Replacing Tyres

[G H B]

I'd like better road grip from my front (drive) wheels and have been asking suppliers if there is a better tread pattern replacement for my camper tyres -ie. fit non-camper tyres with more grip.

I will keep my camper tyres on the back because they have a stronger tyre wall for the much greater rear axle load.

None of them has said it's not possible but in each case have passed me on to another supplier - supposedly a specialist - and after several calls I have got nowhere.

My van is a Burstner/Ducato 3.85 tons and 3+ years old.

The present tyres are 215/70 R15 CP 109R

I am not after off road tyres just something that will give slightly better grip - particularly on hairpin bends going up hill.

I am aware of all the issues of tyre mixing and compatible rolling radius etc.

DOES ANYONE HAVE EXPERIENCE OF GETTING BETTER GRIP TYRES.

Thanks for reading all this.

G

 

 

[Derek Uzzell]

Welcome to the Out&AboutLive forums, Gordon.

 

Grip on dry roads will depend on the tyre’s ‘footprint’ (ie the area in contact with the road surface) the tyre’s compound, the weight being placed on the driven wheels and the road-surface itself. This is why RWD rear-engined Formula 1 racing cars with wide slick tyres and a design that creates high down-force have so much grip in dry high-speed corners on a high-grip race-track.

 

Front-wheel drive motorhomes when loaded tend to have more weight on their rear wheels than their front wheels and, when accelerating uphill in hairpin bends, there will be weight-transfer towards the rear. The turbocharged diesel motors used in modern motorhomes have a lot of low-revs torque and, given the relatively small footprint of a 215/70 R15 tyre inflated to a high pressure, it won’t be difficult to provoke wheel-spin in such a situation.

 

The only relevant recent-ish comparative tyre test I’m aware of was carried out by the German motorhome magazine “Promobil” in 2013 and involved Fiat Ducato panel vans fitted with 215/70 R15 109 specification tyres inflated to 4.0bar front and rear. Six tyres were tested (including two “CP”-marked) and the tyre with the highest overall score was Hankook’s “Vantra LT (RA18)”.

 

http://www.hankooktire.com/uk/passenger-cars/hankook-vantra-lt-ra18.html

 

The Promobil testing included braking and handling performance on dry and wet roads and resistance to aquaplaning on wet roads, but the sort of ‘acceleration grip’ you seem to want was not tested. It’s logical, though, that if a tyre performs well during braking and cornering on dry and wet roads, it should produce better grip when accelerating than a tyre with inferior dry/wet braking/cornering performance. And on that basis, a good bet for your Burstner’s front tyres would be the Hankook product.

[Robbo]

Welcome to the forum.

 

Before you consider replacing the front tyres, it might be worth visiting a weighbridge and checking the actual load on the front axle (in fully loaded condition) so you can determine the optimum tyre pressure. See https://www.tyresafe.org/check-your-pressures/motorhomes/

 

Remember, any additional load placed behind the rear axle will reduce the load on the front axle.

 

As Derek mentioned, the footprint of the tyre on the road is one of the parameters to consider when assessing grip. An over-inflated tyre will effectively reduce the footprint.

 

As an example, I run my front tyres at 50psi based on a 4250Kg chassis with 225/75R16CP tyres.

 

You might consider winter tyres which have a softer compound and more grip but tend to wear out quicker. However, depending on mileage, they'd probably last until you needed to replace, based on the 5 to 7 year replacement period as recommended by tyre manufacturers,

[Agaric]

I have the Hankook tyres on my Burstner, I inflate them to 52psi, the max pressure for these tyres is 65psi.

The rears I have at 63psi.

 

I've never had a problem with traction even though I tend to find every French road that has a steep hairpin bend, being a bit of B road traveller.

[Keithl]

Hi Gordon and welcome to the forum,

 

Another option might be to replace ALL your existing 215/70 R15 CP 109R tyres with none CP 225/70 R15 112R tyres.

