[braisler]

Hey, fellow Insighters! Or is that fellows with Insight? I have a query for the group. I bought a Red 2000 MT A/C Insight with 88000 miles about 6 months ago. The joker who had a car before me, switch the tires out to the wrong size and not LRR. I'm not looking at the car right now, so I can't say the brand, but I have checked them online and they are not low rolling resistance. They are 185s instead of the original equipment 165 Potenzas.

Now, since buying the car, I have had somewhat disappointing MPG results. Yeah, it still kicks everything else out there on the road including some motorcycles, but I still want it to perform the way that it should. The best that I have been able to manage with very careful driving technique and occassionally irate drivers behind me (because I am ONLY going the speed limit and not 10-15 MPH over) is a paltry 56.4 MPG for a tank. If I drive more keep up with traffic style, the MPG is more like 52-53. Since this is a MT not CVT, I thought I should be getting more like 65, maybe even pushing 70 with careful driving.

So the question that I am faced with is should I switch out the tires on my car now at a cost of $300+ just to get back to the Potenzas? The tires that are on the car now are in good shape, about 70% tread left which means that they would be good for the next 20-30K miles minimum.

So for the purposes of this exercise, let's assume that I am going to get 30K miles out of the tires and that my mileage will remain around 54 MPG. That means, that I would use roughly 555 gallons of fuel for that distance and if fuel is at $3/gallon, it would cost me $1666. If I change the tires, I might reasonably expect to get 65 MPG average, putting me at 461 gallons at a cost of $1384 and a savings of $284. If I am able to attain 70 MPG, the equation shifts further in favor of switching the tires since it would mean 428 gallons, costing $1285, and saving $381. But all of this is based on the assumption that switching the tires will give me the fuel economy that I have been missing. It could be that there is some other hidden problem with the car that is affecting the fuel economy. I had the LAF sensor replaced just after I bought the car, but I don't know the full history on the car since I am not the original owner. I do know from the dealer that the battery array has not been changed.

Is there anything that I have overlooked in my calculations? I know that I have addressed things from the detached economics standpoint. I haven't addressed the emotional satisfaction that I might derive from getting the absolute best fuel economy out of my little baby. I am quite jealous of you folks out there who are getting 75+, 80+, 90+ MPG out of your Insights. I would love to be able to get the best that I can out of this car, I am just trying to decide whether the tire switch is the right thing to do. Thanks for letting me talk this out.

Cheers,

Brian

 

[boogetyboogety]

Looks like you did your homework, figuring out the RI carefully and thoughtfully. One minor, piddly thing thing you might have overlooked: after you take the non-LRR tires off, sell the set and add that $$ to your savings. But it seems to me by your own calculations that switching over to Potenza LRRs like you're supposed to have on your Insight will make your tire investment pay for itself in the next year or two...

Also: Check some threads here for some replacement costs savings on the set, I understand Tire Rack and Costco, for instance, have some compelling prices... I bet others will jump in here and provide you with verification or other sources...

 

[originalbadbob]

Tire Rack has OEM tires for around $55 plus shipping.
Rick Reece and I did a comparison with my LRR Sumitomo tires (which came with my car and are currently under my house in trash bags), which you can find by doing a search for "tire + comparison + test"

[moderator insert: I quote it all the time Bob :!:

See:

Tire Comparison Test
http://www.insightcentral.net/forum/vie ... 38&start=0

[end insert]

I'm glad I switched, as my mileage went up a lot, and they have paid for themselves easily.

Yes they may "hunt" on a grooved surface, but I got to the point where I would let go of the wheel when going over a place in the highway where they were doing construction and it felt weird, like a motorcycle on the same type of pavement, but it didn't go anywhere other than straight. They also don't ride as well, especially pumped to 50, but I'm glad I switched. My mileage in 35000 miles has gone from 54.7 lmpg (when I bought the car with 33000 miles on it) to 72.1. I expect to hit 75 lmpg this summer although it is going up very slowly now.

robert

 

[jtmco]

Brian-

It sounds like you are at about the break even point economically. If that is the case, you could put the $300 in the bank until you need new tires and make the interest (maybe a whopping $10-$15 per year) :lol:

One item you didn't address: What part of the country are you in? Was it very cold where were you were the last 6 months? Has your mileage improved as the weather warmed up? It might mean you are doing better than you thought you were with the existing tires.

