235/40/18 fitment, rolled lip/camber?

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235/40/18 fitment, rolled lip/camber?

Postby lojk » Sat Aug 08, 2015 12:46 pm

I have an 07 b spec wagon and it's time for new tyres. Every tyre shop recommends 225/40's to replace the uncommon 215/45/18's, but the difference in rolling diameter is putting me off.

I was thinking of getting some 18x8 +44 Rota Gravels wrapped in 235/40/18 Eagle f1 assymetric 2's as they are the closest to stock diameter.

Car is stock height, I don't need a stretched tyre, and I figure the 235's will fill the arches a little better.

The wheel shop has suggested I'll need to roll the lip in the rear, is this a sure thing? Should I do it anyway for safety
Will normal camber be suitable up front? I'm looking for good fitment front and rear.

Can anyone with experience with this setup give some feedback? :?
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Re: 235/40/18 fitment, rolled lip/camber?

Postby andy_mac » Sat Aug 08, 2015 1:10 pm

Its quite a common size to be going for. Heaps of examples of similar setups on here.
You really need some rear camber adjustment to get them fitting which in stock form these cars don't have. Need adjustable length lower arms or upper control arm offset bushes. Have got my rear fitting in pretty well with 1.5degrees in the rear, no rubbing so far. Front only has 1 degree but would need more if i was going lower.
Rolling isn't a definate but will give you that bit of extra clearance for peace of mind.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby Mosti » Sun Aug 09, 2015 12:06 pm

I was going to ask this same question. Looking at putting 235 40 18 on some 18x8 +48 wheels. Currently running 225 40 lowered on coilovers and around 1 bumpy corner near my house, the front left tyre snags on the inner lip if I'm going to fast (over say 30km/h) Natural rear camber after lowering should be enough for plenty of clearance without rolling the guards but I'm guessing the fronts will have to be done
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Re: 235/40/18 fitment, rolled lip/camber?

Postby lojk » Sun Aug 09, 2015 4:33 pm

Hmm, Seems like it could be a bit of mucking around to get right.

I might just stick with the stock rims for now, and get the best tyre I can onto it. be that 225/40 or 215/45

thanks for the input
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Re: 235/40/18 fitment, rolled lip/camber?

Postby dr20t » Sun Aug 09, 2015 5:40 pm

Rear will definitely need lipping at the very minimum.

Fronts should have some rolling to be safe
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Re: 235/40/18 fitment, rolled lip/camber?

Postby HyRax » Mon Aug 10, 2015 11:52 am

I'm running 8.5" Rota Gravels with 235/40/18 rubber and it (just) fits fine. Since lowering with coilovers, I have added 1.75 degrees of camber to the front to tuck it under the guards, but the 8" version of the wheels will NOT require this.

You will NOT need to roll the front or rear guards for 8" wide Rota Gravels. You only need to consider the rears for the 8.5" wide version, and even then only if you plan to lower and load up the back regularly with passengers, shopping or anvils. My rears are rolled, but looking back, they didn't really need to be done.

See my profile thread for pics of my car for comparison to yours.

As for the rolling diameter with 235/40/18, yes - it will change by 5% compared to stock. This will correct the speedo (where 100kph indicated equals 96kph actual with stock wheels, corrected to 100kph=100kph with new wheels), but your odometer will now be short by 5%.

And yes, don't do stretched tyres. 235 on 8" will give you a small amount of muffin to protect the rim. On 8.5" it is exactly straight in line with the rim.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby dr20t » Mon Aug 10, 2015 1:53 pm

Really depends on the offset

My 18x8 +40 offset wheels with 235 40 18's definitely needed a roll front and back (unless I ran 3 degrees camber)

As for rolling diameter, the slightly smaller tyre is better for acceleration (bumps up gearing ever so slightly) and you can definitely notice this.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby lojk » Tue Aug 11, 2015 8:30 pm

Hyrax, what tyres specifically are you running?

dr20t, what brand wheels/tyres do you have, 18x8 +40's should only sit 4mm further out than the +44's I'm looking at, but would sit 2mm further in than the wheel Hyrax has. So there must be other variables to this?

Is there more/less space in the rear arch on a wagon, or is it the same...?

Given peoples different responses saying they do or don't fit, it seems a bit hit and miss as to whether they fit cleanly.

The rota +48 offset rims offered in the US is probably a better fit with the larger 235 tyre, but I suppose everybody is after the flush/stretched tyre look.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby HyRax » Tue Aug 11, 2015 9:23 pm

lojk wrote:Hyrax, what tyres specifically are you running?

I'm running 235/40/18 Kuhmo KU36's on 18x8.5" +44 Rota Gravels.

  • On stock suspension, stock height, stock camber:

    Image
    Click image for full size.


  • On coilovers, lowered only 1cm, stock camber on rear, 2 degrees negative camber on the front:

    Image
    Click image for full size.


  • Wheel closeup (stock suspension, stock height, stock camber):

    Image
    Click image for full size.


  • Flushness (stock suspension, stock height, stock camber - the angle of this photo makes it look as though it's not sticking out, but it is - by no more than half an inch, probably slightly less):

    Image[
    Click image for full size.


  • Strangely, I've not taken any close-up wheel photos of the 2 degrees of camber. Will have to address that later.


The rears fit fine with stock suspension. No camber required. There can be a TINY bit of rub over bumps and dips when the rear is fully loaded with passengers and boot load. This rub is on the inner plastic guard, not the outer body. Rolling the guards does not fix this.

