Salisbury or Quaife ATB?

[Brian S.]

My name is Brian and I am the powertrain captain for Drexel Racing. After a disappointing season, the team is considering a complete redesign for Drexel's next car. One of the decisions on the table is the differential. We currently run an ICP Variloc Salisbury-style differential. We had purchased a Taylor Race MK2 which features a Quaife ATB for our hybrid/electric team recently, but only two senior design teams worked on it and only did theoretical work. Consequently, we now have the option to use either diff, but I am not sure which one suites our needs better.

Since the Variloc is adjustable, it gives us many more options for chassis setup. However, we have not touched the diff since I joined the team three years ago and not much is known about it between all of the team members (including myself). I have no idea when the last time the clutch plates were replaced or the preload was checked. From our records we are running 80/80 ramps, so it is essentially set up as an open diff. We also do not have wheel speed readings (working on that) so the only way we can tune it is through driver feedback. Unfortunately, we currently don't have any experienced drivers that are capable of this.

This leads me to the Taylor Race MK2. For starters, it weighs 4 lbs. less than the Variloc. However, to my knowledge, it is not adjustable. This would require us to set up the suspension to work with the Quaife ATB, which I feel we are much more capable of doing. It also requires much less maintenance, which should save us time and money in the long run.

With these arguments, I feel the Taylor Race MK2 is the better choice. However, I am not sure if giving up the adjustability is worth it. Does my argument for the Taylor Race MK2 sound valid? Any feedback from teams running a Quaife ATB diff would be greatly appreciated as well.

Brian

[SNasello]

Your arguments all sound valid. It sounds like you have already made a decision.

It also sounds like no one in your team understands the pros of the salisbury diff, or how to maintain it properly. The question I have is, how adjustable is the Variloc? Do you have a bunch of different ramp combinations that you can build in? Different shims to adjust preload? Can you adjust preload externally? If the answer is no then you might as well be running an open diff, or anything else for that matter.

I would suggest doing some more reading on how the various options work, what the pros and cons are, and then think about what the best option is for your team.

[Brian S.]

Thanks for the response.

They have many different combinations of ramps available on ICP's website, and they will make custom ramps as well. However, I do not think we have any of them around at the shop. The pre-load is only internally adjustable using shims. It is a fairly out-dated design (I think we've had it since 2005, not sure though) and was designed for larger cars like Formula 1000. From the few times I've driven last year's car, I can tell that it could use a lot more locking on corner exit as it loves to oversteer.

Since our team has been one of those teams that is finishing their car at competition, having an adjustable diff doesn't really help. However, that is not a good enough reason for me because I'm going to do everything I can to make sure that doesn't happen this year.

I guess a better question is would maintaining and tuning our current diff be better use of our time than re-designing our rear shear-plate, diff hangers, sprocket, and half-shafts for the Taylor Race MK2?

[Jay Lawrence]

If you're one of the teams that finishes their car at comp, why not remove the complexity/mass/time/etc by running a spool. We ran a Torsen for several years (similar in properties I think to the Taylor) and only had issues with it when our setup was off (lifting inside) but then switched to a KAAZ Salisbury diff. It was lighter and more adjustable, but even with a month of tuning we didn't have time to tune it (there are many more aspects of the car that take up your time), plus it leaked. Since then the team has gone to a spool and it is working very well.

Can't comment really on the Taylor diff, but personally I'd remove adjustability from your criteria; it just creates more variability to try to tackle in a very limited time frame.

[Brian S.]

Thank you for your input.

The Quaife is similar to a Torsen but is better, according to Quaife's website. I really can't find much documentation on it other than general information on Taylor Race's and Quaife's websites. I understand the Salisbury better, but as you said, it may be above our heads to be able to tune it effectively in conjunction with suspension tuning. According to Taylor Race’s website, the Quaife works well with stiff springs and soft ARB’s, which is how our car is currently set up. I don’t feel we will be able to get our car working well with a spool, but we may consider it for our 2015 car. We are trying to not change too many things this year, but a change to the Taylor Race MK2 might be worth it for the sake of simplicity.

Does anyone have any more info on or experience with the Taylor Race diff/Quaife ATB? I’m going to contact Taylor Race to see if they can give me some more info on it.

[dmacke]

Our team has run a Torsen for the past couple of years and it has worked well for us. We were able to get it a bit lighter than the Drexler without issues and have been happy with our performance. Granted our team isn't quite to the point where we have the time to tune our differential so we haven't tried a Salisbury type. The Taylor Race is a good differential if you have deep enough pockets. Our team does not.