 

This would give you approx 12 mm more tread width (approx 5% greater than 215's) AND the added advantage of being able to run at a potentially lower pressure hence improving grip.

 

Looking at pages 81/82 of Conti's tyre handbook https://blobs.continental-tires.com/www8/servlet/blob/85806/e0854f2c7866c64da551474b998ef8b3/download-technical-databook-data.pdf I guesstimate you could possibly lower your front tyre pressures by around 0.5 bar or 7 psi.

 

Obviously you would have to get weighbridge axle weights to confirm exact pressures required but that is my estimation.

 

Worth looking at if you are that desperate!

 

Oh and I say you would have to replace ALL your tyres as I do not believe you can have smaller tyres on the rear than the front! Well I certainly would not want to.

 

And an added advantage is also the increased safety margin of the 112R Load Index.

 

The only downside is you would increase your rolling radius/circumference by approx 2% so giving very slightly higher gearing.

 

Keith.

[Brian Kirby]

Right hand uphill hairpins (in right hand traffic) are always a bit "iffy" (left hand with left hand traffic). :-) Apart from the relatively low front axle load being exacerbated when travelling uphill, the inside track of a right-hand hairpin frequently involves an extreme camber change at the apex of the turn which seriously unloads the front right hand wheel.

 

I would strongly recommend a trip to a weighbridge with the van fully laden and with everyone on board, to check the individual axle loads (as well as the all-up weight) and adjusting the tyre pressures in accordance with the linked Tyresafe document, or by contacting the tyre manufacturer's technical department for recommended tyre pressures.

 

If you are using the pressures recommended in the motorhome handbook, you are very likely to be running the front tyres over-inflated relative to actual load, as the recommended pressures are almost invariably based on the maximum permissible axle load and, with most motorhomes, this will not be the case.

 

Reducing the pressures in line with the table should increase the footprint of the front tyres, which should improve traction and reduce the harshness of the ride, and may also give some improvement in general handling and directional stability.

 

If the tyres are Continental Camping, I have gained the impression that they have a fairly hard tread compound, and that the finer elements of the tread pattern do not extend to the full depth of the tread. This seems to reduce the ability of the tyres to drain surface water effectively. I have experience minor aquaplaning with these tyres when no more than 50% worn. They seem to be designed as a "summer tyre".

 

My solution then was to fit Michelin Agilis camping which and M+S rated and, at the same running pressures, seemed to give better traction and, no doubt in part due to newness, a quieter, slightly less harsh, ride, but I suspect are also a softer tread compound. But, a tail heavy FWD motorhome is always going to need cautious use of the accelerator off the apex of a tight uphill hairpin if the right hand tyre isn't going to be provoked into "chirping" a bit on the way round!

[veletron]

Hi

 

I have just put some all season Vredestein Comtrac 2's on the front of mine - not had chance to test em yet though! M+S + snowflake marked and £80quid each from camskill.co.uk based down in the lakes. Cost me an extra £20 per tyre to get em fitted though so compare online vs getting them ordered in locally.

 

I'll post an opinion once they have been used on some snowy roads or wet grass!

 

Nigel

[Will86]

I'm puzzled !

 

How can anyone ascertain what 'grip' their vehicle is achieving whatever design of tread they have ?

 

There are countless variations of surface and conditions.

 

G&HB. I would be interested to know why you ask. You sound like a seasoned traveller with an interesting past.

 

Will

 

[Deneb]

Gents, a word of caution.

 

Whilst it may seem logical to want the grippiest tyres at the front of the vehicle, particularly with front wheel drive, it is actually quite dangerous to have tyres which are substantially newer, have deeper tread, or otherwise have higher levels of grip in certain circumstances (i.e. winter tyres) only at the front of the vehicle. You actually need the best tyres on the rear axle, irrespective of whether the vehicle is front or rear wheel drive.

