Drivetrain

Wheels, tires & gearing math

The 17 in recommendation stands. Run 17x8 fronts at 4 in BS or less and 17x9 rears at 4.5 to 5 in BS, with a ~27.9 in rear tire such as a 275/50R17 and a 245/50R17 front. Do not use the +8 mm VN515 17x9.5 on the rear, because it is about 5.5 in BS and too deep. Pick the gear by transmission on a 28 in tire: TH400…

Research run 2026-10-12. Prices are US retail as seen in vendor pages or search-result snippets on that date; "snippet" = seen in a search result but the page itself would not load (summitracing/jegs/cjponyparts/vividracing returned 403 to fetch). Anything I could not confirm says "price not confirmed".

The pick

Good
~$1,200-1,500 (Vision 57 15x8 at $105 each, or Speedway Smoothie at $176.99 each, plus 4 Cooper Cobra 275/60R15 at $194 each from Coker)
Better
~$1,750-2,350 (4 American Racing Torq Thrust II 15 in at $214-324 each, plus BFG Radial T/A RWL: 2 x 255/60R15 at $225 and 2 x 275/60R15 at $224 or 295/50R15 at $294)
Best
~$2,300-2,700 (17 in Torq Thrust II or US Mags Scottsdale/Baja at ~$322-374 each, plus 4 Nitto NT555 G2 275/50R17 at $249 each; several 17 in prices not confirmed)

Primary pick (all-around, 2042-proof): 17" wheels, 28" rear tire, 3.42 or 3.73 gear, with the transmission decision driving the gear.

  • Wheels: staggered 17x8 front (about 4" backspacing or less so the inner lip clears the lower control arm) and 17x9 to 17x9.5 rear (4.5"-5" BS; 4.53" BS at -12 mm is the proven C10 number for US Mags Scottsdale and American Racing Baja 2526). American Racing Torq Thrust II (VN515) gives the classic look at a Better-tier price ($322 per 17x9.5, carid) 24; budget roughly $1,250-$1,500 for four (front 17x8 price not confirmed). CORRECTION: the +8 mm VN515 17x9.5 is ~5.5" BS, too inboard for the rear per 2; ask for a lower-offset rear or use the Scottsdale/Baja 4.53" BS 17x9 and confirm inner clearance with the actual drop.
  • Tires: front 235-245/50R17 (about 26.5"), rear 275/50R17 (~27.8"); a Nitto NT555 G2 275/50R17 is $249 each (Giga Tires, 2026-10-12) 3251. Tire budget: ~$1,000-$1,150 unmounted for four. Because a teen will drive this in Kansas City winters, prefer an all-season 17 for the daily if grip in cold matters; the NT555 G2 is summer-only, and I could not confirm a 275/50R17 all-season price (the BFG g-Force Comp-2 A/S Plus I found is the 25.7" 275/40R17 size, too short). Plan on a dedicated winter set or keep it a fair-weather truck. For a vintage look on a budget, the 15" fallback below.
  • Why 17 over 15: the 15x8 rally reports with 2.5" drop spindles show lower-control-arm/inner-rim contact 810; forum advice was that most guys who lower these go to bigger wheels (17"+ per 10; 18-20" per 848). 15" tire choice is narrower than 17", though the Radial T/A and Cobra are both currently in stock at Coker; the earlier cited "national backorder" thread is from 2012 and was about a different size, so it is not evidence of a current shortage 46. 17" has summer and all-season tires from every major brand, which is the real long-term-supply argument for a 2042 daily.
  • Gear: with TH400 (rebuild), choose 3.42 (2,870 rpm at 70 mph on 28") or the more relaxed 3.08 (2,590 rpm; a 454 with ~500+ lb-ft has the torque, and if the axle already carries a 3.07/3.08 gear it avoids a regear), 3.73 is too tall in revs for a TH400 (3,130 rpm). With 4L80E, choose 3.42-3.73 (2,160-2,350 rpm at 70). With T56 Magnum 0.63, choose 3.73 (1,970 rpm at 70); with the 0.50 6th, 4.10 (1,720) becomes sensible, but first gear/launch then feel very short with the 454's torque.
  • Drop: a 2/4 to 3/5 (about 2.5" spindles front, flip kit or 4" lowering blocks rear) is the fitment sweet spot; see below.

Budget fallback (15" classic look, all prices confirmed): 15x8 front / 15x10 rear on Torq Thrust II ($213.99 polished, $323.99 chrome) or Vision 57 Rally (~$97-$106 each); tires BFGoodrich Radial T/A RWL 255/60R15 front ($225) and 275/60R15 rear ($224) or 295/50R15 ($294); all from Coker. That is about $1,750-$2,350 for the set (four Torq Thrust II at $214-$324 = $856-$1,296, plus tires $898-$1,038) depending on wheel finish and rear tire. The Torq Thrust 15x8 (3.79" BS) meets the <=4" front rule; other 15x8s with 4.5" BS were warned against in 10. Front wheels no more than 4" BS; rears 5" BS minimum per the forum "3/4 drop" wheel-fitment thread 2.

