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Discussion Starter · #1 ·
Hello,

I know a while back in another post I asked for info on going up to 17's for aftermarket wheels instead of the current stock size of 16. I was curious if going up one size would mess with the Speedometer, Odometer or anything like that. Everything I read about it and even responses on here said it would not mess with it. I ordered new wheels and tires (MSR 046 in size 17 and some Maxxis Tires to match), the place I ordered them from does a ton of aftermarket work and also a lot of dealership mod cars. They also said that these wheels and tires would not change any of the settings or meters in the car. I got these put on Friday and have noticed pretty much instantly that the MPG went down on the car. I refilled the tank and drove it around for a while and it was getting about 4 MPG less than it did before. I know the weight of the new wheels and tires can mess with MPG sometimes but would not imagine that much. So I filled the car back up and manually calculated the MPG and I got an average of 34.9 MPG where as the car was saying 31.6. I drove it around more over the weekend and the car was still getting around 31 to 32 MPG. I filled it up again yesterday and manually figured up the MPG and I got 35.2 MPG. So my question is has anyone else come across this? it sounds like the new wheels and tires despite them being 17's and the CRZ having an option for 17's these may have thrown something off in the car. I do not know much about wheels and tires but I knew enough to ask questions before I got an upgrade to bigger ones so since everywhere I looked and everyone I checked with all agreed it would not impact anything I cannot figure out why it is... any info would be greatly appreciated.

Thanks,
-R
 

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When I asked my deal about getting 17"s and messing with anything they told me when they install the optiona 17"s they do chance a few things (the service writter was not sure what) but I am willing to bet the stock MPG calc assumes stock rim size (possibly even tires) so it could through it off. I have not looking into how the car calculates MPG but I plan on doing that this week.
 

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Discussion Starter · #3 ·
well my guess is the car figures up MPG just like I do. It divides how many miles I have gone by how much gas in the tank has been used... so if say I go 50 miles and I used 2 gallons then my MPG is 25. My concern is if the MPG is thrown off then maybe the Speedomater and Odometer is thrown off, making the car show its going fewer miles and also a slower speed than it really is. If that is the case and the Odometer has been compromised then unless I am wrong that could void the warranty :(

-R
 

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If the overall diameter of the oem 17" upgrade is larger than the stock wheels and tires, then yes the dealership would alter the cars calculation of distance traveled per tire rotation (revolutions per mile) This changes speedometer, odometer, and mileage ratings.

If someone knows the tire diameter of the 16's vs 17's we could verify this, I cannot search for them at the moment.

Dealership may also be able to adjust for aftermarket wheels tho if this is the case.
 

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do some reading and its common sense.

larger tires mean your speedo will read slower than you're actually going and your odometer will read lower than you actually travelled. on top of that your MPG may suck due to the higher rotational mass.

smaller tires are the exact opposite. You will notice more "pep" due to the lowered rotational mass and your speedo will read faster than you're actually going as well as the odometer.

its reccomended not to change outer diameter any more than 3% of a difference.

for 17" tires,

205/45/17, 215/45/17, 235/45/17 all have differences of 0.7% or lower. 235/45/17's have a difference of 0.17% they are pretty much perfect. However they are a little wide for the fender liners. Pairing that size with a light rim will give you the same MPG's as normal. with the added grip, looks and handling.
 

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Discussion Starter · #6 ·
Well I talked to Honda and they said there is nothing they can do, when they put the 17's on a CRZ they dont mess with anything. They also said there is nothing they can flash or change to make it read different, these cars are already set to handle up to 17 inch wheels if they are the same basic specs as the OEM 17 offered. I talked to the place that put the new wheels on and they are having me come in because they dont believe it should be causing any changes. I did do reading before I got these put on and I also asked question, so yes I know bigger wheels can throw stuff off sometimes and more weight can lower MPG. That is again why I asked multiple ppl as well as checking with the installer and Honda. The installer says these wheels are almost dead on with the specs of the OEM 17 in wheels offered from Honda, so if Honda says nothing has to be flashed then the car should be good. It is not the cars real MPG that has dropped its the MPG the car is saying it is getting that has dropped, as I mentioned above the MPG I get when I figure it up averages in with what I got before the new wheels and tires and I did more than one refill of the tank to check the figures again and again. Hopefully I will find out more info when I get it looked at after work today. I am glad that Honda did let me know it wont impact the warranty on the car other than the Wheels and Tires since they are not OEM. I was concerned that if the new wheels messed with the Speedometer/Odometer that might mess with the warranty but like the Honda guy said, if that was the case then they could not offer modified cars on their car lots with aftermarket wheels or even larger OEM Wheels and still have a warranty on the rest of the car.

