Tyre Sizing for New Rim

Hi current wheel size is 185/70/R14

I want to get 16x8 wheels but need to use 205/45/R16 but it is technically not allowed.

Will 16x7.5 be ok to run 205/45/16 set up?

Option 1 16x8 205/45/R16
Option 2 16x7.5 205/45/R16
Option 3 15x7 195/45/R15

Comments

  • There's more to a wheel than just it's width and diameter. What's the offset? What's the size and offset of the current wheels? Is the change in track legal where you are? A 205 will fit on a 7.5 wheel but it'll be stretched and look ridiculous though not as much as the 8" width. While there's some variance in tyres, for a 7.5 you should really be looking at a 215

    • New wheel is +20 offset idk what the current is I think it might be +45. Can't do 215 as increased width in tyre may cause fender issues

      • Can't say for sure without all the specs if there'll be fit or legal issues but it sounds like you need a 6.5 - 7" wide wheel.

        • 7.5 smallest I can find in this design

          • +1

            @Importmonster: Then you need another wheel design or a different vehicle. Let's assume the old rim is 6" wide and +45 offset. Your new wheel is going to be push out towards the guard by around 45mm. If that somehow fits without fouling you're also going to exceed the max allowed 25mm track change meaning the vehicle wouldn't be road worthy and insurance void.

            • @apsilon: It does fit I've seen it, fenders rolled on back

            • @apsilon: How about 15x7 with 195/45

              • @Importmonster: It still depends on the offset. Legally you can only have a max track increase of 25mm (12.5mm per side).

                • @apsilon: Sorry the current offset is +40 with 14x6 how do I measure the offset I can get away with? Can I use a 25 offset

                  • @Importmonster: You should do the math as ultimately you're the one responsible but you've got ~25mm wider wheel and 20mm difference in offset so I think it'd be well over the allowed change.

                    You could look into what's involved in having the new wheel engineered to be legal. No idea how that works in VIC.

                  • @Importmonster: Is "40" printed at/near the hub side of your existing wheels? Are your existing wheels factory or aftermarket?

                    Sometimes it is best to start from the make and model, then go from there (in case you have not already done so): https://www.wheel-size.com/

                    • @dazeet: Yeah they are original basically stockies with wheel ornaments on top. I'm thinking i might just keep the car OG for now.. Couldn't see 40 on the inside of the hub. Also the website you linked has incorrect information for my make and model.

                      • @Importmonster: Apologies Importmonster for being unclear. The markings are usually found on the inside of the wheel. For example, this wheel is 17x8 with an offset of 55.

                        No worries then - as long as the error is with the web site, and the current factory wheels are meant for that particular model, and not the other way around. For instance, a regular Lancer that usually runs factory "46" wheels, but instead has Evo factory "38" wheels on it (just hypothesising here - not sure in this particular case if it will cause clearance issues without further mods!).

                        I also find this web site helpful with experimenting and documenting the specific differences.

                        All the best with this if and when you wish to revisit this again :)

  • https://tiresize.com/comparison/
    helps pick same rolling diameter (or within local guidelines if you look them up on your state government registration site)
    FYI - the tyre you have specified would actually be too small in diameter to be legal in SA (assuming the 185/70-14 is smallest on tyre placard of the vehicle)
    .

  • Why not go up to 17"?

    Which state do you live in?

    • VIC, 17 won't work

      • Why not?

        205/40R17 on 17x7" rims

        Rolling circumference difference of about 3% and will look sweeter

        • Can't find any mesh design In 17x7 also its also old school not performance so might look odd with 17s

        • Isn’t it a max 2” increase in rim diameter or you need engineering?

          • @Euphemistic: Not in VIC

          • @Euphemistic:

            the overall diameter of any replacement rim and tyre must not be:
            1. more than 15mm greater than largest diameter tyre specified by the vehicle manufacturer for that model or vehicle series; or
            2. more than 15mm less than the smallest diameter tyre specified by the vehicle manufacturer for that model or vehicle series

  • With a username like that I would have thought you would just run what ever tyres you want and then borrow canary tyres from a mate when you get defected?

  • +1

    yes, go big stretchy boi

  • +1

    Some types of wheel need different types of wheel nuts. Also check out the bore size.

    My guess is your car is FWD. If yes, that offset will put extra stress on your front wheel bearings and drive shaft angle.

    • +1

      drive shaft angle.

      Wheel offset has absolutely nothing at all to do with shaft angle.

  • -1

    Does your car have a pre-collision safety system? if you do, do not change the radius, if you do, your vehicle will not function correctly and it may fail to save you and/or your loved ones, should the unfortunate happen.

