Help me understand re-gearing
- Thread starter TJim
- Start date
Might jump a size? Decide on your final tire size before regearing.
30’s - 3.73
31’s - 4.10
33’s - 4.56
Slightly different perspective than @JMT. This depends on how committed you'll be to a tire size. If you're certain you'll stick with a 30" tire, then 4.10 would put you in a good place RPM wise for a 30" tire (Assuming a true size of 29.5" ). If however you think you'd ever go to a 31", 32" or 33" tire (True size 30.5", 31.5" or 32.5"), 4.56 would be a better choice. Given the cost of gearing, this is an important decision, i.e. you have to build to your tire size.
Here's the simple math, assuming real tire size 1/2" smaller than stated, at 70mph:
30" = 2746 (4.10) or 3054 (4.56)
31" = 2656 (4.10) or 2860 (4.56)
32" = 2572 (4.10) or 3054 (4.56)
33" = 2492 (4.10) or 2772 (4.56)
Going with 4.10 also gives you the option of only re-gearing the rear. Since 4 cyl TJs came with 4.10, you could source one of those, assuming you can find one cheap, and swap it.
Here's the simple math, assuming real tire size 1/2" smaller than stated, at 70mph:
30" = 2746 (4.10) or 3054 (4.56)
31" = 2656 (4.10) or 2860 (4.56)
32" = 2572 (4.10) or 3054 (4.56)
33" = 2492 (4.10) or 2772 (4.56)
Going with 4.10 also gives you the option of only re-gearing the rear. Since 4 cyl TJs came with 4.10, you could source one of those, assuming you can find one cheap, and swap it.
UKTJ
TJ Addict
I may have this round my neck but is there not another point to consider here? If you go to 3.73 doesn't it fit in the existing carrier, but if you go above that you need to swap out the carrier as well? That on the basis it is a 30 front and 44 rear, which pretty much all export TJs seem to have been.
UKTJ
TJ Addict
TJs are as rare as Unicorn poop in the UK, you're lucky enough if you can find one to drive let alone finding one to rip up for spares
JM_TJ
TJ Enthusiast
Good point, I have the same set up.
Thanks for replies @Irun and @JMT. Great info to think about. So it sounds like on the current 245s I'm already on the wrong ratio 3.07. Re changing tire size, I haven't decided yet but I realise that has a huge bearing on what ratio I go for. Either way, it sounds like I need to re-gear.
I'm doubting it's a 3.07, the optional Dana 44 rear axle you have only came with 3.73. It'd be an absolute dog on the highway if you only had 3.07. What you probably saw on your VIN check was the base 3.07 but perhaps didn't notice that the optional Dana 44 you say you have came with 3.73 which would also change the front axle to a matching ratio.
JM_TJ
TJ Enthusiast
Yeah, it's not great on the highway. Here is what the VIN check says. I'll check the stamp on the axel when I get a chance.
- * Dana 30/186MM Front Axle
- * 3.07 Rear Axle Ratio
- * Heavy Duty Dana 44 Rear Axle
I hear you, but the optional rear Dana 44 never came in 3.07... it was always geared to 3.73 in the TJ. And when it came with the Dana 44, the factory of course geared the front axle to match.
JM_TJ
TJ Enthusiast
Jerry is correct. Here in the US I've never seen a Dana 44 with anything other than 3.73 gears. The only option was Limited Slip, or not. I'm wondering if European models might have had 3.07?
