Rear tyres R17 225/45 or 245/45?

[Vitalijus]

Which size would You recommend from Your own experience ?

Does it make any real difference (in practice not only in theory)?

[Linas.P]

For winter tyres 100% 225, they will actually be better for driving in winter, you can also go for 225/50 if you want to keep speedometer indicating somewhat similar speed as before. I had square 225/50 for winter and they were great.

For summer, I had 235, 245 and 255 and I probably would go for 225 or 235 in future. Basically, 245 and 255 in my opinion ruins the balance of the car. Lexus did it deliberately, because understeering is considered "safe" by those who can't drive, but I find it just annoying. 225 in front and 235 in rear would give you perfect balance, or as close one could get to it i.e. car would neither understeer, nor oversteer and if you go past the limits all 4 wheels will slide (which in IS250 is not very likely). Square 225 set-up would make IS250 feel like RWD car should and there would be slight oversteer, which could be fun combined with the right skill. And I don't mean it would be unsafe or anything, it is not very powerful car, 225 is plenty to keep it on the road, but the balance will be little bit more natural for RWD, little bit of oversteer. Nice bonus - if you have square 225, then you can rotate the tyres and that means set will last longer as you can wear them down more evenly. Keep best tyres always in the rear. That said 225 will look a little bit silly in the rear on standard wheels and offsets, so 20-25mm hub centric spacer would be nice.

Also remember entry-lever IS250 came with 205/55/16... so 225 is really PLENTY for this car.

[Vitalijus]

So, in a real life 245/45 is not that popular (as a summer tyre)? 🙂

[Linas.P]

I think most people replace tyres like for like, very few people I know experiment with the sizes. But from early on I never liked how IS250 handles, my first one was F-Sport with 18", so it is even worse 225/255. I just hate that you come to the corner with RWD car, accelerate mid-corner and it pushes out the front end. It not suppose to be like that. 

And all that is just tyre widths/grip. Wider summer tyres have more grip in dry, so automatically if you get way narrower tyres in front and way wider in rear - your front will lose grip before rear, despite car being RWD. This is done for "safety", because assumption is that driver is inexperienced and will not know how to handle oversteer. Basically with such rear balance you can push car as much in corners.

Again - I assume most of car will have whatever was fitted on them from factory, so they will have 245s in the rear. But that is neither best tyre size for the car, nor really there is any need to stick with it. As for 245/45/17 not being most common tyre size in general... yeah it could be.

[Vitalijus]

And do the 245/45 tires require any corrections to the headlights, i.e. raise them up? (My height control sensor (89406-30140) is broken and I'm not going to invest 640 EUR in a new one).

[steve2006]

If it’s just the actuator rod that has broken you can easily make one for a few €€s and a little time, in the UK that would result in the annual test (MOT) being failed

[Linas.P]

2 hours ago, Vitalijus said:

And do the 245/45 tires require any corrections to the headlights, i.e. raise them up? (My height control sensor (89406-30140) is broken and I'm not going to invest 640 EUR in a new one).

So that depends on the tyre circumference. As I said if you go for 225/50, then circumference is close enough not to cause issues.

2 hours ago, steve2006 said:

in the UK that would result in the annual test (MOT) being failed

Not necessarily, as long as the level of headlights stays correct it would pass. It basically then becomes manual adjust. 

But you right, that is what I have on my GS300. Some idiot somehow managed to brake actuator and previous owner then fixed it with piece of metal and few screws. Looks really dodgy, but in principle it works. 

[Newbie777]

I have 245/45/19 on my Lexus LS600hl and 245/35/20 on my other car (Bentley Continental GT) So great on the big heavy cars. Not sure how 245 will ride on your car.

[H3XME]

On 1/27/2024 at 9:40 PM, Linas.P said:

225 is plenty to keep it on the road, but the balance will be little bit more natural for RWD, little bit of oversteer. Nice bonus - if you have square 225, then you can rotate the tyres and that means set will last longer as you can wear them down more evenly. Keep best tyres always in the rear. That said 225 will look a little bit silly in the rear on standard wheels and offsets, so 20-25mm hub centric spacer would be nice.

Also remember entry-lever IS250 came with 205/55/16... so 225 is really PLENTY for this car.

+1 

GOOD 225s is plenty. Michelin Pilot Sport 5s etc. Better mpgs, enough traction and doesn't make the car so dull to drive.

 

[BkS]

225/45/17 is the best size. Keeps handling neutral, and these cars don't have enough power to cause a loss of rear grip unless you're purposefully giving it some welly in the wet. You don't have to worry about headlight alignment or anything like that.

Overall height difference going from a 245 to a 225 is 18mm in the rear. The benefit of going to a smaller width tyre includes lower rolling resistance which decreases fuel consumption, as well as improving driving dynamics. 

You will absolutely need a 20mm spacer otherwise the rear wheels will look lost in the rear arches.