Mambo ya kuzingatia unaponunua tairi za gari

[Chacha Kisiri]

Ushauri wako mzur but Kuchek upepo kila baada ya wiki its too much unless ubora wa tire zako uwe hafifu mno i suggest may b monthly. Also rotation inategemea KM ulizotembea wataalam washauri ni KM ngapi ufanye rotation.

Mkuu, swala la how long kupima upepo na kufanya rotation za tairi are judgement issues and depend on circumstances. Mfano kama gari unalolitumia kila siku kwenda kazini na kurudi nalo nyumbani then unafanya mizunguko mingine ya kawaida, its most preferably kuwa unapima upepo kila wiki. Hii inatokana na tabia ya tubeless tire kuwa zinajiongeza upepo na saa nyingine zinajipunguza zinapokuwa barabarani. Mfani Mimi huwa napima kila wiki na mara nyingi naweka 38 PSI tairi za nyuma na 35 PSI tairi za mbele. Sasa huwa nikienda kupima tena in the following week naweza kuta tairi moja ya nyuma ina 42 PSI na nyingine 40 PSI. Za mbele nazo naweza kuta moja imeshuka to 30 PSI na nyingine may be imejiongeza to 37 PSI.

Sasa kama nikisema niwe napima kila mwezi maana yake by the time naenda kupima naweza kuta tairi moja ya nyuma ina 50 PSI na nyingine may be 43 PSI. Za mbele hivyo may be moja inaweza kuwa 38 PSI na nyingine 33 PSI (It depends). Maana yake ni nini? Maana yake kwamba nitakuwa natembea na gari kwa muda mrefu bila ya kuwa proper tire pressure. Hii inaweza ikapelekea baadhi ya tairi kuisha mapema kuliko zingine, gari kukosa balance kwa kuwa itakuwa imelala upande wenye upepo mdogo na hivyo kuumiza suspension system za upande mmoja zaidi. Kibaya zaidi baadhi ya tairi zilizojaa kupita kiasi zinaweza kupasuka na kupelekea kupata hasara zaidi.

Kwa hiyo kutokana na madhara yanayoweza tokea kwa kukaa muda mrefu bila kupima upepo na kwa kuwa kupima upepo ni gharama ndogo sana inashauriwa kwa gari linalotumika kila siku for domestic routes basi ni vyema ulipime upepo kila wiki. Kwa upande mwingine, kwa gari ambalo hulitumii kila siku, mfano gari unaliendesha mara moja kwa wiki then unalipaki, kupima upepo baada ya mwezi mmoja si vibaya.

Aidha, kwa gari ambayo inaenda safari ndefu mfano unatoka Dar kwenda Mwanza (KM 1200)unashauriwa upime upepo angalau mara moja unapokuwa umefika katikati ya safari kuepuka tairi kukupasukia njiani. So kwa mazingira ya safari ndefu huna sababu ya kupima baada ya wiki. Ndiyo maana hata mabasi ya safari ndefu ambayo yanapataga ajali za kupasuka matairi saa nyingine unakuta tairi ni mpya kabisa may be imenunuliwa last week na nembo zake inaonyesha ita-expire three years to come lakini inapasuka within a week! Kwa nini? Ni kwa sababu ya uzembe wa kutopima upepo mara kwa mara. Matokeo yake tairi inajijaza upepo na kupitiliza kiwanga cha juu na matokeo yake ni kupasuka kwa tairi na maafa kwa abiria na mali zao.

Kuhusu tire rotation
Kama ilivyo kupima upepo, tire rotation is also a judgment issue and depend on the circumstances. Kwa gari ambazo ni for domestic purposes. Ni vyema ufanye rotation kila unapofanya service (Yaani either after KM 3000 or after Six month - whichever is earlier). Kwa nini? Tairi za mbele zinapokaa kwa muda mrefu bila kufanyiwa rotation zinatabia ya kuisha kwanza kutokana na kuwa involved sana na friction during cornering na pia kutokana na kwamba zinabeba uzito wa engine na hazijazwi upepo mwingi kuliko za nyuma. So ni vyema na zenyewe zikapata unafuu within a short period kukaa nyuma na zile za nyuma ziende mbele ili zote ziishe kwa pamoja.

