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Weights - just the numbers....


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Hi All

 

Okay - here's a car-caravan matching question, but I haven't revealed car/caravan, kerbweight, MTPLM to avoid comments like "My Robin Reliant pulls great...".  etc.  All that is in the table below are the results from using the CMC matching service.  Three columns - the first is my current set-up, and it actually works quite well.  My only issue is having to drop down through the gears when going uphill on a motorway to maintain a speed between 40 and 50 mph.  The second column is the match with the new car I'm thinking of buying.  The third column is new car and potentially new (heavier) caravan.  The only additional feature to mention is that the current figures use my car's actual kerbweight and my caravan's MTPLM.  When towing, I have an addition 250kg in the car and am always about 20 kg below the MTPLM (everything is weighed).  This will be the same scenario with new car and heavier caravan - so kerbweight ratios are actually more favourable.

 

Any comments on my new car and/or new car&heavier caravan setups?  Additionally, how much impact does bhp have?

 

image.png.9033454ab646f38167dbb103bfda0d61.png 

 

Thanks

 

Paul

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On your current car you say you have used actual car weight, is this the unladen weight of the car on a weigh bridge or is it the loaded up car including the 250 kg mentioned ?

 

Not sure what you mean by nose weight ratio since I have never used the CMC matching service. Anyway, the values you have given would not seem to give a cause for concern.

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Paul1957 - yes, it's the unladen weight of the car, including normal liquids and a full tank of petrol - no passengers.  The 250 kg is passengers and kit.

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"Additionally, how much impact does bhp have?"

 

It only has an impact if you actually use it.

Sorry if that comes across as obvious, but if the stated power is achieved at way higher engine revs than you can endure reving at, you don't get that power so it has no impact.

 

Power just determines how fast things happen, more power developed the faster you accelerate or go up the hill.

Even low power can climb the same hill if geared correctly, just at proportionally a slower speed.

With low power you will never accelerate as fast as with high power, if you rev high enough to develop that power.

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50 minutes ago, JTQ said:

"Additionally, how much impact does bhp have?"

 

It only has an impact if you actually use it.

Sorry if that comes across as obvious, but if the stated power is achieved at way higher engine revs than you can endure reving at, you don't get that power so it has no impact.

 

 

Speak for yourself! Some of us have no problem using the full range of an engine, although I would back off a bit on long hills, although this is usually needed anyway to keep legal!

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10 hours ago, Paul90125 said:

Any comments on my new car and/or new car&heavier caravan setups?  Additionally, how much impact does bhp have?

 

image.png.9033454ab646f38167dbb103bfda0d61.png 

 

Thanks

 

Paul

 

This kind of number crunching is rather pointless and personally I would pay more attention to if your new or old towcar is a good, average or bad towcar.

How important power is depends on how much you will be towing and how but personally I want a disel with power without having to rev it high.

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7 hours ago, Stevan said:

Speak for yourself! Some of us have no problem using the full range of an engine, although I would back off a bit on long hills, although this is usually needed anyway to keep legal!

 

I made no suggestion I am not prepared to use my engines full power if called on. It is a diesel so that is achieved at modest revs, 3750. However, more typically I would work within the peak torque envelope reaching 2250 RPM, so indeed I rarely achieve its full power of 258PS, if not needed.

 

 

Should I tow with a petrol engine, let say using the new Honda CR-V 2.0 hybrid, then to reach full power I could need to sit at 6,200 RPM. 

Psychologically, then for me  sitting with the engine buzzing up at that RPM would be less comfortable

 

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10 minutes ago, JTQ said:

 

I made no suggestion I am not prepared to use my engines full power if called on. It is a diesel so that is achieved at modest revs, 3750. However, more typically I would work within the peak torque envelope reaching 2250 RPM, so indeed I rarely achieve its full power of 258PS, if not needed.

 

 

Should I tow with a petrol engine, let say using the new Honda CR-V 2.0 hybrid, then to reach full power I could need to sit at 6,200 RPM. 

Psychologically, then for me  sitting with the engine buzzing up at that RPM would be less comfortable

 

Unless you were driving a distinctly underpowered outfit up a very long hill It would never be "sitting with the engine buzzing up at that RPM"! After just a few seconds at, or around, full power it is invariably necessary to either change gear, or back off to stay within the speed limit!

 

 

 

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11 hours ago, Paul90125 said:

My only issue is having to drop down through the gears when going uphill on a motorway to maintain a speed between 40 and 50 mph.

Speaking personally, I would be concerned if I had to change down to maintain 40 to 50 mph on a motorway. I know the legal minimum speed is 30 mph for most of us but I would be seriously concerned if I could not maintain 50mph on a UK motorway without changing gear, traffic conditions permitting.

