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#1 | ||
Regular Member
Join Date: May 2018
Posts: 38
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What's the tallest sidewall you can put on a standard g6e falcon fg,I'm just really looking for a softer ride,I have 235/40/R18s on at the moment and it's just too thuddy over bumps.
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#2 | ||
FF.Com.Au Hardcore
Join Date: Jan 2005
Location: Hervey Bay
Posts: 5,213
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If your car has a 6 speed auto you can't change the tire size without upsetting the transmission.
You have to reset the tire size in the PCM to match the physical, but the size can only be one of the factory spec sizes available at the time. It won't allow you to specify a custom size tire. |
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#3 | ||
Thailand Specials
Join Date: Aug 2009
Location: Centrefold Lounge
Posts: 49,030
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I think the FGII EcoLPI XR6 came with 235/50R17 - can that be picked in the PCM options on the reflash?
Would have to change wheels, and they're a bit pricier than the more common options too. |
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#4 | |||
Miami Pilot
![]() Join Date: Jan 2005
Location: ACT
Posts: 21,701
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Quote:
On an 18” rim, you can run 245/45/18 with no clearance or other issues.
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The Hammer: FG GTE | 376rwkw | 1/4 mile 11.793 @ 119.75mph 1.733 60' (4408lb) 1 of 60 FG MK1 335 GTEs (1 of 118 FG Mk 1 & 2 335 GTEs). Mods: Tune, HSD/ShockWorks, black GT335 19” staggered replicas with 245 & 275/35/19 Michelin Pilot sport 5s Daily: BF2 Fairmont Ghia I6 ZF, machine face GT335 19” staggered Replicas with 245s and 275s, Bilsteins & Kings FPV 335 build stats: <click here> Ford Performance Club ACT |
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#5 | ||||||
FF.Com.Au Hardcore
Join Date: Jan 2005
Location: Hervey Bay
Posts: 5,213
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Quote:
The problem of only being able to program factory fitment options seems to stem from the tyre size being converted into a calculated circumference and tyre RPM figure that the PCM uses. I think tuning software get around that by being able to program the circumference and RPM figure directly. Quote:
The transmission constantly and fastidiously monitors the rotation speeds of the front wheels to determine how it operates at any one time and the physical wheel rotation speed needs to match the calculated size programmed into the PCM for the trans to perform properly. From the ZF Australia god himself, I paraphrase some parts of his reply to me from a while back: Quote:
Quote:
As soon as I took my foot of the accelerator it would downshift. Turning corners it would shift down an extra gear. It would shift down an extra gear in downhill mode. It would hold gears before upshifting in a straight line, like it would hold 4th forever before shifting into 5th at 60km/h... Same with moving into 6th at 100km/h. It basically thought it was constantly in cornering mode and was an extremely frustrating car to drive. In your car your tyres work out to be a larger rolling circumference than the original, but about 15mm. It might simply be that because is the opposite case to me that its delaying downshifting and isn't operating in as sporty a manner as it should. Maybe its just something you haven't noticed or are used to. I suppose its possible that if you find a tyre close enough in circumference size to the programmed originals you won't ever notice a problem. If you're ever unfortunate enough to blow a front tire and have to put on a different size spare you will see. You'll think the transmission has gone mental. In my car a spare on the front will see it hold 1st to 4th to nearly at the redline. It won't shift past 3rd under 60km/h and will be lucky to shift into 5th at 100km/h. If I want it to shift up I have to manually shift. This video is always a good demonstration of how the transmission behaves with when it sees different rolling sizes between the fronts. |
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#6 | |||
Starter Motor
Join Date: Dec 2019
Posts: 15
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Quote:
I've searched the forum trying to get some good information on alternative tyre sizes for a stock 2013 FG Ute with 19" rims and can't seem to find anything definitive. Basically I want to alter the tyre sizes from factory. Modifications are off the table and I don't agree with rolling guards on cars that have value Anyone know if the following is an issue with stock guards and stock 19" wheels; Front; 255/35R19 Rear 285/30R19 |
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#7 | ||
FF.Com.Au Hardcore
Join Date: Mar 2011
Location: VIC
Posts: 1,130
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I run 235 55 R17 on my FG ute for years. Car drives perfect and transmission behaving exactly the same. You can fit an even taller tyre if you run a difference offset. But with standard Falcon offset you cannot fit a taller tyre than that.
On your G6E i would run 245 45 18. That's what my brother has on his G6E and it has been fine. Ride is softer than the original 245 40 18s. |
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#8 | |||
FF.Com.Au Hardcore
Join Date: Jan 2005
Location: Hervey Bay
Posts: 5,213
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Quote:
The transmission has sensors on the input and output shafts to detect shaft speeds. It also takes the input of the engine rpm. So at any one point it knows exactly what gear its in by the differences in input to output shaft speeds and any slip within the transmission and converter based on those shaft speed and engine rpm differences. You can monitor it in Forscan and watch the slip and ratios come together as it shifts. In extension to that, it also knows at any one point of the output shaft speed what the wheel rpm should be based on the programmed diff ratio and tyre size. So in my mind I think the transmission has an expectation of what the wheel speeds vs transmission speed SHOULD be at any one time. It uses these programmed variable to create a baseline at any speed and any variations in normal operation of wheel rpm from that baseline then determines the shift strategy and behaviour. So if you go and change the tyre size to an extent without telling the PCM that it is changed, you are physically altering the baseline outside of what the transmission is expecting. In the case of my car the tyres were changed to a size that was physically smaller in circumference (43mm circ and 15mm diameter), which changed the expected RPM in operation, the transmission must have always thought I slowing down when I wasn't. Or when I was slowing down or turning a corner it thought I was doing it more aggressively than I was. And that manifested in this annoying behaviour of holding gears and aggressively and more often downshifting when it wasn't expected. Conversely others have written here that they have changed to tyres that were larger in circumference than original and haven't suffered any ill effects. But in reality it might have had the opposite effect of my experience that this change in rpm makes the transmission less aggressive than it normally would be. Or its possible there is an overall tolerance in tyre sizes before it starts to misbehave. And there would have to be given that overall a tyre will shrink somewhere around 12 to 15mm in diameter over its life as the tread wears down. So small changes wouldn't cause an issue. As you said, it all has to do with tyre rpm... And what Theo from ZF told me in that email. By changing tyres you are changing what the expected rpms should be which causes issue with the logic that is solely trying to detect variations in tyre speeds. That's my theory... If that makes sense. |
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