Rough package totals (wheels + tires, excluding mounting): Good ~$1,200-$1,500 (Vision 57 $420 or Smoothie $708 per set of 4 + Cooper Cobra 275/60R15 4 x $194 = $776); Better ~$1,750-$2,350 (Torq Thrust II 15" + Radial T/A RWL); Best ~$2,300-$2,700 (17" Torq Thrust II/Scottsdale + 275/50R17 Nitto etc.). Totals are estimates: several 17" prices not confirmed.

Why it matters

Three decisions lock together here: tire diameter, rear gear ratio, and transmission top gear. Tire diameter times gear ratio sets cruise rpm; wheel diameter and backspacing decide whether the stance you want (a 2/4 to 3/5 drop is what most square-body builders call "the standard") fits at all. On a 454 with a 5,500-6,000 rpm powerband and a 35-minute interstate commute, the target is roughly 2,000-2,500 rpm at 70 mph with an overdrive, or under ~3,000 rpm with a plain TH400. That window is reachable with a ~28" tire and a 3.42-3.73 gear, but not with a 4.10 and not with a stock 3-speed unless the gear is on the tall side.

Platform facts that matter: 1973-87 2WD C10 uses 5x127 (5x5) with a 78.1 mm center bore; the stock 15x6 wheel has about 13 mm offset 1. A 1970 truck can be 5- or 6-lug, so count lugs on your 1977 (a half-ton 2WD should be 5) 1. Forum owners say 1977 half-tons came with the 12-bolt rear, and the rear axle is narrow (same width as the 2WD trucks, narrower than the 4x4 front track), which one moderator attributes to GM cost-saving by sharing one axle across many truck types 9. The narrow axle is why wide rear tires are limited by the springs/frame rather than the fender, and why 10-inch-plus wheels "may require tubs or chassis work, not just a drop" 1. (Verification 2026-10-12: the 5x127 / 78.1 mm / 15x6 facts in 1 were re-read and are correct; the 13 mm stock offset figure was not visible on the re-fetch, treat it as unconfirmed. A 3/4-ton C20 is 6x139.7, so a heavy-half C10 should still be 5-lug, but count lugs anyway.)

The "big meats out back" goal is easy at ~275-295 mm width on a 15x8 to 15x10 or a 17x9-9.5. One forum summary says the best you can do without tubbing a dropped truck is about 11.5" wide tires; a stock 12-bolt should clear 12.5" slicks at a milder drop 5. Those are drag-style numbers; for a street truck 275-295 mm is the sweet spot.

The decade-long Walter plan favors long-term tire availability: 17" has far deeper street-tire supply than 15" in 2042, while 15" gets you period-correct raised-white-letter looks today. See Recommendation.

Options

Wheels (all 5x127; confirm every listing says 5x5/5x127 and check hub bore)