The fronts fit fine with stock suspension, however they do stick out approximately half an inch. There is no rubbing over yumps and bumps at speed on the front unless you lower the car, and then the rubbing occurs just above where the front bumper join line meets the quarter panel join line. Two degrees of camber will tuck the wheels inside the guards but you will get still rubbing on the inner guard in the same place over hard yumps at speed if you lower too much - I originally had 2cm lowering and then raised the car back to 1cm lowering to eliminate the high-speed yump rubbing - your mileage will vary depending on the spring rate of your coilovers (if you go that way for lowering). Additionally, in the case of Kuhmo KU36 tyres, the tyre noise will increase substantially due to the large tread blocks on the inside being more in contact with the road with the extra negative camber.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby fedaykin » Wed Aug 12, 2015 10:31 am

Excellent information.
The KU36 has 'square' shoulders, so tyres that are more 'rounded' (e.g. Pirelli, Michelin, Continental, most Potenza) should give you a tad more clearance.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby lojk » Fri Aug 14, 2015 4:39 pm

Thanks for the extended information Hyrax, your car looks great.

I've decided for the time being to just get some original sized tyres, and keep the stock rims for now.
I'll likely spend the money saved on rims on some handling mods instead and maintain the stock appearance for now.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby HyRax » Fri Aug 14, 2015 5:18 pm

lojk wrote:I'll likely spend the money saved on rims on some handling mods instead and maintain the stock appearance for now.

At the very least get some 225 tyres put on your factory rims rather than go with 215's.

As for handling, consider fatter front and rear swaybars and replacement front control arm bushes (Whiteline KCA334 and Whiteline W0506 spring to mind, aka an "anti-lift kit"). Best bang for your dollar.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby lojk » Sun Aug 16, 2015 12:12 pm

I see, I've already booked in to get a set of 215/45 Bridgestone re003's. I'm sure they will do the job just fine.

I know that the smaller 225's would give better acceleration, and probably slightly firmer ride/tighter handling due to reduced sidewall height?
But the speedo would read under wouldnt it?

It's a tuned b spec so it's pretty quick for day to day stuff already.

Yep the whiteline sway bars are where i was going to start handling wise.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby RX25SE » Sun Aug 16, 2015 1:30 pm

lojk wrote:But the speedo would read under wouldnt it?


Correct.
You will be adding to the (roughly 9%) error that already exists.

To correct the factory error, you would need to go the other way, 225/45-18 would solve part of this.

It would seem that those running the 225/40-18 don't seem to have too many concerns regarding the speedo error, just use your GPS to find the true speed and adjust your driving to suit.
Personally, I think a 225 really needs to be on a 7.5" rim, not the 7.0". I'm in the process of getting new tires and will do the same as you, sourcing a 215/45-18 Yokohama AD08R. This would give me a least the same, if not more grip than a 225 in a cheaper tyre.
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Re: 235/40/18 fitment, rolled lip/camber?

Postby HyRax » Sun Aug 16, 2015 1:31 pm

lojk wrote:I know that the smaller 225's would give better acceleration, and probably slightly firmer ride/tighter handling due to reduced sidewall height?
But the speedo would read under wouldnt it?

Taking 225/45/18 as the example, the 225 bit is the width of the tyre, in this case 225mm. The 45 is the height of the sidewall which is a percentage of the tyre width, in this case 45% or 101mm. The 18 is of course the size of the rim the tyre is designed to fit over.

So, a 225/45/18 tyre will have a taller sidewall than a 225/40/18 tyre. For a stock Liberty 2.5i which ships with 215/45/17 tyres, the closest rolling diameter match for an 18" rim to factory is 225/40/18 (you're adding an inch to the rim, so we need to remove roughly an inch from the tyre sidewall - 5% usually does the job while staying within spec).

Where the speedo reads different is if the rolling diameter of the tyre is larger or smaller than the original spec. Legally, the speedo cannot read under what your actual speed is, and from factory most speedos are deliberately slightly off to account for tyre wear, so 100kph on the speedo can equal an actual speed of 96kph. This of course can create a false sense of security for some who say that they sped past a cop at 110kph in a 100 zone and didn't get pulled over, simply because they weren't actually doing 110. If the tyre is smaller than spec, then your speedo will read higher than actual speed and this is a Bad Thing(TM).

Using the 2.5i example again, while 225/40/18 is a good match to the factory 215/45/17 wheels, you can correct the speedo by going for 225/45/18 tyres instead. This makes 100kph on the speedo about 100kph in actual speed. The downside is that your odometer is now slower by 5% (ie: you'll travel 5.25 kilometres for every 5 kilometres indicated).

lojk wrote:It's a tuned b spec so it's pretty quick for day to day stuff already.

Yes, for the most part you wouldn't notice much difference at all unless you went side by side with someone (excusing all other factors such as general state of car, driver competency, etc).

The width will help mostly in lateral grip, when taking corners at speed, though really wide tyres tend to "tramline" easily. The sidewalls help a lot with acceleration and heavy braking. Those with rubber bands as tyres find that they can't accelerate or brake as well as someone else with the exact same car and normal tyres because the sidewall can't flex as much (if at all) to allow the tyre the opportunity to have proper contact with the road (this is why drag cars have monster sidewalls on their tyres - look at a photo of one launching).

There are of course a whole bunch of other factors such as swaybars, camber, centre of gravity, road temperature, design of the tyre tread, and compound used that all impact how well your car grips the road as well, but for simplicity's sake the above forms a large chunk of the science.

lojk wrote:Yep the whiteline sway bars are where i was going to start handling wise.

Excellent. You'll have a lot of fun with that. :)
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