I have watched countless videos and read countless articles about bump steer (from proper race shops/engineers) but this is honestly one of the clearest explanations I've ever come across. The distance between the inner and outer pivot points growing smaller the further the tie rod is from parallel, and how this therefore causes changes in the toe angle, is a brilliant way to think of it. Seriously well explained dude!
Just a little tip for putting those tie-rods and rack ends together. Bit of copper slip or anti-seize will go a long way towards making your wheel aligner happy down the road as it'll prevent them from rusting into place with water ingress and keep them adjusting nicely in the future. Saves them from having to break out the blowtorch or giant pipe wrench to get them loose and potentially damaging them in doing so.
@@MotiveVideo Better safe than sorry, especially for the people at home, I deal with a lot of 4x4 stuff and more often than not, Everything is seized and a "delight" to adjust.
Excellent tech as usual mate 😎👌🏻 I'm glad you addressed the tie rods, as I have longer aftermarket ones that I've been advised to cut down to fit my anti bump steer rod ends. I feel more confident to be able to trim them down now. Keep up the great work as always.
Unfortunately you were only partially right. There is much more to geometry that changes, but what is desired is to have tie rods parallel to lower wishbone, so that complete wheel assembly moves in the same arc... otherwise like your content.
Not parallel, the kinematic force center needs to point at the instant center for zero bumpsteer. You need to take into account the upper control arm/strut/whatever you have as well. And in a dynamic situation, you need to take into account compliances.
It varies based on application but for “street/drag” we run -1 degree and 2mm total toe out up front with 5 degrees castor on the rear 2.5mm total toe in and -0.5 degrees neg camber
I have the same gktech tie rod ends, and ended up with the same adjustment problem. We used shortened z32 inner rods. I've got a terrible steering shake that I've tried everything to sort out. We just discovered play in the driver's side kingpin, so having that rebuilt at the end of the month to see if that fixes it. Fingers crossed.
Please dont misunderstand that you want to eliminate steering during suspension moment. It is needed, example, under hard brakes / nose dive you want extra toe in to counteract the loads on bushes trying to toe out. Likewise the rear end under squat/ hard acceleration, it will naturally try toe in, so the geometry will counteract with toe out. 🍻 cheers
it might be worth mentioning that most of your bump steer problem would have been from fitting the roll centre adjustment lower ball joints on there own, just lowering a car on its own doesn't make a massive amount of bump steer on its own as both the steering arm and lower arm move as per factory together. you need to space both roll centre ball joints and tie rod ends the same 25mm at the same time, or not at all. by doing one and not the other you are changing the angle between the lower arm and the steering arm which causes the wheel to turn through its motion of suspension travel causing the bump steer.
The thread on the tie rod ends that come in the kit look quite long. Would it be poasible to cut those shorter rather than modifying the standard rack tie rods (or getting replacements) ? Just about to order the same kit for mine to got with the Roll center spacers.
I read up a bit on this, and it mentioned that the wishbones should be the same angle as the tie rods to keep it all within a good amount of toe control from bottom of the arc to the top.
@@MotiveVideo Do bear in mind you don't necessarily want to. You should aim to point the kinematic force center (= tie rod + rest of assembly) at the instant center of the wheel around the ride height you want in order to get least bumpsteer, taking into account component deflection from tire torques moving the instant center and kinematic force center away from where you think they are. This is one reason why zero bumpsteer on paper might not be zero bumpsteer on track even with solid joints. Also, elastokinematic toe is allegedly toe-in on Skylines by-design so you might want just a bit of toe-out compression bumpsteer and toe-in extension bumpsteer at least on the front to tune it out like they do from factory, although a stiff car might benefit from close to 0 bumpsteer and just handling it with static toes. Most of the compliance is from the wheel-rim so don't think just because you have solid joints that everything is solid.
Extra weight on the front? Sounds like you need a billet alloy block, Andrew! 3.6 litre go go go! (although I think that block actually weighs more than a stock cast iron 2.6 litre block lol...)