Tier Brand & model Size / BS Part # Price (vendor, 2026-10-12) Link Notes
Good Speedway "Smoothie" steel 15x8, 4.25" BS, 5x5.5 listing (verify 5x5) 282272 $176.99 each raw steel (Speedway, snippet) 18 Cheapest period look; need caps/trim rings. The 5x5.5 in listing title conflicts with 5x5 elsewhere, confirm pattern before ordering.
Good Vision 57 Rally (cast, "American Muscle" style) 15x8, -6 mm offset (~3.75" BS), 5x127, 81.7 mm bore 57-5873 $105 each / $420 per set (threepiece.us, page fetched 2026-10-12); Vivid Racing ~$97-$106 (snippet only, page 403) 1920 Cheap, 15x8 rally look. Forum owners report 15x8 rallies hitting the lower control arm once 2.5" drop spindles go on 810. Quality tier is entry-level.
Better American Racing Torq Thrust II (VN515) 15x8, -18 mm, 83.06 mm hub, 3.79" BS W2059-V (polished) via CJ Pony Parts polished from $213.99, chrome from $323.99 each (CJ Pony Parts, snippet) 21 Fits C10 1960-87 per listing; -18 mm / 3.79" BS / 83.06 mm bore / 5x5 confirmed by a search result 2026-10-12, but the CJ page itself returned 403 so the price is snippet-only (other vendors list 15x8 TT II at ~$223 in 5x4.75 and 15x7 5x5 at $220). The 83.06 mm bore is larger than the 78.1 mm hub; GM 5x5 wheels are normally lug-centric (conical-seat nuts center the wheel), so confirm the nut seat type rather than assuming rings are needed.
Better Cragar 08/61 S/S 15x8, 5x5.5 listing crr-08850 (Summit) $346.87 each chrome (Summit, snippet) 22 Same bolt-circle caveat: the Summit listing reads "5 x 5.50", so I did not confirm a true 5x5 version at that price. Jegs lists $247.08 for a multi-fit pattern, not 5x5.
Better US Mags Rambler 15x8 (listing I saw is 5x4.5) W955-V $353.00 each chrome (Mustang fitment; page 403, price not re-verified) 23 I did NOT confirm a 5x5 Rambler price. Treat as "price not confirmed" for C10.
Best American Racing VN515 Torq Thrust II 17x9.5 17x9.5, +8 mm, 5x127, 83.06 mm VN51579574 (carid) $322 each / $1,288 per set of 4 (carid, snippet; page 403 on re-fetch, listing title and +8 mm confirmed in search result) 24 CORRECTED: +8 mm offset on a 9.5" wheel is roughly 5.5" backspacing (inboard, measured BS = (width+1)/2 + offset), about 0.5" deeper than the 5" rear guideline from the forum 2. On the narrow C10 rear this risks inner-tire contact with leaf spring/shackle. Do not buy this offset for the rear without checking inner clearance; look for ~0 to -6 mm offset (5" BS) or a front-only use.
Best American Racing Baja 17x9 17x9, 4.53" BS, -12 mm W6019 (CJ Pony Parts) price not confirmed 25 Fit data confirmed, price not.
Best US Mags Scottsdale 17x9 17x9, -12 mm, 4.53" BS, 5x5 W2270-V (CJ Pony Parts) price not confirmed on CJ (403); an eBay set of 4 17x9 Scottsdale for C10 was listed $1,496 (~$374 each, snippet) 26 Direct 71-87 C10 fitment and 4.53" BS at -12 mm confirmed in the search-result title. Note this is one 17x9 size for all four corners; fronts at 4.53" BS exceed the ~4" front limit in 2, so use it only at the rear or pick a lower-BS 17x8 front.
Best Billet Specialties Street Lite 15x10 etc.; 17" new BRS23510L6135 (15x10 black) price not confirmed; a used pair 17x8 sold $780 27 Forged-looking billet 5-spoke; 12.6 lb. Not verified for 5x5.
Not priced Weld, Ridler, Rocket, Detroit Steel branded n/a n/a Weld Draglite 15x8 snippets found only for 5x4.5/5x4.75 at $399; no 5x5 price found 28 Ridler and Rocket: I found no 5x5 pricing. Not recommended on cost grounds for this build anyway.

Tires (all prices per tire; diameters are the spec-sheet numbers where seen)

Tier Brand & model Size Part # / Dia. Price (vendor, 2026-10-12) Link Notes
Good Cooper Cobra Radial G/T RWL 275/60R15 28.07" dia, 10.7" wide $194.00 (Coker; SKU 125101579776; page fetched 2026-10-12, price/SKU/dia confirmed) 11 RWL, load index 107 (2,149 lb at 35 psi), T-rated 118 mph, UTQG 440 A/B. Stout value; not a performance tire.
Better BFGoodrich Radial T/A RWL 255/60R15 SKU 6306500, 27.10" dia $225.00 (Coker, confirmed 2026-10-12; load index 102, 1,885 lb at 35 psi) 12 Front tire for staggered 15" setup. S-rated (112 mph).
Better BFGoodrich Radial T/A RWL 275/60R15 28.0", 743 rev/mi (tiresize.com, confirmed) $224.00 (Coker, snippet only: the cokertire URL previously cited was dead and the guessed www URL 404s; price not re-verified) 1314 Classic.
Better BFGoodrich Radial T/A RWL 295/50R15 SKU 6308245, 26.60" dia $294.00 (Coker, confirmed 2026-10-12; load index 105, 2,061 lb) 15 The "big meat" rear on a 15x10; but 26.6" is shorter, raising rpm 5% vs a 28" tire.
Better Mickey Thompson Sportsman S/T 275/60R15 28.1" dia, 10.7" wide, 740 rev/mi ~$202.19 (Walmart/TFS, snippet) 16 S/T is MT's all-season muscle-car radial.
Better Mickey Thompson Sportsman S/R 28x10.00R15LT 672-6640 (Jegs) $389.09 Jegs / $383.79 Walmart (snippets; Jegs 403 on re-fetch, not re-verified) 29 "Flamed" tread hot-rod look; load 1335 lb at 35 psi, H-rated. MT's own page confirms the line exists in 15" and 17" (3 sizes).
Better BFGoodrich g-Force Comp-2 A/S Plus 275/40ZR17 ~25.7" dia $191.99-$209 (Discount Tire / Mavis) 30 Great street tire, but 25.7" tall is too short for a 28" gearing target.
Better BFGoodrich g-Force Comp-2 A/S 255/40ZR17 25.0" dia, 10.24" wide, 400AA $174.99 (snippet) 31 Same limitation.
Best Nitto NT555 G2 275/50R17 XL 108W 27.87" dia, 746 rev/mi (confirmed) $249.00 (Giga Tires, 20% off $311.25, page fetched 2026-10-12; the $222 in the earlier draft did not hold up) 3251 Closest to a 28" street tire in 17". It is a SUMMER ultra-high-performance tire: poor in cold and snow, so not ideal as a teen's year-round tire in Kansas City. See all-season note in Recommendation.
Best Mickey Thompson Sportsman S/R 28x6.00R17 27.9" dia $370.69 (tires-easy, sale from $463.36, fetched 2026-10-12) 33 Hot-rod flame-tread skinny; 28" tall so not a short front; expensive for the value.
Best Mickey Thompson ET Street S/S 275/60R15, 295/55R15 etc. n/a $285.99 (275/60R15), $310.79 (295/55R15) (snippet) 34 Drag-radial: sticky, wear fast, poor in rain. Not for a daily/teen car.
Avoid Nitto NT555RII 275/40R17 25.67", 810 rev/mi $289-$292 (Discount Tire/SimpleTire) 35 DOT drag radial, short and wet-sensitive.
Avoid Toyo Proxes 4 Plus 275/40R17 tiresize ~$158 each in a $632 set of 4 (TreadDepot, snippet) 36 Great grip but short sidewall; same 25.7" diameter issue.
Not found Michelin Pilot Sport 4S 285/35ZR19 $413.99 (Walmart) n/a n/a 37 Comes only in 18"+ for this width range; no 15"/17" tall sizes. Too short a tire for gearing anyway.