Kwa upande wa gari ambayo inatembelewa may be kwa wiki mara moja tena kwa route fupi fupi then unai-park. Kufanya rotation even after six month sio vibaya.

 

[Chacha Kisiri]

Mkuu nakubaliana na ww....but m I ryt nikisema kwa kuna wakt inabid uisaidie gar kubadili gear....unapokuwa umekanyaga accelerator continuously mlio wa gar/engine huenda ukiongezeka huku gauge ya temp ikipanda...but gauge ya temp ikifk level 3 kuna ma2....ukiendelea ku'accelerate gear huchange wakt mlio wa engine umekuwa mkubwa sn na temp imefkia level 4 or above....alternatively temp gauge ikifk lv 3 then ukarelease accelerator pedal na kupress again slowly gar hubadili gear ikiwa kweny mlio wa kawaida na temp gauge huaproach haizid lev 3 na kurud chn gear ikishachange....hyo theory unaionaje mtaalam?

Mkuu, jaribu ku-type vizuri. Nimeshindwa kupata mtiriro wa unachokizungumza. Ikiwezekana avoid vifupisho na zingatia symbol za "full stop" na "mikato" kwenye sentensi ili tuelewane vizuri.

 

[chayowa]

Mkuu, swala la how long kupima upepo na kufanya rotation za tairi are judgement issues and depend on circumstances. Mfano kama gari unalolitumia kila siku kwenda kazini na kurudi nalo nyumbani then unafanya mizunguko mingine ya kawaida, its most preferably kuwa unapima upepo kila wiki. Hii inatokana na tabia ya tubeless tire kuwa zinajiongeza upepo na saa nyingine zinajipunguza zinapokuwa barabarani. Mfani Mimi huwa napima kila wiki na mara nyingi naweka 38 PSI tairi za nyuma na 35 PSI tairi za mbele. Sasa huwa nikienda kupima tena in the following week naweza kuta tairi moja ya nyuma ina 42 PSI na nyingine 40 PSI. Za mbele nazo naweza kuta moja imeshuka to 30 PSI na nyingine may be imejiongeza to 37 PSI.

Sasa kama nikisema niwe napima kila mwezi maana yake by the time naenda kupima naweza kuta tairi moja ya nyuma ina 50 PSI na nyingine may be 43 PSI. Za mbele hivyo may be moja inaweza kuwa 38 PSI na nyingine 33 PSI (It depends). Maana yake ni nini? Maana yake kwamba nitakuwa natembea na gari kwa muda mrefu bila ya kuwa proper tire pressure. Hii inaweza ikapelekea baadhi ya tairi kuisha mapema kuliko zingine, gari kukosa balance kwa kuwa itakuwa imelala upande wenye upepo mdogo na hivyo kuumiza suspension system za upande mmoja zaidi. Kibaya zaidi baadhi ya tairi zilizojaa kupita kiasi zinaweza kupasuka na kupelekea kupata hasara zaidi.

Kwa hiyo kutokana na madhara yanayoweza tokea kwa kukaa muda mrefu bila kupima upepo na kwa kuwa kupima upepo ni gharama ndogo sana inashauriwa kwa gari linalotumika kila siku for domestic routes basi ni vyema ulipime upepo kila wiki. Kwa upande mwingine, kwa gari ambalo hulitumii kila siku, mfano gari unaliendesha mara moja kwa wiki then unalipaki, kupima upepo baada ya mwezi mmoja si vibaya.

Aidha, kwa gari ambayo inaenda safari ndefu mfano unatoka Dar kwenda Mwanza (KM 1200)unashauriwa upime upepo angalau mara moja unapokuwa umefika katikati ya safari kuepuka tairi kukupasukia njiani. So kwa mazingira ya safari ndefu huna sababu ya kupima baada ya wiki. Ndiyo maana hata mabasi ya safari ndefu ambayo yanapataga ajali za kupasuka matairi saa nyingine unakuta tairi ni mpya kabisa may be imenunuliwa last week na nembo zake inaonyesha ita-expire three years to come lakini inapasuka within a week! Kwa nini? Ni kwa sababu ya uzembe wa kutopima upepo mara kwa mara. Matokeo yake tairi inajijaza upepo na kupitiliza kiwanga cha juu na matokeo yake ni kupasuka kwa tairi na maafa kwa abiria na mali zao.