Thanks,
-R
 

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Discussion Starter · #8 ·
Thanks for the info Chase but the cars actual MPG has not decreased, its just the MPG Meter on the dash is saying its getting lower MPG than it really is... so it seems like the new wheels and tires (despite being roughly the same specs as the OEM 17 Honda Wheels and Tires) are throwing off the cars readings.

-R
 

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wait you already have the wheels on? You never said what size tire you went with. Thats the key factor into if your speedo will be messed up...

*facepalm...

Try to space things out instead of typing a mountain of text. its quite hard to read.

also you never looked into the weight of your wheels. generally 17" wheels will be heavier them OEM hence a decrease in MPG, faster to wear out brakes, etc.

stock wheel weight is 36.5 lbs.

I just googled the rim you chose, it looks HEAVY (and real ugly) you wont see good MPG with them. Sorry about your (bad taste) Luck.
 

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Discussion Starter · #10 ·
Sorry its the Style 045 not 046 and they are the black ones with the red lip and look good on the car.. last time I checked this was a discussion about what might be causing the issue not what you think looks good or smart ass remarks by you about taste and such or posting more words than you can read. It is already obvious that if someone post anything with too many words in it you have issues reading it, that is most likely the reason why you posted info that did not match with the info I posted. How would my MPG go down if I had not put the tires on yet? I also mentioned in the very first post that they were put on Friday! anyway back on subject. MSR shows these wheels are 21.9lbs per wheel, so if 36.5lbs is the weight of the stock OEM wheels these are wayyy lighter. I will post an updated once I get done with the installer this afternoon and we see what is causing it since they say the wheel and tire specs are fine and should not be throwing it off and Honda says if they match the OEM specs it should not be throwing it off either.

Thanks,
-R
 

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36.5 pounds is combined wheel and tire weight.


21.9 pounds is a heavy wheel. My 18x8 arent even that heavy. Did you ever calc ur mileage manually before the install?
 

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Discussion Starter · #12 ·
Yes I did manually figure up the MPG before to see if the MPG Meter in the dash was correct (this is my first car that has had one of those so I wanted to be sure). Everytime that I manually figured up the MPG it was pretty much dead on with what the car showed. Now when I manually figure up the MPG myself I show the car getting better MPG than the MPG Meter in the dash is saying it is getting. I did also try driving the car the same way and the same routes this weekend and then refilling it a few times. When I refilled the car and checked the MPG manually it always showed the MPG higher than the car was showing and my manual figure was closer to the normal 35-36 MPG my car gets roaming around in town where the car was showing its MPG as 3-4 MPG lower.

Thanks,
-R
 

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21.9 lbs for the rim plus say 23 lbs for the tire puts you at almost 45 lbs. thats almost 10 lbs more per corner of unsprung weight.

Unsprung weight has more effect on a cars performance than sprung weight.

For every pound of unsprung weight you add, its the equivalent of adding 5-10 lbs (the actual weight is arguable ive heard both 5 or 10 lbs) of sprung weight. PER CORNER.

so adding those wheels say at 45 lbs, youve added:

45-36.5=8.5lbs of unspring weight per corner, *4 is 34 lbs of added unsprung weight.

Multiply that by 5 at the low end and youve added 170 lbs to your car, multiply that at the high end of 10 lbs and youve added 340 lbs to your car.

on top of that you have to add your weight, passenger weight and cargo weight.

you think carring an extra 340 lbs isnt going to have an adverse effect on fuel economy? think again.

OP you may have asked a ton of people about your wheels, but clearly you didnt ask the right people.

we had lots of into and discussion about unsprung weight and improving the cars looks and handling without destroying fuel economy.
 