Fitment & gotchas

  • Bolt pattern / bore: 5x127, 78.1 mm; many aftermarket wheels have a larger bore (83.06 mm on American Racing). Use hub-centric rings or confirm the wheel centers on the lug nuts. 1970 trucks can be 5- or 6-lug: count 1.
  • Drop spindles and 15x8: 2.5" drop spindles cause lower-control-arm contact with the rim's inner edge on most 15" wheels; fixes reported: switching to 15x7 at 3.75-4" BS, aftermarket tubular lower arms, or going to 17"+ 81047. Grinding the stock LCA was done by one owner 8 but another reported a control arm breaking after material was removed 47; do NOT grind load-bearing control arms on a truck a teenager will drive. Another owner confirmed the rim, not the tire, touches the stock LCA 47. Aftermarket tubular LCAs fixed it for one owner on 275/60-15 with 2.5" spindles and 4" rear 47.
  • Backspacing: forum rule of thumb is front under 4" BS and rear 5" BS minimum for tucking 2; a stock 1984 Scottsdale ran 8" factory rallies (4" BS) with 31x10.50x15 and no rubbing at stock height 8. A 17x9 with 4.5" BS and 275/60/17 was reported with "lots of room inside, not much outside" without rolling the fender lip 6.
  • Wheel weights: crimp-on weights hit the tie-rod knuckle/boots on a 15x8 with drop spindles; one owner went to stick-on weights, which can dislodge from caliper-bracket contact 8.
  • Lug nuts: aftermarket wheels need the correct seat (conical vs flat/mag) for the 5x5 studs; GM 5x5 studs are believed to be 1/2"-20 (not verified here). Buy the nuts to match the wheel's seat and torque with a wrench, never an impact gun, on alloys.
  • 10" fronts: "If you're using 10s on front and rear you can't tuck the front" 2. Wheels 10" and wider may need tubs or chassis work 1.
  • Rear: notching the bed support beams may be necessary with lowered leaf springs 2. 15x8 with a 4" kit may not fill the fender as hoped 8. A drop can be less than advertised (a 3" spindle measured 1.75" on one truck, a 4" kit "looked less than 4") 8. Truck springs settle, so measure after a few hundred miles.
  • Load rating: the Cooper Cobra 275/60R15 is rated 2,149 lb per tire and the Radial T/A 295/50R15 2,061 lb at 35 psi; plenty for a half-ton, but the MT 28x10.00R15 is only 1,335 lb at 35 psi, so check that against rear axle weight (verify truck GVWR rating) 111529.
  • Drag radials (NT555RII, ET Street S/S): sticky but short-lived and wet-sensitive; not appropriate for a car a teenager will drive in rain 3435.
  • Speed ratings: Radial T/A and other RWL tires are S/T rated (112-118 mph); fine for 75 mph but not for a track.

