I have seen a few questions recently about installing oversize wheels/tires on 'Stars. Found this table that I thought might be of interest:

It starts with the stock wheel/tire diameter at 26.70"


WHEEL SIZE TIRES TIRE SIZE OVERALL DIAMETER
16" KUMHO ASX 235/60R16 27.1"
17" KUMHO STX 225/55R17 26.8"
18" KUMHO ASX 235/50R18 27.3"
19" TOYO T1-S 255/40ZR19 96Y 27.1"
20" TOYO T1-S 245/35ZR20 95Y 26.9"
21" TOYO Proxes T1R 255/30ZR21 93Y RD 27.1"

 

I don't even want to know how much 21" tires cost!

 

I have 20s on my Aerostar and found good pricing on the internet. I paid 130 each but now paid about 100 each for the 255/35x20 Wanli 1098. Will have to try them in the snow since mine is AWD.

 

Thats not too bad, but I think 20" is a much more common size then 21". Heck, 22" and 24" are probably more common then 21" too!

 

How well does a 255/35/20 tire fit in the Aerostar wheel wells? What offset or backspacing are on the wheels? That seems like some very narrow strips of sidewall between the wheel and road; about 3.5" vs the stock 6.4".

 

I have a 15mm postive offset and they don't hit anywhere on the vehicle. The ride isn't too different from my stock 215/70 x14 on good roads.

 

Funny, I missed B-Aerostar's reply until I did a scan tonight.

Do you find the bigger tires make the van handle better? (at least on dry roads?) Have you had to drive it through deep water yet? There was a torrential rain here last night, and even the stock skinny tires were having trouble in the deep waters.

 

Handling is better, I have a friend with a BMW X5 and I stay right behind when we come off of the exit ramps at double the posted speeds. Braking better too. The tires are 3 season designs(Summer,Spring and Fall).

 

A bigger wheel and lower profile tire should make the turn-in crisper, and assuming that the lower profile tire has a grippier tread compound, it should also increase the limits of adhesion. However, what a lot of people don't realize is that a very large wheel is a very heavy wheel, and unsprung weight is not your friend. Let's say that the stock 14" alloy wheels weigh 15 lbs. I don't know if they do or not, but it's a reasonable number. A stock replacement 215/75-14 tire weighs about 23 lbs, so the combined weight is 38 lbs per corner. A 20" wheel can easily weigh 35 lbs on its own, and then the tire adds another 26-27 lbs or so.

Now the wheel/tire combo weighs about 62 lbs, so have you added almost 100 lbs of dead weight to your van. That's 100 more lbs that the 4.0 (or worse - 3.0) liters of pushrod fury has to pull. What's more is that the additional weight is both unsprung and rotating. Chances are that the shock valving and spring rates are way off for carrying that heavy of wheel and tire combination up and down over bumps and through corners. But also, the inertial effect of the heavier combination requires a lot more torque to overcome just to get it rolling.

If you did back to back acceleration comparisons with the same van using stock wheels/tires and then a 20" combination of the same rolling radius, you'd find that the stock package will always be faster, just because of the weight and inertia difference. The laws of physics bend for no man, so you might as well use them to your advantage...

 

Yeah you right about the performance. Its has some mods done but it slower than before and the worse gas mileage of any vehicle I have ever owned

 

I agree, larger wheels are more of a styling thing. Unsprung weight is the enemy.

ken

 

The very act of "putting more rubber on the road" means adding more weight to the tire at the worst possible place; out at the perimeter where it will create the most angular moments. The same applies to getting bigger wheels. Not only is this going to slow down acceleration, but also braking. But knowing that this will be the performance cost, you can decide on how much of this you're willing to accept for the added traction that you would get.

The Ford GT supercar uses 18" wheels up front and 19" in back, both with really wide tires wrapped around them. I'm sure it's for more than show. They help give the car neck-snapping acceleration and eyeball-popping stopping power. But then, its suspension was designed to handle this amount of unsprung weight.