The "hump" or lack thereof in the back seat
03-24-2019, 11:18 AM
#1
Pro
Thread Starter
The "hump" or lack thereof in the back seat
Was at the Vancouver Autoshow a couple days ago and got a chance to look at most of the cars I was considering against the RDX and a thing I've noticed before but noticed much more starkly this time is that Honda/Acura are the only manufacturers that seem to have eliminated the driveshaft hump that is common in the back seat. The German brands and Volvo have these gigantic tunnels in the back that make their back seats just 2 seaters while the RDX and CR-V have just a hint of a hump making them a real 3 seater in the back. For my wife and I this was a significant feature (we want to be able to have baby and the grandparents in the back from time to time).
Wondering if those folks who are engineers know what the tradeoffs are for having a smaller hump. I don't see a higher ride height being a side effect and I'm not sure what else is being routed underneath the car that requires gigantic humps.
Wondering if those folks who are engineers know what the tradeoffs are for having a smaller hump. I don't see a higher ride height being a side effect and I'm not sure what else is being routed underneath the car that requires gigantic humps.
03-24-2019, 11:38 AM
#2
Was at the Vancouver Autoshow a couple days ago and got a chance to look at most of the cars I was considering against the RDX and a thing I've noticed before but noticed much more starkly this time is that Honda/Acura are the only manufacturers that seem to have eliminated the driveshaft hump that is common in the back seat. The German brands and Volvo have these gigantic tunnels in the back that make their back seats just 2 seaters while the RDX and CR-V have just a hint of a hump making them a real 3 seater in the back. For my wife and I this was a significant feature (we want to be able to have baby and the grandparents in the back from time to time).
Wondering if those folks who are engineers know what the tradeoffs are for having a smaller hump. I don't see a higher ride height being a side effect and I'm not sure what else is being routed underneath the car that requires gigantic humps.
Wondering if those folks who are engineers know what the tradeoffs are for having a smaller hump. I don't see a higher ride height being a side effect and I'm not sure what else is being routed underneath the car that requires gigantic humps.
Most FWD offerings in the Market have eliminated that hump which makes the second row actually useable for 3 people. The FWD offerings that have not probably just are not packaged as well as those that have.
03-24-2019, 03:34 PM
#3
Skeptic
The RDX is either FWD or AWD available in all trim packages. There's no hump in any of them.
Independent rear eliminates the need for any movement in the rear drive shaft, so the space it needs is fixed and much smaller. All the movement is in the individual axials.
Independent rear eliminates the need for any movement in the rear drive shaft, so the space it needs is fixed and much smaller. All the movement is in the individual axials.
03-24-2019, 04:39 PM
#4
Pro
Thread Starter
The reason a Majority of those German offerings have a large hump is because they are RWD based and therefore have the transmission/rear driveshaft running through that hump. Most FWD offerings in the Market have eliminated that hump which makes the second row actually useable for 3 people. The FWD offerings that have not probably just are not packaged as well as those that have.
Based on photos that I've seen the no/tiny humpers are the RDX, CR-V, Santa Fe, and NX (didn't check all compact/mid-sizers) while every Euro brand product (Volvo, MB, BMW, Audi, Alfa) are big humped with a few middle of the road ones (QX50, CX-5).
03-24-2019, 09:23 PM
#5
The reason a Majority of those German offerings have a large hump is because they are RWD based and therefore have the transmission/rear driveshaft running through that hump.
Most FWD offerings in the Market have eliminated that hump which makes the second row actually useable for 3 people. The FWD offerings that have not probably just are not packaged as well as those that have.
Most FWD offerings in the Market have eliminated that hump which makes the second row actually useable for 3 people. The FWD offerings that have not probably just are not packaged as well as those that have.