[jlangholzj]

Originally posted by dmacke:
Our team has run a Torsen for the past couple of years and it has worked well for us. We were able to get it a bit lighter than the Drexler without issues and have been happy with our performance. Granted our team isn't quite to the point where we have the time to tune our differential so we haven't tried a Salisbury type. The Taylor Race is a good differential if you have deep enough pockets. Our team does not.

I don't view our team as having "deep pockets" necessarily and we've got several. 2 of the original diffs with the aluminum center section as well as one of the new MKII's.

As a disclaimer, I've never worked with any of the other diff companies....HOWEVER...Taylor ALWAYS is around comps and will usually get back to you pretty quick on questions and parts ordering.

We chose the Taylor because I'm not entirely sure if we'll ever reach the point of needing to tune the diff. Hopefully this summer I'll get around to actually seeing what the slip% is around corners just to have it.

One last thing, wouldn't more lock on corner exit make oversteer worse? (just a question I have personally...Never really looked at diff tuning)

[dmacke]

Originally posted by jlangholzj:

I don't view our team as having "deep pockets" necessarily and we've got several. 2 of the original diffs with the aluminum center section as well as one of the new MKII's.

As a disclaimer, I've never worked with any of the other diff companies....HOWEVER...Taylor ALWAYS is around comps and will usually get back to you pretty quick on questions and parts ordering.

We chose the Taylor because I'm not entirely sure if we'll ever reach the point of needing to tune the diff. Hopefully this summer I'll get around to actually seeing what the slip% is around corners just to have it.

One last thing, wouldn't more lock on corner exit make oversteer worse? (just a question I have personally...Never really looked at diff tuning)

I guess you could classify our team as poor then. We would rather use the money saved from buying a $500 diff and some aluminum vs a $3000 diff on other areas of the car. Agreed on the part of tuning the diff. I don't see that as a point our team will reach anytime in the near future.

[Brian S.]

Originally posted by jlangholzj:
One last thing, wouldn't more lock on corner exit make oversteer worse? (just a question I have personally...Never really looked at diff tuning)

My understanding of it is that when both wheels are accelerating at the same speed (locked), they make the car want to go straight, thus reducing oversteer at corner exit.

[jlangholzj]

Originally posted by dmacke:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jlangholzj:

I don't view our team as having "deep pockets" necessarily and we've got several. 2 of the original diffs with the aluminum center section as well as one of the new MKII's.

As a disclaimer, I've never worked with any of the other diff companies....HOWEVER...Taylor ALWAYS is around comps and will usually get back to you pretty quick on questions and parts ordering.

We chose the Taylor because I'm not entirely sure if we'll ever reach the point of needing to tune the diff. Hopefully this summer I'll get around to actually seeing what the slip% is around corners just to have it.

One last thing, wouldn't more lock on corner exit make oversteer worse? (just a question I have personally...Never really looked at diff tuning)

I guess you could classify our team as poor then. We would rather use the money saved from buying a $500 diff and some aluminum vs a $3000 diff on other areas of the car. Agreed on the part of tuning the diff. I don't see that as a point our team will reach anytime in the near future. </div></BLOCKQUOTE>

Geese now you have to go and make me feel bad macke! http://fsae.com/groupee_common/emoticons/icon_smile.gif I understand how it is. I took us about 8 years of picking and choosing to get those three diffs!

Back on the subject of Diff tuning, thinking about it again it does make sens Brian. I was thinking more about when you lose traction how it tends to oversteer more. But relating back to driving hotrods with a spool....they don't want to corner that great!

[kcapitano]

One last thing, wouldn't more lock on corner exit make oversteer worse? (just a question I have personally...Never really looked at diff tuning)


My understanding of it is that when both wheels are accelerating at the same speed (locked), they make the car want to go straight, thus reducing oversteer at corner exit.

Its dependent on weight transfer. If the weight on the rear tires is evenly distributed between them then both tires will resist changing speeds an equal amount and the car will want to go straight. If, however, there is a large percentage of weight on just one rear tire then that tire will react more longitudinal force then the opposing rear tire and a yaw moment will be introduced. This affect can lead to power on oversteer during hard cornering with a spool setup.

In regards to your original question, learning to maintain and tune your current diff would, in my mind, be a much more effective use of your time than redesigning your powertrain to accommodate the MK2. Without experience tuning your suspension and differential setup you won't be able to validate the effect of changing your differential. Redesigning everything for the new diff will also require more resources during the design phase, which won't help you finish the car sooner and without validation you will be right back where you are currently in a few years.

