Karmann Gipsy Posted August 7, 2006 Share Posted August 7, 2006 Hi All The van is a Volkswagen T4 based Karmann Gipsy coachbuilt, on the chassis cab base. GVW is 2810kg. Off to France in a couple of weeks. At the last service, the garage recommended changing all four tyres due to cracking. The ones on it were 195/70x15 load rating 97. My tyre fitter (Who is also a friend) recommended Goodyear G26 Cargo tyres, with a higher load rating of 104/102R, so I took his advice. Pressures I have used up until now were 3.2 bar front, 3.6 rear. However, when I looked in my VW handbook (Which is in German, so difficult for me to read!!), it seems to say that these pressures are right for the 97 load tyres, but that the 104/102R type should have 3.6 bar front, 4.5 bar rear if loaded more than 1800kg (Which it always is!) This is quite an increase, so I want to be sure which pressures to use. My local VW agent was no use, and neither my friend nor I have had any luck contacting Goodyear for advice. Should these tyres have substantially higher pressures ? Many thanks for any and all advice!! Link to comment Share on other sites More sharing options...
Dave Newell Posted August 7, 2006 Share Posted August 7, 2006 Load your 'van up to what you will be carrying on your holiday, go to your local public weighbridge, weigh the two axles separately then contact Good Year who should be able to tell you the correct tyre pressures for the load you are imposing on them. D. Link to comment Share on other sites More sharing options...
Karmann Gipsy Posted August 7, 2006 Author Share Posted August 7, 2006 Dave Part of my problem is that I have been unable to get any advice from Goodyear. It seems that they dont deal with technical queries (Or at least, I have had no luck so far!!) Link to comment Share on other sites More sharing options...
Brian Kirby Posted August 7, 2006 Share Posted August 7, 2006 Possibly, you spoke to the wrong bit of Good Year. I think you'll need the commercial vehice tyres section. You may have got through to the car tyres bit only. Have a hunt on their web site for their contact numbers. I'd be surprised if they don't have a technical section somewhere. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 7, 2006 Share Posted August 7, 2006 A load index of 104 indicates that a tyre has a design maximum loading of 900kg, hence (for a 'single-wheel' axle) an axle-loading of 1800kg. So, if you are loading your motorhome's rear axle beyond 1800kg, you are loading the tyres on that axle beyond their design limit. (You must really have been pushing your luck with your old (1460kg) tyres!) I've checked Michelin's handbook and for their Agilis 81 195/70 R15C 104/102 pattern a pressure of 65psi (4.48bar) is recommended for an axle-load of 1800kg. For the same tyre pattern 3.6bar would be suitable for a static axle-load of around 1500kg. You might find that recommended pressures for Goodyear G26 Cargo tyres have a different load/pressure curve, but it's unlikely to be that different. It's a requirement for the USA market that tyres sold there carry data showing their maximum load capability and the inflation-pressure appropriate to that load. You should be able to find this information moulded into your new tyres' sidewalls. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 8, 2006 Share Posted August 8, 2006 A second helping... Somewhere on your motorhome (possibly within the engine compartment) will be a data-plate carrying details of the vehicle's maximum permitted overall weight, the maximum permitted front-axle load, the maximum permitted rear-axle load, and the maximum permitted 'train' weight (ie. the weight of the vehicle plus anything being towed). If you are unable to weigh your motorhome in a representative 'fully loaded' condition, then probably your best option is to inflate its tyres using pressures suitable for the maximum permitted axle-loads. As I said previously, it's likely that the load/pressure profile for a 195/70 R15C 104/102R Goodyear G26 Cargo tyre approximates closely to that of an equivalent Michelin Agilis 81. Axle-load-to-pressure data for the latter tyre are as follows: 1800kg 65psi (4.5bar) 1640kg 58psi (4.0bar) 1480kg 51psi (3.5bar) 1300kg 43psi (3.0bar) (Michelin advise that intermediate figures can be derived via a simple linear graph.) If you are able to obtain accurate axle-weights for your 'van via a weighbridge then Michelin normally suggest that the inflation pressure suitable for the 'static' front-axle datum be increased by 10% to cope with weight transfer under braking and cornering loads. To allow some sort of comparison with your old tyres, Michelin's 195/70 R15C 97S pattern is Agilis 41 Reinforced (essentially a heavy duty car tyre) and its axle-load-to-pressure data are: 1460kg 65psi (4.5bar) 1320kg 58psi (4.0bar) 1050kg 43psi (3.5bar) You can see from this that Agilis 41 with a Load Index of 97 needs a significantly higher inflation-pressure to support the same axle-load as Agilis 81 with a 104 Load Index. This is pretty much what one would expect and the only explanation I can offer as to why your German VW handbook appears to contradict this is that the book-data relate to different VW T4 variants and that you are not taking this into account. The VW section in Michelin's technical booklet suggests that a 195/70 R15C 97 tyre (eg. an Agilis 41) would only be suitable for a Caravelle MPV or small T4 van and that tyres with a Load Index of at least 100 (1600kg axle-load) would be normal for the remaining models. I have to say that your original 'Load Index 97' tyres seem, on the face of it, very puny for what's clearly not a mini-motorhome and that your friend's advice to move to a higher-rated tyre makes perfect sense. Link to comment Share on other sites More sharing options...
Karmann Gipsy Posted August 8, 2006 Author Share Posted August 8, 2006 Derek Many thanks for your help and advice. I agree that the old tyres dont seem to have been very suitable-they were on it when I purchased a year ago and were apparently fitted in Germany prior to import. I am glad that I was advised to upgrade. I am going to try increasing the rear pressures to 65psi as suggested and will see how we go. I have already set the fronts to 53 psi which would seem to be adequate. Thanks again for the advice. Link to comment Share on other sites More sharing options...
Don Madge Posted August 8, 2006 Share Posted August 8, 2006 [QUOTE]Karmann Gipsy - 2006-08-08 7:22 PM Derek Many thanks for your help and advice. I agree that the old tyres dont seem to have been very suitable-they were on it when I purchased a year ago and were apparently fitted in Germany prior to import. I am glad that I was advised to upgrade. I am going to try increasing the rear pressures to 65psi as suggested and will see how we go. I have already set the fronts to 53 psi which would seem to be adequate. Thanks again for the advice.[/QUOTE] John, These are the tyre pressures and axle weights for my Timberland LWB Ducato with a MAM/GVW of 3300kg Tyres. Goodyear Cargo G26 205/70 R15C 106/104R Front axle weight 1680kg (Max allowed 1750kg) Rear axle weight 1620kg (Max allowed 1850kg) This puts me at 3300kg MAM. Front tyre pressure 54psi (3.72bars) Rear tyre pressure 62psi (4.27bars) At present I've done almost 42,000 miles on this set of tyres and there's still plenty of wear left. Regards Don Link to comment Share on other sites More sharing options...
mansell Posted October 16, 2006 Share Posted October 16, 2006 What does everyone find is best for a Hymer Mercedes 640 Starline? Link to comment Share on other sites More sharing options...
Dave Newell Posted October 17, 2006 Share Posted October 17, 2006 As said before, load it, weigh it, contact your tyre manufacturer for their advice. D. Link to comment Share on other sites More sharing options...
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