Bike models › Mountain
GT Aggressor Sport 27.5 (2019): specs, upgrades and what fits
GT's widely sold entry 27.5-inch hardtail with a 6061 aluminum Triple Triangle frame, 75 mm SR Suntour M3030 coil fork, 21 speeds on a SunRace 14-34 7-speed cluster and 160 mm mechanical disc brakes; it sold new for $450. The 2017-2020 Aggressor Sport and Comp are close; geometry here is from the same-year Aggressor Expert frame. Best for: Beginner trail riding and dirt paths.
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My take, from the specs
A fair used pick for beginner trail riding and dirt paths. The 160mm mechanical discs and 27.5in wheels are a good base, but the 75mm coil fork is basic and the 7-speed freewheel limits gearing upgrades. When buying, check the rotors and pads, spin the freewheel for rough spots, and look at the fork stanchions for scratches or rust.
Sizes: M: 5′6″–5′11″ (168–180 cm)
Stock specs
| Type | Mountain |
|---|---|
| Year | 2019 |
| Price when new | $450 |
| Sold at | GT dealers and sporting-goods stores (discontinued; common used) |
| Wheels | 650b × 57 mm tires |
| Gears | 3×7 · 42/34/24T · 14–34T |
| Brakes | Tektro Mechanical disc, 160 mm |
| Fork | SR Suntour M3030, coil, 75 mm |
| Rear derailleur | Shimano Tourney (model not listed) |
| Shifter | Shimano EF41 EZ Fire, 3x7 (integrated with brake levers) |
| Crank | All Terra Triple (square taper est.) |
| Bottom bracket | Generic Square-taper BB (type not listed) |
| Axles | Quick release |
| Seatpost | 27.2 mm |
| Sizes | XS, S, M, L, XL |
| Stock colors | Satin Black w/ Chartreuse & Slime Lime |
Upgrade limits
How far each part can go on this frame, and why. Measure your own bike to confirm the estimated ones.
| Part | Limit | Why |
|---|---|---|
| Widest tire (current wheel size) | 57 mm | Unknown until measured. Your 19 mm internal rims suit roughly 28–49 mm tires. |
| Tubeless | Not recommended | Tubeless needs a rim built to seal (bead hook + channel) and tubeless-ready tires. |
| Valve type | Unknown | Decides which tubes and pump heads fit. Presta tubes fit Schrader rims with a grommet; not the other way. |
| Replacement wheels | Quick release · 100/135 mm · 6-bolt disc | Any wheel matching axle type, spacing and brake mount fits. Rear also needs the right freehub. |
| Biggest rear cog | 34T (now 34T) | Set by the rear derailleur (Shimano Tourney (model not listed)): max low sprocket 34T, total capacity ?T. A hanger extender can add a few teeth (hit-or-miss on non-Shadow derailleurs); a new derailleur is the reliable way to get more. |
| Front gears | 3x (42/34/24T) · needs 38T capacity | A 3x drivetrain needs a front derailleur and left shifter. Your rear derailleur must take up (biggest − smallest ring) + (biggest − smallest cog) = 38T. Going 1x drops the front derailleur: simpler and quieter, with a slightly smaller range. |
| Chainring size | Unknown (now 42T) | Estimated from similar frames. Measure the chainring-to-chainstay gap to confirm. Check whether your ring is bolted or riveted. Spindle length (? mm) sets chainline; a big change in ring size may need a different BB spindle. |
| Gear count upgrades | Freewheel (≤8) | Threaded freewheel: up to 7/8-speed freewheels only. More speeds needs a new rear wheel with a freehub. |
| Cranks & bottom bracket | Square taper · 68 mm shell · ? mm spindle | Any square-taper crankset fits with the right spindle length. Upgrading to Hollowtech II needs a new BB (same threaded shell). |
