[Bob.W]

Hi All,

Live in rural NSW, high rainfall area and the paved surface quality often varies from ordinary to horrible (thank you Coffs Harbour Council!).

The stock tyre & rims on the 2018 PD Elite we have is 225-45 R17.  Michelin Primacy 3's on them. Usually run mid 30's PSI all around. But alas the PD seems to have a pretty firm suspension which is terrific on nice roads, not so much here.

Outside the box ideas to assist this - considered acquiring some smaller steel rims & then running tyres with larger sidewall ratio, which could/should be a tad more forgiving on the roads - but I'm not sure if this is essentially going to make SFA difference?

I believe you just need to use a Speedo calibration website like this to ensure you're essentially like for like in overall end size:
Speedometer Calibration

So in theory a 225-45 R17 is near identical in overall external diameter to a 205-65 R15.....or do I have that wrong somehow?

I'll retain the 17" rims and tyres - as obviously look a lot better - and a downside is less rubber on the road for braking, handling etc.

Completely daft idea or has vague merits?   I would not consider anything below a R15, an R16 in 205-55 is again near identical to the stock sizes.

Thanks in advance.

[BrendanP]

I guess the trim levels in Australia differ, but in the UK, the entry level S model had 15" alloys, the SE had 16" alloys, and the Premium had 17" alloys. I would have thought the 15" or 16" wheels would be a substitute for the 17" wheels, unless the brake calipers are bigger. I don't see why they would be unless the car had a lot more power. Is it worth having a look on eBay for sets of wheels?

If there are other members that have a similar car with smaller wheels, they may offer to tell you what their VIN number is, then you can use www.partsouq.com to identify the part numbers of those wheels, and also check the part numbers of the suspension and brake parts to verify they're the same parts as on your car.

[The Gonz]

Many ways to go about acquiring them but as far as your reasoning on ratios and outcome is concerned, that's sound.

[Bob.W]

@The Gonz
Much thanks for the reply - do you feel it would make much of a difference in terms of the ride quality/tolerance to surface bumps or marginal? 

And do you feel the lesser amount of rubber on the road would be an issue?   We're quite conservative drivers so not pushing things to limits etc.

I get a tad confused by rim sizes etc cars need - is it a particular 15" rim only the i30 would accept - read about offset etc with them.

[The Gonz]

@The Gonz
Much thanks for the reply - do you feel it would make much of a difference in terms of the ride quality/tolerance to surface bumps or marginal?

I have no way of quantifying it for you other than to consider the reverse - how much harsher the ride becomes when going low-profile.

And do you feel the lesser amount of rubber on the road would be an issue?   We're quite conservative drivers so not pushing things to limits etc.

You answered your own question with your conservative driving. If the tyres are a legal dimension, they are not outside the safety envelope.

I get a tad confused by rim sizes etc cars need - is it a particular 15" rim only the i30 would accept - read about offset etc with them.

Offset is a real thing affecting track width and possibly panel contact, so do pay attention, but if you're going from wide to narrow, there should be no such concern.

[TerryT]

Hi Bob.  When I got my new i30 SR in 2018 fitted with 225 x 40 x 18” tyres I found that the road noise I heard in the cabin (with windows up) was annoying me when driving on ‘gravelly’ patches of say, the M4 motorway.  I blamed their narrow 40% aspect ratio and the oem brand (Hankook, not known for silent street running).  Have to say I wasn’t put off with their ride, comfort-wise on sealed or dirt roads but then I was probably used to a firmer ride after spending years driving my street/track WRX/STI with its firm suspension setup.

But, I gave up my idea of switching wheel/tyre setups after my cost benefit analysis showed it didn’t warrant the time and effort needed to research and then buy the “best” wheels and the “best” tyres when compared to the miserable mileage I spend in the car…averaged about 2,000 km p.a. over 6 years.  Blame COVID for a lot of that!

You mentioned: “...and a downside [with 15” wheels] is less rubber on the road for braking, handling etc.”  Yes, and while you’re not on a racetrack, that is something I’d think more about before deciding...but you seem a responsible driver so it shouldn't be a problem for you. 

BTW, often the nominal tyre width sizes quoted are different when you put a tape measure over them, especially between brands.  For instance, I found that my street/track Hankook RS3 tyres of 235 x 45 x 17” were, from memory, closer to 215(!) wide after measuring them.   Something to consider, it can be a lottery.

