Silverfc88

iTrader: (7)

What are the offsets of the wheels themselves?

1QWIK7

iTrader: (33)

I think if you go REALLY wide like 20mm, 25mm etc, then safety becomes a factor but i dont think a 5, 10 or even 15mm spacer will cause a great deal for problems.

Roen

iTrader: (2)

He's argued that point before, but I don't recall him ever providing evidence on why scrub radius is meaningless. I, for one, would like to hear why he thinks that is so.

I've seen a bunch of his posts and his background is drifting. However, and from what I've seen on this forum, drifters' advice on suspension setup works for drifters, and not much else.

From what I know (and subsequently felt on my car), too much scrub radius causes any pulling in the brakes to be greatly exagerrated, as well as tramlining.

Risky Devil

iTrader: (1)

Run what suits you. Even if, its completely off what everyone else normally runs.

or the Rx7club.com way, is run what everyone else runs, including, tire & wheel set

ups and even alignment set ups...

So please, enlighten me. How does scrub radius effect in real time street driving.

Since 90% of our cars are driven on the street.

How does it personally effect your car.

Don't tell me text book explanations.

skatingsamurai

dont think this has been covered in this thread yet but, when you increase the scrub diamete...im assuming this is a tech term for the width of the tire tracks, you can **** up your bearings by putting to much leverage on them? this happens becuase the actual width of the rim does not extend far enough in to support the hub in the right spot...right? at least thats what it seems like. please correct me if im wrong though. i thought of it as like if your in a push up position with your arms 90* there is a certain amount of support capable because of the distance from your hand to to humerus and when you increase the "scrub length" more stress is put on the inside, creating more leverage, and more stress on your pecs.

do i have it completely wrong??

grade247

lol thank you for asking this I got a set of desmond regamaster with a +45 offset I could prob clear with 10mm spacers right?

Spirit Rx-7

iTrader: (15)

these are the spacers i broght, you choose bolt pattern and from 5mm-12mm thickness, also you just tell him your center bore, and they'll make it hubcentric. I also would recomend extending your studs with arp if you buy these.

http://cgi.ebay.com/ebaymotors/WHEEL...QQcmdZViewItem

Roen

iTrader: (2)

Tramlining is the most noticeable side effect. If you drive on uneven roads with lots of ruts, the ruts will start steering your car. I have lots of these roads around my area, and especially with the high grip tires that I run, it only makes the problem worse. Couple that with some of these poor roads leading into sharp, narrow turns on a two lane highway and you have yourself an exciting ride everytime you drive on those roads.

Regardless of that, I sometimes run 15 x 7, +24 wheels......talk about the car driving itself.

Josh18_2k

iTrader: (3)

true that^ i'm on 17x9 +24 w/ 245's and the car does what it wants to on older highways. gotta hang on to the wheel. maybe power steering would help..
its the trade off to going wide, or at least having flush fitment. more camber counters the effect, so that kinda nice.

Black91n/a

Scrub radius is defined as the distance from intersection of the steering axis (a line drawn between the strut top and the control arm ball joint) and the ground plane, to the centerline of the tire. It varies with offset (obviously), camber, if you're changing it with "crah bolts", and less obviously with tire size (larger scrub radius with smaller tires). It will not change when adjusting camber with camber plates, but it's effects can be minimized by partially unloading the outside edge so that the effective scrub radius is smaller, whis is one big reason why drifters don't seem to notice the difference so much.

It has the effect of increasing tramlining, as was said before, and it uses up more energy when going around corners, causes you to have to drag the tires over the pavement more when turning while stopped (more effort to park) and other things.

There's a reason that GM did a redesign of the Corvette suspension partway through the C4 production run to get a zero scrub radius, and it's a big reason why most modern cars have such high offset wheels, to move that steering axis intersection towards the center of the tire means that the hub gets pushed out and therefore you need more offset.

Roen

iTrader: (2)

There are benefits to low offset though:

You do get an increase in cornering grip at the expense of transitional response.

Thus, if your road course is full of long sweepers with no chicanes or tight esses, that's not such a bad thing to do.

Autocrossing though, I would leave the offset as stock.

Black91n/a, according to your calculations, what's the largest tire width/wheel width combination that will fit under stock scrub radius?

Black91n/a

The increased grip aspect is a function of track width, not necessarily offset, but that's how you can reasonably acheive it. Lower offsets also makes your suspension effectively softer (longer lever arm).

You can get a 225 in the front with stock offset on a 7" wheel, but it's iffy.

For our case, the increased scrub is worth it to be able to fit wider tires.

Roen

iTrader: (2)

I guess I should find 7.5", +40 wheels with 225 tires and see how much spacer I need to minimally clear the strut tower. I guess I may have to go with a proper coilover setup instead of GC/Koni, as I need to gain wheel clearance.

I wonder if anyone knows about clearance issues using the AWR coilovers or the Mazda Competition/Koni setup.

That's probably a RETed question.