How much lower than factory height before you need the correction kit. For example if a vehicle is only 20mm lower than standard factory height does the bump steer correction kit help? Great information by the way. Cheers
Well I'm not a Skyline expert like Motive but hear me out: I wouldn't suggest it on a very mildly lowered vehicle. The reason is that the bumpsteer is not severe at all at those heights, in fact in an ideal rear geometry you basically don't have any until 70mm lowering or so although this is just theory and in reality all your joints will have deflected away from ideal so you need to check it yourself. The front has toe-out compression bumpsteer which you can tune out with tie rod spacers. Messing with just one axle and not both axles (Pain in the ass for the rear suspension, you would need to engineer a new knuckle) will mess up your roll couple, and while it might indeed be good to have the front roll center higher than OEM for big-power cars, you will still need to do extra work to account for it. I think due to the rear being a bit trailing as well, messing with the knuckle will also inherently change your antisquat and antilift a little bit. That in mind if you're having front bumpsteer issues on such a mildly lowered car I'd get a height-adjustable tie rod (but not lower balljoint) and just experimentally find a good setting using spacers or whatever to change its height. For the rear you can also get such items although the common cause for toe-out compression bumpsteer is inappropriate upper link lengths due to aligning in positive camber from the design value. So experiment with your rear's fore upper arm length relative to the aft upper arm length before you buy any parts IMO. Might just be that you have crazy bumpsteer from that which you won't fix by screwing with the tie rod and lower balljoint at least if they are located at all where they should be.
My PRP front subframe spacers measured in at 9mm and worked a treat on my RB30 conversion but I did have to get longer subframe bolts. Did you get custom ones from them @ 7mm?
What subframe bolts did you use and where did you get them? I'm about to go 9mm spacers, so I'm happy I saw your post before I had the car jacked and unbolted!
@@mute_style I went to an engineering supplies store and bought some there with lock nuts and washers. I think they were grade 10.9 and I used a bit of flat bar on the top side of the chassis legs like the OEM ones have on the R34.
What you're talking about here is only half of the relevant information, and simply following this video and spacing the end link down might give you _worse_ bump steer. The other half you need to pay attention to is the angle of the tie rod relative to the control arm(s). Ideally the tie rod and control arm should be parallel.
@@rob9068 Spacing the subframe down, effectively moving the inner pivot on the lower control arm down, and then spacing the _outer_ pivot on the tie rod down, is the exact opposite of what you want to do if your goal is to compensate for that first change. The tie rod spacers worsen that scenario.
@@MotiveVideo In isolation I don't doubt that it is. But there are other factors that aren't mentioned at all in the video. If there is something wrong about what I'm saying, please let me know. Not here to attack you of course; all I want to do is learn :)
@@jckf Jim you're right for racecar-style control arm shimming but you need to remember that the rack also moves when the subframe spacers are installed. Although like you said it's not a guarantee that moving the tie rod down is correct because the upper arm still exists on these cars. The whole geometry matters, including which side of the wheel the rack and tie rod is on. I just checked in software, and the FD3S front geometry needs the tie rod to be raised for less toe-out bumpsteer, more towards 0 bumpsteer; opposite of the Skyline geometry IIRC. Also, while it's true one arm should be parallel with the tie rod ie: they should be part of the exact same arm for 0 bumpsteer like in old cigar-shape racecar rear suspensions, that's rarely the case if the tie rod is located between the arms such as in just about every car. You need to point the kinematic force center at the instant center for 0 bumpsteer.
"For all you stance boys out there..." *my 20yo self watching this episode saying yeah, well if I buy the cheapest coils I can find and dampen them as stiff as they go, I can still slam my car mate... Cant have bump steer if you don't have suspension. hahaha
Tires need usually about -2 to -4 camber at typical outside tire loads to generate maximum lateral force. It's because the contact patch pressure is uneven if the wheel is straight or positive cambered and the contact patch is under stress from cornering. Bear in mind that when most cars roll, they effectively lose camber because the geometry doesn't have 100% camber recovery. For 1 degree of roll you won't gain -1 degree of camber necessarily. The wheel-rim, upright, suspension joints etc. also flex severely and you can have easily +2 degrees of camber loss mid-corner. That's why the old touring car R32s ran a ton of negative camber, just to get that -4 or so mid-corner that they need. It's also why minimizing roll is good; it doesn't do anything to load transfer but it does retain more camber in the corner. When load increases typically optimal camber angle increases, so maybe in some tracks it is good to run a bit above the optimal on flat ground so you get the actual optimal angle for banked, high-load corners for example. Just don't forget the unloaded inside tire especially in the driven axle; you need to find a good compromise. It can be one reason why RWD cars have a little bit less rear camber typically for track applications.
