The Ultimate TRUE TIRE SIZE Database

BaddestCross

BaddestCross

Active Member
Clutch said:
We still talking about Mastercraft Courser MXT’s? Catahoula does. I’ve never ran them but seen them in person and they look great.


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catahoula said:
I like em a lot. I do not see why more do not run them. I would purchase again...and listen to Clutch and get 35's!!!!

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Lol. Well there you go. 👍

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
 
F

Fionayeti

Guest
Tire and gear question!

Okay, dumb question, perhaps. But all this tire talk has made me think!

So I'm running 315/75r16 (35's) Mastercraft Courser MXT's with 5:13 gears. I should set my Superchips to 34.6 which is the true measurement of the tire. Correct? (Yes, I know Superchips only gives you half measurements so I'd set to 34.5) This keeps me right at 2400 rpms' at 70 mph and even up to 80 mph my overdrive stays put and doesn't kick down. Jeeps got some good power with this setup.

Now if I go to 37's, say a 37x12.50r16 and their true measurement is, say, 35.5 ... I should set my Superchips setting to to 35.5. But, will the 5:13's handle that setting and keep me at about 2500 rpms at 70mph and keep the overdrive steady? - Because if i set Superchips to 37 there's no way the 5:13's will stay at 2500 rpm's at 70mph and the overdrive will kick down more often. Or do I need to go to 5:38's? Am I being clear? Sorry! I'm trying not to do a gear change!
 
BaddestCross

BaddestCross

Active Member
Fionayeti said:
Okay, dumb question, perhaps. But all this tire talk has made me think!

So I'm running 315/75r16 (35's) Mastercraft Courser MXT's with 5:13 gears. I should set my Superchips to 34.6 which is the true measurement of the tire. Correct? (Yes, I know Superchips only gives you half measurements so I'd set to 34.5) This keeps me right at 2400 rpms' at 70 mph and even up to 80 mph my overdrive stays put and doesn't kick down. Jeeps got some good power with this setup.

Now if I go to 37's, say a 37x12.50r16 and their true measurement is, say, 35.5 ... I should set my Superchips setting to to 35.5. But, will the 5:13's handle that setting and keep me at about 2500 rpms at 70mph and keep the overdrive steady? - Because if i set Superchips to 37 there's no way the 5:13's will stay at 2500 rpm's at 70mph and the overdrive will kick down more often. Or do I need to go to 5:38's? Am I being clear? Sorry! I'm trying not to do a gear change!
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You always set to measured tire size. The RPMs will be different because of the increase in tire size... The programmer is telling your Jeep's computer what the tire size is so it will calculate the correct speed for the speedometer display and correct shift points if you have an automatic transmission.

Refer to the charts available in the FAQ post here and you will see what your RPM will be (give or take) with 37s, your 5.13s, and whatever engine and trans you have.

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
 
BobNH

BobNH

Member
I have found online the possible missing link to tire sizing. 63360/(revolutions per mile)/pi
I have been comparing this formula to a variety of tire measurement posts, where the mfg supplies the rev per mile data at least, and damned if it doesn't come up with what folks are measuring.

A guy here at work just installed 35x12.5x15 Mickey Thompson MTZ's. I measured them at 33.5". I came back to my desk and looked them up. It states 601 revs per mile. So, 63360 (inches in a mile)/601=105.42429. That number gets divided by pi, or 105.42429/3.14159=33.55762. Again, this does require the mfg to actually provide that revs per mile data to work.

I have new tires coming this weekend, so I am going to do this again with mine, but for anyone who wants to include this calculation with their additions, as long as Eddie doesn't mind the additional data, I personally would be interested in how it works out against the tape measure.

Thanks. Been reading too damn many specs this week...
 
WJCO

WJCO

Meme King
BobNH said:
I have found online the possible missing link to tire sizing. 63360/(revolutions per mile)/pi
I have been comparing this formula to a variety of tire measurement posts, where the mfg supplies the rev per mile data at least, and damned if it doesn't come up with what folks are measuring.

A guy here at work just installed 35x12.5x15 Mickey Thompson MTZ's. I measured them at 33.5". I came back to my desk and looked them up. It states 601 revs per mile. So, 63360 (inches in a mile)/601=105.42429. That number gets divided by pi, or 105.42429/3.14159=33.55762. Again, this does require the mfg to actually provide that revs per mile data to work.

I have new tires coming this weekend, so I am going to do this again with mine, but for anyone who wants to include this calculation with their additions, as long as Eddie doesn't mind the additional data, I personally would be interested in how it works out against the tape measure.

Thanks. Been reading too damn many specs this week...
Click to expand...

You need a beer.
 
BaddestCross

BaddestCross

Active Member
BobNH said:
I have found online the possible missing link to tire sizing. 63360/(revolutions per mile)/pi
I have been comparing this formula to a variety of tire measurement posts, where the mfg supplies the rev per mile data at least, and damned if it doesn't come up with what folks are measuring.

A guy here at work just installed 35x12.5x15 Mickey Thompson MTZ's. I measured them at 33.5". I came back to my desk and looked them up. It states 601 revs per mile. So, 63360 (inches in a mile)/601=105.42429. That number gets divided by pi, or 105.42429/3.14159=33.55762. Again, this does require the mfg to actually provide that revs per mile data to work.

I have new tires coming this weekend, so I am going to do this again with mine, but for anyone who wants to include this calculation with their additions, as long as Eddie doesn't mind the additional data, I personally would be interested in how it works out against the tape measure.

Thanks. Been reading too damn many specs this week...
Click to expand...
Science for the win! Since that's finally settled, can we all get back to measuring our fucking tires, plugging the number into the programmer, and call it a day?

My head hurts... Where's my bottle of Jack? 🤣

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407
 
BobNH

BobNH

Member
New ko2's

285/70r17 E, 30psi (I asked for 32, they put 1 at 30 so I had to match them all, will fix all tomorrow to 32)
Spec says 32.8 diameter
Rotations per mile=635
(63360/635)/3.14159=31.76
20180414_101024-1.jpg
 
wrbrd

wrbrd

New member
I have an AEV pro cal ,according to the database I should be using the highest point or the shoulder size to get my speedometer correct? Thank you for patience!


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TrailHunter

TrailHunter

Hooked
TheGrendel said:
Wish one of the new KM3 guys would post their results on here. Keep this database up to date.
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I talked with a BFG rep yesterday and they said the 37x12.5x17 KM3 would be released in October. It will be offered in a 6 ply (C) and an 8 ply (D). I tried to get weight/height specs but no luck.

I think someone installed 35’s recently... was hoping they would post it up here as well.
 
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