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Discussion Starter #1
What's up guys, I a newbie here. I never knew so many people out really love caddys like I do.

Anyways I own a 92 Deville with a 4.9L. I bought the car about a year ago with about 170K on it. I'm at 190K and the car is still strong as hell...

Since I have owned the car I only use 93 octane gas and have been getting about 250-275 miles to a tank of gas. Ever since I put twenty inch wheels on the car I only get 200-220 miles to a full tank of gas, about 14.5 miles to the gallon.

Is it the weight of the rims causing the engine to work harder and use more gas or do I need to perform some maintance to the car?

Since I have owned the car I placed the plugs and wires, air and fuel filter, PCV valve, EGR valve, map sensor, water pump, thermostat, belt, oil line, and radiator hoses.

I drive about 70 miles round trip a day back and forth to work. Gasing the car up every couple of days is now a pain in the a**

I really could use some help..
 

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Logically speaking that is what it is.
The question is how much do those rims weigh?
How much of a difference is there between the stock ones?
What was your mileage prior?
 

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92_Deville_on_20's said:
Since I have owned the car I only use 93 octane gas and have been getting about 250-275 miles to a tank of gas. Ever since I put twenty inch wheels on the car I only get 200-220 miles to a full tank of gas, about 14.5 miles to the gallon.

Is it the weight of the rims causing the engine to work harder and use more gas or do I need to perform some maintance to the car?
20 inch Rims? Dammit boy! What size tires?

post a picture I got to see this!

as far as your second question goes, NO

you put them high heel pimpin shoes on your ride! unless your tires are the tickness of a condom your geer ratio is different now. bet your speedometer is off too. :histeric:
 

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Discussion Starter #4
245-35-20.

So far I have not seen anyone with a 92 like mine here in Atlanta sitting on 20's. I sure other people did it before but I have never seen it done here.

I will work on getting some pics up.
 

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Discussion Starter #5
JJhomer83 said:
Logically speaking that is what it is.
The question is how much do those rims weigh?
How much of a difference is there between the stock ones?
What was your mileage prior?

I had 16 in Eldorado chrome rims prior to the 20's. The 20's weigh a ton compared to the 16's.

I was getting about 275 miles a tanks full before, now I'm getting about 200-220.
 

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92_Deville_on_20's said:
I had 16 in Eldorado chrome rims prior to the 20's. The 20's weigh a ton compared to the 16's.

I was getting about 275 miles a tanks full before, now I'm getting about 200-220.
THe rims is killing your mileage. THe weight alone. THink about when you have 5 people in the car compared to just you..

Caddy_freak is right about your speedometer being off i would check that.
 

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Discussion Starter #7
JJhomer83 said:
THe rims is killing your mileage. THe weight alone. THink about when you have 5 people in the car compared to just you..

Caddy_freak is right about your speedometer being off i would check that.
Is the speedo going to be showing that I'm going faster or slower then I'm actually traveling.
 

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2005 CTS-V, 1994 Infiniti Q45
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Smaller than stock tires= slower, and you will put LESS miles on your car....

Larger= Faster, and you will put MORE miles on your car!!

You can have it adjusted to compensate for this..... How, I cant tell you! You always must consider what your doing when you put different size tires on your car.... If they are a different diameter, more things are gonna be affected than you think!!!
 

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01 frontier , 89 Shelby CSX vnt
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basiclly you went from a wheel that weighed at max 25 lbs , to a wheel that weighs 40-50 lbs , youve added at least 15-20 lbs at each corner , so you have around 80 lbs total more unsprung weight that has to be spun or the equivelnt of adding 2-3 times that weight into your trunk with stock wheels ...add 300 lbs to any car and the gas milage will suffer

and i havent even mentioned handling , these cars handled like turds to begin with it must handle like oil coated turds on a icey road to hell now

i would like to see pics of a deville tucking 20s tho
 

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Personally I think that the bigger Diameter of the overall wheel ( tire and rim )
is what is killing your gas mileage, not the extra weight. it's like putting a ten speed bike in hight gear and then trying to go from a dead stop. not easy!

Well that's how your motor feels every time you take off.
If you had a rear RWD car you could lower the gears in the rearend to compensate for that.

Now as far as the speedometer, With a bigger diameter wheel. One rotation of the wheel covers more distance than before, so less rotations of tire per measured distance of forward travel, your speedometer uses these rotations to callculate your speed. By putting bigger rims you have changed the value of the rotations. your meter has not changed its math, this means that your speedometer will show you going slower than you really are.

Do a little experiment, put your old wheels back on for one full tank of gas.
throw a dead body in the truck. and drive. I bet you get better gas mileage with the added weight than you did with just your rims! :histeric:
 

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1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
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elwesso said:
Smaller than stock tires= slower, and you will put LESS miles on your car....

