read my sig , 5.29s ftw.
4.88 or 5.29 ring and pinion experience (2 Viewers)
- Thread starter lenross1
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Not sure how useful that is.
Not a comparison of any kind. Bad may have been the wrong word. The trade is Highway performance vs offroad. I did 90+ comfortably across Nevada and Utah and the gears performed great on the Rubicon and Moab. Probably some places the 5.29's gears would have required a little less braking going downhill. I don't have 5.29's, so I can't state how they would have been. I believe the key is the trade and you will also notice those who have made swaps seem to be very happy with what they have.
Not sure how useful that is.
All diff gearing does in an automatic transmission at highway speed is adjust cruising RPM (an increase of about 200 between the two @ 70 mph). A difference of 70 mph driving to 90 mph driving is a greater RPM than 4.88 to 5.29 at any 80 series diff ratio. Said differently, if you think driving 90 mph with 4.88's was fine, then you are in effect saying that driving 75 mph with 5.29's is fine, because the RPM will be close to identical (and I'd agree that it is fine).
I have lived with 5.29's for a year and a half. There is no question that 4.88's are a better all around match for 35's for most 80 series owners, and you'd be nuts to have forced induction and a gearing limited top end that is near or below Western speed limits. You simply can't argue 4.88's and a supercharger for all around performance.
My only point all along has been that it's only a couple hundred RPM difference for an entire step down in gearing. As long as you don't drive regularly over 70 mph, 4.88's provide you absolutely nothing as an advantage, because you will have taller gearing that you don't utilize to cruise at high speeds. I'll be the first to admit that the 80 will cruise all day long at speeds over 75 mph on 35" tires, and you do not get to have your cake and eat it to with 5.29's on 35's.
Most people who do 5.29's on 35's are on their way at some point to 37's, which means we only spend on gearing once. That's the nice thing about it - don't like the RPM's on 35's and it's cheaper to go 37's than it is to regear
1973Guppie
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I know........
5.29's, 37 inch tires and some mark's gears in the tranny
5.29's, 37 inch tires and some mark's gears in the tranny
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Right now it is basically a daily driver that wheels from time to time. my trend has always been to go to bigger tires eventually. So far on this truck i went from 315s (34.5 inches tall) to 36s (35.5 inches tall). the 36s are 15.50 wide (actual width 14.5 inches) and really noticed a slow down when i upgraded from the 315s to 36s. Which is what got me thinking i need to regear. i plan on wheeling it more in the future. i rarely go above 70-75 mph.
Probably the only reason i would go as low as 5.29s is because there is not a significant transfer case low range available for the 80 that does not call for signifcant modification. So my reasoning is to go as low as possible to make up for the tcase. i have been told that the automatic makes up alot for the lack of low t case gearing but how much? is there a mathematical formula similar to the formula used to figure out what ring and pinion you need? i know thats an easy question to answer!
something like:
1st gear x tcase gearing x ring and pinion gearing x auto torque converter slippage multiplier = the holy grail 100 to 1 crawl ratio.
if there is a formula what is it?
Probably the only reason i would go as low as 5.29s is because there is not a significant transfer case low range available for the 80 that does not call for signifcant modification. So my reasoning is to go as low as possible to make up for the tcase. i have been told that the automatic makes up alot for the lack of low t case gearing but how much? is there a mathematical formula similar to the formula used to figure out what ring and pinion you need? i know thats an easy question to answer!
something like:
1st gear x tcase gearing x ring and pinion gearing x auto torque converter slippage multiplier = the holy grail 100 to 1 crawl ratio.
if there is a formula what is it?
The formula is to stop fawking around with gearing math and put 37's on your rig with 5.29's so you don't have to do it twice
Here's what to do:
Lock out overdrive and hit 70 mph. That's about 100 rpm over what 5.29's will be like at that speed. 4.88's will be about 200 rpm below that. If you like what 5.29's feel like, get them and enjoy the extra gearing offroad. If you don't like that RPM, 4.88's are a no brainer.
1973Guppie
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low gearing: tranny x tc x r/p = crawl ratio
RPM's: mph x Axle ratio x Tranny OD x Transfer case ratio x 336 / tire diameter = RPM's
I have been told a good rule of thumb is to double what you get with the above low gearing calculation when using an auto tranny.
So, for example, I have been thinking of how I will setup my 80 when I have the $$:
low gearing: 2.95 x 2.488 x 4.88 = 36:1 crawl ratio, x2 for automatice = 72:1 crawl ratio
low gearing (with mark's gears): sub 3.115 tc ratio = 45:1, x2 for automatic = 90:1 crawl ratio
I am thinking the sweet spot is the above with mark's gears and 4.88's, I only want to run 35 mud terrains and would like to keep my highway comfortable, 37's are too high, the mark's gears and 4.88's would give me a good highway speed and keep things stock and give me a nice low gearing off road. I think coupled with a slee 4 inch lift it would be just about perfect.
MPH: 70 x 4.88 x .765 x 1 x 336 / 35 = 2508 rpm's at 70mph
interestingly enough if I were to go to 5.29's it would not give me that much of a lower gearing and would sacrifice (from what I have heard) strength in the ring and pinion, not as nice of gearing on road/highway and require me to really run 37 inch tires. I rarely drive over 70mph, usually I set the cruise at 70 and just take my time.
hope that helps, let me know if I screwed any of this stuff up above,
can anyone state what the stock rpm's should be at 65/70/75 for comparison purposes? in the end the goal for me would be to keep the vehicle running as it would stock on the road/highway.
Noah
I've had 5.29's for 2 weeks now, and although I haven't wheeled with them yet to see the off-road performance gain with increased compression braking, the torque converter now locks 3rd at 35 mph, and in 4th, it locks at 42 mph. For city driving, that means to me that the tranny will last longer. The rpm's might seem a little high, 2650-2700 at 65 mph, but in reality the (my) rig should not be driven much past that anyway with 5-6" lift. I will also be pulling my off-road trailer and will like the 12% lower than a stock set up. I am glad I did not go with 4.88's.
It all depends on what you are going to do with the truck. If I was building an expedition type rig with 35's being the biggest tire I would be running (true measurement, not what's writen on the sidewall), I would run 4.88's. I went 5.29's because I am usually playing in the rocks and I knew I was going to run a 37"+ tire. My 5.29's and 37" bias Iroks is perfect. When I get the $$ to do dual transfer cases, I will step up to a 39.5" Irok and be even happier that I went 5.29's!
Old thread revival. When you guys are talking tire size, are you talking advertised size or literal size? I'm running 37in BFg KO2s which are light (for 37s) and only measure out to 35.5in tall when on the truck. I like 37s, and low gearing. But I also like being able to drive 75mph on the highway and not drop 20mph going up steep grades. So would 5.29s be too low considering my small 37s?
