GT frame technology handbook V.03
GT HISTORY 3
GT TECHNOLOGIES 4
SuspensionPhilosophy
i-DriveExplained 4
AddressingPedalInducedBobbing 4
AddressingWheelTrajectory 5
AddressingFrameDesign 5
TripleTriangle 5
InternalTransmission 5
ForceOptimizedConstruction 6
FRAME TECHNOLOGIES 8
Integratedheadsetsystem 8
Internalheadsetsystem(semi-integrated) 8
Replacablederailleurhanger 9
Replacabledropout 9
Boxedchainstays 9
Forgedframecomponents 9
Buttedtubing 10
Hydroforming 10
Mechanicalforming 10
FRAME MATERIAL 11
Carbonfiber 11
6000&7000SeriesAluminum 11
Chrome-Moly&Hi-TensileSteel 11
FRAME CARE GUIDELINES 1 2
EPILOGUE 13
TABLE OF CONTENTS
Thefollowingisaguidetohighlightandexplainthedifferent
technologiesthatgointoaGTbicycleframe.Itexplainswhy
wedothethingswedoandhowtheriderwillbenefitfrom
them.Thereare3sections:
Section1talksaboutGTspecifictechnology.Theseare
featuresthatweredesigned,engineeredandinsome
cases,patentedbyGTBicyclesforourexclusiveuse.
Section2talksaboutframetechnologiesthatarecommon
totheindustryandexplainswhyGTengineershavechosen
tousethem.
Section3talksaboutdifferentframematerialsthatGTuses
intheirproductsandwhatbenefitscomefromeachofthem.
GTBicycleshasadesignphilosophycalledTechnological.
Thismeansthatanythingwedesignislogicalfroma
technicalstandpoint;everythingisthereforareason.
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GT has produced bicycles to be faster, stronger
and better than any other bicycle on the market.
With over 30 years of design, manufacturing
and racing heritage it’s no wonder that GT
Bicycles frame designs are on the forefront
of bicycle technology.
GT history
4
GT technologies
SUSPENSION PHILOSOPHY
i-Drive EXPLAINED
Pedalfeedbackisoneofthebiggestreasonssuspensionbikeshaveinefficientpedalingcharacteristics.
Pedalfeedbackiscausedbyanadditionalunwantedreactionaryforce that causes the pedals rotate backward during rearwheeltravel.Thisiscausedbytherearwheelgettingfurtherawayfromthefrontchainrings.Thechainneedsmoreslacktomakeup for thisdistance changeandpulls backon thefrontchainwheel.Thiscreatesareverserotationinthecrankset,inturndisruptingtheriderspedalcadenceandrequiringmoreenergyfromtheridertoovercome(SeeFig.A).
With i-Drivetechnology,we’veallowedthebottombrackettomoveseparatelyfromthefronttriangleandreartriangleinawaythatcounteractspedalfeedback.Duringthismovement,thedistancefromthepedaltotheseatdoesnotchange.Forthe most part, pedal feedback is eliminated and the riderdoesn’thavethatextrapedalforcetoovercome(SeeFig.B).
Somesuspensiondesignslockoutthesuspensionuntil theriderhitsabigenoughbumporrelyon“platformshocktech-nology”toincreasepedalefficiency.Inbothofthesecases,activesuspensionhasbeencompromisedtoincreasepedalingefficiency.Withi-Drivetechnologyyougetefficientpedalingandanactivesuspension100%ofthetime.
ADDRESSING PEDAL INDUCED BOBBING
Pedal induced bobbing is an event in which the force ofyour downwardpedal stroke causes the rear suspension tocompressresultinginenergyloss.Thisiscontrolledbyaddingback inasmallamountofpedal feedback,alsocalledanti-squat.Toomuchanti-squat(orpedalfeedback)willlockoutthesuspension;reducesuspensionactionandultimately,alossofpedalingefficiency.Toolittleanti-squatresultsinefficiencylossfrompedalinducedbobbing.
WhatwehaveachievedinaGTsuspensiondesignisanaturalbalancebetweenthedownwardbodymovementcompressingthesuspensionandasmallamountofanti-squatextendingthesuspension.Theresultisaneutral-feelingsystemthatremainsactiveoverthesmallbumpsyetdoesnot“bob”whenpedaling.
