Lift-Off Oversteer w/ Lightweight Flywheel? (New Bench Racing BS Inside!) - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Suspension, Brakes, Drivetrain discuss the wondrous effects of boost and your miata...

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 05-13-2010, 10:50 AM   #1
Elite Member
Thread Starter
 
Join Date: Dec 2008
Location: Colorado
Posts: 1,669
Total Cats: 36
Default Lift-Off Oversteer w/ Lightweight Flywheel? (New Bench Racing BS Inside!)

So as the title states, would having a lighter rotational assembly lessen, worsen, or not affect a cars tendency to transition into oversteer if the drivers lifts a bit mid-corner? Would the transition be more gradual one way or another?

My thinking is this: When you lift mid-corner, you are taking weight off the rears because the car will naturally want to decelerate. On top of that, you are probably at relatively high RPM, and the engine is going to naturally want to decrease revs. You are more or less doing a bit of engine breaking similar to down shifting though not as powerful. So less weight on the rears coupled with engine breaking means they cont hold traction since they are already working for grip to keep the *** end of the car from just plowing ahead.

So if you lower the mass of the rotational assembly (with a lighter flywheel or a cut crank or rods/pistons etc) then you have an engine that will change RPM quicker when free reving, but also be less of a drag in things like down shifting. I noticed on my last car that going from stock 19Lb or so flywheel to a 11Lb unit meant that I did not get quite so much deceleration from down shifting.

So I suspect that this lower inertia means that the engine will actually be less likely to hold revs up against aero and rolling friction forces with 0% throttle. Basically a 30Lb weight spinning will store more energy than a 10Lber. So the 30Lber will hold speed longer against a friction force than the 10Lber.

So (breathes) the car with the lighter rotational assembly will actually decelerate harder without maitenance throttle mid corner and that might actually result in less weight on the rears/more transfer to the fronts.

Does a lighter flywheel make lift-off oversteer more likely as a result?

This is why I shoudl not wake up at 3:30 and drink strong coffee.
Sparetire is offline   Reply With Quote
Old 05-13-2010, 11:37 AM   #2
Senior Member
iTrader: (18)
 
Join Date: May 2008
Location: Big Bear Ca
Posts: 990
Total Cats: 8
Default

I love waking up to this kind of question.

From my highly unscientific mind, this sounds entirely logical. But how much of an affect? Dunno. Do you have a dataloger, skid pad near your home, and tons of time on your hands?
dstn2bdoa is offline   Reply With Quote
Old 05-13-2010, 12:20 PM   #3
Elite Member
iTrader: (12)
 
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 6,868
Total Cats: 66
Default

Yeah I don't think it'll make much of a difference.
Doppelgänger is offline   Reply With Quote
Old 05-13-2010, 12:57 PM   #4
Elite Member
iTrader: (8)
 
Join Date: Dec 2008
Location: Kingston, Ontario
Posts: 2,791
Total Cats: 71
Default

it could be my tune, but i have a bit of a bump in the driving when going from 0 to 5% or the inverse of that when cruising... it seems to be less noticable when driving hard, but its still there.

Everything is tight and new except my trans.
shlammed is offline   Reply With Quote
Old 05-13-2010, 01:33 PM   #5
Newb
 
Join Date: Apr 2010
Posts: 15
Total Cats: 0
Default

With a lightweight flywheel the engine will be able to change speeds more quickly than before thanks to rotational inertia.

So in theory, the car's deceleration should be greater with a lightened flywheel and thus bring more weight forward upon complete release of the gas pedal.

In theory... I can't say one way or another if there's a real-world difference. I have a lightweight flywheel and the only time I notice it is if I'm shifting lackadaisically and the engine revs drop further than is needed for the next gear
JGard is offline   Reply With Quote
Old 05-13-2010, 01:46 PM   #6
Elite Member
iTrader: (1)
 
Join Date: May 2009
Location: Jacksonville, FL
Posts: 4,682
Total Cats: 216
Default

Lightweight flywheel causes insane oversteer because it takes weight off the front.
Just like a turbo kit causes INSANE understeer because it puts weight on the front.

/Hyper logic
Full_Tilt_Boogie is offline   Reply With Quote
Old 05-13-2010, 01:59 PM   #7
Elite Member
Thread Starter
 
Join Date: Dec 2008
Location: Colorado
Posts: 1,669
Total Cats: 36
Default

Quote:
Originally Posted by dstn2bdoa View Post
I love waking up to this kind of question.

From my highly unscientific mind, this sounds entirely logical. But how much of an affect? Dunno. Do you have a dataloger, skid pad near your home, and tons of time on your hands?
Time? Check.
Place to test? Check.
Car? Not so check. Hence the time.

Quote:
Originally Posted by Full_Tilt_Boogie View Post
Lightweight flywheel causes insane oversteer because it takes weight off the front.
Just like a turbo kit causes INSANE understeer because it puts weight on the front.