That's my two cents. To tell you a little of my experience, in 2012 I redesigned my team's drivetrain to work with a Drexler after having used a Torsen for over 10 years. My motivation was purely for reliability and finishing the car sooner and we never really looked at how the diff affected the car. Our drivers haven't noticed a significant difference, but this summer we are looking at doing some diff testing to validate its effects. Unfortunately its difficult to change the setup and because we don't now very much about it the diff testing is very low on our priorities list.

[AxelRipper]

$500 Torsen? Too expensive, heavy, and unadjustable.

I have to say, if you have the money and want something that is lightweight and can bolt up to your car and work spectacularly, the Taylor is hard to beat. When you can justify why you chose it in design for other reasons than it was easy and everyone says its great I imagine it works even better.

There is a differential out there that is cheap, light, and tunable, and requires about as much work if not less than a standard Torsen. (This paragraph sounds like something that Claude or Z would write, but I'll be kind and go a step further and give you the answer)

The front differential from an ATV. In our case it was the Honda Rubicon. Take it, machine off the ring gear (if you're using the newer style one) and build your bearing/sprocket adapters. Our setups have been about the same weight as the newest Taylor. And the diff costs under $300 online, brand new.

Now the adjustability is where it gets fun. Its a cam and pawl differential. There's a shim in there that you can change thickness of to go from nearly open to full spool. The internals will wear a bit, but it works quite well.

And if your suspension is tuned wrong (lifting inside tires, it opens up) then you can just pop it apart, grab the mig and spool it. http://fsae.com/groupee_common/emoticons/icon_razz.gif

[dmacke]

Originally posted by AxelRipper:
$500 Torsen? Too expensive, heavy, and unadjustable.

After a couple years of design iteration our housing, gears, and bearings weighs less than 6 pounds. It's always a work in progress but I think it gives us more design flexibility.


The front differential from an ATV. In our case it was the Honda Rubicon. Take it, machine off the ring gear (if you're using the newer style one) and build your bearing/sprocket adapters. Our setups have been about the same weight as the newest Taylor. And the diff costs under $300 online, brand new.

This is definitely intriguing though. Will look into it.

[Z]

Brian,

The type of differential you choose is a major top-level design decision if you want a really competitive car. The whole car concept is affected greatly by the type of diff (eg. High or low powered engine? Middle or more rearward weight? Aero or not? Etc.). On the other hand, if you are only aiming for mid-field, then almost any old diff will do (providing it doesn't break!), with a spool being the cheapest and most reliable.

So very briefly, regarding your "whole car concept" decision making;

If Torsen, then you don't want the inner-rear-wheel lifting when exiting corners. So with the Torsen (and likewise with open-diff) you want more front roll-stiffness than rear, or more rear weight, or lots of aero, or a low powered engine, or just don't be in a rush...

If LSD, then you can easily set it up to be an "open" diff (minimum preload and ~90 degree ramps), or a "spool" (max preload and more angled ramps). This covers most of the range of the other car parameters. Only when you want something inbetween (ie. because you are already at the front of the field) do you need to know how to "tune the diff". Here ~90 degree braking-ramp, 45 degree accel-ramp, and some preload gets you most of the way.

Z

(PS. Kcapitano has it right regarding corner exit with a spool. That is a good example of how the same diff can give you severe oversteer or understeer, depending on the rest of the car setup.)

[Jay Lawrence]

Just a comment on the cam & pawl: we used one on a couple of cars and did not like it (this is prior to me being on the team). For us it gave a kind of ratcheting feeling, particularly on corner entry. This is probably tunable to a certain extent, but from what I was told the drivers were not big fans of it.

[Brian S.]

Thank you for all of the input guys, I really appreciate it.

I am trying to get a proposal together for the direction I would like to take this year’s car, and this diff choice is what I am stuck on. We just got back from Lincoln a few weeks ago with a car that has yet to move under its own power, as it struggled to pass sound and then the scavenge pump for the dry sump failed. This was the first time in four years that we did not complete every event. It seems that the few members we have left want to scrap this design completely and start over from scratch. They also want to do a 2 year build. I am trying to propose that we only slightly tweak last year’s design and spend a few months before competition testing and tuning. While we test and tune the 2014 car, I would like to start working on a fresh redesign for the 2015 season. We do not have many knowledgeable designers, but we have an adequate amount of good manufacturers, so I feel that this plan could work well for us.

