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Herbie

FWD with LSD vs RWD open diff

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Hi guys, curious to see what people think. All things being equal, weight, power, driver skill etc., which would be faster on the track? 
 

I track an R53 with LSD and was wondering if an equally weighted/powered open diffed RWD will be better. Of course there are too many variables. Nonetheless, interesting to see what different people think.

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8 hours ago, Herbie said:

Hi guys, curious to see what people think. All things being equal, weight, power, driver skill etc., which would be faster on the track? 
 

I track an R53 with LSD and was wondering if an equally weighted/powered open diffed RWD will be better. Of course there are too many variables. Nonetheless, interesting to see what different people think.

Well, the Mini is similar in specs to an NC Miata (most tracked ones have a lsd). I'd bet the NC would be faster with the same setups, but really the differences are academic at best. The NC has much more overhead and potential and will be more fun and cheaper to run. RWD is dynamically superior to FWD for track applications (especially for tire management).

If you're looking to upgrade, I've got a 2022 BRZ coming in an a couple of weeks and am looking to sell my 2014 BRZ. 

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Thank you so much for this response and congrats and the upcoming BRZ. Your statement that RWD is dynamically superior explains why people always tell me to “upgrade” to RWD. That always baffled me because my MINI would keep up with many RWD cars. I was asking about open diffed RWD because e46 330ci got me curious. Twins are getting more and more expensive where I live. So do NC miatas. Forget s2k and e46 m3s. 

Would you mind elaborating please what makes RWD superior aside from the obvious things such as two wheels most of the work on FWD, weight distribution, traction? I’m afraid I would not know how to drive, or rotate a RWD car. Do you trail brake like in FWD? Or do you brake much earlier and get on the gas to rotate? Been tracking for almost 3 years, but never have in a RWD. Will I be able to drive a RWD as fast? Or will I suck not knowing how to drive it?

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13 minutes ago, Herbie said:

Thank you so much for this response and congrats and the upcoming BRZ. Your statement that RWD is dynamically superior explains why people always tell me to “upgrade” to RWD. That always baffled me because my MINI would keep up with many RWD cars. I was asking about open diffed RWD because e46 330ci got me curious. Twins are getting more and more expensive where I live. So do NC miatas. Forget s2k and e46 m3s. 

Would you mind elaborating please what makes RWD superior aside from the obvious things such as two wheels most of the work on FWD, weight distribution, traction? I’m afraid I would not know how to drive, or rotate a RWD car. Do you trail brake like in FWD? Or do you brake much earlier and get on the gas to rotate? Been tracking for almost 3 years, but never have in a RWD. Will I be able to drive a RWD as fast? Or will I suck not knowing how to drive it?

The biggest noticeable difference between FWD and RWD is just how tough FWD is on those front tires. The mini is one if not the best handling FWD cars and I've had a blast driving, but a FWD cars suffer from terminal understeer and begin to lose traction under acceleration due to weight transfer. You can make just about any car rotate with setup and technique. The FWD cars just overwork the front tires even when you're driving them well (they do the braking, turning, and accelerating after all). 

You won't have too much issues swapping platforms. You'll have to do less work to rotate the RWD cars than most FWD platforms, you do have to work the steering a bit more with the RWD cars (opposite lock to control oversteer instead of just adding throttle with the FWD cars).

An 86 or NC/ND Miata might have a slightly higher purchase price than an e46 330ci, but running costs of the NC and twins will be much lower (not to mention they're newer cars than the BMW and don't suffer the BMW tax for parts). You can get an NC or 86 and set it up for trackdays for under $15k ($10k-$12k for a very well setup NC and $12k-$15k for the 86), an older NA/NB Miata is going to be around $10k (or less, depends on how crazy the used market has gotten with them, used to be closer to $5k-$7k). You might have to wait another 6 months to a year for used prices to drop back down (or scour the web/classifieds for a deal). A sub $10k BMW won't be cheap to make track ready (suspension, brakes, wheels and tires), and the BMW is about as fun to wrench on as your mini (the 86 and Miata are laughably easy to work on). I don't really see a 330ci as a big upgrade over your Mini, and it'd take some parts to make it as fun at the track. 

