Rookie seeks tire tutorial

[Norris Marshak]

I have an OME lifted FJ60 with 235X 15 close -to -stock tires. They are nearing the end of their wearworthiness. I would appreciate it if I could learn the changes that will come with 31X10.5X15 All Terrain tires. I know there are a few established 60 threads on tires, but I hope I can learn here, specifically, the potential changes in speedometer accuracy, gas mileage on the open road and around town, and performance on hills, as well as anything else that I should anticipate. I have an H55f 5 speed and a stock rear, not a 4.11. Many thanks.

[gaylon]

I do not know the gearing of the 5 speed, I am not so lucky as to have had to replace mine yet, but going from 235'sv (really small - are you sure?) to 31x10.5 is about a 3" increase from 28 to 31 inches. That would make for a roughly 12% difference. At 235's I would think your speedo is running a bit low and with the new tires it will run a bit high, how much - maybe 2% high or so. Stock tires should be near to 30" in diameter, so 1 inch over is not much.

[ontherox]

That would make for a roughly 12% difference. At 235's I would think your speedo is running a bit low and with the new tires it will run a bit high

Other way around,the bigger the tire the slower your speedo will read than actual road speed.Bigger tires turn less per mile than smaller tires.

[RockDoc]

TLC FAQ - 8.1 Transmission & transfer Case Ratios (All :1)

^^
This might help, shows gear ratios of the various transmissions. With rubber overdrive, and an overdrive in the tranny, I doubt you will use fifth much, but you should be good off the line with the ratio for first.

[Heartworm]

Yeah, what Roc Doc says. 5th gear might not be to helpful except on the flat or downhill. But 4th would be better than it was for highway. You really need to start thinking 4.11s for the future if you want to go taller tires. Then, you could go 33s easy.

[gaylon]

Originally Posted by ontherox

Other way around,the bigger the tire the slower your speedo will read than actual road speed.Bigger tires turn less per mile than smaller tires.

Yup, you are most definitely correct. I was thinking calculating mpg, larger tires mean the odometer, not the speedometer reads lower than actual. Sorry, I never speed in my FJ60.

[RredFJ40]

With my 33's and 3.73's I still need a fifth gear (I wish I had one). I'm currently going around 63 at 2500 rpm - my desmogged 2F has more than enough power to take an overdrive on the flats.