Here are the specs of our 2013 car:
Weight: 491 lbs wet, half tank of fuel, 52% rear
Power: Most recent dyno run was 76 whp (CBR600F4i)
Aero: None, but we have an undertray that was developed, just needs to be made

Z,
From what you are saying, it sounds like our current Salisbury style diff would be great for what I want from our 2014 car. I feel that the Taylor Race MK2 will work well if we decide to make a small, single-cylinder car with aero for 2015, which is what I would like to do.

Not having to adapt the Taylor Race MK2 to our current design will save us a lot of time that we can use to develop other areas of the car or just test longer. I also feel that the design judges will appreciate an attempt to tune our diff as that was one of the things they called us out on.

For those of you suggesting cheaper diff alternatives, thank you, but we already have both of the diffs I am considering. However, I will look into some of these suggestions for the 2015 car.

Brian

[jd74914]

Originally posted by Jay Lawrence:
Just a comment on the cam & pawl: we used one on a couple of cars and did not like it (this is prior to me being on the team). For us it gave a kind of ratcheting feeling, particularly on corner entry. This is probably tunable to a certain extent, but from what I was told the drivers were not big fans of it.

Sorry for the hijack Brian, I just wanted to comment on this for anyone reading who hasn't played with a cam and pawl. We experienced the same ratcheting feeling as well as a very high level of wear with our cam and pawl setup. For reference, our car is about 100 whp (75 kW) and would wear pawls in maybe 4 hours of driving.

Last summer we designed a Salisbury loosely-based on a BMW e30 differential and so far have been very pleased. All drivers have reported that it is much easier to drive than the previous cam and pawls. Like everyone else here, we also haven't had the time to test it, but with our clutch/preload combinations it has been very driveable (our main goal).

I think you're going the right way reusing the old Salisbury design. If you had enough problems competing in all events, you want to fix the things that stopped you, not redesign "successful" parts.

[Z]

Originally posted by Brian S.:
While we test and tune the [modified 2013 =] 2014 car, I would like to start working on a fresh redesign for the 2015 season. We do not have many knowledgeable designers, but we have an adequate amount of good manufacturers, so I feel that this plan could work well for us.
Brian,

That sounds like a good plan, especially if you can keep the same team together over the two years. If your "good manufacturers" spend a season modifying->testing->re-modifying->re-testing your current car, then they should become reasonably "knowledgeable designers" by next year.

With regard to your current car, I would suggest that the modification program involves as much "simplification" as is feasible. As in, "Do we really need this part? It keeps flexing, and sort of binding-up, and, err... Why don't we just toss it, and mount that bit direct to the chassis?" I know there is a lot of resistance to this sort of thinking, but I have found that real testing often proves that you don't really need that part after all.

Some suggestions for parts that can be "tossed" (yes, I do keep harping on about it, but anyway... http://fsae.com/groupee_common/emoticons/icon_smile.gif).

* Pushrods and rockers. Just mount the spring-dampers directly between chassis and wishbones. See pics of U of Cincinatti at FSAE-Lincoln-2013 for clues.

* Steering-R&P AND a Bevel-Gear-Box. You only need one or the other (eg. a 3:1 BGB with a Pitman-Arm at the bottom eliminates the R&P, and is smoother, stiffer, cheaper, less free-play, etc.)

* Anything more than a push-pull-rod for gear changing. And while you are at it, just a hand-clutch so you can toss that extra foot pedal...

Doing above will make your designers a lot more knowledgeable as to what is really needed on the 2015 car.
~o0o~

Back to diffs.

I am sure that your current car, being relatively high-powered and with only ~half-weight on rear wheels, can smoke both its rear tyres coming out of almost any FSAE corner (ie. they are all fairly low speed, so high torque is available). So the Salisbury-LSD is probably the better option. If in worst case you are getting far too much inner-wheel spin, then you increase pre-load and ramp-angle to make it more like a spool.

The proposed 2015 car, being lighter, with lower power engine and aero, would be better matched to the TR2-Torsen. In fact, with more rear weight (say, about 60%), then a plain open-diff could work well enough.

Note that with, say, ~2/3 rear-weight and equal sized tyres all round, it is natural to carry most roll-loads (= LLTD or ERMD) at the front. This has the outer-front-tyre carrying ~1/3 of the cornering forces (because inner-front is almost unloaded), and both rear-tyres sharing the other 2/3 of the cornering forces. So equal loading on all (3) tyres, and good balance. This also has both rears planted at mid-corner, so good acceleration out of the corner even with an open-diff.

