how does scrub radius and track width affect handling: any experts??
09-25-2014, 02:14 PM
#11
What about contact patch?
05-04-2015, 12:34 AM
#12
Bringing this one back from the dead because I've been researching track and scrub recently, and frankly, I think the info in this thread is dead wrong and it only takes a few minutes with a dynamics calculator to show why. In all my research across many boards and blogs, I see two kinds of statements: "Well, I think increasing rear track should increase push, cause I just think so" and "I have done the math, and increasing rear track decreases push."
I realize many people actually say "increasing track increases grip on the same axle." That's technically a correct statement but is very misleading. Increasing track on either axle decreases weight transfer on both axles, but primarily does so on the OPPOSITE axle. Increasing rear track width increases overall grip everywhere, but changes the balance towards OVERsteer, not understeer, because the majority of added grip is added to the front, not the rear. Pop some S2000-estimate figures into a dynamics calculator, change the front or rear track and see what happens to weight transfer.
If you want an extreme real-world example, look at the Morgan 3-wheeler. That car has a wide front track, zero rear track, and is the definition of UNDERsteer. It's also why many supercars and race cars run wider front tracks, to help put the power down at the rear on corner exit.
It's even common sense when you stop and just think about it. Widening track causes the outside tire on that end to load up more than the outside at the other end. As we all know from springs and sways, increased loading on one end means grip improves on the opposite end.
I realize many people actually say "increasing track increases grip on the same axle." That's technically a correct statement but is very misleading. Increasing track on either axle decreases weight transfer on both axles, but primarily does so on the OPPOSITE axle. Increasing rear track width increases overall grip everywhere, but changes the balance towards OVERsteer, not understeer, because the majority of added grip is added to the front, not the rear. Pop some S2000-estimate figures into a dynamics calculator, change the front or rear track and see what happens to weight transfer.
If you want an extreme real-world example, look at the Morgan 3-wheeler. That car has a wide front track, zero rear track, and is the definition of UNDERsteer. It's also why many supercars and race cars run wider front tracks, to help put the power down at the rear on corner exit.
It's even common sense when you stop and just think about it. Widening track causes the outside tire on that end to load up more than the outside at the other end. As we all know from springs and sways, increased loading on one end means grip improves on the opposite end.
04-20-2016, 01:59 PM
#13
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thomsbrain is correct...with a Mac Strut. The S2000 utilizes an SLA set up, correct? So if the spring and damping rates are corrected with wider track (motion ratio) then thomsbrain is still correct.
Increasing front track width increases initial turn-in understeer but improves steady state. All of the potential downsides to increasing track width, kick back, scrub radius, potential increase in bearing wear, less mechanical leverage i=on tie rods etc are correct...
Increasing rear track in theory increases initial turn-in oversteer but improves steady state at the back end.
My car is driven via the front wheel...increasing front track has proved to be an asset after weighing all of the variables. I also increased rear track but by less. I had to compensate by adding in a bit more neg camber...the increase led to less camber and toe compensation.
But as was written, drive it and see... I increased the front track on my 2006 JCW Mini 22mm per side and 12mm per side rear. The results were very nice...I imagine by feel, because I did not test this, that this set up may have ruined outright slalom performance...guessing that too much width is bad.
Increasing front track width increases initial turn-in understeer but improves steady state. All of the potential downsides to increasing track width, kick back, scrub radius, potential increase in bearing wear, less mechanical leverage i=on tie rods etc are correct...
Increasing rear track in theory increases initial turn-in oversteer but improves steady state at the back end.
My car is driven via the front wheel...increasing front track has proved to be an asset after weighing all of the variables. I also increased rear track but by less. I had to compensate by adding in a bit more neg camber...the increase led to less camber and toe compensation.
But as was written, drive it and see... I increased the front track on my 2006 JCW Mini 22mm per side and 12mm per side rear. The results were very nice...I imagine by feel, because I did not test this, that this set up may have ruined outright slalom performance...guessing that too much width is bad.
04-20-2016, 06:05 PM
#14
I'd like to comment one the centerpoint steering thing as mentioned above. Supposedly *some* scrub radius increases steering feel. Although there are a lot of (interdependent) variables to consider.
07-15-2016, 12:46 PM
#15
Kinda bringing this back from the dead.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-size.com/calc/?whee...cl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-size.com/calc/?whee...cl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
07-15-2016, 05:28 PM
#16
You get wider track and more grip, so you create a bit of understeer and tram lining but you more than make up for it with extra grip and a wider track. Just keep it within reason and you should be ok.
07-16-2016, 08:10 PM
#17
Kinda bringing this back from the dead.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-size.com/calc/?whee...cl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-size.com/calc/?whee...cl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
07-16-2016, 10:59 PM
#18
It sounds like you are assuming that the factory setup has a zero scrub radius, this may or may not be true as I have never measured it. I would say that increasing scrub radius a small amount, in the ~1/2" range you're talking about, is not that big of a deal. Remember, more scrub radius can help add steering feel and weight, as well as slightly increase self-centering. Also keep in mind that running those tire widths with those offset will likely require a lot of camber on a lowered car with stock fenders. This extra camber will move the center of the contact patch in a little bit and reduce your "effective" scrub radius.
07-17-2016, 10:56 AM
#19
Originally Posted by LemonJus' timestamp='1468615615' post='24017562
Kinda bringing this back from the dead.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-siz...wcl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-siz...wcl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
07-18-2016, 02:03 AM
#20
The scrub radious is not modified by just adding more or less camber. The imaginary line drawn between the top and bottom joints of the upright moves exactly the same as the wheel angle. Only might affect very slightly (not even suspension software model it sometimes) is because the contact patch might move towards the centre of the car when you add more camber...
I have increased the track width on my car drastically with new fenders and I am doing some suspension analysis and plan to use some custom-made brackets to bring the scrub radious back in (9" et29)
It sounds like you are assuming that the factory setup has a zero scrub radius, this may or may not be true as I have never measured it. I would say that increasing scrub radius a small amount, in the ~1/2" range you're talking about, is not that big of a deal. Remember, more scrub radius can help add steering feel and weight, as well as slightly increase self-centering. Also keep in mind that running those tire widths with those offset will likely require a lot of camber on a lowered car with stock fenders. This extra camber will move the center of the contact patch in a little bit and reduce your "effective" scrub radius.
I have increased the track width on my car drastically with new fenders and I am doing some suspension analysis and plan to use some custom-made brackets to bring the scrub radious back in (9" et29)
Originally Posted by LemonJus' timestamp='1468615615' post='24017562
Kinda bringing this back from the dead.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-siz...wcl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.
I've been doing a lot of research lately on running a square setup and playing around with various calculators on how each aftermarket wheel affects my suspension geometry and this thread along with the "Wheel Fitment" thread has been uber helpful.
Here's my conundrum - most if not all non-OEM wheels have very low offset. The usual reliable suspects like RPF01s, TE37s, etc. only have about +45mm offset.
Using the calculator here to figure out how things will play out inside my wheel, it seems it will create a positive scrub radius thus adding to understeer: http://www.wheel-siz...wcl=30mm&sr=0mm
The question is, by going square, I'm adding a WHOLE lot more rubber up front (255/40/17 all round vs the OEM 215/45 up front) which should negate the understeer from the positive scrub right?
My brain hurts.