jackiss2888

iTrader: (3)

I was just wondering, after putting 18's from a 2004 max on, the total wheel size is 2 inches more than it was stock. I know my speedo is off my 2 mph slower than what it really is.

I was just wondering, though, after getting horrible gas mileage, would my trip counter be off too? It seems that it would make sense for it to be showing less miles than what is actually true.

njmaxseltd

iTrader: (19)

If you put the correct size tire on your 18's your speedo will be accurate.
Your poor mileage is do to the incorrect tire size and a heavier wheel.
Both your odometer and speedo are affected.

Frank Fontaine

Yeah, that's pretty bad. You are not any given mph off, you are about 5.556% off. The faster you drive, the more off you are. When your speedo says 70, you're going about 74 mph. When it says 60, you're doing about 63. You'll find your 2 mph error at around a 35 mph indication by your speedo.

There are two factors working against you in such a setup. Not only are the tires 10 mm wider than what would be +2, they are 45 series when you should have a 40 (235/40-18). That's why your overall diameter is 1.4" larger now.

quasidynamic

iTrader: (2)

Dood nice idea but the tires gotta go! How slow is your car of the line with those wheels on it?? any noticable diff? Anyway, get a new set of 235/40 tires and sell your tires on ebay or the org. Hopefully you can come close to breaking even... The tires you have are a popular size so you shoudlnt have too much trouble finding a buyer... Good luck.

Devin

jackiss2888

iTrader: (3)

yea, the car is defintely slower, i can feel it. But when i said the speedo was off, I was going 62 when a friend was going 60.

as for the tires, i wont be abel to sell them until I sold the tires i currently have, which are the stock 6 gen tires. i am severly low on cash so...

but yea, does this all mean that i am getting more miles to a tank than my trip says?

chillin014

iTrader: (67)

i want to buy some wheels , like stock 5th gens but before i buy any i want to know im not going to mess up my speedo. so if anyone has any advice...whats the correct combo's for wheel and tire

quasidynamic

iTrader: (2)

Yes you are getting about 5% better gas mileage since yer trip is off by 5%.. it's all proportional. Your car thinks the wheel revolves one full turn when in fact it has only revolved about 95% of a complete turn. This adds up over time which is why yer trip is off by more than a tad...

I would suggest putting yer stock rims back temporarily... removing the tires from the 18s, selling them, and when you get the money for them go put new tires on teh 18s then swap with yer stock wheels again. you may also try sellign the tires in your local newspaper...

Good luck.

Devin

quasidynamic

iTrader: (2)

there are no "special" rim/ tire combos that will or wont mess up yer speedo... all you have to do is a little math and make sure yer wheel diameter is close to stock. I'm not sure what stock tires for teh 4th gen were (changed mine long time ago) but for argument sake lets say they were 205/60-16. to get the diameter of this wheel... 205mm is the width of the tire, 60 is the sidewall height expressed as a percentage of the width and 16 abviosuly is the rim diameter. so, take .60 * 205mm = 123mm sidewall. convert mm to inches by dividing by 25.413 (just a conversion factor). This gives you a 4.84" sidewall. So you have a 16" rim + two 4.84" sidewalls = 25.68" wheel diameter.

so you want an 18" rims for example... take the 25.68" - 18" = 7.68" divide by 2 = 3.84". This means your sidewall must be 3.84" or 97.5mm. I did a lil guess and check, but if you divide by the middle number in the tire size (60% for the stock size) then you will get the width of the tire you need in mm. So lets try / 40%... This gives a sidewall of 243.84... close to 245. in this case a 245/ 40-18 would work and yer diameter would be 25.72", only .03" off of stock. This is certainly acceptable as variations in tread account for more than .03"! Alternatively if you want a narrower tire since 245 is pretty wide... divide by 45% and get 215mm width. so a 215/ 45-18 tire would work also with a diameter of 25.62", a difference of .06" from stock.

Anyway, hope this helps you decide which wheels/ tires to buy. Again, I am not sure if i was right about the stock size tire for the 4th gen max, so dont go off of my numbers. the idea is to get the right numbers and do the math yourself. Good luck.

Devin

chillin014

iTrader: (67)

thanks man, yeah i think they are 15. but in the end imm hoping the people who i buy my tires from and get to put them on my wheels/car arent stupid enough to mess it up.

Black Maxima

If you want 17's get 215/50-17 tires. That's what I have and according to the tire size calculator they are < .1% off from my stock 205/65-15's.

Conrad283

iTrader: (2)

It's pure physics. Centripital forces. Bigger wheels = more energy to turn them.

jackiss2888

iTrader: (3)

well, the answer to that problem isnt really physics, more common sense. but the percentages are physics.

thanks guys for the help, also, if anyone of you hear anyone wanting some tires, dont forget about me.

2 Da Max

iTrader: (2)

nice rims btw!

mansurxk

iTrader: (14)

if you were going 60 adn your speedo said 62, then your reporting more MPG than you really are getting. lets say your consistently going 60 adn its reporting 62, then your doing 1% more gas mileage than previously. you wouldnt have noticed that. my assumption is that the heavier wheels are causing poor gas mileage, because you shouldnt have noticed it if it was int he range of 1%.

large diameter=more rotational mass....=more work needs to be done to move the wheel a certain distance.

quasidynamic

iTrader: (2)

dont trust the tire shop... no one cares about your car like you do... they just wanna sell tires... its best that YOU know what you need before you go to ensure they dont mess it up...

Devin

chillin014

iTrader: (67)

makes sense

96white

235/45/17 is perfect, speedo is 100% on.

chillin014

iTrader: (67)

yeah im gonna go for 17's, donno what the tire situation would be, im guessing buy new ones

Black Maxima

Correct! But, my wheel width is 7 inches. The 235/45-17 are .5 inches too wide for my wheels.

jackiss2888

iTrader: (3)

Nah, I was going 62, but the speedo said 60. I set cruise at 60 and a friend reported it to be 62 mph.

And 2 Da Max, thanks for the compliment.

Again, thanks guys.

PAREDLINE

Ouch my head hurts. Larger wheels do not have more rotational mass because smaller wheels still have the same total size. Remember the tire circumferences do not change that much.

A larger wheel and shorter sidewall will give better mileage per gallon due to the fact that the tire is not absorbing as much energy. However, this is only when weight is not a factor. Larger wheels tend to weigh more. So any benefit is outweighed by the weight of the wheel.

I should write more but I have nothing more to say

jackiss2888

iTrader: (3)

the tire/wheel combo is 2" larger in diameter than the old combo. this has produced a 2mph deficet at 60mph (it is really 62 when it says 60). the weight is def. an issue, they are much larger, weight twice as much, and the tires are big.

im just trying to find out roughly on a full tank, how many miles will the trip be off and which way? I'm pretty sure it will say less than what is true.

quasidynamic

iTrader: (2)

why is it .5 inches too wide? a 235 (9.25") tire on a 7" rim is actually about perfect. I have 225s (8.85") on my stock 6" rim and they fit perfect. You always want yer tire width to be greater than your rim width. for one, it looks better, and two the wider tire will protect your rim.

Devin