Kuhusu tire rotation
Kama ilivyo kupima upepo, tire rotation is also a judgment issue and depend on the circumstances. Kwa gari ambazo ni for domestic purposes. Ni vyema ufanye rotation kila unapofanya service (Yaani either after KM 3000 or after Six month - whichever is earlier). Kwa nini? Tairi za mbele zinapokaa kwa muda mrefu bila kufanyiwa rotation zinatabia ya kuisha kwanza kutokana na kuwa involved sana na friction during cornering na pia kutokana na kwamba zinabeba uzito wa engine na hazijazwi upepo mwingi kuliko za nyuma. So ni vyema na zenyewe zikapata unafuu within a short period kukaa nyuma na zile za nyuma ziende mbele ili zote ziishe kwa pamoja.

Kwa upande wa gari ambayo inatembelewa may be kwa wiki mara moja tena kwa route fupi fupi then unai-park. Kufanya rotation even after six month sio vibaya.

Yeah..... Umeeleza vizuri mkuu.... Point taken..... Cheeers

 

[TCleverly]

Mkuu, jaribu ku-type vizuri. Nimeshindwa kupata mtiriro wa unachokizungumza. Ikiwezekana avoid vifupisho na zingatia symbol za "full stop" na "mikato" kwenye sentensi ili tuelewane vizuri.

hili swali ni kwako na GOODRICH pia....je nikinunua matairi mapya mawili,niyaweke nyuma au mbele[maana yangu gari itakuwa na set moja mpya moja ya zamani]?

mimi binafsi huwa nawaambia mafundi waniwekee matairi mapya mawili nyuma ya zamani waache mbele,ninaposema ya zamani sio vipara,ushauri huu nilipewa na wataalam wa matairi wa kwik fit.

 

[Johnsecond]

Utakuwa mzito tu !
Anamaanisha P ni kwa matumizi ya abiria au binafsi.

hahahah wewe ndio mzito sasa kwa taarifa yako.

 

[MZALENDOWAKWELIKWELI]

Bila kusahau kilometers baada ya kuanza kulitumia, hii inafuta miaka ya kuishi kwake ikiwa dukani tu, tairi nyingi hazizidi 7000kms

Sijaelewa....unamaanisha baada ya 7, 000km (yaani baada ya service 2) tair haifi tena?

 

[Gamba la Chuma]

Mkuu, jaribu ku-type vizuri. Nimeshindwa kupata mtiriro wa unachokizungumza. Ikiwezekana avoid vifupisho na zingatia symbol za "full stop" na "mikato" kwenye sentensi ili tuelewane vizuri.

Pamoja Mkuu.
Na wazungu wakifanya hivi sijui kama tutaambulia kitu

 

[Gamba la Chuma]

i just ignored bcoz its irrelevant......sio kila swali mtu analouliza hajui jibu lake.....mimi huwa napenda kuchallenge watu hata kama jibu ninalo......maswali yote niliyouliza nina majibu yake....

Hapo umekuwa kama Zitto kabisaaaa !

 

[Gamba la Chuma]

Sasa TCleverly tujulishe jibu kama unaweza !

 

[MZALENDOWAKWELIKWELI]

Mileage sahihi za kufanya service kisayansi ni Km ngp especially ukitumia oil quality kama BP Oil? Coz inadaiwa 3,000km ni myth but haina scientific grounds....

 

[Goodrich]

hili swali ni kwako na GOODRICH pia....je nikinunua matairi mapya mawili,niyaweke nyuma au mbele[maana yangu gari itakuwa na set moja mpya moja ya zamani]?

mimi binafsi huwa nawaambia mafundi waniwekee matairi mapya mawili nyuma ya zamani waache mbele,ninaposema ya zamani sio vipara,ushauri huu nilipewa na wataalam wa matairi wa kwik fit.

Walikwambia hivyo kwa sababu gari yako ni rear wheel drive na ushauri huo ni sahihi.