 

All tyre manufacturers recommend this, and this link from Kumho explains the reasons better than I can or currently have the time to go into.

 

http://kumhotyre.co.uk/kumho-news/should-you-fit-new-tyres-to-the-front-or-rear/

 

Suffice to say in my working life which involved investigating the circumstances of serious and fatal collisions I have seen several incidents where newer tyres fitted on the front axle, or conversely much more worn tyres to the rear, have been a contributory factor in those incidents.

 

Whilst you may not notice any ill effects in normal driving conditions, it is when something unforeseen happens that might cause you to take sudden action, that the danger is most likely to arise. Heavy (emergency) braking for example, or sudden steering input whilst the vehicle is already unsettled, such as traversing a bend, can lead to a sudden and vicious breakaway of the rear of the vehicle with very little if any warning, making it difficult if not impossible to control.

 

I would recommend that newer tyres are always fitted to the rear axle, and if you intend to fit winter tyres, they should be on all four or more wheels, particularly not just at the front. This is even more important with modern vehicles that are fitted with stability control systems, as the activation of these systems combined with differing tyre conditions could in certain circumstances exacerbate rather than prevent a loss of control.

[colin]

As above, you should consider weighting both axles, it occurs to me that you may well be overloading the rear axle and underloading the front resulting in wheel spin.

[Derek Uzzell]

Keithl - 2017-12-01 4:14 PM

 

...Another option might be to replace ALL your existing 215/70 R15 CP 109R tyres with non-CP 225/70 R15 112R tyres.

 

This would give you approx 12 mm more tread width (approx 5% greater than 215's) AND the added advantage of being able to run at a potentially lower pressure hence improving grip...

 

Fitting 215/70 R15 or 225/70 R15 tyres was discussed here

 

http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/215-70-15-or-225-70-15-/31852/

 

As Steve928 pointed out in that thread (in his posting of 27 February 2014 9:09 AM) the 10mm wider section-width of a 225/70 tyre does not automatically translate into a 10mm wider tread-width.

 

...Oh and I say you would have to replace ALL your tyres as I do not believe you can have smaller tyres on the rear than the front! Well I certainly would not want to...

 

I also would not choose to put wider tyres just on a motorhome’s front wheels, but as far as I'm aware there are no regulations that would forbid this being done. There’s nothing in the MOT inspection manual about the front tyres (or wheels) of a vehicle causing test-failure merely because they are larger than the rears, and AL-KO offers a ’13-inch chassis’ that has smaller-diameter wheels on the rear axles.

 

http://www.alko-tech.com/en/fiat-ducato

 

I echo Deneb’s advice about having the ‘better’ tyres on the rear axle. Gordon has not said what mileage his Burstner motorhome has covered, but its rear tyres are over 3-years old. If a pair of new tyres were to be fitted, they should really go on the rear axle and, if ‘full-house’ winter tyres were to be chosen, they should really be fitted to all four of the Burstner’s wheels.

 

Like Agaric I’ve never had any ‘grip’ problems when driving a motorhome on the road. I’ve had problems obtaining traction off road (but that’s to be expected) and, in the past, I’ve had very exciting moments driving FWD cars on wet roads (always my own fault). People drive differently - I’m very fussy about my driving position, how delicately I can operate the accelator pedal and ensuring that there’s no hint of ‘roughness’ in the pedal’s action. If I stamped on my Rapido’s accelerator-pedal on an uphill tight bend, I’d anticipate torque-steer in the dry plus wheel-spin in the wet, and I’m confident that fitting different tyres to the motorhome’s front wheels would have no miraculous effect.

[G H B]

THANKS TO ALL FOR THEIR CONTRIBUTION.

I need to think a few things through especially lining up tyre pressure with the actual load. I live on an island and access to weighbridges is not easy, and I tend to be in transit in the UK during in national holiday periods.

Just for info I do load up to near the limit on the back axle (but not over) and the tyres (except for one) have done 15K.

