AWD experiment.
Thread Starter
TECH Apprentice
Joined: Oct 2007
Posts: 307
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Smaller wheels do spin more. In order to spin the wheels faster at the same engine RPM, you need a lower numerical gear, not higher.
285/35/19 = [(285 * .35) / 25.4] * 2 + 19 = 26.85
235/40/18 = [(235 * .40) / 25.4] * 2 + 18 = 25.40
26.86 ~ Tire revolutions at 60mph: 751.02
25.40 ~ Tire revolutions at 60mph: 793.97
Engine Rev's at 60mph 751.02 * 3.15 = 2365
Gear Required for 2365 engine rpm with 793 tire revs = 2.98
Doing the math, you might be better off with a 235/45-18 front tire and a 3.08 gear.
285/35/19 = [(285 * .35) / 25.4] * 2 + 19 = 26.85
235/40/18 = [(235 * .40) / 25.4] * 2 + 18 = 25.40
26.86 ~ Tire revolutions at 60mph: 751.02
25.40 ~ Tire revolutions at 60mph: 793.97
Engine Rev's at 60mph 751.02 * 3.15 = 2365
Gear Required for 2365 engine rpm with 793 tire revs = 2.98
Doing the math, you might be better off with a 235/45-18 front tire and a 3.08 gear.
The actual dimensions are: 245/45/18. With the great math provided by hammertime, the front gear should be: 3.17.
So the difference is (if im not mistaken): 0.63%.
Would I be ok with that difference? (if using same gears)
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Great info. Thanks! But.... I just found out the front tires I gave are wrong. Woops
The actual dimensions are: 245/45/18. With the great math provided by hammertime, the front gear should be: 3.17.
So the difference is (if im not mistaken): 0.63%.
Would I be ok with that difference? (if using same gears)
The actual dimensions are: 245/45/18. With the great math provided by hammertime, the front gear should be: 3.17.
So the difference is (if im not mistaken): 0.63%.
Would I be ok with that difference? (if using same gears)
Jon
If you have a Silverado SS transmission it is a 4L65e just a upgraded 4L60e. I broke 2 output shafts on my Silverado SS with a magnacharger and a trailblazer converter on street tires. I had to buy a cryo'd output for like $500 OUCH.
Thread Starter
TECH Apprentice
Joined: Oct 2007
Posts: 307
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Thanks Jon. Now I got a new dilemma; seems kind of hard to find a 3.15 front differential. 'guess I'll need the rear one too to match the late gears available. Does anyone has suggestions on that? The only ones I have found are from BMWs.
Last edited by LSfan70s; Sep 8, 2009 at 08:11 PM. Reason: wrong spelling
^^^ why not find a matching set of diff's out of a single vehicle? maybe like a 4wd Colorado or Canyon? Or a half ton truck? the colorado/canyon axles are a little narrower i think. If you have drive train out of a TB then get the driveshafts too and you wont have to buy new yokes to mate to oddball diffs. Simplify things IMO, it outta keep the cost down too. if you find 3/4 ton or 1 ton stuff itall be alot stronger too so you shouldnt have to get upgrade performance stuff.
On The Tree
Joined: Jan 2008
Posts: 109
Likes: 5
From: Where you least expect me
If it has the ratio you want and you're converting an non-AWD chassis (IE, fabbing your own front diff mounts anyway), then why shouldn't you use a BMW diff? The large case diffs used in the 5 and 7 series cars are quite strong.
