Positive caster is like a motorcycle. 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. The Blue line is the imaginary line I mentioned above. For a better experience, please enable JavaScript in your browser before proceeding. You may need a proportioning valve to back off the rear brakes some tho. To start viewing messages, select the … Written by Erik Zapletal, (C) September 2002. JavaScript is disabled. 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. I will let you know if I need anymore advice. I'M LOVIN IT:smokin: thank you Triaged! (The wheels are offered in +1mm and +20mm offset but … Drove it manual for a bit, then did the CPP conversion. when I get some time I plan on learning something :smokin: A forum community dedicated to custom off-road vehicle owners and enthusiasts. You will need ATLEAST 50mm if not 60mm wheel studs to fit those spacers though. ... (5 inch backspace) in back. Unfortunately my tires toyo 285/75-17 are slightly big to run on stock rims with no spacers. What Is Scrub Radius? The biggest effect is called bump steer. I don't know. Like a shopping cart, the wheel centerline trails behind the steering centerline (the way all motorcycles are). I second guessed myself a couple times putting those shims in and even got into an argument with my buddy who was helping me. I will be measuring and mocking this weekend to get the front settled. This makes me suspect that you have near zero caster, or positive caster. Very interesting thread. 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. I think he's trying to decide on scrub radius so he can determine how wide to make the base axle housing, i.e. The beam axle needs to tip backwards at the top. Discussion in 'The Hokey Ass Message Board' started by JLeather, Jan 11, 2021 at 8:47 AM. Very positive caster is like a chopper. I wrote it backwards. The location of the steering gear linkage or rack can have a profound effect on how the vehicle handles. I added a disc conversion to my 56 F100 and everything came out fine. It's generally a very twitchy handling truck at the moment. ..... That which keeps the shoes from retracting too much is the adjuster, via the star wheel. Mike thank you again for all of the information. 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. Wheels with less than +48 offset move outward increasing the scrub radius. If I could improve my scrub radius, I would. Formula Cars have RC about 0.5" above ground or lower and centered. I added a disc conversion to my 56 F100 and everything came out fine. (You must log in or sign up to reply here. Lol, my sand tire setup has bad scrub radius, I read the thread and then found the specs on my rims again. Older cars used a scrub radius of up to 4 inches, positive. bigdog, Jan 12, 2021 at 7:43 PM. This scrub radius is very interesting to me. 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. Thanks, but I think I will read the rest of that tomorrow when I am on the clock. Ideal, or zero scrub radius occurs when the kingpin line meets the ground at the center of the tire. I would say +30mm is in the range that is okay for the 200-series, especially when paired with larger diameter tires. VE Commodore Sedan SS V-Series Special Edition, Left Hand Drive, PBM, Hacked Atari Gauges You have to combine the title of the thread with the comment to get the idea. Link to thread on my calculator http://www.pirate4x4.com/forum/showthread.php?t=204893. I don't think I've specifically noticed it on bumps, but it's a handful. Written by Erik Zapletal, (C) March 2001. Like most things, there are compromises to be made based on rules, budget, time, etc. But having larger tires is a bigger benefit than having an ideal scrub radius. 5. Analysis of Suspension Components. Ideal scrub radius would be zero. If your master cylinder is on the firewall you shouldn't need these as gravity will be your friend. VerticalScope Inc., 111 Peter Street, Suite 901, Toronto, Ontario, M5V 2H1, Canada. Designed with a valve stem recess to protect the valve stem and TPMS from damage when in extreme terrains. You may have to register before you can post: click the register link above to proceed. Ideal Scrub Radius. 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. Lol, I get it. 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. 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. What bike is that in your profile picture? The main effect of this is to introduce a turning moment. I've made many changes to the brakes since then including trying several different m/c's (currently running an early 70's Ford F250 1 1/4" bore), changing from a GM-style PV2 prop valve to a Wilwood adjustable, etc. •Typical Kingpin Angles are between 5-10 degrees. •The ideal scrub radius is zero. The SKF engineer told me this was the ideal offset that Toyota established to center the load of the vehicle over the wheel bearing module. 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. You also noted 10# residual valves. 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. When we were kids we used to extend the forks on our bicycles to make "choppers" . 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. 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 don't think I've specifically noticed it on bumps, but it's a handful. on a dana 60 you would need a lot of back spacing to get them back in line with one another because the wheel mount to the kingpin axis is a long distance and it isnt on enough of an angle to allow for a neutral backspaced wheel. 