I will check the axle loads but it will be approximate - and will then adjust pressures.

I will possibly go for the Hankook tyres or perhaps Michelin depending on the state of each tyre when I get them inspected next week.

Thanks again.

Gordon

[Brian Kirby]

G & H B - 2017-12-02 8:59 PM

 

THANKS TO ALL FOR THEIR CONTRIBUTION.

I need to think a few things through especially lining up tyre pressure with the actual load.

I live on an island and access to weighbridges is not easy, and I tend to be in transit in the UK during in national holiday periods.

1 Just for info I do load up to near the limit on the back axle (but not over) and the tyres (except for one) have done 15K.

2 I will check the axle loads but it will be approximate - and will then adjust pressures.

I will possibly go for the Hankook tyres or perhaps Michelin depending on the state of each tyre when I get them inspected next week.

Thanks again.

Gordon

Gordon, please don't take this amiss, but there seem to be a couple of contradictions in the above. :-)

 

1 In view of your comment regarding access to weighbridges, one is (gently!) tempted as ask how you know you remain within the rear axle limit? :-)

 

On the existing tyres (but what are they?), I'd guess that the front pair, assuming both have covered the same mileage, will be relatively heavily worn and the rears lightly so. I assume the one that has not covered 15K miles is the original spare and the present spare is the most heavily worn of the originals. If so, don't forget that if replacing tyres you may need to fit the present spare, which should be compatible with whatever you get fitted. I don't know whether, for example, a Continental Vanco Camping should be fitted to the same axle as a Hankook or an M+S rated Michelin Agilis Camping, but would guess that the general advice would be not to do so.

 

2 Depends on what you mean by "approximate"? :-) The pressures for load tables aren't that precise (though there will be a calculation to umpteen decimal places behind them!) but, IMO, it will be preferable to know your maximum axle load conditions with some precision, so that you can be certain you are setting the tyre pressures to cope with the absolute worst case.

 

Personally, I think it preferable to weigh twice: once unladen, and once fully laden with absolutely everything, and everyone, on board. This means full water tank, full gas cylinders, all liquids, clothing, food, books, etc. etc., so that the only variation in weight as you travel will be downward. By comparing the unladen weighing with the laden, you can then get some idea of how much of your load falls onto which axle. This may be instructive as motorhomes behave like see-saws with the rear axle as the fulcrum. This means that load placed behind the rear axle reduces front axle load, while adding more than its self-weight on the rear axle. This can mean that if load is removed from behind the rear axle the front axle load rises even though the overall load has reduced.

 

Since over-inflation is generally safe (with only increased wear on the centre tread band, some reduction in traction, possibly braking efficiency, increased harshness, and a maybe greater sensitivity to "tram lining", as a consequence) its consequences are more an irritant than a danger. Under inflation, on the other hand, is dangerous, because under-inflated tyres get hotter, especially when worked hard, and this can lead to the tread breaking up or sudden blow-outs.

 

FWIW, therefore, I think it safer to establish the maximum feasible axle loads with some accuracy, and then apply approximation to setting the corresponding pressures to the tyres, on the basis that working to the next load band up gives a margin for error, and against loss of pressure in use.

 

Apologies if the above all seems somewhat obvious.

[George Collings]

Frankly the difference in grip between different tyres under extreme conditions is marginal . If mountains are your thing you need RWD and even then the inside rear wheel will spin on occasions. The worst case scenario for any vehicle is being baulked mid hairpin. I have done well over 100,000 miles across back road Europe and its not happened yet.

[Grumblewagon]

I've experienced sidewall failures on Michelin tyres on two of my previous vans. My current van was fitted with (original) Michelin Agilas , and although the tread was still sound, they were showing signs of severe cracking on the side walls.

 

I replaced them with Nokian C line cargo tyres which have a slightly better spec. So far, they're doing great and are noticeably quieter than the original tyres.