305/40/19x11 and 275/40/19x10 on Ford Performance Track Handling Pack?

[The_Fireball]

Done a lot of reading and none the wiser so looking for some answers. I've got a new set of SVE350 rims at 19x11 for the rear and 19x10 front. These replace the existing UK GT wheels (PP wheels). According to this tyre fitment guide, the ideal like for like with these wheels, maintaining staggered setup and no adjustments is:

Front: 19x10” ET40 with 285/35/19 tyres
Rear: 19x11” ET52 with 305/30/19 tyres (results in shorter rear wheels though)

My existing/old setup is:
Front: 19x9” ET45 with 255/40/19 tyres
Rear: 19x9.5” ET52 with 305/40/19 tyres

I've recently had a new set of PS4s on the rears of my existing setup, so was hoping to move them to the new fronts (becoming 19x10 275/40), and just get a new set of rear tyres. Seems a shame to bin them, plus that's £450 of new rubber for nothing. The question is: what to put on the rears? 305/30/19 or 305/35/19 are both going to come in shorter on the rears then the 275/40/19 on the front, which is going to look off and I presume not be great for the car geometry. Worth noting I've got the Ford ProCal tool that allows you to code in a new tyre circumference to ensure speedo vales are correct after a change.

305/40/19 would fix this, but it's not clear if that is even feasible. Guys on this thread say that a 305/35/20 works. Now according to willtheyfit.com, the 305/40/19 setup would only be 5.1mm taller overall, so presumably that works. I just can't find anyone else listing 305/40/19 as being used.

Add even more to this mix - I've got the Performance Track Handling Pack to go on soon, which will drop everything 1" all round. I suspect I know the answer here: new rubber all round...or will 305/40/19 work on the rear without rubbing and messing around? If it is new rubber all round, why not go for 305/35/19 on the rear so they're not lower then the front wheels?

Help greatly appreciated!

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[1 old racer]

305/40's that is a very tall tire. Are you sure you want to even try to fit that under a slightly lowered car?

 

[The_Fireball]

305/40's that is a very tall tire. Are you sure you want to even try to fit that under a slightly lowered car?

That's the point really, is that just going to be a headache? Sounds like it will be, but if I go for 305/35 on the rear, is the 6.5mm shorter rear tyre Vs front going to cause me issues?

 

[Ewheels]

That's the point really, is that just going to be a headache? Sounds like it will be, but if I go for 305/35 on the rear, is the 6.5mm shorter rear tyre Vs front going to cause me issues?

The tire diameter makes such a small difference, it's not worth losing sleep over. A 305/40 vs a 305/35 is only 4.2% off in circumference. So over the course of 100k miles, the odometer will only be off 4200 miles....that's nothing. If you're planning to sell the car down the road, and extra 4200 miles out of 100k will not affect your sell price


If you're worried about the front/rear sidewall height looking different, see if you can return two of the wheels and go 19x10 square or 19x11 square.
I have no idea why people go staggered anyway. Mustangs drive SO much better with a square setup

 

[The_Fireball]

Fair point about the odometer, but I'm not fussed about the odometer reading; the ford procal ECU tool can be used to adjust your car for that anyway.

It's more about if a 305/40/19 is going to fit in the rear with a 1" drop without rubbing on anything.

 

[Ewheels]

Fair point about the odometer, but I'm not fussed about the odometer reading; the ford procal ECU tool can be used to adjust your car for that anyway.

It's more about if a 305/40/19 is going to fit in the rear with a 1" drop without rubbing on anything.

Understood.
I run 305/30 with a 1" drop without issue. Looks like 305/40 is 2.4 inches taller tire. That does seem fairly substantial, though I don't know for certain if you'd have any issues.

 

[kz]

Fair point about the odometer, but I'm not fussed about the odometer reading; the ford procal ECU tool can be used to adjust your car for that anyway.

It's more about if a 305/40/19 is going to fit in the rear with a 1" drop without rubbing on anything.

I don't think anyone here will tell since I haven't seen anyone try - I'd risk a gues that it could rub.

Also - don't know if that matters to you but it will look absolutely ridiculous (IMO) with that high of a profile.

 

[The_Fireball]

I don't think anyone here will tell since I haven't seen anyone try - I'd risk a gues that it could rub.

Also - don't know if that matters to you but it will look absolutely ridiculous (IMO) with that high of a profile.

Oh that does matter .

Yes the absence of any similar threads is telling enough that this is a silly option. Given some other examples I saw yesterday, think the 305/35 on the rear will be barely distinguishable from the front 275/40, so will probably do me fine until it comes time to get some new fronts, at which point 285/35 will probably be the right choice.

cheers chaps!

 

[kz]

275/40 looks "thick" on the rear IMHO and 305/40 will have half an inch of taller sidewall (4.3" vs. 4.8"). It'll make it look like an off road car...

But now I am curious how it'll look so you should totally do it ;-)

 

[I Bleed Ford Blue]

If you run 305/35 in the rear and 285/35 front it will get you as close to the original overall diameter of the stock tires as you can get.

 

[Grintch]

305/40's that is a very tall tire. Are you sure you want to even try to fit that under a slightly lowered car?

Theoretical tires sizes don't help if no one makes them.

305/40 & 305/35 sizes have very limited tire selection/availability. This is another reason people like to go square because 285/35 and 305/30 sizes that have good selection and availability give a diameter miss match.

I guess you could run 295/30 & 305/30, or 275/35 & 285/35. 285/30 is a bit too short IMHO.

 

[The_Fireball]

Ended up looking at 285/35 and 295/35 in MPS4S, which seems also to be a common choice here. Mostly as I want the incredible grip I've had with the MPS4s. Of course annoyingly they don't do 305/35 in that tyre yet, if they ever will.

 

[shogun32]

This is another reason people like to go square because 285/35 and 305/30 sizes that have good selection and availability give a diameter miss match.

this isn't Audi Quattro - mismatch doesn't matter spit.

 

[MyStang]

The_Fireball,
Here's a picture of a 1" drop and 305/35/19

 

[Grintch]

this isn't Audi Quattro - mismatch doesn't matter spit.

People like stagger because of the looks. Having the rear tires a smaller diameter than the front tires spoils the look.

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