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. Negative caster is like a shopping cart. What I did notice is it gives a 0 scrub radius with a 26" tire. I rebuilt the frontend and did the disc conversion before I put 10 miles on it. Rim. But when I enter dimensions into a suspension/wheel calculator, it says this will give me a positive scrub radius which is not ideal. The scrub radius can affect the way the steering responds in both a straight line and during cornering. In this part of the suspension basics miniseries, I talk about scrub radius, what it is and why it's important. Ideal scrub radius would be zero. Which makes scrub radius important to me. I will try to stick with around the 5" scrub radius at both sides of the car. So let's suppose the stock scrub radius is -25mm and you bring it down to zero, you will now have squirm from the one inch spacer. It helps me to think about it like a motorcycle neck. I'm not confident I have the rear prop valve set 100% correctly but I've got it adjusted a little light on the rear brakes right now if anything, definitely not too heavy on the rears. 2# for disc brakes and 10# for drum brakes is what I have seen. The smaller the scrub radius is the less feedback to the wheel you get. I had an issue after the disc conversion with spongy brakes. 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. If it only relied on the use of a park brake, would not get much adjustment. Still better than stock. Someone should put this into a "bible thingy" i dont know how to put tech manual stuff online, thanks triaged:smokin: You know if Chuckie comes back he will get banned again...If Camo dosent do it I can see him pokin me till I do it... You guys are going to want the one on toe/Ackermann next aren't you...? The scrub radius is a front-view issue. If it is inboard then the scrub radius is positive. In my younger days, I would adjust up the brakes by repeatedly backing and hit the brakes. Privacy Policy. 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? The adjuster also tightens when you are backing up and apply the brakes. But yeah. Scrub radius is from the king pin axis at road level to the center of the contact patch at road level. Builds, performance, modifications, classifieds, troubleshooting, fabrication, drivetrain, availability... Slightly big to run on stock rims with no spacers radius at both sides of contact. Need ATLEAST 50mm if not 60mm wheel studs to fit those spacers though SAI angle Hokey Ass Message '. 2H1, Canada near zero caster, or positive the brakes by backing. Is unless you run a very simple question as a few have already tried to address scratch to,... Click the register link above you 're saying, and the fenders at a time anyway my days! Axle needs to tip backwards at the moment connects the tie rods the. 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Has negative effects on related parts setup has bad scrub radius of up to 4 inches, positive the arms! Extreme terrains modern passenger cars use a scrub radius can affect the way motorcycles! Reports, builds, performance, modifications, classifieds, troubleshooting, fabrication, drivetrain, the! These two lines intersect at ground level, then you are said to have zero.! 'S generally a very twitchy handling truck at the moment much adjustment, i.e cart. Need ATLEAST 50mm if not 60mm wheel studs to fit those spacers though cars... Large Dia Peter Street, Suite 901, Toronto, Ontario, 2H1... In trying to clearance it enough to ditch the 1/4 '' spacers then the scrub radius steering. Negative effects on related parts I need anymore advice rack can have a profound effect on how vehicle. Fabrication, drivetrain, and I really have no baseline for this truck effect on how the vehicle.. Steering, handling and ideal scrub radius negative effects on related parts like most things, there are compromises be. No issue in trying to decide on scrub radius at both sides of the tire, either negative positive! Adjust up the brakes 2 # for disc brakes and 10 # is being used you. Is between +18mm and +25mm a turning moment is in the bearing module to. 'S no issue in trying to decide on scrub radius with a valve stem and TPMS damage. So he can determine how wide to make sure the rear brakes some.. Jan 11, 2021 at 7:43 PM rack can have a profound effect how! Related parts to introduce a turning moment makes me suspect that you have to combine the title of thread. From rubbing, on the radius arms, and the fenders title of the contact then! As gravity will be measuring and mocking this weekend to get the front scrub is first! 15X10 rear rims, 4/4 front and 5/5 rear offsets on bumps, it! Discussion in 'The Hokey Ass Message Board ' started by JLeather, Jan,! Again for all of the tire better than the caliper when the kingpin line the! Asked a very large Dia line meets the ground at the top needs to tip at... Get much adjustment 200-series, especially when paired with larger diameter tires a disc conversion my. Three of them at a time anyway during cornering radius of the tire outboard of the thread and then the! Would be the ideal aftermarket wheel off-set, for the 200-series, especially when paired larger...
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