 

[Rolandi]

Tunashauriwa kufanya service after every 3,000km. Sasa na foleni zetu hizi unatembea 10km kwa saa nzima, bado tusubiri tu km 3,000. Mi si mtaalam wa mambo haya ila nafikiri mzunguko wa engine ndio unadetermine mda wa service. Au gari ikisimama oil haizunguki?
Wataalam tufafanulieni tafadhali

 

[Goodrich]

Tunashauriwa kufanya service after every 3,000km. Sasa na foleni zetu hizi unatembea 10km kwa saa nzima, bado tusubiri tu km 3,000. Mi si mtaalam wa mambo haya ila nafikiri mzunguko wa engine ndio unadetermine mda wa service. Au gari ikisimama oil haizunguki?
Wataalam tufafanulieni tafadhali

Umbali wa kufanya service ni estimate au umekadiriwa tu.
Kwa sababu gari ikiwa mpya hata utembee km 5,000 ukimwaga oil utaona sio nyeusi na bado ina viscosity nzuri.
Lakini gari chakavu ukiweka oil ukatembea hata km 600 tu ukiimwaga utaona ni nyeusi imeungua na haifai.
Pia gari inayoendeshwa sehemu za baridi km Iringa inatunza ubora wa oil kuliko inayoendeshwa kwenye joto kama Dar.
Na pia service sio engine pekee, ni kila kitu kinapaswa kuangaliwa.
Hivyo,
Kuna mambo mengi ambayo mwisho wa siku km 3,000 ni mkadirio tu.

 

[Jerrymsigwa]

Umbali wa kufanya service ni estimate au umekadiriwa tu.
Kwa sababu gari ikiwa mpya hata utembee km 5,000 ukimwaga oil utaona sio nyeusi na bado ina viscosity nzuri.
Lakini gari chakavu ukiweka oil ukatembea hata km 600 tu ukiimwaga utaona ni nyeusi imeungua na haifai.
Pia gari inayoendeshwa sehemu za baridi km Iringa inatunza ubora wa oil kuliko inayoendeshwa kwenye joto kama Dar.
Na pia service sio engine pekee, ni kila kitu kinapaswa kuangaliwa.
Hivyo,
Kuna mambo mengi ambayo mwisho wa siku km 3,000 ni mkadirio tu.

Hivi hizi oil na vipuri hutofautiana nchi na nchi? Yani kwa Aussie wanafanya service baada ya kilometa 10,000 na gari zinatembea poa hadi kilometa laki6

 

[Gamba la Chuma]

Mkuu, swala la how long kupima upepo na kufanya rotation za tairi are judgement issues and depend on circumstances. Mfano kama gari unalolitumia kila siku kwenda kazini na kurudi nalo nyumbani then unafanya mizunguko mingine ya kawaida, its most preferably kuwa unapima upepo kila wiki. Hii inatokana na tabia ya tubeless tire kuwa zinajiongeza upepo na saa nyingine zinajipunguza zinapokuwa barabarani. Mfani Mimi huwa napima kila wiki na mara nyingi naweka 38 PSI tairi za nyuma na 35 PSI tairi za mbele. Sasa huwa nikienda kupima tena in the following week naweza kuta tairi moja ya nyuma ina 42 PSI na nyingine 40 PSI. Za mbele nazo naweza kuta moja imeshuka to 30 PSI na nyingine may be imejiongeza to 37 PSI.

Sasa kama nikisema niwe napima kila mwezi maana yake by the time naenda kupima naweza kuta tairi moja ya nyuma ina 50 PSI na nyingine may be 43 PSI. Za mbele hivyo may be moja inaweza kuwa 38 PSI na nyingine 33 PSI (It depends). Maana yake ni nini? Maana yake kwamba nitakuwa natembea na gari kwa muda mrefu bila ya kuwa proper tire pressure. Hii inaweza ikapelekea baadhi ya tairi kuisha mapema kuliko zingine, gari kukosa balance kwa kuwa itakuwa imelala upande wenye upepo mdogo na hivyo kuumiza suspension system za upande mmoja zaidi. Kibaya zaidi baadhi ya tairi zilizojaa kupita kiasi zinaweza kupasuka na kupelekea kupata hasara zaidi.

Kwa hiyo kutokana na madhara yanayoweza tokea kwa kukaa muda mrefu bila kupima upepo na kwa kuwa kupima upepo ni gharama ndogo sana inashauriwa kwa gari linalotumika kila siku for domestic routes basi ni vyema ulipime upepo kila wiki. Kwa upande mwingine, kwa gari ambalo hulitumii kila siku, mfano gari unaliendesha mara moja kwa wiki then unalipaki, kupima upepo baada ya mwezi mmoja si vibaya.

