I just bought a new Honda Insight with 15" wheels. Can I change to 16" wheels when I have to replace the tires? Will that reduce the fuel economy? Will it increase stress on the engine?
Is there any benefit to increasing the diameter of the wheel? Would you think that a Mohawk hair do was worth $2,500?
If you do increase actual tire diameter, your speedometer and odometer will both under read and that will cause a decrease in apparent fuel economy, even if your actual fuel economy increases slightly.
The Insight is engineered for fuel economy so its probably already optimized for maximum fuel economy.
It’s vehicles that are geared towards maximum acceleration rather than fuel economy that can benefit from a overall increase in gear ratios.
When it’s time to replace the tires, I would worry more about replacing them with tires that are designed for low rolling resistance like the OEM tires are than trying to out-engineer Honda.
If you change to larger wheels and choose the correct tyres, the diameter of the new wheels should be close to the originals. There will be more steel and less rubber and air between you and the road. That will mean more precise driving and a little rougher ride. It likely will mean more expensive tyres and it will mean the tyres will be more venerable to road damage, like pot holes. If the diameter is close it will not do anything for or to the engine. It likely will mean more expensive tyres and that will likely be more than the total lifetime fuel savings you may or may not get.
A few things.
Make sure you replace with eco minded in MPG tires. The newest designs include low rolling resistance tires. The wrong tire can be a a few MPG loss if not careful. This has nothing to do with size but tires themselves.
The new rims cannot be the cheap rims as they typically are very heavy. Look closely at weight of new 16" rims when selecting tires. Honda likely uses lightweight materials in their rims to help MPG.
The speedometer will be fine if you upsize correctly. TireRack.com is excellent for a tire and wheel package and knowledgable. I don’t fell ordering tires is a bargain or ideal however their wheel/tire packages prices are excellent.
If you’re switching for looks, then the above comments are correct. If you’re switching for better handling, there are several better-handling 15" tires for your car listed at tirerack.
Forged wheels are stronger and lighter weight, but they are VERY pricey.
A cheap 16" rim on TR costs just under $100, but weighs 18 pounds. The lightest weight rim(13.7lbs) costs $219. The 15" version of those wheels weighs 9.5lbs and cost $199.
It will probably reduce your fuel economy, but it’s hard to say without knowing what wheels you’re looking at. If you get very expensive ultra-light wheels, then you’d be fine, but of course you’d blow all your fuel economy money on the wheels and then some.
If you get inexpensive 16 inch wheels they’ll probably be a good deal heavier than the factory wheels (especially since the factory wheels on the Insight are designed with fuel economy and therefore lightness in mind). The heaver a wheel is, the harder the engine has to work to turn it, which means using more gas.
If you want to get really technical, it also makes a difference where the weight is located - -if you take 2 wheels, each weighing 15 pounds, but one wheel has most of its weight around the hub while the other has most of its weight around the rim, the first wheel will get better mileage than the second.
So basically, the short answer is that there is no short answer. We’d have to know exactly what wheel you’re looking at before we could give you any sort of a prediction.