Pro stock wheels or not

[ibad57]

Im looking for a link that might help with understanding tire height and rear gear-overdrive trans effects
Im building an air ride 72 with stepside and would like to mod the rear fenders for some 31x18.50-15 MT they are 7" wider than what is curently on truck
i belive i have 3" between tire and frame clearance and by wideing fender 4" they could fit provided i install better panhard baror watts setup
and chose correct back spacing
Really need to know tire height verse gear and rpm at 60 mph
these tires are 30" tall and i have factory dif with 1972 factory gear????????

[SCOTI]

Factory gears ranged from 3.08's to 4.11's depending on drivetrain options so you'll need to know exactly what you have to be accurate. And for the record..... a 31 x 18.5 Mickey-T is 31" tall not 30.

Making assumptions on the rear drive ratio & trans ratio.....

.70 x 3.08 = 1,420 RPM @ 60mph
x 3.42 = 1,557 RPM
x 3.73 = 1,698 RPM
x 4.11 = 1,871 RPM
x 4.56 = 2,076 RPM (best choice for this tire height)

[ibad57]

it has 308 gear

[SCOTI]

Definitely need to change that w/31" tall tires & OD. As a matter of fact, w/those gears, there's no need for the OD trans.....

31 x 1.00 x 3.08 = 2,003 RPM @ 60mph
http://www.csgnetwork.com/multirpmcalc.html

[c10addict]

The 66 Nova I built has 31x16.5x15 et streets on it with 4:56 gears... 60 mph is 3000 rpm... If that helps..


If you are bagging this truck and widening a set of rear fenders you will also want to cut stretch the fenders top to bottom so you can get it lower.. Step side fenders in the stock location with a 31" tire are not gonna allow the truck to get real low in the rear.. Move the top of the fender to the bottom of the bed rail to pick up some extra clearance then cut the fender in half and stretch it to put the bottom back where it belongs..

[c10addict]

Originally Posted by SCOTI

Definitely need to change that w/31" tall tires & OD. As a matter of fact, w/those gears, there's no need for the OD trans.....

31 x 1.00 x 3.08 = 2,003 RPM @ 60mph
http://www.csgnetwork.com/multirpmcalc.html

Nice link Scoti!

[66chevy PROSTREET]

Originally Posted by SCOTI

And for the record..... a 31 x 18.5 Mickey-T is 31" tall not 30.

the overall height depends on your rim width also. i have 31x16.5, but once i mounted them on my 10" rim it pulled them down to nearly 30"s overall. i've also seen the same thing happen if you mount a tire on too wide of a rim for the tire.

30"tire + 3:73 + turbo400= 2200rpm@60mph, in my case.

[SCOTI]

Originally Posted by 66chevy PROSTREET

the overall height depends on your rim width also. i have 31x16.5, but once i mounted them on my 10" rim it pulled them down to nearly 30"s overall. i've also seen the same thing happen if you mount a tire on too wide of a rim for the tire.

Of course . . .... "Your height my vary." But, for a general guideline, if a manufacturer lists the tire as 31" tall, I would go w/that dimension until I could verify otherwise.

[66chevy PROSTREET]

i agree

[67 cst swb]

Now, I'm going outta memory here, but...
doesn't a 31 x 18.5 x 15 tire fit within the stock inner lip of the rear fender opening and the stock frame? Of course you would need to TUB the inner bed.
I thought a local guy (yes this was years ago & on a fleetside) I thought he cut out the rear wheel wells completely bolted on a set of big backspacing 15 x 14 rims with 31 x 18.5's on 'em... with the stock trailing arm and everything... I also remember he could not fit 33 x 21.5's but the 31 x 18.5's worked.... Hmmmm. Anyone clearer on this?

[IvelDesigns]

do you have a build thread? I'd like to see some of the work you've done.

[ibad57]

Thanks for the input and link thats a great tool for saving on costly mistakes
my son inlaw has camaro with disc brakes im not sure of the with or gear size has anyone used camaro or are the to narrow? but sounds like I need a gear change
Whats a good gear for useing 31 tall and just street. Gas and power are a 50-50 requirement its running stock 350 from 72 with r4 auto?
what is good rpm to cruz 60 and still pull small 600 lb boat without lugging?As far as the build thread I keep intending to start one but I will money will make it a slower build to achive the goal but soon
Thanks for the advice to all

[66chevy PROSTREET]

i'm using a 1981 camaro rear end, at first it was stock width and it fit fine.

[SCOTI]

Originally Posted by 67 cst swb

Now, I'm going outta memory here, but...
doesn't a 31 x 18.5 x 15 tire fit within the stock inner lip of the rear fender opening and the stock frame? Of course you would need to TUB the inner bed.
I thought a local guy (yes this was years ago & on a fleetside) I thought he cut out the rear wheel wells completely bolted on a set of big backspacing 15 x 14 rims with 31 x 18.5's on 'em... with the stock trailing arm and everything... I also remember he could not fit 33 x 21.5's but the 31 x 18.5's worked.... Hmmmm. Anyone clearer on this?

I had 31x18.5's on 15x14's w/a stock width 67/68 12bolt & custom back-spaced wheels. No frame mods & they fit.

[ibad57]

m going for the pro stock look and that much rubber shouldn't need a posi
for turning would I be better off with limited slip for turning?