# Truths about Haldex and running a staggered setup.



## ceese (Jul 2, 2011)

I realize that this post could be viewed as little redundant, repetitive and overly simplified - But with that said my goal is to create a thread that answers any and all Haldex related staggering questions in a way that is clearly defined and easy to understand for those that are new to this. I'd like to clear up all myths and misunderstandings in one place. 

One thing I realize is that when it comes to performance mods is that I'm learning and getting smarter but I'm not the smartest person in this room (Some of you guys really know your sh!t). With that said I've been doing some research on creating a staggered setup for my A3 with both performance and appearance in mind. So I'm looking for real and knowledgeable feedback and answers here. Feel free to correct or affirm my statements but please only respond if you are certain of that your comments are correct. 



*1. *Contact patch is irrelevant to the safe operation of Haldex and its effects on the A3 drive train? 

ie. A Haldex is not affected by the width of your wheels and tires - so if you wanted to run 10" wide wheels and tires in the back and 8" wide wheels and tires in the front *this COULD be a completely safe setup* if the overall circumference of the wheels matched identically. The problem is finding two different width tires with the exact same circumference when mounted. 

Another variation is that you could run the same size rims with identical tire sizes in front and back but use a more aggressive offset or spacers in the back or vise versa for the front and it would have no effect on the Haldex whatsoever. This is a completely safe set up although no discernible performance and used primarily for appearance. 

*For example * 
Rear Wheels = 18"x8" ET 35 wheels with 225/40/18 Conti pro sports 
Front Wheels 18"8" ET 42 wheels with 225/40/18 Conti pro sports​ 


*2.* A Haldex is only affected by the overall circumference (diameter) of you wheels. Running tires that have more than 4% difference in diameter long term can create undue stress on the drive train and ultimately lead to failure? 

*Question:* Does anyone know where the 4% difference rule actually came from or is this safety zone the forum version of an urban myth. ie. actual documentation? I couldn't find it anywhere but the forums. I read somewhere that it originally came from an email by a Haldex engineer. 



*3. *If you wanted to be super anal you could go with an 8" wide tire up front and a 10" wide tire in back with slightly different stock diameters and have the tread from the larger of the two shaved to be a perfect match of smaller diameter tire. This would give you a wider contact patch in the back for rear wheel acceleration with an upgraded Haldex, a visually more aggressive stance and be 100% safe. You could also reverse this setup with the wider tires on front to help compensate for the under steer on the A3. Either of these would be perfectly safe. 




*EXAMPLES OF SETUPS THAT WILL AND WON'T WORK BASED OFF OF THE OEM 18" TIRE SIZE OF 225/40/18* 

*1.53 mm difference is only a .25% difference so this set up is completely safe under the 4% rule* 

 

*24.3 mm difference is 3.7% difference so this is still just under the 4% rule and would be considered safe but probably not the best idea. * 

 


*40.3 mm difference is a 6.1% difference and will eventually break your drive train. 
*


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## A3_yuppie (Jun 5, 2006)

ceese said:


> ... a staggered setup for my A3 with both performance and appearance in mind.


 You do realize that the Haldex system on the A3 drives the rear wheels *only *when slip is detected, such that having wider rear wheels and tires would be *adverse *to performance?


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## VWAddict (Jun 12, 1999)

I've always worked WITHIN 3% even on 2WD cars. -More than that starts to have an exponential effect on braking capability, and that's a SERIOUS concern. 

I'm currently looking into a wheel size difference on one of my other cars (the Porsche), and since it originally came with staggered 16" wheels, and since 16" tires are no longer made in those sizes as a full set by any manufacturer who sells in the US, I'm contemplating stepping up to 18" rims, where staggered tire sizes as full sets are still abundantly available. 

All of my calculations have been aimed to be WITHIN 3% for that reason alone, completely irrespective of any 4WD issues. -In point of fact, the numbers are all within 2%, being 1.5% front and 1.75% rear, both in the SAME direction... i.e. both larger, not one larger and one smaller. 

As for my A3, I have 20mm spacers on the rear. -Looks just fine to me, though I do hear the VERY occasional scrape when I hit surface changes under strong cornering preloads for example. 




A3_yuppie said:


> You do realize that the Haldex system on the A3 drives the rear wheels *only *when slip is detected, such that having wider rear wheels and tires would be *adverse *to performance?


 
Width has ZERO relevance to Hadex engagement, I don't know what point you're trying to make here, maybe I misunderstand... 

Since Haldex has to detect slip by comparison of front and rear rotation, it looks for an INCREASE of front wheel speed compared to rear. 

If you choose SMALLER circumference front tires than rears, you'll INCREASE sensitivity to trigger the rear drive... (since even under normal, slip-free straight-line driving, the fronts are already turning slightly faster) if you use LARGER, you'll DECREASE the sensitivity for the threshold at which the rears are engaged. 

