Rake: Is it that important?
03 January 2004, 09:51 AM
#1
I have an STi V3 with ALL the Whiteline parts and some demon MRT parts too. The suspension was set-up by Ralliart to radical Whiteline settings. The car is driven on the road and hill climb competition.
The Car sits flat to the road, no nose-down rake which the P1 has for instance.
Question; It is beneficial to dial in say a 1 deg nose down rake?
I have a race set hill climb 911 which MUST have a 1 deg rake to balance the very stiff suspension/chassis. Very different cars, but what about the Scooby?
Graham.
The Car sits flat to the road, no nose-down rake which the P1 has for instance.
Question; It is beneficial to dial in say a 1 deg nose down rake?
I have a race set hill climb 911 which MUST have a 1 deg rake to balance the very stiff suspension/chassis. Very different cars, but what about the Scooby?
Graham.
Well done Graham. we just need Webby to be around to see this now...
03 January 2004, 01:32 PM
#3
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intresting question which i will be following
my coilover kit came from a jap import, i did not touch the settings, just swapped it over and it sits with a nose down rake
i think the car they were removed from was a track car (all the parts like cusco bars and stuff and compleatly batterd and unloved bodywork
)
my coilover kit came from a jap import, i did not touch the settings, just swapped it over and it sits with a nose down rake
i think the car they were removed from was a track car (all the parts like cusco bars and stuff and compleatly batterd and unloved bodywork
)
03 January 2004, 07:25 PM
#4
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certainly set our rally cars with a 10mm nose down rake..........very un-nerving handling if its flat or ar** down!!!
applies to most cars to be fair.........
alyn - asperformance.com
applies to most cars to be fair.........
alyn - asperformance.com
03 January 2004, 07:38 PM
#5
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How do you know then if you Subaru has positive (nose down) or negative (nose up) rake ?
I have measured the ride heights : 345mm front and back (taken from the centre of the wheel till the fender above...)
Creepy
[Edited by Creepy - 1/3/2004 7:40:09 PM]
I have measured the ride heights : 345mm front and back (taken from the centre of the wheel till the fender above...)
Creepy
[Edited by Creepy - 1/3/2004 7:40:09 PM]
04 January 2004, 12:18 PM
#6
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Graham
Altering rake has corner weight and aerodynamic implications
You may introduce some positive rake to put a little more weight over the front of the car, and improve air flow under it
Would an under body tray be legal in your class ?
Altering rake has corner weight and aerodynamic implications
You may introduce some positive rake to put a little more weight over the front of the car, and improve air flow under it
Would an under body tray be legal in your class ?
04 January 2004, 03:54 PM
#7
I can do anything in the class except change the side profile, move the engine position or change the suspension pick up points.
My STi drives well enough as it is, all level, but can I get more grip by adding rake?
Graham.
My STi drives well enough as it is, all level, but can I get more grip by adding rake?
Graham.
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04 January 2004, 07:12 PM
#8
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911,
Did you check out this thread, as suggested by Fat Boy previously?
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=198864
A careful read should reveal all
Creepy,
According to numbers supplied by Whiteline, your car should have ~17 mm of forward (positive) rake - 345mm front and 328mm rear being level on a Classic.
John
[Edited by superstring - 1/4/2004 7:14:04 PM]
Did you check out this thread, as suggested by Fat Boy previously?
http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=198864
A careful read should reveal all
Creepy,
According to numbers supplied by Whiteline, your car should have ~17 mm of forward (positive) rake - 345mm front and 328mm rear being level on a Classic.
John
[Edited by superstring - 1/4/2004 7:14:04 PM]
05 January 2004, 11:20 PM
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I have 345 mm on 4 wheels so that will be safe then...
And a rake of 34mm...
And a rake of 34mm...
No, you only have a forward rake of 17mm, meaning that the rear of the car (measured at some point on the floor pan, I imagine) is 17mm higher than the front. If you put a carpenter's level on either rocker panel (not sure if you use that term
), you should see that the car slopes forward slightly.As far as being "safe", you might want to read John Felstead's post from this thread:
http://www.scoobynet.co.uk/bbs/thread.asp?threadid=285997
I think he sums it up pretty well.
