Scrub Radius - Suspension Design - Explained

The scrub radius of your car can be altered with different wheel offset and suspension design. This will affect how the tire contact patch interacts with the road during cornering, braking, and acceleration, and can cause unique toe characteristics depending on the design. A positive scrub radius tends to be beneficial while braking into a turn. A negative scrub radius tends to better for braking stability in the event of brake failure or split-mu braking. Typically the scrub radius is configured to be as small as possible to minimize the effects under braking, but squirm (from zero scrub radius) is also undesirable.
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[@laddaevolta]

i like how you align you white board to edge of the camera screen

[@EngineeringExplained]

+Tango965 Haha thanks. Maximize useful (visible) space!

[@Leofred2000]

+Tango965 Keeps my ocd happy :)

[@EdyAG90]

just engineer things

[@Bluuplanet]

You've been spending too much time with wheel alignment tools.

[@benpowersification]

I honestly thought I knew a bit about the physics of cars... until I found this channel. Sooo much learning. Excellent channel.

[@REVAMPtheindustry]

+benpowersification fo real

[@RaceTeq17]

Squirm - particularly at corner entry - is reduced to negligible amounts with more negative camber.

[@dagananderson9118]

That helps to understand why the change in offset of my winter wheels has changed the handling so much. Thanks man.

[@unclegeorge6175]

You're incredible. I have worked on cars for a long time but very little in suspension geometry.. Depended on others to perform alignments. This the first time I have heard of scrub radius. Your presentation is straight forward and easy to follow. You have enlighten me to point of realizing subtle steering/braking issues that I have come across. These youngsters and I was once, do not take into consideration for their modifications. Aesthetics is more important than road worthy. Knowledge is king and that is why your called an engineer. Thank you for sharing.

[@OlumideAyeni]

This is the best explanation i've seen on kingpin offset (scrub radius). Thank you!

[@videomaniac108]

Thanks Jason for your lucid and interesting presentation on this subject. Additionally, I think that the addition of a small amount of scrub would be beneficial in helping to take up some of the slack in the steering system, from component clearances, by slightly preloading the suspension.

[@GarageRacers]

Once again learned something invaluable... Thanks Jason!

[@lolololololololol513]

Thanks for the video, been looking forward to this every since I got new wheels with lower offset

[@DUSM]

Your videos are very informative! Great explanations and clearly stated. Thank you for sharing your knowledge.

[@NukeFromOrbit]

finally somebody explains it properly, thank you very much. I see lots of people with wider rims and plates on their car, not knowing what happens to their steering

[@donaldasayers]

Citroen used a steering geometry with zero scrub radius, zero kingpin inclination, zero camber and zero castor angle. Steering feel was added artificially by the power steering.

[@paulaxford6754]

Excellent and concise explanation. I thought it might have been useful to add that the resulting torque on each steering axis due to SR is balanced via the steering rack under ideal conditions, and how high SR can adversely affect steering under poor road conditions.

[@bosborn1]

Boy I would love to see this explanation as it would pertain to solid front axles that use either kingpin or balljoint knuckles. Since the scrub radius would be consistent from side to side no matter what.

[@Mikeb8134]

You did a great job of explaining, I wish you would have given some examples or insight on what scrub radius certain groups (e.g., F1, NASCAR) use.

[@mrd9534]

Great video Rich!

[@scottm4267]

Nice job! Appreciate your time & efforts!

[@Bluuplanet]

When I bought my old '79 Volkswagon Rabbit, VW used the terminology "Positive Roll Steering Radius" and "Negative Roll Steering Radius". The Rabbit had a negative roll. The center of pivot was toward the outside if the contact patch. With the car sitting still, turning the steering wheel from extreme right to extreme left, the right front wheel would make a slight rotation backward and the left wheel would roll slightly forward. The wheels would tilt noticeably outward when the steering was not pointed straight forward. If I was careful to point my car straight on a straight road, I could let go of the steering wheel and the car would not deviate even if I were traveling on one side of the crown of the road. The steering would self-center well, but seemed immune to road embankment variations.

[@CORZER0]

Great info in a concise package, thanks!

[@drink15]

Can you do a video on glazed rotors?

[@mariusfurtuna9422]

i can feel this when i change to lower offset wheels. i always wondered why! the car steers as i brake, but i noticed it is even worse when the surface is not flat.

