Hey. Just been thinking about my mileage (again).

I noticed in some posts about mileage that people, regardless of everything else, seemed to have better mileage in their bricks with narrower tires compared to my 205/55/16's on Hydras. I am running a car with the estimated lowest mileage - B230F turbo, AT, 4.3(highest) differential. I don't really need the extra big tires, so long as I don't drive like a moron, so I'm considering buying 4 rims from pickNPull getting a super cheap set of tires, and seeing how it works for this summer. I'm going to be living out at my parents house - which adds an extra 18 miles to every trip to the store, the movies, work, etc. and it might be a good proving ground.

So, before I go spending money (and meticulously recording my results for you all ;) ) if you're intrigued, maybe we can post tire size, AT, diff size, turbo or NA, and city/hwy mileages. Might as well see if we can all save some dough for a little less traction.
Thus, I will go first.

90 740 turbo - 205/55//16. 17/23

On another note, I'm planning on a new radiator (crappy, leaky 2-row aftermarket rad), E-fan conversion, and toying with the idea of a differential replacement to the mid-grade (3.8?) differential.

Thanks everyone!
-Will
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1990 740 Turbo, on its way to stock specs, maybe beyond

The best data I have is for the '90 740 NA w/AW70L, 185-65-15 on original steel rims. All numbers highway, 35 PSI all around, w/AC.

-Unknown (brand forgotten) original tires obtained w/car did about 30 MPG.

- Goodyear "Eagle HP" on original steel rims yielded 27-29 MPG highway. (however, phenomenal tread life; retired at 75,000 miles w/plenty of tread but deteriorating/checked sidewalls after too much ozone in D.C. and Atlanta).

- Switching to Michelin "Energy MXV4 Plus" bumped it back to 29-31 MPG highway.

Sadly this car is hard-pressed to get 20 MPG in city driving.

Hm, I didn't take into account the difference in 16" and 14" tires. The thing is though, I picked up a spare tire (a 14"er from pickNpull for 12$ with a good tire) and compared its ride height. It's identical in size from hub to edge of tire to my 16" tire. The rim makes up more of the tire and when I mounted it on the car, I saw that the distance from the ground to frame looked to be the same. Also comparing the 14" tire to the 16" on the hydra, with the car sitting on hydras (and the tire compressing slightly) the 14" appears to be larger. I can take some photos if you want. It was last summer when I did all this at first, but I think I'm remembering correctly.

I realized I would have to change how I drive, because with just that one narrower tire on my car, I got a nice long loud squeal taking a corner by my work how I normally do - just barely.

-* Yes, my car is overheating, or at least leaking and requiring constant addition of coolant. I would replace the radiator before the experiment. Had this one rodded and resoldered last year.
-* I've lost mileage over the years I've had the car to mystery causes. Used to run 220 miles to almost the end of a tank, and now it's closer to 180 or 190. With highway only miles, I can make 235 or 240, but just barely.

-Will
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1990 740 Turbo, on its way to stock specs, maybe beyond

Just remember that by increasing the diameter of the tire you are using you also lower the number of times the tire revolves per mile / kilometer whatever .... I currently am driving a 95 Chevy S 10 with 235 75 R 15 tires which are noticeably taller ( and wider) than the 205 75 R 15 tires it left the factory with. According to the tire size calculator the tire is 6.02% larger than the stocker ... and according to my TomTom Nav system at a registered 100 kph I am actually travelling 106 kph .... sure makes that 6.02% look right on the money .... now, the thing to remember is that you will have to add 6.02% more miles/kilometers to the odometer reading to be able to work out the correct metrage/mileage..... So for those of you running oversize wheels and tires it might behoove you to go to one of the tire calculator sites and find out what percentage larger or smaller the tire you are using is in comparison to what it left the factory with .... You might NOT be getting as bad mileage because of those bigger tires as you thought. Next set of tires going on the truck are going to be 235 65 R 15 .. if you check with the tire calculator, you will find that they are almost identical in perimeter to the original 205 75 R 15 tires.

Ole Reliable, my 122 is running 205 75 R 14 wheels and tires and they are almost identical in size to the original 6.00 15 tires and rims that came on the 122. I think it works out to something like 2 revolutions per mile difference between the two tire sizes.... and the last good run I had with Ole Reliable I was getting 31 mpg highway in blistering hot weather on the 401 in Ontario.

Anyway, that's my 2 cents worth ..

Brett

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Brett Sutherland & the 1.5 million mile 122 CANADIAN --- WINDSOR, Nova Scotia the birthplace of HOCKEY www.ecvintagevolvo.com

Some people run tire pressures in the range of 50 psi . a lot more than max allowed for fuel economy. You will not like to try that with cheap tires , another problem with cheap tires is that their carcass sometimes will bubble etc etc.
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DD-1990 240 DL SW M47II FI 3.1 220 K miles Turbo Sways,Custom headlight circuit ,Insulated roof,Tinted Glass,

My '87 740GLE sedan with AW70L has been a work in progress with its sometimes-22-year-old parts (like the cap and rotor!). Currently I've been getting high teens in stop-and-go downtown traffic, and up to 25 or so on the highway. I run 195/70R15's on 5-spoke aluminum rims.

Ari

Before I crashed it on an icy road back in January, my 88 745 GLE (B230F, M46, 3.31 axle, free flow (turbo) exhaust, front splash pan in place, permanent roof rack) with 205/60 15 tires (normally kept @ 36 PSI) consistently got 28-29 in mixed driving, and 31-32 on long trips if I kept it down to 70 or less. My driving style is one of gradual acceleration (rarely exceeding 3000 RPM) and relatively high cruising speeds. I actually noticed a slight improvement in mileage (and a huge one in cornering ability) with the big tires compared to the stock 185/70 14s that were on the car when I got it. I assume this was due to their larger diameter increasing the effective gear ratio.

I don't know what mileage my 244 (89, B230F, M47, 3.31) is getting, with the same big tires on it, because the odometer doesn't work, but I have estimated it at 25 to 28 depending on conditions. For some reason, this car doesn't seem to have as much power as the 88 wagon did.

If you indeed have a 4.30 rear axle (never seen one, but 4.10 is not that unusual) with a turbo and an automatic, your car is currently set up for drag racing. Your best option would be to install a 3.73 axle, which was the usual one for turbo automatics. You will need one from a 90 or newer car, with ABS if yours has it, to get the correct tone ring for the speedometer and ABS to work properly.

If you really want max MPG, find an M46 and either a 3.54 or 3.31 rear axle. This is a much more involved conversion. (or just buy another car---non-turbo, stick shift)

Unless your car is overheating, replacing the radiator will not help your mileage. However, it would be a good idea in order to prevent a sudden catastrophic failure

hello
going from 15 inch tires to 17 tires on my nine forty turbo lost me one mpg.
good luck
mike

for got to give tire size.
15 inch wheels with stock size tires.
17 inch tires 225-45-17.
using a online speed calculator the speedo is within 1 mph so the height is about the same, but a much wider tire.
good luck
mike