My winter ties are smaller than my summer tires

[ballisticmike]

I,m waiting for my custom tunes. On the order form i indicated the OEM tiresize. Since then i mounted up some blizzaks that are 1.3 inches shorter than stock. And next spring i plan to get new summer tires that are about .75" taller than OEM size. So... Is it simple for me to adjust the tiresize in the programmer using the available tables? Or not so simple? My other plan is to ask Corey to send me a third tune with winter tire size, and my other tune with summer size. Thoughts? This my be a good way to simplify the whole thing.

Example-
perf87 (has summer tire size)
perf93 (has same summer tire size),
snowtire87 (identical to perf87 but has winter tire size).

[XPerties]

I'm not an expert on this stuff, just learning as I go but I went from 255's to 295's and it changed nothing regarding speedometer so if your worried about that aspect it shouldn't matter BUT you can adjust the tire size very easily.

[88Racing]

Jack has put together this nice little packet about changing things like tire size:http://dygytalworld.ehost-services13...ead.php?t=1101
Its pretty easy once you get the hang of it. The next thing is finding a tire size calculator then you got it whipped!
Pegasus has a tire size calculator. I think?
I would probably put the size tire in the tunes that you would run the most.

Lars

[Longshot270]

Originally Posted by 88Racing

Jack has put together this nice little packet about changing things like tire size:http://dygytalworld.ehost-services13...ead.php?t=1101
Its pretty easy once you get the hang of it. The next thing is finding a tire size calculator then you got it whipped!
Pegasus has a tire size calculator. I think?
I would probably put the size tire in the tunes that you would run the most.

Lars

Haha, I think that Jack's Q&A should be added to the instruction booklets.
And yes, pegasus does have a good tire size calculator that lets you adjust for squish. Most of the ones on the internet dont. It can also compare two different sized tire for the changed engine to tire ratio for gear swaps. Its a nice little combo hidden in pegasus.

[ballisticmike]

good, so it sounds very straight forward to me. My concern was when i spoke to the tire dealer. I told him i would just use my programmer to adjust tiresize and that would fix the speedo accuracy. But he said there are other concerns, like shift points and possibly ABS brake program being impacted adversely. Any truth to this? Just want to be sure.

[88Racing]

ABS-no effect. Monitored by pcm but not controlled by it. Not a problem.
Shift points-1"-2" in tire size differences probably won't hurt them. 5"-6" tire size differences then your looking for gears to compensate.
Tire dealer sounds like he may want to flash program your truck and get some extra $$$$!

Lars

[88Racing]

Goto here to get the downloads:
http://dygytalworld.ehost-services13...p/Support.html
Download pegasus and its usb drivers and also download the gear ratio calculator. Then you can play around with your tire sizes and your gear ratio to see if it will work or not.
You can also post up what sizes your looking at getting and you gear ratio. One of us guys can tell you what's going to work also. Hope this helps!

Lars

[ballisticmike]

i installed and used the pegasus calculator. i tried to post a screen capture, it wont let me
using the defaulted 5% squish it showed these findings-
my gear ratio 3.73
effective gr 3.90
new ratio- 3.56- does this mean it recommends i replace my gears(that aint gonna happen)

oem tires- 275/55-20-
snows- 265/50-20

soooo, the above means what? i need new gearset or just program my gryphon when it gets here?

[88Racing]

Your gryphon oem tire size value is 2484mm w/6% squish. That's what I use and its verified using a gps. I have that same oem tire size.
A 285/50-20 would keep you in the same size.
A 265/50-20 would be 1/2"-3/4 less in height from the oem.
So about 2475mm for gryphon tire size value w/5.5% squish for the snows.
The gryphon uses milimeters instead of inches.
A 1/2" isn't that much to require a gear change.
The other thing is the oem 18" spare tire is the same size as the oem 20" tire.

Lars

[Longshot270]

Pardon my ignorance but why do you lower the squish when figuring the snow tire? If going to a slighly narrower tire, I would expect if anything for the squish to go up. Is there a difference in material or something? :nerd: