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-   -   Why have a transmission tunnel in FWD cars vs a flat floor at the rear? (https://www.team-bhp.com/forum/technical-stuff/101657-why-have-transmission-tunnel-fwd-cars-vs-flat-floor-rear-2.html)

I started driving and have grown up during the age of the Amby and Padmini's, which being rear wheel drive cars had a transmission hump on the rear floor. It was understandable as the propeller shaft to the rear differential went through this. We graduated to Front Wheel drive cars with a transverse engine/ gearbox placements and the rear wheels only acted as the trailing wheels with either an independent or axle suspension.
However what beats me is the persistence of the annoying transmission hump on the floor of modern FWD cars. It is a big problem when trying to seat 3 people in the back seat.
Wondering if this is a design flaw of some lazy car design engineers (cut/copy/paste from old model floors), or are there some technical/engineering benefits.?

My guess is for securing the following from the rear to the front:

• Fuel Lines
• Brake lines
• Wiring

Nothing else that I can think of. If you want to see no hump, see the Civic, its flat!

Interesting thread though, I had wondered the same but never managed to find out.

IMHO a hump serves dual purpose. One in case a model has to be fitted with rear wheel/all wheel drive you do not have to redesign or manufacture a separate part. Two a hump in middle adds strength to floor pan.

Civic may not have a large hump but I am sure it will carry many small spines.

Some of the modern cars especially the higher end versions do not have this hump.
Even I have wondered about this and thought that this could be due to structural reinforcement of the chassis.
Even if this is a reason, I am sure there could be some ways to eliminate this nuisance.

you could add exhaust layouts as well.

wouldn't it be better to have several smaller humps/spines for all the lines like brakes, fuel, exhaust etc. and then level them from above?

Agreed. In most of the countries, even a sedan is used with a maximum of four including the driver, barring a few countries like India. So, manufacturers do not mind central hump as it does not affect the comfort level of four people on board.

@Sudev: Sir, I would agree on the strength part as there might be merits there, however cars like the ANHC do not have an AWD or RWD option across the globe, and looking at the underbody there is no space for putting a gear box (the petrol tank is below the drive seat) or a differential. Most importantly these are transverse mounted engines.
Even my old Indica has a huge hump, I don't think Tata ever planned a AWD/RWD.

@J.Ravi: These days even bigger segment cars come with 3 head restraints for the back seat, so cant agree that they would only be 4 seater.

Very interesting thread. There must be a strong reason to do this. It cannot be just that other countries just don't seat more than 4 people.
For instance even Indica, designed for India (although designed by Idea which is not Indian ) has this hump. It must be a design constraint - I don't know what.

Very curious to know the correct answer.

strength, most definitely yes.
Space for lines/exhaust, yes.
for the civic, i DID hear about this sometime back.
apparently the suspension layout is such that it allowed the designers to place the bulkier bits of the exhaust system further back, allowing the ,ahem, hammering, of the bump.

Guess it was needed for RWD cars of yore. Dont see the need now. If it serves to strengthen the chassis, is it solid or hollow inside?

doesnt need to be solid.
see this:

http://www.team-bhp.com/forum/techni...ml#post2366223

Guys,

The primary purpose of the 'hump' is chassis stiffening. In monocoque vehicle designs, that is the single most important stiffening to the floor plan on the chassis.

All other uses are simply by-products of this hump. In RWD/AWD vehicles this 'hump' is even greater.

Newer vehicle designs are trying to minimize this, due to perceived intrusion of cabin space by customers.

Agree with most of the guys here.
Most of the FWD cars have the hump to add rigidity to the floor pan, while some like the SX4 have a bigger hump for the AWD system.
hmm... was thinking about one point that FWD used against RWD is that FWD liberated more space. Doesn't the floor hump negate that benefit?

huh?. where does SX4 have and AWD?.