How it touches other systems

  • Rear axle section: gear ratio choice drives tire diameter choice; the rear axle width (12-bolt narrow, 9" or 14-bolt wider options) sets the maximum tire width/backspacing. A wider axle or a 9" changes the BS figures above.
  • Transmission: TH400 vs 4L80E vs T56 swings cruise rpm by 25-50% at the same gear and tire. A 3.42 with 4L80E gives 2,160 rpm at 70; with TH400 2,870. Converter stall must also match the cam; a tall rear gear plus a loose converter hurts launch.
  • Brakes: wheel inner clearance depends on the caliper/rotor you pick. A big-brake kit can force 17"+ wheels; 1977 C10 front discs are standard on the half-ton (verify on the truck, owner reported drums all around). Western Chassis spindles with specific brake parts were mentioned in the drop-spindle clearance thread as changing rally-wheel clearance 10; not independently verified.
  • Suspension/drop: the drop level decides tire height and width; a 3/5 or deeper requires smaller tires or tub/notch work. Steering stops may need tuning with bigger rubber.
  • Speedometer / ECU / gauges: tire and gear change require speedo calibration (see above); if the truck is converted to EFI with a 4L80E, VSS calibration must also be correct 41.
  • Engine: with a 5,500-6,000 rpm powerband you want ~2,000-2,500 at highway cruise; over 3,000 rpm hurts noise and wear on a long commute. Cam choice (vacuum for power brakes) is unaffected by wheels.
  • Exhaust: a 3" dual system with lowered stance leaves less ground clearance; check exhaust routing before settling on a drop.

Check on the truck

  1. Count the lugs and measure bolt circle (should be 5x5) and hub bore (78.1 mm expected).
  2. Confirm front brakes: the 1977 half-ton should have front discs; owner said drums all around. Measure rotor/caliper or look behind the wheel.
  3. Identify the rear axle: 12-bolt (8.875") vs other; read the ID tag/axle ratio code (3.07/3.08 vs 3.42 etc.). Original ratio not confirmed for this truck.
  4. What drop is already planned or installed (spindles, springs, flip kit)?
  5. Is a 17" look acceptable, or is period 15" with white letters the priority? (affects fitment risk and tire supply).
  6. Which transmission are you leaning toward? It changes the gear pick: TH400 -> 3.42; 4L80E -> 3.42-3.73; T56 -> 3.73.
  7. Do you want RWL (period) lettering or modern black sidewall?
  8. Count TH400 speedo drive gear teeth for the driven-gear calculation.
  9. Max rear width: measure frame to inner fender and leaf spring to tire gap at planned ride height.

Formula, speedometer, and rpm tables

Formula: rpm = mph x (final drive ratio x top-gear ratio) x 336.13 / tire diameter (in), where 336.13 = 63,360 in/mile / (60 min/hr x pi). Tire revs per mile = 20,168 / diameter 38. Real rolling diameter under load is about 3% smaller than the spec-sheet diameter on the two tires that publish revs per mile (Nitto NT555 G2 275/50R17: 27.87 in spec vs 27.03 in at 746 rev/mi; BFGoodrich 275/60R15: 28.0 in vs 27.14 in at 743 rev/mi; section 91 - the earlier '1-2%' here was an assertion), so real rpm is about 3% higher than shown. Add 3% to every table below. Ratios used: TH400 1.00 in 3rd (1st 2.48, 2nd 1.48); 4L80E 0.75 overdrive (same 2.48/1.48/1.00 as TH400 for 1-3) 39; T56 Magnum 0.63 (XL/standard, 1:1 4th with 0.80 5th, 0.63 6th) or 0.50 (the 0.74/0.50 5th/6th variant, GM TUET11012) 40. The T56 stays out of overdrive territory; 0.50 is a very tall 6th, usable only with ~3.73-4.10.

Spec-sheet tire diameters seen: 255/60R15 = 27.1" 12; 275/60R15 = 28.0-28.1" 1416; 295/50R15 = 26.6" 15; 275/40R17 = 25.7" 35; 31x10.50R15 truck tire ~31". Calculated: 275/50R17 ~27.8", 245/50R17 ~26.7", 295/45R17 ~27.5".

Values rounded to the nearest 10 rpm. (Computed by script, 2026-10-12.)