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RDX10 (03-24-2019)
03-24-2019, 10:40 PM
#6
But we're talking about all cars with AWD so they still have the driveshaft going to the back. AIUI, if they don't send 100% of the power to the rear then they can use lighter, smaller parts but there's still a shaft going to the back. Are the shafts really that much smaller that it can eliminate a 4-8 inch hump?
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supafamous (03-24-2019)
03-24-2019, 11:02 PM
#7
Drifting
The basic structure of a particular "transverse engine" crossover is the same, whether it is FWD or AWD. It would make no financial sense for the manufacturers to design and build two different body structures. IMHO it makes no sense to make an SUV without AWD anyway, but that's a whole different conversation.
As for the "hump". As has been hinted at, German crossovers typically have a longitudinal RWD based engine and transmission configuration, which means they typically have a big chunk of the transmission, a central transfer case, and a front driveshaft to fit into the middle of the vehicle. This is far more bulky than a rear driveshaft, which need not be much wider than the exhaust. Jeep Grand Cherokee/ Dodge Durango are the same way.
FWD based "transverse" engine and transmission configurations package all of the engine, transmission, and front "transfer case" in front of the firewall. Only the rear driveshaft runs under the vehicle. The rear differential is behind the rear seats.
As mentioned by NooYawkuh, and correctly I think, independent rear suspension design, with articulating "half shafts" from the rear diff to the rear hubs, allows the rear driveshaft and rear differential to be mounted quite close to the underside of the vehicle. This provides for adequate ground clearance without jacking the vehicle up to the sky and/or resorting to elevating the drivetrain into a tunnel. This is in contrast to traditional "body-on-frame" SUVs. But unless you're cross-shopping Suburban, Sequoia, Land Cruiser, or Gelandewagen ( for instance ), that distinction isn't very important. ( OK, Wrangler too, but if you're really cross-shopping that, you're on your own... ).
One interesting aspect of the design of 3rd-gen RDX is that the rear driveshaft is actually three interconnecting driveshafts with fixed angular offsets. I remember some commentary from a designer that this allowed them to mount the engine and transaxle very low to reduce the overall height of the center of gravity, and thereby enhance the handling of the vehicle.
As for the "hump". As has been hinted at, German crossovers typically have a longitudinal RWD based engine and transmission configuration, which means they typically have a big chunk of the transmission, a central transfer case, and a front driveshaft to fit into the middle of the vehicle. This is far more bulky than a rear driveshaft, which need not be much wider than the exhaust. Jeep Grand Cherokee/ Dodge Durango are the same way.
FWD based "transverse" engine and transmission configurations package all of the engine, transmission, and front "transfer case" in front of the firewall. Only the rear driveshaft runs under the vehicle. The rear differential is behind the rear seats.
As mentioned by NooYawkuh, and correctly I think, independent rear suspension design, with articulating "half shafts" from the rear diff to the rear hubs, allows the rear driveshaft and rear differential to be mounted quite close to the underside of the vehicle. This provides for adequate ground clearance without jacking the vehicle up to the sky and/or resorting to elevating the drivetrain into a tunnel. This is in contrast to traditional "body-on-frame" SUVs. But unless you're cross-shopping Suburban, Sequoia, Land Cruiser, or Gelandewagen ( for instance ), that distinction isn't very important. ( OK, Wrangler too, but if you're really cross-shopping that, you're on your own... ).
One interesting aspect of the design of 3rd-gen RDX is that the rear driveshaft is actually three interconnecting driveshafts with fixed angular offsets. I remember some commentary from a designer that this allowed them to mount the engine and transaxle very low to reduce the overall height of the center of gravity, and thereby enhance the handling of the vehicle.
Last edited by Wander; 03-24-2019 at 11:10 PM.
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RDX10 (03-26-2019),
supafamous (03-24-2019)
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03-26-2019, 03:39 PM
#8
The basic structure of a particular "transverse engine" crossover is the same, whether it is FWD or AWD. It would make no financial sense for the manufacturers to design and build two different body structures. IMHO it makes no sense to make an SUV without AWD anyway, but that's a whole different conversation.