Z

[Brian S.]

Z,

I am familiar with a lot of your ideas for the simplification of fsae cars from reading the suspension thread and others, and I have to say that I agree with most of what you say. Our paddock was actually right next to Cincinnati’s at Lincoln and I really liked their suspension setup. I brought a few of my teammates over to it and told them that we should do direct-actuation if we do a complete re-design, and I just got a bunch of blank stares. It’s tough to propose simplification ideas especially to our young members who want to make a mini-F1 car. It’s even worse if you propose to simplify a system that someone else is working on because they think you’re insulting their intellect by “dumbing it down”. I had a nice “I told you so” moment when the overall results were posted and I saw Cincinnati placed 9th overall.

At Drexel we have a five year program because we have 3 6-month co-ops. This helps us in that we can keep members for an extra year and there are always people at school in the summer. However, it hurts us because people will disappear for 6 months. I have two more years, so I will be overseeing the next two cars. Hopefully we can all pull together to make a very good car in 2015.

Back to diffs,

I appreciate everyone’s help in making this decision. I am going to order some new ramps and any parts I need for servicing the diff from ICP. We are currently running 80x80 ramps, so I was thinking of getting 45x80, 60x80, and 60x70. Do these sound like good choices?

Brian

[SNasello]

Brian,

those ramp angles sound like pretty good choices to me to start with. If you end up using the diff over the next few years you can slowly build up a range of spare parts for it that you can use to tune it on the new car.

You should also look into getting shims of various thicknesses to adjust the preload, if possible. Also, think of a method to measure the preload in your diff, so you can check if it is in spec when you do find a setup that you like.

[jlangholzj]

Originally posted by SNasello:
Brian,

those ramp angles sound like pretty good choices to me to start with. If you end up using the diff over the next few years you can slowly build up a range of spare parts for it that you can use to tune it on the new car.

You should also look into getting shims of various thicknesses to adjust the preload, if possible. Also, think of a method to measure the preload in your diff, so you can check if it is in spec when you do find a setup that you like.

Also by using some wheel speed sensors on the inboard side of your diff you can log your actual %sip or bias through corners to help quantify how the changes in ramps and preload are affecting the performance.

[Brian S.]

Originally posted by SNasello:
You should also look into getting shims of various thicknesses to adjust the preload, if possible. Also, think of a method to measure the preload in your diff, so you can check if it is in spec when you do find a setup that you like.

Will do, thanks for the advice.


Originally posted by jlangholzj:
Also by using some wheel speed sensors on the inboard side of your diff you can log your actual %sip or bias through corners to help quantify how the changes in ramps and preload are affecting the performance.

I am working on that as well. We have a Race Technology DL2 that has been collecting dust for three years that I want to integrate into this year’s car. The retaining nut on the back of our spindles is already slotted so all I really need to do is come up with a mounting solution for the sensor.

[jpusb]

Hi Brian, excellent discussion you started. I will leave my input (although it will only guide you to what you have already decided).

I was in my team from 2007 to 2010. Driving AutoX and endurance from 2008 to 2010 (at MIS). We have used a Torsen for ages (since our first car in 2002). In 2008, we finally got to a VERY reliable design, that didn't break and was light. It costed the team a lot of effort and testing to get there. The same design has been used since then.

In 2008, having tested like crazy during 2007, we moved up in the field considerably (from usually 35+ in AutoX, to the top 15). But it was first year doing so and we had many other things still to take care of. Through 2008, 2009, we were in the top 15 in performance, and in 2010 we did a loooot of performance testing: car setup, electronics, bla bla bla. Long story short, I would have liked (as a driver and being in the vehicle dynamics team) an adjustable diff to make the car even better. It takes a bit to get to that point, but not too much, and it's not rocket science either, AND you will eventually get there.

I would say keep the Salisbury, and leave it almost as an open diff. It will give your drivers more time to understand everything else and then you start locking more (if the setup asks for it). Keep in mind that with slick tires, good track temp, and a LSD diff, you will be able to tell who could be a good driver and who won't. Maybe an open diff does not filter this too much, I don't really know, but anyway.

AND what you said about keeping basically the same car (at least all that is not considerably wrong with it) and focus on testing is PRICELESS for a team in the situation you described yours. Incredibly, a LOT of people won't buy this, because their engineer minds won't let them. People seem to forget that testing is also engineering, and they try to win the competition in SolidWorks. This has been a problem in my team for years, every years someone tries to comeup with new things to design instead of new ways to analize data, organize tests, increase testing times, use each test more, etc.