John
06 January 2004, 08:48 PM
#14
They were based in Merrit, but we covered 850Km over two days on each rally, so covered a large area of central BC. It's a rally held every February, great fun. http://www.rallybc.com/archives/Tbird_home.htm If you fancy a play in the snow it's worth entering, they have classes for novices and you can do this in a normal road car. 2001 we had a stage on a frozen lake, which was "interesting" 
This is me and Jamie on the 2002 event.
and on the 2001
This is me and Jamie on the 2002 event.
and on the 2001
07 January 2004, 01:46 AM
#16
Hi Guys
Sorry for the delay, only just noticed this.
In answer to the original question (apologies if it's moved on, haven't had a chance to read the whole thread)...
Firstly.. Whether the handling effects of rake are good or bad (as most things in suspension geometry) is subjective depending on the driver.
The main things (by main, I mean just the things that have a dramatic and critical affect on the handling of the car) you are affecting when changing ride heights are :
c/g height
roll centre height
distance between roll centre and c/g height
roll axis (angle of a straight line between rear and front roll centres)
c/g axis (as above for c/g)
u/b aerodynamics
This means there is a whole hill of stuff changing when you make these adjustments. But..
There are no circumstances that I can think of where negative rake would be a good thing for performance.
Almost always a little bit of rake is beneficial to a competition car, and scoobies tend to work well with a bit of rake (maybe 10 - 15mm lower at the front? - experiment and test for best results).
What should it do (usual disclaimer - you never know for sure until you've tested it, but the following is likely)?
Less understeer / more oversteer
Slightly more snappy rear end
Possibly slightly reduced turn-in bite "feel" - (although you'll get used to this and realise it's actually working better - it just feels odd)
In addition, the mere fact that you're messing about with so many critical geometry settings means that you could end up with some very odd handling so testing is a must.
Cheers
Simon
Sorry for the delay, only just noticed this.
In answer to the original question (apologies if it's moved on, haven't had a chance to read the whole thread)...
Firstly.. Whether the handling effects of rake are good or bad (as most things in suspension geometry) is subjective depending on the driver.
The main things (by main, I mean just the things that have a dramatic and critical affect on the handling of the car) you are affecting when changing ride heights are :
c/g height
roll centre height
distance between roll centre and c/g height
roll axis (angle of a straight line between rear and front roll centres)
c/g axis (as above for c/g)
u/b aerodynamics
This means there is a whole hill of stuff changing when you make these adjustments. But..
There are no circumstances that I can think of where negative rake would be a good thing for performance.
Almost always a little bit of rake is beneficial to a competition car, and scoobies tend to work well with a bit of rake (maybe 10 - 15mm lower at the front? - experiment and test for best results).
What should it do (usual disclaimer - you never know for sure until you've tested it, but the following is likely)?
Less understeer / more oversteer
Slightly more snappy rear end
Possibly slightly reduced turn-in bite "feel" - (although you'll get used to this and realise it's actually working better - it just feels odd)
In addition, the mere fact that you're messing about with so many critical geometry settings means that you could end up with some very odd handling so testing is a must.
Cheers
Simon
07 January 2004, 07:41 PM
#17
Thanks for the tech stuff Simon!
I messed about with my 911 in my early days of sprinting and hill climbing, and too much rake resulted in evil roll oversteer. The 911 is very weird on the 'edge' and needs an equally novel approach to catch in time(!)but getting to 1 degree is spot-on(nose down), but the suspension is very stiff and body roll almost non existant. My 911 is only 60 mm off the deck!
This weekend i'm going to sift through all this excellent detail and summarise what to try first. I know that my Sti sits level and i can get understeer sometimes even with 2.5 deg neg AND 4 deg caster to kill it off. Maybe a dose of rake will trim it in as I had to do with the 911.
All this is with Kumho v70's, and I will be on crossply slicks this season, have I just opened another can of worms?????
Great thread, adds huge value to the Scoobynet as I know a lot of enthusiasts follow these subjects.
Keep it coming.
Graham.
I messed about with my 911 in my early days of sprinting and hill climbing, and too much rake resulted in evil roll oversteer. The 911 is very weird on the 'edge' and needs an equally novel approach to catch in time(!)but getting to 1 degree is spot-on(nose down), but the suspension is very stiff and body roll almost non existant. My 911 is only 60 mm off the deck!
This weekend i'm going to sift through all this excellent detail and summarise what to try first. I know that my Sti sits level and i can get understeer sometimes even with 2.5 deg neg AND 4 deg caster to kill it off. Maybe a dose of rake will trim it in as I had to do with the 911.
All this is with Kumho v70's, and I will be on crossply slicks this season, have I just opened another can of worms?????
