FWD 1/ 1.5/ 2 way questions...

maxo

maxo

New member
Salut les mecs... les filles aussi!

Je magasine les lsd en ce moment et bien que je comprenne bien les différences au niveau technique entre les 3 types de lsd, j'ai de la misère à comprendre comment ces 3 types affectent de différentes façon le comportement du véhicule. Pourquoi je voudrais un 1.5 vs un 1 way.

Quel est l'avantage d'avoir un diff qui lock off throttle quand j'effectue mon turn in? Si ça lock, ça pousse non? En ce moment avec mon diff OEM, (1 way), au turn in, aussitôt que je termine le freinage, je gaz toujours très légèrement pour stabiliser le transfert de poids jusqu'à je trouve la grip et que je puis recommencer à gazer plus franchement plus ou moins à l'Apex... Quest-ce qui sera différent avec un 1.5?
 
D'après ce que je sais, je pense que tu as raison pour un FWD: 1.5 = plus de stabilité au freinage, voiture qui pardonne plus. 1 = turn-in plus agressif. À moins que ta voiture ne soit nerveuse (surtout à haute vitesse), je ne vois pas pourquoi tu irais avec un 1.5, encore moins un 2-way.

J'ai cherché vite vite pour voir si je n'étais pas dans le champ, ça semble se confirmer même si c'est pas une source "officielle": http://wikicars.org/en/Limited_slip_differential

If there is no additional coupling on over run, the LSD is 1 way. This is a safer LSD, as soon as the driver lifts the throttle, the LSD unlocks and behaves somewhat like a conventional open diff. This is also the best for FWD cars, as it allows the car to turn in on throttle release, instead of ploughing forward.
Click to expand...

Évidemment, pour une propulsion, c'est différent. Disclaimer: je peux me tromper.
 
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The main advantage of a diff that locks-up off-throttle is it helps prevent inside front lock-up during trail braking which could be beneficial on a car without ABS. Setup dependant, ymmv, yadi-yadda-yadda...

2-way locks up the same on/off throttle. 1.5 way locks up less off throttle. 1.5 way is what is typically used in FWD setups...

BTW, some years ago formula1 teams experimented with connecting the front wheels together via a differential to improve trail braking and found significant gains (track dependant). This was later considered as equivalent to ABS and banned. Apples and oranges of course to our applications but just an interesting info tidbit for you.
 
jsi said:
The main advantage of a diff that locks-up off-throttle is it helps prevent inside front lock-up during trail braking which could be beneficial on a car without ABS. Setup dependant, ymmv, yadi-yadda-yadda...

2-way locks up the same on/off throttle. 1.5 way locks up less off throttle. 1.5 way is what is typically used in FWD setups...

BTW, some years ago formula1 teams experimented with connecting the front wheels together via a differential to improve trail braking and found significant gains (track dependant). This was later considered as equivalent to ABS and banned. Apples and oranges of course to our applications but just an interesting info tidbit for you.
Click to expand...

Ok mais quand tu tournes en freinant et que le diff lock, comme les 2 roues sont supposées tourner à la même vitesse, la roue extérieur va forcément tourner plus vite que celle intérieur (plus de distance à parcourir)... Donc il y a soit un roue qui tire l'autre ou une qui pousse l'autre non? C'est pour ça que je comprends difficilement comment je ne vais pas avoir de sous virage en entrée de courbe...?!? 1 way, tu lift et ça devrait pivoter... 1.5/2way ça lock, donc ça devrait pousser? non?
 
Unless your a drifter, stay away from 2 Way.

Sometimes depending on setup, 1.5 Way can be a bit aggressive for a FWD Car.

1. Purchase Diff
2. Install
3. Wait until April
4. Enjoy. haha.
 
maxo said:
Ok mais quand tu tournes en freinant et que le diff lock, comme les 2 roues sont supposées tourner à la même vitesse, la roue extérieur va forcément tourner plus vite que celle intérieur (plus de distance à parcourir)... Donc il y a soit un roue qui tire l'autre ou une qui pousse l'autre non? C'est pour ça que je comprends difficilement comment je ne vais pas avoir de sous virage en entrée de courbe...?!? 1 way, tu lift et ça devrait pivoter... 1.5/2way ça lock, donc ça devrait pousser? non?
Click to expand...

Le 1.5 "lock" beacoup moins quand tu lift...

Bref, easy button: Achete toi un Kaaz.
 
