Why is it that i swapped out my 36/14.5/15 for a set of 33/12.5/15's and my truck is now slower? Im running stock gears and could pull 75mph on the highway..it took a while but got there. Now with the 33's im struggling to keep up in traffic in a 65. What is even more puzzling is i can get to 65 faster then with the 36's but am capped there. The truck is also running 100 times better in general I killed this missing problem and did a mild tune up. I just dont get it. My speedo was way off with the 36's but having a friend pace me i got to 78 with the 36's and tonight coming home i was ripping on the truck and in a 65mph zone traffic was blowing by me. Im ready to throw the 36's back on just to drive on the highway(they look better anyways)

 

What kind of tires? The more agressive the tread the more resistance. If the 36's are old and bald they will offer less rolling resistance than new 33 inch swampers.

 

E brake isn't frozen is it?

 

The 36's are MT baja's the centers are worn but still do better in the snow then the 33's. The 33's are BFG A/T ko's and are new. The MTs have aboutthe same tread depth as the bfgs in the centers so they should offer the same amount of resistance. Id think the MT's would be more. ITs a 14.5 wide not 12.5 wide and the lugs on the edges of the MT's are really deep.

 

Well, at the same indicated speed, you're going about 10% slower with the 33's than the 36's...

 

What load range BFG did you put on that thing, and how much pressure you running them at? If it is a Load Range E (10 ply) you may want to kick yourself for putting on a tire made for one ton trucks that pull over 9,000 lb. There is no practical reason for using such a heavy duty tire for a little 4Runner if this is the case.

 

Dug up an oldie, there did ya.
Anywho.
You're "geared down" now with the 33's. All the proper laws of physics are at work here, nothing more. The tires are the final "gear", hence the need to gear down, when adding larger tires. Most people don't get the concept, don't feel bad. But, anytime you gear down your ring & pinion, without adding larger tires, or in this case just use smaller tires, your maximum (top) speed is lowered. All your gears will be shorter, reaching shift rpm quicker. Including 5th gear, which you noticed already.

 

The thread is only a month and a half old. Not old by any means by YotaTech standards.

I am confused by your post, MudHippy. What you wrote would be true if he had changed his gears to accommodate the 36" tires, but from what he indicated, that wasn't the case. So, if he is running stock gears, then the opposite of what is happening would be true, I would think. Going back to a "closer to stock" size of tire would place the shift points closer to stock, allowing the truck to shift more normally. Maybe I am confused, here...

 

the real question is.. what are you measuring your speed by?

the speedometer of your friend's car, as you said? use GPS if you can.

my truck reads that im going 3-4 mph slower than i actually am.

 

Let's see if I can elaborate, visualize running 33's on the front and 36's on the back of your rig. O.K., so whatever speed your traveling the 33's are ALWAYS spinning faster than the 36's. Keep that notion in mind, same mph not the same rate of spin.

Now back to the thread at hand.

Take that thought and apply it to this. Due to the fact that the 33's are spinning faster than the 36's at equal mph, you'll reach redline rpm faster. Essentially running out of gear before you would with the 36's, which would be spinning slower at the same speed, as would the engine, a direct corelation.

Bottom line, topped out in 5th gear, you will be going faster with the 36's. Way much so.

 

I gotcha now... I was stuck on stupid there for a bit. But for the 36's to "run better", wouldn't his truck have to have been regeared, and now that he's back to 33's, it's a problem? I guess that's what's stumping me here... Either that, or I need more coffee.

 

i dunno, but coffee sounsd good to me. hippy, sounds good to me. but at the same time the truck would have to b working harder to spin the 36's. i dunno. i think everyone should run stock with 29's like me. lol yay 14 inch rims. PUKE

 

Correctomundo. I like tea, myself. If he was to lower the gears and then run the 36's, he would also lower the MPH, not RPM, at which his engine would redline, in any gear, including 5th. Thus lowering the top speed his engine could push his vehicle. The same exact effect he's achieved by running the 33's without raising gears. More explaining below.

 

Coffee good, tea better.

You are also correct, about the engine needing to work harder to push 36's, without lower gears to help. I heard it translated like this once, "It's like your vehicle is climbing uphill all the time, as far as the the engine and the rest of the drivetrain is concerned". We've all driven up a hill, enough said.

But, if you were to apply more power to the higher geared 36's (Nitrous) they could be pushed to a higher top speed (mph), by said engine, before running out of gear (redline).

The only reason to lower gears is to add torque, i.e. using smaller tires or raising the ring & pinion gears' ratio. At the loss of maximum top speed.

The only reason to raise gears, i.e. use larger tires or lower the ring & pinon gears' ratio, is to gain a higher top (max) speed. At the loss of torque.

Thems the trade-offs. Not all of them, just what's relavent here.

 

If I recall, those big tires are the ones that are worn out all wierd. I think they only rolled on the center 1/3rd of the tire on the road. (I remember you telling me about how your friends noticed that on a wet road, only the center of your tires got wet!)

rollin' resistance of new 33s is higher 'cause they are in better contact with the road?