Difference in lugging "violence" between cars

[rationull]

Just a curiosity:

Merging from a rural highway onto the freeway today on my way to work, somebody in front of my slowed way, way down in order to pull off on the shoulder, so I had to get back up to speed quickly. I was still in 4th or 5th gear (5MT), which would've been fine normally, but apparently I had slowed down more than I thought b/c when I got on the gas the car shook pretty badly (and loudly) as it lugged for a second before I downshifted.

Now, I'm no stranger to driving a stick and I know this feeling well, but it was a much more violent reaction than I'm used to just in terms of the vibration and noise. It occurred to me that this might be the first time I've ever lugged in this car (my '11 Subaru).

This got me thinking a little. Is there anything to the idea that maybe lugging could be more violent in an longitudinal engined AWD or RWD vehicle than a FWD one since the vibrating parts are connected to more spots along the body (e.g the way the engine mounts are situated in relation to the engine, trans mount further back on the chassis, driveshaft connected to the diff which is mounted to the body)?

 

[dparm]

I think a lot of it has to do with the overall chassis stiffness, motor mounts, engine weight, etc. Everything has a resonant frequency.

 

[expat]

Yes, my Spitfire has a cam-y engine but also has a frame mounted Diff and a frame that is quite flexible .
Especially if I back up slow, without slipping the clutch, things get a little shaky.

 

[spackard]

I think you have a lighter flywheel than an inline-4, and less crankshaft weight, plus, no counterbalance shaft.

I used to carpool with a lady who drove a Nissan small pickup. She always shook that truck. Just couldn't merge and concentrate on rpms at the same time.

 

[JosephHarmon]

Why not just down shift?

 

[rationull]

Originally Posted By: JosephHarmon
Why not just down shift?


Of course, I downshifted when I realized the car was shaking like heck and not going anywhere

 

[yonyon]

It was probably just shaking like that because it was scared. Merging into highway traffic while accelerating from low speed in the wrong gear can be tough and it may have been worried about getting it's bumper scuffed.

 

[david_ES2]

Lmao good one

Id have a heart attack too if you were trying to.merge on the freeway barely moving in 5th gear lol

 

[Lead Shoes]

Because something is not balanced properly, like Dparm said, my stock civic with poly mounts will do the same if found under 2k rpm in any gear.

 

[SteveSRT8]

Originally Posted By: rationull
This got me thinking a little. Is there anything to the idea that maybe lugging could be more violent in an longitudinal engined AWD or RWD vehicle than a FWD one since the vibrating parts are connected to more spots along the body (e.g the way the engine mounts are situated in relation to the engine, trans mount further back on the chassis, driveshaft connected to the diff which is mounted to the body)?


As noted above, the tuning of the various mounts and so forth has a huge effect on this. I also think this may be related to Subaru's flat 4 engine design.

My car happily lugs out at under 1000 rpm fully locked up in 4th gear with stock programming. Nary a shudder or shiver. But a V8 is a well balanced design.

 

[Hokiefyd]

Originally Posted By: rationull
Is there anything to the idea that maybe lugging could be more violent in an longitudinal engined AWD or RWD vehicle than a FWD one since the vibrating parts are connected to more spots along the body (e.g the way the engine mounts are situated in relation to the engine, trans mount further back on the chassis, driveshaft connected to the diff which is mounted to the body)?


No, it's generally the other way around. Powertrain impulses are generally perceived more by the passengers in a TFWD layout than in a LRWD/AWD layout. This is because an engine's motion will generally be about the crankshaft. That is, the engine will rock side to side. In a LRWD setup, that rocking motion is perpendicular to the direction of travel, so there's little impact on forward momentum. But in a TFWD setup, that rocking motion is in the same direction as the direction of travel, so any forward/rearward action you get will have more of an impact on the forward momentum. In the absolute sense, there isn't much change, but you'll feel it more in the cabin.

 

[ledslinger]

I wouldn't be surprised if some cars are engineered to limit the noise of lugging. Such as through motor mount design or adding weights.

 

[The_Jeff]

Originally Posted By: ledslinger
I wouldn't be surprised if some cars are engineered to limit the noise of lugging. Such as through motor mount design or adding weights.


There may also be a car out there set up opposite: Torture the driver while he's lugging so he shifts and makes everything perform better! Easiest way is with ridiculously retarded timing so there's no power under a certain RPM.

They aren't above sabotaging their own cars. Look at Ford/Firestone trying to "scare" people with low inflation pressures so they wouldn't corner aggressively.

 

[NateDN10]

In our Subaru, the engine's side-to-side motion when cranking the engine to start is more noticeable than in transverse I4 engined cars I've been in. You can feel it from inside the car. At idle speed or anything above, it's buttery smooth, but you can really feel it when cranking.

It's probably the same phenomenon the OP noticed, since in both cases the engines are spinning at below normal idle speed.

 

[friendly_jacek]

Anyone wants to bet Pb will go up in the UOA?

 

[rationull]

Originally Posted By: friendly_jacek
Anyone wants to bet Pb will go up in the used oil analysis?


From one or two very brief lugging events? We'll see. I actually was planning on getting a used oil analysis on this fill, but unfortunately I don't have a baseline so we'll never know if it really went "up"

 

[MrHorspwer]

The driveline layout is the reason why Subaru's lug and shudder so bad.

A longitudinal mounted engine that is attached to the front drive axle requires mounts to control movement on two axis.

A set of engine mounts controls engine torque (side to side) and the upper dogbone and transmission mount controls driveline torque (front to back).

It's really the worst of both: Side to side lugging of a longitudinal mounted RWD engine and the driveline lash of a transverse FWD.

 

[TFB1]

While there are many variables as mentioned, a 4cyl engine will always be prone to a higher amount of low speed shake/shutter than a 8cyl, due to cylinders only firing at 180* intervals vs 90* in the 8cyl...

 

[rationull]

Originally Posted By: MrHorspwer
The driveline layout is the reason why Subaru's lug and shudder so bad.

A longitudinal mounted engine that is attached to the front drive axle requires mounts to control movement on two axis.

A set of engine mounts controls engine torque (side to side) and the upper dogbone and transmission mount controls driveline torque (front to back).

It's really the worst of both: Side to side lugging of a longitudinal mounted RWD engine and the driveline lash of a transverse FWD.


I guess I hadn't thought about it, but do RWD layouts generally not have dogbone style longitudinally oriented mounts?

 

[Hokiefyd]

Originally Posted By: rationull
I guess I hadn't thought about it, but do RWD layouts generally not have dogbone style longitudinally oriented mounts?


That is correct: they do not. That is because a longitudinal design doesn't try to rock forward and backward in the vehicle; it will rock side-to-side instead.