When to change tyres ?

The Bargee wrote:General Grabber AT3   235 65 R16C  Load Rating 121 (single wheel)

Hi Bargee.  My van is a similar age to yours but is coach built with 15 inch wheels which rules out Grabbers.  Out of interest though, what prompted you to change your tyres, what tyres did the van have and roughly what axle masses are you working to?

I could wax eloquent on this, but I will try and spare you.

GG’s seem to last a long time. 80k + miles on my 4x4’s.

They are not unduly expensive.

They can hardly fail to improve traction even on a one wheel drive van, although I have not really had that much comparative experience as yet, i.e. I haven’t got stuck since I changed the tyres, but I did before, but there is always another bog.

They might increase fuel consumption slightly, but almost too small to measure.

I have run them on 4x4’s for some years and obtained high mileages and a smooth ride.

With the van, on standard Contivans, we were shocked how hard we hit the potholes and we were fighting a battle of the rattles. Many of the rattles were eliminated early on, but some remained. The Grabbers cured most of the last rattles. Quite simply a stronger tyre but with more supple side walls.

I bought a VW Touareg on 20” wheels a couple of years ago and found it very harsh on bad roads. Changed the wheels to 18” on all seasons tyres. Big improvement! Then changed the tyres to G.G’s. Fantastic improvement in ride. It absolutely wafts along now.

Personally and in your position (but without experience of your particular model) I suspect I would be looking at changing the rims to 16” (if that is feasible) and try the Grabbers, or look forward to the time when GG produces a 15” version at a suitable load rating.

So, in my opinion, much better tyres in so many ways. Certainly as a direct comparison to the same diameter Contivans the difference in ride comfort is remarkable.

In fairness I should add that BF Goodrich all terrain tyres may offer all the same benefits. I did nearly a million miles on these in Disco’s, but went off them when the newer KO’s proved noisy after half mileage. That might not be an issue for some MH owners of course.

Thanks Bargee.  

I think the Contivan is a C tyre so its interesting that A-S chose not to fit a CP tyre.  It seems on PVCs they sometimes fit C and sometimes CP.  Was the size the same as you have now and if so was it the 8 ply version with a 115 load index (which comes as C and CP) or like your current tyre the 10 ply version with a 121 load index (which only comes as C)?

I'm too tight to change my wheels and hubs to R16.  Upgrading my current CP R15 tyres from 215/70 to 225/70, which means the Michelin Crossclimate Camping, should improve my front wheel traction and through the higher load index of 112 rather than 109 allow me to get closer to my rear axle's MTPLM of 2000 kg without risk of either tyre being overloaded and without running the rear tyres at their maximum load and pressure.  I can't go any higher than 112 with a 15 inch wheel but I think that is high enough.

Caraman wrote:Thanks Bargee.  

I think the Contivan is a C tyre so its interesting that A-S chose not to fit a CP tyre.  It seems on PVCs they sometimes fit C and sometimes CP.  Was the size the same as you have now and if so was it the 8 ply version with a 115 load index (which comes as C and CP) or like your current tyre the 10 ply version with a 121 load index (which only comes as C)?

I'm too tight to change my wheels and hubs to R16.  Upgrading my current CP R15 tyres from 215/70 to 225/70, which means the Michelin Crossclimate Camping, should improve my front wheel traction and through the higher load index of 112 rather than 109 allow me to get closer to my rear axle's MTPLM of 2000 kg without risk of either tyre being overloaded and without running the rear tyres at their maximum load and pressure.  I can't go any higher than 112 with a 15 inch wheel but I think that is high enough.

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Caraman wrote:Thanks Bargee.  

I think the Contivan is a C tyre so its interesting that A-S chose not to fit a CP tyre.  It seems on PVCs they sometimes fit C and sometimes CP.  Was the size the same as you have now and if so was it the 8 ply version with a 115 load index (which comes as C and CP) or like your current tyre the 10 ply version with a 121 load index (which only comes as C)?

I'm too tight to change my wheels and hubs to R16.  Upgrading my current CP R15 tyres from 215/70 to 225/70, which means the Michelin Crossclimate Camping, should improve my front wheel traction and through the higher load index of 112 rather than 109 allow me to get closer to my rear axle's MTPLM of 2000 kg without risk of either tyre being overloaded and without running the rear tyres at their maximum load and pressure.  I can't go any higher than 112 with a 15 inch wheel but I think that is high enough.

Sorry, I can’t tell you exactly what the original tyres were. I was just glad to see the back of them! They were certainly Contivans, C rated, and a lower load index, but that is as much as I can recall.

