Remember now... I didnt start this thread. I am saying that 45 series tires should have been put on the car from the beginning..PERIOD. 40 series tires look silly...especially on the front because there is such a big gap in the wheel well. And as the guy who started this thread has said.. they make the car ride hard. There is nothing wrong with 45 series tires, they will do exactly what he wants them to do without drastically changing the ride or handling characteristics of the car.

A 45 series tire will affect acceleration and handling very minimally, infact, if he purchases the same summer tires or a set of ultra high performance tires, there will likely be no change. You talk as if I am suggesting he get those old school "belly" tires like what you would find on a Buick Roadmaster or something..come on now!

So you know, if he were to change his 40 series tires to a 45 series, there would be only a 2% decrease in revolutions per minute at the same speeds.. .this likely correlates to less than a 2% decrease in the final gear ratio... So what did I just say? Suppose the IS 350 has a final drive ratio of 3.42:1...that would be equivalent to a 3.42 gear in the rear end. With a 45 series tire that final gear ratio will decrease to about 3.4119 or something like that. So as I said he wont loose much of anything if at all. Thats why you must do your research before you do anything like this.

Your suggesting he get a 17 inch rim and a 50 series tire to maintain the stock wheel diameter? It wont handle as crisp as it does now or with the 45 series tires... he will also liklely get more oversteer.... Well, I know what I'm talking about, I didnt have to look it up on the internet either. Lastly, the tow and camber will virtually be unaffected by a 45 series tire... If you get a 19 in or a 20 inch rim then you have to worry more about geometry or change the ride height SIGNIFICANTLY, then you will need to worry about suspension geometry.

toodles

Lorna

 

You made some comments that lead me to believe that you don't know entirely what you're talking about. But not worth getting into an argument over, DaSweetgrl. Let's just agree that the originator of this thread probably didn't buy the right car or rim/tire option for the car. And that he either needs to live with the firm ride, buy a smaller set of rims and some all-season rubber, or buy a different car all together. Those really are the only proper options.

 

Or like I said, he can get a 45 series tire and keep all of his original equipement. Most people do not buy smaller rims... they usually get bigger rims and shorter tires.. even 30 and 35 series tires. Since he wants the ride to be a little softer, the best thing to do is to buy a tire with a little more meat. A 45 series tire accomplishes this. So what if the ride height increases by half an inch??? so what!! People do this all the time and with even more aggressive tire/wheel packages. Some people put 19's on the back and 18's on the front to give the car a little more rake... some people put 22's and 24's on these little cars. What's my point?...he can do what ever he wants to do. The way I suggest just happens to be the cheapest way, and it keeps the car BONE STOCK!

I know exactly what I am talking about baby cakes, which is why you chose not to challenge me. You probably dont even understand the relationship between tire height and gear ratios/acceleration and revolutions per minute...whatever sir!

Lorna

 

It's clear that I'm debating with a 13 year old I'm done with this conversation.

 

You know I'm right boo... your just a typical man, but you dont know everything

 

wow...this thread is so fiesty. everyone should just chilllll

How about the original poster just get wings for his car so he can fly. Ride issue should no longer be a problem.

 

1) Changing the front tires will NOT affect the Speedometer. The speedo is calculated off the transmission, which is affected by the Drive wheels. In the case of the IS... the rear wheels

2) Suspension geometry will change, this is due to the larger sidewall. If the poster is worried about this... then he probably doesnt care that the car rides stiff. Anyway, 225/45/18 is still a low profile tire and will still handle very well, it is VERY VERY VERY unlikely that the OP will notice any ill effects on cornering. Maybe someone who roadraces all the time would notice.

3) I would suggest 245/40/18s in the front, in lieu of 225/45/18s.That will increase lateral grip, while giving you a thicker sidewall. However, to do so you would need wider front rims 18x8.5s like in the rear. Also I am not sure if that size would clear without rubbing. You may also consider 235/40/18s on the current wheel, though this will only give you about 5" in sidewall height(on each side, total diameter will be 1" greater than stock.

4) Da sweet girl is right, the small front tires do look odd, the wheel gap is huge in the front compared to the back. I have wanted 245/40s in the front since i got this car, but dont know what wheels I want.

5) For the OP, check your tire pressures. The fronts should be set to 35PSI, and the rears 38. Have fun.

 

The 245's up front should help reduce understeer as well, if that matters to you.

 

Well thanks again everyone for the great info. I went to the Lexus mechanic to see what he thought. First, he told me to get an ES350. I said I didn't want to pay for a re-badged Camry. Especially one that drives like a boat and isn't nearly as eye-popping as my IS. Then he said I made a mistake in getting the 18" wheels. I told him I had no choice, all IS's in Cali come with 18" tires. I really wanted the 17" to begin! So then he copped out and told me to call Lexus Customer Relations which I plan to do, telling them it sucks that the 18" tires are not really an option. I asked about the 40's vs. 45's. He said it may work, but it wouldn't make as much a difference as changing to 17". I asked him how much it would cost, does he have the parts and tires... and he told me to call Customer Relations... weird, he doesn't seem to want my $.