| Pedal thread | 9/16" × 20 | Every adult multi-piece crank uses 9/16". One-piece kids/cruiser cranks use 1/2". |
| Brake pads | Shape unknown | Disc pads only fit calipers with the matching shape. |
| Rotor size | 160/160 mm now · front up to 180 mm | 6-bolt rotors. Going bigger needs a caliper adapter: adapter type depends on the mount (post, IS or flat). Most steel forks allow 180 mm; check the fork if a max rotor is printed on it. |
| Caliper upgrades | Long-pull (MTB) mechanical | Your levers pull a lot of cable, so upgrade calipers must be long-pull (MTB) versions: TRP Spyke, Juin Tech M1, Avid BB7 MTB. Road calipers (TRP Spyre, BB7 Road) would feel mushy. |
| Stems & bars | 1-1/8 steerer · 31.8 mm bar clamp | Any stem for a 1-1/8 steerer with a 31.8 mm clamp fits. You can cut a bar narrower but not wider. |
| Drop-bar conversion | Possible with mods | Needs road brake/shift levers (microSHIFT R8 makes 8-speed ones that pull Shimano 8-speed cable correctly), a drop bar, tape, and road-pull brake calipers because road levers pull less cable. Usually $250+. |
| Seatposts | 27.2 mm | 27.2 mm is the most common size: suspension posts and external-cable dropper posts are easy to find. Internal droppers need internal routing the frame does not have. |
| Racks, fenders, bottles | No rack · No fender · 0 bottle | Threaded eyelets at the dropouts and seat stays take a rack and fenders. Fork leg mounts take cargo cages. |
| Max load (rider + cargo) | Unknown | Wheels are usually the weak point under heavy loads. Stay under this with rider plus luggage. |
Best upgrades by area
Three options that fit the GT Aggressor Sport 27.5 (2019) as-is in each area, from budget to best. ★ marks the one most worth the money. How we pick. Typical US prices, checked October 2026. They change often: check the price at the store.
Upgrades that fit as-is
Brakes
- TRP Spyke mechanical disc calipers, long pull (pair), $$$$. Disc-brake part ↔ your disc brakes · Long-pull caliper ↔ your flat-bar (long-pull) levers
- Juin Tech M1 cable-hydraulic calipers, long pull (pair), $$$. Disc-brake part ↔ your disc brakes · Long-pull caliper ↔ your flat-bar (long-pull) levers
- Jagwire Mountain Pro brake cable kit (Kevlar KEB-SL housing), $$. Made for flat bars ↔ your flat bar
- Shimano Tourney BR-TX805 mechanical disc calipers, long pull, post mount (pair), $$. Disc-brake part ↔ your disc brakes · Long-pull caliper ↔ your flat-bar (long-pull) levers
- Shimano SM-RT56 160 mm 6-bolt rotor (1 rotor), $. Disc-brake part ↔ your disc brakes · 160 mm rotor ↔ your 160 mm front rotor
- Galfer Wave 160 mm 6-bolt rotor, 1.8 mm (1 rotor), $$. Disc-brake part ↔ your disc brakes · 160 mm rotor ↔ your 160 mm front rotor
- Shimano SM-RT86 Ice-Tech 160 mm 6-bolt rotor (1 rotor), $$. Disc-brake part ↔ your disc brakes · 160 mm rotor ↔ your 160 mm front rotor
Comfort
- Ergon GP1 ergonomic grips, $$. Made for flat bars ↔ your flat bar
- Budget ergonomic lock-on grips, $. Made for flat bars ↔ your flat bar
- 35° rise 60 mm stem, $. 1-1/8" steerer matches · Get the 31.8 mm clamp version for your bar
- Suspension seatpost 27.2 mm (budget), $$. 27.2 mm post ↔ your 27.2 mm seat tube
- Redshift ShockStop suspension seatpost 27.2, $$$$. 27.2 mm post ↔ your 27.2 mm seat tube
- WTB Volt saddle, $$. Medium-width shape that suits most riders. Measure sit bones if comfort is the goal.
