My stock rears (275/35/19) are at 3/32 inch and I want to change them out once the snow is gone to the Pilot Super Sports with a slightly wider track (285/35/19). I was going to get the Pilot Super Sports for the front to stay the same size as the OEM tires, but was reading that increasing the ratio between the rear/front can induce more understeer. Should I keep the front tires at the stock 245/40/19 size, or should I increase to 255/40/19 or a different size to keep the original balance the same?

 

To maintain the same relative diameters you would ideally use a 250x45 front. Since that is not available, either size you propose is equally close. I would go for the additional tire patch of the 255.

 

If I go for the 255 fronts, should I keep the aspect ratio at 40 or either increase or decrease it.


I have hubcentric spacers on my wheels (I think 10mm front and 25 mm rears). I do not think wheel rub would be an issue with increase the front width, but I am also wondering if it will hamper steering feel? I would think not since it is a modest increase.

 

You need to stick with the same aspect ratio (35). If you drop to 30, you would have to increase the tire size to 275 or 285 to maintain similar tire diameter to the rear.


Using the 255 will offer the best balance (no difference in over/understeer), giving you a 10mmm patch increase both front and rear.

 

+1

It's possible the rear spacers may be too much if they are really 25mm, because you're adding another 5mm tire width to the outside (and 5mm inside), making them equivalent to 35mm spacers. Your front 10mm spacers in front will probably be fine.

Most people with spacers used 15mm on all 4 corners. Are you sure your rears are really 25mm?

 

I just had a chance to go into the garage and take a picture of the spacers. They are H&R part #5035633, which are indeed 25 mm spacers. The fronts are 10 mm spacers. If I go to the 285s in the rear, with these spacers, I assume that would be the equivalent of the width of a tire that was 310? Does anyone know if that is just too wide, or will they fit without rubbing?

 

Just need clarification...if the stocks are 245/40/19 on front and I am moving up to 255s, should I keep the stock aspect ratio and go with a 255/40/19 or should I go with a 255/35/19?

 

The problem with your 25mm rear spacers is that they will push whatever tire size you have that same distance outboard because the offset of the wheel is fixed. From your picture it looks like your 275 rear tire was already extended beyond the fender lip. With a 285 tire, you're going to be extending it another 5mm both inside and out so you would then effectively have a 30mm spacer.

You can add a wider tire than even 285, perhaps up to 305-315, but you'd have to have a different wheel offset. For example the OEM 20" wheels on the F-Type use 295s, but they have a different offset than your wheels, which keeps the wheels tucked under the fender lip.

I think you're going to need to lose the 25mm spacers in the rear if you want wider tires. 15mm spacers on all 4 corners is what most use because you don't want the tire extending beyond the fender lip.

 

I realize that having the tires stick out past the fenders is considered an "open" wheel and not the safest/most legal thing, but I do like the look. If it fits without rubbing, would it have any adverse driving effects?

 

I've discovered that the front tires are throwing back some rocks to the rear quarter panel near above the area where factory film is applied and chipping the paint. This might help you calculate tire sizes.

Tire Size Calculator

 

Actually, your current setup will rub if you bottom out the suspension as a result of hard cornering or encounter a large dip or pothole at speed. Adding a wider tire probably won't make it any worse.

 

The sidewall on the 275/35 is 96mm and on the 285/35 is 100mm.
on the 245/40 it is 98mm and on the 255/40 it is 102.
Note in both cases the side wall is (only) 2mm taller in front than in back, so the 285/35rr and 255/40fr are a good match


The 255/35 has a sidewall of only 89 mm, making tire almost a full inch smaller in diameter than the 285/35.
Go with the 255/40 unless the 285/35 fits on the front as well (which I doubt)

 

No, it would have the same (interference) effect as putting on a 335 tire. When adding a wider tire, the additional width is shared on the inside and outside of the wheel. The width of a 25mm spacer reduces the outer fender clearance by the full width of the spacer, causing the same effect on outside fender clearance as adding 50mm to the width of the tire (which would reduce both inner and outer fender clearance).

 

Look at his pictures above. He's already outside of the fender lip on 25mm spacers with his OEM 275 tires and wheels. He implies that hasn't been rubbing for him, so that likely means he's not yet compressed the suspension enough.

 

I agree. If the car had a live axle, that wheel might still tuck up into the wheel well on full compression, but with the double wishbone suspension it will move up into the fender on that same plane.

 

Have you considered getting another set of 10mm spacers and using them on the rear?

 

After reading the helpful information in this thread, I am starting to have some doubt about changing from my current set up.

 

As long as you're thinking about buying new tires have you considered a set of 20" wheels? They will have proper offsets that would allow you to get a lot more tire on the car.

That's what I did on my base car, which came with 18" wheels.