In the meantime, I'm getting more use to the ride. 70% of the time it drives like a Lexus and I'm supremely happy with the car. Damn it looks fine. 30% of the time I long for my Acura Integra.

I test drove the IS250 four different times at three different dealerships all with summer tires. I took it over freeways, city roads, super windy roads in the hills, even on the same roads that feel bumpy to me now! I'm mad at myself for not picking this up before I bought. I at least could have bargained hard for the dealer to take off the 18's and put on 17's. Now I'll have to 'double pay' first for the 'option' of 18" wheels second to change them back to the 17's.

 

igotanewis, you should really keep your eyes open for someone w/ the 17's, that would like to swap for the 18's. Put a "wanted" post in the for-sale section of this, and other Lexus message boards. Or, there might be people that bought 24" spinners for their IS, and have the factory set or 17's to sell. Sure beats paying Lexus retail price for a new set.

I agree with the Lexus mechanic, that switching to a slightly taller sidewall will do little to improve the ride. Not to mention all the downsides that've already been discussed. Going to 17" wheels is probably the smartest option.

 

Too bad you arent in VA, my cousin would love to have the 18s. He has 17s on his 250.

The 17s with 225/45/17s, has the same sidwall height as 18s with 245/40/18s or 245/45/18s.

So, the stiffness should technically be the same, given the same tire.

 

i dont buy getting new tires and wheels changes the suspension geometry, no one tells you to get an alignment after getting a new set of wheels/tires. The car couldnt tell the difference when the OD is close or the same. The position of the hub in relation to the other suspension parts unchanged even if you upgrade to larger wheels and thinner tires.

Only when you have a bad alignment already or you take apart one of the suspension parts whether it be new springs, shocks/struts, coilover, camber kit whatever then you need to realign because the suspension geometry changed, not for just tires and wheels

 

It is true that if you go to a wheel that is bigger or smaller than stock you will need to adjust the tow and camber to make the suspension geometry closer to specifications, or else the wheels wont track eacother properly and you will wear your tires down faster.... sometimes it can be done without buying a camber kit or drilling the camber plates on top of the strut mount or wherever they may be., but it all depends on how much the change in wheel height varies from spec. Only if you make a significant change in wheel height/diameter is this a problem. Small changes, like changing from a 40 series to a 45 series tire will most likely keep the geometry acceptable within the stock specification range. A good alignment shop can tune your suspension to the way you drive. Aligning to stock specifications may help your tires last longer, but it may not be the best alignment for sharp turn in's or sport driving... People who autocross usually dont align their cars to spec and the cars handle better than stock... but the tires wear out sooner because the car was aligned for best handling capability and not optimal wear... all of these things can be played with based on how you intend to use the car. A really good alignment usually takes 2 to 3 hours to get right.... What the factory gives you is "acceptable"... i.e. it will do for day to day driving.

FF's claim that geometry changes when going from 40 series to 45 series is way off and unfounded. The difference in height is so minute that it wouldnt' really matter, but you do get a little more tire to soften things. You know, I would even try a 50 series tire, but you will have to do your research on that because I am pretty sure that the diameter(wheel height) of a 255/50/18 is at least 27.5 or maybe even 28 inches tall...while stock is only 25 inches. Just do your homework. All these guys out here putting 20's and 22's and 24's on these cars, so there is no reason why you cant put a slightly taller tire on your stock wheels and save some money. You just dont want the car to look doofy though..so do your homework.

Lastly... The TPMSensors may or may not fit properly on whatever 17" wheels you get... If you get new TPMS's, the dealer has to program the ID codes into the PCM to make the low tire warning lights go off. The TPMSensors is not cheap either... they cost about $600 or more from Lexus for 4 of them. In so many ways you are better off just trying to get a tire to fit your stock rims. Save your money, you'll need for the day you curb one of your wheels and want to change it.


And FF... you're an idiot

Lorna

 

I'd say stick with
With the stock 18X8s....
225/45/18s in the front if you want a softer ride with worse handling
or go
235/40/18s if you want a slightly softer ride with slightly better handling(not as soft as 225/45s

Upgrade to 18X8.5s in front and get
245/40/18s
This may have some rubbing as the tires are wider

 

OK, you just finally admitted that changing tire diameter does change suspension geometry, and in the same breath claim that switching from 40 to 45 series will not. And in the following breath call me an idiot.

*falls off chair*