The Bargee wrote:
Sorry, I can’t tell you exactly what the original tyres were. I was just glad to see the back of them! They were certainly Contivans, C rated, and a lower load index, but that is as much as I can recall.

Thanks.  Won't the tyre pressure label on the C pillar tell you what size the tyres were and the pressures might give a clue if they were 8 ply or 10 ply.  If the load index was lower I expect they were 8 ply with a maximum pressure of 4.75 bar whereas your current tyres have a maximum pressure of 5.0 bar

PLOUGHLIN wrote:

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Thanks Ploughlin.  I didn't know this tyre existed.  I know the 215/70 I currently have on my 15 inch rims can be replaced with a 225/70 with only a small difference in rolling circumference.  I've no idea if the 215/80 will fit or what impact it will have on the rolling circumference.  I notice that this Grabber AT3 has a much lower economy grading of E than the Michelin Crossclimate Camping's C and more worryingly has a less good wet braking grading of B than the Michelin's A.  It's also a noisier tyre 75dB instead of the Michelin's 72dB.  Whilst it has 10 plies  rather than the Michelin's 8 plies, its load index of 112 is no higher and its carcass can only tolerate a cold tyre pressure of 5 bar rather than the Michelin's 5.5 bar.  As its not a CP tyre its sidewall is likely to be less stiff which, combined with lower rear pressures, will be less resistant to body roll.  It is a cheaper tyre than the Michelin but not by much.  Another interesting thing I have learnt tonight is that the Grabber AT3's manufacturer - General Tire - was purchased by Continental in 1987.

My old tyres (on PVC) were indeed C rated.

The new Grabbers are slightly smaller rolling radius.

I am not sure how credible the various Euro tyre ratings are. On my Touareg, which is the quietest car I have ever owned, I just notice a very slight whistle on certain very smooth road surfaces. In the van I notice no difference in tyre noise at all, but a distinct reduction in bangs and rattles!

As I have said before I have not done a direct fuel consumption comparison (by brimming) on the van but the computer used to say about 29-30 mpg, and it still says about 29-30 mpg. On the Touareg I would say my average has dropped very slightly, from a brimmed average of about 40 down to about 38.5 now. So possibly a slight loss in economy.

Wet weather? I had some scary Pirelli Akros tyres on an early Discovery many years ago, which were lethal in the wet. Since using BFG AT's and GG AT3's I have never had any concerns about wet weather handling. I had a set of Goodyear Vector All Seasons tyres on my Touareg before changing to Grabbers and I would say that the Grabbers are better in the wet. Accelerating off a wet roundabout needed care on the Goodyears! (and I am not a boy racer!)

I have done all the comparisons on Euro figures etc. and my personal conclusion is that they do not tell you a lot. Each to their own etc. I am a big fan of Grabbers on both my cars and my van. What I can't comment on is the effect on body roll in a large coachbuilt. The Grabbers are specifically designed to have more supple side walls. I can's say I j have noticed any difference at all in my PVC, but a heavier body might see some difference.

Thanks Bargee.  

Did you get any further with the size and pressures of your original tyres off the C pillar label?  

If the radius of your Grabbers is slightly less then the rolling circumference will also be less which will affect the mpg shown on the van computer.  It's possible this is masking a loss of economy.  For your size of Grabber, the economy grading was only a drop from C to D but on the 15" tyre Ploughlin found it dropped from C to E.  Similarly it was only on the 15" tyre that the wet braking dropped.  I don't know how accurate and relevant these gradings are but they must mean something.  The main thing is you are happy with your Grabbers.  I don't think they would suit me.  One website describes them as suitable for 50/50 off-road and on-road use.  My off-road use on grass pitches doesn't register on that scale.  As you have suggested, I doubt the supple sidewalls are suitable for my type of van which is why it was type approved and supplied with CP tyres.

Yes, clearly there will be a difference in figures due to the changed rolling circumference.

The original tyres were 215/75 R16C. 

The new GG's are 235/65 R16C. The new ones are 0.7" less in diameter than the Contivans.

The old tyres did 703 revolutions per mile. The new ones do 720 revolutions per mile.

As you say the system is now working on inaccurate data, viz. there is a 1.024 increase in miles recorded if my arithmetic is correct (?).

I have never quite got my brain round how the volume of fuel actually burnt is measured in a diesel engine in order for the computer to compute MPG but I suspect that may be a moveable feast. Either that or diesel fuel is of very variable quality.

To throw another spanner in the works I suspect that the slightly changed gear ratios due to the smaller tyres might actually improve matters for a fully loaded Boxer van, at least in urban conditions.

However, any actual difference in MPG remains of minimal concern to me for what will be a low mileage vehicle, probably no more than 12,000 miles per annum. I have been more concerned about the change in tyres for my car, which does 40,000 p.a.

