Towing with X5

[JCL]

Originally Posted by KnudsonsM3

A diesel will ALWAYS be better for towing. Anyone who says otherwise is ignorant. The low end of the diesel and massive torque coupled with the better mpg while towing make gas engines look obsolete.

That is an ignorant statement, IMO.

Low end torque is good for towing. A turbocharged direct injection gasoline engine has good low end torque as well. Torque peak on the 35i obviously isn't as high as the 35d, but it comes in at a lower rpm on the models I checked. And the torque band is much wider, meaning less shifting.

The peak torque number that matters is at the wheels, also known as rim pull. Engine torque is a good starting point, but that is why we have transmissions, to create rim pull. Flywheel torque is good for winning magazine comparisons though.

High diesel mpg is a good starting point, but an economic analysis will include the local cost of diesel fuel, and the higher purchase price of the diesel. I can make the economics work based on my local fuel prices, but given that the breakeven point is around 80,000 km without even considering the time value of money, it isn't a very attractive investment, towing or not.

Finally, diesels typically have little retarding capability unless they are fitted with an exhaust brake or similar retarding device. Basic science, and very important for towing any significant weight. Not sure how the latest BMW diesel performs here (I haven't towed with one) but it is a point to check on if you live near hilly areas (and if you don't, why would torque matter so much?).

I think port injected naturally aspirated engines look obsolete. The use of the Otto cycle vs the Diesel cycle doesn't dictate which one has direct injection and turbochargers these days.

[Skier1]

Originally Posted by JCL

That is an ignorant statement, IMO.

Low end torque is good for towing. A turbocharged direct injection gasoline engine has good low end torque as well. Torque peak on the 35i obviously isn't as high as the 35d, but it comes in at a lower rpm on the models I checked. And the torque band is much wider, meaning less shifting.

The peak torque number that matters is at the wheels, also known as rim pull. Engine torque is a good starting point, but that is why we have transmissions, to create rim pull. Flywheel torque is good for winning magazine comparisons though.

High diesel mpg is a good starting point, but an economic analysis will include the local cost of diesel fuel, and the higher purchase price of the diesel. I can make the economics work based on my local fuel prices, but given that the breakeven point is around 80,000 km without even considering the time value of money, it isn't a very attractive investment, towing or not.

Finally, diesels typically have little retarding capability unless they are fitted with an exhaust brake or similar retarding device. Basic science, and very important for towing any significant weight. Not sure how the latest BMW diesel performs here (I haven't towed with one) but it is a point to check on if you live near hilly areas (and if you don't, why would torque matter so much?).

I think port injected naturally aspirated engines look obsolete. The use of the Otto cycle vs the Diesel cycle doesn't dictate which one has direct injection and turbochargers these days.

Well that is your opinion ,Sorry but that is a complete load of piffle , a turbo diesel will shit over a petrol, you obviously havent driven one. Diesels also have a better retardation due to the higher compresssion ratio. There is no way I would contemplate towing with a petrol unless I was towing a fuel tanker behind me.

[JCL]

Originally Posted by Skier1

Well that is your opinion ,Sorry but that is a complete load of piffle , a turbo diesel will s**t over a petrol, you obviously havent driven one. Diesels also have a better retardation due to the higher compresssion ratio. There is no way I would contemplate towing with a petrol unless I was towing a fuel tanker behind me.

Yes, that is my opinion. I have driven many turbo diesels, and a few naturally aspirated diesels. I have had a turbo diesel Passat (red badge, A6 engine) and a diesel LR Discovery. Class 3 driver's license (unlimited GVW on highway, with air brake endorsement, meaning almost exclusively diesel.

I also worked in the diesel engine industry (engineering, sales, service) for 26 years. 15 to 8000 hp.

Diesels inherently have no effective engine retardation other than friction. That is simply because while they have a higher compression ratio, they are not throttled. When the air in the cylinder is compressed, it is then decompressed, for no net work, thus no retardation. If you want to have retardation (which occurs naturally with a throttled gasoline engine) you need to include an exhaust brake of some type, Jake or otherwise. That is why those devices were designed. That device opens an exhaust valve after the compression stroke, releasing the compressed air (and making lots of noise). There are also hydraulic retarders. All designed to overcome the limitation of the diesel engine with respect to lack of engine retardation.

If you want to learn more about diesel engines and their development, and the challenges faces (including lack of engine braking) suggest you read Cruickshank's book on the Cummins engine company and the engineering development of the diesel engine concept over 75 years.

I am glad you like your diesel engine. But please don't spread so much piffle. It makes you look like a w**ker.