Good luck!

JP

[scotty young Taylor Race]

Well I can tell you what diff I think you should run.....
With our diff you make adjustments to the chassis. Springs , ride height and sway bar. It will act the same way as it did on day one.... 4 years from now. there are not parts to wear out. Send me an e mail. I will give you some good tech info Brian..

[Brian S.]

Originally posted by jpusb:
Hi Brian, excellent discussion you started. I will leave my input (although it will only guide you to what you have already decided).

I was in my team from 2007 to 2010. Driving AutoX and endurance from 2008 to 2010 (at MIS). We have used a Torsen for ages (since our first car in 2002). In 2008, we finally got to a VERY reliable design, that didn't break and was light. It costed the team a lot of effort and testing to get there. The same design has been used since then.

In 2008, having tested like crazy during 2007, we moved up in the field considerably (from usually 35+ in AutoX, to the top 15). But it was first year doing so and we had many other things still to take care of. Through 2008, 2009, we were in the top 15 in performance, and in 2010 we did a loooot of performance testing: car setup, electronics, bla bla bla. Long story short, I would have liked (as a driver and being in the vehicle dynamics team) an adjustable diff to make the car even better. It takes a bit to get to that point, but not too much, and it's not rocket science either, AND you will eventually get there.

I would say keep the Salisbury, and leave it almost as an open diff. It will give your drivers more time to understand everything else and then you start locking more (if the setup asks for it). Keep in mind that with slick tires, good track temp, and a LSD diff, you will be able to tell who could be a good driver and who won't. Maybe an open diff does not filter this too much, I don't really know, but anyway.

AND what you said about keeping basically the same car (at least all that is not considerably wrong with it) and focus on testing is PRICELESS for a team in the situation you described yours. Incredibly, a LOT of people won't buy this, because their engineer minds won't let them. People seem to forget that testing is also engineering, and they try to win the competition in SolidWorks. This has been a problem in my team for years, every years someone tries to comeup with new things to design instead of new ways to analize data, organize tests, increase testing times, use each test more, etc.

Good luck!

JP

Thanks for your advice and support. Sounds like we should start with the 80/80 ramps we have in there now and then add locking to the acceleration side or just add preload if we need it. Since I am one of the more experienced drivers of the group now, I'll probably be doing at least some of the testing. Hopefully this will help as I can get direct feedback on changes.



Originally posted by scotty young Taylor Race:
Well I can tell you what diff I think you should run.....
With our diff you make adjustments to the chassis. Springs , ride height and sway bar. It will act the same way as it did on day one.... 4 years from now. there are not parts to wear out. Send me an e mail. I will give you some good tech info Brian..

Email sent. Thank you for your input.

[Some Guy]

Originally posted by Brian S.:
I appreciate everyone’s help in making this decision. I am going to order some new ramps and any parts I need for servicing the diff from ICP. We are currently running 80x80 ramps, so I was thinking of getting 45x80, 60x80, and 60x70. Do these sound like good choices?

Brian

Just keep in mind that if you guys are running a slipper clutch (or decide to at some point), the decel ramp angles dont matter that much.

[ksjandir]

Its dependent on weight transfer. If the weight on the rear tires is evenly distributed between them then both tires will resist changing speeds an equal amount and the car will want to go straight. If, however, there is a large percentage of weight on just one rear tire then that tire will react more longitudinal force then the opposing rear tire and a yaw moment will be introduced. This affect can lead to power on oversteer during hard cornering with a spool setup.

In regards to your original question, learning to maintain and tune your current diff would, in my mind, be a much more effective use of your time than redesigning your powertrain to accommodate the MK2. Without experience tuning your suspension and differential setup you won't be able to validate the effect of changing your differential. Redesigning everything for the new diff will also require more resources during the design phase, which won't help you finish the car sooner and without validation you will be right back where you are currently in a few years.

That's my two cents. To tell you a little of my experience, in 2012 I redesigned my team's drivetrain to work with a Drexler after having used a Torsen for over 10 years. My motivation was purely for reliability and finishing the car sooner and we never really looked at how the diff affected the car. Our drivers haven't noticed a significant difference, but this summer we are looking at doing some diff testing to validate its effects. Unfortunately its difficult to change the setup and because we don't now very much about it the diff testing is very low on our priorities list.

So did you ever end up validating the switch over to the Drexler? Our team at UCD is currently thinking about making the switch over to Drexler from the Torsen T1, and would greatly appreciate any input as how your switch went and if you saw any performance increases.