CO
MM
ON
LIN
KA
GE
GT
I-D
RIV
EFIG.A FIG.B
Section 1
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ADDRESSING WHEEL TRAJECTORY
Wheeltrajectoryorwheelpathisimportantbecauseitiscrucialthattherearaxlemoveinthesamedirectionasthebumpforce.Ifthewheelpathdoesnotlineupwiththedirectionofthebumpforce,theriderwilllosemomentumwitheachbumptheyhit.GTsuspensionbikesaredesignedwithasingle,highpivottogivethebikesanarcingwheelpathwhichmovesupandback.Thisallowsthesuspensiontoaccuratelyfollowthebumpforcefrombeginningtoendwithouttheriderlosinganymomentum.
ADDRESSING FRAME DESIGN
Framedesignsthatrelyonmultiplelinkstoattachthefrontandreartrianglesaresubjecttoframeflexandlongtermdurabilityissues.Eachadditionalpieceinalinkagedesignisanadditionalareathatissubjecttoflex.
AlthoughGTsuspensionframeswithi-Drivetechnologyhaveatotalof4pivots,thesuspensionworksasasinglepivot(cantilever)design.Byusingthistypeofframedesign,we’vebeenabletoconstructastiffrearendusingboxconstructionandanoversizepivot.Singlepivotframedesignsaresimple,costeffectiveandtroublefreemechanisms.
TRIPLE TRIANGLE
Bylengtheningtheseatstaystonotonlyattachtotheseattubebutalsoweld
directlytothesidesofthetoptube,GTengineershavedecreasedthesizeof
thefrontandreartrianglesandaddedathirdtriangle.Thisreductioninsize
yieldsamuchstrongerandrigidstructure.
Notonlywillthestrongerframelastlongerthroughyearsofbombingdownyour
favorite,rockyfireroadbuttheincreasedrigiditywillimproveresponsivenessin
pedalingandsteering.TorsionalflexisgreatlyreducedonaTripleTriangleframe
design.
Besides,whatotherbrandcanberecognizedevenifthedecalshavebeenremoved?GT
INTERNAL TRANSMISSION
AnInternalTransmissionframedesignisonethatdoesnotuseaconventional,
externallymountedderailleurtochangegears.Thereareanumberofbenefits
tothistypeofframedesign.
Thefirstbenefitofaninternaltransmissionisthatthetransmissionmassis
housedinthecenteroftheframe.Thisallowsthedesignertoreducetheun-
sprungweightoftherearwheel.Un-sprungweightisthemassonthebikethat
isdirectlyconnectedtothewheelsandswingarm,andnotisolatedthroughthe
suspension.Bydecreasingthismass,itallowsthesuspensiontorespond
quickertochangesintheterrain.
Thesecondbenefitis,nowthattheconventionalrearderailleurandcogsethavebeenremovedfromtherearwheel,thehubflanges
canbemovedoutwardandcenteredonthehub.This,asyouknow,createsastrongerandstifferwheel.
Thethirdbenefitis,bymovingthegearchangingmechanismtothecenterofthebike,youeliminatethepossibilityof
damagingthemostvulnerablecomponentonthebike,therearderailleur.Theshiftingmechanismisnowprotectedwithinthe
frameandhaslessofachanceofbeingdamagedevenduringaseverecrash.
ThemostimportantbenefitofanInternalTransmissionframedesignisthatitwillopenthedoorforfutureframeandsuspension
designs.Bygettingawayfromastandardshiftingmechanism,GTengineerscanimprovenotonlyintheareaslistedabovebutthey
canalsoimproveonthebicyclesperformanceincludingpedalingefficiencyandwheeltrajectories.
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ForceOptimizedConstructionisGTBicycle’sproprietarycompositemanufacturingprocessinwhichtheconstructionofeachframeis
optimizedtogivetheframeexceptionalstrengthandstiffnessintheareasthatneeditmostbutatthesametimeremovingmaterial
intheareasthatneeditleast.Thereare4importantfactorsthatmakeupForceOptimizedConstruction:
Optimized Tube Construction-Forcesenterabicycleframefromboththerider
andtheterrain.Theseforces,push,pull,twist,stretchandcompressevery
tubeontheframeineverydirection.ByusingFiniteElementAnalysis(FEA),
eachtubeonaGTcarbonframeisdesignedwiththeseforcesinmindandthey
aregivenacrosssection(ashape)tocounteractthoseforces.