- Race Face Chester riser bar 31.8 x 740 mm, 25 mm rise, $$. Made for flat bars ↔ your flat bar
- Brooks C17 All Weather saddle, $$$. Vulcanized rubber top that flexes like a hammock, and this All Weather version is fully waterproof. No break-in like leather. Firm, not padded: made for long…
- Bikeroo oversized comfort saddle, $. Wide, soft and sprung for short upright rides on cruisers and hybrids. On rides over an hour wide padding can chafe; a firmer saddle that fits your sit bones…
- Ergon GA3 lock-on grips, $$. Made for flat bars ↔ your flat bar
- Selle Royal Respiro Moderate saddle, $$$. Made for a 60° "moderate" back angle (most flat-bar hybrids). Very upright cruisers suit the wider Respiro Relaxed. Standard round steel rails.
- Fizik Terra Argo X5 saddle (150 or 160 mm), $$$. Pick 150 mm for narrower sit bones, 160 mm for wider. Round 7 mm alloy rails fit every standard clamp.
- Ergon SR Allroad Core Comp saddle (men's or women's), $$$. Comes in S/M and M/L widths (measure your sit bones) and men's and women's shapes. Round CroMo rails; 120 kg rider limit.
- Ergon GP5 ergonomic grips with built-in bar ends (S or L), $$$. Made for flat bars ↔ your flat bar
- Ritchey Comp 2-Bolt alloy seatpost 27.2 mm, $$. 27.2 mm post ↔ your 27.2 mm seat tube
- Thomson Elite seatpost 27.2 x 330 mm, $$$. 27.2 mm post ↔ your 27.2 mm seat tube
- Ergon CF Allroad Pro Carbon flex seatpost 27.2 mm, $$$$. 27.2 mm post ↔ your 27.2 mm seat tube
- Cirrus Kinekt 2.1 Aluminum suspension seatpost 27.2 mm (LR or XR spring), $$$$. 27.2 mm post ↔ your 27.2 mm seat tube
- Race Face Ride riser bar 31.8 x 710 mm, 25 mm rise, $$. Made for flat bars ↔ your flat bar
- SQlab 30X alloy riser bar 31.8 x 780 mm, 12° backsweep, $$$. Made for flat bars ↔ your flat bar
Control
- External dropper post 27.2 mm, 100 mm drop + remote, $$$. 27.2 mm post ↔ your 27.2 mm seat tube
- Race Face Chester composite flat pedals, $$. Big platform with pins. Feet stay put on bumps and in rain. Install with an 8 mm hex key (no wrench flats).
- ROCKBROS aluminum flat pedals, $$. Budget metal platform with pins. A big step up from stock plastic.
- Shimano PD-M520 SPD clipless pedals (cleats included), $$. Nearly indestructible two-sided SPD pedals. You also need SPD (2-bolt) shoes, about $60–100 more. Set the release tension low and practice unclipping before…
- Crankbrothers Stamp 2 aluminum flat pedals (small or large), $$$. Sized by shoe: small for US men's 5–10, large for 10 and up. Grease the threads and tighten to about 35 Nm.
- OneUp Components Aluminum flat pedals, $$$. Bearings and bushings can be serviced with a cheap kit instead of replacing the pedal. Grease the threads and tighten to about 35 Nm.
- Shimano PD-EH500 dual-sided SPD / flat pedals (cleats included), $$$. Comes with SM-SH56 multi-release cleats, which are easier to get out of in a panic. You still need 2-bolt SPD shoes to clip in.
- Shimano Deore XT PD-M8100 SPD pedals (cleats included), $$$. Cup-and-cone bearings are fully serviceable and last for years. Shoes with a 2-bolt SPD cleat sold separately.
- KS eTen-R external dropper 27.2 mm, 100 mm drop + KS Southpaw remote, $$$. 27.2 mm post ↔ your 27.2 mm seat tube
- PNW Components Pine external dropper 27.2 mm (90 or 110 mm) + PNW Loam lever, $$$$. 27.2 mm post ↔ your 27.2 mm seat tube
Utility
- USB rechargeable front + rear light set, $$. Daytime flashing lights cut collisions. Required by law at night.