[@casa0123]

Hi your videos on suspension systems and and the terminology that goes with it are very interesting. Could you do a video on the De Dion tube system....It was very popular with Alfa Romeo cars

[@Vpr310]

Cool, something I didn't understand but now do.

[@Miragedude28]

I am learning so much stuff, thanks dude:)

[@christiaanroos4479]

please give more information regarding SR and which cars use which cars use which setup and how it is used in motor sport. More videos on suspension geometry and its applications would be nice

[@chair6180]

Another awesome episode! Hey Jason, can you plz explain the differences between brake rotor, and brake pad materials? may be event debunk some carbon ceramic rotor lies, if any? there are some contradictory ideas on the interweb. Don't know who's right. plz help Thanks. And lastly, still loving the show! Happy Thanksgiving!!!

[@whythefuckdowehavethisherenow]

Finally understand this. Great stuff.

[@upendrasura2921]

So good explanation....I was damn confused about this earlier....thanks

[@user-cx2bk6pm2f]

Really liking your videos! Thumbs up.

[@kevintran4273]

Can you explain in more detail how having FWD or RWD cars affect toe-in/out under acceleration?

[@mattmers]

You should do a video on Passive rear wheel steering. SAAB ReAxs is a good example.

[@Boosterized]

I'm no engineer but I learned a lot because of this channel.

[@MrSlowestD16]

The concept sounds sort of similar to trail on a motorcycle, though in terms of right/left in this case, not front/back on a bike. I'm wondering if somebody could draw connections between the two. Definitely wouldn't mind you doing a video on motorcycle rake angles and trail distances. The rake angle is usually directly associated with responsiveness vs stability, but how the trail factors in is usually not as clear. Definitely wouldn't mind an EE video on that!

[@mikegrady4]

Trail is what controls stability or responsiveness. More trail equates to more straightline stability at elevated velocities. Less trail equates to a more responsive feel at elevated velocities. Rake, axle centerline offset, and front tire diameter all play into the trail equation.

[@Baladibt]

Do "wheel hop" next. Cheers.

[@platvis379]

Great info. How mutch positive scrub radius is acceptable in a 4x4?

[@j.e.branson9262]

Great Video!

[@liormolvin]

great info. do you have examples of cars with positive and negative scrub values.

[@6rimR3ap3r]

If I get this right that's the "Lenkrollradius" in German. There was a lot of discussion about that in our German GT86 forums. Finally instead of getting "dat stance tho" by offset +35rims I kept my wider wheels at OEM +48 offset.

[@timbrown4629]

Dominik Heidrich I was wondering this myself. I found some nice Konig Runlite but they're 35et and I don't want to ruin my handling. Stock is 48et (2011 Subaru Legacy) so I'm leaning to the 45et Enkeis right now since it's a small difference

[@alextak432]

awsome video, thanks

[@NoblePineapples]

Very informative video, thank you. I like your face.

[@CheetoChop1]

Thanks man crystal clear. So what's a good scrub radius for a jeep that's 71" tall and 72" wide with 35x12.50r15x8 with 3.75 bs abs 2" spacers? It was worse before The spacers but my jeep is still a bit squirmy right now and this video possibly helped diagnose my problem. Thanks! I'm thinking I should be a little on the negative side.

[@automotivesociety4627]

Great video! Very informative and interesting as always. One question though, what role do wheel spacers play in affecting the scrub radius? Would the effect be the same as if you were increasing wheel width and offset?

[@EngineeringExplained]

Yep, I'll have a video on this next week!

[@maplesyrup2944]

+Engineering Explained Good, I'm looking forward to that

[@Overseerdv]

@Engineering Explained Awesome vid! How can one determine what scrub front&rear a car would come stock with based on its suspension geometry, so not as to undermine the OEM engineering? I am looking to switch to wider front and rear wheels (staggered setup-rwd) and trying to get as close to stock offset with the added dimension(s). Thus far, I have matched front precisely, but rear is roughly +/-10mm positive scrub. Lastly, is this amount of change going to be as detrimental being on the rear axle of a double wishbone suspension type? Any assistance would be greatly appreciated.

[@GTFour]

Could you do a video in super strut suspension please :)

[@Zickcermacity]

Good explanation of scrub radii! Now: My 2010 Honda Accord EX, from the factory, has zero scrub radius. The steering is light(50-series low profile tires on 17" wheels), and return could be a little faster. I am considerig mounting the OEM 16" rim(and 60-series narrower tire) Honda used on the same year LX trim. That wheel will lend positive scrub radius to my geometry. What would be the effect on my EX's steering with positive scrub radius added?

