BMI's DB12R
09-25-2007, 07:46 PM
#1771
lol
09-25-2007, 08:42 PM
#1772
I have had similar problems with AE and IRS lower arms, but the 'cure' was different.
On the AE arms, the bottom face is not flat. As you tighten up the screws, the arm deflects until it 'becomes' flat to the chassis. This gives rise to changes in castor and/or ride height. The other thing it does is distort the chassis, giving rise to uneven ride height under the cells from one side to the other.
By sanding the bottom of the arms until they are flat, these problems are avoided. Sometimes, it seems that if you sand one arm, the ride height problem goes away, but my experience is that it is actually clamping the arm flat, and that's why it works.
On the IRS lowered AE arms, and the new IRS arms, the issue arises from the lack of a countersink. Look at an AE standard lower arm, and there is a big countersink in the bottm - none on the IRS arms of either type. The screw's countersink is deeper than the chassis thickness, so to get the screw flush with the underside of the chassis, the countersink sticks through the top.
When the arms are tightened, it is the countersink that contacts first, and this sends the arm any way it can. Put a countersink in the IRS AE lowered arms, or in the washer closest to the chassis on the IRS arms, and this problem goes away. (I wrote to DiffDude on this, and received a very nice reply).
Before you go sanding/filing the arms, put a countersink into the IRS arms/washers (of either make/type) and then fit the arms. Don't overtighten (that chassis distortion thing again!) and then measure. Every time I do this the dimensions come out spot on, and there is almost zero difference in ride height across the chassis. I've fitted three sets like this (including my DB12R!) and I'd say the IRS arms are simply the best!
Sorry this is a bit wordy, no pictures!! HTH
On the AE arms, the bottom face is not flat. As you tighten up the screws, the arm deflects until it 'becomes' flat to the chassis. This gives rise to changes in castor and/or ride height. The other thing it does is distort the chassis, giving rise to uneven ride height under the cells from one side to the other.
By sanding the bottom of the arms until they are flat, these problems are avoided. Sometimes, it seems that if you sand one arm, the ride height problem goes away, but my experience is that it is actually clamping the arm flat, and that's why it works.
On the IRS lowered AE arms, and the new IRS arms, the issue arises from the lack of a countersink. Look at an AE standard lower arm, and there is a big countersink in the bottm - none on the IRS arms of either type. The screw's countersink is deeper than the chassis thickness, so to get the screw flush with the underside of the chassis, the countersink sticks through the top.
When the arms are tightened, it is the countersink that contacts first, and this sends the arm any way it can. Put a countersink in the IRS AE lowered arms, or in the washer closest to the chassis on the IRS arms, and this problem goes away. (I wrote to DiffDude on this, and received a very nice reply).
Before you go sanding/filing the arms, put a countersink into the IRS arms/washers (of either make/type) and then fit the arms. Don't overtighten (that chassis distortion thing again!) and then measure. Every time I do this the dimensions come out spot on, and there is almost zero difference in ride height across the chassis. I've fitted three sets like this (including my DB12R!) and I'd say the IRS arms are simply the best!
Sorry this is a bit wordy, no pictures!! HTH
This DEFINITELY makes sense--thanks for sharing.
When I measured my arms it was un-installed held flat against my tempered glass set up "board" and measured that I found the difference so the countersink (or lack thereof) made no difference in my case. I DEFINITELY plan to run the new IRS arms this year and am interested (and expect they will be) if they are better than the lowered molded AE ones.
I will definitely add a countersink to my arms, either style, as there's certainly nothing to lose doing so!
Thanks again,
Scottrik
09-25-2007, 08:56 PM
#1773
What do you guys mean by add a countersink to the arms?
For what?
For what?
09-25-2007, 08:59 PM
#1774
If you look at an AE 1/12 lower arm at you'll notice there is a chamfer/countersink in the arm for the 8-32 mounting screws. Read the above post to see how the lack of same CAN affect (certainly not will) how the arm sits on the chassis plate when it is tightened down.
