Thinking of Lowering Your Car? Watch This First.

What happens to the suspension roll centers when you lower your car? Will your car handle better or is it just for looks?
What are roll centers?
Part 1: • The Complete Guide To ...
Part 2: • The Complete Guide To ...
Chapters:
Introduction 0:00
Finding the Roll Center 0:32
Effect of Lowering 1:47
The Impact of Lowering 2:35
Roll Axis Skew 3:08
Balance of Suspension Characteristics 4:12
Can we Fix It? 5:55
A Warning 6:19
We Can Only Fix the Front 7:00
Should You Do It? 8:15
Suspensions Explained
Huibert Mees

[@vercingetorige400]

wonderful, but you broke so many hearts with this

[@TranceFur]

On the bright side, there are roll center correction kits for most cars worth modifying :)

[@guillermo7549]

Hi Huibert, I discovered your channel a couple of weeks ago and I find just great that somebody who put his knowledge to the test in the industry is creating this content. Great job. It’s just a pity that such specialized content doesn’t catch the attention of a broader publicum that would justify investing more resources on it. There’s nonetheless one thing or two I would tend to disagree with. One is that you affirm that a low RC on one axle tends to reduce the grip on that axle: When we lower the front RC, we make the car more understeering. I have always taken the contrary to be truth, following this rationale: 1) We take a car with whichever weight distribution, CoG height, roll center heights… We just take it as a starting point, everything that matters is the changes we create in the following points. 2) Now we lower the front RC by whichever distance (by moving a couple of hardpoints, not by lowering the car). Quite a few things have changed at the same time on that end of the car, so it might be difficult to figure out how that axle behaves now. Now we have less load transfer over its suspension arms, but we surely have more over the elastic elements. Figuring out which one is bigger is not an easy task. So let's try a different path: let’s see what’s happened to the total load/weight transfer and to the rear axle. We haven't change almost anything there, so it might be easier to analize. 3) What happens to the total load transfer of the vehicle? Nothing. We haven’t changed the height of the CoG, nor tracks, nor anything that affects the total load transfer in a significant way. Hence we must assume that the combined wheel transfer of the two axles remains the same 4) We have moved the front RC but didn’t touch the rear one. In this way we get a more skewed roll axis. The distance between the CoG and the roll axis has increased, and so has the lever arm between the both and with it the roll moment. The front axle will quite surely not be able of compensating for this extra roll moment, as we have actually reduced the amount of load transfer that happens over the suspension links. The result is, the roll angle for any given lateral acceleration hast increased - a roll angle that is acting on both axles 5) As we have not changed the geometry of the rear axle but subjected it to an increased roll angle, the amount of lateral load transfer in that axle will be bigger: We have increased the load transfer over springs and ARB because of the increased roll angle. But as its RC remains at the same height, we haven't changed the load transfer finding its way through the suspension arms. The total load transfer at the rear axle is thus higher. 6) If the total lateral load transfer must remain the same because of 3) and we increase the portion of it occurring on the rear axle, then we must conclude that the amount of load transfer on the front axle is smaller, leading to a front axle with more grip potential and therefore less understeering. So, lowering the roll center at on axle decreases the load transfer on that same axle. Lowering the RC at the front makes the car less understeer, as much as the RC heights concerns (everything, bump/roll steering, etc remaining equal) If I got it right, you seem to affirm the contrary to my way of thinking. Will you be so kind as to give it a thought and point out where I’m wrong? Thanks

[@mikeherring9639]

Thank you for being a content creator, I feel like I learned more yesterday and today than I learned in years of industry provided training !!!!😮

[@tslaton]

I hope that your channel continues to grow, your videos are great and very informative. all factual information without bias or opinion.

[@Levibetz]

What might be an interesting video (and something I'm interested in doing) is to take an existing car's suspension mounting points, and redesign a suspension for racing. For example, a sedan that would ideally be lowered significantly, or that has had the track width widened significantly.

[@datadrivenmqb]

Great video/series! I've been working on some very basic videos specific to the VW MQB platform which will have led me to the same conclusions as you've drawn (lowering any more than the slightest amount is likely not good for performance). Also confirmed that roll center correcting ball joints are garbage on this platform with wild amounts of bump steer (~10mm toe change PER SIDE over +/- 38mm bump and droop travel from ride height). There are no great ways to correct the amount needed short of custom fabrication. You saved me a bunch of time having to explain roll centers so will be referring to this in an upcoming video. Keep it up!

