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Discussion Starter #1
Upgraded my wheels from 17" to 19" Drag wheels 245/40 & 275/35 Hankooks.

I used to be able to see 32 mpg on the readout, now I can only get 29. The bigger wheels with wider rubber = lots more unsprung weight. Losing 10% mpg sucks, but that's the price you pay for the looks.



My 0-60 was 5.3s using stock wheels (shown below), need to see what the 0-60 is with the new kicks:tongue.


 

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NICE CAR!!! Sorry about your ok milage. I got 15 at best in my 83 t bird and that IS the best I've ever gotten.
 

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yeah, also the increased rolling resistance will lower your MPGs, I noticed that on my Infiniti when I went from Michelins to Bridgestone
 

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Don't trust the readout. Measure manually, (miles since last fill)/gallons pumped to shutoff.

Better to post timeslips, 0-60 is illusory.
 
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This is really the first post I can remember seeing on this topic. I get great mpgs with my CAI, tune and stock 17x7 and have been wanting to switch to 18x8.5s or 18x9s. However I have wondered how adversely these would affect mpgs even if the wheels were lighter. I'm sure it isn't just the weight and contact patch that cause a difference but also most plus size wheel options push you into shorter tires. That will impact fuel economy as well.
 

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When you change tire size did you reprogram the cars PCM to compensate for the shorter tires?

If not then it throws off everything associated, speedo, fuel economy readout, transmission parameters in the automatic, etc.
 

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Upgraded my wheels from 17" to 19" Drag wheels 245/40 & 275/35 Hankooks.

I used to be able to see 32 mpg on the readout, now I can only get 29. The bigger wheels with wider rubber = lots more unsprung weight. Losing 10% mpg sucks, but that's the price you pay for the looks.

Nice what size are they? Could you also let me know the bolt pattern like 5 on 100mm I have looked into these before and really want them. And who did you order them through?:bigthumbsup
 

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Car & Driver did some testing on "upsizing" wheels and found that the gas mileage was reduced with the larger wheels. Larger tires have a higher rolling resistance, which does effect gas mileage. Going from 17" to 19" wheels dropped the gas mileage almost 2 mpg.



The stock 17" tires/wheels were making 742 revs/mile while the new rear 19"rear wheels/tires are making 782 revs per mile. So if you haven't had the Bama tune corrected, your mpg will change a little more after it is corrected.
 

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yeah, also the increased rolling resistance will lower your MPGs....
Exactly, rocket science it isn't. Which is why people with the larger wheels & higher gear ratios rarely post what their mpg are. A number that is very similar to what a 5.0L will produce (after all, the load is the same), minus the HP & torque.

Agree that your ecu will need to be revised for the new wheels.

Your wheels do look great btw!
 

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Discussion Starter #10
Thanks for the kind words, y'all. I love looking at the car, I catch myself looking at the window to sneak a peak from time to time, does make me smile :yelpleased:

I got the Drag dr-37 wheels at discount tire direct, these are not light weight, so are not too expensive. The wheels are staggered 8"/9.5". The tires are 245/45 & 275/40. I bet the wheel tire combo weighs in at ~70lbs. For reference, the OEM wheel/tire weighs in at 48lbs.

I'm not sure if you have to change the ECU based on front or rear wheel diameter (anybody know?). Assuming the rear, the diameter difference is 0.15%, so I don't think a change is needed.

I will start checking mpg at the pump, but I would imagine the readout should give me a good indication of relative mpg differences. I can't figure out over what time period or distance the readout averages the mpg calculation (anybody know?). I originally thought that the averaging is done since last reset, but if this were true the avg should stay pretty constant after a while. But even after driving continually for almost 2 hours there is still variation on the readout when hitting hills or punching it. Maybe the averaging is only over the last 5-10 miles or so.

No drag strips near where I live in the bay area, CA - I am envious of y'all that live near a strip!!! So all I can do 0-60s on a secluded street without worrying about the fuzz. I video the speedo and use my video editing software to cut the video from a frame before the speedo starts moving, until it hits exactly 60. The timing is dead accurate, but I suppose it doesn't take into account any inaccuracy in the speedo - I guess that's why it's a bit "illusory".

FWIW, The stock 0-60 is supposedly 6 seconds (I never tested this). Using Bama 91s, the time dropped to 5.3 (5.34 actually). 91p the time is 5.3s. And with the 91r, the time is....wait for it...........5.3s.
 

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You have now said two different sizes of tires between the first post and this latest post, which size tires do you now have???

I figure they are 275/35/19.
 

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And looking at a tire size calculator, it looks like a little over 5% difference, you definitely need to adjust the tune for the difference if you want the speedo and the fuel economy readout to be close to right.
 

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Discussion Starter #13
My bad on the original post. It is 275/40/19 in the rear. Should I still get the ECU tuned for this?
 

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Hmm, okay, nope, looks like no need to reprogram, almost identical diameter to the original 225/60/17's that come on the manual cars. Actually just a LRCH taller than the originals.
 

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IIRC you need to tell the comp. that the fronts are differant than the rearsso it knows why the fronts are running faster than the rears.
Traction control and all that stuff.
Mike
 

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Discussion Starter #17
Thanks for the tips, I'll get new bama tunes to fix the ECU for the new wheel sizes. Put the cowl hood spear decals on today - this is the last of the appearance mods for me. The CAI is next.



 

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My bad on the original post. It is 275/40/19 in the rear. Should I still get the ECU tuned for this?
So the stock tire generated 742 revs/mile and the new tire (corrected size) generates 751 revs/mile. Not a significant difference. So in terms of gas mileage, what you see is what you get.
 
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