Steering geometry question
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default Steering geometry question

    I've just removed my steering rack and decided to drop the car back down onto some turntables.

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    Immediately the wheels went into a state of massive toe in.

    Should the road wheel sit more or less straight ahead with no steering attached??

    I think I'll undo the mods I've made and see what difference it makes, But I curious to what should happen.


    Jo

  2. #2
    1000+ Posts Kim Luck's Avatar
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    A combination of steering axis, castor and camber, do you think? The wheels aren't usually pointing straight ahead and dead vertical with the steering axis also dead vertical to the road on any car.
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    1000+ Posts daffyduck's Avatar
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    I would spin the car around the block to make the suspension settle and then put it back on the turn tables.

    Via the aussiefrogs App

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    1000+ Posts schlitzaugen's Avatar
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    The weight of the car is trying to push down as far as possible and because of the caster angle, the wheels allow the chassis to go lower when toed in. Remember when you turn the wheel around a corner, the wheel inside the corner is effectively lifting the car because of the caster angle. That is what the weight of the car is fighting and now because there is no rack to keep the wheel where it wants to be, it will push a little bit further down than when the rack is attached giving a more pronounced toe in. Totally normal, leave things alone (if when rack is attached geometry is fine).
    Kim Luck likes this.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by daffyduck View Post
    I would spin the car around the block to make the suspension settle and then put it back on the turn tables.

    Via the aussiefrogs App
    That will be fun without a steering rack.


    Jo

  6. #6
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by schlitzaugen View Post
    ...Totally normal, leave things alone (if when rack is attached geometry is fine).
    Nah, geometry is not fine.
    Its deviated far enough from standard that standard spec is irrelevant, and my alighnment guy needs to basicly make it up as he goes along.
    Longer lower control arms fitted and about -3 degrees camber.
    It bites like a slot car, but has issues with putting the power down. The car is a fair bit more powerfull than standard too so that doesn't help.
    I guess steering geometry is a compromise between cornering and straight line stability, and mine is heavily biased to cornering, which is a bit silly because the fuego corners well anyhow and has power down and braking issues at the best of times.

    Jo

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    1000+ Posts schlitzaugen's Avatar
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    Be careful with too much camber (and 3 deg can be too much) because this affects everything else. The contact patch, scrubbing radius, and so on. You might be giving away more than gaining at some point. Keep in mind on cornering suspension is deflected too, so things change again and not necessarily for the better.

    Racing R/C cars (keep in mind that in R/C a small change has a huge effect) I found that cambered rear wheels help more with speed going around corners than front wheels, but our cars are AWD. One degree made a huge difference. In FWD cars, having a really tight diff is more important, so I would suggest your problem might be more easily cured with an LSD of some designation. Real cars have gone that way a while ago (RS Meganes and others have LSDs). I don't know what to recommend, in R/C you can just tighten your ball diff to the nth degree until it becomes a solid axle.

    I guess my point is that camber should be a last resort rather than a first port of call. Toe in-out settings should be explored first (after transmission settings - i.e. diff bias and suspension settings have been decided on).
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

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    1000+ Posts Kim Luck's Avatar
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    If I could afford one on any car, this is what I'd have.....

    Torsen Products Page
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    Quote Originally Posted by jo proffi
    It bites like a slot car, but has issues with putting the power down. The car is a fair bit more powerfull than standard too so that doesn't help.
    After driving my Fuego with 30psi getting shoved through it I can pretty confidently say you have no idea what it is to have 'issues' with traction on a fuego

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    1000+ Posts daffyduck's Avatar
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    Quote Originally Posted by jo proffi View Post
    That will be fun without a steering rack.


    Jo
    D'oh!

    Via the aussiefrogs App

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    I'd also be picking that the camber is the main issue. You can keep the oem lower arm and slot the upper arm ball joint holes to give it a little bit negative camber (0.5 - 1 degree)

    Also, if you run a few degrees more caster you will get more negative camber once the car is turned (which is when you need it more).