The circumference is ALL that matters to Haldex under slip-free conditions. The WIDTH may have an influence on when lateral slip begins under cornering loads, but don't forget that as contact patches get WIDER, they also get SHORTER, for a constant tire pressure and static corner weight. 

If the considerations are purely aesthetic, be mindful of the fact that front/rear circumference changes can mess up the Haldex, and that large WIDTH increases will not buy a larger contact AREA, without significant reductions in tire pressure. (A bit of a simplification, but a worthwhile rule-of-thumb.)


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## JRutter (Nov 25, 2009)

My bias has been to try run the widest profile tires possible with the same size front and rear so that I can rotate them easily to get more life out of them. The car is pretty susceptible to understeer, so running wider tires up front helps in that regard. Wider rubber also helps weight the steering a little, which I like. I'm with Keith that for a staggered setup, keeping the circumference difference as small as possible, with the rears > fronts is the best scenario. I would encourage you to go wider than 225 up front though.


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## ceese (Jul 2, 2011)

JRutter said:


> My bias has been to try run the widest profile tires possible with the same size front and rear so that I can rotate them easily to get more life out of them. The car is pretty susceptible to understeer, so running wider tires up front helps in that regard. Wider rubber also helps weight the steering a little, which I like. I'm with Keith that for a staggered setup, keeping the circumference difference as small as possible, with the rears > fronts is the best scenario. I would encourage you to go wider than 225 up front though.


 I agree that's the best possible set up for our cars. I'm probably eventually going to go with a third set of wheels specifically for the track - Lower profile sidewalls to prevent rubbing and matching wider tires and wheels on both front and back. If I could go with 9" wheels even with a little poke, I'm not worried about how it will look at the track if it buys me better handling and stopping. 

My street set up where I don't drive aggressively (just for looks) will probably be my CH 028s with 225/40 on front and back for summer and I'll add 8mm spacers to the back wheels. Not sure what wheels I'll move my winter tires to but they are 235/20/18 and this set up works really well in the snow so probably some ET 50 wheels and lose the rear spacers for winter.


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## Zetetic (Mar 21, 2007)

Is there any issue with the traction difference between 8" and 10" tires? That's a 20% difference in tread patch between front and back. I know Quattro would compensate for some of that but... ???


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## DjSherif (Apr 27, 2005)

A3_yuppie said:


> You do realize that the Haldex system on the A3 drives the rear wheels *only *when slip is detected, such that having wider rear wheels and tires would be *adverse *to performance?


 2010 A3's and newer running a Gen IV Haldex do not have to wait for slip to happen in order for the power to be transferred to the rear wheels.


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## LWNY (Jul 30, 2008)

DjSherif said:


> 2010 A3's and newer running a Gen IV Haldex do not have to wait for slip to happen in order for the power to be transferred to the rear wheels.


 Gen II does not need slip to occur for power to be transferred. It just need wheel rotational differential between the rear and front axle to generate pump pressure. There is almost always rotational difference between the two since the rear wheels almost always takes a different path from the front. 

I don't know if 4% is a hard definition for clutch based AWD, since the computer determines when there is actually real slip and if it the front and rear are constantly rotating with a 6% difference, it might just think that is the way it is. If you are drive continuously in a circle, the rear wheel travels a shorter distance by more than 6%. It doesn't mean the clutch would be fully engaged. If that is the case, the rear axle would be wound up continuously and you would be hearing some bad noise the whole time.


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## A3_yuppie (Jun 5, 2006)

DjSherif said:


> 2010 A3's and newer running a Gen IV Haldex do not have to wait for slip to happen in order for the power to be transferred to the rear wheels.


 VWaddict and DJsherif: I am not too familiar with the intricacies of Haldex operation, so thanks for pointing out the correct information. But my first point was just that generally it does not make sense to install wider rear tires on a front heavy, largely FWD vehicle, as AFAIK Haldex is not full time AWD.


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## TBomb (Sep 23, 2009)

A3_yuppie said:


> VWaddict and DJsherif: I am not too familiar with the intricacies of Haldex operation, so thanks for pointing out the correct information. But my first point was just that generally it does not make sense to install wider rear tires on a front heavy, largely FWD vehicle, as AFAIK Haldex is not full time AWD.


 Pretty sure that the RS3 runs the same Haldex system, and it runs wider tires up front than in back to help offset the understeer. Rear stagger is for looks, front stagger is for performance :thumbup:


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## ceese (Jul 2, 2011)

TBomb said:


> Pretty sure that the RS3 runs the same Haldex system, and it runs wider tires up front than in back to help offset the understeer. Rear stagger is for looks, front stagger is for performance :thumbup:


 That's exactly what I was getting at in my original post. Keep in mind though, if someone is finding the need to run a reverse stagger for better performance they most likely have an updated Haldex on thier car so they will be getting more power to thier rear wheels than an oem vehicle.


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## JRutter (Nov 25, 2009)

^^^ yeah - wide all around!


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