My new van is it a light or maxi chassis?

[Robinhood]

Brian Kirby - 2020-06-22 11:55 AM

 

I'm wondering whether that Maxi lower final drive ratio more than compensates for the higher overall gearing imposed by 16" wheels, leaving the effective overall ratios lower on the maxi than on the Light chassis. Does anyone know?

 

 

It would all depend on what tyres are fitted, of course, but if one considers 15" and 16" wheels with a typical profile CP tyre, then the overall difference in gearing (to the road) is only in the order of 2%; you could probably get a greater variance with different -profile tyres on the same size rim, and I doubt it would make a noticeable difference.

 

If you look at Mike's figures above, you'll note (and I've highlighted this before) that the intermediate ratios and final drive for the Comfortmatic are very different to the manual. This is rather more likely to deliver a perceptible difference in driving characteristics. I think you may be noticing that difference in internal ratios, rather than any effect of the wheel-size.

 

In terms of ride, then I think you're making an "apples and pears" comparison. Your Exsis would have been on a light version, but with an Al-Ko chassis, giving completely different ride characteristics to a heavy-chassis'ed PVC conversion. Nonetheless, having gone exactly in the reverse direction, I don't find anything to criticise in my current Exsis (35L Al-Ko). It isn't noticeably any worse in handing than the preceding Globecar (Maxi), and the ride is fine (subjectively, at least, this is one of the quietest 'vans on the road I've had, which rather supports the "decent ride" view - unless it is simply much better screwed together - and I rather err in favour of the former). It does have the 16" wheels, though - maybe that's the secret ;-).

[Derek Uzzell]

Robinhood - 2020-06-22 1:41 PM

 

It would all depend on what tyres are fitted, of course, but if one considers 15" and 16" wheels with a typical profile CP tyre, then the overall difference in gearing (to the road) is only in the order of 2%; you could probably get a greater variance with different -profile tyres on the same size rim, and I doubt it would make a noticeable difference.....

 

I’m doubtful that’s the case.

 

According to Continental’s Technical Databook, the rolling circumference of their 215/70 R15CP tyre (the standard OE specification for a Ducato X290 with a ‘light’ camping-car chassis) is 2069mm (+1.5%/-2.5%), which is the distance along the road that a point on the tyre tread’s surface will travel for a single rotation of the road-wheel.

 

Continental gives the rolling circumference of their 225/75 R16CP tyre (the standard OE specification for a Ducato X290 with a ‘heavy'’ camping-car chassis) as 2254mm (+1.5%/-2.5%) 2254 is a roughly 9% increase over 2069.

 

There’s an online calculator here

 

https://alloywheels.com/tyreCalculatorResults2

 

that provides the results shown on the attached file

[colin]

Keithl - 2020-06-22 1:20 PM

 

colin - 2020-06-22 12:19 PM

 

That's where me and Nick disagree, I had driven several x250's including a weeks hire of a WildAx on a LWB 35L chassis, but no XLWB 35H before buying our van, I was surprised as to how harsh the suspension is compared to the 35L.

 

What tyre pressures are you running at? Many times people blame suspension when lowering pressures is all that is needed.

 

Keith.

 

I run the correct pressures for the max load I'm likely to carry,

[Robinhood]

Derek Uzzell - 2020-06-22 6:27 PM

 

I’m doubtful that’s the case.

 

 

I think you misunderstand Brian's question and my answer.

 

AFAIK Brian was asking about the overall gearing difference between a Maxi with 16" wheels, and a"light" with 15" wheels (given his experience of both).

 

The difference in overall tyre circumference is (depending on which tyres you pick) somewhere between 8 and 9%, (I used the rolling circumference from the Conti tables), but the different final-drive ratio compensates for this, bringing the difference in overall gearing at the road (i.e. what the driver would perceive) to little over 2%.

 

I've implicitly pointed out that this comparison is for manual versions of both; if you compare manual and Comfortmatic then the calculations (because all the ratios are different) are different. Brian's empirical experience may be because of this.

 

The difference in circumference between, say, a 225/65 and a 225/75 16" CP tyre is, however, over 6% - the variance between different tyre types on the same 'van can be considerably greater than the variance Brian was originally asking about.

 

With a difference between a 215/75 and a 225/75 15" CP tyre, being around 2%, a light 'van equipped with the latter would have very similar overall gearing to a standard Maxi.

[Brian Kirby]

Thank you all for your replies, and apologies to Roger for drawing his string off topic.

 

I'd imagined the answer would be much simpler than turns out to be the case, plus I couldn't understand Mike's table of ratios as I couldn't distinguish which was the final drive ratio, and which other ratio related to which of the six gears plus reverse. They are all labelled "1"!

 

In addition, I hadn't realised that the Comfortmatic box, which I had understood to be a standard manual box with robotised gear selection, had different gear ratios from the standard manual box. The Hymer tyres were 215/70 R 15 CP Vanco Campers, while the Knaus is on 225/75 R 16 CP Michelin Agilis Camping.