[@danbartlett9963]

Hey man I was wondering if you could elaborate on this but utilizing an off-road perspective. I know a lot of trophy trucks and class 1 buggies use equal length control arms but the suspension travel is so much that it also plays a role on steering linkages and steering angles. Could you delve into the geometry that makes up steering on high suspension travel vehicles?

[@THEBOULDER236]

Very well...Explained ;D

[@CharlesNam]

Jason, what happens to scrub radius when you add negative camber? More specifically, now that the tire is tilted, does that make the tire centerline obsolete in regards to contact patch?

[@toddmohler3473]

Very informative video. We have the first DF Goblin kit car in idaho. Would be very interested in getting your opinion on alignment and suspension setup for a non-standard vehicle. Hit me up if you would like to see the vehicle or have any input on the setup. Cheers

[@Burden-THE]

Hey, I always come back to wheel change, and suspension geometry. It's confusing! When I learn something, it's usually soon forgotten. Assuming a stock scrub radius is recommended, how would an additional (+) 3mm offset affect handling, vs 7mm? Would even 10mm be an insignificant value overall, or would I worry about affecting the cars handling?

[@sonsan64]

thank you

[@TrueRacerAcademy]

mind blown

[@jimjimaco4217]

may i ask u something which might sound silly,but i am not an expert,the king pin is determined by the angle of the suspension,or by the point which the wheels steer?thanks for these wonderful videos....

[@EgypTTM]

Question! McPherson suspension wise. How will a wheel spacer or offset have effect on scrub radius and how can you figure out these two (spacers and offset) in order to have a 0 or negative scrub radius for optimum handling? Also! Out of topic now but say you got a same wheel size and use a spacer say 25mm with 0 wheel offset, will it have the same effect on wheel bearing(stress) as no spacer but a -25mm offset? The wheel will be sticking out away from car 25mm in both ways but which will have least load on bearing? Keep in mind that a -25mm offset will increase the distance between the wheel flange and suspension components that might rub with inner wheel.. Just trying to take out the 14x6 +38mm offset wheel and put a 15x8 (custom made offset and back spacing) and I don't know how to calculate this.. all I know is that I need a wide track on my 88 vw mk1 with least stress on bearing and optimum handling feel.

[@jackyphotos]

Good vid, does it mean that double wishbone usually have breaking unstable compare with mcpherson? thanks much.

[@scottwilliams6835]

How does this relate to earlier suspension types? Like the one used in Fords of the 60's and early 70's? Upper and lower control arms with the spindle suspended between them. Spring and shock on top of the upper control arm in the shock tower. Strut rods and sway bar.

[@garylowe8601]

Can you do a video on push rod actuated suspension please?

[@andrewthompsonuk1]

When I started driving most cars did not have power steering. I was always under the impression that they had a positive scrub radius to make the steering lighter. If you try to turn the wheel when stopped with a positive scrub radius the wheel will rotate slightly. On the big cars you had to be very careful not to put your fingers in the steering wheel when maneuvering as the wheel could jerk around. Interestingly I drove an old 50 seater bus once that had no power steering and it was actually not too bad.

[@SpecialEDy]

My first vehicle was a 64 Chevy Pickup that I owned for the better part of a decade. It had 4 drums, no power brakes or power steering. The steering wheel was probably an extra 6 inches in diameter larger than a modern steering wheel and angled away from the driver with the bottom closer to you so you could really put two hands on it and crank. It was also over 5 turns from lock to lock IIRC. At a stop it took some serious muscle to turn, if you were rolling you would just let go of the wheel after the turn and it would spin back to straight at an insane speed.

[@carbongames3772]

Hi, Can you please explain if why are we adjusting the wheels to toe out on FWD cars with McPherson suspension if it tends to toe out during acceleration.

[@jaspinderpalsingh9463]

Which is the best book and is easy to understand for vehicle dynamics

[@alhamedi66]

thank you . how to fit big wheels and tire 33" 35" with lift kit without spoil the wheel alignment . or what the right way to fit bigger tire and wheels . for on road use aggressive look only .

[@hetzijzoal]

Where can I find more in depth information about this subject ? Books/papers? For cars and especially motorcycles

[@SuperNoob247]

Can you do a video on glazed donuts.

[@taekwandokid89]

Is it true that altering the scrub radius or the steering axis inclination is harder on other components such as wheel bearings?