Thanks Motive Garage! We can use some basic home-made equipment to analyse and correct bump-steer. Go to: /watch?v=K3_LsWn-AwY "Fixing extreme bump steer on my Fiesta ST180" (Not my Video but please LIKE) Using 20mm MDF and a DTI (Dial Test Indicator), we can simulate the plane that Andrew is describing here. By mounting the DTI on a hinged angle plate you can jack the hub up and down (spring removed) and gauge the bump-steer each time you adjust it by whatever means i.e. track rod end, subframe height etc. I can't wait to dial the bump-steer out of my Focus ST!
Would’ve been good to see actual measurement to quantify the change and the correction. What about extended lower ball joints ? Aren’t they usually used together with bump steer rod ends to help keep the LCA parallel with the tie rod as now the LCA and the tie rod have got different arcs.
Moving the lower balljoint is more about changing the location of the Roll Centre. Bump Steer is to be adjusted / corrected independently, but if a change to the lower control arm has been used then you will most likely need to make a correction for Bump Steer also.
Half the guys out here just want to put in coilovers and just slam them out - they do not at all understand the complexity and the engineering it takes what the total stroke of the shock is, the weights of the spring in relation the camber,caster, LCA all come into play. Suspension is a true art and just lowering your car is in no way improving it if your not working to its correct values. You see guys just slam in Pedders coilovers then lower it the whole way you dont accomplish anything, buying the part is only going to work correctly if used correctly. I more appreciate the guys whom will go ahead speak with MCA and shockworks or fulcrum suspension, Provide the proper weights of the car, the tire sizes and wheel size the type of LCA's and UCA's if they have adjustable caster rods it all needs to work in unison - thinking that changing out your OEM to a BC coilover then slamming it defeats its purpose. To explain it properly to people takes alot of effort and alot of aided drawing. it needs to be a better education that suspension tuning and suspension dyno are a real thing and take ALOT of time and energy with RND and engineering to get right.
I have watched countless videos and read countless articles about bump steer (from proper race shops/engineers) but this is honestly one of the clearest explanations I've ever come across. The distance between the inner and outer pivot points growing smaller the further the tie rod is from parallel, and how this therefore causes changes in the toe angle, is a brilliant way to think of it. Seriously well explained dude!
Thank you. We could go into much more detail but really, we want to explain the fundamentals to the masses.
Thanks for taking the time to explain this!
Killer explanation of how bump steer works and proper correction of it.
Gotta say even the underside of your Skyline GTR looks like new ! Love it mate
As a mechanic, great explanation. Your videos go far more in depth then most. Keep it up!
simple words to explain everything
and a cool gtr to show the practical side of it
killer content as always
Just a little tip for putting those tie-rods and rack ends together. Bit of copper slip or anti-seize will go a long way towards making your wheel aligner happy down the road as it'll prevent them from rusting into place with water ingress and keep them adjusting nicely in the future. Saves them from having to break out the blowtorch or giant pipe wrench to get them loose and potentially damaging them in doing so.
We did that at the alignment shop :)
@@MotiveVideo Better safe than sorry, especially for the people at home, I deal with a lot of 4x4 stuff and more often than not, Everything is seized and a "delight" to adjust.
Very informative. Learnt something today. Im pretty sure many persons especially those who lower their car have no idea about this bump steer problem.
Excellent tech as usual mate 😎👌🏻
I'm glad you addressed the tie rods, as I have longer aftermarket ones that I've been advised to cut down to fit my anti bump steer rod ends. I feel more confident to be able to trim them down now.
Keep up the great work as always.
Suspension is my weakest knowledge point so this was a great video to learn from. Thanks for the awesome content as always.
Love that choo choo from the turbo.
Perfect explanation dude, thx a lot, you just made it much easier to me to explain it to others myself from now on :-)
That song on the intro.. I need a full length version of this!
Great explanation! Time for some new whiteboards markers though
Best Whiteboard Science I’ve seen in a long time.
Excellent explanatory video. Well done sir!
