i have a chart that torque posted a while back and i have tried it out on my truck ..i have 30 " tires on my truck and i ran at 60 mph and its running between 2200 and 2300 rpm at 60 but ...on the id tag on the rear end ..its a dana 60 it show 3.08 as the ratio ..my question..hopefull torque can help...is that if my tranny has the speedo gear for the 3.54 or 3.73 would that throw the calculation off..i know that the rear axle was changed before i bought the truck and then i also changed out the rear axle after i purchased it..any input would help..thanks ...im just trying to save some time..by not pulling the cover.and making a mess...thanks take it easy

 

I guess what you are trying to achieve is to have the proper speedo gear so your speedo will show correct speed.

Therefore Yes, it is important to correlate the tire size, and axle ratio in your calcuations.

 

not exactly ..im wondering if the speedo gear is calibrated for the 3.54 or 3.73 and im running 60 acording to the speedo..i will get the rpm reading of the 3.54 or 3.73 gears even if i have a different gear ratio..but in all actuallility i will be doing 60 mph by the speedo if i have 3.08 i would actually be going faster then that ...am i correct? thanks for the input

 

First of all you need to see if your speedo is correct. Do this by going thru a few of those radar signs along the road or checking your time going past several mile markers on a nice flat section of road.

Once you have determined your speedometer calibration you can check your speed and RPMs against the chart.

Remember that chart was made for a std transmission with no slippage. An automatic transmission slips, and with that high stall converter you have your C6 will slip a LOT.

 

What is the actual size of those tires ?

Don't give me the height,I need the size.

The F150 truck came with 70 series tires L70-R15

70 - (Tire height) This means the distance between the tread on the ground and the bottom portion of the rim in proportion to the tire width. 70%

If the tire is 8" wide
the tire height is 70% of that or 5.6"

The shorter the tire height, the faster the wheel turns to go the same distance.

 

hey mil1ion ... i have P245/75r16 on the truck now ...but i have purchased a set of 15 inch 8 lug wheels that im gettting ready to put on so i know that the tire will be smaller ..im going with 275/60R15 on the back when i do that so i know that they will be smaller there for throwing it off even more.but seeing how torque said that chart was for a manual transmission setup..so im just going to go ahead an pull the cover and check it out but thanks for all the input on this matter

 

15" rims would not fit on my 78 F250, the 16" rims barely clear the calipers as it is.

 

o ooo were the rims aftermarket or steel.. the ones i got were magnesium..just curious

 

My rims are aftermarket steel wheels which are nice and thin, strong, and durable. I don't like alloy wheels, they break way too easy.

I run LT265/75R16's on the wheels and I have less than 1/8" clearance (maybe 3/32") to the steel rim from the calipers. I keep looking for scratches on the wheels. Wheels flex while your truck runs during cornering and on rough roads. You can grind some of the high spots off the calipers also.

Some guys have run 15" wheels but it requires strange offsets and spacers.

 

hey torque u were right the 15 inch wheels wont fit not even close to fitting..thanks for the input

 

That's what we are here for.

 

78truckpower429, I had 15x8 steel wheels on my dana 60 front end. Unless you're willing to grind the heck out of your calipers and install longer,thicker studs&spacers,though,it isn't worth it. I finally went to 16.5's.

 

well mines just 2wd and i dont think i can grind enough off the caliper in order for the wheels to fit ..and still have some caliper left if you know what i mean ..but i just figure im going to have to stay with my 16's and leave it alone...but thanks for the input ..time to do some more ebay..lol...take it easy