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    Quote Originally Posted by schlitzaugen View Post
    The weight of the car is trying to push down as far as possible and because of the caster angle, the wheels allow the chassis to go lower when toed in. Remember when you turn the wheel around a corner, the wheel inside the corner is effectively lifting the car because of the caster angle. That is what the weight of the car is fighting and now because there is no rack to keep the wheel where it wants to be, it will push a little bit further down than when the rack is attached giving a more pronounced toe in. Totally normal, leave things alone (if when rack is attached geometry is fine).
    a technical point nicely explained

    cheers! Peter

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    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by Kim Luck View Post
    If I could afford one on any car, this is what I'd have.....

    Torsen Products Page

    Torsens are usually on the rear of AWD cars. Probelm is, if one wheel loses traction, then all of the torque is lost on that wheel because then the torsen behaves like an open diff. I think the best for a FWD car is a Quaife, but you have to be careful what bias you choose.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

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    1000+ Posts Kim Luck's Avatar
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    I was under the probably mistaken impression that the RS 265 had a version of the Torsen diff. Am I mistaken?

    http://www.torsen.com/files/Torsen%2...al%20Sheet.pdf

    Whatever, this clever piece of machining can be applied to front wheel drive, rear wheel drive and the centre diff on an open centre diff like a gland rover. It is based on mathematical equations which are a little above my head however if you've seen them work, you'll know why there is nothing better. If you were born after 1988, it was invented in your lifetime!

    P.S: I was born before 1988.
    Last edited by Kim Luck; 8th July 2013 at 01:17 AM.
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by 4cvg View Post
    a technical point nicely explained

    cheers! Peter
    Yes, thank you schlitzaugen.

    I'm starting to really understand the effects of castor on tracking now, and your explanation has helped make it clearer.

    I downloaded a neat angle gauge app for my phone yesterday and spent a while just rocking the wheel back and forward to observe its travel.
    The mods will come off and today I'll fit the OE suspension which will return the car to regular geometry.

    Jo

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    Hi Still having trouble with the format here. Not wishing to hijack the thread either but I was surprised to see Kim say the torsen was invented in 1988. Not so It may have been revised, bought out or ?? But according to the site; http://www.torsen.com/files/Gleason%...del%20List.PDF the oldest listed application of the Gleason torsen is for a 1947 Jeep CJ series. I too was born before 1988 Jo, All front geometry relies on balancing the steering forces on one wheel by the opposing wheel. Only a simple castor will track straight without any other input. Jaahn
    Quote Originally Posted by Kim Luck View Post
    I was under the probably mistaken impression that the RS 265 had a version of the Torsen diff. Am I mistaken?
    http://www.torsen.com/files/Torsen%2...al%20Sheet.pdf
    Whatever, this clever piece of machining can be applied to front wheel drive, rear wheel drive and the centre diff on an open centre diff like a gland rover. It is based on mathematical equations which are a little above my head however if you've seen them work, you'll know why there is nothing better. If you were born after 1988, it was invented in your lifetime! P.S: I was born before 1988.

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    BVH Roger Wilkinson's Avatar
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    Quote Originally Posted by jaahn View Post
    All front geometry relies on balancing the steering forces on one wheel by the opposing wheel. Only a simple castor will track straight without any other input.
    All, that is, except for Citroen DS, GS and SM, which have centre point steering geometry where the pivot axis passes through the top and bottom centres of the wheels. You could lose a front wheel at highway speed and not feel anything.

    Roger

  18. #18
    1000+ Posts Kim Luck's Avatar
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    Quote Originally Posted by jaahn View Post
    Hi Still having trouble with the format here. Not wishing to hijack the thread either but I was surprised to see Kim say the torsen was invented in 1988. Not so It may have been revised, bought out or ?? But according to the site; http://www.torsen.com/files/Gleason%...del%20List.PDF the oldest listed application of the Gleason torsen is for a 1947 Jeep CJ series. I too was born before 1988 Jo, All front geometry relies on balancing the steering forces on one wheel by the opposing wheel. Only a simple castor will track straight without any other input. Jaahn
    Not the first time I've been mistaken, jaahn! I think Gleason invented the original Torsen diff in 1958 but the new series T-2 with "Invex" gearing and superior performance came out on '88. Through the years they have been fitted to just about anything that moves. My original link post#8 has a list of the different types.
    Don't it always seem to go that you don't know what you've got 'til it's gone............

