175/70-13
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Thread: 175/70-13

  1. #1
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    Default 175/70-13

    This size is optimal for R12 family vehicles on standard rims but it has also been declining in popularity & thus forming a short list of decent tyres to consider has become harder than was once the case. Various froggers enthuse about various particular tyres (in my case, Conti's EcoContact3s & Bridgestone's dual layer tread compound AR10s - both now not available) but an intriguing new candidate might be worth consideration - to wit: Hankook's Kinergy Ex.

    Yes it's an Eco tyre designed for low rolling resistance & that is a priority in some tension with handling crispness & with wet grip (in compound sensitive conditions). Structure & compound are the key parameters for achieving low R.R.. The Ex is intriguing nonetheless as it seems to promise to have both crispness & wet grip.

    One of the major influences on handling crispness is sidewall design & the key is to have low slip angles by having forces applied at the rim transferred to the tread without excessive twisting distortion of the sidewall. Usual ways of achieving this are two.

    One is by means of so called "flippers" - sidewall fabric turn-ups at the bead or extra fabric folds inserted at the bead area. Although not designed with handling crispness in mind, "extra load" variants of tyres usually have two sidewall plies, not one, & this extra layer can add torsional stiffness to the sidewall in much the manner of a flipper.

    The other is by so-called "fillers" - the wedge of rubber in the bead area between the sidewall ply & the turn-up of it after going around the bead wire. Vary the dimensions & stiffness of the rubber filler & one thereby affects the torsional stiffness of the sidewall.

    The Ex is intriguing in that it extends the sidewall ply turn up in the manner of a super long flipper to form a second sidewall ply. Rationale is apparently sidewall strength in resisting inpacts. This is an odd feature in a low R.R. tyre as, when low R.R. is achieved by way of structure, the sidewalls are usually very light to reduce energy wasteful intra-tyre heat generation by way of flexing. They are thus vulnerable to damage & this is one reason why some of the European "green" tyres are not coming to rough, tough Australia (we get the Pirelli P1 "ordinaire" for instance & not the more eco-orientated P1 Verde). Anyway, the Ex has effectively two ply sidewalls & that can only be to the good for handling crispness even if that's not their design purpose.

    It also has hard rubber fillers. This time explicitly meant for achieving handling crispness.

    The Hankook propaganda sheet also explicitly talks about crisp response. To see such a matter given such prominence is a bit unusual in this class of tyre; so this is promising, especially when one can see how this might be actually achieved given the structure.

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    I spend some time on this because tyre sidewall torsional tautness is an important trait for the R12 family's handling feel & response.

    Hankook also make wet grip claims (as is now commonplace, they use silica in place of some carbon black as a compound filler although the detail of this is clearly directed more towards lowering R.R. whilst marginally improving wet grip compared to their unidentified reference tyre).

    No test results of the Ex at this stage but the related Kinergy Eco K425 & the Optimo K415 & K715 have generally tested well. So, all very promising looking: there's some chance of an important size for many froggers having available a tyre that both grips well enough in the wet & handles crisply. I have no direct experience of it but I suspect that it's the class leader (of what's available in Australia anyway) on these two parameters.

    There's some chance of a Tasmanian friend with an R17 fitting them &, if he does, I shall attempt to be permitted to have a fang in it in the wet. Thus, more to follow in due course perhaps.

    cheers! Peter
    Last edited by 4cvg; 6th December 2014 at 01:54 AM.
    addo and Sunroof like this.

  2. #2
    Too many posts! JohnW's Avatar
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    That is interesting - thanks Peter.
    JohnW

    Renault 4CV 1951
    Renault R8 1965
    Renault Scenic 2005 (wife's)
    Renault Scenic 2007 (mine)
    Renault Scenic 2006 (daughter's)
    CitroŽn CX Pallas 1980

    National Co-ordinator, Renault 4CV Register of Australia

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