From your table my advice is to change the car - keep the caravan.

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Fourwinds Hurricane 31D Motorhome. Also MGTF135 1. 8i Roadster (fun) & Volvo V70 3.2Ltr LPG (everyday car)
Unless otherwise stated, my posts will be my personal thoughts and have the same standing as any other member of Caravan Talk.

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51 minutes ago, Stevan said:

Unless you were driving a distinctly underpowered outfit up a very long hill It would never be "sitting with the engine buzzing up at that RPM"! After just a few seconds at, or around, full power it is invariably necessary to either change gear, or back off to stay within the speed limit!

 

 

 

 

That's the very point, the OP's current set up has not copious reserves of power, but the options improve things.

 

Nevertheless, my original point remains valid, if the maximum power is achieved at  revs the driver  does not use, then the "specified power" rating is irrelevant as it is not developed.

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I really do not understand the aversion some people have to changing gear! I was taught to always be in the right gear for the speed and circumstances. If this means dropping from 6th to 5th when towing a caravan up a motorway incline at 60mph, so be it! Likewise, if best acceleration up to motorway speed involves holding 3rd up to 60mph, then dropping straight to 6th, so be it.

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Mr ZF sorts my gear selection out and tends to be reticent to use 8th with our 1900 kg van in tow  at UK motorway speed and more so on the French Autoroutes with their lower limit; even if I tell it to  go there it soon decides it knows better.

 

Holding down a gear or otherwise getting the revs up with modern diesels for  at least short bursts is no bad thing in it exercises the turbo's hot end vanes or brings in sequential turbo charging, both features best frequently used to keep free and operable.

 

 

 

Edited by JTQ
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12 hours ago, Paul90125 said:

My only issue is having to drop down through the gears when going uphill on a motorway to maintain a speed between 40 and 50 mph.

The only time I would drive at those speeds on a motorway would be through roadworks or when that was traffic speed or on the rare nearly deserted sections. At anything below 50 I would consider myself a rolling roadblock on a motorway. Are these speeds speedo or satnav? If I drove at 50mph my speedo would actually show about 57!

 

I have 136 bhp X-Trail and tow a 1,500kg MPTLM van - probably a tad over 40bhp available. At 40mph I am pretty sure that on the sort of hill that has slow HGVs  for a mile or so I would be down to third gear. Not enough revs for that sort of situation otherwise to utilise BHP at low speed. Whilst I usually drive in 6th gear in hilly sections I may just leave in 5th.

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Alan

 

2005 Nissan X-trail 4WD diesel and Swift Charisma 540 2012 Lunar Clubman ES  2018 Lunar Clubman ES

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As above  you simply cannot expect a  car to tow a van on anincline without considering changing gear-surely. Change gear according to conditions and to make sure you have aaccleration if needed; even our 190bhp 400nm torque Nissan prefers 5th at 50mph as 6th is a quite high overdrive type gear to get economy. In our last outfit -not the Nissan but a petrol I have been in 4th out of 6 gears to maintain 50 and it wasn't revving like mad-it was happy!

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25 minutes ago, JTQ said:

That's the very point, the OP's current set up has not copious reserves of power, but the options improve things.

 

I have never had a problem with my theoretical 42 bhp per tonne. Depending on gear ratios the last two columns show very adequate bhps

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Alan

 

2005 Nissan X-trail 4WD diesel and Swift Charisma 540 2012 Lunar Clubman ES  2018 Lunar Clubman ES

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1 hour ago, Gordon said:

I know the legal minimum speed is 30 mph for most of us

 

Pedant alert - there are no minimum speeds on uk motorways - the concept of a legal minimum is only used in a couple of places, one I believe is the Mersey Tunnel.

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2015 VW Touareg 3. 0 V6 TDI + 2013 Lunar Clubman ES

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2 hours ago, Stevan said:

I really do not understand the aversion some people have to changing gear! I was taught to always be in the right gear for the speed and circumstances. If this means dropping from 6th to 5th when towing a caravan up a motorway incline at 60mph, so be it! Likewise, if best acceleration up to motorway speed involves holding 3rd up to 60mph, then dropping straight to 6th, so be it.


I tend to agree - over the years of driving diesels we have all become obsessed with ‘lower revs is better’ without recognising it should be ‘appropriate revs is best’. 
 

My Passat will pull in 6th on the flat at 60mph but needs knocking down to 5th at anything other than the whiff of a gradient and 4th for meaningful gradients - for my next trip away I’m going to experiment by staying in 5th all the time at 60mph; ultimately the engine is only turning at the same speed as 6th at 70mph (1800rpm) so I am hardly thrashing it, I’ll see if the car feels better overall and if it has an impact on economy; very unscientific but I’ve tried it for shorter periods before and I am fairly convinced there will be no difference but it may well be more relaxing with substantially less gear changing.

