67mustang302

I'm amazed at how so many people think that staggered front/rear tire sizing is bad for handling, when virtually EVERY current production performance car runs staggered front/rear sizes. It helps a lot with braking, since most of the load shifts to the front....the larger rear tires helps make up for the traction loss so you can utilize more rear brake.

Like I said, it really depends on the setup. And there are a ton of variables that determine what works best on any setup.

More front traction bias(softer front vs rear) will tolerate a larger rear tire. Lower front roll center will handle a larger rear tire. More front roll couple percentage bias will handle a larger rear tire. More(larger) rear sway bar bias will handle a larger rear tire. More power will handle a larger rear tire(in a RWD car). Better suspension geometry up front will handle a larger rear tire(which is EVERY solid axle RWD car on Earth). Better Ackerman angle for cornering(or alignment in general) will handle a larger rear tire. Less slip angle will handle a larger rear tire.

And then you can balance the traction bias to some extent with tire pressures. Higher pressure = more traction when cornering, lower = less. So run higher front and lower rear pressure(38/32psi for example).

And larger rear and smaller front doesn't have to mean huge drag radials in the rear and a skinny drag tire up front. It can mean a larger front tire, and simply a larger rear tire.

The main reason tire sizes are staggered on performance cars is because the front wheels have to turn to steer, which limits the maximum tire width that can be used. It's all about real estate. Equal tire size on all 4 is easy for rotation purposes, but won't necessarily work well for handling(AGAIN, depending on the setup).

A lot of Classic Mustang people complain about stiff rear springs, then they run 540 or 620 springs in the front, and then a GT or a 4 leaf at most in the rear with a soft shock. So they have a hugely biased soft rear suspension, and it turns the car into an understeering vehicle. In that case, yeah....a larger rear isn't going to help. Stiff front + soft rear = understeer....soft front + stiff rear = oversteer.

More tire = more traction. Period. If you add more rear tire and the car understeers worse, don't blame the lack of cornering on having too much traction. Blame it on having imbalanced suspension. Correct the imbalance first. If adding more rear tire makes the car understeer, then remove some front sway bar and/or add more rear sway bar, adjust tire pressure, put softer shocks out front....something. Correct the imbalance. Because from a practical functioning standpoint, just about every RWD V8 performance car on Earth should never be able to have enough rear tire....for accelerating or turning.

2+2GT

Wouldn't it follow, then, that a larger front tire would allow for better braking, by allowing higher caliper pressure, or even a larger brake rotor, and since most braking is done by the front tires, massively improve overall braking?

tx65coupe

I say get same size tires on all 4 corners it will drive and handle better. The larger rear ones are only really beneficial for drag racing in my opinion.

I had staggered tires before and won't do that again, except for maybe a pair of tires for going to the races, if I ever even do that.

While some of the new cars are setup with staggered tires, time and engineering went into their design. Thats not the case here.

67mustang302

Theoretically, yes. Actually, more tire everywhere will help with braking, especially in the front. Though you would have to make sure it's not so heavily front biased that it's difficult to steer under braking. But again, the real world engineering limitations mean that there's only so much space available to fit tires under all 4 corners. So the best alternative is generally to fit the largest tires under all 4 corners you can, and balance the suspension to utilize it.

Fronts end up being smaller cuz they have to turn to steer the car. So wheel well space and suspension components get in the way of larger tires.

67mustang302

Only for drag racing? Then why is it that the best handling performance cars in the world all have larger rear tires? It's not a matter of "it's a new car with time an engineering into it." It's a simple matter of suspension balance. Factory Classic Mustangs had terrible suspension from geometry, to balance and everything in between. And even when people replace it, they often select widely out of balance suspension components. Typically far to stiff up front relative to the rear....so the car understeers and wider rear tires make it more pronounced.