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    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by mistareno View Post
    I'd also be picking that the camber is the main issue. You can keep the oem lower arm and slot the upper arm ball joint holes to give it a little bit negative camber (0.5 - 1 degree)

    Also, if you run a few degrees more caster you will get more negative camber once the car is turned (which is when you need it more).
    Surprisingly enough, in the world of (again) R/C cars we have a wide range of caster adjustability, but it turns out the more caster, the more sluggish the car is to react in cornering. Fast guys will always hover around zero caster or just one-two degrees.

    Keep in mind these cars pull completely unachievable G's around corners for a real car (not with a human at the wheel anyway).
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

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    Quote Originally Posted by schlitzaugen View Post
    Torsens <snip> Probelm is, if one wheel loses traction, then all of the torque is lost on that wheel because then the torsen behaves like an open diff.
    Not really what I understood about them. Yes if one wheel loses traction then all of the torque is lost on that wheel but it's transferred to the other wheel. Rather the opposite to an open diff where all of the torque goes to the wheel that's lost traction.

    cheers! Peter

  21. #21
    1000+ Posts schlitzaugen's Avatar
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    I think my explanation was a bit confusing. I meant the torque is lost through that wheel (the one with no traction). This is because of the straight cut "link" gears it incorporates between the "satellites" (see picture).

    http://www.miata.net/garage/Torsen-T1.jpg

    I guess more modern versions have gone sort of the way of the Quaiffe with helical gears everywhere which retains the torque bias regardless of wheels having traction or not. Perhaps this sort of makes it torque non-sensitive (as opposed to what the name implies).
    Last edited by schlitzaugen; 8th July 2013 at 10:13 PM.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

  22. #22
    1000+ Posts jo proffi's Avatar
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    I put the OE lower control arms back on today, and the front end seems a lot less weird.
    It still toes in on the turn tables when the weight is put on the wheels, but no where near as strongly as it did.
    Camber is back to close on 0 degrees. There goes the outside edge of my tyres.

    I took the time today to add some grease nipples to the urethane bushing and radially slot the sleeves below the nipples.
    Bought a grease gun and some nasty black grease and made a big mess of things.
    At least I can now lube the bushes without pulling the arms off.

    Its going to be a few weeks before the rack gets seen to (blown seal) so I'll probably add a nipple to the urathane caster rod bush too.
    For the first time in my life I'll be able to do a 'grease and oil change' instead of just changing the oil.

    Jo

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    Quote Originally Posted by jo proffi View Post
    I put the OE lower control arms back on today, and the front end seems a lot less weird.
    It still toes in on the turn tables when the weight is put on the wheels, but no where near as strongly as it did.
    Camber is back to close on 0 degrees. There goes the outside edge of my tyres.

    I took the time today to add some grease nipples to the urethane bushing and radially slot the sleeves below the nipples.
    Bought a grease gun and some nasty black grease and made a big mess of things.
    At least I can now lube the bushes without pulling the arms off.

    Its going to be a few weeks before the rack gets seen to (blown seal) so I'll probably add a nipple to the urathane caster rod bush too.
    For the first time in my life I'll be able to do a 'grease and oil change' instead of just changing the oil.

    Jo
    If you slot the ball joint holes of the top arms by about 5mm and slide the ball joint in you can get a bit of negative camber without adversely affecting anything else (obviously toe will need to be reset).

    As a matter of interest, what offset wheels are you running?

    I had a 7.5 inch wide 35 offset rims on the old car and the new ones are a 7 inch 40 offset.

    My old car had a noticeable (not savage) amount of tram-lining and wondering under braking with a 45 profile on a 16 inch rim, the current car has no tramlining at all and tracks really well even on a 40 profile tyre on a 17 inch rim.

    There are a few other changes (spring rates etc) but the geometry would be pretty similar between both cars.

    I have a feeling that the lower offset was enough to change the geometry from a slightly negative scrub radius to a slightly positive one?

  24. #24
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by mistareno View Post
    As a matter of interest, what offset wheels are you running?
    Its hard to tell without measuring them, but I'd say from looking at them on the car, about 35mm on a 7 inch rim. Scrub radius is clearly +.


    I agree about 40mm being a good offset for the front.

    jo

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    To make pushing it around easier get a piece of 1"angle and drill a hole at each end the same length as the TRE centres and fit to steering arms using good fitting bolts and nuts.

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