Tyre Charts

[steveandlisa]

Hello peeps,

 

Can anyone explain to me why the "Tyresafe and Continental" tyre charts conflict with one another for the same given tyre sizes and loads and which one I should use?

 

Ta

steveandlisa

 

[Keithl]

Tell us where you have found the anomaly and we'll have a look.

 

Keith.

[steveandlisa]

Hi Keith,

 

I was comparing the two charts shown in a thread I started a couple of days ago 03rd Sept (Tyre pressures "sorry")

The tyres I am running on are 215/70/15C 109/107R, not listed in the Tyresafe chart so I used 225/70/15C`s as a comparison shown on both charts (the other one being Continental`s)

 

Tyresafe suggests a tyre pressure of 48psi front for axle weight of 1860kg & 54psi rear for axle weight of 2060kg.

 

Where as Continental suggest 58psi F & 65psi R for the same? I`m a little confused :$

 

Regards

steveandlisa

[Robinhood]

...I think it is a mis-read, as for the 225/70/15C (109) tyre I get (within roundings) similar values from both.

 

(There are a few anomalies between the two documents - I question the ply-rating used on the Motorhome Tyres document sometimes), but in general, the figures are much the same.

 

The Continental-based pressures originally quoted by me should be a reasonable starter, but use of the weighbridge, and preferably confirmation of the recommended pressures from the tyre manufacturer would be better (and, if running below maximum axle-weights, a better ride).

[colin]

As Robin says, the 225 on both Tyresafe and Conti are roughly the same, but they ain't 215 Conti gives 58/65 for this.

[Keithl]

Steve, (or is it Lisa?)

 

Conti do not list a 225/70 R15 with a Load Index of 109 so I would guess you are comparing the Tyresafe figure for the 109 with the Conti 112.

 

After looking further into this I actually suspect there is a typo on the Tyresafe listing as Conti do not seem to recognise a 225/70 R15 109 and seen as Tyresafe do not list a 215/70 R15 109 I think the former line should actually read 215/70 R15 109.

 

It may be worth getting in touch with Tyresafe to try and clarify this anomaly.

 

Keith.

[Robinhood]

Keithl - 2016-09-05 4:57 PM

 

Conti do not list a 225/70 R15 with a Load Index of 109.......

 

Keith.

 

...they do on the version of the data I have ;-)

 

and the figures are commensurate with the Tyresafe ones.

 

Nonetheless, the OP does not have this size tyre, and the 215/70 R15 Continental figures are currently his best bet.

[Brian Kirby]

steveandlisa - 2016-09-05 1:52 PM

 

Hi Keith,

 

I was comparing the two charts shown in a thread I started a couple of days ago 03rd Sept (Tyre pressures "sorry")

The tyres I am running on are 215/70/15C 109/107R, not listed in the Tyresafe chart so I used 225/70/15C`s as a comparison shown on both charts (the other one being Continental`s)

 

Tyresafe suggests a tyre pressure of 48psi front for axle weight of 1860kg & 54psi rear for axle weight of 2060kg.

 

Where as Continental suggest 58psi F & 65psi R for the same? I`m a little confused :$

 

Regards

steveandlisa

If you look across the Tyresafe pressures for a 225/70 R 15C tyre with a load index of 109, you will see that they are all relatively low for the same load (or that the load carrying capacity at the same pressure is relatively high) when compared to all the other 225/70 15C tyres listed. This leads me to conclude that the Tyresafe data for this size tyre may not be reliable, and is certainly not reliable for a 215/70 R 15C tyre.

 

However, if you compare the Tyresafe data for a 215/70 R 15CP tyre with a load index of 109 with Continental's VancoCamping tyre of the same size and speed rating, you will see that the pressures for load correspond very closely (allowing for variations in the load per axle as stated in the two publications). If you then compare these with Conti's pressures for loads for their 215/70 R 15C tyre with a load index of 109, you will see that they are identical to those for the CP tyre.

 

My conclusion would be to inflate Continental tyres as recommended in Continental's Databook, as Continental manufacture the tyres whereas the Tyresafe data is generic. I would always use specific data where it is available in preference to generic data, and data that relates directly to the tyre as fitted in preference to anyone else's data for a similar sized tyre, and never use data that relates to a different size of tyre however marginal that difference in size may appear, whatever its source.

 

You have not said what make your tyres are, nor what your actual axle loads are when fully laden. As has been suggested the wisest initial course of action will be to take your fully laden van (with everyone and everything on board, and all reservoirs full) to a weighbridge to get its actual axle loads in that condition (because until you do that you cannot know whether either axle, or the whole van, is overloaded). Then (after having made any necessary load adjustments and re-weighed) to consult the technical department of the manufacturer of your tyres for their recommended tyre pressures for those actual axle loads, and to adopt those.

 

Resorting to the maximum permissible axle loads as one's yardstick, in the hope that this will provide a sufficient margin for errors, is unsafe, unless and until one has proved one's laden van does not exceed these loads. Overloaded tyres are, by definition, under-inflated, and under-inflated tyres overheat in use and become prone to catastrophic failure. Inadvertent overloading of motorhomes, and the consequent failure of their tyres, was the reason behind the introduction of "Camping (CP)" tyres, which are constructed to give, in effect, a greater factor of safety against overload. This is frequently achieved in conjunction with inflation to higher than "normal" pressures. There is no legal obligation to use Camping tyres, but the substitution of "C" tyres implies a greater necessity to ensure that the tyres are within their specified load range, and are correctly inflated.