What's the typical setup a lot of Classic Mustang owners use? 540-620 front springs with a 1" front sway bar(or there abouts) and then a GT or 4 leaf rear with no sway bar. Then the same shocks all the way around. That's a recipe for imbalanced suspension.....far to stiff in the front relative to the rear. No rear sway bar, soft rear spring(typically chosen because stiffer rear gives a harsh ride, particularly in leaf spring cars), and the car is slightly nose heavy anyway. So it understeers heavily, and wider rears make it more noticeable. But the problem isn't staggered tire size, it's a way out of balance suspension.

Tires = traction. ALL of the forces generated by the vehicle moving are controlled by the 4 tiny contact patches where the 4 tires contact the ground. More contact area = more total friction to counteract those forces. That means better handling, braking etc. That's why high performance cars typically run the largest tires they can fit underneath(with cost and production factors being an issue in mass produced cars), and because of engineering constraints with front suspension and steering components, rears end up being wider.

Even Honda's 4 cylinder S2000 runs staggered larger rear tires.

The reality is that most cars with altered suspension are quite a bit out of balance. You want to know what a closer balanced suspension is in a Classic Mustang? My setup....620 springs in the front with a 1.125 sway bar and 5 leaf out back with a .75" sway bar. KYB Gas-A-Just all around right now. The rear is MUCH stiffer than what most people run on street cars, but that car is pretty close to neutral balance with a very slight tendency to understeer. But it easily oversteers in a turn with a little bit of throttle. It could prolly do a bit better with a 1" sway bar up front to give the front a tad more traction. But it also rides pretty stiff, and while it doesn't bother me, others don't like it.

Most people don't want a 5 leaf rear with a .75" sway bar so what do they do? They leave the front stiff then put a soft rear in it. And it pulls the suspension way out of balance. If you're only going to run a GT or 4 leaf rear with no sway bar, then the front should NOT be 620 with a big sway bar. More like a GT coil spring with a 1" sway bar at most.

But don't blame staggered tires on understeer or poor handling. More traction isn't the cause of poor handling. Bad suspension is. If you don't want a stiff rear, then run a softer front as well so the suspension is closer in balance. Then you'll find that you can run a larger rear tire, have a better handling car all the way around and have more traction on acceleration. A car with softer suspension that's balanced will handle a lot better than a car with stiffer suspension that's way out of balance.

Rat fink

I had L-60-15 on all 4 corners of my 69 Mach

tx65coupe

I agree that within reason wider tires are better since there is more contact patch so there is more rubber on the road. I'm not saying to go out and get pizza cutters.

I also see what your saying about the suspension being unbalanced.

Really wide front tires will make the car prone to road wandering, so bigger tires are not always the best idea.

The time and engineering that went into the newer cars is how they got the suspension balanced. How else is one going to do it?

67mustang302

Most of the time and engineering in new cars for suspension actually goes into multi-link placement and steering geometry(some of which is extremely complex due to the multi-plane geometry involved). Suspension can be balanced by changing spring rates for instance. It doesn't take a bunch of time and engineering to put a stiffer spring in, or add a sway bar. Suspension balance and suspension design aren't necessarily the same thing.

And also remember, the "time and engineering" factor for a Classic Mustang is now over 40 years. We have the advantage of being able to look back at the thousands and thousands of different setups run in different situations to have a better idea of what works and what doesn't. For instance, we know the factory upper a-arm location sucks.

Mis-matched springs and sway bars though, likely account for the vast majority of handling deficiencies in modified cars.

66 tang

my buddy has a 68 cougar with 245 60 14s front and rear, it looks great from all angles, my vote is same size all the way around cant go wrong, skinnies in the front make it look like a grandma car, no offense to the staggerd guys

kalli

well for me it's practicality. have 225s in back and would like more as i'm traction limited on hard accelleration even with posi. for the front I currently have 205s and don't want any wider as I have manual steering. I kinda like how it drives thios way, however I must admit that I don't do any hard cornering with the car (too precious).

you could always work with the aspect ratio as well