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Old 07-25-2003, 07:44 AM   #5581
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Quote:
Originally posted by Johnnytc3
Can anybody here give some insight on what adding bump steer spacers to the TC3 does?
Johnnytc3 - Adding washers between the steering block and ball stud changes the amount of bump steer. Bump steer is the front wheels toeing out as the suspension compresses. When there is more bump steer, the car will steer more aggressively on turn entry and in the center of the turn. Getting the car to steer well without excessive bump steer usually results in a faster setup.

Don't forget that changing between different castor blocks (0,2,4 degree) will change the amount of bump steer. For example, the 0 degree castor block will require washers to keep the same amount of bump steer as a 4 degree block with no washers. If you want to stay consistent, keep the distance between the ball stud and the ground constant when you make other setup changes.
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Old 07-25-2003, 08:58 AM   #5582
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Mike D-so do you think as a base set-up for Carpet/Foam/stock racing that you should run a shorter ballstud when running say 6 -degrees of Caster.

- or -

The opposite and that is run the stock long ballstud (silver) when running lots of caster and add spacers when running 0 or 2 degrees of caster?

I dont test nearly as much as I did a few months ago-so just looking for info and theories before hitting the track. I get maybe one 4 minute practice session before a race anymore.Thanks in advance!!
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Old 07-25-2003, 09:08 AM   #5583
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Hey Ray! Thanks for the lube info.

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Old 07-25-2003, 09:23 AM   #5584
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fuzzy-no problem-always willing to help!!
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Old 07-25-2003, 09:25 AM   #5585
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Quote:
Originally posted by rayhuang
Mike D-so do you think as a base set-up for Carpet/Foam/stock racing that you should run a shorter ballstud when running say 6 -degrees of Caster.

- or -

The opposite and that is run the stock long ballstud (silver) when running lots of caster and add spacers when running 0 or 2 degrees of caster?

I dont test nearly as much as I did a few months ago-so just looking for info and theories before hitting the track. I get maybe one 4 minute practice session before a race anymore.Thanks in advance!!
For Carpet/Foam/stock racing I usually run 4 degree blocks with no spacers and kit ball studs. I think the biggest speed difference comes from driver feel then actual setup. Kind of like radio exponental, it makes no difference on how fast the car is... just how fast and easily somebody can drive the car.
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Old 07-25-2003, 09:52 AM   #5586
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Mike D-I agree. The way my car steers is of utmost importance to me. I know exactly how I want my car to feel from corner entry to exit. if it doesnt feel like that I can usually dial it in. The hard part is that sometimes what feels great to me isnt that fast in lap times. So I make changes to make it faster-the perfect feel I like goes away a bit-but my laptimes drop. The flip side is it often leads me to clip apexs or be a little sloppy on corner exit.

But I am always willing to try a different set-up because I know I can change my car back.

Theres a million set-ups that work well on the Tc3. But only few of the are truly superior!!!
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Old 07-25-2003, 10:32 AM   #5587
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MikeD - If bump steer causes the front tires to toe-out when the suspension is compressed, it would seem to me that it would cause the car to steer less aggressively. The outside tire would compress a lot more than the inside tire causing the outside tire to turn more the opposite of your intended direction. The outside tire would fight against the inside tire in a turn. Can you explain it in a little more detail? Thanks
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Old 07-25-2003, 10:43 AM   #5588
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Quote:
When there is more bump steer, the car will steer more aggressively on turn entry and in the center of the turn. Getting the car to steer well without excessive bump steer usually results in a faster setup.
What would I need to do for less bump steer?

I am running stock set up, rubber, stock motor. Infield the car handles good for me. However I am having problems on big sweepers. Initial turn in is controlled, then mid turn (at the apex) the car bites hard and darts inward. (does that make sense?)

I more than likely need to adjust something else (droop, shock placement, etc?). But what you described sounds like how my car is handling now

Any ideas?
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Old 07-25-2003, 11:39 AM   #5589
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Sssssssssst...Ssssssst...

Gee Roger, you'd think you didn't know what kind of car I run... LOL

Art
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Old 07-25-2003, 12:45 PM   #5590
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Quote:
Originally posted by DOTMAN
MikeD - If bump steer causes the front tires to toe-out when the suspension is compressed, it would seem to me that it would cause the car to steer less aggressively. The outside tire would compress a lot more than the inside tire causing the outside tire to turn more the opposite of your intended direction. The outside tire would fight against the inside tire in a turn. Can you explain it in a little more detail? Thanks
DOTMAN - Toe out will increase steering when entering a corner. Too much toe out can make the car wander and be less stable on and off power.

Also, using the Ackerman shims on the steering rack will increase steering on turn entry and reduce steering on turn exit. The Ackerman shims cause the inside front wheel to turn more in relation to the outside front wheel.

So what does all this mean? When turning, the outside front and rear tires support a majority of the cornering loads. Ignoring other chassis setup changes and assuming that the tires are not sliding, the amount that the car turns depends greatly on the amount that your outside front wheel is turned. This is because it is loaded much heavier then the inside front wheel and is generating higher traction loads. So no matter how you modify your steering geometry, the outside front wheel will be turned the same amount.

