quick question.

what RPM are most of you at at 35mph. im running between 1800 and 2000 and that just seems kinda high to me, the tranny shifts into 4th. am i crazy or does that seem a little a high?

thanks

98 D1 78k

 

while I can't remember if thats correct it probably is. The disco engine is already weak and so I guess they just gear the transmission low. also the transfer case is a 1.2:1 and the axle is 3.5 i believe to 1

At 70mph your rpms should be just under 2500 [or close to it]
65 - 2250

4th gear should kick in at about 51-53 on the spedometer. [or is that just when the torque converter locks up.] But heres the kicker.. The spedometer is about7% fast. so while your turning 2500 at 70 mph and you think thats alot, your really only going 65!!

Thats why when I when with larger tires 17.5% larger than stock, my actual speed is 5mph FASTER than what the speedometer reads at 65 which is an increase of 10mph over stock. I now get BETTER gas mileage with the larger tires on the highway but I get worse gas mileage in the city than stock and the truck is even more sluggish than before.

 

cool, thanks for the quick reply, i keep forgetting this thing doesn't act like your standard 4x4.

i have noticed the speedo discrepancy too, when in doubt i flip on the gps. along those ive got a tire question. what size would correct that? and whats about the largest you can go on a stock suspension?

 

well if stock is 28.5" and is 7%slow thatll be 28.5x1.07 = 30.5

On stock suspension you cant really go much bigger. Id say 245/70/16 if you offroad and 235/85/16 if you dont offroad. Though 235/85 may require some trimming, and definatly rub off road. with a 2.5" lift you can run 235/85 just fine.

But remember when you increase your tire diameter your throwing off your odometer.. say for me with the 17.5% increase. Every mile my odometer shows I actually traveled almost 1.2m.

When you get bigger tires your MPG will go down but remember to multiply either the calculated mpg or the distance by the % increase in tires and that will show you your TRUE mpg.

 

ok, but isnt the odometer run off the same mechanical cable and drive that runs the speedo. so if thats the case isnt the stock odo off by that same 5%? and therefore if a tire size increase could compensate for the goofy speedo readings would it not also correct the odometer?

or am i just nuts

or mistaken in thinking that the speedometer and odometer work like the one i had in my old 81 cherokee

 

No your correct that's why I said

Stock tire size x 1.(percent off) = corrected size.

But odometer will not be off.