Great thread, adds huge value to the Scoobynet as I know a lot of enthusiasts follow these subjects.
Keep it coming.
Graham.
07 January 2004, 08:17 PM
#18
The main diference between Crossply's and Radials is the slip angles they run at. I used to run my Westfield on Crossply road legal slicks, which allowed me to run much higher slip angles before losing traction. The transition from on the limit grip and loss of traction is much smoother too, which makes them an excelent choice for hillclimbing where you are looking for relatively calm charicteristics.
If you do go down the crossply route you need to reduce the camber you run, 1 degree negative is pretty much the limit they can tolerate, at the rear i would aim for no more than 0.5 degrees, where as radials are much happier in 2-3 degrees of camber range.
If you do go down the crossply route you need to reduce the camber you run, 1 degree negative is pretty much the limit they can tolerate, at the rear i would aim for no more than 0.5 degrees, where as radials are much happier in 2-3 degrees of camber range.
07 January 2004, 08:36 PM
#19
Oh, I forgot about the geometry shift for the crossplys...Have been advised by BMTR about this, just forgot.
Friend of mine hill climbs a very tidy Cossie 2 WD and went to ACB10's, probably the tyres you had on your car John, and then to cross ply slicks. Never changed a thing and beat me....bast@rd.
I'm bothered now you have said this John, but you are right.Easy to fix mind and the first test hill climb weekend is in late march so tons of time.
Glad you told me!
Graham.
Friend of mine hill climbs a very tidy Cossie 2 WD and went to ACB10's, probably the tyres you had on your car John, and then to cross ply slicks. Never changed a thing and beat me....bast@rd.
I'm bothered now you have said this John, but you are right.Easy to fix mind and the first test hill climb weekend is in late march so tons of time.
Glad you told me!
Graham.
07 January 2004, 09:09 PM
#20
Yes, i ran ACB10's, brilliant tyre.
The other main consideration on crossply's is wheel rim width, you should at the very least have a rim as wide as the tyre, for example an 8/22x15 needs an 8-8.5" rim, 7/22x15 needs a 7-7.5" rim. With a radial you generally have a narrower rim than the tyre width.
Crossply's tend to be very much lighter than radials too, which improves response and reduces the gyroscopic effect of the wheel, all important in a sport where 10ths make a big diference in your results. Tyre presures are generally much lower with crosplys too, they seem to work best around 20psi on a lightweight car and maybe 25psi on something like a saloon.
The other main consideration on crossply's is wheel rim width, you should at the very least have a rim as wide as the tyre, for example an 8/22x15 needs an 8-8.5" rim, 7/22x15 needs a 7-7.5" rim. With a radial you generally have a narrower rim than the tyre width.
Crossply's tend to be very much lighter than radials too, which improves response and reduces the gyroscopic effect of the wheel, all important in a sport where 10ths make a big diference in your results. Tyre presures are generally much lower with crosplys too, they seem to work best around 20psi on a lightweight car and maybe 25psi on something like a saloon.
08 January 2004, 03:26 AM
#21
911, you're more than welcome.
One thing I would humbly suggest also is that you may want to have a closer look at your driving style? Obviously I have no idea how you drive, but a 911 and scooby couldn't be further apart in terms of handling characteristics and therefore the driving techniques to get them to work.
If driven like a RWD car, almost any scooby would understeer like mad. If you tuned this out, you would end up with a very slow car in comparrison to a well set-up scooby driven well.
Cheers
Simon
One thing I would humbly suggest also is that you may want to have a closer look at your driving style? Obviously I have no idea how you drive, but a 911 and scooby couldn't be further apart in terms of handling characteristics and therefore the driving techniques to get them to work.
If driven like a RWD car, almost any scooby would understeer like mad. If you tuned this out, you would end up with a very slow car in comparrison to a well set-up scooby driven well.
Cheers
Simon
08 January 2004, 12:38 PM
#23
hmmm.. good question.
I know that Don Palmer has huge experience in 4WD limit handling coaching, so he's worth a look - he's also world class in terms of driver coaching.
Not sure of actual specialists.. but always beware.. look for reputation, and recomendation from people you are SURE know what they're talking about.
Cheers
Simon
I know that Don Palmer has huge experience in 4WD limit handling coaching, so he's worth a look - he's also world class in terms of driver coaching.
Not sure of actual specialists.. but always beware.. look for reputation, and recomendation from people you are SURE know what they're talking about.