The 15” wheel setup I suspect would give you slightly quicker/lighter steering over your 17” wheel but the size and weight of the 15" wheels and tyres would be an influence.  I believe speedo inaccuracy with your 15” wheel setup is about 2kmh high at say, 100kmh which is not much.  But need to always consciously factor that difference in if you are like many who auto-drive about 5kmh+ over a posted speed limit of 100kmh thinking that the HWP will ignore you.  You would be actually doing closer to 107kmh+ and some of our revenue collectors will take more of an interest in you. 😊

The 16” wheel setup you mentioned is a not-bad compromise.  No problems with the speedo as actual vehicle speed is only marginally below the speedometer’s reading, so no mental calculations to make.  Your suggested 16” setup has the same tyre width as the 15” (which is about ¾” narrower than your 17” oem), so about the same tread on the road as the 15”.  If I am right about steering effort for the 15” wheel, then the 16” would be closer to the oem 17” setup.  But, 16" tyre has less aspect ratio (55%) than the 15" (65%), so less "comfort'. 

BTW, what size is your dinky horrible space-saver spare tyre?  If it's 15" then you shouldn't have a problem with your suggested 15" wheel setup as far as clearing brakes and suspension parts (same if it's 16") but it depends on the new wheels offset (ET).

Now I’ve got this far, I’m thinking that Surferdude would also likely have a better contribution to your question.

Below, my Hankook RS3's with a nominal 255mm width.  I measured them at 250mm wide, which is a lot better than many other tyres I used.

[TerryT]

Bob.  In your original post you mentioned you have a "2018 PD Elite" and in your signature you show "2017 PD 5 door"?  I don't keep up with model variants but 2017 or 2018? 

[TerryT]

Bob.  In your original post you asked: So in theory a 225-45 R17 is near identical in overall external diameter to a 205-65 R15.....or do I have that wrong somehow?

No, you're not wrong.  The two are close enough subject to a couple of minor points I offered in my post above.

[Bob.W]

Hi TerryT,

appreciate the replies - all noted, yes technically it is a 2017 (MY18 coding) but I belive they're for all intents identical sans the complicance plate.

Yes, I'd not make the change if I had to pay significantly for the 15" or 16" rims, but you do often find the OEM sizings sold off very cheaply on FB or Gumtree by folks putting larger rims and low profile tyres on their cars. Its one of those things I'd keep a look out for but not chase - as will it make much difference? Hard to say but I would not think it would be a magic solution - there's a reason everyone out here drives big SUVs etc (mind you tht could also be said of inner city Sydney etc!)

Oh no I have a fullsize spare 17" rim with a Michelin Primacy on it - which I rotate withthe rest of them (always odd to me that folks let their spare die of old age never being used!)

As is normal the Hyundai speedo definitely has that 5% or so buffer of accurate speed already on them - which is weird, why do they not simply give an accurate reading?  Haha why do that on cars but not thermometers, kitchen scales etc. Go figure.

[TerryT]

@ BobbieW .  Thanks for the response and clarification re your year model.

The Gonz pretty much summed up in two paragraphs what I said in a page!! 

You answered: "Oh no I have a fullsize spare 17" rim...".  Good one!  Me to.  I figured you'd be as clever and good lookin' as myself.  The last thing you bushies( )  want is a dinky tyre-saver limiting you to 80kph!

[Bob.W]

I figured you'd be as clever and good lookin' as myself.  The last thing you bushies( )  want is a dinky tyre-saver limiting you to 80kph

Am sure I'm nowhere near as good looking ;-)

Hmm turns out it appears it's illegal to put smaller width rims on your car that the manufacturer does - but bigger is no issue (subject to limitis of course).   So R15's would appear a bridge too far, 16's I think would be ok being that the non-Elite/Premium models that same year came in those (205/55R16).  But I have serious doubts about the 'juice being worth the squeeze' on the hassle/cost of changing those over ie 45 sidewall ration vs 55's.

Perhaps might revisit as an exercise closer to needing new tyres but that'll be a decent way off. Honestly as great a lil car as it is - just real suited to these bodgy roads - and a total change to another car would likely give better bang for buck than piecemeal efforts like this.

[TerryT]

...So R15's would appear a bridge too far, 16's I think would be ok...But I have serious doubts about the 'juice being worth the squeeze' on the hassle/cost of changing those over ie 45 sidewall ration vs 55's.

"...doubts about the 'juice being worth the squeeze'".  That's a good saying.   Was the same for me in my wheel/tyre combination exercise.