 

Bob (Robinhood) is correct in his understanding of my question. It was indeed the difference in overall gearing between the manual Maxi on 16" wheels, and the Comfortmatic "light" on 15" wheels, both shod as above (though I confess that I'd assumed that the circumferences of Conti and Michelin tyres of equivalent spec and size would be negligible).

 

There is of course a further difference between the engines, apart from the 130PS Maxi to 150PS "light", in that the former is Euro 6 and the latter Euro 5, so possibly the HP/torque outputs better suit the ratios of one box than the other.

 

But I'm still left with this apparently livelier van on a Maxi chassis at 9,000 recorded miles than its Comfortmatic predecessor on the light chassis but with a 20PS advantage at 25,000 recorded miles. I was expecting to feel the opposite. Having said that, the difference diminishes once into the 5th and 6th gears.

[Robinhood]

The table posted by Mike shows three columns:

 

The manual gearbox on either version : The comfortmatic on the "light" : and the comfortmatic on the Maxi,

 

The entries in each column are (from the top) the gear ratios of gears 1 to 6 respectively (the ratio is "to 1"), followed by reverse.

 

Below that is the final drive ratio, two entries for the manual gearbox (since the final drive is different on the light and Maxi), and one for each of comfortmatic light and Maxi, which have their own column because they differ from each other rather more than just in final drive.

 

The summary is that the manual gearbox has the same gears (1-6) for both the light and Maxi, but different final drive ratios. Any overall gearing "on the road" however, remains largely similar due to the difference in wheel/tyre size. (We're not sure, however, which combination light chassis with the optional 16" wheels leaves the factory with).

 

The comfortmatic will not quite be the same, since as well as different final drive (Light and Maxi) they have different gearing in some of the intermediate gears, hence the experience won't be the same across the board.

 

I had compared only the manual versions (as it was easier), but hadn't done exactly the calculation you'd asked for, Brian (though I had alluded to the fact that throwing the comfortmatic into the ring would probably give a different view)..

 

So, using Mike's figures above, and allowing for the different wheel sizes between light and heavy, I've just done a quick "through the gears" for Brian's core examples.

 

If I haven't made a mistake, across the board, at the road (allowing for tyre size effect) the comfortmatic light will be lower geared than the manual Maxi. In the lower gears, the difference is substantial, by the time 6th is reached, the difference is almost but not quite made up.

 

I'm not sure that that explains Brian's impression of a "livelier" Maxi, but it does highlight a significant difference below 5th and 6th, which might lead to a quieter time, and later gear-changing, in the lower gears.

 

 

[Brian Kirby]

Robinhood - 2020-06-23 5:02 PM

The table posted by Mike shows three columns:

The manual gearbox on either version : The comfortmatic on the "light" : and the comfortmatic on the Maxi,

The entries in each column are (from the top) the gear ratios of gears 1 to 6 respectively (the ratio is "to 1"), followed by reverse.

Below that is the final drive ratio, two entries for the manual gearbox (since the final drive is different on the light and Maxi), and one for each of comfortmatic light and Maxi, which have their own column because they differ from each other rather more than just in final drive.

The summary is that the manual gearbox has the same gears (1-6) for both the light and Maxi, but different final drive ratios. Any overall gearing "on the road" however, remains largely similar due to the difference in wheel/tyre size. (We're not sure, however, which combination light chassis with the optional 16" wheels leaves the factory with).

The comfortmatic will not quite be the same, since as well as different final drive (Light and Maxi) they have different gearing in some of the intermediate gears, hence the experience won't be the same across the board.

I had compared only the manual versions (as it was easier), but hadn't done exactly the calculation you'd asked for, Brian (though I had alluded to the fact that throwing the comfortmatic into the ring would probably give a different view)..

So, using Mike's figures above, and allowing for the different wheel sizes between light and heavy, I've just done a quick "through the gears" for Brian's core examples.

If I haven't made a mistake, across the board, at the road (allowing for tyre size effect) the comfortmatic light will be lower geared than the manual Maxi. In the lower gears, the difference is substantial, by the time 6th is reached, the difference is almost but not quite made up.

I'm not sure that that explains Brian's impression of a "livelier" Maxi, but it does highlight a significant difference below 5th and 6th, which might lead to a quieter time, and later gear-changing, in the lower gears.

Thanks Bob, I think that explains all.

 

From what you have said, I think most of the reason I thought the Comfortmatic comparatively sluggish lay in the meal it made of the upshifts from 1 - 2, and 2 - 3, after which it was much better. That, coupled with its lower ratios, meant that it changed up earlier, and more slowly, than I do with the present Maxi.

 

With the Maxi and its "longer" gearing, I am reaching higher road speeds in each of the lower ratios (plus upshifting quicker than the Comfortmatic :-)), and so more easily keeping station with the rest of the traffic.

 

I think it is those earlier and more ponderous Comfortmatic upshifts that give me the impression that the Maxi is a livelier drive, and not, as I supposed, its lower overall gearing. So, thanks for taking the time to work all that out.

 

Worth a beer, that, if we ever escape from Covidland! :-D Further apologies for the OT.