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BRZ4Science has pretty much nailed the description.   going from FWD to RWD is usually not terribly taxing to the driver, assuming you're going to something relatively low powered.  I wouldn't jump into a ZL1 and expect to be immediately quick- there are just too many dynamics that change between a low powered FWD and a high power RWD.   BUT..  going from a low FWD to a low RWD like a Miata, BRZ, etc..   no problem.  I went from a torquey Maxima that could light the front tires up in 3rd on the track, to a ~120whp 240SX and was faster by my 2nd or 3rd day at the track despite a 20MPH difference in speed on the straights.

For the RWD, you still can trail brake into the turns, but you can also get onto the gas and move speed through the turns, and accelerate quicker out.   with a FWD, you drive it a little more point-and-squirt.  slow it down, rotate it (mostly off the gas), then get on the gas to accelerate out.   they don't continue to rotate well while you're on the throttle since they're being pulled straight by the torque to the fronts.

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On 10/16/2021 at 8:14 PM, BRZ4Science said:

 You might have to wait another 6 months to a year for used prices to drop back down (or scour the web/classifieds for a deal).

I don't mind waiting, but my fear is prices might continue to rise with everything going on in the world. I regret not buying a BRZ for sub 10K early in 2020.  Now, salvage titled automatics are being posted for 15K.  Do you think prices will drop? 

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1 hour ago, Matt93SE said:

BRZ4Science has pretty much nailed the description.   going from FWD to RWD is usually not terribly taxing to the driver, assuming you're going to something relatively low powered.  I wouldn't jump into a ZL1 and expect to be immediately quick- there are just too many dynamics that change between a low powered FWD and a high power RWD.   BUT..  going from a low FWD to a low RWD like a Miata, BRZ, etc..   no problem.  I went from a torquey Maxima that could light the front tires up in 3rd on the track, to a ~120whp 240SX and was faster by my 2nd or 3rd day at the track despite a 20MPH difference in speed on the straights.

For the RWD, you still can trail brake into the turns, but you can also get onto the gas and move speed through the turns, and accelerate quicker out.   with a FWD, you drive it a little more point-and-squirt.  slow it down, rotate it (mostly off the gas), then get on the gas to accelerate out.   they don't continue to rotate well while you're on the throttle since they're being pulled straight by the torque to the fronts.

Please pardon my ignorance. I like to really get into understanding the dynamics. Where it gets confusing to me is throttle off oversteer on some cars (E30. S2k etc.) while others oversteer on gas.  Or do all RWD cars oversteer on both front or rear traction loss? I guess my question is, why does losing rear traction cause oversteer and why does losing front traction cause oversteer. I have a hunch but not a clear understanding yet. Do all RWDs do this?

Will RWD be easier to correct oversteer/understeer than FWD where stepping on gas straightens it.

In a RWD, what would happen if you throttle off oversteer, do you correct by gassing? How about understeer? do you brake or do you gas to rotate?  

 

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7 hours ago, Herbie said:

Please pardon my ignorance. I like to really get into understanding the dynamics. Where it gets confusing to me is throttle off oversteer on some cars (E30. S2k etc.) while others oversteer on gas.  Or do all RWD cars oversteer on both front or rear traction loss? I guess my question is, why does losing rear traction cause oversteer and why does losing front traction cause oversteer. I have a hunch but not a clear understanding yet. Do all RWDs do this?

Will RWD be easier to correct oversteer/understeer than FWD where stepping on gas straightens it.

In a RWD, what would happen if you throttle off oversteer, do you correct by gassing? How about understeer? do you brake or do you gas to rotate?  

 

Oversteer requires the rear tires to lose traction first and can occur on turn-in, during mid corner, or on corner exit.

Turn-in oversteer is usually from transferring weight off the rear tires and onto the front tires (either through braking or lifting off the throttle). Any driving configuration can experience oversteer on entry, but this is the primary (and often the only) type of oversteer a FWD car will experience. Often called an inertial drift.

MId corner oversteer is a weird scenario and is often due to a problem or mistake (not always though). In the middle of the corner if you are still trail braking you can get oversteer (most corners you should be done braking before this point). Typically mid corner you should be adding throttle which will put weight on the rear tires making the car less likely to oversteer. It is possible to lose traction in the rear before the front in steady state cornering just due to setup with a RWD car (it's almost impossible to do with FWD).