[@user-rd5nc1nb9f]

i’d love a video about ride quality. like how to improve it for example or at least the factors that influence it

[@user-yx5wd5yy6h]

your videos are a treasure for those who are in one way or another connected with car design. thank you for your work.

[@TM-fx5le]

Are you able to make a video on what affects bump steer, or possibly how to correct roll centre in the rear of a double wishbone?

[@trottermalone379]

When lowering your suspension makes the handling a nightmare, the easiest solution might be to get rid of the suspension… I purchased a modified Jaguar XK150 that could be the poster child for what not to do specific to lowering the chassis. When I got it home and up in the air to look things over, it was clear that whoever performed the modifications had had this epiphany as it was resting on the bump stops at the front and the rear had less than two inches of travel. I’m still struggling to get the suspension back to one that promises manageable handling and that has more compliance than the tires.

[@AnnDee4444]

I know of one instance where this isn't exactly correct, but only because of bad original design. Supposedly the Chevrolet A-Body, G-body, & 2WD S-10 front suspensions have a factory roll center that is underground, and they also have severe factory bump-steer. Roll-center adjusters (a.k.a. tall ball joints) and taller knuckles (spindles) are available and are supposed to raise the roll center and somewhat correct bump steer while simultaneously lowering the ride height.

[@suspensionsexplained]

Thank you for your comment. Even if those trucks had poor original design, the ride and handling team would have had to deal with this in some way. I assume you are talking about early generation A and G body cars which had 4 link rear live axles. Those would have fairly high rear roll centers as would the S-10 with a leaf spring rear axle. Lots of roll axis skew if the front roll centers are below ground. I feel sorry for the ride and handling team that had to deal with that! Not an easy task to make something like that work well.

[@TranceFur]

Brilliant explanation. I did notice that my car felt extremely good after fitting a new set of coilovers which were adjusted to a factory ride height out of the box. They may have actually been higher than the factory ride height. Unfortunately I can’t stand how E36 M3s look at that height, but it was an interesting experience. Will be trying a front bump steer correction kit soon, and I actually wouldn’t mind if the handling balance skewed more toward oversteer.

[@bobnine]

Wouldn't the lower CoG mitigate the effects of the higher roll moment? Ie the car wants to roll more, but the lower CoG makes it more difficult to roll. I think you need to make some animated diagrams to help explain what the effects of the higher roll moment actually are and maybe do some simulations in beemng or similar...

[@TM-fx5le]

Did you watch the video?

[@magnusdanielsson2749]

Skoda and Audi actually offer many of their cars with different ride heights Theyre called something like "standard", "sport" (audi has s-line and sport offering different amount of lowering) and "rough terrain". And the difference is about 15-30mm in either direction. So one would assume that amount of change is fine. I have a Pontiac Fiero where the front is a double a-arm and the rear is mcpherson. The rear rollcenter migrates outside the vehicle and below ground when theres a large amount of body roll. Seems like an odd solution but I assume they had some reason for it (economics being one since they could design a different rer suspension). The car is famous for wanting to spin (especially since its a rear midengine car..) Then again the body doesnt roll very much so I guess that mitigates things to some degree.

[@suspensionsexplained]

That's a good point. If the OEM produces versions at different ride heights then they have sets of springs, dampers, bushings, and anti-roll bars all tuned for each other to work as a system at each ride height. Using those parts to lower your car would be a good way to go about it.

[@Harry-uo2cr]

Your videos are awesome, thank you

[@CanadaLuke]

