225 60 15

[jgarverick]

anyone running this size tire or similar? i need to run a 25.7 in tall tire with the new tranny to make the gearing work out to what its set at at the factory (5.3 w/t56). tried search but its too difficult to search numbers. pics appreciated. thanks guys.

[SCOTI]

Originally Posted by jgarverick

anyone running this size tire or similar? i need to run a 25.7 in tall tire with the new tranny to make the gearing work out to what its set at at the factory (5.3 w/t56). tried search but its too difficult to search numbers. pics appreciated. thanks guys.

What rear end ratio was that 'factory' set-up using? Are you also using the same gearing? That will affect the calculations.

[62gmc910]

If you go to tire mfg web sites they sometimes have the actual tire dimensions listed but they usually go by rolling radius and some even give revs per mile

[jgarverick]

sorry guys i guess i worded this strangely. i am considering running a 25.7 in tall tire. this is the stock tire height of a 2001 z28 that i'm pulling the transmission from. its also very close to a 225 60 15 overall height. both my truck and the z28 are running 3.73's. i'm trying to find someone that is running these tires so i can see what it looks like on our trucks cause i'm thinking they'll look too small and if they do then i'll have to start lookin for a set of 4.11's or 4.56's. i'd try it out myself but the truck is pretty disassembled right now. so if anyone is running something close to a 225 60 15 please post a pic and tell me how you feel about them. thanks guys

[62gmc910]

these are 235 60 15 / 295 50 15 only one size bigger

[SCOTI]

Originally Posted by jgarverick

sorry guys i guess i worded this strangely. i am considering running a 25.7 in tall tire. this is the stock tire height of a 2001 z28 that i'm pulling the transmission from. its also very close to a 225 60 15 overall height. both my truck and the z28 are running 3.73's. i'm trying to find someone that is running these tires so i can see what it looks like on our trucks cause i'm thinking they'll look too small and if they do then i'll have to start lookin for a set of 4.11's or 4.56's. i'd try it out myself but the truck is pretty disassembled right now. so if anyone is running something close to a 225 60 15 please post a pic and tell me how you feel about them. thanks guys

What works for the Z may not work so well in your truck. Areodynamics help the f-body slip through the air efficiently so that it can utilize that gearing/OD combo (although 3.73's aren't OE gearing).

I don't know of any trucks offered w/a 6spd (dbl OD) from the factory w/only 3.73's. Have you researched what drivetrain combos (motor, trans ratios, gearing, tire OD) come in full size trucks? I would steer my choices toward what a truck came w/vs. an f-body.

[TR65]

Hey JG,

With the T56 you have so many gears that all a taller tire shoud give you is better gas mileage in 6th.

I am running a T56 with 3:73 gears, gives about 1500 RPM in sixth at 70 mph with 235/75R15.

Check out the Speed Analyzer at Keisler

http://www.keislerauto.com/speed_analyzers.php?sa=gm_6

Good luck,

TR

[SCOTI]

Lower operating RPM's does not garantee better milage. Keeping the motor in it's peak torque range is ideal for efficiency. More than one board member has lost mpg's when swapping to OD w/less than optimal gearing/tire OD.

[TR65]

Scoti,

I am talking about highway cruising.

I have driven LS motors with 6 speeds continuously since 1998. I currently get 23.5 mpg driving to work with a 430HP LS3. The key to good mileage with these engines on the highway is getting into sixth gear as quickly as possible. It is clear using a scan gage or the instant mpg readout.

TR

[jgarverick]

thanks for the replies guys, i think i'm going to pick up a set of tires and try them out. if it runs well and looks good then i guess i'll stick with them. i've analyzed alot of gear ratios and tire combinations already and this seems the simplest way to go. i think its really going to come down to what the truck feels like in 6th gear on the highway. another thing i'm a bit worried about is how the truck will drive on state highways at around 60 mph.

@69gmc910 thanks for the pic man, what drop are you running?

@tr65 how does your truck feel at 60? do you just use 5th?

[62gmc910]

[QUOTE=jgarverick;3692313]thanks for the replies guys,

@62gmc910 thanks for the pic man, what drop are you running?