/Hyper logic
Iz true! oh noes!
Sparetire is offline   Reply With Quote
Old 05-13-2010, 04:59 PM   #8
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

I think the closed-throttle engine compression has a far stronger braking effect than the lighter flywheel, so the effect on lift-throttle oversteer will be negligible. Maybe in 1st gear it might be noticeable, in the same way acceleration may be noticeably better in 1st.
JasonC SBB is offline   Reply With Quote
Old 05-13-2010, 06:03 PM   #9
Elite Member
iTrader: (8)
 
Join Date: Dec 2008
Location: Kingston, Ontario
Posts: 2,791
Total Cats: 71
Default

Jason, would the effects of engine compression not be more noticable in extreme cases?

I know my car in 3rd and even 4th you can feel the transition quite clearly.
shlammed is offline   Reply With Quote
Old 05-13-2010, 06:38 PM   #10
Elite Member
iTrader: (4)
 
Join Date: Sep 2006
Location: Charlotte, NC
Posts: 3,049
Total Cats: 4
Default

Non-issue because you shouldn't be lifting off of the throttle mid-corner.
Efini~FC3S is offline   Reply With Quote
Old 05-13-2010, 06:53 PM   #11
Elite Member
iTrader: (8)
 
Join Date: Dec 2008
Location: Kingston, Ontario
Posts: 2,791
Total Cats: 71
Default

but its fun to oversteer.
shlammed is offline   Reply With Quote
Old 05-13-2010, 10:07 PM   #12
Elite Member
Thread Starter
 
Join Date: Dec 2008
Location: Colorado
Posts: 1,669
Total Cats: 36
Default

Quote:
Originally Posted by JasonC SBB View Post
I think the closed-throttle engine compression has a far stronger braking effect than the lighter flywheel, so the effect on lift-throttle oversteer will be negligible. Maybe in 1st gear it might be noticeable, in the same way acceleration may be noticeably better in 1st.

You are probably right. And too true that liftoff should not be happening anyway. I know I will be getting a lighter flywheel when I do a clutch, so really its more intelectual than anything.
Sparetire is offline   Reply With Quote
Old 05-13-2010, 10:21 PM   #13
Senior Member
iTrader: (23)
 
Join Date: Oct 2009
Location: Chatsworth, SoCal
Posts: 948
Total Cats: 1
Default

Quote:
Originally Posted by Efini~FC3S View Post
Non-issue because you shouldn't be lifting off of the throttle mid-corner.
I don't agree there are sometimes when you actually need to do so. This is called throttle stearing my friend. If and when done correctly it is quite a valuable tool to haev in your bag. Although you don't want to get out 100%. Just a little.

Have a great day,
Jared
Jfornachon is offline   Reply With Quote
Old 05-13-2010, 10:50 PM   #14
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

If it oversteers too much on corner entry either put a smaller sway bar on or talk to your doctor about testosterone gel.
hustler is offline   Reply With Quote
Old 05-13-2010, 11:42 PM   #15
Elite Member
Thread Starter
 
Join Date: Dec 2008
Location: Colorado
Posts: 1,669
Total Cats: 36
Default

The non-***** mod is the most important without a doubt. Not a problem anyway, my natural tendency is to try to mash the throttle to get out of anything bad anyway. Which is how I wheel hopped my way to driving a 100 and nothing HP pickup right now.
Sparetire is offline   Reply With Quote
Old 05-14-2010, 01:06 PM   #16
Elite Member
iTrader: (4)
 
Join Date: Sep 2006
Location: Charlotte, NC
Posts: 3,049
Total Cats: 4
Default

Quote:
Originally Posted by Jfornachon View Post
I don't agree there are sometimes when you actually need to do so. This is called throttle stearing my friend. If and when done correctly it is quite a valuable tool to haev in your bag. Although you don't want to get out 100%. Just a little.

Have a great day,
Jared
Thank you for that, how enlightening. I know what throttle steering is. I also know that if you're lifting mid-corner you have already blown the corner because you suck. There's a big difference between making slight throttle corrections throughout the corner to change slip angles and completely lifting off the throttle and inducing oversteer.
Efini~FC3S is offline   Reply With Quote
Old 05-17-2010, 04:29 PM   #17
Newb
 
Join Date: Apr 2010
Posts: 15
Total Cats: 0
Default

unless you're an an AutoX, where I've found throttle steering to be the majority of how I make my way around a course...especially some of the tighter sections.
JGard is offline   Reply With Quote
Old 05-17-2010, 04:34 PM   #18
Elite Member
iTrader: (1)
 
Join Date: May 2009
Location: Jacksonville, FL
Posts: 4,682
Total Cats: 216
Default

*facepalm*

You never let out of the throttle all at once, thats not "throttle steering", that is called being a *****, and it makes this happen:
Full_Tilt_Boogie is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Twitchy car (tail happy problem) bigben Race Prep 16 09-11-2015 04:41 PM
Open diff issues on right hand turns Seefo Race Prep 22 07-26-2015 10:42 PM
What did i just get myself into?!?! (bought a former ice racer) Rocwandrer Meet and Greet 14 07-03-2012 01:48 PM
My official de-noob post Zoot Meet and Greet 3 04-13-2012 04:14 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 03:33 PM.