Very insightful as always. While I personally don't lower my car since I understand the down sides and the unpredictability at the handling limits, I do wish you could do an example on some cars that are extremely popular to be lowered, like a FRS, or g37. What would the roll center changes be like front vs rear? Also, with the roll center decreasing substantially, and that would reduce roll a lot, which I'm sure many people who lower their cars would appreciate and attribute it to "better handling". Plus a lot of people who lower their car would also install anti roll bar kits which almost always increase the bar size in the rear way more than the front (if not outright adjustable via mounting holes). I know from a OEM engineer's stand point, some of the sacrifices in ride, handling balance, stress limits, durability, bump steer etc would make almost any suspension changes on their own unacceptable, but my question to you is, are typical 30mm lowering kits/coilovers + adjustable anti sway bars to neutralize the balance that bad? Maybe they would make some of the characteristics out of range for a OEM product, but still within an order of magnitude in terms of safety, balance and material stress that they could be considered? I just wonder how out of range such typical suspension "upgrades" are in terms of a car's balance and the stress limits of the unchanged suspension components. ps. Personally I don't bother modifying my suspensions, I just buy a great handling car to start with and maybe put on higher quality dampers and leave the rest alone, the above questions are merely out of curiosity.

[@suspensionsexplained]

Unfortunately, analyzing a specific car would mean knowing the details of the suspension geometry which requires some very large and expensive equipment, or access to the internal data from the OEM which they are very unlikely to share with someone like me. I would love to do it though!! Your statement about decreasing the roll center decreasing the amount of roll is not correct though. When the roll center drops, the roll moment arm (the vertical distance between the center of gravity and the roll axis) increases so the amount of roll will increase. You can decrease the roll again with stiffer springs and bigger anti-roll bars but you're messing with even more of the parameters that control the handling of the car. Unless you have access to a test track and can drive the car at the limit in a controlled way, you have no idea what sort of handling balance you are left with. That was the point I was trying to make.

[@CanadaLuke]

@@suspensionsexplainedI see, I misunderstood that part about the roll center. Pretty much all lowering kits will come with stiffer springs, or worse, progressive springs which are then paired with cheap dampers. I can see why you're annoyed by the installation of basically any aftermarket suspension components, since changing one thing means you put so many other parameters out of spec and out of tune. I've seen exactly zero aftermarket company who releases documentations for roll center changes among other important factors that one should consider. The more expensive kits would sometimes include spring rate, but that alone isn't enough information. Still, all OEM suspensions are designed for some amount of understeer, and most aftermarket suspension try to reduce that by having stiffer rear springs and stiffer rear sway bar. I guess there's not much more to say in specifics other than "Buyer beware", since these "upgrades" would change the handling balance in often times unpredictable ways. For a lot of enthusiasts, reducing understeer could be a fun and relatively safe modification to do. Maybe a video idea for later is to discuss what modifications you would personally approve of (if any)? I personally think higher quality dampers (on OEM springs or OEM sports model springs) and sometimes adjustable rear sway bar to dial out some of the built in understeer are upgrades that produces fewer complications, and could make a car more "fun" to drive without making too many sacrifices. Thoughts?

[@mry82]

Yes, how much is too much, for a given car, is a good question. I have had 2 lowered cars (~1.5"... 92 Prelude, and e46xi AWD, which is raised a little in stock form, so maybe there is some leeway there? The BMW was lowered when I bought it...). I run poly bushings and stiffer springs... I drive pretty hard, carving up Appalachian back-roads, and never had any weird experiences compared to all the other cars I did not tinker with. @@CanadaLuke

[@nobodynoone2500]

Depends on the suspension. On some cars, a little lowering helps, and improves the camber curve old the wishbones until your roll center drops below the optimal point. I've worked out MANY suspensions that were underground after lowering! In fact I would say it's quite common, possibly the norm, on slammed cars. Most common cars for modification (civics, corvettes, etc) have roll center correction devices and even knuckles available. I HIGHLY recommend them. Just make sure they are serviceable.

[@suspensionsexplained]

Thank you for your comment. Unless you are changing the position of suspension joints, lowering a car doesn't actually change the camber curve, it just puts you on a different part of the curve. I agree with you that most slammed cars will have roll centers below ground. I would guess that those drivers probably don't care since it's all about the looks in many of those cases. New knuckles to address the roll center height are the best way to avoid problems but they have to be engineered so that the outer steering tie rod also ends up in the right place relative to the lower ball joint. Again though, all the correction devices I have seen are for the front. I haven't come across any that address the rear suspension. Maybe I'm not looking in the right places.