Aidha, kwa gari ambayo inaenda safari ndefu mfano unatoka Dar kwenda Mwanza (KM 1200)unashauriwa upime upepo angalau mara moja unapokuwa umefika katikati ya safari kuepuka tairi kukupasukia njiani. So kwa mazingira ya safari ndefu huna sababu ya kupima baada ya wiki. Ndiyo maana hata mabasi ya safari ndefu ambayo yanapataga ajali za kupasuka matairi saa nyingine unakuta tairi ni mpya kabisa may be imenunuliwa last week na nembo zake inaonyesha ita-expire three years to come lakini inapasuka within a week! Kwa nini? Ni kwa sababu ya uzembe wa kutopima upepo mara kwa mara. Matokeo yake tairi inajijaza upepo na kupitiliza kiwanga cha juu na matokeo yake ni kupasuka kwa tairi na maafa kwa abiria na mali zao.

Kuhusu tire rotation
Kama ilivyo kupima upepo, tire rotation is also a judgment issue and depend on the circumstances. Kwa gari ambazo ni for domestic purposes. Ni vyema ufanye rotation kila unapofanya service (Yaani either after KM 3000 or after Six month - whichever is earlier). Kwa nini? Tairi za mbele zinapokaa kwa muda mrefu bila kufanyiwa rotation zinatabia ya kuisha kwanza kutokana na kuwa involved sana na friction during cornering na pia kutokana na kwamba zinabeba uzito wa engine na hazijazwi upepo mwingi kuliko za nyuma. So ni vyema na zenyewe zikapata unafuu within a short period kukaa nyuma na zile za nyuma ziende mbele ili zote ziishe kwa pamoja.

Kwa upande wa gari ambayo inatembelewa may be kwa wiki mara moja tena kwa route fupi fupi then unai-park. Kufanya rotation even after six month sio vibaya.

Good explanation.
Thanks !

 

[bysange]

Hii thread imenisaidia sana vitu vingi nimevifuatilia na sasa kuna utofauti mkubwa sana.jf oyeeeeee

 

[Richard Mlangi]

Hii thread imenisaidia sana vitu vingi nimevifuatilia na sasa kuna utofauti mkubwa sana.jf oyeeeeee

Even me !
Nilipangua matairi ya gari yangu ili ya nyuma yalingane na ya mbele yalingane.
Sasa shwaaari

 

[amu]

Jamani juzi nlikuwa natafuta 2tyres za pickup namba 225/75/R15 nkapata duka moja wanauza 220,000 kwa moja mpaka 190,000 sasa kwingine anauza 400,000 kwa moja nikiri yote sijayaona maana nlikuwa napiga simu.Sa tofauti mbona kubwa embu mnisaidie au ndo mchina yupo hapo?

 

[TCleverly]

Walikwambia hivyo kwa sababu gari yako ni rear wheel drive na ushauri huo ni sahihi.

who told u my car is rear wheel drive??nilikuwa na front wheel....kwa maelezo yao haijalishi ni front au rear,new tires must be fixed at the rear,partly worn,front...here is the reason

Most vehicles are equipped with the same size tire at every wheel position. Ideally all of these tires should also be of the same type and design, have the same tread depth and be inflated to the pressures specified by the vehicle placard or owner's manual. This combination best retains the handling balance engineered into the vehicle by its manufacturer.
However due to a front-wheel drive vehicle's front tires' responsibility for transmitting acceleration, steering and most of the braking forces, it's normal for them to wear faster than rear tires. Therefore if the tires aren't rotated on a regular basis, tires will typically wear out in pairs rather than in sets. And if the tires aren't rotated at all, it's likely that the rear tires will still have about 1/2 of their original tread depth remaining when the front tires are completely worn out.

Intuition suggests that since the front tires wore out first and because there is still about half of the tread remaining on the rear tires, the new tires should be installed on the front axle. This will provide more wet and wintry traction; and by the time the front tires have worn out for the second time, the rear tires will be worn out, too. However in this case, intuition isn't right...and following it can be downright dangerous.

When tires are replaced in pairs in situations like these, the new tires should always be installed on the rear axle and the partially worn tires moved to the front. New tires on the rear axle help the driver more easily maintain control on wet roads since deeper treaded tires are better at resisting hydroplaning.