Now look at an IRS "lowered" AE arm. IRS mill .060" (ish) from the molded AE arm mount so it can move the arm itself closer to the track so you can use smaller tires. If you look at the 8-32 mounting hole you will see that the chamfer/countersink is removed when that material is removed. That factoid is how I tell standard AE arms from "lowered" IRS arms at a glance.
It sounds like the new IRS "reversible" arms maybe also lack this chamfer/countersink. Not a problem as it is certainly easy to add on your own.
Scottrik
Now look at an IRS "lowered" AE arm. IRS mill .060" (ish) from the molded AE arm mount so it can move the arm itself closer to the track so you can use smaller tires. If you look at the 8-32 mounting hole you will see that the chamfer/countersink is removed when that material is removed. That factoid is how I tell standard AE arms from "lowered" IRS arms at a glance.
It sounds like the new IRS "reversible" arms maybe also lack this chamfer/countersink. Not a problem as it is certainly easy to add on your own.
Scottrik
09-25-2007, 09:07 PM
#1776
If you look at an AE 1/12 lower arm at you'll notice there is a chamfer/countersink in the arm for the 8-32 mounting screws. Read the above post to see how the lack of same CAN affect (certainly not will) how the arm sits on the chassis plate when it is tightened down.
Now look at an IRS "lowered" AE arm. IRS mill .060" (ish) from the molded AE arm mount so it can move the arm itself closer to the track so you can use smaller tires. If you look at the 8-32 mounting hole you will see that the chamfer/countersink is removed when that material is removed. That factoid is how I tell standard AE arms from "lowered" IRS arms at a glance.
It sounds like the new IRS "reversible" arms maybe also lack this chamfer/countersink. Not a problem as it is certainly easy to add on your own.
Scottrik
Now look at an IRS "lowered" AE arm. IRS mill .060" (ish) from the molded AE arm mount so it can move the arm itself closer to the track so you can use smaller tires. If you look at the 8-32 mounting hole you will see that the chamfer/countersink is removed when that material is removed. That factoid is how I tell standard AE arms from "lowered" IRS arms at a glance.
It sounds like the new IRS "reversible" arms maybe also lack this chamfer/countersink. Not a problem as it is certainly easy to add on your own.
Scottrik
Could you possibly get a pic for me? I dont have my 12th yet, so I cant really picture that...
I get what you mean though
Thanks
09-25-2007, 09:28 PM
#1777
Picture this... 
First pic is the standard AE arm, second is the IRS "lowered" AE arm. They mill .060" off the face that contacts the chassis/ride height shims when assembled onto the car. You can see in the pics that the IRS one the threads are all the way to the "top" of the hole (bottom, actually, as-installed...the first threads taken by the screw).
I think the chamfer/countersink is there because like almost all molded parts in RC they use the mounting screw to create the threads. A screw doesn't really "cut" threads, so to speak, it just moves material around to force them. The chamfer/countersink gives some space for that displaced material to go without disturbing the mounting face. The IRS arm relies on similar threading methodology but the chamfer/countersink of the original piece has been lost.
That said...I use an inexpensive (under $5) 8-32 tap and eliminate the problem altogether. That way the thread is actually cut into the part. The original holes ARE a bit larger than would have been left ordinarily for a cut thread (specifically to allow thread "forcing") but since the parts "clamp" the cut threads pose no problem. What you DON'T want to do is cut threads into something that is used for adjustment and needs to hold the screw snug without "clamping" force. Tends to make 'em too easy to move.
hth,
Scottrik
First pic is the standard AE arm, second is the IRS "lowered" AE arm. They mill .060" off the face that contacts the chassis/ride height shims when assembled onto the car. You can see in the pics that the IRS one the threads are all the way to the "top" of the hole (bottom, actually, as-installed...the first threads taken by the screw).