 

The only thing that will probably get on my nerves is the car telling me to change up to 6th all the time on the flat!

Edited by FrankBullet
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This BHP per tonne thing.

Is this the tow car or the entire fully loaded outfit?

My Touareg is very roughly 100 bhp per tonne driven solo, very roughly 50 bhp per tonne with the full outfit and all the gear.

 

I like, and feel very safe with, the ability to accelerate up a steep slip road and join a stream of traffic (mainly HGVs) doing 55 mph or a bit more with the outfit doing 55-60 mph to easily merge in.

 

Once cruising there aren't many hills which require a change down.

Noting that I use the "Sport" setting on the automatic gear box when towing because that seems to suit the towing dynamics best.

 

YMMV

Hymer Nova 580 2016 and VW Touareg 2009 SE

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15 minutes ago, FrankBullet said:


I tend to agree - that get the years of driving diesels we have all become obsessed with ‘lower revs is better’ without recognising it should be ‘appropriate revs is best’. 
 

 

Not "all", I for one, never bought into that attitude, which may be connected to why I have never really taken to diesels!

 

 

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OP obviously feels his current towcar is adequate. On paper, the new car/caravan looks similar, or slightly better. 

 

In reality, with no idea of the outfit, it might be substantially better, or indeed much worse. Towing is not all about power, nor gearing and certainly not economy, which some people seem to obsess about. In my mind, stability is more important, and different towcars will behave very differently. 

 

My choice is a very heavy and powerful automatic, hooked to a relatively light van, fortunately I’ve never had any concerns about stability, even though I do tow quickly. 

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Thing is you can't tow quickly . 60 on dual/mways and 50 on a roads-that is just designed to annoy other drivers. About time it was 60 across the board. 

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14 minutes ago, LittleGreyCat said:

This BHP per tonne thing.

Is this the tow car or the entire fully loaded outfit?

My Touareg is very roughly 100 bhp per tonne driven solo, very roughly 50 bhp per tonne with the full outfit and all the gear.

 

I like, and feel very safe with, the ability to accelerate up a steep slip road and join a stream of traffic (mainly HGVs) doing 55 mph or a bit more with the outfit doing 55-60 mph to easily merge in.

 

Once cruising there aren't many hills which require a change down.

Noting that I use the "Sport" setting on the automatic gear box when towing because that seems to suit the towing dynamics best.

 

YMMV

 

Power to weight is fully loaded outfit

 

My very first outfit was just 38 bhp/ton and was hard work even with the 50 mph towing speed limit in those days - present outfit is 63 PS/tonne and is fine at any speed

 

 

5 minutes ago, Jezzerb said:

Thing is you can't tow quickly . 60 on dual/mways and 50 on a roads-that is just designed to annoy other drivers. About time it was 60 across the board. 

 

I think you'll find that any unification of speed limits is likely to be downwards - many authorities are rolling out 50 mph limits across all single carriageway roads in their area.

Edited by Black Grouse

2015 VW Touareg 3. 0 V6 TDI + 2013 Lunar Clubman ES

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The one thing I would point out is that the noseweight ratio of 113% is illegal. Not sure how he got this as it depends on loading and can be adjusted to what is legal in most cases. If it cannot be got it down, then it should not be on the road.

I would not want an outfit that cannot manage 50 mph on the motorway although it is not illegal and there are others traveling at that speed but not many.

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15 minutes ago, LittleGreyCat said:

This BHP per tonne thing.

Is this the tow car or the entire fully loaded outfit?

My Touareg is very roughly 100 bhp per tonne driven solo, very roughly 50 bhp per tonne with the full outfit and all the gear.

 

I like, and feel very safe with, the ability to accelerate up a steep slip road and join a stream of traffic (mainly HGVs) doing 55 mph or a bit more with the outfit doing 55-60 mph to easily merge in.

 

Once cruising there aren't many hills which require a change down.

Noting that I use the "Sport" setting on the automatic gear box when towing because that seems to suit the towing dynamics best.

 

YMMV

Yes, it's the actual weight of the entire outfit.

The old rule of thumb was that below 40bhp/ton represented hard work, 40 bhp/tonne becomes tolerable. It was never so precise that using bhp or PS, or ton or tonne is actually important.

Below 30bhp/tonne is downright hard work and frustrating. Better than 50bhp/tonne is even better than 40bhp/tonne.

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No substitute for horses-you don't have to use it! My philosophy anyway!

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