fuel economy or driving dynamics that changed consumer perception in US, most of the manufacturers are steering away from body-on-frame construction in mid size SUV segment. Most significant change is Ford Explorer going monococque way and recently dodge durango and Nissan Pathfinder followed the suit.
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Old 3rd December 2012, 12:29   #32
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Default Re: Monocoque SUVs : Advantages and Disadvantages

The monocoque chassis is not the skin only. It contains thicker members to take care of the various stresses. It is just that the "chassis" has been incorporated into the body, so that it is one continuous structural member. This makes manufacturing less labour intensive and the total structure lighter, hence reducing costs.

Regarding the "body on chassis" construction

. I automotive world the body panels are used to produce a few million pieces before their cost is recovered. So manufacturing a few thousand panels a yer will require years to ammortise the cost. Hence if you are producing say ten or twenty thousand pieces a year your manufacturing costs are lower.

. You can keep changing the body every year and bolt it on the existing chassis at minimal cost. A lot of older sports car manufacturers whose annual sales were less than a few tens of thousands took this route to produce inexpensive (compared to others) models.

. The ladder frame chassis is extremely strong and can take a lot of abuse, hence its popularity with the truck and off road vehicles. Further with the same basic vehicle you can have a range of body options - an important requirement for commercial operators.
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Old 3rd December 2012, 13:23   #33
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Default Re: Monocoque SUVs : Advantages and Disadvantages

Quote:
Originally Posted by Aroy View Post
The monocoque chassis is not the skin only. It contains thicker members to take care of the various stresses.
I agree with your observation Sir, Areas of high stress in the moncoque structure are strengthened by box frames, I frames, bulkheads and by some other means. Type of construction being discussed in this tread is technically called unibody design.

But the moot point of my post is that it is the commercial and other technical/manufacturing/enviromental considerations which are leading the automotive design towards monocoque type of construction. It is not the operational parameters such as handling/ drivability or ground clearance etc which are driving his change. Therefore to draw absolute conclusions about the operational parameters from this change may not be correct. Those are incidental to this change and are affected by host of other factors beside the constructional design.
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Old 4th December 2012, 15:41   #34
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Default Re: Monocoque SUVs : Advantages and Disadvantages

it is easy for us laymen to "imagine" the body-on-frame being the "tougher" structure rather than the monocoque. However, the 2013 range rover, which is a serious offroad vehicle, is a monocoque.

I believe, there is nothing 'sacred' about body-on-frame being the tough guy -> it all boils down to how strong the load-bearing structure is capable of bearing :
1) the verical loading (the chassis is trying to rip itself off from the wheels in the downward direction)
2) the torsion load on the chassis coming from the axles during offroading (where all wheels are on different heights, the structure is twisted like a ribbon pakoda)
3) the tow-loading (the wheels are trying to rip off from the chassis in the direction of intended motion, when hauling another car/ cargo)
4) the lateral-loading (the chassis is trying to rip itself off sideways from the wheels, when going through a corner, due to centrifugal force).

When there is a 'body' separate from the 'chassis', we have an additional candidate in 4) which is also trying to rip itself apart sideways, from the chassis. When there is no separate body (monocoque), we dont have this additional component contributing to 'roll'.

Suffice to say, in my opinion, monocoques are equally capable, just that the cost associated will be higher.

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Last edited by suhaas307 : 7th December 2012 at 17:30. Reason: editing references to alcohol
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Old 4th December 2012, 19:21   #35
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Quote:
Originally Posted by venkyhere
it is easy for us laymen to "imagine" the body-on-frame being the "tougher" structure rather than the monocoque. However, the 2013 range rover, which is a serious offroad vehicle, is a monocoque.
An excellent and insightful post for all us laymen out here. Thank you.

