Grey Funnel Posted October 23, 2006 Share Posted October 23, 2006 A couple of years ago there was corespondence in Interchange re difficulty in changing gear when the gear box heated up, think the boxes were Fiat Ducato. Anybody recall how the problem was cured as I have this occuring on my 1992 Hymer 544. The Hymer weaves when overtaking/being overtaken on motorways. My garage feels the tyres are to blame as they are full section and appear tall. Tyres are185x14, would like to fit 15" or 16" wheels (freebies) but can not get any info on which aspect ratio would give same rolling diameter. Any clues where to look? Link to comment Share on other sites More sharing options...
Guest Peter Harnden Posted February 8, 2008 Share Posted February 8, 2008 Ref Rolling Radius Tyres Go to any competent tyre specialist and they can refer to the michelin tyre manual, this gives all the information you require. Most experienced tyre fitters will give you this info Link to comment Share on other sites More sharing options...
Derek Uzzell Posted February 9, 2008 Share Posted February 9, 2008 Grey Funnel: I was going to mention Delphin Designs (gear-change problems) and Airide (overtaking sensitivity), but I note that, when you raised these issues in 2006, a) that company was suggested to you then as a source of advice and b) your Hymer already has 'air-bags'. I don't think changing the tyre specification will provide a magic cure, but (for what it's worth) the rolling circumference of a Michelin 185 R14 Agilis 61 (or 81) is given in Michelin's handbook as 1970mm. The nearest equivalent for a 15" diameter wheel would be a 205/65 R15 Agilis 51 (1960mm), but I'd be more tempted to opt for a 195/70 R15 Agilis 81 at 1985mm. If you just wanted to lower the profile a touch, then a 195/75 R14 Agilis 81 (1965mm) would do this and save messing about with changing wheel diameters. (All these alternative tyres have a load-bearing design-capability at least as high as the 185 R14 Agilis 81 and similar size/specification tyres from other manufacturers will have rolling circumferences and load-bearing capabilities similar to the Michelins.) Forget 16" wheels as all 16" 'commercial' tyres have a rolling circumference above 2000mm. Any plan to alter a vehicle's original wheel/tyre size obviously needs to be undertaken with circumspection to ensure the change has no adverse impact (eg. wider tyres contacting the wheel arches). Link to comment Share on other sites More sharing options...
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