UKTJ
TJ Addict
Ouput from my vindecoderz sheet is as follows:
*E7: Seats - Cloth Low-Back Bucket; -AZ: Agate; 01M: FAM: AN TRACKING: 90715T13 MY:2000; 01R: FAM: AN TRACKING: 90816T08 MY:2000; 106: Zone 06-Export; 1AU: Export Homologated; 25D: Customer Preferred Package 25D; 2TD: Customer Preferred Package 2TD; 3D2: Intl. Price Protection B; 3HG: Coso Wt. & D.M.; 3HM: Coso Spbr Not Required; 3HQ: Market Homologation; 3HW: Export Ocean Freight; 3HZ: Export Insurance; 3VP: Customer Preferred Discount; 4AL: 1Ntl 37 Day Schedule; 4HC: Special Scheduling Condition III; 4XT: Delete Domestic Warranty Manual (Cos; 4YB: Export Option Requirements; 594: Vehicle Order Tracking; 5I9: Right Hand Drive (RHD); 5IS: TJ-Vehicle Family; 6CT: Certificate of Conformance; 6EM: Label - European E Mark; 6F2: Paint Order ; 6MP: Plate - Manufacturer; 878: Western Europe Region Group; 895: European Region; 8CN: United Kingdom Country ; A68: 4.0L Eng(ERH)/5Spd M/T Nv3550(DDD); ABB: European Equipment Group; ABE: Export Equipment Group; ABU: United Kingdom Equipment Group; ADC: Convenience Group; ALS: Special Edition Group; APA: Monotone Paint; BAU: Alternator - 117 Amp; BCD: Battery - 500 Amp Maintenance Free; BGA: Brakes - Power Front Disc/Rear Drum; CAC: Seats - Low Back Bucket; CDB: Seats - Reclining Front; CFM: Seat - Rear Folding; CGG: Seat Belt Buckle - Traveling Inboard; CGW: Air Bags - Front, Next Generation**; CKE: Carpet - Front Seat Area; CKF: Carpet- Rear Seat/Wheelhouse/Cargo; CKT: Cargo Tie Down Loops; CLC: Floor Mats - Front; CLS: Sport Bar - Rear w/Full Padding; CSA: Spare Tire Cover; CUF: Console - Full Length Floor; DBB: Transmissions - All Manual; DDD: Transmission - 5-Speed HD Manual; DHN: Command-Trac Part Time 4WD System; DJJ: Axle - Front, Dana 30/186MM; DMM: Axle Ratio - 3.07; DRK: Axle - Rear, Dana 44/226MM; DSA: Axle - Anti-Spin Differential; ERH: Engine - 4.0L Power Tech I-6; GBB: Windshield Glass - Tinted; GCB: Glass - Front Door Tinted; GCF: Door - Full Metal w/Roll-up Windows; GRE: Mirror - Left; GSE: Mirror - Right; GTE: Mirrors - Manual, Remote Control; GXX: Sentry Key Theft Deterrent System; HCD: Heater -w/Instrument Pnl Ventilation; JAY: Instrument Cluster w/Tach; JCK: Speedometer - 110 MPH Primary; JHA: Windshield Wipers - Var Intermittent; JJA: Lighter - Cigar; JJF: Horn - Single Low Note; JKA: Glove Box - Locking; JKL: Headlamp Leveling System; K5Z: STRIPE/BADGE/MOLDING/COLOR; KFR: STRIPE/BADGE/MOLDING/COLOR; KWR: STRIPE/BADGE/MOLDING/COLOR; KXR: STRIPE/BADGE/MOLDING/COLOR; LBB: Lamps - Courtesy; LDA: Lamp - Underhood; LMJ: Headlamps - Halogen ECE; LPG: Lamps - Rear Fog; LPS: Lamp - Center Hi-Mount Stop; MB5: Bumper - Rear Black; MBA: Bumper - Front Painted; MCH: Bumper Extensions; MFP: Headlamp Bezels - Chrome; MFR: Front Frame Overlay - Black; MFT: Grille - Body Color; MWB: Sport Bar w/Padded Side Bars; NA1: Emissions - Export; NB3: Euro Stage III Emission Vehicle; NBK: EVAP Control System; NF1: Fuel Tank - 19 Gallon w/Tethered Cap; PSB: Bright Silver Metallic Clear Coat; QSB: Bright Silver Metallic Clear Coat; RAA: All Radio Equipped Vehicles; RBL: Radio-AM/FM Cass, w/Changer Control; RCD: Speakers - Four; RDD: Antenna - Fixed; SBA: Steering - Power Rack and Pinion; SCE: Steering Wheel - 2-Spoke Soft Feel; SDA: Suspension - Normal Duty; SHA: Stabilizer Bar - Front; SHC: Stabilizer Bar - Front and Rear; SUA: Steering Column - Tilt; TBB: Spare Tire - Full Size; TBR: Tire Carrier - Outside; TRK: Tires - P225/70R16 BSW All Terrain; TZH: Michelin Brand Tires; VJX: Black Soft Top; WDF: Wheels - 16 X 7.0 Alum,"Icon"Silver; WKB: Wheel - Matching Spare; WLZ: Wheels - All Aluminum; XCY: Upgraded OBD-II Connectors; XEE: Skid Plate Shield - Fuel Tank; XEF: Skid Plate Shield - Transfer Case; XEV: Tow Eye Brackets; XJF: Fuel Filler Cap - Tethered; XLL: Language - English/UK; XPF: Protective Coating and Remover; YAB: Build To BUX Market Specifications; YHU: 3.2 Additional Gallons Of Gas; Z5B: Payload Rating - 1800; ZAV: Spring - Left Rear; ZBG: Spring - Left Front; ZNV: Spring - Right Rear; ZPG: Spring - Right Front |
