High speed cornering

Linas.P · June 21, 2018

I though IS200t was only sold in F-Sport and Premier Trim, hence all came with 18" staggered as standard. BMW330i has perfect 50/50 weight distribution, whereas I tend to believe 300h has something like 52/48 even though you have Battery in the rear. From outset that is not the best car for high speed cornering due to weight distribution and the heavy Battery relatively high up in the rear.

Again I am sure that is fine with ancient UK speed limit, but OP seems to be living in EU where 90MPH+ is common.

wharfhouse · June 21, 2018

Yes - IS 200t was only in Sport, F Sport and Premier so all on 18" rims in that case I assume - although out of curiosity I looked in my owners manual and the 18" rims (225 front and 245 rear) are also specified as 36psi both front and rear too...

According to everything I have read/found the IS 300h has a 50/50 weight distribution. The IS 250 (Mk III) was 54/46 when launched but I guess the extra Battery weight on the 300h brought it back to 50/50 !

IS300h · June 21, 2018

8 hours ago, Linas.P said:

which then actually leads me to another point - so if Lexus has decided that for sportier feel you need to run 18" with staggered tires and higher pressure in the rear, it could be assumed car with 17" and 225's on rear running lower pressure would result in say... less engaging driving dynamics. My point - it is hardly an issue with the specific tyre - more with the fact that R17/225/45 tyres on the rear axle is sub-par option for high speed cornering.

I had actually originally planned to run staggered 17"s with 245s in the rear. But this was strongly discouraged by my dealer as I would get problems with the ABS system...

Honestly, this still sounds incredible to me so I'll see if I can get some more info on that, not just from the dealer.

Fact remains though that the tyres in my case made an extraordinary difference, I'm still trying to get my head around how a company like Dunlop can make such bad "performance" tyres.

One thing I will also try though is to slightly increase the pressure on the rear tyres, just to see if it'll have a noticeable effect.

Linas.P · June 21, 2018

5 minutes ago, IS300h said:

I'm still trying to get my head around how a company like Dunlop can make such bad "performance" tyres.

That is what I am trying to say - Dunlop Sportmaxx RT and RT2 specifically are great tyres, I would choose RT2's any day over rather dreadful (in my opinion) Potenzas S001. The problem you have is wrong tyre size, under-inflated and for wrong purpose. Obviously, as mentioned again my experience is only based on driving up-to 70MPH and maybe above that speed these tyres looses their performance.

As for staggered set-up you dealer talking BS - if that would create problems with ABS/ESP or what not... then how can they explain exactly same systems working in exactly same car on 18" wheels running R18/40/225 front and R18/40/255 rear. Those are larger diameter wheels and more aggressively staggered then 17 set-up.

J Henderson · June 21, 2018

Can't see how the ABS would be affected by going wider, as long as the aspect ratio is adjusted accordingly. ie: 245/40R17 instead of a 45 profile.

How wide are the 17" wheels on an IS300h though? Ideally, they ought to be about 8" wide to accommodate a 245...

Linas.P · June 21, 2018

3 minutes ago, J Henderson said:

Can't see how the ABS would be affected by going wider, as long as the aspect ratio is adjusted accordingly. ie: 245/40R17 instead of a 45 profile.

How wide are the 17" wheels on an IS300h though? Ideally, they ought to be about 8" wide to accommodate a 245...

I tend to believe wheels are identical 8J front and rear, again I don't see reason adjust aspect ration. Exactly same car comes out from factory with 18" and 255/40 in the rear which are clearly not same ratio as 17" 225/45 and certainly not the same as 16" 205/55. So aspect ratio plays no major role in thing like ABS working, otherwise Lexus themselves would not allow so much discrepancy between grades.

J Henderson · June 21, 2018

Mk3 IS has a 35 profile rear tyre on models with 18" wheels, which equates quite roughly with a 225/45R17.

Regarding the soft sidewalls. I'm not a fan, especially given how rife pot-holes are these days. I always get XL tyres.

wharfhouse · June 21, 2018

4 minutes ago, Linas.P said:

I tend to believe wheels are identical 8J front and rear, again I don't see reason adjust aspect ration. Exactly same car comes out from factory with 18" and 255/40 in the rear which are clearly not same ratio as 17" 225/45 and certainly not the same as 16" 205/55. So aspect ratio plays no major role in thing like ABS working, otherwise Lexus themselves would not allow so much discrepancy between grades.

