H2 rims with 315/75R17. Un-lifted k2500. Can I go that merciless?

[Rocket Surgeon]

Yes... another one of those threads. Sorry. Very sorry.
I have 285/70R17 currently, while they may be great mud tires, they are not highway friendly... NOT IN THE LEAST.

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Without lifting, without cranking the torsion bars, can I put H2 rims with 315/75R17 tires on?
I believe this truck is set to stock height currently.
I may be able to pick up some good H2 painted 7 spoke alloy rims with BFGoodrich tires with 50% thread.

SPecIal Notes:
Stock 245/75R16 at 30.47”
current 285/70R17 at 32.71” 7.4% taller
proposed 315/75R17 at 35.6” 12.8% taller from a hummer H2.
No shift tables... SHE A MANUAL!
Speedo calibration is already messed up. It is 8% slow. It wants a larger tire!!! It wants a 35.5" based on calculations. ?!?!?!?!?!? Not yet verified if computer and speedo are synchronized.

Short term:
Both front fenders can be sacrificed as they are already on the alter of the gods of rust.
Bed is passable but I would not object to trimming if needed.

Longterm:
I intend on having replacements for the fenders found and stored.
Might sacrifice and replace fender flares for feasibility if needed.
Replacing the tires with a more reasonable size.


Also, can the bumper be spaced forward 1" to 2"???

OH MY!!!!!

a few more truck details here:

Lets see them 8 lugs!! 2500-3500 Photo thread!

I will shamelessly post mine.

www.gmt400.com

 

[b454rat]

They won't fit. I have those rims and wouldn't fit with a 4" lift. I ran the rims on couple different trucks, 285/70s will fit with slight crank.

 

[OutlawDrifter]

If you're already reading slow(which makes sense with a taller than factory tire), going up in diameter will make the speedo read even SLOWER.

 

[Rocket Surgeon]

thanks all.

I had found a set of stock hummer rims with tires, but the deal did not work out... they sold.

Neighbor has a C2500 Burban twin to this truck with 265/65R17 Falken Wildpeak A/T on silver 7 spoke Hummer wheels... $1200+ tires is out of budget, currently... plus I still would need rims.

My math DID fail me there!

 

[Rocket Surgeon]

Ok, road tested with live data.

running 285/70R17 at 32.71” 7.4% taller than stock

Live data indicates 64 at GPS 70mph
at GPS 70, the cluster indicates 74mph
or 64 live data vs 74 indicated on cluster.

SUMTING WRONNG HERERE.

this indicates the vehicle is traveling 9.4% faster than the computer expects.... Closer to stock size...

And my speedo needs more testing to determine what the freak is going on. Basically test accuracy at several set speeds. If the needle was ten mph fast at 70, and the error was consistent, than all speeds should rear 10mph high... and they don't appear to do that. Something is BORKED.

more testing needed.

ALSO... are a 97 and 98 cluster interchangeable? Quick google says yes. I could quick swap my two clusters and see if the error reading is or is not consistent with a specific cluster. Maybe even test with faces swapped. I mentioned a Borked Buick elsewhere that required the circuit board swapped.

And there is JY choices to look at, but all have automatics... probably same cluster circuit board...

 

[GoToGuy]

In your math your try to mix / multiply apples and oranges.
Speed ( velocity ) it determined by time and distance. As you said you had it half right. It's a percentage of error.
Hold your GPS speed stable at 60 for 15 seconds. What is your vehicle indicated speed?
As example= GPS stable speed 60 mph. Truck speedo indicates 66 mph. Therefore the tires are smaller diameter than OE installed. Smaller diameter more revolutions per given distance, measured in miles. This one's easy indicates a 10% error. If the GPS indicated 30 then the truck speedo would be 33.
Then the reverse is true. A larger diameter tire than OE installed would result in a speedometer indicating lower than actual GPS indicated speed. Less revolutions per mile.
It's not 10 mph over at any speed.
12 inch wide tires are going to cause problems. Think turning radius or suspension compression in turns holes rocks, rough roads.
I wouldn't focus on size percentages. Just take the diameter. Measure from center of wheel to three points on fender. The 315's are 17.5 " radius right. Get your 17.5 " piece of string hold one end on wheel center then swing it around give you an idea how much it fill in wheel well. Rough idea that is.
You can it " live data" do you mean your getting data from the OBD port? And it is not the same as truck speedometer? I would have to look up where PCM gets speed data. Versus where dash speedometer gets data.

 

[GoToGuy]

I have used " live data" , only read about it. Are you able to in settings and change installed tire size? And or make changes to PCM speed? Good luck.