[Robinhood]

Brian Kirby - 2016-09-05 5:36 PM

 

If you look across the Tyresafe pressures for a 225/70 R 15C tyre with a load index of 109, you will see that they are all relatively low for the same load (or that the load carrying capacity at the same pressure is relatively high) when compared to all the other 225/70 15C tyres listed. This leads me to conclude that the Tyresafe data for this size tyre may not be reliable, and is certainly not reliable for a 215/70 R 15C tyre.

 

 

Brian,

 

as per my post above, the Tyresafe figures, although at first glance appearing anomalous, actually agree with Conti values (which are in the data I have, but not the link Keith posted).

 

I think the apparent anomaly arises from the fact (that I've already alluded to) that the Tyresafe values don't show the Ply Rating (PR) of the tyre, and the comparison of the figures doesn't show that one tyre is 6PR, and the other 8PR.

 

In addition, I can't agree (from the data I have), if I am interpreting your statement correctly, that Continental's recommended pressures for 215/70 R 15CP and 215/70 R 15C tyres are the same. They differ slightly on my data for the front, and dramatically for the rear (with a max 5.5 bar supported by the CP tyre, but 4.5bar for the C)

 

 

[steveandlisa]

Hi again,

 

I`ve found a thread from Derek Uzzell, RE: Tyre Types and pressures. Posted 28th Sept 2012.

It seems he is in agreement that some of Tyresafe`s guides are questionable, he also points out the same discrepancy I was referring too.

 

Regards

Steve ;-)

[Brian Kirby]

Robinhood - 2016-09-05 6:04 PM

 

Brian Kirby - 2016-09-05 5:36 PM

 

If you look across the Tyresafe pressures for a 225/70 R 15C tyre with a load index of 109, you will see that they are all relatively low for the same load (or that the load carrying capacity at the same pressure is relatively high) when compared to all the other 225/70 15C tyres listed. This leads me to conclude that the Tyresafe data for this size tyre may not be reliable, and is certainly not reliable for a 215/70 R 15C tyre.

 

 

Brian,

 

as per my post above, the Tyresafe figures, although at first glance appearing anomalous, actually agree with Conti values (which are in the data I have, but not the link Keith posted).

 

I think the apparent anomaly arises from the fact (that I've already alluded to) that the Tyresafe values don't show the Ply Rating (PR) of the tyre, and the comparison of the figures doesn't show that one tyre is 6PR, and the other 8PR.

 

In addition, I can't agree (from the data I have), if I am interpreting your statement correctly, that Continental's recommended pressures for 215/70 R 15CP and 215/70 R 15C tyres are the same. They differ slightly on my data for the front, and dramatically for the rear (with a max 5.5 bar supported by the CP tyre, but 4.5bar for the C)

 

Strange! I was quoting from the 2013/14 databook, but I also have a copy of the 11/12 databook, which shows the same values. It shows both C and CP tyres running to 2060kg at 5.5 bar as single fit at the rear, both with a load rating of 109, both as 8PR. There is one difference which, as I read the chart, is that the C tyre gets a speed rating of S (180kph) whereas the CP "only" gets R (170kph). But hey, these are motorhomes, and I get uneasy at 130kph! :-)

 

Possibly due to a fairly recent change in Conti's tyre range. The 13/14 databook does cover a range of nine different "C" tyres, including winter and camper tyres. Odd, nevertheless, that a (I assume newer) databook should be so different. What year is yours?

 

Nevertheless, I still think the main point is that it would be unwise to use data from a different manufacturer, and especially relating to a different size, or load or speed rated, tyre, to try to approximate to safe pressures, especially when actual axle loads are unknown.

 

As has been said before, Michelin are adamant that the only pressure to be applied to their Agilis Camping of the same size (though it is Q (160kph) speed rated) is 5.5 bar - take it or leave it. I am aware that Michelin are deferring to ETRTO in this, whereas Conti have made their own rule, but I assume the Q rating on the Michelin is due to some engineering difference. Interesting that both companies are members of BTMA, who ultimately are responsible for publishing the Tyresafe leaflets, yet Michelin if asked actually resile from the Tyresafe data, while making no reference to this in the published material. No wonder it gets confusing!

[Robinhood]

Brian,

 

as already discussed, there is only really one definitive way to sort out the appropriate pressures (though there have been arguments even on that!).

 

I had visions, however, of the OP running his tyres at 5.5bar, a pressure for which the non-CP tyres are definitely not designed, hence some (safer) advice..

 

Whilst there might be some debate, in general the tyre pressures quoted by different manufacturers for a given specification of tyre will be similar, and most times, the same. This is particularly true of non-CP tyres (as witness the correlation between the non-manufacturer-specific Tyresafe values and the specific Conti ones). Without specific advice available from a manufacturer, if I were looking for figures I would readily use the appropriately quoted Conti values.

 

In the absence of better info, I would suggest the OP applies the Cont-derived pressures (and certainly not 5.5bar!).

 

As set out, the apparent anomaly referenced is simply (I believe) due to the Ply-Rating difference. The same values as the Tyresafe data are available in the Conti data, but appear "out of sync" since they apply to 6PR tyres, whereas the rest are 8PR. (For confirmation, check the relative values in the Conti tables for tyres of any size that exist in 6PR and 8PR versions - the load indices may vary - and in each case that I've found, the 6PR ones are quoted as taking higher loads at any given pressure than the 8PR ones). It may seem counter-intuitive, but I suspect that it is all to do with heat-dissipation in a more flexible sidewall.

 

There is no anomaly!

 

(..and as we both know that, before getting ETRTO cold-feet, Michelin used to readily quote variable pressures for specific rear axle-loads for CP-rated tyres - I still have on file several emails giving me just this - and they were broadly in line with the pressures that would have applied to a non-CP tyre).