    • +1

      Nope no fancy tech like that not even an air bag

    • That sounds like a bit of an urban myth. If you have a link to relevant studies or factory recommendations would be good.

      collision sensors use radar/cameras etc to measure distance to other objects. Wheel rotation is measured by rotation sensors for maximum braking force. Factory wheels are likely to vary in diameter between models due to change in rim diameter and different sized tyres, then it’s probaky also calibrated to account for tyre wear (tyre diameter shrinks as tread wears off)

      • Definitely not an urban myth :) I’ll ditch the Pre-Collision System wording and stick to Collision Avoidance System (CAS) here.
        https://ec.europa.eu/transport/road_safety/specialist/knowle...

        collision sensors use radar/cameras etc to measure the distance to other objects.

        This is correct.

        Wheel rotation is measured by rotation sensors

        Correct as well. They are called Wheel Speed Sensors.
        Now C=2πr (C=πd) comes in. r(radius) = d/2 (d=diameter). C = Circumference, which is the distance a wheel travel per 1 revolution.
        There are scholarly articles published by universities that you can find on the basics of CAS.
        However, what you have asked for is just as simple as the above.
        If the wheel is 16 inches = distance travelled per 1 revolution is 100.53 inches (255.3462 cm).
        If the wheel is 17 inches = the distance travelled per 1 revolution is 106.81 inches (271.2974 cm).

        then it’s probaky also calibrated to account for tyre wear

        Yes, tolerances are there for minor variations, before you have any issues with CAS due to tyre wear, you will have grip issues. To give you some context, tread is measured in mm.
        You can read about how a wheel speed sensor work by following these links.
        https://en.wikipedia.org/wiki/Wheel_speed_sensor#Speed_senso...
        https://www.bosch-mobility-solutions.com/en/solutions/sensor...
        https://www.youtube.com/watch?v=YeXlmdlXp2s
        https://electronics.stackexchange.com/questions/408970/how-d...
        ABS comes into play here. When braking, the vehicle systems needs to find which wheel is slipping (helps with TRC) and which wheel is locking up, and that’s why wheels have wheel speed sensors. and yes, each wheel gets a wheel speed sensor.
        Different manufacturers use different technologies to achieve CAS, so it can vary a little, but not wildly, as the principle is the same.

        factory wheels are likely to vary in diameter between models due to changes in rim diameter and different sized tyres

        Manufactures can offer different wheel sizes at times to "upgrade". When they do, CAS is programmed for the pre-determined wheel size.
        CAS is achieved by multiple systems working together at once and speed sensors play a critical role in this. As per the above, if you have a different radius than what the manufacturer specified, CAS will not work as intended.
        This is how CAS in Toyota known as PCS works.
        https://www.youtube.com/watch?v=gbnoFbb8G8Q

        Having said this all, you can still change the rim size then get a reduced sidewall tyre (low profile tyre) to keep the diameter the same.

        • None of the links you provided indicate changing the overall diameter of the wheel will affect the CAS. I wouldn’t be surprised if these modern systems use GOS to help the computer determine road speed. The CAS will rely on the speed differential between the obstacle and the vehicle, actual road speed is less important. It’s all about how fast the GAO is closing and wether the vehicle can stop before crash.

          ABS systems have no concept of road speed, it’s all about wheel rotation speed. They brakes are applied hard enough to lock the brakes for a split second then back off a bit, then ally again. Not much more than that. .

          Manufactures can offer different wheel sizes at times to "upgrade". When they do, CAS is programmed for the pre-determined wheel size. CAS is achieved by multiple systems working together at once and speed sensors play a critical role in this. As per the above, if you have a different radius than what the manufacturer specified, CAS will not work as intended.

          I’ll bet they don’t rely on reprogramming the wheel diameter from the factory. Yes, different sized rims will have different sized tyre to make a similar diameter overall, but it will most likely be close enough for he system to cope with, not dissimilar to work vs new tyres.

          Sure, if you step outside the orange res too much it’ll cause issues, but I’d guess if you don’t exceed the ‘not engineered mods’ you will most likely still have a fully functioning vehicle.

          • @Euphemistic:

            None of the links you provided indicate changing the overall diameter of the wheel will affect the CAS

            All CAS systems developed by each manufacturer are proprietary. I will not disclose the ones I have access to just to prove a point in Ozbargain, besides I'll be breaking company IP. If you dig enough, you may be able to find it in a repair manual, it will not explain everything.

            ABS systems have no concept of road speed, it’s all about wheel rotation speed. They brakes are applied hard enough to lock the brakes for a split second then back off a bit, then ally again. Not much more than that.

