In Oct, I replaced all 4 tires on my 2001 Prius at Sears. Before the replacement, I regularly got 44-48 mpg; now I only get 30-32 mpg. Sears says they put the right size tire on (Guardsman Plus) and the problem must be something else. I took it to the dealership and they said the tire size is correct, but the weight-bearing ratio (??) is wrong, but that would only account for 3-4 mpg less. The “check engine” light isn’t on, but the dealership ran a diagnostic test and didn’t find anything wrong. The dealership also suggested that driving in colder weather may result in lower mileage (but 15 mpg less???).
Any suggestions about the problem?
Your Prius came with low rolling resistance (LRR) tires. Are the Guardsman Plus tires LRR? That may be the problem.
Cold weather is likely culprit. How long have you owned this vehicle? A few winters at least?
The tires may give a 4-5mpg drop max if high rolling resistance vs low on before.
Probably a combination of cold weather and the Sears tires.
Ed B.
As was already suggested, the problem is almost sure to be those tires, with an additional drop in mpg as a result of continued cold weather conditions.
Not that many tires are the true LRR type necessary for the Prius to achieve its advertised gas mileage. Unfortunately, you did not do enough due diligence prior to buying tires.
Next time, instead of focusing merely on price and size, be sure to research other factors also, including the rolling resistance of tires before purchasing them.
Sorry!
You should be aware that the new tires have worse rolling resistance than worn tires - all other things being equal. This means that even if you had replaced the tires with exactly the same thing, you would have taken a hit in F/E department.
Replacement market tires are designed for either good wear or good traction. OE tires are geared more towards rolling resistance - and you improve that property by sacrificing treadwear and / or traction. Perhaps you noticed that the OE tires were defficient in those areas. So you took another hit by purchasing replacement market tires.
And lastly, I get a lot of comments this time of year about F/E going down. Certainly the gasoline formulation, and the cold weather have adverse affects.
“You should be aware that the new tires have worse rolling resistance than worn tires - all other things being equal. This means that even if you had replaced the tires with exactly the same thing, you would have taken a hit in F/E department.”
somewhat true, but in this case i suspect the sears tires have AN INHERENT GREATER ROLLING RSISTANCE.
i used to get 40 mpg OVERALL with my '03 corolla. to save the cost of mounting/dismounting winter tires, i bought a set of ‘aftermarket’ tires and alloy wheels which also happened to be 1" oversize. this did add to its sportiness and cornering ability, but at a cost!
my mileage plummeted to 33 mpg! this, despite a nearly identical driving style. (i WAS able to corner at higher speeds, a hypermiler trick; still not sufficient to maintain the previous FE.) the oversize tires simply had more rolling resistance, a side effect of the sporty intent of putting more rubber on the road.