What I have yet to do with the van is actually do a brimmed test against a known physical mileage (bearing in mind that the odometer readings will also change with any change in tyre rolling diameter). I have done this with the Touareg using my standard test route down to our place in Falmouth (273 miles each way almost every month for the last 25 years) which is what my various cars over that period and various sat navs have been telling me is the distance, and Google Maps seems to agree! I have not yet got round to doing the test with the van yet, and probably will never bother.

However, even relating actual ground miles to fuel burnt is also inaccurate since it all depends upon the strength and direction of the wind, state of mind (in terms of driving style!) etc. etc. 

Suffice to say that I feel that any difference in consumption between the original tyres and the new ones is absolutely minimal, which supports my impression that the Euro figures are not that useful.

Like I think I inferred and/or said, I would not hesitate to fit GG's again on my vehicles, but I don't know how they might fare on a slightly more top heavy motorhome (not the subject of this original post). Having said that, I have never noticed any issue on the 5 slightly top heavy older style Discoveries that I did a million miles in after I fitted AT tyres.

However, there are other significant advantages that remain. I expect a very long life from these new GG tyres (based on substantial past experience), they do not seem to suffer punctures (famous last words!), the ride comfort (and noise in an MH) is most definitely vastly improved, and they will surely offer more traction on a grass site, which was actually the prime reason for fitting them in the first place.

... and to answer your other question I ran the original tyres at 60 psi all round as delivered to me, and I run the new ones at about 55 front / 60 rear, as per the tyre fitter's recommendation and as supported by various online advice.

Bargee - thanks for your patience - my curiosity has been satisfied!  There appear to be two versions of the 215/75 R16 C tyre.  One with a load index of 113 which might be 8 ply, and has a CP equivalent, the other with a load index of 116 which might be 10 ply and doesn't have a CP equivalent.  Whatever, using the TyreSafe on-line calculator a pressure of 60 psi was for axle masses of around 1860 kg and 1867 kg, so not much difference.  The 10 ply different sized Grabbers have a larger volume and higher load index.  Using the on-line calculator, 55 psi front and 60 psi rear equate to a front axle mass of around 1900 kg and rear axle mass of around 2020 kg, so the front a little higher than before and the rear more so.  If you had set your previous tyres around these higher axle masses, they would have been firmer still.  Clearly the Grabber's more aggressive and wider treads should deliver better traction on grass and their higher load index should mean they are never required to operate at or close to their maximum permitted pressure and load.

If you cover 12k miles per year in your Kingham plus 40k in your car, that will be much more than most of us.

The tyres on my Symbol will be in need of renewal in the next year or 2 if not sooner. Whilst I’m in complete awe with regards to you guys and your knowledge on the subject, I must admit I’m very confused. 

Any chance of a simple recommendation of an upgrade to the standard tyres my van was fitted with from new. I will advise what I’ve actually got fitted on the van tomorrow.
Cheers.

Dbvwt wrote:The tyres on my Symbol will be in need of renewal in the next year or 2 if not sooner. Whilst I’m in complete awe with regards to you guys and your knowledge on the subject, I must admit I’m very confused. 

Any chance of a simple recommendation of an upgrade to the standard tyres my van was fitted with from new. I will advise what I’ve actually got fitted on the van tomorrow.
Cheers.

It would also be useful to know the maximum rear axle mass you are ever likely to have.  This will either be the axle's MTPLM of 1900 kg or a lower figure.

Also useful to know if you use the van in the winter.

Caraman wrote:
It would also be useful to know the maximum rear axle mass you are ever likely to have.  This will either be the axle's MTPLM of 1900 kg or a lower figure.

Also useful to know if you use the van in the winter.

This is where my confusion begins!! I’ve never weighed my van so can’t answer exactly (even if I did fully understand all those different figures!). What I will say is that I travel about as light as you possibly can. A single non electric bike on the door mounted rack and my beer in the rear fridge are about it at the back. I do tend to travel with a full fresh water tank but that isn’t fully at the rear.
Also, I SORN my van over winter.
Edit.. just been outside to check, my existing tyres are Bridgestone Duravis 215/70 R15. Load rating 109/107 SLT.

We do weigh ours about once a year en route to the first ferry, so full and that's full fuel, water, gas all clothing and all food. We also carry 7 x 2ltrs bottled water, 4 of them right in the back.

My point being is that the weight is virtually constant, as is the loading, as would yours be. As are the individual axle weights, don't have them handy but we are usually 3020Kg out of a max in our case of 3200Kg..

So, just get it weighed as you usually use it, it'll be more than near enough, this is a motorhome not a spacecraft!

