mikedog

I previously had P205-75R14 tires on my '88 2wd PU. I've recently upgraded to 27x8.50R14 light-truck tires and I really like the way the new LT's make the truck look. However, I've noticed that it takes longer to get up to speed now. It kinda feels like I went to a higher (lower numerically) axle ratio.

Does anyone know exactly how much taller the LT 27x8.50's are versus the P205-75R14 sized tires? My truck seems to be a little slower to get to the (3K+) torque peak now with these new tires on it.

Will a lower (higher numerically) axle gear get my performance back to where it was before the tire change? How much lower will I need to go? 4.50? 4.70? 5.00+? I have a 4-speed man.

kyle_22r

the 205s are about 26"

do you know your current axle ratio? 88 2wd trucks(non 1 ton) had a choice of 3.07, 3.42, 3.58, and 3.73. 1 tons could be had with 4.10 and 4.30 ratios.

i'm gonna take a shot in the dark and go with the idea that you have a 3.42 axle, so to correct it you'd want to take the next step up to the 3.58s. should put you pretty close back to stock. you could even go to 3.73s for more power

L33T35T 4Runner

the old tires are 26.1 inches. the new tires are 27s, so you're speedometer is going to be slightly off, and it will slow down your truck now that it changed the proper gear ratio for your tires

L33T35T 4Runner

here's a really good site for more info

http://www.1010tires.com/TireSizeCalculator.asp

mikedog

Thanks. So, the new tires are about an 1" taller than the old P205-75R14's.

The thing that gets me though is that the truck is alot slower to get up to speed. Also, it seems as though the torque peak has shifted a alot higher with the LT's on it. Now it pulls to about 5K rpm's. Before, it would stop pulling at about 4400 rpm's. I didn't think just a 1" increase in tire height would be that noticeable. Man, I can just imagine how 35's or 38's would feel on a 4x4 with the stock rear axle ratio.LOL! Yikes!


Kyle,

I always thought I had 4.10's. You put it in 3rd gear at 70 mph and look at the tach to find out what rpm's it's at and that tells you the axle ratio. I'm pretty sure I'm just over 4k+ rpms in 3rd gear at 70 mph. In 4th gear, the tach reads 3000+ rpms at 70/75 mph on the freeway. You still check it in 3rd gear with a 4sp right?

kyle_22r

i don't think so. all toyota transmissions(at least the ones in trucks) have a 1:1 4th gear, so no overdrive. they're basically a 5 speed without 5th gear :pat:

Glenn

Not exactly. A 5 speed will have shorter gear ranges than a 4 speed. The only gear ratio where they are the same is 4th where it is 1:1 and maybe reverse.

mikedog

Ahh, okay. So "4th gear" is 1:1. I must have 3.27's now. At 70mph in 4th, I'm two ticks over 3K on the tach with these tires.

Do you know what a 5-speed 22r revs at in 5th at 70/75mph? Just curious.

Glenn

Most 5 speeds on Toyota 4wd trucks are 0.85:1. I don't know what they are on 2wd trucks, but probably the same since Toyota chose to change the gears in the differentials between 4wd and 2wd, so don't see why they would do the transmission ratios as well. But I could be wrong.

kyle_22r

using a crawl ratio calculator(it's good for more than just that!) i came up with the following, these are RPMs for 70 miles per hour with a 1:1 4th gear and 27" tires:

3.07: 2674
3.42: 2979
3.58: 3118
3.73: 3249