[@rhkips]

If I've understood correctly, this isn't just an alignment thing; if you do something as simple as adding a spacer to the wheel or use an aftermarket wheel with a different offset, the scrub radius will be altered and so too will the vehicle's handling, correct?

[@EngineeringExplained]

Correct!

[@rhkips]

Engineering Explained Awesome! Wow, I think I just learned everything I did wrong with my last car, LOL. Great video man, thanks a bunch! Learned a lot! :D

[@JS-nt3cn]

+rhkips You got it. It's worth keeping in mind that, changes to the ride height (raising or lowering) will also change the steering axis. Very similar to how camber changes in particular due to dissimilar radii of the control arms/struts.

[@mrburgermaster]

+Engineering Explained Good thing my summer set of wheels are just 5mm more negative in offset than my stock/winter wheels. Your videos are very helpful, however, I'm hesitant to modify my car because I now consider all the factors that the mods may affect, lol.

[@turboseize]

+Joe Smathers But that does not apply to double-wishbone setups, or do I miss something?

[@workouthax]

+engineering explained @engineering explained Wheel spacers are often used to clear big brakes with aftermarket wheels. How does wheel width affect offset and scrub radius. I drive a lancer evolution x and the stock wheel size is 18x8.5 +38. The options i have that clear the brembos are 18x9.0+25, 18x10.0+35, 18x10.5+15, 18x10.5+25. I'm just want to figure out which size will not negatively affect performance (if any).

[@martinwink2063]

Great video! Only thing that's not really clear to me, in what scenario would you want a positive scrub radius?

[@ayushgupta5061]

i think he said it would be beneficial while brakiing during a turn

[@mrpetit2]

On normal cars a 0deg scrub radius is undesireable as it makes steering on low speeds very heavy, for example when parallel parking. Especially in the past when a lot of cars didnt have power steering.

[@aripapagianis8269]

When you say you want a little bit of scrub radius, can you put some numbers with that? I’m building a RWD buggy and debating on wether to run slightly negative or slightly positing in the front suspension

[@glavoc]

Can you explain how the Citroen DS center point steering works....

[@alexandrugherghescu]

I love your vids, but sadly English is not my native language, so I can't figure out what some words do mean. In my tongue there is no translation for "camber", for example, and there are not so many specific words for most of the engineering terms found in English. Of course, I am to solve this translation problem as I am going to apply for a bachelor's degree in Automotive Engineerig, but this is going to happen in two years from now, since I am in 10th grade. Back here( in Romania, my home country), the education system requires twelve years of studying before going to university. I would like to have a chat with you some time, to get some advice and to learn from you what's best for my future career. Looking forward to getting your response, and until then, keep up the good work!

[@PiyushTirale]

Q. Plz show Advantages of positive scrub radius? Why positive scrub radius is used at front in rear wheel drive or off road vehicles?

[@zackherzer]

Can you do an episode on leaf springs?

[@calbeer]

What is considered too much positive scrub radius for a FWD car? Or what is an optimal amount of positive scrub radius? For a daily driver/ occasional track day.

[@Phasterphaster]

I thought weight transfer was diagonal across the chassis, so isn't the more salient dimension the change in diagonal axis from one corner of the car to the other when you add wheel spacers? On my 2004 BMW 330i ZHP, we added 10 mm wheel spacers to the front wheels to dial the stock, inherent understeer out of the car. All other things being equal (sway bar settings, PS9 Coilover heights, spring rates, etc.) it had a tremendous effect in making the car very "throttle pivotable." Based on your calculations, this should have had virtually no effect on handling balance. But now the car is easily pivoted and rotated around it's polar moment with the throttle. Is the car's front to rear balance just that sensitive to small transient weight transfer changes? That's why I suspect the diagonal is a key component in the changed handling dynamics ... ?

[@smithlorenzo]

You said a little bit of positive scrub radius could be ok. How does 11/16 sound to you?

[@SCHUMACH3R]

Why is positive scrub radius commonly used in double wishbones setup? And is there any site to lookup for the value of specific car model, i.e. Golf MK5 or W140 S class?

[@nickamarit]

My E46 (stock wheel offset +47mm) has E90 wheels (+34mm offset) on, and the increased positive scrub of 13mm does make the car squirrelly on heavy braking. I sort of regret getting those E90 wheels on my car now.

