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Upgrading Is250 To Isf Wheel - Tyre Sizes


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Hi guys,

Can anyone tell me what tyre size to use if I were to upgrade my stock IS250 wheels (235/35/17 front and 245/35/17 backs) to ISF wheels?

I'm really noob at this and want it to be legal without rubbing. The car is stock btw!

Thanks and Merry Christmas to all :)

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Legally you can go 2"over standard size rims so 19s would be legal.Also i think a variation of + or - 5% in rolling diameter is allowed over standard.Correct me if i'm wrong!.I reckon your best option would be 18s.Looks good and decent rubber is still a reasonable price.Also the crap roads we have to put up with particularly in Sydney.My car has,i think the F sport rims on it which are front 225/40/18 rear 255/40/18.For ride,looks and handling i think this is a good combo.

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I have recently upgraded to ISF wheels with 225/35/19 at the front and 245/35/19 at the rears.

Slight rubbing at the front when turning corners but nothing major to worry about.

Ride and handling are no problems, however best thin I like, it makes the car look good. Just gotta get it lowered a little

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... want it to be legal without rubbing. The car is stock btw!

Here's some information I learned after visiting the Website for Transport and Main Roads, Queensland. The last line will be interesting to anyone who has considered using IS F wheels on an IS 250/IS 350.

  • Although each state determines what modifications are allowed on vehicles registered in that state, light vehicle modifications are generally guided by the National Code of Practice for Light Vehicle Construction and Modification (NCOP). Section LS deals with tyres, rims, suspension and steering.
  • There are certain basic modifications allowed without certification, provided that the vehicle continues to meet Australian Design Rules, "the in-service provisions of the [Australian Vehicle Standards Rules] and rules found within the NCOP.

I will paraphrase some of the key rules here - for more information, refer to the NCOP:

  • No scrubbing allowed. When testing for scrubbing on a 5-seater sedan, you must load it with 415 kg of weight.
  • The diameter of the tyre must not be more than 15 mm larger "than that of any tyre designated by the vehicle manufacturer for that model." Stock IS F tyres would be much too large at the front, even if your IS 250 manual/tyre placard suggested sizes for 18" wheels as used on IS 250 Sports/F Sport. However, the CL recommendation of 225/35R19 and 255/35R19 would be OK.
  • There are rules regarding maximum increase in tyre width and diameter, but not aspect ratio. But aspect ratio is a function of diameter and width anyway. As long as you meet diameter and width requirements, and the aspect ratio of the fronts don't differ to the rears by any more than 10, you're fine. In short, using 225/35 instead of 225/40 at the front is OK.
  • "When converting a passenger car’s wheels and tyres to those fitted to a manufacturer’s variant or high performance version of that model, the matching suspension components such as springs, shock absorbers and sway bars from the high performance model must also be used." This might suggest that an IS 250 fitted with IS F wheels must also be fitted with IS F suspension. You could argue that this rule doesn't apply, since you're only fitting "IS F wheels", and only two out of four "IS F tyres". But I'm not a lawyer, and I'm not going to offer legal advice on this matter. :-)
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  • 4 weeks later...

  • 3 months later...

Recently just had this setup but will changed the tyre to 235 soon.

Front 245 35 R19

Rear 245 35 R19

Lowered with Eibach Prokit

Rear has a lot of clearance but front rub a little towards the inner plastic cover when turning. Heat gun and a little pressing on the black plastic cover sort the rubbing issue.

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  • 3 months later...

Cheers thanks, can i ask why do people run a lower profile on the back.

I seem to see alot of people running 225/35/19 front and 275/30/19 rear.

is it due to the side wall ? or just looks ?

Thanks again

The 30's are not actually lower profile than 35. Remember that the Profile number (middle one) is actually a percentage, not an actual width.

For a 225/35/19 - The tire's width is 225mm, the profile (cushon or tyre height Edit: or sidewall)) is 35% of 225 which is 78.75mm.

For a 275/30/19 - the profile works out to 82.5mm, it will be higher than the fronts.

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Ok thanks heaps, so I should be looking at going small profile on the back than to keep the over all Diameter close to the same.

As long as you're comparing it to the correct pair. i.e if you're increasing the rim dia on the front, the tyre profile will get lower, same for the rear tyres.

Just don't compare the profile between front and rear :P

What's your current setup ?

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So, on the front's if you're increasing to 17 inch, then you should look for 225/45/R17 - which will result in a -0.38% error.

or for 18 - 245/35/R18 (+0.51% error)

or for 19 - 255/30/R19 (-0.59% error)

Probably worth searching these forums as well for Tyre size recommendations as some of these sizes may require rolled fenders or it will scrub, maybe illegal as well.

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225/45/18 and 255/40/18 would be better match imo. Speedo won't be out at all.

oh, I was on a tyre size calculator website. and it shows

Tyre Overall Tyre Diameter

205/55R16 632

225/40R18 637

225/45R18 660

255/35R18 636

255/40R18 661

Unless the website ive been using is wrong ?

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