Larger= Faster, and you will put MORE miles on your car!!
I think that's the wrong way. A 10" tire would have 31.4" circumfrence, so you go 31.4" per revolution of the wheel and a 20" tire would have 62.8" circumfrence, so you go 62.8" per revolution of the wheel, and the odometer is based from the tranny so it wouldn't change, but you'd actually be going twice as far on the 20" wheel.
 

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Maybe I did get it mixed up. Its all so confusing :bonkers:
 

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http://www.miata.net/garage/tirecalc.html

Your speedometer shouldn't be off by too much. You'll be going 61mph when it says 60mph.


Stoneage_Caddy said:
basiclly you went from a wheel that weighed at max 25 lbs , to a wheel that weighs 40-50 lbs , youve added at least 15-20 lbs at each corner , so you have around 80 lbs total more unsprung weight that has to be spun or the equivelnt of adding 2-3 times that weight into your trunk with stock wheels ...add 300 lbs to any car and the gas milage will suffer
:2thumbs: Rotational mass is a blood sucking parasite.
 

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well, your wheels are larger, therefor it is like having higher gear ratios, so the enigne is under more stress and I bet acceleration is not too good either...

....my speedo is off around55+ like on the thruway, when it says I am doing 75, I am really doing 80 (according to the VSS when the car is in diagnostic mode) are 55 it is off by 2mph or so, then as I go faster the gap gets bigger.....
 

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01 frontier , 89 Shelby CSX vnt
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i dont think they are that much bigger , id like to see the diffrence in overall hieght between the stock wheel and tire combo and the aftermarket wheel and tire , he may have been able to plus size them (changing wheel diamter but not overall diamaeter)

the change in the speedomoter would change expoentialy as the speed increased for example we shall say .035 mph for every mph over uhhhhh 1 mph (not sure here )so if it is off 2 mph at 55 it would be off 2.7 mph at 75 mph

i dont know absolutely how much off it would be going with diffrent overall heights as im not real good at math but thats just a therorectical idea on how it would work IMHO
 

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Discussion Starter #17
Stoneage_Caddy said:
i dont think they are that much bigger , id like to see the diffrence in overall hieght between the stock wheel and tire combo and the aftermarket wheel and tire , he may have been able to plus size them (changing wheel diamter but not overall diamaeter)

the change in the speedomoter would change expoentialy as the speed increased for example we shall say .035 mph for every mph over uhhhhh 1 mph (not sure here )so if it is off 2 mph at 55 it would be off 2.7 mph at 75 mph

i dont know absolutely how much off it would be going with diffrent overall heights as im not real good at math but thats just a therorectical idea on how it would work IMHO
On the subject a little I see that you have FWD sr20det. I'm guessing a jdm bluebird engine right?

Which chassis is it in..G20, Sentra, 200sx?

I just purchased a s13 coupe from my brother in law. I plan to purchase a jdm s13 front clip with a red top sr20det, when I get a chance and I will do the front end conversion and the engine swap. A friend of mine did the swap and wiht minor upgrades and stock turbo his was able to run low 13's on POS pep boy tires.

I just recently sold my turbo civic si that was a real sleeper. It had abosutely no exterior mods, just a 1.5 drop and 15in gunmetal rotas and Falkin Azenis tires. I ran a greddy turbo kit with the hondata stand alone system, built the bottom end, dropped the compression to 9.0 to 1. It also had a Kaaz lsd and a gsr tranny. It laid down 280whp at 15 psi. On 24in M/T slicks it ran high 12's with a best run of 12.83 at 109mph.
 

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01 frontier , 89 Shelby CSX vnt
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well it was a jdm bluebird turbo setup , was going to be mated to a low port sr20de with cams from a 1991 highport , very conservitive setup , max 8 psi and was shooting for around 200-220 hp , my goal was for a G20 that could back up its handleing with the power the chassis was ment to have , very cheap but high quality deal when one uses all nissan parts

it was a 1996 G20

but sadly the weekend the parts were to go on the car was destoryed in a crash , i was sstationed in alaska , and was headed back from a commanders call when i hit a patch of ice and went off a cliff , the car went roof-first into a tree , wrapping the car around the tree with its roof , lucky for me the seat failed

unforetunelty i still have the 3k in parts laying in my garage , but i know i wont be able to use one , i went out to buy another one and suffred a panic attack just sitting in the replcemnt g20 , so im back to square one , selling ym parts and finding a new project

pic of me and car after crash : http://server.madisonross.com/~cadillac/forums/attachment.php?attachmentid=232

the honda sounded like a hoot , but youll have more fun with the 240
 

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Discussion Starter #19
I think I solved the problem. I replaced my O2 sensor and just from driving around town for about a day I seems like it is solved. I will fill up tonight before going to work and run the tank full to empty to see if it really made a difference.

:cool:
 

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Hopefully it fixed it!!!!
 
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