Opinions on Downsizing Wheels?
Champion
Joined: Aug 2005
Posts: 3,313
Likes: 8
there is a small benefit to acceleration
by going to a smaller & lighter wheel and tire
the smaller tires are generally less expensive too
if you want to know the science of
"the flywheel effect"
it is complicated mathematics
but you can start here:
http://en.wikipedia.org/wiki/Moment_of_inertia
bicycle racers can actually show you simple ways
to measure the 'J' of your wheels
with a length of wire and the stopwatch in your cellphone tools
by going to a smaller & lighter wheel and tire
the smaller tires are generally less expensive too
if you want to know the science of
"the flywheel effect"
it is complicated mathematics
but you can start here:
http://en.wikipedia.org/wiki/Moment_of_inertia
bicycle racers can actually show you simple ways
to measure the 'J' of your wheels
with a length of wire and the stopwatch in your cellphone tools
Record Breaker
Joined: May 2007
Posts: 1,152
Likes: 2
From: Milledgeville, GA
I admit that most of my reason for keeping the stock 20s on my truck is appearance. The Ram is such a large truck that the 20s just look at home on it where they would have looked absurd on my 92 GMC extd cab 4x4.
Thread Starter
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Rookie
Joined: Sep 2008
Posts: 55
Likes: 0
Great write up!
How many have actually checked the calibration of the odometer vs. gps or other trucks? My Ram came from the factory with 20's and shows them on the factory window sticker. However, my odometer is off 2.7%-3.0%. The difference between the 20's and 265 17's is 4%.
Also my speedometer is off by 2-3 miles per hour via gps and roadside police radar trailers.
Seems to me the factory left the 265 17" setting in the computer.
Has anyone else checked all this on their trucks?
FYI, 4x4's came standard with 265 17's if you look at standard build sheets.
How many have actually checked the calibration of the odometer vs. gps or other trucks? My Ram came from the factory with 20's and shows them on the factory window sticker. However, my odometer is off 2.7%-3.0%. The difference between the 20's and 265 17's is 4%.
Also my speedometer is off by 2-3 miles per hour via gps and roadside police radar trailers.Seems to me the factory left the 265 17" setting in the computer.
Has anyone else checked all this on their trucks?
FYI, 4x4's came standard with 265 17's if you look at standard build sheets.
Here is my opinion
A larger circumference tire has more weight; my truck weighs 2400Kg (5300 lbs), what is an extra 120 lbs as a percentage maybe 2.2%. So yes this will reduce your gas mileage, but not significantly
The tire however takes a couple minutes to heat up while driving, until this heated point has been reached, your friction between the tire and the road will be greatest, thus much reduced gas mileage for this period. This can be mitigated by using Nitrogen in the tire as Nitrogen does not suffer the same heating and cooling effects as air, plus Nitrogen is better for rubber life.
Getting back to friction, if we go for a skinnier width tire, there is less friction, thus a fuel savings, but who wants a skinny tire on a truck, less carry capacity generally.
I would wager that most people do not go to their dealer to have the vehicle recalibrated after changing their tire size. I had $160 ticket when I changed the tire size on my Dakota to a tire that had a greater sidewall aspect ratio than recommended. I installed a GPS devise and the vehicle displayed speed was low by 10%. The dealer recalibrated this for me. So if someone changes the tire size from 20” to 17” and does not have their speedometer calibrated, toss their results out the window, these will be invalid.
Trailer hauling, I chose to keep the stock 20” on my Ram as the sidewall aspect ratio is relatively small. This would help elevate some sway from the trailer. The higher the aspect ratio, the higher the rim from the ground, the more flex the tire has.
Bottom line, yes marginal increase in fuel mileage, worth the cost of changing tires, not in my opinion as the smaller tire also turns more frequent, thus increasing the contact time to the ground and thusly wear
A larger circumference tire has more weight; my truck weighs 2400Kg (5300 lbs), what is an extra 120 lbs as a percentage maybe 2.2%. So yes this will reduce your gas mileage, but not significantly
The tire however takes a couple minutes to heat up while driving, until this heated point has been reached, your friction between the tire and the road will be greatest, thus much reduced gas mileage for this period. This can be mitigated by using Nitrogen in the tire as Nitrogen does not suffer the same heating and cooling effects as air, plus Nitrogen is better for rubber life.
Getting back to friction, if we go for a skinnier width tire, there is less friction, thus a fuel savings, but who wants a skinny tire on a truck, less carry capacity generally.
I would wager that most people do not go to their dealer to have the vehicle recalibrated after changing their tire size. I had $160 ticket when I changed the tire size on my Dakota to a tire that had a greater sidewall aspect ratio than recommended. I installed a GPS devise and the vehicle displayed speed was low by 10%. The dealer recalibrated this for me. So if someone changes the tire size from 20” to 17” and does not have their speedometer calibrated, toss their results out the window, these will be invalid.
Trailer hauling, I chose to keep the stock 20” on my Ram as the sidewall aspect ratio is relatively small. This would help elevate some sway from the trailer. The higher the aspect ratio, the higher the rim from the ground, the more flex the tire has.
Bottom line, yes marginal increase in fuel mileage, worth the cost of changing tires, not in my opinion as the smaller tire also turns more frequent, thus increasing the contact time to the ground and thusly wear
3rd gen Ram, Newbies
Joined: May 2008
Posts: 3,815
Likes: 0
From: Chicago
Tire size should stay the same, so no extra revolutions. Same engine rpm, and wear. The increase in MPG comes from a much lower ROLLING INERTIA, not from a significant drop in mass.
Nitrogen in non-racing tires is useless, air is roughly 80% nitrogen anyway.
People have said they have seen anywhere from 1-3 mpg just by changing wheels. I can't confirm, but it can't hurt. It will help off-road (not that you need it just for trails).
I say go for it, just don't do it only for mpg. I will likely follow with black wheels when it's time to change tires.
Only downside is that you will lose just a little bit of stability towing, but most 2500 and 3500s you see towing car carriers and 40' trailers are on 17" wheels anyway, i'm sure you'll be fine with only a 25' trailer.
Nitrogen in non-racing tires is useless, air is roughly 80% nitrogen anyway.
People have said they have seen anywhere from 1-3 mpg just by changing wheels. I can't confirm, but it can't hurt. It will help off-road (not that you need it just for trails).
I say go for it, just don't do it only for mpg. I will likely follow with black wheels when it's time to change tires.
Only downside is that you will lose just a little bit of stability towing, but most 2500 and 3500s you see towing car carriers and 40' trailers are on 17" wheels anyway, i'm sure you'll be fine with only a 25' trailer.
