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PostPosted: Thu Oct 18, 2007 1:58 pm 
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Keith Quistorff wrote:
To clarify, my statement was that a bigger bar would offer no additional grip when a smaller bar already lifts the inside front tire. Did Eric's Spyder lift the front tire with any front bar other than the biggest?


I can't say for sure since he had already settled on the big bar by the time I came along, but I'm betting it did lift a wheel prior to that bar. Note that I tended to stlil be able to get wheelspin with that big bar on occasion (particularly in 180's on concrete), but Eric didn't seem to have the trouble. Smoothness and getting some good initial turn-in, I'd bet.

I think the answer to this is clear. Chuck needs to rent a site for a couple days. Buy a bunch of suspension parts and tires and wheels. Then we invite Sam, me, Keith, Feinberg, Casto, and anyone else who has participated in this and we start testing. That's clearly the only way to know for sure. :twisted:


--Donnie


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PostPosted: Thu Oct 18, 2007 2:27 pm 
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Donnie Barnes wrote:
I think the answer to this is clear. Chuck needs to rent a site for a couple days. Buy a bunch of suspension parts and tires and wheels. Then we invite Sam, me, Keith, Feinberg, Casto, and anyone else who has participated in this and we start testing. That's clearly the only way to know for sure. :twisted:


--Donnie


That is not as far-fetched as it sounds! :D

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PostPosted: Thu Oct 18, 2007 4:17 pm 
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JamesFeinberg wrote:
Richard Casto wrote:
Keith Quistorff wrote:
To clarify, my statement was that a bigger bar would offer no additional grip when a smaller bar already lifts the inside front tire.


I pretty much agree with you that once that wheel is off the ground it doesn't have any additional impact on weight transfer, ...


I'm not sure I totally buy that argument. I tend to think there are way to many variables at work to make blanket statements like that and I've definitely seen instances where more bar and the resulting higher/sooner wheel liftoff makes the car faster.


Jim you missed the second part of what I said. And that is the sooner liftoff part of a stiffer bar. So we probably agree on that. I have no personal experience, but I would guess that you get much less of an effect once the wheel is up in the air.

Regarding dynamics once one wheel is off the ground. The front sway bar is coupling the left and right springs so if you lift the right front wheel you compress the left front. This effectively increases the left front spring rate. The larger the bar, the more they are coupled and the higher the spring rate. An infinitely stiff bar would couple them 100% which would mean the spring rate on the left would be double it's normal value once the right wheel is off the ground. The weaker the bar, the smaller percentage of the coupling. This might also account for some of what you see with a larger bar even AFTER one wheel is off the ground?

I need to dig out my copy of Fred Puhn's suspension book this evening to see if it talks about this at all or not.

Donnie Barnes wrote:
I think the answer to this is clear. Chuck needs to rent a site for a couple days. Buy a bunch of suspension parts and tires and wheels. Then we invite Sam, me, Keith, Feinberg, Casto, and anyone else who has participated in this and we start testing. That's clearly the only way to know for sure. :twisted:


Works for me! 8)

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PostPosted: Thu Oct 18, 2007 5:10 pm 
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Richard Casto wrote:
Jim you missed the second part of what I said. And that is the sooner liftoff part of a stiffer bar.


I didn't miss it-- I just wasn't addressing it. You asserted that there is no additional impact on weight transfer after it lifted off and I'm saying I don't fully buy that argument.

This has been discussed ad nauseam in many different contexts and I'm not really that interested in the "theoretical" side of it. All I can say is what I've seen in practice and that's all I was relaying.

I've spent a lot of time plowing through the physics and I just don't think it's practical to rely on mathematical models of the situation. Feel free to knock yourself out with it, however. :D

Jim


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PostPosted: Thu Oct 18, 2007 5:18 pm 
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Donnie Barnes wrote:
Keith Quistorff wrote:

I think the answer to this is clear. Chuck needs to rent a site for a couple days. Buy a bunch of suspension parts and tires and wheels. Then we invite Sam, me, Keith, Feinberg, Casto, and anyone else who has participated in this and we start testing. That's clearly the only way to know for sure. :twisted:


--Donnie


Donnie, you forgot liquor, Chuck needs to bring liquor and beer. You simply can't have an good testing session without a lot of booze and tequilla shooters :-) I'm trying to remember which Carroll Smith book I read that in.

Yep, the 1 1/4 inch solid three-piece bar on the 2180 pound Spyder pretty much elimiated the wheelspin and made the car transition like a rocketship. The guys at Speedway Engineering asked how much my car weighed when when I ordered the big bar and were in disbelief when I told them. We used toe-out (on a mid-engine car) and lots of rear shock to counteract the push from the massive front bar, which seemed kind of crazy, but made sense to me. The car still lifted the inside front with the smaller 1 1/8 inch bar, but the extra bar size transformed that car into a missle when we hit the setup.

