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Why do people "up size" their after market tyres?

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  • Why do people "up size" their after market tyres?

    Hi, I wonder if people can share why they purchase larger diameter tyres when replacing the standard tyres.

    For example instead of opting for the same 265/70R16 size as per standard, they purchase 265/75R16 (while still using the standard rims).

    We thought that when lowering the tyre pressure :
    - the 75 ratio will allow the tyre diameter to drop maybe back towards around 70 so the ground clearance would not suffer so much
    - and it will bulge more to give that extra bit of traction

    Are they true?

    Are there any other reasons?

    Wouldn't the speedometer accuracy problem or the reduced torque be an issue when the tyres are inflated to normal level?

    How about fender / underbody clearance?

    How about the legalities?


    Thanks and regards,

  • #2
    265/75/R16 are the MOST common tyre size used on 4wd's in Australia - lots of makes, tread patterns, load ratings, ply ratings etc etc in that size.

    "the 75 ratio will allow the tyre diameter to drop maybe back towards around 70 so the ground clearance would not suffer so much"

    I used to think the same thing, but any increase in tyre size will increase ground clearence, floatation and in turn, more traction.

    In the regards to speedo - the increase in tyre size from a 265/70 to 75 is negligable on the speedo reading to actual speed. If you were to jump to a 285/75 or 255/85 you would certainly find a difference.

    Generally doesn't interfere with fender clearence

    A tyre increase in that size is legal in most states.

    Cheers,
    Jayden
    NP GLS DID Auto: ARB Bar, Warn XD9000, Rear ARB Locker, Dobinsons, Bilsteins, 33" BFG MT's, 61Lt Sub Tank, Striker 170's, Dual Batts, etc. etc. etc.

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    • #3
      Exactly what Ranger J said above. Bigger tires are better to a certain point. With my 285/75s I noticed about 5-7mph or so off at cruising speed. So not to bad but you have to think about it while driving. Another thing that you need to think of unless you regear the differentials is the Fuel Economy will drop some as well if you go bigger. Thats the only negative I have found. But hey,... its worth it.
      03 NP, 34" tires, Fully skiplated, Custom rocksliders, custom winch mount, OME HD springs/shocks, and Aeroflow exhaust, Locked Front and Rear.

      Happiness is like peeing your pants, everyone can see it, but only you can feel the warmth.

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      • #4
        Can you get different diff ratios for larger tyres in NM/NP?
        --
        Marquis
        SOLD - NT MY10 DiD, ARB D/Bar, Airtec, LRA 81L, Bil/Lov 2", BCDC1220+AGM, P3

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        • #5
          One of the main reasons was that there were not many tyres available in LT rating in 70 series - you had to go to 75 to get them. A note of caution is that in NSW at least, changing from 70 to 75 series is enough to be over the RTA allowable diameter increase.

          Pat
          2016 Mitsubishi NX Pajero GLX
          2011 Landrover Freelander II SD4

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          • #6
            Thanks

            Thanks all for the replies.

            It is interesting to read that we can be legal in one state but might no longer be when driving cross our state borders.

            I opted for the exact same size when replacing the factory tyres so for now I wouldn't need to worry.

            Best regards,

            Jonathan

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            • #7
              Originally posted by psproule View Post
              One of the main reasons was that there were not many tyres available in LT rating in 70 series - you had to go to 75 to get them. A note of caution is that in NSW at least, changing from 70 to 75 series is enough to be over the RTA allowable diameter increase.

              Pat
              Same for Victoria (currently) - this change is more than the 15mm permitted. Hopefully the proposed guidelines for 50mm get adopted by all states.

              BF Goodrich are about the only AT tyres available in 265/70R16 with LT construction - so if you want another brand tyre with LT construction, or mud tyres, you need to go to 75.

              The extra traction effects from lowering pressures isn't because the sidewalls bulge (the tyres would need to be 0psi for BFG ATs to get extra traction this way - have a look at the shape of the tyre - it's straight sidewalls with a square edge on the tread when viewed front on), but to lengthen the "footprint" of the tyre. So more tread and surface area on the ground lengthwise, not sideways.
              Ben

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              • #8
                What he said.... and
                bigger tyres mean you can crawl over things more easily. Just think of your little skateboard wheels getting stuck on a stone when you were a kid... A larger wheel just crawls straight over it. The only down side to fitting larger wheels is that your low range isn't quite so low anymore in the rough stuff and you might find your dropping down a gear on the road where you wern't before like up hills.

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                • #9
                  hello
                  I have BF Goodrich A/T 265/75/16
                  They work great at low pressurs in sand mud loose gravel and on the road i run them at 38 psi with no dramas, although they are noisy at speed
                  But above all ,,,they look really cool BUT only if the
                  'WHITE WRITTINGS ON THE OUTSIDE' Think i might start a white-out club !!
                  cant understand people that hide it on the inside ??
                  hope i havnt opened a can of worms here !!?
                  NX ARB bar totally stock,, for now and the trusty old NM Exceed ,Injected LPG. ARB Sahara bar 12000lb Tigerz11winch,Lightforce genisis ,2x stealth LED bars, rear LED reverse light, GU Patrol black wheels 32"BFGs ,custom alloy roof rack with twin awnings,, snorkel, Milford barrier, custom rear storage ,triple batteries,fridge slide,Pioneer touchscreen unit, 50L Waeco,UHF,lots of scratches down the sides, new super powerful engine!,bash plates, 3" lift,polyairs Dobinsons,extractors ,Maxtrax

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                  • #10
                    Originally posted by green monster View Post
                    they look really cool BUT only if the
                    'WHITE WRITTINGS ON THE OUTSIDE' Think i might start a white-out club !!
                    cant understand people that hide it on the inside ??
                    hope i havnt opened a can of worms here !!?