Sebdavid said:
D'après ce que je sais, je pense que tu as raison pour un FWD: 1.5 = plus de stabilité au freinage, voiture qui pardonne plus. 1 = turn-in plus agressif. À moins que ta voiture ne soit nerveuse (surtout à haute vitesse), je ne vois pas pourquoi tu irais avec un 1.5, encore moins un 2-way.

J'ai cherché vite vite pour voir si je n'étais pas dans le champ, ça semble se confirmer même si c'est pas une source "officielle": http://wikicars.org/en/Limited_slip_differential

Évidemment, pour une propulsion, c'est différent. Disclaimer: je peux me tromper.
Click to expand...

1 way (accel. seulement)
Sur une voiture traction va aider beaucoup pour la sortie de virage, la roue intérieure étant beaucoup moins chargée que l'extérieure, surtout si la voiture est puissante. Les diffs OEM sur les FWD c'est du 1 way (accel. seulement)

1.5 Way et 2 way (accel. + decel.)
La différence avec le 1 way c'est que le 1.5 et le 2 way vont offrir une résistance en décélération aussi.

Maintenant entre le 1.5 et le 2 way c'est le pourcentage de lockup en décélération qui est différent, le 2 way va agir à une valeur de torque moins grande (donc plus facilement) que le 1.5.

En sortie de virage les 2 vont se comporter de la même façon qu'un différentiel 1 way. Par contre, si par exemple tu décides de relâcher l'accélérateur pour faire une correction à mi-virage, il va avoir un effet déstabilisant sur la voiture: souvent du sous-virage mais surtout un «kickback» dans le volant.

L'avantage du 1.5 et 2 way vs 1 way:
Au freinage, le 1.5 et le 2 vont avoir un effet stabilisant, par exemple si la surface est bossée ou que les 2 roues ne sont pas sur le même type de surface, le freinage va moins souffrir et la voiture va être beaucoup plus stable.

Une voiture traction qui a 67% de son poids statique sur l'essieu avant peut avoir en freinage jusqu'à 75% sur les roues avant, l'avantage du 1.5 et 2 way est là, puisque les roues avant sont très chargées et que la moindre variation de grip entre les 2 roues avant va rendre l'auto instable au freinage.

Et pour l'entrée en virage avec un 1.5 ou 2 way, il y a toujours moyen de diminuer le sous-virage en jouant à l'avant (toe, barre anti roulis, ressorts, etc.)
 
jsi said:
The main advantage of a diff that locks-up off-throttle is it helps prevent inside front lock-up during trail braking which could be beneficial on a car without ABS. Setup dependant, ymmv, yadi-yadda-yadda...

2-way locks up the same on/off throttle. 1.5 way locks up less off throttle. 1.5 way is what is typically used in FWD setups...

BTW, some years ago formula1 teams experimented with connecting the front wheels together via a differential to improve trail braking and found significant gains (track dependant). This was later considered as equivalent to ABS and banned. Apples and oranges of course to our applications but just an interesting info tidbit for you.
Click to expand...

(Everything below is just an opinion)

If you are locking up an inside front on a FWD car, that means you have some severe setup issues...

If we are talking autocross (or a very slow, pointy-shooty type road circuit with lots of braking and turning at the same time), then yeah, I would probably agree that a 1.5-way would be ideal and you can compensate for the understeer with allignment setup. But anything you do to the allignment to help turn-in thanks to the 1.5-way will hurt straight line performance...

In a road-race car, personally, I see a 1.5-way useful in 4 situations:
1. In the wet when you want to brake on the rumble-strips/painted lines (stupid, IMHO)
2. If you have an overly HUGE front sway-bar (also stupid, IMHO).
3. If the static weight distribution over the front axle is so skewed to one side. (It happens, but still stupid, IMHO)
4. A combination there-of of the above... (Need I mention what I think of this...? :D)

I have been shopping for a diff myself and most of the feed-back I have gotten in terms of outright performance (directly from manufacturers) is that you don't want anything but a 1-way diff on a properly setup FWD race car...

With a 1.5- or 2-way, your turn-in will suffer, trailing throttle oversteer will suffer, and if you compensate for these with suspension setup, straight-line ultimately suffers...
 
Moi mon choix s'est arrêté sur le Quaife par rapport à ses qualités à mon avis c'est le meilleur choix.


Product Description
The QDF5U Quaife ATB Helical LSD differential transforms your car’s performance. Unlike a conventional plate-style limited slip differential, theQuaife ATB Helical LSD differential relies on gears rather than clutch plates for its operation. That means it is much smoother in operation.