Although, when you go to such an extreme to compensate for a problem on a stock car, like the wheelspin on the Spyder, it creates other issues. In this case, the window of hitting the right setup was narrow and always moving.

Whether or not that was the best set up for the car, I don't know, but it was definitely the best Spyder in the country. You just never know what will work on a car for autox. The bottom line is thinking it out first, as you guys are doing, then doing some trial and error is the only way to really find out...sometimes crazy stuff works, as per my example above.

Eric


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PostPosted: Thu Oct 18, 2007 5:22 pm 
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Richard Casto wrote:
I need to dig out my copy of Fred Puhn's suspension book this evening to see if it talks about this at all or not.


Why wait? Google Books has it online for free (for now).

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PostPosted: Thu Oct 18, 2007 6:01 pm 
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Wes Eargle wrote:
Richard Casto wrote:
I need to dig out my copy of Fred Puhn's suspension book this evening to see if it talks about this at all or not.


Why wait? Google Books has it online for free (for now).


LOL, I have the original edition of that book...haven't looked at it in many years. Heck, I even had a Capri like in the book! Mine was a Capri II though. I cracked a piston on it at the old Rocky Mount airport in an autox back in 1981 revving it too high. I built a nasty little motor for that thing and with an Isky cam, headers, Offy manifold and 4bbl Holley, it really really wanted to rev like a banshee, which of course I obliged. :) All the way to its deathbed. :(


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PostPosted: Thu Oct 18, 2007 6:17 pm 
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JamesFeinberg wrote:
You asserted that there is no additional impact on weight transfer after it lifted off and I'm saying I don't fully buy that argument.


Actually Jim based upon what I said, you are correct. What I was meaning (but didn't say very clearly) was that in static conditions (i.e. set speed around a skid pad) that the wheel that is off the ground has zero to do with weight at that point as the car is suspended by three wheels. But what we are really talking about is dynamic handling (i.e. weight transfer with "transfer" being very much a dynamic aspect) and in that case I agree that there is a bunch of stuff going on and that I can see different bar sizes affecting things even with one wheel off the ground.

I also seem to have lost my copy of "How to Make Your Car Handle" and the only stuff only shows a handful of pages. :(

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PostPosted: Tue Nov 13, 2007 5:11 pm 
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Well I'll soon be learning how durable the R1s are. Found a guy in Phoenix who has six of them brand new 255-40-17 and I got them for $800 for all six. (at $240 each new, that's a good deal). He roadraces in NASA and decided to switch to 18" wheels for wider sizes.

Now I need to decide ... track tires or autocross tires? Hmm...

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PostPosted: Tue Nov 13, 2007 5:18 pm 
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I think you'll be in good shape with the suspension setup and front camber you have for very long wear out of them (great price by the way!). The 330i with the pins tapped out and no load in it only has -0.9 degrees camber; with me in it, it just around -1.2. :evil: (just checked this past weekend at Hubcap Heaven).

My RF is showing a few cords on the sidewall to treadface junction (similar to where the Hoosier corded completely after less than 20 runs) as of this weekend. The tires have 22 + 52 + 8 = 82 runs on them now. Jackie and Ash (William) ran them down in Atlanta for 12 timed runs and about 40 fun runs :( , so they got hammered pretty hard on that RF due to a course dip under cornering load. The LF looks fine, and the rears are in great shape. I can flip the fronts on the rims now and continue.

Now I just need to decide what if any car I want to autox next year...sure wish I knew what class a 135i would be in. 8)

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PostPosted: Tue Nov 13, 2007 7:00 pm 
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You have enough BMWs!

GET THE GT3!!!!

You are very generous; I think I've run more runs on your BFGs than mine!

Go ahead and get yourself a nice Christmas gift.


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PostPosted: Tue Nov 13, 2007 7:30 pm 
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William Gravely wrote:

GET THE GT3!!!!



x2!

Are you seriously thinking about the 135? I'm still anxious as hell to see one in person.


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PostPosted: Tue Nov 13, 2007 7:41 pm 
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Matt McGrain wrote:
William Gravely wrote:

GET THE GT3!!!!



x2!

Are you seriously thinking about the 135? I'm still anxious as hell to see one in person.


Not really, but if it was classed competively, it would be fun to compete in one...especially if the rumor of a potential limited slip option comes true (doubt it though). I'm not sure how much fun trying to mange so much wheel torque, right from low rpm too, would be without an LSD. The 330i is the first car I've autocrossed in 25 years without an LSD, and at times even with its limited torque output (relative to 135i) that isn't much fun.

The thought of competing against Les in SS with a GT3 sounds fun though. :lol:

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PostPosted: Tue Nov 13, 2007 7:47 pm 
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Chuck Branscomb wrote:
The thought of competing against Les in SS with a GT3 sounds fun though. :lol:


Heck yeah! Though you'll probably kick my butt.


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PostPosted: Wed Feb 27, 2008 6:33 pm 
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Location: Probably somewhere near an autocross.
bump

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