Tire scrub radius: Unfortunately most folks pick their wheel tire combo based entirely on no rubs or looks good with very little consideration on scrub radius (SR). Look at the pic below to help understand. SR of zero (+1 to -.50) is best for stability (over or under this amount adds a bunch of road force into your steering (and thus your steering ends, ball joints, track bar etc) - keep in mind Death Wobble is when road force causes positive feedback - that is like dribbling a basketball as opposed to just letting it bounce and eventually stop). The more negative your SR - the higher the propensity to death wobble if any parts wear or bend or become loose. A higher positive SR will want to wobble - but is more easily held (that is the positive part of the feedback) neutral by the steering linkage and stabilizer. Scrub radius is the difference between the green line (tire contact center) and red line (steering axis inclination) intersections with tire contact. Positive has the green line outboard - negative has it in board. Assume all three tires in the diagram are 31 stock tires. If you change rim width (with same offset - left compared to center) or backspace (center compared to left) you make a direct change to this. If you change diameter you make a direct change - as you can see a larger diameter tire will move tire contact further away from axle center and further away from (or towards) that intersection of the lines... Look at the right most picture - it is VERY close to 0 - IDEAL. Again assuming - stock Rubi 32 - now assume we put a 35 on it and the tire contact goes all the way down to where the green line is well inside the red line - TONS of negative. Thats mounting 35s on a stock wheel. Yep It clears and since it dont rub (add I dont stuff the suspension into rocks in a mall crawler) so it works and the lift manufacturer (and forum members) who said I must run a maximum 4.75 backspace are wrong - correct? NO. This is a setup that is near guaranteed to be chasing a death wobble later when joints are worn (if not right away). AND that backspace was the recommended backspace to match the tires the lift was sold for. Look at Teraflex 2.5 spring for example. Its sold based on up to 35 tire and requires maximum Backspace of 4.5 - thats the BS for the 35 (and ostensibly 9 wide wheels). What if I want 33s? I want more Backspace (4.75) - if I want 37s I want LESS backspace (4.25)! In the grand scheme - you have to choose. Based on your planned use. YOU are in a quandary. Back space can be decreased with spacers. It can not be increased without replacing the wheel. The wheels that will work well with your planned 35s WILL NOT work well with your current tire!
Posted on: Mon, 15 Sep 2014 19:13:03 +0000
Trending Topics
Recently Viewed Topics
© 2015