Mix Match Tires - ABS Functionality?

In my opiniy, don't you think the tire differentials would affect aerodynamics?
195F vs 175R?

Since the tires at the rear might be spinning at ....%, that might accelerate tire wear.

If you aren't concerned about the ABS lights showing on the dashboard, well go ahead. But to me, such an arrangement would impact on MPG.

Dxta

 

Sounds like you would be causing both handling issues and computer issues. A set of helper air springs in the rear might level the car, but why do it at all? You're going to need to raise the suspension height to successfully autocross in a Prius anyhow, since the factory clearance under the car is only 4 inches (about 100mm) placing numerous cooling system parts in harm's way. You don't want to lose the Hybrid System cooling while out on the course. Maybe a skid plate would help ahead of the cooling components.

 

The only answer to the abs light you're talking about, would be to try em out and see what happens. Sure, it would definitely lit!

 

The only thing i'm thinking is the ABS system in this car is already a hypersensitive pain in my nice person when it comes to wheel slip and reducing power...

So, you already hate the "every now and then" issue that arises when you hit a speed bump or certain road features that cause the anti-skid/abs to activate. But you want to add fuel to the fire by having rear tires that are always turning faster than the front tires? Glutton for punishment? Or are you thinking the car may only activate anti-skid/abs if the front wheels are spinning faster than the rear, in which case it may activate less frequently? The true answer to that is above my pay-grade, but it's an interesting question.

Heck, go for it and see what happens. Worse thing that could happen is the anti-skid/abs stays activated the entire time you're driving. That would make for a long drive....

 

That's pretty much all I can think too.

 

I still can't get what he wants to achieve with the mix tires, either.

 

Parking on grass with a hot catalytic converter is a prescription for a grass fire no matter what vehicle you drive.

 

If you want the lowest rolling resistance, tire compound is really just as important as size. So I would look at what sizes you can get Michelin Energy Savers in, as they're about the lowest rolling resistance tire that can be found out there. I'm not sure they make a 175 size.

More important is to think about the safety of running such a setup on the streets. The car will likely have a strong tendency to oversteer with the smaller rear tires. Cars with much oversteer are dangerous on the street. To get the car neutral again, you might need to increase the size of the front sway bar or decrease the size of the rear. If the traction control does not fault from normal running, I expect it will make it much more sensitive (ex. if the traction control triggers when there's a 10% differential in tire speed, you're already half of the way there when running different sized tires). In the rain or snow you may see the car behave in the opposite manner - where suddenly it gets very understeery.

If I was going to run undersized tires, I would do it on all 4 corners. I also wouldn't consider it until after doing some pretty extensive other eco mods: lowering springs/coilovers, side view mirror deletes, moon wheel covers, front grill block, weight reduction, etc. I also think there's a 175/##-R14 sized tire that's pretty close in diameter to the stock tire size.