Hydroplaning occurs when the tire cannot process enough water through its tread design to maintain effective contact with the road. In moderate to heavy rain, water can pool up in road ruts, depressions and pockets adjacent to pavement expansion joints. At higher speeds, the standing water often found in these pools challenges a tire's ability to resist hydroplaning.
Exactly when hydroplaning occurs is the result of a combination of elements including water depth, vehicle weight and speed, as well as tire size, air pressure, tread design and tread depth. A lightweight vehicle with wide, worn, underinflated tires in a heavy downpour will hydroplane at lower speeds than a heavyweight vehicle equipped with new, narrow, properly inflated tires in drizzling rain.
If the front tires have significantly less tread depth than the rear tires, the front tires will begin to hydroplane and lose traction on wet roads before the rear tires. While this will cause the vehicle to understeer (the vehicle wants to continue driving straight ahead), understeer is relatively easy to control because releasing the gas pedal will slow the vehicle and help the driver maintain control.

However, if the front tires have significantly more tread depth than the rear tires, the rear tires will begin to hydroplane and lose traction on wet roads before the fronts. This will cause the vehicle to oversteer (the vehicle will want to spin). Oversteer is far more difficult to control and in addition to the initial distress felt when the rear of the car starts sliding, quickly releasing the gas pedal in an attempt to slow down may actually make it more difficult for the driver to regain control, possibly causing a complete spinout.

Experience
Members of Tire Rack team had the chance to experience this phenomenon at Michelin's Laurens Proving Grounds. Participants were allowed to drive around a large radius, wet curve in vehicles fitted with tires of different tread depths -- one vehicle with new tires on the rear and half-worn tires on the front and the other with the new tires in the front and half-worn tires on the rear.
It didn't take long for this hands-on experience to confirm that the "proving grounds" name for the facility was correct. The ability to sense and control predictable understeer with the new tires on the rear and the helplessness in trying to control the surprising oversteer with the new tires on the front was emphatically proven.
And even though our drivers had the advantage of knowing we were going to be challenged to maintain car control, spinouts became common during our laps in the car with the new tires on the front and the worn tires on the rear. Michelin advises us that almost every driver spins out at least once when participating in this demonstration!
Experiencing this phenomenon in the safe, controlled conditions of Michelin's Laurens Proving Grounds rather than in traffic on an Interstate ramp in a rainstorm is definitely preferred!
Recommendations
Tires should be serviced periodically following the rotation patterns provided in the vehicle's owner's manual or as established by the industry to help enhance wear quality and equalize front-to-rear and side-to-side wear rates. The minor differences in tread depth between tires that might be encountered immediately after periodic tire rotations at 5,000-7,500 mile intervals won't upset the vehicle's hydroplaning balance and should not preclude rotating tires. For that matter, any differences in wear rates actually indicate that tire rotations should be done more frequently. Ideally tires should be replaced in complete sets. However when tires are replaced in pairs, the new pair of tires (assuming the vehicle is equipped with the same size tires all of the way around) should always be installed on the rear axle and the existing partially worn tires moved to the front axle.

While insufficient tire rotation intervals and/or out-of-adjustment wheel alignment angles often caused the differences in front-to-rear and side-to-side tire wear rates in the first place, the need to keep deeper treaded tires on the rear axle to resist oversteer conditions caused by wet road hydroplaning is important. Unfortunately this precludes the future possibility of ever rotating tires.
Once a pair of tires has been installed, the only way to escape being forced to drive on mismatched tires continually is to install a complete set of new tires (especially on front-wheel drive vehicles).

 

[Goodrich]

who told u my car is rear wheel drive??nilikuwa na front wheel....kwa maelezo yao haijalishi ni front au rear,new tires must be fixed at the rear,partly worn,front...here is the reason

Most vehicles are equipped with the same size tire at every wheel position. Ideally all of these tires should also be of the same type and design, have the same tread depth and be inflated to the pressures specified by the vehicle placard or owner's manual. This combination best retains the handling balance engineered into the vehicle by its manufacturer.
However due to a front-wheel drive vehicle’s front tires' responsibility for transmitting acceleration, steering and most of the braking forces, it's normal for them to wear faster than rear tires. Therefore if the tires aren't rotated on a regular basis, tires will typically wear out in pairs rather than in sets. And if the tires aren't rotated at all, it's likely that the rear tires will still have about 1/2 of their original tread depth remaining when the front tires are completely worn out.

