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Old 10-12-2018, 06:25 PM   #11 (permalink)
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Well the time is here, I will be finding out the impact of 5# rotational mass added to the tire. 110k on the tires, 380k on the truck. Going to be looking at downhill coasting as well as takeoff & uphill loads. My expectation is takeoff & uphill are going to hurt mpg while steady state throttle on flats or downhill it may improve.

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Old 10-12-2018, 08:17 PM   #12 (permalink)
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My experience on a regular passenger car is rather negative, even when using "eco / aero" wheels that, unfortunately, were also a lot heavier.

Looking fwd to your results
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Old 10-13-2018, 01:44 AM   #13 (permalink)
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I think that's my next tire purchase for the 3500.
I have 3 sets of rims. Dedicated studded snows on steelies, some Michelin highway tires on the 2012 light aluminum wheels, and a worn set on the 2012's to change out.
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Old 10-13-2018, 10:13 AM   #14 (permalink)
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Quote:
Originally Posted by skyking View Post
I think that's my next tire purchase for the 3500.
I have 3 sets of rims. Dedicated studded snows on steelies, some Michelin highway tires on the 2012 light aluminum wheels, and a worn set on the 2012's to change out.
What did you ever end up with after tuning for mpg? Its been a while but last time we talked you were just diving into efi iirc... I have my tune dialed in pretty good now where it seemingly runs the same from 60-100*... Going to work next on the baro correction table for rail pressure. 23.3* is my best.
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Old 10-13-2018, 12:39 PM   #15 (permalink)
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I most often use the truck for towing the 5th wheel. My best highway runs to Portland and back were in the mid-24s, but I have the 3.42 gear set also. typical mixed use commute is in the ~19s, mixed meaning stop and go for part of it in Seattle
Towing the trailer MPG is very much trip dependent. Mountains are going to get me 12, a run down I-5, 15-ish.
My DD is still the beetle in the mid 40s combined with the train and my bike.
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Old 10-13-2018, 06:24 PM   #16 (permalink)
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Tires done, added weight of new tires very noticeable (expected), coasting down the same hill as this morning... Before, speed maintained, after, speed drop by 1.5 mph accordi g to what i see on the gps.

Readjusting speedo, will see how it does next week. Before the swap, 22.4 mpg
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Old 10-14-2018, 12:22 PM   #17 (permalink)
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I'm thinking 275/70 for my truck with the tall gears I have.
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Old 10-15-2018, 10:18 AM   #18 (permalink)
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OK, here is what I know... before with the old tires, 285-70-17's, worn but still had tread left (can post pics if needed), I was able to coast down all of the "flatter hills" between Tacoma & Tukwilla on I5 with a 2~3 mph drop in speeds. Now with the new tire, 285-75-17's, there is no way. Even the steeper drops have lost a noticeable amount of coasting capabilities. Being that the tires are new, heavier (5# comparing new old size tire to new tire according to my son who works at the shop and had access to the #'s) and taller (by 1", same width). The new tires have a noticeable increase in grip (also expected) but to me feel like they are better suited for snowy conditions. The rubber is pretty grippy and I already see a good sized drop in the number of miles driven vs what the fuel gauge says (speedometer corrected). FWIW to anyone, I will post mpg #'s for this tank at the end of the week, last tank was 22.4 mpg.

I did see an approx 75~85 rpm drop from the bump in size. Also, tune needs to be tweeked... Not mentioned on this forum but when I did the driveshaft swap I had to adjust the timing to get the turbo spooled back down around 1000~1100 rpms. Now with the tire swap, I will need to re-tweek it again as I now have some timing rattle (mpg killer) in certain area's of the tune.


Quote:
Originally Posted by skyking View Post
I'm thinking 275/70 for my truck with the tall gears I have.
Look for a weight reduction from your current tire. I think your problem with the lower mpg on the Seattle trip is the hill climbs. Next time you take that trip, pop it in neutral on all the down hill area's on I5 (if you dont take I5, take it) and report back how well it did on the downslopes... Our trucks are near identical so you should be able to coast down most of them with minimal drop in speed.

Also, did you do an aluminum DS? If not, do it... its worth it.

Last edited by steve05ram360; 10-15-2018 at 04:33 PM..
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Old 10-16-2018, 12:50 PM   #19 (permalink)
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Tires do take some time to break-in. One tons, especially among civilian vehicles.

On a Ckass 8, more than 10,000-miles before squirm stops. Break-in continues for about 40k.

5-7k is my expectation on my TurboDiesel.
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Old 10-17-2018, 09:11 PM   #20 (permalink)
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Update + question...
These tires have a 2 ply sidewall, 75 series tire, new to the market. Any issue running this tire with a heavy load? It is a 10 ply E rated tire. The alternate has a 3 ply sidewall.

Rolling resistance has dropped quite a bit, mpg appears to be making a comeback, 420+ miles on them. Still squirrelly .

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