I learnt something quite useful today, thank you.
epic explanations on suspension now i need one on why i would buy a bright orange watch
To match the Motive Video logo on the shirt. Duh
@@MotiveVideo point taken
In Germany we call it Vorspurkurve and I think it sounds beautiful xD
Unfortunately you were only partially right. There is much more to geometry that changes, but what is desired is to have tie rods parallel to lower wishbone, so that complete wheel assembly moves in the same arc... otherwise like your content.
Not parallel, the kinematic force center needs to point at the instant center for zero bumpsteer. You need to take into account the upper control arm/strut/whatever you have as well. And in a dynamic situation, you need to take into account compliances.
Great video guys!
Awesome video. Learn't a lot. Care to share your wheel alignment settings?
It varies based on application but for “street/drag” we run
-1 degree and 2mm total toe out up front
with 5 degrees castor
on the rear 2.5mm total toe in and -0.5 degrees neg camber
Learnt more in this 10 min video than watching the entire channel of "big youtubers".
Thank you. Our genuine goal is to educate and help people first, entertainment second. Many skip that first part.
Very well explained thanks Andrew
I have the same gktech tie rod ends, and ended up with the same adjustment problem. We used shortened z32 inner rods. I've got a terrible steering shake that I've tried everything to sort out. We just discovered play in the driver's side kingpin, so having that rebuilt at the end of the month to see if that fixes it. Fingers crossed.
Good information as usual! Great video!
Great job fixing the bump steer, but what’s up with the wobbly dash (display)?
Please dont misunderstand that you want to eliminate steering during suspension moment. It is needed, example, under hard brakes / nose dive you want extra toe in to counteract the loads on bushes trying to toe out. Likewise the rear end under squat/ hard acceleration, it will naturally try toe in, so the geometry will counteract with toe out. 🍻 cheers
Well done mate great explanation
it might be worth mentioning that most of your bump steer problem would have been from fitting the roll centre adjustment lower ball joints on there own, just lowering a car on its own doesn't make a massive amount of bump steer on its own as both the steering arm and lower arm move as per factory together.
you need to space both roll centre ball joints and tie rod ends the same 25mm at the same time, or not at all. by doing one and not the other you are changing the angle between the lower arm and the steering arm which causes the wheel to turn through its motion of suspension travel causing the bump steer.
In theory, yes, but listen to what we said.
Before the RB30 it didn’t suffer from bump steer. Once it did, we fixed it.
The thread on the tie rod ends that come in the kit look quite long. Would it be poasible to cut those shorter rather than modifying the standard rack tie rods (or getting replacements) ? Just about to order the same kit for mine to got with the Roll center spacers.
Yet another brilliant video... but has there ever been a bad one?
I read up a bit on this, and it mentioned that the wishbones should be the same angle as the tie rods to keep it all within a good amount of toe control from bottom of the arc to the top.
Again I only read this, key board warrior information haha
In the GT-R you can do that with roll centre adjusters, which we also have. Always best to pair them together.
@@MotiveVideo Do bear in mind you don't necessarily want to. You should aim to point the kinematic force center (= tie rod + rest of assembly) at the instant center of the wheel around the ride height you want in order to get least bumpsteer, taking into account component deflection from tire torques moving the instant center and kinematic force center away from where you think they are. This is one reason why zero bumpsteer on paper might not be zero bumpsteer on track even with solid joints.
Also, elastokinematic toe is allegedly toe-in on Skylines by-design so you might want just a bit of toe-out compression bumpsteer and toe-in extension bumpsteer at least on the front to tune it out like they do from factory, although a stiff car might benefit from close to 0 bumpsteer and just handling it with static toes. Most of the compliance is from the wheel-rim so don't think just because you have solid joints that everything is solid.
man that was helpful asf!
Time for some new whiteboard markers i think, worn out for all the plans you have come up with 👌🏼
Where can I get the steering rack re-done
Extra weight on the front? Sounds like you need a billet alloy block, Andrew! 3.6 litre go go go! (although I think that block actually weighs more than a stock cast iron 2.6 litre block lol...)
Billet block is 20kg lighter
However the turbo most hang off it is a lot heavier
Awesome video guys
Need to get a mako instrument cluster insert for that display. It’s wobbling all over the place
Somebody send some darker markers 😂 great episode though
How much lower than factory height before you need the correction kit.
For example if a vehicle is only 20mm lower than standard factory height does the bump steer correction kit help?