Intuition suggests that since the front tires wore out first and because there is still about half of the tread remaining on the rear tires, the new tires should be installed on the front axle. This will provide more wet and wintry traction; and by the time the front tires have worn out for the second time, the rear tires will be worn out, too. However in this case, intuition isn't right...and following it can be downright dangerous.

When tires are replaced in pairs in situations like these, the new tires should always be installed on the rear axle and the partially worn tires moved to the front. New tires on the rear axle help the driver more easily maintain control on wet roads since deeper treaded tires are better at resisting hydroplaning.

Hydroplaning occurs when the tire cannot process enough water through its tread design to maintain effective contact with the road. In moderate to heavy rain, water can pool up in road ruts, depressions and pockets adjacent to pavement expansion joints. At higher speeds, the standing water often found in these pools challenges a tire's ability to resist hydroplaning.
Exactly when hydroplaning occurs is the result of a combination of elements including water depth, vehicle weight and speed, as well as tire size, air pressure, tread design and tread depth. A lightweight vehicle with wide, worn, underinflated tires in a heavy downpour will hydroplane at lower speeds than a heavyweight vehicle equipped with new, narrow, properly inflated tires in drizzling rain.
If the front tires have significantly less tread depth than the rear tires, the front tires will begin to hydroplane and lose traction on wet roads before the rear tires. While this will cause the vehicle to understeer (the vehicle wants to continue driving straight ahead), understeer is relatively easy to control because releasing the gas pedal will slow the vehicle and help the driver maintain control.

However, if the front tires have significantly more tread depth than the rear tires, the rear tires will begin to hydroplane and lose traction on wet roads before the fronts. This will cause the vehicle to oversteer (the vehicle will want to spin). Oversteer is far more difficult to control and in addition to the initial distress felt when the rear of the car starts sliding, quickly releasing the gas pedal in an attempt to slow down may actually make it more difficult for the driver to regain control, possibly causing a complete spinout.

Experience
Members of Tire Rack team had the chance to experience this phenomenon at Michelin's Laurens Proving Grounds. Participants were allowed to drive around a large radius, wet curve in vehicles fitted with tires of different tread depths -- one vehicle with new tires on the rear and half-worn tires on the front and the other with the new tires in the front and half-worn tires on the rear.
It didn't take long for this hands-on experience to confirm that the "proving grounds" name for the facility was correct. The ability to sense and control predictable understeer with the new tires on the rear and the helplessness in trying to control the surprising oversteer with the new tires on the front was emphatically proven.
And even though our drivers had the advantage of knowing we were going to be challenged to maintain car control, spinouts became common during our laps in the car with the new tires on the front and the worn tires on the rear. Michelin advises us that almost every driver spins out at least once when participating in this demonstration!
Experiencing this phenomenon in the safe, controlled conditions of Michelin's Laurens Proving Grounds rather than in traffic on an Interstate ramp in a rainstorm is definitely preferred!
Recommendations
Tires should be serviced periodically following the rotation patterns provided in the vehicle's owner's manual or as established by the industry to help enhance wear quality and equalize front-to-rear and side-to-side wear rates. The minor differences in tread depth between tires that might be encountered immediately after periodic tire rotations at 5,000-7,500 mile intervals won’t upset the vehicle's hydroplaning balance and should not preclude rotating tires. For that matter, any differences in wear rates actually indicate that tire rotations should be done more frequently. Ideally tires should be replaced in complete sets. However when tires are replaced in pairs, the new pair of tires (assuming the vehicle is equipped with the same size tires all of the way around) should always be installed on the rear axle and the existing partially worn tires moved to the front axle.

While insufficient tire rotation intervals and/or out-of-adjustment wheel alignment angles often caused the differences in front-to-rear and side-to-side tire wear rates in the first place, the need to keep deeper treaded tires on the rear axle to resist oversteer conditions caused by wet road hydroplaning is important. Unfortunately this precludes the future possibility of ever rotating tires.
Once a pair of tires has been installed, the only way to escape being forced to drive on mismatched tires continually is to install a complete set of new tires (especially on front-wheel drive vehicles).

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