Monocoque (One Piece) Frame Construction-GTframedesignbeginswithchoosingaconstructionmethodthathasthehighest-
strength-to-weightratioavailable.Lugconstructionaddsweightandcanbeweakerduetothepossibilityofvoidsandpockets
betweenjoints.Thejointscanalsoactasstressriserswhichweakenandeventuallyfail.Monocoqueframeconstructiongives
youastrong,onepieceframewiththelowestpossibilityofconstructionimperfections.
Proprietary Kiting and Sequence Process -Justaswoodandmetalhavea
graindirection,carbonhasafiberdirection.Eachlayerofcarbonfiberused
inourframesisplacedinacertainspotandcertainorientationdependingon
thedirectionofforceonthatpartoftheframe.Thisgivestheriderthemost
compliantandcomfortableridepossible.
TypicalFEAmodelforstudyingpedalingforcesontheframe.
FORCE OPTIMIZED CONSTRUCTION
Apioneerincarbonfiberbicycleconstruction,GTBicycleswasthefirstcompanyintheUnitedStatestoproducethermoplasticcarbon
mountainbikeframesinsignificantquantities.In1996GTBicyclesgloballymarketedtheUSAmadeCarbonfiberLTS.TheSuperBike
II(SB-2),producedincollaborationwithUSACyclingforthe1996AtlantaOlympicGamesisstillthebenchmarkforcarbonconstruc-
tionandaerodynamicdesign.GTBicycles,throughitsextensiveresearchanddevelopmentofcarbonconstructiontechniques,has
numerouspatentsdatingbacktotheearly90’s.
Withametalbicycleframe,thecompositionofthemetalandthemechanicalcharacteristicscannotbeeasilychangedoverthelength
ofthetube.Thiscanonlybedonebyformingorlayeringthemetalatthecostofadditionalweight.Withcarbon,changingtheplace-
ment,thedirectionandthemakeupofeachlayerofmaterialispossible,inturncreatingalighterandstrongerstructure.Thecross
section(theshape)ofeachtubecanalsobedesignedforoptimumstrengthandstiffness.
Twistingforcesputonframetubesduringpedaling.
OUR STORY
OUR REASON
OUR TECHNOLOGY
Proprietary Blend of Fiber Types-Therearemanydifferenttypesoffibersthat
canbeusedtomakeupcarbonfiberframes.GTusesaproprietaryblendof
TR30andTR50fibersindifferentareasoftheframetoincreasestiffnessor
strengthintheplaceswhereitmatters.Again,GTengineersuseFEAtostudy
andcalculateareas inneedofstrengthorsupport togiveyouthestiffest,
strongestandlightestweightframepossible.
This4par tcombinationofbaseconstruction,shapedesignandmaterial/fiberapplicationiswhatForce Optimized Constructionisallabout.
GTengineershaveoptimizedourcarbonframestogivetherideracomfortableridethatisstiffenoughforquickaccelerationsand
responsivesteering,strongenoughforserioususeandyetsuperlightforthatcompetitiveedge.
ThisisForceOptimizedConstruction…
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OUR RIDE
FRAME technologies
INTEGRATED HEADSET SYSTEM
An integrated headset is one that is built in to the frame.
Headsetcupsareeliminatedbymachining thebearingcups
intotheheadtube.
Inadditiontocreatinganeasierassemblytomaintainanda
lighterweight system, thestackheight ismuch lowerwhich
allowsforalongerheadtubetoincreaseframestrength.
INTERNAL HEADSET SYSTEM (SEMI-INTERGRATED)
Aninternalheadsetisaheadsetinwhichthebearingcupsare
recessedwithinthediameteroftheheadtube.
This headset systemallows for amore stylish fork/head tube/
stemjunction.Thedecreasedstackheightinconjunctionwith
aheadtubelengthincreaseallowsforastrongerframe.