17" are 7 1/2J all round

18" are 8J front and 8 1/2J rear

J Henderson · June 21, 2018

In that case. a 245 might look slightly balloon-ish on a 7.5" rim.

wharfhouse · June 21, 2018

1 minute ago, wharfhouse said:

17" are 7 1/2J all round

18" are 8J front and 8 1/2J rear

17" tyres are 225/45

18" tyres are 225/40 front and 255/35 rear

IS300h · June 22, 2018

19 hours ago, Linas.P said:

That is what I am trying to say - Dunlop Sportmaxx RT and RT2 specifically are great tyres, I would choose RT2's any day over rather dreadful (in my opinion) Potenzas S001. The problem you have is wrong tyre size, under-inflated and for wrong purpose. Obviously, as mentioned again my experience is only based on driving up-to 70MPH and maybe above that speed these tyres looses their performance.

I think we're gonna have to agree to disagree on the tyres, I think the pictures speak for themselves. I'm not saying I have perfect handling now with the 225's, but just by changing to the Potenzas the handling improved beyond what I imagined possible, especially as this improvement was only linked to the tyre compound / sidewall stiffness, nothing else. They are the same size, same PSI (which at 36psi I don't think are under-inflated). I do agree with you that at lower speeds the RT2's performed quite well, but from around 65~70mp/h (depending on how sharp the corner of course) it indeed became a whole different story.

For my next set of rear tyres, I'll get some 245s as probably everyone here agrees with you that the "potential ABS problem" story from the dealer is a lie.

Linas.P · June 22, 2018

I agree with you that for that specific purpose Potenza 001s is better tyre, however there are much more for tyre then just high speed cornering. In fact as I mentioned in UK any corner over 70MPH would be illegal anyway, so kind of pointless to make that comparison.

Other thing, I actually agree with... Dunlop marketing is a bit misleading - by no means RT2 is UHP tyre... it is probably at best HP (high performance). GT would be UHP, but based on Dunlop marketing material you would never have guessed. That compounded by inherently wrong decision by Lexus to even fit such size and pressure tires on RWD car results in experience you have. However, say in UK with ancient 70MPH limit and potholed roads RT2 would be rather brilliant tire - especially on front axle.

IS300h · June 22, 2018

Good point, e.g. road noise was better on the RT2 and overall a slightly more comfortable tyre due to the softer compound. In hindsight I should have read more reviews on the RT2's, also considering my slightly more aggressive driving style. Still, I really didn't see this one coming, especially not from Dunlop, but as you say, their poor marketing definitely didn't help either.. The key thing I learned is that at least on the rear axle I need a stiff XL sidewall, especially in cars with a heavy boot.

Who knows, I might be able to get away with placing the RT2's in the front, if not I'll be putting them up for sale... :-)

Linas.P · June 23, 2018

Interestingly this just came out:

Quite relevant to the tread, first of all the comparing under-powered car, which is basically what IS300h is and the several different width of the tyres. Now obviously he uses 18" as a reference, but my take from the video and why I think it is relevant - is the balance. Square vs. Staggered and as you can see on dry that is what matters (that is what I said previously was an issue with RT2's). Goodyear Eagle f1 Asymmetric 3 is basically the same tyre as RT2, it is sister brand, it is same HP tyre, same ratings, same soft side walls (that is to make walls thin and light for better fuel economy).

Anyway, my point was that key to your issue was lack of balance in high speed corners (just my opinion on the issue).

Carl1983 · June 24, 2018

Linas f sport on 18inch is also square pressure on all corners. Nice dig about the 300h being under powered again.

Linas.P · June 24, 2018

3 hours ago, Carl1983 said:

Linas f sport on 18inch is also square pressure on all corners. Nice dig about the 300h being under powered again.

It is factual mate... I don't want to go into statistics again. This time around I mentioned it because the guy reviewing tyres drivers BMW320d and states the car has no power to overcome tyres grip... which is this case is directly applicable to IS300h as it has very similar power and acceleration as BMW320d (actually poverty line BMW is even a bit faster at 7.5s). What matters is that it is in same ballpark and not something like MB C63 AMG or BMW M4 which you see most of the time in these comparisons. As such I found video being very relevant and directly applicable in this discussion.

Jayw13702 · June 30, 2018

..
The air pressure in the rear should not be the same - I cannot say for sure what should it be on IS300h, but on most RWD cars it is few PSI higher e.g. IS250 are 35F and 38R... Even then I still run higher pressures on Sportmaxx RT as otherwise they tend to wear outside (as under-inflated) so for 17" I woudl run something like 38-40 and if I would be planning to do high speed European motorways maybe 40-42.

According to the label on the inside of the door pillar if you run eco then it should be 39psi front and rear

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