Dbvwt wrote:

This is where my confusion begins!! I’ve never weighed my van so can’t answer exactly (even if I did fully understand all those different figures!). What I will say is that I travel about as light as you possibly can. A single non electric bike on the door mounted rack and my beer in the rear fridge are about it at the back. I do tend to travel with a full fresh water tank but that isn’t fully at the rear.
Also, I SORN my van over winter.
Edit.. just been outside to check, my existing tyres are Bridgestone Duravis 215/70 R15. Load rating 109/107 SLT.

Can you confirm your MTPLMs as 3300 kg overall, 1750 kg front axle and 1900 kg rear axle?

Dbvwt - I think I have enough detail.
 
The main difference between your tyres and mine, other than brand, is mine are stronger CP tyres whereas yours are cheaper Commercial (C) van tyres.  The reason for this is that my Nuevo is 260 mm higher with a higher centre of gravity and potentially is 200 kg heavier.  It probably has the same wheel track as your Symbol but is 60 mm wider and is 339 mm longer with a wheel base that is 450 mm shorter resulting in significant overhangs.  If you change to CP tyres which I am not recommending, it will give you a firm ride.  I also see that the current Symbol premium package includes Glide-Rite semi-air suspension which you may have and I don't.

It is recommended that an axle mass does not exceed 90% of the combined maximum permitted loads of its tyres.  As your current tyres have a load index of 109, this limits your axle masses to 1854 kg.  I doubt that in use either of your axle masses gets close to this (but that really needs to be confirmed by visiting a weigh bridge).  On that basis, I see little benefit in raising your load index to the next higher level of 112.  
 
Replacement tyres should not have a lower load index than the tyres it was supplied with.  This fixes your load index at 109.  The only R15 C tyre I am aware of with a load index of 109 is the size you already have – 215/70 – so no change.
 
It’s not clear from the detail you have given but it appears your current tyres like mine are summer and not M&S (mud & snow) rated.  As you don’t use your van in the winter, you shouldn’t upgrade them to all-season.  If you want to improve traction on grass pitches you might look for a summer tyre that has the M&S label.  
 
As my interest is in 225/70 R15 112 CP tyres, I haven’t researched the 215/70 R15 109 C tyres that are available.  There are many.  I recommend you stay with a premium brand rather than a cheaper economy brand.  This will narrow down the choice.  When making your selection, it’s worth looking at the rolling resistance/economy, wet braking and noise ratings of each tyre as they may be different.  Some tyres have additional sidewall protection against kerb strikes which could be useful for you.
 
I don’t want to give a specific recommendation for a tyre which I haven’t seen or used.  That is better coming from Symbol owners who have changed their tyres.  

If what I have said is confusing, buy exactly the same tyre you have now and move on.

Thank you Caraman and Ian. After your detailed replies, I’ve had a think and will replace with exactly the same. I’ve not been unhappy with them and they seem readily available at a price a lot less than I was expecting to have to pay.
One quick question, the DOT on my tyres is 60 2018. I always thought the first number was the week in the year but I guess it isn’t?

Dbvwt wrote:Thank you Caraman and Ian. After your detailed replies, I’ve had a think and will replace with exactly the same. I’ve not been unhappy with them and they seem readily available at a price a lot less than I was expecting to have to pay.
One quick question, the DOT on my tyres is 60 2018. I always thought the first number was the week in the year but I guess it isn’t?

without seeing a photo, I would say the '2018' is the 20th week of 2018 which means the tyre was manufactured during the middle week of May 2018 so its about 5 years and 9 months old.  Best to replace as soon as you bring the van back into use.  As a tyre ages it weakens.  Tyres have aging inhibitors within their compound but for these to work, heat from frequent use is required.  The lack of activity of your tyres whilst the van has been SORN'd will have aged the tyres more quickly than C tyres fitted to commercial vans which, due to their higher mileage, are replaced more often.  This and the damage done to tyres parked up in one place for long periods and the fact that compared to CP tyres your tyres are weaker and less tolerant of UV means IMO they should be replaced early during the age 5 to age 7 time window.

It's not that number Dave, to the right of that will be an oval shaped border with 4 numbers in it, first two are the week second two are the year.

Or it could be as Caraman says, should I be wrong.

Either way be sure to buy tyres that are less than 6 months old, don't accept any older than that.

This is what my manufacture date number looks like - 44th week of 2018.  Sorry its upside down:

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Thanks again.
I misled you slightly it was 6C18 not 60 2018. A bit further round is 3917 which makes more sense.

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It has to be 3917, week 39, 2017. There's only 52 weeks in most years!!!!!