            Wrong, ABS is much more than that, and no they don't lock brakes.

            I wouldn’t be surprised if these modern systems use GOS

            Did you mean GPS? If not I'm sorry for the misunderstanding, but if yes, No!! GPS is very unreliable. Reception is subject to a multitude of external factors(weather, built-up areas with high rises, interference..etc) and can be inaccurate. The most reliable way for a vehicle to find the speed of the car is by observing the vehicle itself, that's why Wheel Speed Sensors are still in use from F1 cars to everyday mass-manufactured vehicles.

            It’s all about how fast the GAO is closing and whether the vehicle can stop before a crash.

            I think you meant Gap? While the gap matters and one piece of the calculation, stopping a vehicle before a crash means getting the momentum of the vehicle to 0. p = mv (p=momentum, m=mass v=velocity). If you don't stop the vehicle momentum will not be 0. Newton's first, second, and third laws (Newton's laws of motion) will apply which means damage.

            I’ll bet they don’t rely on reprogramming the wheel diameter from the factory

            Wrong. They set the parameters as per the factory-fitted wheel size.

            • @KMeister: Apologies for typos. My fingers are fat and my screen is small.

              Does the CAS system rely on the speed of the vehicle, and in what sense? I don’t need specifics or proprietary systems, but understanding how they work will really help. In my experience, when the manufacturer says something doesn’t work it is more likely they want to sell you proprietary stuff than it not actually working wit third party stuff.

              As for GPS. I didn’t meant that it is only what the vehicle uses, but that it is probably used to verify the vehicle computer speed reading. Had a bicycle computer that did that years ago, compared the two readings, then used the wheel circumference/rotation to record speed.

              You misread my comments (or I mistyped). ABS brakes read the wheel speed, and as it approaches lockup, releases and reapplies the brake pressure to maximise the stopping power doesn’t it? If it’s more than that, care to comment on what more it does? I’ve experienced ABS systems working and that’s certainly what it feels like.

              If the factory resets the wheel size into the CAS in order for t to work properly does it tell you when it’s different? Does it recognise that a space saver spare tyre is installed and let you know the system will malfunction?

  • You can't go any bigger than 16" as your only legally a +2 fitments and 17 would be +3.

    Any decent tyre and wheel reseller should be able to tell you what offset and width you can go so as to not exceed track widths

    • +2

      Per above, there seems to be no limit on increasing rim diameter in the vehicle mod guidelines. Width has a max 25mm increase, tyre diameter has max increase but not rim size.

      • It's an ADR nation wide

        • Can you provide a link. If this is true I’m surprised it’s not mentioned in the guidelines.

            • @Stevek1960: The rim diameter +2 thing appears to only apply in WA. There is no mention of rim diameter in the other states listed. I actually linked that article earlier.

              Track width, rim width and overall wheel diameter are mentioned in all other states.

              This is consistent with my other searching. I have found no other reference to rim diameter ‘+2’ in NSW, Vic, Qld or SA.

              • @Euphemistic: I am in qld and it applies and have also lived in nsw where it also applies.
                ADR means Australian design rules not Victoria design rules

                • @Stevek1960: Link please. I can’t find it. The link you provided only indicates it’s necessary in WA, ADR or not.

                  This link: http://club4x4.org.au/wp-content/uploads/2015/10/14-017-VTDA...

                  Says “Commonly touted wheel/tyre replacement options, of ‘Plus 1’, ‘Plus 2’, ‘Plus 3’ do not identify specific sizes and are not recognised by VicRoads”

                  I’ll happily accept your assertion it’s in the ADR, if you can show me. Otherwise, I don’t think it’s a thing.

    • Yes they said not legal but can still do it

    • Maybe in Qld but not in Vic

      • It's an ADR which is nation wide

  • 45/16 alternative should be a 50/15 or 55/15, not 45/15. Else your gearing will drop and speedo will be out too far.

    • Thanks, sorry 50/15 is what i was meant to write. Think im just going to do the 45/16

      • Wrong

      • Unless you are running MASSIVE tyres, or your car is very low, you should have no scrubbing at all on the guard liners

      • Suspension geometry won't change with tire size

  • It will peal off

  • What car?
    Depends how 'legal' you want it.

    Ride height will 100% impact fitment too, you can have a wheel that will sit outside the guards, but when the car is lowered and you get a bit of camber, it can fit.
    Tire size, youll ideally want to match the OD as close as you can.
    Tire width is also impacted by the brand and type of tyre - I'm running a 205 semi slick on a 6.5" and its a BIG tyre, and bulges out quite a lot. On a more road oriented tire, this wouldn't be such an issue.

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