                    You probably have opened up a can of worms!

                    When i upsized to my current set, my research didnt include how the writing of the tyre was displayed! To me it was a non-issue.
                    Turns out when the tyres got put on the wheels and subsequently on the car, the white writing is on the inside.
                    Ok i admit that it probably does look good on the outside [be good to see what it would look like though on mine] but honestly it does not worry me.

                    4000 or so K's later they still look in tip-top condition and perform beautifully- thats what im after!

                    Oh, and i upsized for the ground clearance- got 40mm and all legal
                    '99 NL Escape, Manual - Bullbar, roofrack, cargo barrier, D697LT, Tough Dogs, dual batts, rear draws, Narva 225 HID, UHF, led bar etc
                    Towing: 4.8m Savage Centurion half-cab w/75hp Mariner

                    '99 NL GLS SWB, Auto - Bullbar, D697LT, spotties, UHF, Koni adjustables & King springs.

                    Wanted: Adventure.

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                    • #11
                      inside

                      Hiya,
                      The shop asked me before they put the tyres, in or out, and I opted the white writing on the inside.
                      I suppose it is personal taste but also I am a shy person although it is hard to look inconspicuous in a vehicle weighing 2 tonne plus, sits high (suspension upgrade) and aggressive looking tyres.
                      Cheers,

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                      • #12
                        Spoke to MM today about increasing tyres size (to 265/70 R17's) and their response was there would be no affect on the new vehcile waranty so long as the tyres were within the size/diameter specification set down by VicRoads.

                        Sorry to whip a dead horse, but I decided to again re-visit the VSB14 approval issue and got the run around from VicRoads. Ended up going into a VicRoads office and asked them directly about VSB14. According to them they haven't been issued with VSB14, nor has it been published on their website (or distributed internally) and thus it's not been approved for use in Victoria. Checked the list (see link) and there's no #14. According to the advice they gave section 8 of the ModificationGuide #8 applies....

                        http://www.vicroads.vic.gov.au/Home/...icleStandards/
                        NS oil burner shorty

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                        • #13
                          Is VSB14 is in in NSW?!?

                          VSB's used to be hosted on the RTA website. In the last week they moved them to here, and the appear to have included VSB 14 - National Code of Practice for Light Vehicle Construction and Modification (NCOP).

                          But then they make the following statement:
                          "The Preface and Introduction to the NCOP cover the relationship between the NCOP and jurisdiction's administrative requirements in more detail and should be read by all those who wish to use the NCOP.

                          Certain jurisdictions will need to make changes to their administrative arrangement in order to fully implement the NCOP. Prospective constructors or modifiers should contact the jurisdiction in which a vehicle is to be registered or modified to determine the most up to date information about the business rules or transitional arrangements that may be in force.

                          Please do not contact the Department of Infrastructure,Transport, Regional Development and Local Government about the NCOP. The Department provides the central NCOP website as a service only."
                          Last edited by psproule; 30-05-08, 07:43 AM.
                          2016 Mitsubishi NX Pajero GLX
                          2011 Landrover Freelander II SD4

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                          • #14
                            Originally posted by green monster View Post
                            I have BF Goodrich A/T 265/75/16

                            hope i havnt opened a can of worms here !!?
                            Admitting to BFG A/Ts? Brave move, but I don't know about "can of worms"

                            Size wise, going from 265/70R16 to 265/75R16 is (roughly speaking) 31" to 32", or approximatley 3%. From a gearing/fuel economy/performance viewpoint I believe the change is negligible.

                            "Roadworthy"? Technically, no. "Unsafe"? Definitely not.

                            Benefits of the larger tyre: as noted, most common 16" tyre in the country - largest choice, most likely to find it in remote areas. LT versions also have a very high load rating, which (to me) means it is a tougher tyre, less likely to be adversely affected by vehicle load/rough roads. I agree that larger tyres do have benefits offroad, but I think a 3% difference, on it's own, wouldn't be significant enough to justify the change in this instance.

                            Oh, and laughing at BFG A/Ts? That might open a can of worms.
                            NT Platinum. DiD Auto with 265/70R17 ST Maxx, Lift, Lockers, Lockup Mate, Low range reduction, LRA Aux tank, bull bar, winch, lots of touring stuff. Flappy paddles. MMCS is gone!

                            Project: NJ SWB. 285/75R16 ST Maxx, 2" OME suspension, 2" body lift, ARB 110, 120l tank, bullbar, scratches, no major dents. Fully engineered in SA. NW DiD & auto in place - a long way to go....

                            Scorpro Explorer Box

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                            • #15
                              Have had Yoko's, Pirellis, Coopers and now BFG AT's. Am very happy so far with them.
                              2016 Mitsubishi NX Pajero GLX
                              2011 Landrover Freelander II SD4

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