Do Not Sell My Personal Information Jump to content


Recommended Posts

Dammit. So you decided to stretch a little? Not much I guess.

How about going for a 35 profile? Not ideal for Winter I know, but the back of the car does seem to sit up higher than the front, smaller profile might fix this illusion no?

Link to comment
Share on other sites


255/35R18 is the fitment on the 3rd Gen IS, and a far more common size but the rolling radius would be a full inch smaller than the stock 255/40R18 size on our cars.

The speedo would be quite inaccurate and you would rack up miles on your odometer at an accelerated rate.

Link to comment
Share on other sites

Ok but 245 40 18 would be a much smaller drop in rolling radius. I guess 40% of 245 is greater than 35% of 255 therefore closer to standard?

J Henderson. Any other issues apart from dazzling oncoming drivers? I have self levelling HID headlights so thinking this wouldn't even be an issue for me?

Link to comment
Share on other sites

15 hours ago, Billnick said:

Ok but 245 40 18 would be a much smaller drop in rolling radius. I guess 40% of 245 is greater than 35% of 255 therefore closer to standard?

J Henderson. Any other issues apart from dazzling oncoming drivers? I have self levelling HID headlights so thinking this wouldn't even be an issue for me?

Yes, 245/40 isn't that much smaller than standard. Its only about 6 or 7mm, something like that.

Regarding the self-levelling HIDs, I stand to be corrected but I believe they still work off a set base level and can only do so much. In the past I had the 245s on the rear, along with 235s on the front, so I had the scenario of the front sitting higher than normal, as well as the rear tyre being undersized, and with that setup I did occasionally get high-beamed by other drivers. Fitting the correct 225/40R18 size back on the front stopped this from happening though.

 

I reckon you would probably have to manually adjust the base level aim on the headlamps if you go with a 255/35.

16 hours ago, bobmc said:

Is there not a degree of calibration in the ecu? There is definitely an option in the menu concerning tire changes?

 

I think that Tyre Change option is for re-calibrating the satnav. 

Link to comment
Share on other sites


Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share



×
×
  • Create New...