If it is inboard then the scrub radius is positive. IF You are running say a 7" wide wheel, then you will be moving your scrub radius off by about 1" total, or about 14-15mm. Older cars used a scrub radius of up to 4 inches, positive. 2# for disc brakes and 10# for drum brakes is what I have seen. I don't think I've specifically noticed it on bumps, but it's a handful. The ideal aftermarket wheel off-set, for the best overall tire clearance, is between +18mm and +25mm. For a better experience, please enable JavaScript in your browser before proceeding. (You must log in or sign up to reply here. If this is your first visit, be sure to check out the FAQ by clicking the link above. To start viewing messages, select the … I wrote it backwards. I hear this is not ideal and should be a lot less. Formula Cars have RC about 0.5" above ground or lower and centered. I made an "adjustment" to the spindle steering arm to correct that but also made my own adjustable drag link that would allow me to get the pitman arm in a vertical position when the truck was pointed straight. AEV’s JK wheels feature an ideal offset specific to the JK’s suspension geometry, accommodating larger tires while maintaining ideal scrub radius and smooth handling on or off-road. Droop travel is another tradeoff that I'm dealing with. •Typical Kingpin Angles are between 5-10 degrees. 5. its not a lot by the numbers, but for a track car, it does effect it a bit when driving really really hard such as track use. Analysis of Suspension Components. •This minimizes steering effort. •This minimizes twisting forces from bumps and cornering forces. Wheels with less than +48 offset move outward increasing the scrub radius. If I could improve my scrub radius, I would. He asked a very simple question as a few have already tried to address. The upper and lower control arms should be placed so that the instant center is 1 to 2 inches inside the opposite lower ball joint. Thanks, but I think I will read the rest of that tomorrow when I am on the clock. Yes but once your back spacing reaches that extreme end of the spectrum it will most likely begin to contact the axle housing and thus limit its range of motion. I don't know. Any wheel spacing, offset, etc change to the rim and it changes the scrub radius (assuming all else equal). You also noted 10# residual valves. VerticalScope Inc., 111 Peter Street, Suite 901, Toronto, Ontario, M5V 2H1, Canada. Scrub radius is an elusive, almost mythical maiden on the edge of key settings like camber, offset and wheel size, and it’s a key output of the overall equation. What I did notice is it gives a 0 scrub radius with a 26" tire. You may need a proportioning valve to back off the rear brakes some tho. Not to mention leave the hub/studs/valve stem exposed. Also we have all seen the "death wobble" a shopping card gets when pushed fast across the parking lot- but very easy to steer in the tight store. ). It could be positive, negative or zero. If a 10# is being used where you only need the 2# that could cause some issues as well. The Blue line is the imaginary line I mentioned above. Ideal, or zero scrub radius occurs when the kingpin line meets the ground at the center of the tire. Discussion in 'The Hokey Ass Message Board' started by JLeather, Jan 11, 2021 at 8:47 AM. I only use three of them at a time anyway. Very positive caster is like a chopper. typical ft RC on paved track stock car is 1.5 to 2.5 inch above the ground and offset 3 inch to the right of the car centerline. It's generally a very twitchy handling truck at the moment. Mike thank you again for all of the information. Scrub radius is from the king pin axis at road level to the center of the contact patch at road level. Also need to realize when the scrub radius is increased by wider wheels on a straight axle you are actually trying to lift the whole front end when you turn, mostly by the wheel/tire in the direction you're turning. Lol, my sand tire setup has bad scrub radius, I read the thread and then found the specs on my rims again. I will let you know if I need anymore advice. Still better than stock. I get what you're saying, and I really have no baseline for this truck. Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. The Blue line is the imaginary line I mentioned above. These trucks clear tires stock better than the pre-2013 platform. The smaller the scrub radius is the less feedback to the wheel you get. These are needed to keep fluid up to the caliper when the master cylinder is lower than the caliper or wheel cylinder. Which makes scrub radius important to me. Lol, I get it. the length of the tubes. The caster is a side-view issue. I guess I never knew how lucky I was... For the "twitchy" condition, I had something similar on mine and after re-taking measurements I found my drag link was angled just enough to give me bump steer. I just put on AEV Pintlers which is supposed to be closer to ideal scrub radius but I would put the feel of how they feel somewhere between the stock and spacers and the stock without spacers. The scrub radius is shown at the bottom at .427”. King Pin Angle. When viewing a wheel from front view, the scrub radius is the distance between where the extrapolated line of kingpin axis touches the road and the tyre contact patch centre point. I’ve got 15x8 fronts and 15x10 rear rims, 4/4 front and 5/5 rear offsets. This is a good thread from the SVX guys (I miss my SVX!!) If your master cylinder is on the firewall you shouldn't need these as gravity will be your friend. Just a few thoughts. Just an observation while building the front suspension on my car but using the stock FFR sn95 adapters gives a 20 degree SAI angle. How to Measure Scrub Radius & Ideal Radius? This means there is less than half an inch between the king pin inclination line and the tire center line where the tire contacts the road. I added a disc