Well, your term is certainly more descriptive, but I don't know about a real term, just that I never heard of "scrub radius". In fact, I've never read of this discussed in such detail. How I can tell what you are talking about is by understanding geometry and triginometry very well. Thanks for pointing out these suspension effects!!!

 

Per my 98-2002 Accord Haynes manual:

"The caster on the front end is adjustable by installing shims of different thicknesses on the radius rod"

"Camber isn't adjustable on these models"

 

Bow down to JohnL and his wisdom...

That is the damn best description I've ever read about anything.... just... wow...

i love it! made perfect sense to me, and I think Falkore's paraphrasing helps simplify the concept.

 

Well 'scrub radius' is definitely a well recognised term in auto engineering.

For anyone having a hard time visualingscrub radiusfrom my description I'll try another descrpition:
Before I start note that when an auto engineer talks about the contact patch's relationship withvarious geometrieshe/she will tend to conceptualise the contact patch as a single point that represents the centre of the contact patch. This is of course not completely representative of reality (due to the elastic nature of the tyre and camber angles), but is a useful convienience. We can think of the centre of the contact patch as being 'the point' at which forces generated by the tyre are originated, which makes things a lot simpler.

When we have scrub radius (i.e. + or - rather than zero) the contact patch is offset to the outside or to the inside of the point at which the steering axis intersects the ground, which is typically at a point that is still within the footprint of the contact patch, just offset from the centre of it (unless it's a kart which have absolutely huge scrub radius, but we don't need to go into the reasons for this, which are more complex than for cars).

If we turn the contact patch with a steering input then the point that is the centre of the contact patch will describe an arc centred on the steering axis (at the point where the axis intersects the ground). If we were hypothetically able to turn the wheel through a complete circle then the centre of the contact patch would also describe a complete circle araound the steering axis.

We do need to keep in mind that 'trail' is similar to scrub radius, except that the offset is longitudinal rather than lateral. So, with both scrub radius and trail simultaneously present the centre of the contact patch is both to the side of and to the rear of the steering axis.

Both scrub radius and trail have a 'value', being the measured distance from the steering axis to the centre of the contact patch. All forces generated at the tyre can be concievedof (for convenience) as actingat the centre of the contact patch, and these forces are 'fed' into the steering via the steering axis through the length this distance from contact patch centre to steering axis. As such both scrub radius and trail represent'virtual lever arms' that act as if they werereal levers, multiplying the forces generated at the contact patch as it passes into the steering mechanism. It's essentially the same when you tighten a nut with a spanner (wrench for Yanks), the longer the spanner handle the more torque is imparted to the nut, the longer the scrub radius or trail the greater the force (actually a torque loading) imparted into the steering.

You can see why the value of scrub radius or trail has implications for steering feel, weight etc. However, we need to keep in mind that the values of trail are cumulative (i.e. forces multiplied through trail at both wheels can be added together to find the force as felt at the steering wheel), but the values of scrub radius tend to cancel each other out and are not felt by the driver unless the forces acting at each individual tyre change, in which case the scrub radius is 'multiplying' a different input force at each side and the driver will experience a pull, either momentary or longer lasting depending on exactly what's happening.

In reality the scrub radius itself can also actually change if the real centre of loading moves from one point on the contact patch to another (camber change, traversing bumps / undulations etc), causing a change inthe force mutiplying effectat that wheel even if the actual force at the centre of contact patch loading remains the same.

Fun, isn't it! Or maybe I need to get a life!

 

LOL ...... I wasn't doubting that "scrub radius" is a term, rather that we might have a slightly different term in the states. Kinda like how we have tires while you have tyres. I know that's only a spelling, but you can get the point I think. As for "Auto Engineering", my education is Mechanical Engineering with a few in depth classes on engines and such for electives as well as working on the mini-baja vehicle team and advanced combustion control group, so my jargon may not be up to par either, but I doo know most terms ...... funny thing is, the main stuff about cars I learned in HS. Having rebuilt a couple engines gave me the visual images to understand many of the concepts that make up my degree. For example, I see an engine, pump and compressor as the same basic thing ..... that can be extended to include turbines and impellors .... turbos, fans, etc. When it comes down to it the important info is all in the amount of energy and thus can be compaired.

 

Not unlikely, that US terms might be other than those in the rest of the World that is!

I had another go at describing the nature of scrub radius in case others were having some trouble visualising it. You really need to get a mental picture of some of these things, just knowing the words doesn't help much.

The point is that we spell it correctly, and you guys don't!

It's all Physics (even Chemistry and Biology are Physics once you go below a certain scale). When studying how cars work a basic understanding of first principles will help a great deal.

 

Update: I took my car to another Firestone dealer in the area and they aligned properly at no cost. Pulling has disappeared.

 

LOL ...... you'd be the first person that understands what I mean when I tell people that chemestry is physics at the molecular level!!!!

 

But that's about the limit of my in depth understanding of chemistry!

 

im leaning toward it was just made and sold to me like this. I have never been in a wreck, never even changed a part or anything on the car. Have had it almost 4 years.. and I keep up on all maintenance that’s necessary. I’ve been buying so many tires over the years and never thought anything of it. The mechanic told me when I bought the car a reguakr package was put on not a sport like it needs. Any advice would be appreciated.