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Section 2
REPLACEABLE DROPOUT
ByincludingreplaceabledropoutsonsomeGTmodels,theriderisnotonlyableto
easilyremoveandreplaceadamagedderailleurhangereasilybutcanalsoreconfig-
uretheirframefordifferenttypesofaxlesizesandrearendconnections.
REPLACEABLE DERAILLEUR HANGER
Themostvulnerablepartonabicycleistherearderailleur.Thismechanismhangs
offoftherightsideofthebikeandcaneasilybecaughtonrocks,branchesand
passingcarsifyou’renotlooking.Onceyou’vedonethis,you’veprobablydamaged
thederailleurandquitepossiblystripped,brokenorbentthehangerthatit isat-
tachedto.
Byincludingareplaceablederailleurhangersystemonmostofourmodels,GThas
eliminatedthepossibilityofframereplacementsduetobrokenorstrippedoutde-
railleurhangers.Simplyremovetherearwheelandderailleur,unboltthedamaged
hangerandreplace.
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BOXED CHAIN STAYS
BMXracingisverydemandingwhenitcomestotheamountofflexwhilepedaling
andcornering.Byincreasingthesizeandcrosssectiononthechainstays,GTen-
gineers are able to increase the strength and stiffness of the rear end of the
frame.
Boxed chain stays are a feature in which the stays are made from forming two
halvesofeachstayandweldingthemtogetherasone.Withitssizeandshape,this
monocoquedesigndecreasesflexinawaythatstandardchainstaytubescannot.
FORGED FRAME COMPONENTS
Forgingisamanufacturingprocesswheremetalispressed,poundedorsqueezed
undergreatpressureintohighstrengthpartsknownasforgings.
Theprocessisnormally(butnotalways)performedhotbypreheatingthemetalto
adesiredtemperaturebeforeitisworked.Forgingyieldsagrainstructureoriented
tothepartshape,resultinginoptimumstrength,ductilityandresistancetoimpact
and fatigue. The forging process can create parts that are stronger than those
manufacturedbyanyothermetalworkingprocess.
HYDRO FORMING
Hydroformingisatubeformingprocesswhichusespressurizedliquidto
giveshapetoanotherwiseroundtube.Agiventubeisfilledwithpressur-
izedliquidwhichexpandsthetubeoutwardandfillsamoldofthedesired
shape.
ThisprocessgivesGTengineerstheabilitytocreatecomplextubeshapes.
Hydroformingisusedtoreshapeatubeinordertoincreasestrengthinthe
framedesignandalsotoadduniqueshapesandstyletotubeprofiles.
BUTTED TUBING
A butted tube is a tube in which the wall thickness of the tube changes from one end of the tube to the other. The number
ofwallthicknesschangesalongthelengthofthetubewilldetermineifit’saSingleButted,DoubleButted,TripleButted,etc.,tube.A
buttedtubewillbelighterthanaplaingaugetubeofthesameouterdiameterandhavesimilarstrengthcharacteristics.
Byusingbuttedtubes,GTcanhavetheappropriatewallthicknessforweldingoneachendbuthaveathinnerwallthicknessinthe
middlewhereitisunnecessary;thebenefitbeingalighterweighttube.
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STANDARD BUTTED TUBE DOUBLE BUTTED TUBE
MECHANICAL FORMNG
Mechanicalformingisatubeformingprocessinwhichatubeispressed,
poundedorsqueezedintothedesiredshape.Thisprocessisacosteffec-
tivewaytoproduceuniquetubeshapesfordesignswithrelativelysimple
crosssections.
CARBON FIBER
Onematerialthatisbecomingmorepopularinframeengineer-
ingiscarbonfiber.Thismaterialisproducedbylayeringsheetsof
carbonfiberclothintoamoldintheshapeofthefinalproduct.
Thealignmentandweaveof theclothfibers is important for
thestrengthoftheresultingmaterial.
By using carbon fiber GT designers can create a light-
weight,structurallysoundpar tinvir tuallyanyshape.See
ForceOptimizedContstruction.
6000 & 7000 SERIES ALUMINUM
Probablythemostcommonframematerialchoiceinallofthe
bicycleindustryandadefinitefavoritewithGTengineers.Both
6061-T6and7000seriesaluminumalloysarethemostversa-
tile and widely used aircraft-grade, heat treatable aluminum
alloys.Aluminumalloyshaveaverygoodstrengthtoweight
ratioalongwithimpressivevibrationdampingcharacteristics.