Great information by the way.
Cheers
The aim os to gave the lower arm and tie rod parallel to the ground, or sloping down slightly, not up. 👍
Well I'm not a Skyline expert like Motive but hear me out:
I wouldn't suggest it on a very mildly lowered vehicle. The reason is that the bumpsteer is not severe at all at those heights, in fact in an ideal rear geometry you basically don't have any until 70mm lowering or so although this is just theory and in reality all your joints will have deflected away from ideal so you need to check it yourself. The front has toe-out compression bumpsteer which you can tune out with tie rod spacers.
Messing with just one axle and not both axles (Pain in the ass for the rear suspension, you would need to engineer a new knuckle) will mess up your roll couple, and while it might indeed be good to have the front roll center higher than OEM for big-power cars, you will still need to do extra work to account for it. I think due to the rear being a bit trailing as well, messing with the knuckle will also inherently change your antisquat and antilift a little bit.
That in mind if you're having front bumpsteer issues on such a mildly lowered car I'd get a height-adjustable tie rod (but not lower balljoint) and just experimentally find a good setting using spacers or whatever to change its height. For the rear you can also get such items although the common cause for toe-out compression bumpsteer is inappropriate upper link lengths due to aligning in positive camber from the design value. So experiment with your rear's fore upper arm length relative to the aft upper arm length before you buy any parts IMO. Might just be that you have crazy bumpsteer from that which you won't fix by screwing with the tie rod and lower balljoint at least if they are located at all where they should be.
My PRP front subframe spacers measured in at 9mm and worked a treat on my RB30 conversion but I did have to get longer subframe bolts. Did you get custom ones from them @ 7mm?
What subframe bolts did you use and where did you get them? I'm about to go 9mm spacers, so I'm happy I saw your post before I had the car jacked and unbolted!
@@mute_style I went to an engineering supplies store and bought some there with lock nuts and washers. I think they were grade 10.9 and I used a bit of flat bar on the top side of the chassis legs like the OEM ones have on the R34.
Looks so much better to!
Mk5 Supra guys: "We feel your pain!"
S2000 guys: "First time? :)"
What you're talking about here is only half of the relevant information, and simply following this video and spacing the end link down might give you _worse_ bump steer. The other half you need to pay attention to is the angle of the tie rod relative to the control arm(s). Ideally the tie rod and control arm should be parallel.
He did explain hes already installed gktechs roll center adjusters they do the lca and was spacing these out too match
@@rob9068 Spacing the subframe down, effectively moving the inner pivot on the lower control arm down, and then spacing the _outer_ pivot on the tie rod down, is the exact opposite of what you want to do if your goal is to compensate for that first change. The tie rod spacers worsen that scenario.
What we did is correct.
@@MotiveVideo In isolation I don't doubt that it is. But there are other factors that aren't mentioned at all in the video. If there is something wrong about what I'm saying, please let me know. Not here to attack you of course; all I want to do is learn :)
@@jckf Jim you're right for racecar-style control arm shimming but you need to remember that the rack also moves when the subframe spacers are installed. Although like you said it's not a guarantee that moving the tie rod down is correct because the upper arm still exists on these cars.
The whole geometry matters, including which side of the wheel the rack and tie rod is on. I just checked in software, and the FD3S front geometry needs the tie rod to be raised for less toe-out bumpsteer, more towards 0 bumpsteer; opposite of the Skyline geometry IIRC.
Also, while it's true one arm should be parallel with the tie rod ie: they should be part of the exact same arm for 0 bumpsteer like in old cigar-shape racecar rear suspensions, that's rarely the case if the tie rod is located between the arms such as in just about every car. You need to point the kinematic force center at the instant center for 0 bumpsteer.
This explains why some guys put shims, or one thiccccc shim under the rack.
"For all you stance boys out there..."
*my 20yo self watching this episode saying yeah, well if I buy the cheapest coils I can find and dampen them as stiff as they go, I can still slam my car mate...
Cant have bump steer if you don't have suspension. hahaha
If you get more camber when the suspensions are compressed is it better for the track? With more camber on the outer front wheel
Yes, its designed that way
Tires need usually about -2 to -4 camber at typical outside tire loads to generate maximum lateral force. It's because the contact patch pressure is uneven if the wheel is straight or positive cambered and the contact patch is under stress from cornering.