I think the chamfer/countersink is there because like almost all molded parts in RC they use the mounting screw to create the threads. A screw doesn't really "cut" threads, so to speak, it just moves material around to force them. The chamfer/countersink gives some space for that displaced material to go without disturbing the mounting face. The IRS arm relies on similar threading methodology but the chamfer/countersink of the original piece has been lost.
That said...I use an inexpensive (under $5) 8-32 tap and eliminate the problem altogether. That way the thread is actually cut into the part. The original holes ARE a bit larger than would have been left ordinarily for a cut thread (specifically to allow thread "forcing") but since the parts "clamp" the cut threads pose no problem. What you DON'T want to do is cut threads into something that is used for adjustment and needs to hold the screw snug without "clamping" force. Tends to make 'em too easy to move.
hth,
Scottrik
Last edited by Scottrik; 06-27-2008 at 04:41 PM.
09-25-2007, 09:34 PM
#1778
I get it! So then you can ajust the ride hight, and by that use the smaller tires
Got it!
Thanks man!
09-25-2007, 09:47 PM
#1779
The arms aren't really an "adjustment" in and of themselves (though they could be) because that's a BIG step (though no more than the standard 1/16" washer kits come with and, apparently, expect you to use).
The actual adjustment is done with thin shims that clamp between that mounting surface and the chassis top surface. The CRC shims are .010, .020 and .030" thick (.25, .5 and .75mm). They can be combined to give .040, .050 and .060". I use the Fiber-Lyte carbon fiber shims that are really cool too, though not as fine of increments as the CRC. They are fair-to-pricey and look really "bling" (GORGEOUS carbon fiber...it glows) in your hand but are completely hidden from view in-use. The reason I like 'em is that I measure ride height, tire dia and roll-out in mm so it's one less step (conversion) if I use ride height shims that are measured in mm. I'm lazy that way.
The big things to remember are:
1) remove the sticky backing paper from the CRC shims before use (I've seen guys using them WITH the paper still on twice now), and
2) Cut the CRC shims at the mounting holes. They used to do this for you but had complaints from people who Hercules their cars together. The shims are WAY easier to use if instead of holes they are notches/slots that open out into the long straight side of the shim. That way you only have to loosen the mounting screws to add or remove shims rather than having to take the screws all the way out. Putting the slots open to the long straight side allows the "triangled" side with the little tiny hole at the apex to point out (toward the tire) where you can easily grab 'em to pull 'em out. or tap 'em to make sure they're fully seated against the screw.
3) it seems, to an extent, counter-intuitive but you add shims to reduce ride height and remove shims to raise it (since the shims are on TOP of the chassis plate which is suspended by the arm/wheel). I must confess to that at LEAST twice each season I will dutifully get this backward...want to reduce ride height .5mm, pull .5mm worth of shims out, measure it and find that I now need to reduce ride height by 1mm. Am I the only one?
Also note that I edited my last post and added info re: threading and other "chamfer-effects".
Scottrik
of the feeble mind
The actual adjustment is done with thin shims that clamp between that mounting surface and the chassis top surface. The CRC shims are .010, .020 and .030" thick (.25, .5 and .75mm). They can be combined to give .040, .050 and .060". I use the Fiber-Lyte carbon fiber shims that are really cool too, though not as fine of increments as the CRC. They are fair-to-pricey and look really "bling" (GORGEOUS carbon fiber...it glows) in your hand but are completely hidden from view in-use. The reason I like 'em is that I measure ride height, tire dia and roll-out in mm so it's one less step (conversion) if I use ride height shims that are measured in mm. I'm lazy that way.
The big things to remember are:
1) remove the sticky backing paper from the CRC shims before use (I've seen guys using them WITH the paper still on twice now), and
2) Cut the CRC shims at the mounting holes. They used to do this for you but had complaints from people who Hercules their cars together. The shims are WAY easier to use if instead of holes they are notches/slots that open out into the long straight side of the shim. That way you only have to loosen the mounting screws to add or remove shims rather than having to take the screws all the way out. Putting the slots open to the long straight side allows the "triangled" side with the little tiny hole at the apex to point out (toward the tire) where you can easily grab 'em to pull 'em out. or tap 'em to make sure they're fully seated against the screw.