Last edited by suhaas307 : 7th December 2012 at 17:30. Reason: editing references to alcohol in quoted post. Thanks :)
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Old 7th December 2012, 17:02   #36
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Default Re: Monocoque SUVs : Advantages and Disadvantages

The Monocoque body shell is the advanced/upgraded form of the body-on-frame design. but the reason manufacturers take time to upgrade to the newer format as most of our friends in the forum mentioned is because of the initial cost and gradual phase out of the older design rather than a sudden change. some advantages of the monocoque shell are crumple zones.so other than the reduction in the cost of production the monocoque also provides more safety and comfort to its users.
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Old 21st October 2014, 18:52   #37
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Default Re: Monocoque SUVs : Advantages and Disadvantages

Hi all the contributors to this thread,

I've some very specific questions around chassis of the vehicles, can I request you to pls answer those:
1. From a passenger safety point of view - in similar weighed, similar body safety measured, at the same speed and all other parameters being the same - which vehicle will be better? One having frame chassis or one that has monocoque structure (chassis + body integrated)
2. There are some vehicles that are 4 wheel drive and still are monocoque. How do they achieve powering rear wheels in absense of a frame? How the propeller shaft is placed that powers rear wheels?
3. For vehicle of size Mahindra Scorpio, which one is more comfortable for driver? Front wheel drive or a rear wheel drive? Why?
4. Same question as # 3 above from passenger comfort pls.

I would appreciate if you include any and all points that pop into your mind reading the questions above. Basically, I am a very big fan of frame chassis and rear wheel powered vehicles. I equally hate the arrangement that makes tractive power and steering functions done by the front wheels.

With the new Scorpio, I am finding it even more difficult to decide between XUV500 and Scorpio, so are the above questions. Well, 'shameless' to say that I am myself a mechanical engineer and still have the above questions. Any information on the above will be highly appreciated.

Thanks a ton in advance,
Regards,
Suhas
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Old 22nd October 2014, 12:33   #38
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Default Re: Monocoque SUVs : Advantages and Disadvantages

Quote:
Originally Posted by suhas_pm View Post
1. From a passenger safety point of view - in similar weighed, similar body safety measured, at the same speed and all other parameters being the same - which vehicle will be better? One having frame chassis or one that has monocoque structure (chassis + body integrated)
IMHO ladder on chassis will be poor cousin in terms of safety. Impact force distribution is hallmark of modern vehicle design.

Quote:
2. There are some vehicles that are 4 wheel drive and still are monocoque. How do they achieve powering rear wheels in absense of a frame? How the propeller shaft is placed that powers rear wheels?
Similar arrangement of propeller shaft and differential with CV axels to wheel. AFAIK powering rear wheels has nothing to do with body shell beyond the fact of anchorage points of drive train/axles.

Quote:
3. For vehicle of size Mahindra Scorpio, which one is more comfortable for driver? Front wheel drive or a rear wheel drive? Why?
I do not think there is any difference w.r.t. vehicle size on front or rear wheel drives.

Quote:
4. Same question as # 3 above from passenger comfort pls.
Same as above.

Quote:
I would appreciate if you include any and all points that pop into your mind reading the questions above. Basically, I am a very big fan of frame chassis and rear wheel powered vehicles. I equally hate the arrangement that makes tractive power and steering functions done by the front wheels.
If you are looking for answers to support your likes or dislikes sorry to disappoint. Front wheel vs rear wheel drive has been discussed in other thread(s) here. Search.
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Old 28th October 2014, 18:32   #39
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Default Re: Monocoque SUVs : Advantages and Disadvantages

Modern vehicle safety is based on having a central safety cage for passengers with crumple zones all around. From that point of view Monocoque has an advantage here as the chassis can be designed section by section. In a ladder on frame the shock is transmitted via the rigid ladder frame.
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Old 28th October 2014, 23:46   #40
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Default Re: Monocoque SUVs : Advantages and Disadvantages

Quote:
Originally Posted by suhas_pm View Post
3. For vehicle of size Mahindra Scorpio, which one is more comfortable for driver? Front wheel drive or a rear wheel drive? Why?
4. Same question as # 3 above from passenger comfort pls.
nothing regarding ride comfort, but for climbing up slopes where there is poor grip, rear wheel drive offers better traction
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