Bear in mind that when most cars roll, they effectively lose camber because the geometry doesn't have 100% camber recovery. For 1 degree of roll you won't gain -1 degree of camber necessarily. The wheel-rim, upright, suspension joints etc. also flex severely and you can have easily +2 degrees of camber loss mid-corner.
That's why the old touring car R32s ran a ton of negative camber, just to get that -4 or so mid-corner that they need. It's also why minimizing roll is good; it doesn't do anything to load transfer but it does retain more camber in the corner.
When load increases typically optimal camber angle increases, so maybe in some tracks it is good to run a bit above the optimal on flat ground so you get the actual optimal angle for banked, high-load corners for example. Just don't forget the unloaded inside tire especially in the driven axle; you need to find a good compromise. It can be one reason why RWD cars have a little bit less rear camber typically for track applications.
@@MotiveVideo @Arch Thank you for your answers 😄 Therefore you should not put spacers on a car that will be on the track
great vid! great vid.
There is room for improvement in the rear aswell
Great vid👌👌👌
some one please buy this man a new white board pen!
How many Km on the shazzie? :D
Where can you get those rubber protectors for the spherical bearings?
GKTech provide them mate
Just run without them all they do is trap grit inside and wear out the rose joint.
This would be bump-out, stance boys worst nightmare lol
how long do these last compared to factory units? i'm guessing the dust ingress has a bit of an effect
They have dust covers over the ball joint. We've never worn any out the last 10 years.
that's awesome, thanks for the info!
Okay now explain how the SU-35 can do that "cobra" maneuver.
Lets learn something today
Thanks Motive Garage!
We can use some basic home-made equipment to analyse and correct bump-steer.
Go to: /watch?v=K3_LsWn-AwY "Fixing extreme bump steer on my Fiesta ST180" (Not my Video but please LIKE)
Using 20mm MDF and a DTI (Dial Test Indicator), we can simulate the plane that Andrew is describing here.
By mounting the DTI on a hinged angle plate you can jack the hub up and down (spring removed) and gauge the bump-steer each time you adjust it by whatever means i.e. track rod end, subframe height etc.
I can't wait to dial the bump-steer out of my Focus ST!
when do we see project super car killa go up against some super cars.. dish out some chop chop
Got some parts testing to do next few months. Start racing in April
Would’ve been good to see actual measurement to quantify the change and the correction. What about extended lower ball joints ? Aren’t they usually used together with bump steer rod ends to help keep the LCA parallel with the tie rod as now the LCA and the tie rod have got different arcs.
Moving the lower balljoint is more about changing the location of the Roll Centre. Bump Steer is to be adjusted / corrected independently, but if a change to the lower control arm has been used then you will most likely need to make a correction for Bump Steer also.
Wtf Andrew, Random bump steer video? hahaha! why not HP academy and now MV edition....
Are you going to give one of your GTRs away with LMCT?
Lucky you didn't give it much more power or you would have worn that haltech dash 😅
Cmon andrew, I think its time for a new whiteboard marker mate
We used brand new ones every time 🤷♂️
I think your haltech dash is loose andrew.
The bro can afford a flash laggy turbo but can't afford a new pen...nah great presentation tho thanks for sharing
Laggy? What video are you watching?
Someone buy Andrew some decent markers
They’re brand new
Half the guys out here just want to put in coilovers and just slam them out - they do not at all understand the complexity and the engineering it takes what the total stroke of the shock is, the weights of the spring in relation the camber,caster, LCA all come into play. Suspension is a true art and just lowering your car is in no way improving it if your not working to its correct values. You see guys just slam in Pedders coilovers then lower it the whole way you dont accomplish anything, buying the part is only going to work correctly if used correctly.
I more appreciate the guys whom will go ahead speak with MCA and shockworks or fulcrum suspension, Provide the proper weights of the car, the tire sizes and wheel size the type of LCA's and UCA's if they have adjustable caster rods it all needs to work in unison - thinking that changing out your OEM to a BC coilover then slamming it defeats its purpose. To explain it properly to people takes alot of effort and alot of aided drawing. it needs to be a better education that suspension tuning and suspension dyno are a real thing and take ALOT of time and energy with RND and engineering to get right.