3) it seems, to an extent, counter-intuitive but you add shims to reduce ride height and remove shims to raise it (since the shims are on TOP of the chassis plate which is suspended by the arm/wheel). I must confess to that at LEAST twice each season I will dutifully get this backward...want to reduce ride height .5mm, pull .5mm worth of shims out, measure it and find that I now need to reduce ride height by 1mm. Am I the only one?
Also note that I edited my last post and added info re: threading and other "chamfer-effects".
Scottrik
of the feeble mind
09-25-2007, 09:55 PM
#1780
The arms aren't really an "adjustment" in and of themselves (though they could be) because that's a BIG step (though no more than the standard 1/16" washer kits come with and, apparently, expect you to use).
The actual adjustment is done with thin shims that clamp between that mounting surface and the chassis top surface. The CRC shims are .010, .020 and .030" thick (.25, .5 and .75mm). They can be combined to give .040, .050 and .060". I use the Fiber-Lyte carbon fiber shims that are really cool too, though not as fine of increments as the CRC. They are fair-to-pricey and look really "bling" (GORGEOUS carbon fiber...it glows) in your hand but are completely hidden from view in-use. The reason I like 'em is that I measure ride height, tire dia and roll-out in mm so it's one less step (conversion) if I use ride height shims that are measured in mm. I'm lazy that way.
The big things to remember are:
1) remove the sticky backing paper from the CRC shims before use (I've seen guys using them WITH the paper still on twice now), and
2) Cut the CRC shims at the mounting holes. They used to do this for you but had complaints from people who Hercules their cars together. The shims are WAY easier to use if instead of holes they are notches/slots that open out into the long straight side of the shim. That way you only have to loosen the mounting screws to add or remove shims rather than having to take the screws all the way out. Putting the slots open to the long straight side allows the "triangled" side with the little tiny hole at the apex to point out (toward the tire) where you can easily grab 'em to pull 'em out. or tap 'em to make sure they're fully seated against the screw.
3) it seems, to an extent, counter-intuitive but you add shims to reduce ride height and remove shims to raise it (since the shims are on TOP of the chassis plate which is suspended by the arm/wheel). I must confess to that at LEAST twice each season I will dutifully get this backward...want to reduce ride height .5mm, pull .5mm worth of shims out, measure it and find that I now need to reduce ride height by 1mm. Am I the only one?
Also note that I edited my last post and added info re: threading and other "chamfer-effects".
Scottrik
of the feeble mind
The actual adjustment is done with thin shims that clamp between that mounting surface and the chassis top surface. The CRC shims are .010, .020 and .030" thick (.25, .5 and .75mm). They can be combined to give .040, .050 and .060". I use the Fiber-Lyte carbon fiber shims that are really cool too, though not as fine of increments as the CRC. They are fair-to-pricey and look really "bling" (GORGEOUS carbon fiber...it glows) in your hand but are completely hidden from view in-use. The reason I like 'em is that I measure ride height, tire dia and roll-out in mm so it's one less step (conversion) if I use ride height shims that are measured in mm. I'm lazy that way.
The big things to remember are:
1) remove the sticky backing paper from the CRC shims before use (I've seen guys using them WITH the paper still on twice now), and
2) Cut the CRC shims at the mounting holes. They used to do this for you but had complaints from people who Hercules their cars together. The shims are WAY easier to use if instead of holes they are notches/slots that open out into the long straight side of the shim. That way you only have to loosen the mounting screws to add or remove shims rather than having to take the screws all the way out. Putting the slots open to the long straight side allows the "triangled" side with the little tiny hole at the apex to point out (toward the tire) where you can easily grab 'em to pull 'em out. or tap 'em to make sure they're fully seated against the screw.