I really don't know I just swaped rear springs around until the tires didn't hit the box too bad (its a canadian GMC so its coil rear) and set the torsion bars to get the rake I liked . When I built it you could hardly get any aftermarket so it was just do what you could. I sure got some looks with the eightbolt wheels on a short box

[SCOTI]

Originally Posted by TR65

Scoti,

I am talking about highway cruising.

I have driven LS motors with 6 speeds continuously since 1998. I currently get 23.5 mpg driving to work with a 430HP LS3. The key to good mileage with these engines on the highway is getting into sixth gear as quickly as possible. It is clear using a scan gage or the instant mpg readout.

TR

23.5mpg w/a 430hp LS3 in what?

[TR65]

jgarverick Re: 225 60 15

@tr65 how does your truck feel at 60? do you just use 5th?

I'm usually running for good economy so above 50mph I am normally in 6th. With the T56 you have options.

By the way you can go to a 255/60R15 and only make a 6% change in RPM. A tall tire like a 235/75R15 gives a 13% change. Not a big deal I think.

SCOTI Re: 225 60 15

23.5mpg w/a 430hp LS3 in what?

08 C6

Cruising at highway speed takes only around 30HP. So the engine is going to run way below peak efficiency. As near as I can tell the MPG improves at these low HP levels down to around 1500 RPM and then is pretty flat.

Another thing to think about. Regardless of power output the engine must inject enough fuel on each power stroke to actually fire (the reason DOD is used by GM). Downshifting is detrimental to fuel economy because the engine has to fire a lot more times at the higher RPMs rather than just reducing to idle. I always liked to downshift to "save the brakes" but it costs fuel.

TR

[SCOTI]

Originally Posted by tr65

08 C6

Didn't think it was in a truck.

[1restorick]

On my 63 C10, I'm running a 255/55/16" tire size. This size was the same height as the 255/60/15's" that I had on my rally wheels. I bought the General brand UHP tires. They are directional, very sticky and low priced from the Tire Rack. Here's a photo for reference:

[lakeroadster]

Jason,

You are putting a lot of work into your truck and it has been first class all the way. With all due respect I think you kind of answered your own question. The 225-60-15 at 25.67 inches in diameter is a pretty small tire. It sounds like you are thinking it is too small and it is definately smaller than what the truck originally came with. Bigger - be - better in this case. For comparison a 710-15, which was stock on a 3/4 ton, and still didn't really fill up the wheel opening on our trucks, was 27.98 diameter.

Your probably not going to be happy with this small of a tire. Nothing impacts the overall look of a project like wheels and tires.

Fill up the wheel opening with a big diameter tire and wheel combo that you like. Then punch the numbers into a gearing calculator and swap out the differential for whatever fits the tranny / motor / tire combo.

You will be glad you did.

[SCOTI]

Originally Posted by lakeroadster

Jason,

You are putting a lot of work into your truck and it has been first class all the way. With all due respect I think you kind of answered your own question. The 225-60-15 at 25.67 inches in diameter is a pretty small tire. It sounds like you are thinking it is too small and it is definately smaller than what the truck originally came with. Bigger - be - better in this case. For comparison a 710-15, which was stock on a 3/4 ton, and still didn't really fill up the wheel opening on our trucks, was 27.98 diameter.

Your probably not going to be happy with this small of a tire. Nothing impacts the overall look of a project like wheels and tires.

Fill up the wheel opening with a big diameter tire and wheel combo that you like. Then punch the numbers into a gearing calculator and swap out the differential for whatever fits the tranny / motor / tire combo.

You will be glad you did.

Exactly!

[jgarverick]

i think i have to agree guys. even with a mild drop (2.5/3) the tires would just look too small. however with a 3.73 gear and 275/75/15's i can turn about 1620 rpm at 72 mph which is about as fast as you can go in ohio without getting a ticket. if that lugs it too much, switching to a 4.11 gear would give me about 1800 rpm at 72. i guess we'll see

@1restorick how much drop are you running? that thing looks great man

thanks for the brain food guys.