Grey Funnel Posted October 24, 2006 Share Posted October 24, 2006 My 1992 Hymer 544 has 14" wheels with 185 sect tyres, it moves all over the carrigeway when overtaking/being overtaken. The dealer and my garage have checked the suspension and that's OK, both think the tyre section is too high and is the cause. Later models used 16" wheels with 195x75 tyres. I have been offered a set of 15" or 16" wheels FoC but can not find out the tyre size to use to give the same rolling diameter. Tyre companies do not list this info or reply to e-mails. I also have Airide fitted. HELP Link to comment Share on other sites More sharing options...
docted Posted October 25, 2006 Share Posted October 25, 2006 Grey Funnel It was not later Ducato's that used the larger size wheel it was mainly the turbo versions. That said the size of wheel should not be causing the problem you mention. I had similar size wheels and tyres on my last Hymer with no problem. THe 544 is prone to unbalanced loading with both water tanks, fresh and waste behind the rear axle along with the toilet and kitchen. This is probably the reason the Airride has been fitted. I found it essential to ensure that any weight behind the rear axle was kept to a minimum and any heavy loads carried further forward. From memory I think I kept the Airide at 30psi and this helped give us a smooth ride. Hope this is of help if you require any further info PM me. Good luck Docted Link to comment Share on other sites More sharing options...
Brambles Posted October 25, 2006 Share Posted October 25, 2006 What tyre pressures have you got? Make sure you have the tyre pressures correct for your axle weights. Over inflation not only causes a harsh ride but can also increase the wondering effect when someone overtakes etc. Also important along with this is correct front wheel alignment for tracking, but you did say you had the suspension checked. Jon. Link to comment Share on other sites More sharing options...
Dave Newell Posted October 26, 2006 Share Posted October 26, 2006 Hi Grey funnel, changing to larger diameter wheels with lower profile tyres on to maintain rolling diameter might improve the wandering effect you describe but they will also give a harsher ride quality. The sidewalls of the tyre are actually used as part of the suspension and changinng to a lower profile obviously means there is less rubber there to flex and absorb impacts from the road surface. As the others have already said, look at your loading and get your 'van weighed before you do anything else. D. Link to comment Share on other sites More sharing options...
Grey Funnel Posted October 31, 2006 Author Share Posted October 31, 2006 I decided that the smaller section for same rolling dia would increase stability, ultra low profile tyres do improve grip on sporty car at the expence of ride comfort but going up 1" to 15" wheels should not affect that. However that is now history as the wheels were collected for me and I had some part worn tyres fitted. Two reasons for used tyres, 1. Unless you do a big mileage the tyres have to be replaced before anywhere near being worn out as they become unsafe through age. ( Always used part worn on last camper) 2. There was always the possiblity of the change not working. And it hasn't When I fitted one on a front hub it fouled and on comparing I found the inset is 3/4" greater for same rim width. While waiting for the wheels to arrive I swapped the wheels front to rear and found big improvement, the Toyo tyres do not suit the front of my Hymer, will see what happens when I replace them with a different make. Link to comment Share on other sites More sharing options...
Brambles Posted October 31, 2006 Share Posted October 31, 2006 Hi, think you have just highlighted your own problem, different make tyres on back and front. Are they even the same construction! If you have different make tyres front and rear, or even new/old it will have an affect on stability. Bear in mind suspension set ups and design are based on having 4 tyres all of the same characteristics. Jon. Link to comment Share on other sites More sharing options...
Brambles Posted October 31, 2006 Share Posted October 31, 2006 Futher to last post I do not believe in buying second hand part worn tyres, you have no idea of the history, and indeed even buying a second hand vehicle you have no idea of the state of the tyres and I never feel safe until they have been replaced with new ones. Remember why part worn tyres are available - often removed from crashed write offs I would have thought. Have you also checked the age of the part worn tyres, are the removed because they are 5 ot 6 years old. Not for me I am afraid, but thats just my opinion, and if you have a crash because of secomd hand tyres, do me a favour and don't crash into me!! ;-) Link to comment Share on other sites More sharing options...
vaughan669 Posted November 2, 2006 Share Posted November 2, 2006 I recently departed from 8ply tyres on my 3.85t motorohome in favour of 10ply on the rear and original 8ply on the front. Mistake! The steering wandered so much I ended up putting the 8ply on the rear and the 10ply on the front. Problem solved. Nobody could give me a logical reason for this. Anyway I have replaced the 8ply's with another pair of 10ply. Steers beautifully and a little less wander. The ride is a little harder but there is always a price to pay. As ahother reader mentioned, tyre pressures are critical for axle weight. My tyres run at 79.5psi, which is the recommended pressure for fully loaded. Link to comment Share on other sites More sharing options...
Brambles Posted November 2, 2006 Share Posted November 2, 2006 Hi vaughan, All due respect but I doubt very much you should have 79 psi in your tyres. That is the maximum rating for the tyres. If you are driving a Fiat for example the maximum laden axle weight on the front is no where near an equivalent tyre pressure of 79. More like 60 to 65 max. Only way to be sure of corret tyre presures is to wiegh your axles and comtact tyre manufacturer for advice. It is well worth doing as having the correct pressures will improve road handling, comfort and safetly. Incidently running front tyres at max permissable will give you stabilty issues with cross winds/overtaking another vehicle etc and worst of all grip is vastly reduced when braking especially in the wet. I personally think it is good your four tyres are now all the same, to me it is important to have the same characteristics on all four wheels as that is how the vehicle was designed. Think along the lines of a cross wind evenly on vehicle, if front and rear tyres flex the same amount - you still pointing straight ahead, if the front say flexes a bit more, your vehicle points in a slightly different direction. They also have side oscillations of different frequency and amplitude giving strange effects. Then comes different grip characteristics which can lead to instability, and NEVER (I know you have not) put two different tyres on the same axle. Over to others to comment , maybe I am just babbling a load of nonsence. Jon. Link to comment Share on other sites More sharing options...
Don Madge Posted November 2, 2006 Share Posted November 2, 2006 [QUOTE]vaughan669 - 2006-11-02 11:02 AM I recently departed from 8ply tyres on my 3.85t motorohome in favour of 10ply on the rear and original 8ply on the front. Mistake! The steering wandered so much I ended up putting the 8ply on the rear and the 10ply on the front. Problem solved. Nobody could give me a logical reason for this. Anyway I have replaced the 8ply's with another pair of 10ply. Steers beautifully and a little less wander. The ride is a little harder but there is always a price to pay. As ahother reader mentioned, tyre pressures are critical for axle weight. My tyres run at 79.5psi, which is the recommended pressure for fully loaded.[/QUOTE] Vaughan, You might find the following it useful. I run my Timberland Freedom 11 at the following pressure Front 56 psi Rear 60 psi I have Goodyear Cargos 205/70 R15C 106/104 Q I'm usually running with axle weights at about Front 1650kg Rear 1680 kg with a MAM 3500kg I've done 42,000 on this set of tyres and there's still more there. The Fiat handbook gives so many variations it's a matter take your pick. Don Link to comment Share on other sites More sharing options...
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