TH400 (1.00) 3.08 3.42 3.55 3.73 4.10
60 2220 2460 2560 2690 2950
65 2400 2670 2770 2910 3200
70 2590 2870 2980 3130 3450
75 2770 3080 3200 3360 3690
4L80E (0.75) 3.08 3.42 3.55 3.73 4.10
60 1660 1850 1920 2020 2210
65 1800 2000 2080 2180 2400
70 1940 2160 2240 2350 2580
75 2080 2310 2400 2520 2770
T56 (0.63) 3.08 3.42 3.55 3.73 4.10
60 1400 1550 1610 1690 1860
65 1510 1680 1750 1830 2020
70 1630 1810 1880 1970 2170
75 1750 1940 2010 2120 2330
T56 (0.50 sixth: discontinued, reference only) 3.08 3.42 3.55 3.73 4.10
60 1110 1230 1280 1340 1480
65 1200 1330 1390 1460 1600
70 1290 1440 1490 1570 1720
75 1390 1540 1600 1680 1850

27" tire (255/60R15 front-size, 245/50R17 class)

TH400 3.08 3.42 3.55 3.73 4.10
60 2300 2550 2650 2790 3060
65 2490 2770 2870 3020 3320
70 2680 2980 3090 3250 3570
75 2880 3190 3310 3480 3830
4L80E (0.75) 3.08 3.42 3.55 3.73 4.10
60 1730 1920 1990 2090 2300
65 1870 2080 2150 2260 2490
70 2010 2240 2320 2440 2680
75 2160 2390 2490 2610 2870
T56 (0.63) 3.08 3.42 3.55 3.73 4.10
60 1450 1610 1670 1760 1930
65 1570 1740 1810 1900 2090
70 1690 1880 1950 2050 2250
75 1810 2010 2090 2190 2410
T56 (0.50 sixth: discontinued, reference only) 3.08 3.42 3.55 3.73 4.10
60 1150 1280 1330 1390 1530
65 1250 1380 1440 1510 1660
70 1340 1490 1550 1630 1790
75 1440 1600 1660 1740 1910

29" tire

TH400 3.08 3.42 3.55 3.73 4.10
60 2140 2380 2470 2590 2850
65 2320 2580 2670 2810 3090
70 2500 2770 2880 3030 3330
75 2680 2970 3090 3240 3560
4L80E (0.75) 3.08 3.42 3.55 3.73 4.10
60 1610 1780 1850 1950 2140
65 1740 1930 2010 2110 2320
70 1870 2080 2160 2270 2490
75 2010 2230 2310 2430 2670
T56 (0.63) 3.08 3.42 3.55 3.73 4.10
60 1350 1500 1560 1630 1800
65 1460 1620 1680 1770 1950
70 1570 1750 1810 1910 2100
75 1690 1870 1940 2040 2250
T56 (0.50 sixth: discontinued, reference only) 3.08 3.42 3.55 3.73 4.10
60 1070 1190 1230 1300 1430
65 1160 1290 1340 1410 1540
70 1250 1390 1440 1510 1660
75 1340 1490 1540 1620 1780

30" tire

TH400 3.08 3.42 3.55 3.73 4.10
60 2070 2300 2390 2510 2760
65 2240 2490 2590 2720 2990
70 2420 2680 2780 2930 3220
75 2590 2870 2980 3130 3450
4L80E (0.75) 3.08 3.42 3.55 3.73 4.10
60 1550 1720 1790 1880 2070
65 1680 1870 1940 2040 2240
70 1810 2010 2090 2190 2410
75 1940 2160 2240 2350 2580
T56 (0.63) 3.08 3.42 3.55 3.73 4.10
60 1300 1450 1500 1580 1740
65 1410 1570 1630 1710 1880
70 1520 1690 1750 1840 2030
75 1630 1810 1880 1970 2170
T56 (0.50 sixth: discontinued, reference only) 3.08 3.42 3.55 3.73 4.10
60 1040 1150 1190 1250 1380
65 1120 1250 1290 1360 1490
70 1210 1340 1390 1460 1610
75 1290 1440 1490 1570 1720

31" tire (31x10.50R15 truck-style)

TH400 3.08 3.42 3.55 3.73 4.10
60 2000 2220 2310 2430 2670
65 2170 2410 2500 2630 2890
70 2340 2600 2690 2830 3110
75 2500 2780 2890 3030 3330
4L80E (0.75) 3.08 3.42 3.55 3.73 4.10
60 1500 1670 1730 1820 2000
65 1630 1810 1880 1970 2170
70 1750 1950 2020 2120 2330
75 1880 2090 2170 2280 2500
T56 (0.63) 3.08 3.42 3.55 3.73 4.10
60 1260 1400 1460 1530 1680
65 1370 1520 1580 1660 1820
70 1470 1640 1700 1780 1960
75 1580 1750 1820 1910 2100
T56 (0.50 sixth: discontinued, reference only) 3.08 3.42 3.55 3.73 4.10
60 1000 1110 1150 1210 1330
65 1090 1210 1250 1310 1440
70 1170 1300 1350 1420 1560
75 1250 1390 1440 1520 1670

Reading the tables: a 31x10.50 on a stock-height truck with no drop is what the stock 8" rally owner reports "no rubbing" for 8, but 31" tires fight a drop. For a 28" tire at 70 mph: TH400 + 3.42 = 2,870 rpm; 4L80E + 3.42 = 2,160; 4L80E + 3.73 = 2,350; T56 0.63 + 3.73 = 1,970. A 4.10 with a TH400 is 3,450 rpm at 70 mph, which fails the "no spun-to-the-moon" requirement.

