Please help me beat a dead horse.....

Our 2003 Prius always had neutral, straight-line, stability. You had to steer it all the time because if was just as happy to head off to either side as track down the highway. But in 2009, I wanted to test what happens if the largest diameter, same vendor tires were used. So I drove to Madison WI, ~750 miles, with slightly over stock diameter tires on the front and maximum sized, oversized tires on the rear and swapped them for the return trip.

On the way back, the larger diameter tires made the car significantly better. Straight line stability was significantly improved and the return trip was much easier. So I could change tunes without having to worry I would find myself on the shoulder.

On the way up with the stock sized tires, the odometer calibration was slightly, ~1%, off from the mile markers and GPS. But the return trip was 6% off with slower turning drive wheels.

Now driving with oversized, front tires means the indicated speed and distance is lower by the percentage oversized. The tires are turning slower which reduces 'rolling drag.' So I drive at a slower indicated speed but am actually traveling faster. The downside is acceleration may be slower . . . as if a Prius is drag racer. The indicated MPG is lower but when adjusted for the true distance covered, there is no detectable MPG hit. In effect the mph vs MPG curve is shift up ~6%.

Now our 2010 Prius has never had the neutral stability issues of the 2003. Since the MPG is the same as the 2003 but at 5 mph faster, there is no need for 'over drive' diameter tires. Having towed 1,700 lbs of trailer and airplane 600 miles, I prefer having the tow capability. But if you are having steering stability issues, consider:

• 4-wheel alignment - requires a shim kit but can put both front and rear toe and camber perfect. I did this first but could detect on significant improvement other than the 'bias' to wander off to one side was reduced. Still neutral stability but without a bias.
• larger diameter tires, front or both - use the 'revs per mile' specification to select the tires. You can experiment with just one pair and swap front-and-back to quantify the effect. Use the rear wheel well to measure the critical dimensions and test hitting a speed bump at faster speeds to make sure it does not rub the well on a bump.

GOOD LUCK!
Bob Wilson

 

I agree.

Over the years, I've found certain tires are "better" at following grooves than others. I'd have to put the Yokohama S33 and Kuhmo ASX as two of the worst.

I was very surprised how my Co-worker's prius with Ecopias did not wander like mine with S33's. It was a completely different car.

If those tires are still available, they will definitely be on the top of my list.

 

I had alot of stability issues driving my 04 and now with the 2010 i still feel it with crosswinds and getting behind semi's.. Worst behind the trucks almost have to constantly fight the steering wheel to keep her going straight car really blows around. Kind of crazy because i have had it upto 100 mph and it seems fine at these speeds..

 

Can't wait for the review and pics. thanks for being the guinea pig.

 

Lester, before you buy new rims spend the money on the Michelin Energy Saver A/S. I think you will be happy and won't have to change any thing else.

Ron (dorunron)

 

Lester Williams, your not alone! For those who do not have this "drifting" problem, it feels like you "float" around on the road, and it takes way more concentration and steering wheel input, to keep your car in your lane- then it should. The car just keeps "drifting & floating" around for no apparent reason. (No wind, no ruts, no rain grooves, just floating, and drifting, side to side). IMHO Its not the typical alignment problem, as the car goes straight, letting go of the wheel, yet, will still float, side to side. Our 2014 Prius that has stock standard size Bridgestone EP20 tires on it has had the "floating & drifting" since we bought it. I believe it is an alignment - toe-camber problem. We have a Classic 69 Buick Skylark, and when I restored & rebuilt it I had the front end totally replaced. The mechanic set the toe & camber totally flat, and straight. As much as the car went totally straight, not pulling left or right as an alignment problem would indicate, it drifted & floated all over, just like our Prius is doing now. This with some Hefty, wider- bigger than stock new radials on it. (so wider & bigger tires will not help). I took the Buick back, told the mechanic what it was doing, and he fixed it by putting in an ever slight amount of toe to it, so it was no longer totally flat. No problem with tire wear 10 years latter, but no "floating or drifting" either. So I will be suggesting that to the Toyota service guys when I have my 5000 mile check up done-- soon.

 

I don't think it is anything wrong with the car, alignment or otherwise I am experiencing the exact same thing he is talking about. I experienced it first while driving, then my wife who this is now her car and is coming from a Jeep Grand Cherokee experienced it as well. I truly believe it is the tires.

Now as some have said maybe just a new brand of 15" tire will help, I have the S33's. I was thinking a wider tire would help so that is why I was going to step up to a 17" or 18" tire and go wider. Obviously like many I don't want to give up MPG. Having said that I think there will need to be some sort of compromise. How do I get a safer feeling ride at higher speeds without losing TOO MUCH MPG's.

 

If you have time, try and run two, 10 mile, benchmarks on cruise control over a know route and record temperature and winds:

• under 41 mph - to test the hybrid range efficiency
• over 50 mph - to test higher range efficiency

Try to choose speeds you often see so you'll be able to compare before and after values.

Bob Wilson

 

Will do,,, I will have a fairly good idea of how much of a ''hit'' the mpg will take after this week-end. Elsie lives 80 miles from me [ visiting today ] and will ride over this week-end as we usually go to church together every Sunday, have lunch. I will get new tires on before the trip over-- a ''known mpg route''. I can live with 3-4-5 mpg loss as I registered 59.2 on the dash today for this trip. [ Great reason to drive a Prius, for sure ]

 

New tyres can take a substantial fuel economy hit for the first couple thousand miles.

 

The OEM Bridgestone Ecopias could 'wander' on worn out sections of the road. You know where trucks leave tracks or dents in the asphalt.

My current Nokian WRG3's and previous GY Tripletreads did not exhibit this 'tramline' behaviour.

Hope your new tires are to your liking and track better.

Roland

 

Lester, which tire did you get? The Premier or the Energy Saver A/S. You mentioned them both in this string?

Ron

 

I'm glad to hear there are tires that can get a good number of miles on the Prius. Mine came with Goodyear Assurance, so I have no idea what to expect, not that I really care. I don't put a lot of stock in stock tires, but I hope I get more than the 18,000 I got with the Goodyear Eagle GT+4 that came on my 1988 Grand Prix, what a disappointment those were.

 

Overall, I've seen good mileage out of stock tires. The biggest downer my parents had with their Highlander. Tires lasted around 40K but the real shocker was the road noise AFTER they put new tires on the vehicle.

Part of why the ride was so quiet was that the stock tires were softer rubber...by design. They don't last as long, but they really muffled the ride noise. Putting anything on that had a good lifespan rating came at the cost of how quiet the ride would be. Not something Toyota advertised when they were test driving the vehicle.

 

That many be true of the Highlander, but my experience with our van was just the opposite. The quietest ride was with some 80,000 Michelins, not the 40,000 BFGs it came with.

 

I buy nothing but Michelins. A quiet ride has been my experience with every set I have had. I just bought a 2014 Avalon Hybrid XLE Touring. It has Michelins on it. Same with it, quiet and comfortable. No noticeable road noise. I took a Lexus ES300H for a test drive. I wish I had looked at the tires on it. The road noise was extremely loud and I just drove about 35 MPH.