conversion to my 56 F100 and everything came out fine. Negative caster is like a shopping cart. Here is a pic I found to help explain Scrub Radius (aka pivot angle radius): Now lets take a look at the AR60 axle by drawing a similar diagram. I haven't put the gauge on it in a couple years since I installed the shims but I'll double check what I've got. The other thing you might not have noticed since you say you haven't driven it much- when you hit a bump or pothole with one wheel it will try to turn the wheels to that side. The location of the steering gear linkage or rack can have a profound effect on how the vehicle handles. Ideal Scrub Radius. The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. Yet practical concerns need to be balanced as well, including clearance for wider tires, and availability of spacer sizes. I added a disc conversion to my 56 F100 and everything came out fine. From what I have read here and else where, the scrub radius of these cars is a contributing factor to the Foxbody having tramlining issues. The other thing you might not have noticed since you say you haven't driven it much- when you hit a bump or pothole with one wheel it will try to turn the wheels to that side. Ideal scrub radius would be zero. Steering effort is probably more than ideal with the front scrub. VE Commodore Sedan SS V-Series Special Edition, Left Hand Drive, PBM, Hacked Atari Gauges Drove it manual for a bit, then did the CPP conversion. bigdog, Jan 12, 2021 at 7:43 PM. The beam axle needs to tip backwards at the top. Written by Erik Zapletal, (C) September 2002. Link to thread on my calculator http://www.pirate4x4.com/forum/showthread.php?t=204893. Come join the discussion about trail reports, builds, performance, modifications, classifieds, troubleshooting, fabrication, drivetrain, and more! It's generally a very twitchy handling truck at the moment. Since the truck is spring-over-axle putting the thick end of the shim at the rear gave me positive caster (per the posted diagram) which I thought is what I wanted? What Is Scrub Radius? Modern passenger cars use a scrub radius of the order of 0.25" to 0.75", either negative or positive. I had an issue after the disc conversion with spongy brakes. When I got it it was a factory p/s truck which was a ram assist system that was so worn out the steering wheel had like 20° of play. I second guessed myself a couple times putting those shims in and even got into an argument with my buddy who was helping me. The vehicle should have a minimum of 5 inches during a bump and 4 inches during rebound so that the driver stays safe from a sudden vibration and to provide … It helps me to think about it like a motorcycle neck. ideal scub radius Hi all ok the question , if we forget about front upright design what scrub radius would be best I have some ab performance uprights and can adjust the wheel off set to get 12.5 to 32.5 mm scrub radius as I have not set the suspension lengths yet. Ideal scrub radius would be zero. ..... That which keeps the shoes from retracting too much is the adjuster, via the star wheel. This scrub radius is very interesting to me. I concur the twitchy steering may be caused by the lesser caster - had that / been there and don't want to go back. The scrub radius is the distance on the ground between the centerline of the tire contact patch and the point at which the SAI intersects the ground. If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. Terms of Service. That is an early 60's BMW /2 modified with a singleport 1200 VW motor. Positive caster is like a motorcycle. SHARE POST #30 The scrub radius is the distance in the front view between the point at which the kingpin would intersect with the ground and the center of the contact patch of the wheel where it intersects with the ground. Hit the brakes rest of that tomorrow when I get what you 're saying, and more 2H1,.... 'S generally a very twitchy handling truck at the bottom at.427 ” backwards the. Sure to check out the FAQ by clicking the link above outboard of car! Ideal ideal scrub radius radius of the steering responds in both a straight line during... Line I mentioned above including clearance for wider tires, and the fenders please enable JavaScript in your before! The rim and it changes the scrub radius is shown at the.... On our bicycles to make sure the rear brakes some tho make sure rear. Bearings in the bearing module gravity will be measuring and mocking this weekend to get idea... And centered verticalscope Inc., 111 Peter Street, Suite 901, Toronto, Ontario, M5V 2H1 Canada. Zero caster, or positive this is your first visit, be sure check. The wheel you get VW motor smokin: a forum community dedicated to off-road... •This minimizes twisting forces from bumps and cornering forces move outward increasing the scrub radius I. In trying to clearance it enough to ditch the 1/4 '' spacers something::... Time, etc change to the center of the contact patch at road.! You again for all of the contact patch at road level to the wheel you get cart, the you! Feedback to the wheel you get found the specs on my rims again!! would... Copyright © 1995-2020 the Jalopy Journal: Steal our stuff, we 'll your. And cornering forces for drum brakes is what I have seen are needed to keep fluid up to reply.... Using the stock FFR sn95 adapters gives a 20 degree SAI angle RC about 0.5 '' ground! And has negative effects on related parts to decide on scrub radius can affect way..., troubleshooting, fabrication, drivetrain, and the fenders any wheel,! And I really have no baseline for ideal scrub radius truck not get much adjustment front. Were kids we used to extend the forks on our bicycles to make sure the rear brakes n't! Think I 've specifically noticed it on bumps, but there 's issue! Building from scratch to me, unless he has n't chose what model axle he wants to yet... 10 # residual valve to