Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG)

[rmay635703]

Originally Posted by Arragonis

I would be careful of fitting "bad" or "crap" tyres on the back, even in an FWD car - the rear does a lot more than just being dragged along, and if grip is the issue then understeer is easier to handle for most drivers - lift off, brake etc. A lot of tyre places here (UK) will only fit new tyres to the rear, and move rear ones to the front and most cars are FWD, very few RWD (BMW/Merc mostly) and very few trucks.

Just my 2p.

By crap I meant sporty High RR tires meant for looks not LRR.

But in any event I never did understand why oversteer was hard to handle. I have driven a lot of FWD and even on my cobalt a skid seems to be much more enjoyable than understeer where I have to rapidly turn the wheel back and forth to try to turn. which is quite never racking as you head toward an obstacle head on, oversteer I can sort of avoid and move still and if the backend hits its less dangerous to me at least

When in a skid two things I find desirable happen
1. I loose speed (like braking)
2. I can easily make it stop by doing some recommended and unrecommended things, oddly on my car turning hard and blipping the brake makes it instantly stop. Sometimes just turning the wheel or hitting the gas and turning the wheel work as well. In the winter I've found I can 360 and straighten (but only for fun)

Cheers
Ryan

[wyatt]

Originally Posted by thomason2wheels

I just looked up the available sizes inthe ecopias...its about like it used to be when buying a car. You can have any color you want as long as its black. Or in this case, u have a choice of two sizes...too bad, i would have like to try a set on my old wagon, but not by buying new wheels. Sheeeeeiiiiiiitttttt.

We have a spare set of rims. Steelies off another car, that we got for free. Our intent is to put winter tires on them if we ever move back north. So, buying new rims isn't necessary, but buying new tires will probably be necessary .

[MetroMPG]

Was there a change in circumference from the 17's to the 15's as well?

EDIT: also went to check your fuel log to see what it looked like. Not updated since 2010! Any chance you can add in some previous tanks & come back and post future ones so we can see how this plays out over a bit more time?

[Arragonis]

Originally Posted by rmay635703

By crap I meant sporty High RR tires meant for looks not LRR.

But in any event I never did understand why oversteer was hard to handle. I have driven a lot of FWD and even on my cobalt a skid seems to be much more enjoyable than understeer where I have to rapidly turn the wheel back and forth to try to turn. which is quite never racking as you head toward an obstacle head on, oversteer I can sort of avoid and move still and if the backend hits its less dangerous to me at least

When in a skid two things I find desirable happen
1. I loose speed (like braking)
2. I can easily make it stop by doing some recommended and unrecommended things, oddly on my car turning hard and blipping the brake makes it instantly stop. Sometimes just turning the wheel or hitting the gas and turning the wheel work as well. In the winter I've found I can 360 and straighten (but only for fun)

Cheers
Ryan

OK - by crappy I thought you meant the older tyres - the recommendation here is to put new tyres on the rear, and move the older ones to the front. I will be doing this with both our cars when they need doing.

Understeer is added to most cars for safety - if the front end slides then generally people lift off and the front tucks back in. If it combines with a lighter rear end then people panic, hit the brakes and spin or hit something.

I have no problem with oversteer and FWD, I find it fun - but for Mr or Mrs Commuter on a wet corner late at night it is not a good idea. And you also can't guarantee the rear hitting what you are heading towards, it could be the drivers door

[euromodder]

Originally Posted by Arragonis

I have no problem with oversteer and FWD, I find it fun - but for Mr or Mrs Commuter on a wet corner late at night it is not a good idea.

Though I learned to drive in a rather tail-happy RWD car, the first time I encountered (and caused ) some real oversteer in a FWD, I spun it 360° and met a light-pole midway in the journey.

[niky]

Understeer is always preferable. Because when something unusual happens, people have two instincts:

1. Let go of the gas.
2. Hit the brakes.

Either of these actions will tend to cancel out understeer and cause oversteer.

If the car is set to oversteer, the way to counter this will be to not do either, but to maintain steady throttle (for rear wheel drive) or to increase throttle (for front-wheel drive) and countersteer. Countersteering is intuitive, but what you do with the pedals is not... not unless you know what you're doing.

-

In that Cobalt, you're experiencing oversteer and understeer for two different reasons.

In a front wheel drive, if you are getting terminal understeer, you are going too fast. Way too fast. On a car that is set to oversteer, the only difference in that situation will be you are hitting the obstacle sideways. And no, that is not preferable.

If you get oversteer, you are getting oversteer in a car that is set to naturally understeer because you've upset its balance by jigging where you should have jagged or because you hit a slippery or rough patch midcorner. Without any input from the driver, it will tend to try to straighten itself out, whatever the driver does. Lucky for you. Some cars are not so good at self-centering, particularly cheap ones with no anti-roll bars and crude suspensions.

But if you change that balance... for example, by putting less grippy tires on the back... then your annoyingly dangerous understeer becomes annoyingly dangerous oversteer.

[MetroMPG]

Wyatt - any chance you can post a photo of the 17 inch wheel/tire combo when it was on the car?

I'd like to put this thread in rotation on the home page.

[Arragonis]

Originally Posted by niky

Understeer is always preferable. Because when something unusual happens, people have two instincts:

1. Let go of the gas.
2. Hit the brakes.

Either of these actions will tend to cancel out understeer and cause oversteer...

I agree, in most modern cars the setup is just to reduce the oversteer rather than go into oversteer - sometimes it is so slight that most drivers don't even notice. If they oversteer they think it is unstable, which is kind of true I suppose.

If they hit the brakes something like ASC will make sure they avoid the wall / fence / ditch by preventing oversteer via adjustng the brakes using the ABS system.

[ALS]

I did this with my old Volvo and got better fuel mileage. I went from 195/60/15 to 205/55/16's. The reason I got better mileage was the slight increase in tire diameter which translated into lower rpms on the HIGHWAY. Any increase in wheel tire mass or width will get you lower fuel mileage in a daily driver.

In the Gen III's the 17's will cut your mileage about two to three miles per gallon over the stock 15's.

[wyatt]

Originally Posted by MetroMPG

Was there a change in circumference from the 17's to the 15's as well?

Yes, but just barely. 1/2" difference between the two's circumference. I can take a tape measure to them and get actual circumferences if you like.

EDIT: also went to check your fuel log to see what it looked like. Not updated since 2010! Any chance you can add in some previous tanks & come back and post future ones so we can see how this plays out over a bit more time?

That's my wife's 2005 Prius. I got her to keep and fill out a fuel log that is kept in the car (so those records do exist). I have been meaning to take the log and update the Ecomodder log, but... well, it's on my list of things to do .

I haven't created a fuel log with my 2004 yet because... well, to be honest, I was a bit embarrassed at how "bad" the FE had been. This is on my short list of things to do

Wyatt - any chance you can post a photo of the 17 inch wheel/tire combo when it was on the car?

I'd like to put this thread in rotation on the home page.

My wife took some pictures of them on her car (hope that will work for you). Otherwise, I will have to do some deep searching to see if I have any of them on my car. I can get pictures of the new rims/tires for you no problem. The new rims are off a 2010, and naturally I am driving WITH the hubcaps in place
Also, I would wait a couple tanks before posting to the home page. I know things are more positive, but I would hesitate to show the 64mpg number until I verify (or debunk) with a couple more tanks. For whatever reason, our Prius' here can tend to make the fuel pumps shut off early. I never had that problem with my Swift...