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it it makes any difference to you, after my switch, i can still get almost 4.7 l/100km if i try. And daily driving city i still see 6.3-6.5l/100km. With good calculations and a little knowledge
 

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Discussion Starter · #15 ·
Yeah apparetly Honda and the installer that installed stuff for them, Toyota, Nissan, Ford, Chevy and who has also done the wheels and tires on my last two cars did not know what they were talking about. I cannot speak for the people on here who responsed to my first post asking about any issues with changing out the wheels because I dont know them and there are members from various locations on here. Again yes I understand new wheel and tires increasing weight will impact MPG but them weighing more would not make the car think it was getting lower MPG when in fact it was getting more its normal MPG right? that would be something else off such as the Speedo/Odo. I think we can pretty much put to rest this (the wheels weigh more so the MPG is worse theory) in this case the wheels/tires weight does not appear to be impacting the MPG its something throwing off the cars readings and how it figures up its MPG... hopefully I will find out more after work, they are going to pull the wheels off and throw a set of OEM Honda 17's on and test it and see what readings they get.

Thanks,
-R
 

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Discussion Starter · #16 ·
I do know calculations actually and if my MPG figures are pretty much the same now as they were before I changed the wheels out. Then the MPG really has not changed its just the car is reading the MPG wrong due to the wheels throwing things off. Even as both Honda and AC Sport said, unless I got some super heavy ass tires and wheels then I would not see a major decrease of MPG. They also agree since I can manually figure up the MPG and its more in line with the normal MPG the car got before the new wheels and tires, then it cant be the new wheels and tires have actually impacted the MPG.

-R
 

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There are several factors working against you for MPG when you go to aftermarket wheels/tires...

1) Wheel Weight - Obviously lighter is better
2) Tire Weight - Often overlooked, but can vary dramatically and is also important
3) Tire Width - Wider tires = larger contact patch = more rolling resistance
4) Tire Compound - Stickier compounds = more rolling resistance
5) Tire Outer Diameter - Larger or smaller diameters will change the overall gearing of the car which can vastly affect MPG.

You say you are concerned only about your speedometer accuracy if I read this correctly... and that would only be affected by #5. I haven't seen a post of your tire size yet, if you know that, you can calculate exactly how much your spedo would differ from stock here: Tire size calculator

Another thing you can try... if you have an iPhone or Android phone, get a spedo app, turn it on and drive. Compare the phones speed to your spedo in the car, and see if there is a significant difference. Those phone apps aren't dead accurate, but they are pretty close.
 

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Discussion Starter · #18 ·
Since manually figuring up the MPG is showing higher MPG than the car is showing, then yes my only real concern is the car being off on its readings. I am at work right now so I dont have my car beside me to read the tire size off. One of the things the install shop plans to do is put the car on a machine they have that will read the real speed and distance the car would go in the test enviroment and then run that against the speed and distance the machine says it should have gone and compare them. That will tell us if the Speedo in the car is being thrown off because of the new wheels and tires. The good news is that they dont seem to be trying to give me the shaft since both AC Sport (installer) and Honda feel these wheels and tires should not be causing this. The outcome will either be I keep these wheels and tires and they find a way to correct how the car is reading or we go with some other wheels and tires that dont cause this issue... thanks for the info on the App though :)

Thanks,
-R
 

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You have stated the diameter of the wheels you purchased, but I do not see in any of the posts the size of the tires you put on those wheels.

What size are the tires that you put on the new 17" wheels?

As for the computer and your manual calculations not matching up. A couple things to keep in mind are. First when you fill up, reset your car's trip mpg meter. So that you are reading the fuel economy for that tank and not an average of a long period. Second, you can have a lot of variation in the amount of fuel you fill the tank with, so you need to average out at least 3 fill ups before you can make any accurate observations about actual fuel economy.

The CRZ's MPG meter seems remarkably accurate on my car. It averages 0.3 mpg less than actual. But I suspect that in different cars, the results might be different. But you are correct that while a change in tire size and wheel weight might reduce over fuel economy, the meter should have the same consistency between measure and calculated fuel economy both before and after the change.
 
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