Tried 17 inch rims and tires today!!

[NYH1]

I have a 2007 Dodge Ram 1500 Quad Cab SLT 4x4, Hemi, auto tranny, 3:92 gears/limited slip diff, 20 inch wheels.

I put my parents 245/70-17 rims and tires from their 06 Durango on my Ram today. I didn't want to give them back. It felt like a different truck!

It drove, rode, stopped, steered, took off, handled, it did everything better then it does with the 275/60-20 rims and tires.

I can't spin my tires on dry pavement with my 275/60-20's. If I'm at a dead stop and floor the gas peddle, I'll get a chirp or two and the truck takes off, pretty well. With my parents 245/70-17's, from a dead stop I floored it, blew the tires away, left two 10 to 12 foot long stripes as the truck launched like it never has before. I was amazed. That being said, I don't regularly try to spin my tires. I just wanted to see if the smaller tires would be more responsive and my father knew what I was going to do to, so it was all good!

I was driving on the interstate with the cruise set at 70 MPH (speed limit was 65 MPH). I caught up to a car and had to pass it. I floored the gas, the truck down shifted two gears, one then two....that quick. It pulled very hard to about 85 MPH as I flew by the car and let off. Again, I was amazed. I don't know how fast I was really going because my truck is calibrated for the 275/60-20's. When the cruise was set at 70 MPG, only one car passed me. I passed a few vehicles, but was going with the flow of traffic for the most part.

When I turned at slow speeds, it felt like my LSD was actually working. In other words, If I turned left, I could feel and hear the drivers side rear tire wanting to break lose. The same if I turned right, I could feel and hear the passenger side rear tire wanting to break lose. Every other vehicle (car, trucks/SUV) I've ever had with a LSD did this. Today was the first time I felt this with my truck.

It stopped better. Handled better. It didn't follow the crown of the road on the interstate or bounce around on bumps like my 275/60-20's do.

I'm definitely going to buy 17 inch rims (most likely aluminum). I don't know if I want to go with 245/70-17 or 265/70-17 tires. The 245's are 30.6 inches tall. The 265's are 31.7 inches tall. I really want to see how much better the 17's will pull my trailer though!

[torpedoman]

say bye to whatever gas mileage you were getting. It will drop like a rock thats the reason for the 20 in tires from the factory. You will cover a foot less each tire revolution.

[R.W.Dale]

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

According to this calculator the 17" combo you ran are a good 2" shorter overall than your 20" combo. This is going to effectively lower your overall final drive ratio a bit. This alone would account for most of the performance gains you noted. Another factor may be unsprung weight? Ate the 17's much lighter than the 20's I bet they are. But also bear in mind that your speed-o is reading fast now.

. You will cover a foot less each tire revolution.

not quite with the 20's he's pulling 638 revs per mile

with the 17's that increases to 661 or a little over 4% if the new wheels and tires are lighter this could actually improve MPG

[NYH1]

say bye to whatever gas mileage you were getting. It will drop like a rock thats the reason for the 20 in tires from the factory. You will cover a foot less each tire revolution.

I have 276/60-20 rims and tires (33 inches tall) with 3:92 gears.  My friend has the same truck as mine with the exception of color and tire size.  His truck has the 246/70-17 rims and tires (30.6 inches tall) which is the "standard factory" tire size with 3:92 gears.  He gets 1 to 1 1/2 MPG better on the highway then me, and about the same in the city.

Guys over at dodgetalk.com picked up about 2 MPG on the highway when they switched from 3:92 gears to 4:56 gears.  And even more when they went from 3:55's to 4:56's  Go to dodgetalk.com and check it out.  Back in the days of no overdrive you had to run less gear 3:08, 3:23 or 3:42 and taller tires to get better highway MPG.  And those set ups would hurt your city MPG. 

My truck has two overdrive gears and the MDS system which shuts off 4 cylinders when there is less load on the engine.  Smaller tires and more gear (3:92 and 4:56) will put less load on the engine too.  Guys that switched to 4:56 gears usually gain 2 to 300 more RPM's at 70 MPH then they had when using 3:92's and they still get better mileage.   

[NYH1]

Another factor may be unsprung weight? Ate the 17's much lighter than the 20's I bet they are. But also bear in mind that your speed-o is reading fast now.

The 17's are CONSIDERABLY lighter then the 20's.  I would like to know how much my speed-o was off.  Like I said, I was in a 65 MPH zone and only one car passed me.  I passed a few and went the same speed as most.

[R.W.Dale]

Another factor may be unsprung weight? Ate the 17's much lighter than the 20's I bet they are. But also bear in mind that your speed-o is reading fast now.

The 17's are CONSIDERABLY lighter then the 20's.  I would like to know how much my speed-o was off.  Like I said, I was in a 65 MPH zone and only one car passed me.  I passed a few and went the same speed as most.

No worries your speedo should be reading 2% faster now than you're actually going.

[NYH1]

krochus, I'll probably go with 265/70-17 Goodyear Wrangler SilantArmor tires.  They're 31.7 inches tall.  My friend runs them on his 2004 2500 Ram.  He went with the higher load rating because his is a 3/4 ton.  I'm going to go with the standard load rating. 

The service writer at my sealership said they re calibrate speed-o's all the time on Rams.  A lot of guys that have 20's switch to 17's in the winter.  I'm going to switch for good!       

[GRIMJIM]

I had an '01 with 17's on it and it did handle way better than the 20's I have on my '07. The 20's look a lot better though, it's too bad they don't perform as well.

[Lloyd Smale]

20 inch rims will absolutely suck the snot out of your motor. Ive got a buddy who races his grand national. He gave it to his son and the kid decided he wanted 20 inch getto rims on it. He put tires on them that gave an overal height that was the same as the stock set. raced it one night like that and it cut a full second off his quartermile time. If i were you id do the switch and when those tires wore out switch to a slightly taller tire on those 17 inch rims. something like a 255 17 would get you back in the ballpark. If you get your tire height right your going to see better ride better gas milage and less wear and tear on your suspension. If your happy with your milage as is(make sure your giving it a fair comparison by using your gps to measure the miles traveled) . Just take along a hand held gps and see where your spedometer is reading compared to your actual speed or go to the dodge dealer and have him install a new speedometer gear. I believe dodges still use them. If not the dealer can adj. it through your computer in a few minutes. In my opinion 20 inch wheels are for 20 year old kids. I personaly dont even like the way they look. Looks like your riding on your flipping rims.

[NYH1]

Lloyd Smale, I agree with everything you said. 

The 275/60-20's are 33 inches tall and have 633 revs per mile.  The 245/70-17's are 30.6 inches tall and have 684 revs per mile.  I'm leaning towards 265/70-17's which are 31.7 inches tall have 660 revs per mile.  They spilt the difference in height and revs per mile between he two sizes I've tried.  They're still going to be a lot lighter then the 20's. 

The service writer at the stealership said that recalibrating the speed-o is simple, they do it all the time.