AyWoSch Motors
The Parts Guy
- Joined
- Nov 6, 2020
- Posts
- 4,687
- Reaction score
- 13,649
- Location
- New Mexico
- First Name
- Ayden
- Truck Year
- 1986
- Truck Model
- K1500 Sierra
- Engine Size
- 350ci V8
Hey, just curious, do any of you know how far off the speedometer will be for each jump in tire size?
Figured id put it out there, any of you, who have figured this out already, share the knowledge.
I was wondering today, because i looked at the spec sheet in the glovebox, and my truck came with 235/75r15s originally in 1986, but I have 31x10.50R15s currently. Id guess a 235 is about a 29in, maybe a 30, so im an inch or 2 oversize.
How much would that effect the speed showing? Like lets say it says im going 60mph. Am i going 61, or 65, or... just curious.
And in town we have a few electronic speed limit signs that read you back your speed. Most cars im in, the sign reads alot slower than the speedo. Like in my yukon, sign says 39, truck says 45-46. My boss's truck, sign says 35, truck says 38. But in my caprice, sign says 39, car says 39.
Both of my 2 have tires bigger than they came factory, boss's truck is stock. So are the speedos off, or is the sign off, or both?
Also a sidenote: would changing the rearend to a different gear ratio effect the speedometer?
I assume anything different downstream of the transmission would change it, but maybe im wrong.
Just food for thought, and maybe a place to dump some trivia or info on speedo gears.
Figured id put it out there, any of you, who have figured this out already, share the knowledge.
I was wondering today, because i looked at the spec sheet in the glovebox, and my truck came with 235/75r15s originally in 1986, but I have 31x10.50R15s currently. Id guess a 235 is about a 29in, maybe a 30, so im an inch or 2 oversize.
How much would that effect the speed showing? Like lets say it says im going 60mph. Am i going 61, or 65, or... just curious.
And in town we have a few electronic speed limit signs that read you back your speed. Most cars im in, the sign reads alot slower than the speedo. Like in my yukon, sign says 39, truck says 45-46. My boss's truck, sign says 35, truck says 38. But in my caprice, sign says 39, car says 39.
Both of my 2 have tires bigger than they came factory, boss's truck is stock. So are the speedos off, or is the sign off, or both?
Also a sidenote: would changing the rearend to a different gear ratio effect the speedometer?
I assume anything different downstream of the transmission would change it, but maybe im wrong.
Just food for thought, and maybe a place to dump some trivia or info on speedo gears.
