RX450H 20 inch upsized tyres?

[YvesD]

Hi, apologies in advance, I saw a post from someone a good while back about fitting wider tyres on the RX but try as i might, cant find it again.

I would like to fit either 255/50/20 or 255/55/20 to my car to improve the overall grip on the tarmac and also to improve the aesthetics. For the size and weight of this car it

always seems a bit 'under tyred' to me. Adequate, but could be better.

Anyone with experience of doing this on the RX please?

Thanks

[Bob450]

Hi, I have a NX450h+ with 20" wheels and I spent a lot of time researching tyres because of persistent noise problems. The two tyre sizes you mention are different diameters/circumferences and (since one of them is the original diameter) there is more than a 3% difference. This meant that the speedo reading netween the two will be different, with the possibility of speeding charges for the bigger tyre. Edit https://tire-calc.com/comparison/255-50-r20-and-255-55-r20/

As you mention, these are "wider" tyres. What size is the wheel? I would imagine that the RX450 would have as original 235/55 R20 on 7-1/2" J rims or just possibly 8" J. The wider tyres might possibly not make a proper seal on the 7-1/2" rim. I don't know if this is correct in your case, but there is a lot of information on the net regarding tyre size calculations which might be helpful. Good luck with your search!

Edited September 26 by Bob450
Added tyre size calculator address

[YvesD]

Thanks for your thoughts Bob, appreciated.

I did check the speedo error calc with an online tool and in my case it would pretty much erase the +3mph over my speedo reads compared to road side monitoring signs and independent GPS readout. 

The OEM rims are 20 inch 8J.

I've actually bought an old RX wheel and a used 255/50/20 off eBay and had them mounted. No fitting issues and the extra width looks right and affords extra rim protection.

For reference, the 255/50 tyre is very close to the original 235/55 in overall size, near as makes no difference.

Not got round to mounting the wheel on the car on each corner to check for clearance but not expecting any problems.

Cheers

[YvesD]

Love this stuff 😊

[Big Kev]

I find this of most interest by the fact the sidewall height increases expothingymybob, as the roads in Scotland really are now only fit for armoured tank testing. I  would presume this may lend an element of better rebound out of the potholes. Something I find very disconcertifying is how firm the RX450 suspension is, very similar to all my Rav 4s. This I did not expect on a purported “luxury” marque. Yet everybody raves aboot the smooth quiet ride in that country across the Atlantic where guns are sold with Mars bars….their roads I know to be far, far smoother.

 Your increased tyre width certainly looks the bog’s dollocks and more car relelevant, but watch what excuses you hand your insurance to welch. Totally unnecessary photo…….superb momocar.

[Ray Green]

Dave if you fit them please show a photo or two and rough cost of changing all wheels and tyres they look impressive 

[YvesD]

Morning 😊

I would keep the OEM wheels and just mount the tyres.

A full set of what I have now which are budget but perfectly fine would be about £350 fitted.

A full set of top end All Seasons which I fancy about £750.

Insurers no doubt would demand a totally unjustified premium to the Zero additional risk.

 

[Big Kev]

Methinks that budget tyres on an Rx450:would be a  really bad move.

[Bob450]

I agree with Big Kev. Go to this site and do the calculation for the two sizes, 50 and 60. https://tire-calc.com/ It says that the difference is more than 3% for 255/60 and 255/50 and can be dangerous. For 235/50 and 255/50 the difference is OK.

In addition, wider tyres than oem may be more prone to acquaplaning, and they will cause more mudsplash on the car.

[YvesD]

Ooh, you're a conservative lot🤣

[GSLV6]

There is no lack of traction with the factory wheel and tyre sizes.  Going lower profile and wider won't make a lot of difference but will stiffen the ride and make it less comfortable.  I use Turanza tyres on mine and the grip from those is amazing, wet or dry.

[YvesD]

So, I've been doing the proper due diligence on the alternative tyre fitting today. Man these wheels are heavy🤪

Pictures don't do it justice really, poor lighting conditions, but there are no clearance issues front and rear, looks 'right' 'feels' right.

I measured the Ride height from tarmac to underside of black wheel arch trim. This reduced 4mm front and rear. Exactly as the online tyre calculator predicted. Visually from the side, no different to the eye.

Increased width tyres do not stick out further than the mud guards.

255 tyres have a pronounced 'bulge' to the side wall, again,it doesn't look out of place and of course, more protection for the rim is afforded.

Measured the clearance from top of tyre to underside of the front suspension spring cup. As far as I could tell, 25mm both cases.

As GSLV6 rightly says however, there's no problem with the grip of the standard set up, totally agree.

I'm looking at it from an aesthetics viewpoint only and to me a wider tyre looks better.

Cheers

Note. Photos to follow, need to re-size them

[Bob450]

Well done! The result is very good looking. Both of the tyres have the protective "bead" for the rim edge, but the new ones are very good because they protect the wheel side from curb contact. Happy driving!