Black91n/a

It's a good idea to keep the wheels as close to the suspension as you can, but extra width (wheel and tire, not overall) is worth it in terms of speed (to a point). I wouldn't put up with rubbing for the sake of lower scrub.

Roen

iTrader: (2)

Yea, I hear what you're saying, I'm now thinking of it in an STS2 context, where I'm limited in both tire and wheel. The key then seems to be maximize tire and wheel width, then minimize scrub.

Black91n/a

Exactly.

ilia

iTrader: (4)

Scrub radius matters, some. It's better if you have less, to a degree. Positive scrub and negative scrub do different things. You can read all about this in many books, and talk about it all day if you want, but it doesn't change some basic facts.

What USS CJ is saying is that scrub radius is completely irrelevant when it comes to actually driving a car. What lots of "I'm building my car for the TRACK but have never been on the track" guys fail to understand is that you can optimize setup all day long, but at the end of the day you're still in a pretty damn slow handling 80s road car. It'll never be proper fast. It's really the dude driving. The nut behind the wheel. Drift guys get this. "Road racers" who sit behind a computer all day and bench race never will.

Scrub radius is less important than driving ability, and if you want to put some wheels on, don't worry too much about it. It won't make you that slow. There's only so much wheel you can fit under stock FC fenders, and I can tell you that even at the utmost extremities of that wheel fitment, the scrub radius is not THAT bad. I drive it daily, and it's just fine.



^Many PROFESSIONAL race teams will tell you that good wheel fitment is better than good scrub radius.


PS. OEMs are now running higher offset wheels also because it will typically allow for the packaging of a longer suspension arm, giving a less aggressive camber curve and less geometry change in general. The mu curve of a modern tire does not necessitate as aggressive of camber change, and we can improve all kinds of things by running longer suspension arms.

MAXX65

iTrader: (2)

well........I was expecting a yes or no, maybe a few comments, but I have recieved my answer and I hope anyone else with the same question did too.

thanks guys!

ilia

iTrader: (4)

Yes, wheel spacers are safe. Just put them on safely, and they'll be safe. Recheck them often.

Roen

iTrader: (2)

Same applies in autocross, a lot of people are fast despite their setups, not because of it. But, you can also look at it the other way too, two equal drivers in the same car, the guy with the better setup will win. OR a good setup will even out a slight disadvantage in driver skill. It all depends on which way you look at it.

If you have the money to gain seat time as well as properly set up your car, there's no reason not to, now is there?

Agreed, scrub radius doesn't matter as much in drifting than in racing, hell nor is optimizing a given setup. A good enough driver should be able to slide anything, theoretically, and they're not exactly trying to beat the clock, now are they?

su_maverick

I think that point of this is:

Are wheel spacers safe? - Yes, if they are made properly and checked often
Are they optimal? - No, but few things on our cars are
Will they dramatically change your handling? - Not really. There may be some difference because of changed geometry but the average daily driver will see negligable difference.

Black91n/a

Ummm, excuse me?

It sure as hell is important in every day driving. When you're going down the road and the car wants to jump into the next lane all of a sudden I'd say that's important. Now I'm not saying that it's the most important thing, but it's idiotic to say that it's irrelevant or unimportant.

From what I've seen drifters are the most clueless group out there, mostly teenagers and uneducated 20 year olds who will do whatever pointless mods that they haven't the slightest clue of how, why or if they work, as long as they're labelled with "drift" or if some guy on some forum says that they're great.

Road racers are usually older guys, over 30 professionals, so smart, educated people and they most certainly understand that drivers are very important, they know that when they, in their underprepared car passes the guy in the professionally prepared car or vice-versa. What's the difference? The driver obviously.

Setup still counts for a hell of a lot. I've personally helped a friend shave seconds off his lap times with some suspension work. A properly set up, optimized car will allow the driver to go even faster, which is a good thing. Yes you can drive around a bad setup, to a point, but it's still limiting you. All the pro teams spend loads of time and money making sure their setup is as good as possible.

I specifically said earlier that in our case, with FC's, that wide wheels and tires are of greater advantage than low scrub, but you should still try to minimize it as much as your wheel and tire widths allow.

Oh yea, FC + V8 + 12" slicks = fast car.

ilia

iTrader: (4)

Anyway,

From my experience, on an OEM metal fender FC (with big pull all around), you can't really fit enough wheel or tire to make scrub radius a real problem.

I run 17x9 +20 in the front with a 235 Hankook RS2 tire, and the car drives plenty straight, and does not follow ruts very much at all. I've felt truly bad scrub radius before, and on the FC, on this setup, it's not really a problem at all.

My point is, you can't fit enough wheel on the outside of the hub on a stock fender FC to make scrub radius a serious problem. 9" et 20 is about the outer limit, and that doesn't really create scrub issues.

So we should all stop worrying about it.



My other point is that while RX7club will discuss an insignificant issue ad infinitum, others will just drive their car.

turbogarrett

iTrader: (1)

That statement pretty much throws all your "expertise" out the window.

RETed

Don't you just love it when people talk a lot of ****...


-Ted