Speedometer recalibration

The stock speedometer is cable-driven off a plastic driven gear in the transmission tailshaft. Each tooth added to the driven gear lowers the reading about 2.5%, each removed raises it about 2.5% (CORRECTED from "~5%"); TH400 driven gears come in 34-45 teeth 38. Formula: driven teeth = (drive-gear teeth x axle ratio x tire revs/mi) / 1001, with revs/mi = 20,168 / diameter 38. Because the drive-gear tooth count on your TH400 has not been identified, I cannot give a final tooth count; count the drive gear and use the formula or run a GPS check with a known gear. For error: stock 27.5" tire vs 28" is +1.8% speedo-reads-slow; vs 26.6" is -3.3%; vs 30" +9.1%.

If you go 4L80E or T56, the speedometer path changes (electronic VSS). Options: Dakota Digital VSS generator with pass-through SEN-01-4160 plugs in between the speedo cable and speedo output to give the PCM a signal 41; the Dakota speedo calibrator corrects readings within 1 mph from 50-200% of original 42; the Dakota Digital VHX gauge set for 1973-87 pickups was seen at $945.99 sale (DD732R, Classic Industries; page 403, not re-verified) and the VFD3 six-gauge set for 73-87 C10 is $831.25 at AZ Pro Performance (fetched 2026-10-12; the earlier $795.95 was stale) 4344. Caution: one owner thread reports a tuner saying Dakota's GPS-based VSS did not clear check-engine codes on an LQ4/TH400 swap; the SEN-01-4160 pass-through generator is the mechanical-cable route and still needs the tuner to match the pulse 41. A 4L80E's PCM/TCM wants a specific pulse rate, so the tuner needs to know what the adapter outputs 41. For the 4L80E, the owner's tune must be re-flashed if tire or gear changes.

Gearset cost, for reference: Richmond Excel 836-12BT373 3.73 for GM "8.75" 12-bolt truck, $193.87 sale / $223.99 list (Jegs, snippet 2026-10-12; page 403), Motive 8.875" 12-bolt 3.73 and Yukon 12-bolt truck 3.73 listed at ~$387-$412 45. Note the "8.75" vs "8.875" labeling discrepancy in vendor listings: confirm by measuring the ring gear before ordering. See the rear-axle section for the axle decision.

Fact-check notes

Adversarial check, 2026-10-12. Fetched/checked about 30 URLs; 403 (bot-blocked, price not re-verifiable): summitracing, jegs (3), cjponyparts (3), carid, classicindustries, discounttire, 67-72chevytrucks. Dead: prod.cokertire.com (DNS) and the guessed www.cokertire.com 275/60R15 BFG page (404).

Verified and kept: 5x127 / 78.1 mm / 15x6 stock (threepiece); Cooper Cobra $194 and SKU, BFG 255/60R15 $225 SKU 6306500, BFG 295/50R15 $294 SKU 6308245 (Coker); Vision 57 15x8 -6 $105, PN 57-5873; tiresize diameters (743 rev/mi, 25.67"); 4L80E 2.48/1.48/1.00/0.75 and TH400 ratios; T56 Magnum 2.97 box with 0.80/0.63 or 0.74/0.50 overdrives; the rpm formula and all 140 table cells (recomputed, zero errors); the TH400 speedo formula (x/1001) and 34-45 tooth driven range.

Changed:

  • Nitto NT555 G2 275/50R17 price $222 -> $249 (Giga Tires), diameter 27.87" confirmed; added summer-tire caution for a KC teen driver.
  • Speedo: "5% per tooth" -> 2.5% per tooth; novaresource source removed as invalid for TH400.
  • VN515 17x9.5 +8 mm was called "far outboard"; it is ~5.5" BS (inboard) and likely too deep for the rear. Fixed, and the fronts-vs-4"-BS rule applied to the Scottsdale.
  • Dakota VFD3 $795.95 -> $831.25; Richmond 3.73 $223.99 is list, $193.87 sale; MT S/R 28x6.00R17 price filled ($370.69, 27.9").
  • Removed the "2012 backorder" argument against 15" tires; removed the claim that LCA grinding is acceptable (a broken arm was reported); added 3.08 as a TH400 gear option; corrected the 12-bolt/cost-saving misreading; fixed package totals (Good $1,200-$1,500, Better $1,750-$2,350); replaced dead/mismatched source links.
  • Marked unconfirmed: stock wheel offset, 1/2"-20 stud size, Torq Thrust II 15" and 17" prices, Cragar, US Mags Rambler, Billet Specialties.