[@nobodynoone2500]

@@suspensionsexplainedCorrect about just changing the area under the curve, but once you are lowered, that is now the whole curve as far as you are concerned. Kinda like changing the bias on a tube or transistor. I did find on many cars, a little bit of lowering helped, and then quickly went pear shaped before even an inch in many cases. Very few people are relocating their suspension points. I remember bespoke knuckles available in car mags and catalogs starting with the Chevy and VW lowering craze in the 80s, then minitrucks, then civics, and now just about everything. I'd be suprised if someone didn't make em for the model-t. The design was indeed often more for "hard parkers" than for good performance on the road. And the newest aftermarket geometry-corrected knuckles are mostly for drifters, with their own sets of issues and tradeoffs. To find the "real" stuff for correcting suspension geometry, you have to dig deep in the weeds of the racer parts shops, or make your own. I know there are extentended mounts for the rear of 88-00 civics to fix the upper and lower control arm mounts in the rear, because I have run them, but they are less than common. It's easier to mod the rear suspension than the front leading to more turnkey stuff there. I remember when most lowriders were still solid-axle, just requiring clearance (or tiny wheels lol). Now you have got me doubting my current setup and I'm about to go measure it this weekend. Cheers!

[@nobodynoone2500]

@@suspensionsexplainedAnd don't even get me started on axle and driveshaft alignment horrors with extreme lowering or lifting. Speaking of, might be woirth doing a vid on lifting stratigies and how they affect handling. Might be a popular and helpful video that could save some lives.

[@mry82]

headed out to lift my sports car right now, to improve the handling... imagine the looks you'd get announcing that to most people!@@nobodynoone2500

[@Mr_Hacki]

Thanks for your explanation! For BMW E36 there are options for adjusting the rear Rollcenter and Anti-Squat by removing the origianl joints and put in some exentric ones. My qustion there is, how effektiv this is? I think its is around 25mm exentric. And normaly when using this cars for Racetrack applications they will be lowered by approximately 80mm.

[@suspensionsexplained]

Unless your E36 is an M3, then you will have semi-trailing arms in the rear. That is one of the few suspensions where the roll center will drop LESS than the body will. I don't know what the eccentric joints are that you are referring to, but I would guess they are fairly effective. It's a very simple suspension design so it wouldn't take much to correct the roll center. I would expect that if this modification is for racing then it will be coupled with stiffer springs and anti-roll bars and some track time to make sure everything is working well together.

[@Mr_Hacki]

@@suspensionsexplained thanks for your reply. Every E36 except the Compact series have the Same Suspension Layout. The Compact series shares the Suspension Layout with the E30 and thats indeed a semi trailing arm Suspension. And in Addition to the semi trailing arm Suspension I heard that the Rollcenter is on the top of the Road, independent of the Ride hight? I don't know the Englisch therm for it. In German it's called "Raumlenkerachse". All Kind of E36 have this Layout. So what so you think about that? Is it still that effektiv with the different Suspension Design? Thank you very much in advance!

[@suspensionsexplained]

I know which design you are talking about now. The knuckle is a large casting that connects to the body with a large bushing in the front. Two long lateral arms connect the knuckle to the subframe. Since the lateral links are quite long, I suspect the change in roll center height won't be too bad. The longer the arms are, the less angle change they will go through for a given ride height change. That limits the roll center change. If the eccentric bushings are used on the inner pivot points then I can see how they would help raise the roll center back up. I don't know if it could compensate for a 80 mm ride height change though. That is a very interesting suspension and worthy of a future video. The way it works is all about that front bushing.

[@Mr_Hacki]

@@suspensionsexplained thanks for your reply and your explanation. A Video would be very interessting. Particularly when in use in racing applications.

[@EliteMacFreak]

Wouldn't installing stiffer swaybars offset the roll center change?

[@BrennanKoontz]

Assuming the front and rear move down in similar amounts and you are able to keep your roll gradient similar using stiffer springs and ARB, couldn’t lowering the car be worth it for the decrease in load transfer?

[@CBD47]

Stiffer springs and arb reducing roll, but do nothing about increased roll forces caused by lowered roll center. So stiffering these components in your case just force wheels to handle these increased forces instead of body. Which means adding more load on tyres in turns and may cause its overload

[@garagecedric]

Yes, this is the typical production based race car from the last century, where geometry correction isnt available. The limiting of roll is also a way to minimise the drawbacks of the McPherson strut for example.

[@mry82]

oops... :)