Why the VW Tiguan Allspace has ridges on its roof?

Hans · Aug 12, 2020 05:12 PM

Earlier today, Volkswagen Passenger Cars Malaysia (VPCM) launched its first-ever VW Tiguan Allspace, a long wheelbase, 7-seater (more like a 5+2 seater) version of the regular VW Tiguan.

The Tiguan Allspace is available in two variants – a 1.4 TSI Highline (150 PS/250 Nm) and a 2.0 TSI R-Line (220 PS/350 Nm), the latter is basically a taller Golf GTI with seven seats, adaptive DCC dampers included. The models, all locally-assembled (CKD) in Pekan, will be sold alongside the existing 5-seater Tiguan.

The VW Tiguan family now consists of three models:-

  • Tiguan 1.4 TSI Highline: RM 162,678
  • Tiguan Allspace 1.4 TSI Highline: RM 164,430
  • Tiguan Allspace 2.0 TSI R-Line: RM 208,553

All prices are exclusive of SST, which has been waived for all locally-assembled cars until 31-December 2020.

The 7-seater Tiguan Allspace’s body’s length (4,704 mm) has been stretched by 215 mm, out of which 110 mm is for the longer wheelbase (2,791 mm).

7-seater Tiguan Allspace is easily differentiated by its rear three-quarter window and C-pillar

Of course, Volkswagen didn’t simply stretch the body longer. Body construction is one of the most difficult part of building a car and the biggest problem with long wheelbase cars is maintaining body rigidity.

Yes, a longer wheelbase makes for a more comfortable ride, but that’s only true if the body is rigid enough that it doesn’t flex too much. All solid structures will and need to exhibit some form of flex, even concrete bridges and buildings.

We tend to think the act of bending/flexing a solid material is bad but that’s not true. If a bridge can’t flex under load, it will break and collapse. But too much flex is of course a bad thing. It’s the same with a car’s body.

For example, take two rulers, one long and one short, and try to bend them. You will notice that the longer ruler bends a bit more. It’s the same with longer wheelbase cars. This resistance to bending is what we call body rigidity.

Tiguan Allspace uses the same modular MQB platform as Golf and Passat

At the same time, an unnecessarily rigid body is very uncomfortable to ride in. However, a body with poor rigidity will result in too many movements for the suspension and steering rack’s mounting points, which will result in poor handling.

There are several ways to control a car body’s flex, one of it is to introduce ‘spines’ along the length of the body.

The transmission tunnel hump is necessary not just because the R-Line variant has AWD, but it also helps in maintaining body rigidity

The most obvious is the hump on the cabin’s floor. This doubles as a transmission tunnel for rear- or all-wheel drive cars but you will see smaller versions of the same hump even on some purely front-wheel drive models, especially those that are developed with keen drivers in mind.

Front-wheel drive Honda Civic also has a 'transmission tunnel' hump

These ‘spines’ help minimize the car’s body flex. The Tiguan Allspace has these ‘spines’ even on its roof. These ridges are not needed on the regular wheelbase 5-seater Tiguan, but on the stretched 7-seater Tiguan Allspace, it is necessary. Recall the earlier example of a short ruler vs a long ruler.

Ridges on Tiguan Allspace

Maintaining a high level of body rigidity is important because the Tiguan Allspace R-Line needs to cope with an engine that outputs 220 PS/350 Nm – the same engine used in the Golf GTI. With 4Motion all-wheel drive, the drivetrain’s added mechanical grip on all four corners must be matched by an equally strong body.

Smooth roof of the regular 5-seater Tiguan

Of course, these ridges are not unique to the Tiguan Allspace. In fact they are present in even in many commercial vans, but that’s because these vehicles have to cope with very heavy loads in the rear. Basically any large one- or two-box vehicle (basically any large SUVs and MPVs) will most likely have ridges on its roof.

Alternatively, some manufacturers use other solution like stronger structures beneath the roof panel and around the cabin. This allows for a smooth roof surface but the downside is that the reinforcement structures eat into the cabin space.

The biggest drawback on the Tiguan Allspace - middle row seats don't tumble forward, making entry into the third row difficult