real newb question about tire size and bolt pattern

[crashyyz]

I've just bought an 84 k5 blazer 4x4 and I'm wondering what the usual tire size that's run is. I know that 225/75/15 were the stock or 235/75/15.

Anything a bit larger work without really messing with the gearing? If so, what's the norm?

Also, the rims are a 6 bolt rally wheel that look rather wide. what newer rim styles will work from the GM trucks (if any).. same 6 lug pattern?

thanks much and sorry for the easy questions

 

[AUK5]

you can run up to 33's on the stock suspension. also if you are looking for new rims it is 6 bolt 5.5 spacing.

http://coloradok5.com/tirefitmenttable.shtml

 

[SkulzNBonz]

31's were actually a stock option. As for rim's, I think the standard 6 lug pattern w/ 3 3/4" backspacing is correct. Someone correct me if I'm wrong, my memory may not be completely accurate.

John

 

[crashyyz]

great.. thanks for the info.

I don't know squat about large tires but I'm guessing that 31 x 9.5 x 15 would be the safe bet and that 31 x 10.5 x 15 would be getting on the 'too large' size for stock?

 

[dremu]

great.. thanks for the info.

I don't know squat about large tires but I'm guessing that 31 x 9.5 x 15 would be the safe bet and that 31 x 10.5 x 15 would be getting on the 'too large' size for stock?

31 x 10.50 x 15 will fit fine. I ran these for years on all three of my Blazers (74, 77, 84.)

33 x 12.50 x 15 will fit for a street-only truck. Once you start pushing the suspension, however, they will rub (at least they did on my '74 and my '84.)

All of these were on stock 1970's ralleys, which were 15x8 rims.

Now, as you go up in size, particularly on the 33"s, gearing can be come an issue -- and remember your speedo will read wrong, thinking you're going faster than you are. Your odometer will also be off, so if you use it to calculate fuel economy your numbers will increase, which is against the laws of physics

You might post up what your axle gear ratio is. In short, with 3.08:1's I'd not go larger than a 31", and even then the truck is gonna be gutless. My '84 had the 6.2 diesel and 3.08:1's and it was ... not quick on those 33"s. The others had 3.73:1's and they were okay on either tire size.

You can correct the speedo/odo by changing the gears in the gearbox on the speedo cable (at the transfer case), or take it to a speedo shop and they'll do it for you.

-- A

 

[crashyyz]

thanks dremu, I'm guessing there's a way to figure out the gear ratios from the build sticker?

I won't be doing any offroading (famous last words, I know.. LOL)

I'm soooo green but I love these things

 

[dremu]

thanks dremu, I'm guessing there's a way to figure out the gear ratios from the build sticker?

I won't be doing any offroading (famous last words, I know.. LOL)

I'm soooo green but I love these things

Yup, post up the RPO code. I seem to recall that "GU"-numbers are the gear ratios, but somebody'll know.

-- A

 

[crashyyz]

sorry for my delay on this thread ... I've looked all over the place and can't locate any sticker except for one that says 'don't carry a slide on trailer' in the glovebox.

any other place where this RPO sticker may be located?

thanks
Rob

 

[lectric80]

Now, as you go up in size, particularly on the 33"s, gearing can be come an issue -- and remember your speedo will read wrong, thinking you're going faster than you are. Your odometer will also be off, so if you use it to calculate fuel economy your numbers will increase, which is against the laws of physics

-- A

Umm... I think you meant slower than you are. On mine with 33's, the speedo reads 47 MPH when I am doing 70 MPH. Bigger tire size means slower speedo reading, just try and calculate mileage off that. If I were to try I would be measuring in gallons per mile.

And gearing is important, ask me how bad the 3.08 gears are with 33" tires.

 

[dremu]

Umm... I think you meant slower than you are. On mine with 33's, the speedo reads 47 MPH when I am doing 70 MPH. Bigger tire size means slower speedo reading, just try and calculate mileage off that. If I were to try I would be measuring in gallons per mile.

And gearing is important, ask me how bad the 3.08 gears are with 33" tires.

Dammit, I *know* this ... yes, larger tire diameter == more distance covered, so you're going faster than the speedo reads, i.e. the speedo reads too slow.



Damn physics.

-- A