M4Madness
NAXJA Forum User
- Location
- Springville, Indiana
http://www.go.jeep-xj.info/HowtoSpeedoGears.htm
When we say "back to stock", we are talking about RPM's.
32" tires with stock gears
- Thread starter scar066
- Start date
http://www.go.jeep-xj.info/HowtoSpeedoGears.htm
When we say "back to stock", we are talking about RPM's.
shawnhancel
NAXJA Forum User
- Location
- Hubbard, OH
damn M4Madness. way to execute a kill. Thanks!!!!
codyyy
NAXJA Forum User
- Location
- San Diego, CA
Here is a general chart for gearing and tires. It assumes a manual trans with 1:1 ratio. If auto, RPMs will be slightly higher, RPMs will be slightly lower with OD.
M4Madness
NAXJA Forum User
- Location
- Springville, Indiana
The above chart is at 65 MPH. If you have an automatic transmission with overdrive, multiply the RPM's on the chart by .75 to get your correct RPM reading.
themangeraaad
NAXJA Forum User
- Location
- Halifax, MA
Ohhhh, according to above chart, once I regear I will be in the range of <Jeremy Clarkson Voice> More Power! </Jeremy Clarkson Voice>
2stix
NAXJA Forum User
- Location
- fallbrook Ca.
ive pretty much read through the entire thread and noticed that nobody mentioned the fact that going to lower gearing also can be a downfall in strength with the ring and pinion gears. 4.56s are a decent size, but when you start getting into the 4.88 and lower, that pinion gear starts getting real small and there isnt much gear contact. couple that with large 33" or larger tires and the weight of those tires starts getting to be quite a load on them gears. spin one in the air and slam back down with it and youll find yourself broke in an instant. just something to think about when re-gearing.
- Location
- Bakersfield, CA
So is that why nearly all the Jeeps, buggies, Toyotas, and whatever that run 40" tires use gears higher than a 5.13 ratio? Like 5.29's and higher in toys, 5.38's in a bunch of buggies? Because the gear sets are weaker?
This is a common misconception and is not universally true or untrue. The strength can be related to tooth contact area, which changes based on the tooth count of the various ratios. As an example, in a 9" rear end the 5.38 ratio has a very high tooth contact area and is considered to be one of the strongest ratios. Some think that a smaller pinion is automatically weaker, but it also has more leverage on the ring gear.........so who knows for sure.
Basically, it's not much to be concerned with in most cases. While our XJ/YJ HPD30's only go to a 4.88 gear ratio, many years ago CJ's came stock from the factory with 5.38 gears in low pinion D27's and D30's.
2stix
NAXJA Forum User
- Location
- fallbrook Ca.
well like in most anything there are allways exceptions. but what you are talking about is a ford 9", which was never a factory axle for a jeep. plus there has been many many years for these gears to be engineered for the 9" to make a nice low gear that is still strong. just as there has been time to engineer thick ring gears to use on carriers that before were not possible. most of these people running there jeeps, buggies, toyotas, are also running differant axles than stock. heck my F550 has 5.38s stock, but its HUGE. oh and those CJs that came stock with 5.38s in thier d27s and d30s also came stock with tiny little tires. i really dont want to make this a p!$$!ng match, i just wanted to warn the people that didnt know, that a lower gear may give you better power and fuel economy, but can also be a weak point in the drive train. misconception? if you say so.
codyyy
NAXJA Forum User
- Location
- San Diego, CA
Yeah mine is pretty bad right now. There's a hill that I usually have to go up to get into Clairemont on Balboa, and that road is horrible for my Jeep even just to get it up to speed in high gear. But I have an auto.
srmitchell
NAXJA Forum User
- Location
- Mckinleyville (Humboldt) CA
Im switching to 4.56's soon, but on 31's. I will go to 33's this summer, but funds will force me to stay on these 31's for now.
I get 13/17 mixed, and ideas what I will get after?
I get 13/17 mixed, and ideas what I will get after?
- Location
- Bakersfield, CA
OK, but what's your point? Are you saying someone shouldn't put the correct gears in for their tire size because the gears might be weaker? I understand the theory, and it's debatable based on the ratio and what diff, but I don't think it applies to getting the best ratio for a street driven XJ. I guess I'm saying that even if the gears are slightly weaker, we know we're already increasing the risk of driveline component failure when we get bigger tires.
I also happen to not buy into the perception that higher ratio gears are automatically weaker. Maybe, maybe not.
codyyy
NAXJA Forum User
- Location
- San Diego, CA
IMO there are multiple factors that come into play. I don't think I've heard anyone use the stock axles with say, 38s in their XJ. Usually most people upgrade to stronger axles before then like shortened fullwidths. More than just the ring and pinions are at risk there, like the axle shafts themselves, u-joints, etc.
mbennett
NAXJA Forum User
- Location
- B'ham alabama
Huh?:dunce:
codyyy
NAXJA Forum User
- Location
- San Diego, CA
I mean taking a fullwidth axle like a D60 and shortening it to Jeep specs (I know, I said it weird). However yeah people do just run fullwidths in these vehicles.
scottmcneal
NAXJA Forum User
- Location
- not here
I have 488's in my 89 with 33's on it..The wife has 355 on hers with 32's...Both are auto's. She smokes me in MPG, both street and freeway..Hers get better MPG offroad too..So if you do a gear change with 32's or 33's, i would go with the 456 gears..
themangeraaad
NAXJA Forum User
- Location
- Halifax, MA
But whose is more fun?
