How do you get crawl ratio again?
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Junior User
Joined: Oct 2002
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How do you get crawl ratio again?
I thought it was multiply rear axle ratio by tranny low or first gear ratio, times transfer case low ratio. So if I do that, I'm coming out with a 28 crawl ratio?! I'm confused I thought it would be better than that, at least it feels like it is. I have an 85 F-250, 4.10's, t-18, and not sure what kind of transfer case, I'm not sure if its a NP 208 or a borg warner or whatever. I was never good at math so if someone could help me out, thanks.
Postmaster
Joined: Jul 2001
Posts: 4,038
Likes: 3
From: South Kitsap County, WA
How do you get crawl ratio again?
Hey Blue,
You've got the right idea. Take the highest ratio on all your drive train components (tranny, xfer case, diffs--which should be close to the same, but take the highest since it'll be doing the majority of the pulling). These should be the first gear, 4 L, and the highest ratio in your diff #'s. You'll definitely need to know which xfer case you have as the ratios are different.
Take these three numbers and multiply them.
4.10 x 6.32 x 2.61 (NP208)=67.6:1 crawl ratio
4.10 x 6.32 x 2.72 (BW1345)=70.5:1 crawl ratio
Pretty similar, and this applies if you have the T-18A with the really deep granny low.
-Kerry
You've got the right idea. Take the highest ratio on all your drive train components (tranny, xfer case, diffs--which should be close to the same, but take the highest since it'll be doing the majority of the pulling). These should be the first gear, 4 L, and the highest ratio in your diff #'s. You'll definitely need to know which xfer case you have as the ratios are different.
Take these three numbers and multiply them.
4.10 x 6.32 x 2.61 (NP208)=67.6:1 crawl ratio
4.10 x 6.32 x 2.72 (BW1345)=70.5:1 crawl ratio
Pretty similar, and this applies if you have the T-18A with the really deep granny low.
-Kerry
Thread Starter
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Junior User
Joined: Oct 2002
Posts: 55
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How do you get crawl ratio again?
Thanks Kerry, I checked the truck and it has the borg warner transfer case, giving me a crawl ratio in the 70s, which is better than the 24 i was getting HAHA! I never was good at math. 
I'm hoping thats a decent crawl ratio, the truck feels like it could pull a house down so i'm assuming it is.
I'm hoping thats a decent crawl ratio, the truck feels like it could pull a house down so i'm assuming it is.
Postmaster
Joined: Jul 2001
Posts: 4,038
Likes: 3
From: South Kitsap County, WA
How do you get crawl ratio again?
[updated:LAST EDITED ON 07-Dec-02 AT 10:27 PM (EST)]Pretty decent crawl, I used to drop into granny and 4L just let the truck idle me up my driveway when I had my '82 with a NP435
. The driveway is pretty steep and 150 feet long. If it's not cleared when it snows, I don't get home
.
Just think, some people actually have custom setups with enormous ratios. It's like why have a throttle?
Oh yeah, the places you don't need to crawl over...
-Kerry
. The driveway is pretty steep and 150 feet long. If it's not cleared when it snows, I don't get home .Just think, some people actually have custom setups with enormous ratios. It's like why have a throttle?
Oh yeah, the places you don't need to crawl over... -Kerry