I have the Potenza's and my lmpg is about 59 mpg. I commute 12 miles to work with a mixture of city and highway and if it is really hot out, I run the A/C. I've done as well as 75 mpg on a long trip (55 mph with no AC) and as poorly as 48 mpg (winter with lots of rain, stop and go, defrost).

Good luck.

Jim

 

[braisler]

Thanks for the replies so far. I am leaning towards replacing the tires. And, yes I have considered selling the old set for some extra $$ saved since they are in good shape. I was actually thinking about getting the tires through tire rack which would run me $220+shipping and then taking them to a local used tire place for installation. My hope is that they would be willing to install the new tires for free if I let them keep and resell the old set. Installation around here usually runs about $15/tire? and they might be able to sell those tires for $25 each. I might be able to get that out of them too, but after how long advertising them in the paper.

 

[Guillermo]

Your mileage will improve by about 10% with the OEM tires but your car will feel very different.

 

[braisler]

To answer Jim's questions, I live in Kentucky, so the winter is fairly moderate. I have not noticed a significant change in MPG with the warming temps. My best tank so far was back in Feb-March just after having the LAF sensor replaced. I was kind of babying the car, both because I was concerned about having that CEL come back on and because I wanted to see what the best mileage I could get out of the car would be.

The LMPG on the car is quite low for a MT at 48.9, though that is up from 48.2 since I bought the car.

Guillermo, I understand that the car may have a harsher ride with the smaller tires. Though my ride seems harsh enough with my current tires inflated to 45 psi. Any other differences that I would likely feel? Grooving on uneven road surfaces? Any difficulty with LLR translating to poor braking or slipping during acceleration?

As an aside, this city (Lexington, KY) is an absolute killer on MPG. The traffic control office has ALL of the lights timed incorrectly. I refer to it as the "gotcha" system. In well-planned urban areas, if you drive through a green light and are going the speed limit, you should hit the next few green lights as they are timed to allow smooth flow of traffic. Here in bass-ackwards Lexington, they have the lights timed just the opposite. If you manage to get through one green light, you can be sure that the next will be red. Many times, the light I am sitting at will turn green and 1.5 seconds later, the next light 300 feet up the street will turn red. Gotcha! I would say that I get 30-40 MPG in the 4 miles of my commute within the city and better than 55 once I get out of the city limits.

 

[trunkout]

hell

i'll never go back to stock tires again.....i don't miss that "skating" feeling...

:lol:

 

[bretthans]

Any other differences that I would likely feel? Grooving on uneven road surfaces? Any difficulty with LLR translating to poor braking or slipping during acceleration?

There is a common misconception that LRR translates to poor traction. Rolling resistance is basically energy lost as heat in the tire itself and is determined by several factors, the largest being sidewall construction. Tire manufacturers tend to use cheaper materials at the expense of rolling resistance. They'd rather not put in the silica and other more expensive compounds.

That being said, the OEM Bridgestones aren't great for handling. I'm not convinced it's due to the LRR construction, I think it has more to do with the way the tire is designed. The tire tracks grooves in the pavement like a motorcycle, which is very disconcerting to just about everyone. This is likely due to the tread design, since other tires of similar size on the Insight do not have the same problem. The snow handling is not great either, but you should be fine in KY. I've been doing OK with the OEMs in New England winters so far.

Personally I prefer the increased mileage of the OEMs and I drive accordingly, but I keep hoping some manufacturer comes out with a better-handling tire with the same or lower rolling resistance. I'd love to see heated competition for LRR instead of the niche market it is now.

 

[Willie Williford]

tires

Brett:

The "snaking" you are talking about is NOT due to the design or thread pattern of the tire . It is due to the difference in the TRACK of the Insight 4.5 in difference in the front and the rear.

I use 175's in the rear and have no problems with the rain grooves on the freeways.

Willie