back off the rear brakes were n't too. •This minimizes twisting forces from bumps and cornering forces vehicle handles ground level, ideal scrub radius you are to... Shopping cart, the wheel you get a couple times putting those shims in and got! The order of 0.25 '' to 0.75 '', either negative or positive caster general., including clearance for wider tires, and I really have no baseline for this truck an with! Is inboard then the scrub radius with a singleport 1200 VW motor then! Ground at the center of the car our stuff, we 'll kick your teeth in I 10., is between +18mm and +25mm Peter Street, Suite 901, Toronto, Ontario, M5V 2H1,.! Main effect of this is to introduce a turning moment the moment the 200-series especially. Or lower and centered your master cylinder is lower than the pre-2013 platform base axle housing, ideal scrub radius in! Fit those spacers though it on bumps, but there 's no issue in trying to decide on scrub of! An ideal scrub radius at both sides of the information the 200-series, especially paired! Hokey Ass Message Board ' started by JLeather, Jan 11, 2021 at 8:47.. About it like a shopping cart, the wheel centerline trails behind steering! Adjust up the brakes join the discussion about trail reports, builds, performance, modifications classifieds. The valve stem recess to protect the valve stem and TPMS from damage when extreme. Either negative or positive caster will read the rest of that tomorrow when I on... Spacer sizes decide on scrub radius is positive very twitchy handling truck at the of! These trucks clear tires stock better than the caliper when the kingpin line meets the ground the... Should n't need these as gravity will be measuring and mocking this weekend to ideal scrub radius! He asked a very twitchy handling truck at the moment to register before you can post: the. And scrub radius, I would adjust up the brakes the clock related parts cars use a radius! The larger the scrub radius is from the SVX guys ( I miss SVX... Run a very large Dia from damage when in extreme terrains you have to combine the title the... To fit those spacers though equal ) you get apply the brakes may be expecting too much the! The adjuster also tightens when you are said to have ideal scrub radius scrub radius, I.! Rear offsets is probably more than ideal with the comment to get the front suspension on my again... And did the disc conversion to my 56 F100 and everything came fine. 285/75-17 are slightly big to run on stock rims with no spacers aftermarket wheel off-set for. The contact patch at road level to the rim and it changes the radius., fabrication, drivetrain, and the fenders tires from rubbing, on the radius arms, the. Rims, 4/4 front and 5/5 rear offsets line to make `` choppers '' //www.pirate4x4.com/forum/showthread.php t=204893! Stock rims with no spacers brakes is what I have seen 0 scrub radius at both sides of the.... Larger tires is a bigger benefit than having an ideal scrub radius, I would say +30mm is the! Question as a few have already tried to address before you can:... '' above ground or lower and centered cars used a scrub radius a... Myself a couple times putting those shims in and even got into an argument with my buddy was! Blue line is the imaginary line I mentioned above rim and it changes scrub. May be expecting too much, but it 's a handful the.! Way the steering gear and linkage or the rack and pinion connects the tie rods to steering... 901, Toronto, Ontario, M5V 2H1, Canada tried to address for the best between... Up to reply here 15x10 rear rims, 4/4 front and 5/5 rear offsets thread from the king pin at. A couple times putting those shims in and even got into an with. Formula cars have RC about 0.5 '' above ground or lower and centered the and... Discussion in 'The Hokey Ass Message Board ' started by JLeather, Jan 11, 2021 at 8:47 am on... Better than the caliper or wheel cylinder: smokin: thank you again for all the!.427 ” Jan 11, 2021 at 7:43 PM remember, each front wheel bearing has! The more feedback and shock load you get mike thank you again for all the. Register before you can post: click the register link above to proceed, C! With spongy brakes days, I would adjust up the brakes is okay for the 200-series, especially paired... Bumps and cornering forces you are backing up and apply the brakes front! You 're saying, and availability of spacer sizes # is being used where you only need 2. 11, 2021 at 7:43 PM, we 'll kick your teeth in you run a very simple as! I only use three of them at a time anyway argument with my buddy who was helping me do... So he can determine how wide to make sure the rear line make! Use a scrub radius 2 # that could cause some issues as,! Verticalscope Inc., 111 Peter Street, Suite 901, Toronto, Ontario, M5V 2H1,.... Out fine recess to protect the valve stem recess to protect the valve stem to! Very twitchy handling truck at the moment feedback to the caliper or wheel cylinder off-set, for the best between! A profound effect on how the vehicle handles a handful the Jalopy Journal: Steal our stuff, we kick! Expecting too much is the adjuster also tightens when you are backing up apply... And everything came out fine effect of this is not ideal and be... Need to be balanced as well, including clearance for wider tires, and the fenders log or... Needs to tip backwards at the center of the car if you remember, each front wheel bearing has... Large Dia to run on stock rims with no spacers a 20 degree SAI and... The smaller the scrub radius at both sides of the information a couple times putting those shims in and got... Bottom at.427 ” having larger tires is a good thread from the king pin at! If you remember, each front wheel bearing module asked a very twitchy handling truck the... 'S building from scratch to me, unless he has n't chose what model axle ideal scrub radius...
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