Cheers
Simon
08 January 2004, 05:56 PM
#24
Just back from the Autosport Show today. Think i have found the right slick on the Avon stand now. Take your point about the width. Tried an 8.5 x 16 x 23.3 Avon on a 7 inch rim, would not even go on the rear hub of my STi. I think these slicks will need to be about 7 inches wide to get under the arches...
I once emailed Bill Gwynneth and his rally school about learning 4x4 control, but they never responded. I think for hill climbs you need a good airfield to yourself, mark out some typical curves and go for it! A sideways moment or 4 will be harmless.
I have a suitable place in mind!
911 to STi? I think you are dead right about my driving 'style'. Nine years racing a 911 teaches you something that is useless for anything else! Must try some different ideas, 'slow-in-fast-out' (911) does not work.
Bloody cars.
Graham.
I once emailed Bill Gwynneth and his rally school about learning 4x4 control, but they never responded. I think for hill climbs you need a good airfield to yourself, mark out some typical curves and go for it! A sideways moment or 4 will be harmless.
I have a suitable place in mind!
911 to STi? I think you are dead right about my driving 'style'. Nine years racing a 911 teaches you something that is useless for anything else! Must try some different ideas, 'slow-in-fast-out' (911) does not work.
Bloody cars.
Graham.
09 January 2004, 03:51 PM
#25
I think learning to drive a 911 is a very good basis for an Impreza, it teaches you some fundementals such as the effect of lift off oversteer in a very obvious manner.
I would do as you suggest, find an airfield and go play.
You probably didnt get a reply because his name is Bill Gwynne. LOL
I would do as you suggest, find an airfield and go play.
You probably didnt get a reply because his name is Bill Gwynne.
LOL
09 January 2004, 06:22 PM
#26
Lift-off-oversteer, now there are some memories. I fitted a 6 point roll cage after my first experience in my 911....
It's that return of the tail when the back grips...if opposite lock is not already there you have NO chance of catching it!
Graham.
It's that return of the tail when the back grips...if opposite lock is not already there you have NO chance of catching it!
Graham.
10 January 2004, 12:22 AM
#28
Graham,
I'm at Bill Gwynne's tomorrow to play in his grp N impreza's - on gravel though.I was also with Ian Gwynne today at the Autosport show and he and his brothers are normally very happy to do just what you requested. Why not give them a ring and speak to them, they're all nice guys. Ian looks after the motorsport side (and test drives for WRC teams or did until Hyundai went **** up)but he also does the serious coaching for motorsport - he's taking my friend and his Grp N impreza (which they run in the Kumho/ BTRDA championship for him) up to Cheshire next week for some loose and tarmac coaching, Pete runs the rally school, and Paul does the marketing etc. Daddy Bill is currently out in the Sahara driving back up for McRae etc in the works Nissan team.
Aside from them, Don Palmer and his National Performance Academy, as Simon mentions above, gets a thumbs up - I had a great day at Bruntingthorpe with him a while back and it made a big difference
Cheers
J
I'm at Bill Gwynne's tomorrow to play in his grp N impreza's - on gravel though.I was also with Ian Gwynne today at the Autosport show and he and his brothers are normally very happy to do just what you requested. Why not give them a ring and speak to them, they're all nice guys. Ian looks after the motorsport side (and test drives for WRC teams or did until Hyundai went **** up)but he also does the serious coaching for motorsport - he's taking my friend and his Grp N impreza (which they run in the Kumho/ BTRDA championship for him) up to Cheshire next week for some loose and tarmac coaching, Pete runs the rally school, and Paul does the marketing etc. Daddy Bill is currently out in the Sahara driving back up for McRae etc in the works Nissan team.
Aside from them, Don Palmer and his National Performance Academy, as Simon mentions above, gets a thumbs up - I had a great day at Bruntingthorpe with him a while back and it made a big difference
Cheers
J
10 January 2004, 08:08 AM
#29
J, thanks for that! You obviously know what I need to get out of my nasty 911 habits and to drive this STi thing I have!
J Felstead has reccommended much the same thing. I was planning on hiring Elvington for a morning and try to get my head around the car there. to have some one who realy knows the tricks speeds up the learning no end.
Thanks for the info, Regards, Graham.
J Felstead has reccommended much the same thing. I was planning on hiring Elvington for a morning and try to get my head around the car there. to have some one who realy knows the tricks speeds up the learning no end.
Thanks for the info, Regards, Graham.