Going up to 225/45/R18 from OEM on 06 STI

[Ben]

Looks like I have the option of getting my hands on some Falken tires at decent prices, currently I have the ZE912 in 215/45/R18 and I'm seriously considering the RT615 225/45/R18!

I realise they are different sizes and the diameter will effect my speedo, that said, is it worth it? Will they be too wide? Should I just stick to the ZE912's? Anyone actually done this on a my06 STi or someone with 18/7.5 older style Enkeis?

My speedo already under-reads and doing those 5km road tests I'm under by about 200m or so over a 3-4km so I'm thinking this might actually even this up somehow and makes me wonder why it's reading like that in the first place? Ideas?

[senator]

All MY07 tb sti's were fitted with 225 45 r18 and All MY08 tb sti's were fitted with 225 40 r18

They should fit fine as long as the car still has oem suspension, the speed will always read a little out.

Even my car which has factory fitted ratio sensor especially fitted for the bigger wheels still isn't 100% spot on.

[swingn]

Personally I'd be running a 225/40 18... That being said, it'll only be out a little.

Depending on the tyre manufacturer (IE - Brand) even having the same tyre size can produce a slightly different rolling radious.

[Ben]

All MY07 tb sti's were fitted with 225 45 r18 and All MY08 tb sti's were fitted with 225 40 r18

Interesting, thanks for that senator, very handy info. I might just get some sort of gauge for car speed, even if it's just a navsat for a while to get an idea of the differences.

Personally I'd be running a 225/40 18... That being said, it'll only be out a little.

Thanks for that suggestion, good call, makes a lot of sense.

Need to break out the calculator! Thx for the replies!

[teK--]

Smaller rolling diameter also gives you more torque on the road too.

I'd go 225/40

[Ben]

Smaller rolling diameter also gives you more torque on the road too.

I'd go 225/40

Thanks Tek, looking like 225/40 is the go!!

How awesome is this forum (just quietly) post up a thread and bam, answer galore Brilliant!!

[Ben]

Last Questions!!

Would 235/40 be overkill? The falken FK 452's 235/40 are actually 243, will they fit or am I pushing the relationship with the rim and tyre a bit too far due to profile?

FK 452 or ZE 912? I'm leaning towards FK 452's.

[teK--]

235 is going to rub unless you roll the guards, and it is also a pretty wide tyre to be putting on 7.5 wheels; they will be squirming around a fair bit. (I've done it before on my last car).

[Ben]

235 is going to rub unless you roll the guards, and it is also a pretty wide tyre to be putting on 7.5 wheels; they will be squirming around a fair bit. (I've done it before on my last car).

Thx tek, great info, appreciated, though that might be the case, 225/40 it is then

[sh1ft]

I also have just changed from 215's to now run 225/40's on my 7.5 wide 18" Volks, the tyre fits well and looks good on the rim (sit flush).
A 235 will flare out abit and look kind of wrong! as more suited to the 8" wide rims.

there is a 2km/h display difference on my speedo i have found as i frequently swap between my ome 17" and my 18" volks, best thing to do is check your nav road speed display as its well on the money compaired to the cluster display

but when i when from the 215/45 to the 225/40 on the 18" there was almost no differnce in road speed reading

[Ben]

when i when from the 215/45 to the 225/40 on the 18" there was almost no differnce in road speed reading

Thx sh1ft, that's great, exactly what I was hoping to hear

[smythie]

Smaller rolling diameter also gives you more torque on the road too.

I'd go 225/40

I hate low profiles. 45 is the lowest I would go.

[teK--]

That's probably about 45 :

[coyote]

Ben,

I know more than half a dozen people with 225/45R18 RT615s on their Gen4 Liberties.

They all report no issues and no need to roll guards.

Go for it.

(225/40 may not even have a load rating that complies with your tyre placard)

[Greenman]

I run 225/45/18 Adrenalins on my XT foz.....rated at 95...if that helps....interesting to see what they look like on a Liberty.