Bit of a stream of consciousness I know, but as highlighted it does clearly state Axle Ratio is 3.07. Could this simply be wrong? I have to say I have never looked at the tag on the diff itself. I can't get under mine at the moment, so will be interesting to hear if @JM_TJ can see what it actually says on his diff.
Rough way to tell....put it up on jack stands, spin one tire and count the number of driveshaft rotations. If it spins a little over 3X, then it's a 3.07. If it spins almost 4X, it's a 3.73!
I thought the 3.07 in a Dana 44 was wrong too, but what do I know about a TJ in the UK? You can check the axle ratio either by the tag on the diff (if it's still there) or by the rotation test.
If you get tired of plugging in and checking, recording, and then changing to get values you can compare side by side, you can do this in Excel and just drag down rows for as many options as you want.
Engine RPM = (Speed/60)*axle ratio*transmission ratio*tire revs/mile
Transmission top-gear ratios:
AX15 5th: 0.79
NV3550 5th: 0.78
NSG3706th: 0.84
32RH 3rd: 1.0
42RLE 4th: 0.69
Tire Revs/mile for a BFG AT or MT in "flotation sizes" (ex. 35x12.5):
| Diameter (nominal) | Rev/mile | Diameter (rolling) |
| 30 | 705 | 28.6 |
| 31 | 682 | 29.6 |
| 32 | 659 | 30.6 |
| 33 | 640 | 31.5 |
| 34 | 621 | 32.5 |
| 35 | 602 | 33.5 |
| 37 | 569 | 35.4 |
My apologies, I just noticed you're in the UK and I have no idea what ratios Dana 44 axles ship there with. It very well could be and it now appears that you do have a 3.07 ratio.
JM_TJ
TJ Enthusiast
Weird, I wonder why the UK exports would have such a different ratio. I'll let you know what it says when I find out.
JM_TJ
TJ Enthusiast
Haha, if that's the case, it sounds like I need to get that sorted. Do you have any idea why Jeep would ship exports with a different ratio than the US market?My apologies, I just noticed you're in the UK and I have no idea what ratios Dana 44 axles ship there with. It very well could be and it now appears that you do have a 3.07 ratio.
Sorry, no idea why. What is a bummer for us here in the US is that the Dana 44 is only optional and the crummy/weaker Dana 35 is standard. All you guys outside of the US received nothing but the far more desirable Dana 44. Consider yourself very fortunate.
JM_TJ
TJ Enthusiast
Haha, I’ll trade you my Dana 44 in exchange for the millions of cheap parts you have access to in the statesSorry, no idea why. What is a bummer for us here in the US is that the Dana 44 is only optional and the crummy/weaker Dana 35 is standard. All you guys outside of the US received nothing but the far more desirable Dana 44. Consider yourself very fortunate.
. It is a funny one though. I spoke to a Jeep dealer last year (I was looking at a JL) and he said that a few times a year they convert the Jeep factories to produce the RHD versions in little sprints before going back to LHD. Because of the tight windows, they keep it to a handful of configurations (mainly higher end) so they can maximise output. Hence why our TJs here tend to be better kitted out. It could be a load of bs but that’s what I was told.Similar threads