Exit oversteer is usually due to adding too much throttle too quickly, which uses too much of the available grip for acceleration and doesn't leave enough for cornering. This is also called a power slide.

To counteract oversteer in a RWD, you need to turn into the slide (add opposite lock). You should also maintain constant throttle application to avoid unnecessary weight transfer. In a FWD or AWD car, you can add throttle in addition to (or in some cases instead of) adding opposite lock. When the front tires are powered, they can drag the back part of the car back in-line with the front to help counter oversteer (this isn't an option in RWD cars since the front is unpowered, adding throttle does transfer weight to the rear which will add some rear traction; however, in a RWD car if you've already initiated oversteer adding throttle doesn't normally help since there isn't enough grip in the rear to facilitate the turn let alone any extra for acceleration (adding throttle will just continue the oversteer and end up in a drift or spin).

FWD is typically considered the easier setup since you fix understeer by lifting off throttle and oversteer by adding throttle (also, oversteer is less likely to occur and more difficult to induce). This is one of the factors why FWD has become the most common configuration for consumer cars (manufacturers also tend to use setups that produce understeer instead of oversteer since the former is more predictable and more intuitive for the average driver to deal with). 

The Mini is one of the more tail happy (oversteer prone) FWD vehicles, many RWD cars will have less oversteer out of the box than your mini (setup changes can dramatically alter the behavior of any car, and it's up to the driver to pick the fastest setup for their driving style and course layouts).

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42 minutes ago, BRZ4Science said:

Oversteer requires the rear tires to lose traction first and can occur on turn-in, during mid corner, or on corner exit.

Turn-in oversteer is usually from transferring weight off the rear tires and onto the front tires (either through braking or lifting off the throttle). Any driving configuration can experience oversteer on entry, but this is the primary (and often the only) type of oversteer a FWD car will experience. Often called an inertial drift.

MId corner oversteer is a weird scenario and is often due to a problem or mistake (not always though). In the middle of the corner if you are still trail braking you can get oversteer (most corners you should be done braking before this point). Typically mid corner you should be adding throttle which will put weight on the rear tires making the car less likely to oversteer. It is possible to lose traction in the rear before the front in steady state cornering just due to setup with a RWD car (it's almost impossible to do with FWD).

Exit oversteer is usually due to adding too much throttle too quickly, which uses too much of the available grip for acceleration and doesn't leave enough for cornering. This is also called a power slide.

To counteract oversteer in a RWD, you need to turn into the slide (add opposite lock). You should also maintain constant throttle application to avoid unnecessary weight transfer. In a FWD or AWD car, you can add throttle in addition to (or in some cases instead of) adding opposite lock. When the front tires are powered, they can drag the back part of the car back in-line with the front to help counter oversteer (this isn't an option in RWD cars since the front is unpowered, adding throttle does transfer weight to the rear which will add some rear traction; however, in a RWD car if you've already initiated oversteer adding throttle doesn't normally help since there isn't enough grip in the rear to facilitate the turn let alone any extra for acceleration (adding throttle will just continue the oversteer and end up in a drift or spin).

FWD is typically considered the easier setup since you fix understeer by lifting off throttle and oversteer by adding throttle (also, oversteer is less likely to occur and more difficult to induce). This is one of the factors why FWD has become the most common configuration for consumer cars (manufacturers also tend to use setups that produce understeer instead of oversteer since the former is more predictable and more intuitive for the average driver to deal with). 

The Mini is one of the more tail happy (oversteer prone) FWD vehicles, many RWD cars will have less oversteer out of the box than your mini (setup changes can dramatically alter the behavior of any car, and it's up to the driver to pick the fastest setup for their driving style and course layouts).

Wow, thank you so much for the detailed explanation. This makes total sense to me now. I didn't know that there are three different kinds of oversteer, knowing what they are and their differences explains why there's throttle off oversteer and power slides. I'm convinced I want to move to a RWD platform even though it still scares me a bit. Spinning out and not being able to control the oversteer is traumatic for me. I've spun out more times than I can remember in my old E30 years before I started tracking and kinda stayed away from RWDs. I think I'm ready to track a RWD.  Now its just a matter of whether or not I can find a decently priced one considering crazy price increases of everything or be on the look out. 

Thanks again for your insight, BRZ4Science.  

  

 

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