Possible missing options (not priced): reproduction GM Rally wheels in 15x7 for the front, 16" and 18" wheel sizes as a middle path, aftermarket tubular lower control arms, and an all-season 275/50R17.

Sources 51

  1. threepiece.us (C10 fitment guide: 5x127, 78.1 mm, stock 15x6, wide-rear notes)
  2. gmsquarebody.com (3/4 drop wheel fitment: 15x8 4" BS front, 15x10 5" BS rear, notching beams)
  3. gmsquarebody.com (1979 C15 drop and backspacing thread)
  4. gmsquarebody.com (HELP WITH WHEEL AND TIRE SET UP; Dave777 etc.)
  5. 67-72chevytrucks.com (widest tire without tubs ~11.5")
  6. gmsquarebody.com (17x9, 275/60/17 owner report)
  7. gmsquarebody.com (second post of wheel/tire setup thread)
  8. gmsquarebody.com (clearance with 2.5" spindles and 15x8 rallies)
  9. gmsquarebody.com (Rear axles, what changed in 1977)
  10. gmsquarebody.com (15x8 wheel on 4/6 drop)
  11. cokertire.com (Cooper Cobra 275/60R15, $194)
  12. cokertire.com (Radial T/A 255/60R15, $225)
  13. (DEAD LINK REMOVED: prod.cokertire.com does not resolve and www.cokertire.com/p275-60r15-bf-goodrich-t-a-rwl.html returns 404; the $224 was only seen in a search snippet)
  14. tiresize.com (28" dia, 743 rev/mi)
  15. cokertire.com (Radial T/A 295/50R15, $294)
  16. tiresize.com (MT S/T 28.1" dia)
  17. mickeythompsontires.com (MT Sportsman S/R lineup)
  18. speedwaymotors.com (Smoothie $176.99, snippet)
  19. vividracing.com (Vision Rally 15x8, snippet price)
  20. threepiece.us (Vision 57 $105)
  21. cjponyparts.com (Torq Thrust II 15", snippet price)
  22. summitracing.com (Cragar S/S 15x8 $346.87, snippet)
  23. cjponyparts.com (US Mags Rambler $353)
  24. carid.com (VN515 17x9.5 $322)
  25. cjponyparts.com (Baja 17x9 4.53" BS)
  26. cjponyparts.com (US Mags Scottsdale 17x9)
  27. jegs.com (Billet Specialties Street Lite)
  28. nahrods.com (Weld Draglite $399, wrong bolt pattern)
  29. jegs.com (MT S/R 28x10 $389.09)
  30. discounttire.com (g-Force Comp-2 A/S Plus)
  31. tiresize.com (g-Force Comp-2 A/S specs, 255/40ZR17)
  32. performanceplustire.com (275/50R17 pricing, Nitto NT555 G2 $222)
  33. tires-easy.com (MT S/R 28x6.00R17)
  34. discountedwheelwarehouse.com (MT ET Street S/S prices)
  35. tiresize.com (NT555RII 25.67", 810 rev/mi)
  36. tiresize.com (Toyo Proxes 4 Plus)
  37. lacroixtuning.com (PS4S 285/35ZR19)
  38. TH400 driven-gear formula and 34-45 tooth range confirmed via search results (NCRS/chevellestuff-type pages); the novaresource.org page does NOT cover TH400 (it is a small/large gear chart, 7-18 teeth) so it is not a valid source for this claim.
  39. en.wikipedia.org (4L80E ratios)
  40. moderndriveline.com (T56 Magnum ratios, .74/.50 OD)
  41. gmsquarebody.com (Dakota SEN-01-4160 VSS generator recommendation; verified) and gmsquarebody.com (LQ4/TH400 thread where a tuner said Dakota GPS VSS did not work)
  42. gmsquarebody.com (Dakota Digital speed calibrator, GPS)
  43. classicindustries.com (Dakota VHX gauge set 73-87 pickup)
  44. azproperformance.com (Dakota VFD3 $831.25, fetched 2026-10-12)
  45. jegs.com (Richmond 12-bolt truck 3.73)
  46. forabodiesonly.com (2012 thread about 225/60R15; not current)
  47. gmsquarebody.com (275/60-15 with 2.5" spindles, LCA contact)
  48. gmsquarebody.com (20" vs 15" on drops; 245/60/15 + 275/60/15 recommended)
  49. gmsquarebody.com (dropped truck wheel threads index)
  50. giga-tires.com (Nitto NT555 G2 275/50R17 $249, 27.87", fetched 2026-10-12)
  51. jegs.com (Toyo Proxes 4 275/40R17 listing)