- Pletscher adjustable kickstand, $$. Handy for errands. Check it clears the rotor and chainstay.
- Lisen clamp-style handlebar phone mount, $. Cheap and tool-free for maps on paved rides. On rough gravel or trails a locking mount (Quad Lock or Peak Design, about $45–70 plus a case) is much safer.
- Topeak TopLoader top tube bag (0.75 L), $$. Keeps snacks, keys and a multi-tool within reach. Straps on, with a rain cover. Check your knees do not rub it when you stand up.
- Knog Oi Classic bell, $. Slim ring bell that wraps the bar. Large fits 23.8–31.8 mm bars; Small fits 22.2 mm kids and BMX bars. Required by law in some places.
- Wald 137 front basket, $$. Made for flat bars ↔ your flat bar
- Planet Bike Beamer 200 + Blinky Squared USB light set, $$. USB rechargeable, tool-free mounts. Use flash mode in daylight. Rear light is 30 lumens: good for town, modest on fast roads.
- Cygolite Metro Plus 800 + Hotshot Pro 150 USB light set, $$$. Nine headlight modes including a daytime flash. Aim the beam slightly down so you do not blind oncoming riders.
- Trek (Bontrager) Ion Pro RT + Flare RT light set, $$$. Daytime-running flash modes on both lights. ANT+ lets a Garmin or Wahoo show battery and switch them. Full power runs about 1.5 hours; medium lasts much longer.
Drivetrain
- KMC X8 8-speed chain with Missing Link, $. 6/7/8-speed chain ↔ your 7-speed drivetrain
- KMC Z7 6/7-speed chain (116 links), $. 6/7-speed chain ↔ your 7-speed drivetrain
- KMC Z8.3 6/7/8-speed chain (116 links), $. 6/7/8-speed chain ↔ your 7-speed drivetrain
- KMC X8 EPT 6/7/8-speed anti-rust chain with Missing Link, $$. 6/7/8-speed chain ↔ your 7-speed drivetrain
Tires
- WTB Trail Boss Comp 27.5x2.25 wire (pair), $$. 57 mm tire ↔ your ~57 mm clearance
- WTB Byway 650b x 47 TCS (pair), $$$. 47 mm tire ↔ your ~57 mm clearance
- WTB Horizon 650b x 47 TCS (pair), $$$. 47 mm tire ↔ your ~57 mm clearance
- Teravail Washburn 650b x 47 Light & Supple (pair), $$$. 47 mm tire ↔ your ~57 mm clearance
Gearing
- Shimano Tourney MF-TZ500-7 7-speed freewheel 14–28, $. 7-speed ↔ your 7-speed drivetrain · 28T biggest cog ↔ your derailleur's 34T max
- Shimano Tourney MF-TZ500-7 7-speed freewheel 14–34 (MegaRange), $. 7-speed ↔ your 7-speed drivetrain · 34T biggest cog ↔ your derailleur's 34T max
- SunRace 7-speed freewheel 13-28 (MFM3S), $. 7-speed ↔ your 7-speed drivetrain · 28T biggest cog ↔ your derailleur's 34T max
- SunRace MF-M300 7-speed freewheel 14-34, $$. 7-speed ↔ your 7-speed drivetrain · 34T biggest cog ↔ your derailleur's 34T max
- Shimano Acera RD-M3020-8 SGS 7/8-speed rear derailleur (40T max), $$. 7-speed ↔ your 7-speed drivetrain · Shimano cable pull ↔ your shifter
Fits with small changes (17)
- Shimano BR-MT200 hydraulic brake set (pair, levers included), $$$. Replaces your brake levers. Your shifter stays.
- Shimano BR-MT420 4-piston hydraulic brakes + BL-MT401 levers (pair), $$$. Replaces your brake levers. Your shifter stays.
- Wald 8095 swept touring handlebar 25.4 mm, $$. Clamp is 25.4 mm; your bike's is 31.8 mm. Needs a shim or a matching stem/bar.