The QDF5U Quaife ATB Limited Slip Differential LSD is designed to prevent the complete loss of drive that occurs with a conventional differential when one wheel slips. While requiring some torque in the slipping wheel, the Quaife unit is progressive in action but never locks, controlled power is transmitted to all the driving wheels

Best suited to high powered front, all and rear wheel drive systems, The Honda Quaife ATB differential is ideal for autocross, lapping and road racing where it outperforms other LSD systems including clutch-type LSD. With low heat generation (no diff cooler required) and unlocking under throttle lift and deceleration the Quaife LSD provides a predictable, stable power transfer in cornering, braking and transitions while preserving the reliability of the differential unit, lap after lap.
Installation is identical to the normal differential with bearing pre-loads and pinion mesh being restored to the original manufacturer’s settings. Servicing of the unit is simple as all gear pinions are free fitting and normal final drive lubrication oils are retained. Due to the internal design of the Quaife ATB differential, all driving wheels must be elevated when servicing brakes, wheels etc.



Product Features:

• Controlled power transmitted to all driving wheels

• Never locks, inherently safe

• Automatic in operation

• Eliminates harsh torque steer and understeering characteristics of other types of LSD

• Gear operated (No plates to wear or break)

• Benefits all year round, regardless of traction conditions

• Direct replacement for standard unit

• Low heat generation

• Retains normal axle lubrication

• Limited Lifetime Warranty
 
Any helical diff in no way out performs a clutch diff on the track. I used to be of this school of thought, but in practice, clutch pack > gear diffs all day long...

The major setback of any gear diff is that when one wheel is in the air, you essentially have an open diff. Also, even with a Wavetrac, I have never felt the sensation of having the nose "sucking in" under throttle on corner exit. They just aren't aggressive enough.

Wavetrac themselves have told me for circuit use, I would be better off with a clutch-type differential.
 
Synoptic Tuning said:
(Everything below is just an opinion)

If you are locking up an inside front on a FWD car, that means you have some severe setup issues...

If we are talking autocross (or a very slow, pointy-shooty type road circuit with lots of braking and turning at the same time), then yeah, I would probably agree that a 1.5-way would be ideal and you can compensate for the understeer with allignment setup. But anything you do to the allignment to help turn-in thanks to the 1.5-way will hurt straight line performance...

In a road-race car, personally, I see a 1.5-way useful in 4 situations:
1. In the wet when you want to brake on the rumble-strips/painted lines (stupid, IMHO)
2. If you have an overly HUGE front sway-bar (also stupid, IMHO).
3. If the static weight distribution over the front axle is so skewed to one side. (It happens, but still stupid, IMHO)
4. A combination there-of of the above... (Need I mention what I think of this...? :D)

I have been shopping for a diff myself and most of the feed-back I have gotten in terms of outright performance (directly from manufacturers) is that you don't want anything but a 1-way diff on a properly setup FWD race car...

With a 1.5- or 2-way, your turn-in will suffer, trailing throttle oversteer will suffer, and if you compensate for these with suspension setup, straight-line ultimately suffers...
Click to expand...

Je vais essayer de retrouver un article que j'avais trouvé qui m'a fait prendre ma décision finale... Mais en résumé, ce que ça disait, c'est qu'au départ il n'y avait que les 1.1 way (1way) et que lorsque les 1.5 sont arrivés, il y a eu réticence de la part de plusieurs à les utilisés car en théorie, il devait créer plus d'understeer à l'entrée de virage. Mais certains ce sont adapter à l'utilisation du 1.5 et ont fini par être plus rapide que ceux qui utilisait les 1.1... Finalement, les 1.5 sont devenus le standard car ils sont malgré la théorie, plus rapide en pratique...

Moi j'ai acheter un 1.5 on verra bien! De toute façon, ce qu'il y a de bien avec un Kaaz, c'est qu'il est assez facile de passer d'un 1.5 way a un 1.1 way... Donc je faire l'été avec pis si ça fait pas mon affaire, bin je le changerai! :D
 
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Guys, the only data point I can contribute is this: apparently (after furious online searching), the differential in my Megane R26 is a Torsen unit. And it works absolutely brilliantly in practice, both on track and on the street. dry or wet (disclaimer: OEM suspension and street tires). I've never driven a FWD car that pulled to the inside of the corner on throttle application so aggressively. No understeer, just pure pull to the apex; it's kind of bewildering, actually. The car also has an independent steering-axis front suspension, which is supposed to help mainly with reducing torque steer, of which there is indeed remarkably little for a 230hp FWD car.

Whether that is applicable or even relevant to your discussion/application is above my pay grade. You figure it out.

Torsen diffs don't work with a wheel in the air, but with a front-engine, FWD car, that is unlikely to happen, right?
 
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