As for the "hump". As has been hinted at, German crossovers typically have a longitudinal RWD based engine and transmission configuration, which means they typically have a big chunk of the transmission, a central transfer case, and a front driveshaft to fit into the middle of the vehicle. This is far more bulky than a rear driveshaft, which need not be much wider than the exhaust. Jeep Grand Cherokee/ Dodge Durango are the same way.
FWD based "transverse" engine and transmission configurations package all of the engine, transmission, and front "transfer case" in front of the firewall. Only the rear driveshaft runs under the vehicle. The rear differential is behind the rear seats.
As mentioned by NooYawkuh, and correctly I think, independent rear suspension design, with articulating "half shafts" from the rear diff to the rear hubs, allows the rear driveshaft and rear differential to be mounted quite close to the underside of the vehicle. This provides for adequate ground clearance without jacking the vehicle up to the sky and/or resorting to elevating the drivetrain into a tunnel. This is in contrast to traditional "body-on-frame" SUVs. But unless you're cross-shopping Suburban, Sequoia, Land Cruiser, or Gelandewagen ( for instance ), that distinction isn't very important. ( OK, Wrangler too, but if you're really cross-shopping that, you're on your own... ).
One interesting aspect of the design of 3rd-gen RDX is that the rear driveshaft is actually three interconnecting driveshafts with fixed angular offsets. I remember some commentary from a designer that this allowed them to mount the engine and transaxle very low to reduce the overall height of the center of gravity, and thereby enhance the handling of the vehicle.
As for the "hump". As has been hinted at, German crossovers typically have a longitudinal RWD based engine and transmission configuration, which means they typically have a big chunk of the transmission, a central transfer case, and a front driveshaft to fit into the middle of the vehicle. This is far more bulky than a rear driveshaft, which need not be much wider than the exhaust. Jeep Grand Cherokee/ Dodge Durango are the same way.
FWD based "transverse" engine and transmission configurations package all of the engine, transmission, and front "transfer case" in front of the firewall. Only the rear driveshaft runs under the vehicle. The rear differential is behind the rear seats.
As mentioned by NooYawkuh, and correctly I think, independent rear suspension design, with articulating "half shafts" from the rear diff to the rear hubs, allows the rear driveshaft and rear differential to be mounted quite close to the underside of the vehicle. This provides for adequate ground clearance without jacking the vehicle up to the sky and/or resorting to elevating the drivetrain into a tunnel. This is in contrast to traditional "body-on-frame" SUVs. But unless you're cross-shopping Suburban, Sequoia, Land Cruiser, or Gelandewagen ( for instance ), that distinction isn't very important. ( OK, Wrangler too, but if you're really cross-shopping that, you're on your own... ).
One interesting aspect of the design of 3rd-gen RDX is that the rear driveshaft is actually three interconnecting driveshafts with fixed angular offsets. I remember some commentary from a designer that this allowed them to mount the engine and transaxle very low to reduce the overall height of the center of gravity, and thereby enhance the handling of the vehicle.
I do admit though, I've not done much research on other manufacturers driveshaft designs so I am not certain if multi piece driveshafts are a common thing and the VW design was just poor.
03-26-2019, 04:04 PM
#9
Drifting
I hope that multi part driveshaft design doesn't lead to premature failure of the driveshaft carrier bearing. VAG decided to go with a 2 part driveshaft on the VW Touareg and Porsche Cayenne and they stupidly used rubber around the bearing supporting the shaft and due to vibration and heat that rubber would degrade and cause catastrophic failure at random times.
I do admit though, I've not done much research on other manufacturers driveshaft designs so I am not certain if multi piece driveshafts are a common thing and the VW design was just poor.
I do admit though, I've not done much research on other manufacturers driveshaft designs so I am not certain if multi piece driveshafts are a common thing and the VW design was just poor.
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