[@Synthwave89]

I was thinking of getting 17x8 +35 wheels for my brz but now I'm leaning towards the same wheel in +45 offset. Looks be damned, the most important feature for me is handling.

[@nickamarit]

@@Synthwave89 You can get +45 offset wheels and then get 10mm spacers to test how the new scrub radius (from a +35 offset wheel) will feel, which can help you for your future purchase... but I honestly think you'll like it better at near-stock scrub radius if you value handling over looks.

[@This0is0pointless]

So I'm assuming something like drop spindles on a truck would cause more positive

[@brettwilliams657]

What is the minimum and maximum negative scrub radius? What should you aim for?

[@theresonly1truth138]

God bless you.

[@dmitrylosangeles4111]

great video

[@dmitrylosangeles4111]

but pls talk a little slower.. hard to follow

[@grindsman22]

So scrub radius doesn't have any negative effect on the rear wheels, right? I was looking at getting a staggered set of wheels to fit the rear arches perfectly. The fronts will be wider than factory fit but with a zero scrub radius, the rears need to be offset by 8-10 mm to fit perfectly.

[@slim__dunc]

Would the squirm be a negative if you were mainly using the vehicle in the snow? Would it cause you to lose traction easier in turns? Also, where can I find info on my current amount of scrub radius on my stock car so I can insure my offset will not take it to zero or positive?

[@carguy466]

sooo for my crosskart (RWD 30/70 weight distribution) I should have positive toe for it to go smoother fast and corner better?

[@wIzKid16100]

Hey would less offset affect alignment in the long run? I have a brand new car and I’m scare of ruining anything Stock wheel spec is 18x7.5 55mm and I’m looking at these wheels and they’re 18x8 45mm, would it cause any stress on the suspension in the long run?

[@jerrychaney7100]

Which would work best for front axle "cutting"/ steer brakes on a rwd street performance vehicle?

[@kstaats13]

So if I'm looking at changing wheels on my vehicle and staying he same tire size, but going with a different offset from 55 to 40 I am looking at generating (assuming my vehicles scrub is zero to start) about 19/32's of positive scrub. Will this be noticeable in day to day driving and braking? Or will it be virtually unchanged being such a small amount of scrub being added. Thanks.

[@jalins6]

What is slip angle as it relates to suspension? And how can I reduce it?

[@LoveLikeaHurricane]

So if I were to push the centerline of the tire further to the outside of the car towards the fender....I'll end up having more positive scrub radius...which seems to have the least desirable characteristics on a performance car.

[@jabadahut50]

is 38mm too much scrub radius? I'd like to widen my cars track width by 3 inches on each side so I figured 3 inch wider wheel and 38mm less offset on the wheels (which totals to about 3" unless my math has been done improperly) would put the outer face of the tire 3 inches farther out.

[@Danny-yh3xb]

Can you explain how wheels with different offset than oem, especialy on a rdw car (negatively) affects geometry? Example: bmw e91. Oem size is 8j et34 front. 8,5j et37 rear. Very stable at high speeds. I put on a square setup (8j, et30) and the car is all over the place!. A golf 6, oem offset is around 52, i put on wheels with 40 offset, also this car is all over the place

[@zdfnhxfgjnhxfgnj]

Say I've got 2 sets of wheels, one with a high scrub radius and one with a low scrub radius. lets say I have a very light car with a "racey" caster of 3 deg. Could I change the wheels SR effectively giving me a different caster "feeling" without actually changing caster? One set of wheels for on road/ heavy steering but stable and the other for autocross/ easy fast steering but twitchy?

[@MFP2241]

Does getting out of zero scrub radius on the back while keeping zero up front affects handling in any way?

[@mollendinousa]

Can going from a 55mm offset to a 42mm affect my car? Handling and braking?

[@QuiznosBear]

So, simple ways to minimize scrub... camber & offset, yes? adv/disadvantages of each?

[@whorayful]

Everyday I find another car fact I had no idea existed. This one explains so clearly why an SUV I owned years ago handled like crap.

[@exnuke1972]

So the slight negative scrub (-5/16" / -8 mm) after I get wider tires on the same rims should be good. Thanks

[@MarvinConnell]

How does, lowering a car, affect it's scrub radius? Does lowering a car: 1. induce Positive scrub radius? or 2. induce Negative scrub radius? Thanks...

[@rajajeetravelvlogs8061]

Brooo. Thanks man. I think I should start paying you my uni tuition fee instead.