Aluminumframescanbemadelightandstiff,makingsurethe
powercomingfromyourlegstranslatestopowerinmovingthe
bike.
CHROME-MOLY & HI-TENSILE STEEL
GTutilizesavarietyofchrome-molyandhi-tensilesteeltubesets,
rangingfrom100%chrome-molyframestoamixofchrome-moly
andhi-tensilesteeltubesforastrong,yetcost-effectiveframe.
Incrediblylightanddurablebicycleframescanbemadefrom
steel tubing. Manycyclistsprefersteeloverothermaterials
duetothecomfortlevelandridefeelthisframematerialcan
provide.Don’tforget…SteelisReal.
FRAME materials
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Section 3
12
FRAME CARE GUIDELINES
Itiscriticaltoconstantlyinspectyourcompletebike,includingframeandcomponentsfordamageandnormalwearbeforeeachandeveryride.Theridingconditionsandactivitiesthatbikesareusedforhasincreasedthewearonbicyclesandforthisreason,GTBicyclesrequiresthatyouinspectyourframefrequently.
•Visuallyinspectyourframebeforeeachride •Lookforcracksand/orimperfectionsinthematerial •Beawareofanyabnormalitiesinridequalityofyourframe •Abnormalframeflexorshiftingandbrakingperformance •Alwayslistenforabnormalnoisesduringyourride •Soundslikecreaking,tickingandpopping
Ifyoudiscoveranyabnormalitiesinanyoftheabovecategories,orifyourbikehasbeencrashedorputthruabnormalstress,pleaseseeanauthorizeddealerforinspection.
Examplesofdamagingactivities: •Ridercrash •Abruptstopimpacts •Runintogaragewhileincarrack
Ifyouhavecrashedorstressedyourframeinawaythatyou’renotsureifitisdamaged,itisalwayssafesttotakeyourbiketoanauthorizeddealerforacompleteinspection.
CARBON FRAMES Althoughcarbonmaterialhasbeenproventobeextremelystrongandcanbeconstructedintobicycleframesthathaveexceptionallyhighfatiguelife,carbonitselfcanstillbeeasilydamagedwhencrashedorputthruanabnormallyhighstressincident.Adamagedframemaynotshowanyvisiblesignsorthesesignsmaybedifficulttoseewithoutmeticulousinspectionbecausethedamagemaybeunderneaththesurface.
Warning:Damagedcarbonfibercanfailsuddenlywithminimalnoticeandcauseseriousinjuryordeath.
ALUMINUM AND STEEL FRAMES Aluminumandsteelframescantakedirectimpactsverywellandarenotlikelytofailcatastrophicallybutitisstillveryimportanttoinspectyourframebeforeeachride.
OUR POLICY •Warranty–PacificCycleoffersalimitedwarrantyonallofitsframesagainstmanufacturingdefectandmaterials.Anywarranty claimsmustbeplacedthroughavalidPacificCycledealerandmustincludeproofofpurchase.Warrantyisonlyvalidtothe originalowner.Pleaseseethebicyclesownermanualoryournearestdealerformoredetails.
•CrashReplacementProgram-Becauseenoughpeopledolaydowntheircarbonbikesinavarietyofways(racing,drivinginto garageswiththebikeonthecar,others…),thatwouldnotbecoveredunderthewarrantypolicy,PacificCycleoffersacrash replacementprogram.WithavalidproofofpurchaseandaPacificCyclelicenseddealer,wecanhelpreplaceyourbroken framewithanewframeorcompletebikeatareducedcost.Pleaseseeyourdealerformoredetails.
GT: technological
A philosophy of design and engineering that
is guided by sensible rational thought rather
than the latest marketing fad. Technological
design is a system that deals not only with
the end product but with all aspects of the
product life cycle from conception to eventual
obsolescence. Throughout design, development
and manufacturing, GT uses its 30 years of
experience to build bicycles that illustrate a
complete holistic consideration of the product
and its eventual owner. With an increasingly
crowded marketplace the philosophy of Tech-
nological design and engineering marks a clear
path towards products that make sense.
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