- Sunlite Northroad Touring alloy handlebar 25.4 mm, 3.5" rise, $$. Clamp is 25.4 mm; your bike's is 31.8 mm. Needs a shim or a matching stem/bar.
- Nitto B352AA Albatross handlebar 25.4 mm, 55 cm, $$$. Clamp is 25.4 mm; your bike's is 31.8 mm. Needs a shim or a matching stem/bar.
- Stan's NoTubes tire sealant 16 oz, $. In tubes: needs tubes with removable valve cores (Presta or Schrader to match your rims).
- Orange Seal Endurance tubeless sealant 16 oz, $. In tubes: needs tubes with removable valve cores (Presta or Schrader to match your rims).
- SILCA Ultimate Tubeless Sealant 16 oz, $. In tubes: needs tubes with removable valve cores (Presta or Schrader to match your rims).
- Shimano Deore BL-M6100 + BR-M6100 2-piston hydraulic brake set (pair, levers included), $$$$. Replaces your brake levers. Your shifter stays.
- Shimano Deore BL-M6100 + BR-M6120 4-piston hydraulic brake set (pair, levers included), $$$$. Replaces your brake levers. Your shifter stays.
- Shimano SLX BL-M7100 + BR-M7120 4-piston hydraulic brake set (pair, levers included), $$$$. Replaces your brake levers. Your shifter stays.
- Shimano SM-RT56 180 mm 6-bolt rotor (1 rotor), $. Your front rotor is 160 mm: a 180 mm rotor fits with a post +20 mm caliper adapter (check your fork's max rotor size).
- Galfer Wave 180 mm 6-bolt rotor, 1.8 mm (1 rotor), $$. Your front rotor is 160 mm: a 180 mm rotor fits with a post +20 mm caliper adapter (check your fork's max rotor size).
- Shimano SM-RT86 Ice-Tech 180 mm 6-bolt rotor (1 rotor), $$. Your front rotor is 160 mm: a 180 mm rotor fits with a post +20 mm caliper adapter (check your fork's max rotor size).
- Kalloy Uno SP-602 alloy seatpost 25.4 x 350 mm, $. Your seat tube takes 27.2 mm: needs a 25.4→27.2 shim.
- Thomson Elite seatpost 25.4 x 330 mm, $$$. Your seat tube takes 27.2 mm: needs a 25.4→27.2 shim.
- Sunlite adjustable suspension seatpost 25.4 mm, $$. Your seat tube takes 27.2 mm: needs a 25.4→27.2 shim.
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Buying one used? Fair prices
Worked out from the price new ($450), age and condition, not live market data. If it needs tires, a chain or brakes, take off what fixing them would cost.
| Condition | Today (2019 model) |
|---|---|
| Like new | $135–$180 |
| Good | $120–$155 |
| Fair | $95–$130 |
| Needs work | $75–$100 |
See what these really sold for on eBay · Other used bike prices
Geometry (size M)
| Stack | 589° |
|---|---|
| Reach | 431 mm |
| Head angle | 69.5° |
| Seat angle | 72.7° |
| Chainstay | 435° |
| BB drop | 45 mm |
| Wheelbase | 1112 mm |
| Head tube | 110 mm |
| Seat tube | 430 mm |
| Standover | 762° |
Compare with
- Huffy Stone Mountain 26 · compare frames side by side
- Schwinn High Timber ALX 29 · compare frames side by side
- Trek Marlin 5 Gen 3 · compare frames side by side
- Specialized Rockhopper Sport · compare frames side by side
Sources: Bicycle Blue Book: 2019 GT Aggressor Sport (full spec, MSRP $450, colour) · 99 Bikes (AU): 2019 GT Aggressor Sport 27.5 (M3030 fork, Tektro mechanical disc, WTB SX19 rims) · Bike Insights: 2019 GT Aggressor Expert 27.5 geometry (same-year frame; used as estimate)