The difference that bump steer and ackerman shims make is that the inside front wheel will be turned more when entering a turn then if either were not used. Since most people don't drive with their steering lock-to-lock, they don't notice that they are steering more when ackerman and bump steer is added. In general, increasing the radio dual rate to make your wheels turn more then ideal will make your car slower on the track. This is why bump steer will make the car less stable, enter the turn more aggressively and have less steering overall and on turn exit.
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Old 07-25-2003, 04:04 PM   #5591
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What MikeD didn't mention is that, since you're putting so much of the load on the outside front tire, you're more or less dynamically steering with IT - you don't really notice that it's bump-steering its way to a more toed out condition.

But, the reason it's more aggressive is that the INSIDE tire is being turned more because of the increased toe-out condition. This assists the turn-in and mid-turn and gives more turn because if it were toe-in that tire would be turning slightly LESS and fighting the turn - if it were at 0 toe-in/out it would not be helping or hindering, it would be more or less neutral.
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Old 07-25-2003, 04:33 PM   #5592
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I'm sure you're both right, it just doesn't seem logical. In the case of a low traction asphalt track (as an example), your setup would probably result in a considerable amount of chassis roll. In a left turn, the right wheel with bump steer would turn away from the turn causing a push condition. The left wheel wouldn't compress much...may even lift slightly which would nullify the toe-out effect of the inside wheel. I have found however, that logic and reality can be far apart with RC cars. I'm sure there are other physics related factors I missing too.
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Old 07-25-2003, 04:36 PM   #5593
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Quote:
Originally posted by DOTMAN
I'm sure you're both right, it just doesn't seem logical. In the case of a low traction asphalt track (as an example), your setup would probably result in a considerable amount of chassis roll. In a left turn, the right wheel with bump steer would turn away from the turn causing a push condition. The left wheel wouldn't compress much...may even lift slightly which would nullify the toe-out effect of the inside wheel. I have found however, that logic and reality can be far apart with RC cars. I'm sure there are other physics related factors I missing too.
The thing is, during your left turn - when the front right tire is deflecting out because of bump steer, you don't notice it since you are actively steering the car around the corner - you just input more steering. It's a very small amount and you don't notice it.

It affects the inside tire because you've input more steering to compensate for the right tire's toe-ing out - so even though the left tire isn't changing it's toe, the right tire's change is affecting the left tire. . .
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Old 07-26-2003, 03:07 AM   #5594
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DOTMAN - i think the confusion arose because when they say more bump steer they mean using more spacers=less toe out when suspension compresses. you are thinking of bump steer as being the effect of the wheels toeing out, correct?
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Old 07-26-2003, 09:29 AM   #5595
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Its as easy as this... with your tires pointing straight and the car at rideheight and zero toe... you push straight down on the front shocktower, you will see a little toe out deflection. Since the inside position of the steering link is mounted to the rack and does not move left or right... the steering block mount of the steering link on each side "moves" towards the centerline of the car. This chassis travel distance down is "taken" proportionately from the steering, causing toe out. That is why the steering link needs to be as close to chassis level as possible... so there is little deflection through the range of travel. The higher the ballstud on the steering block, or the more overall suspension travel there is... the more deflection through range of suspension travel... or... bumpsteer. This, added to caster camber and tire additive location on the front tires is somewhat of an art and is a useful tool to dial in the steering to your preference. (PRACTICE) The real kicker is... when cornering... this amount is "divided" between left and right tires... one side being higher than the other... the outer, inside link mount (in relation to the turn) pushing the camber link towards the tire (and lower than the inside, inside link mount), and the steering link being pulled away from the tire... and the exact opposite on the other side.... Similar to a ballstud being mounted vertically pointing up has more effect on camber change than one mounted pointing down. When it is mounted pointing up.. the ballstud will tend to push the link to the side and away from the centerline of the car. (generally) When it is mounted pointing down, it will tend to pull the link to the centerline of the car... but to a point only, and then has no effect, except through extreme suspension travel.

I prefer the steering link level with my suspension arm... but this also depends on asphalt or carpet racing because of tire size, droop, and the effects an overall lower height can change on rollrate going from larger to smaller diameter tires. (The taller the tire... the lower you take the chassis to meet rideheight, the lower the inside mount for ALL links is going to be...camber, steering) With foams your tire size is almost always smaller than rubber... so you would be able to run your steering link closer to arm level... which will be real close to chassis level. The size of rubber tires makes you drop the chassis more, and there is a severe angle added to the arms for the car to make ride height (5mm), so making the steering links level with the arms isnt the way to go.... >whew<

Toe out adds steering coming into the corner...excessive toe out can make the car wander on the straights... and a handful on a less than grippy track. Neutral toe, and toe-in, in my personal choice, are rarely used on anything four wheel drive. About half a degree of toe out is a standard for me... anything more than a degree of toe out, and i feel need to work on the other end of the car. Again, excess toe on either end will tighten the car and make it drive inefficient and inconsistent... each end fighting for supremacy of the available grip. Hope this helps...and i didnt confuse anyone...
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