3) it seems, to an extent, counter-intuitive but you add shims to reduce ride height and remove shims to raise it (since the shims are on TOP of the chassis plate which is suspended by the arm/wheel). I must confess to that at LEAST twice each season I will dutifully get this backward...want to reduce ride height .5mm, pull .5mm worth of shims out, measure it and find that I now need to reduce ride height by 1mm. Am I the only one?
Also note that I edited my last post and added info re: threading and other "chamfer-effects".
Scottrik
of the feeble mind
Hmm, This is all new lol, Theres alot more to 12th then what meets the eye compared to TC......
But im guessing that the kit comes with all these shims and all? To run the carpet setup that the BMI crew put in, ot do I need more parts?
And I re read it, makes more sense now, I should get one for me
09-25-2007, 10:06 PM
#1781
I think Jason MAY have the IRS rear axle height adjusters (also measured in mm...hence my complete conversion to metric measurements on my cars) since I think he does a fair bit of IRS content in the kits.
I'd really like to try one of his kits...I've got some of his other stuff and it is REALLY top-notch product. I'll probably have to wait until next year though...
Unless he needs a sponsored driver in Montana...
09-25-2007, 10:13 PM
#1782
I honestly don't know, but I'd be surprised (pleasantly) if it did. I've NEVER seen a car kit come with decent adjustment shims...just the 1/16" washer mentioned above. The shims really come under the heading of "pit gear" (like shock oils, different springs, etc) more so than "kit parts". No worries though because the CRC shims are only $8-10 from retailers/mail-order houses everywhere including direct from CRC.
I think Jason MAY have the IRS rear axle height adjusters (also measured in mm...hence my complete conversion to metric measurements on my cars) since I think he does a fair bit of IRS content in the kits.
I'd really like to try one of his kits...I've got some of his other stuff and it is REALLY top-notch product. I'll probably have to wait until next year though...
Unless he needs a sponsored driver in Montana...
I think Jason MAY have the IRS rear axle height adjusters (also measured in mm...hence my complete conversion to metric measurements on my cars) since I think he does a fair bit of IRS content in the kits.
I'd really like to try one of his kits...I've got some of his other stuff and it is REALLY top-notch product. I'll probably have to wait until next year though...
Unless he needs a sponsored driver in Montana...
I had a TON of those shims, but I lost them one day at the track lol
I had every size purple shim they make!Oh well......... I need to get my list all done, then the add on parts
And Jay already told me im the next team driver..... Hes only waiting for me to get my gear for the car
09-25-2007, 10:23 PM
#1783
Also
Does LRP even make a X-11 10.5?????
I could of sworn they did, and now I cant find it lol
Does LRP even make a X-11 10.5?????
I could of sworn they did, and now I cant find it lol
09-25-2007, 10:51 PM
#1784
Tech Fanatic
Scottrik - all good advice, thanks. How can you get the shim placement wrong by forgetting to add when you should take away? I don't know what you mean, I've haven't done that - well, not since the weekend anyway!! 
We must be of the same certain age - it gets worse as the clock ticks on!
As Scottrik says, it isn't a situation you find on every car and every lower wishbone, but it happens. I had one on the DB12R I built. I just do it as a matter of course now, and don't have any issues with set-up. When the spacers go in, they are usually a larger diameter than the screw, and so don't cause a problem.
We must be of the same certain age - it gets worse as the clock ticks on!
As Scottrik says, it isn't a situation you find on every car and every lower wishbone, but it happens. I had one on the DB12R I built. I just do it as a matter of course now, and don't have any issues with set-up. When the spacers go in, they are usually a larger diameter than the screw, and so don't cause a problem.
09-25-2007, 11:25 PM
#1785
Scottrik - all good advice, thanks. How can you get the shim placement wrong by forgetting to add when you should take away? I don't know what you mean, I've haven't done that - well, not since the weekend anyway!!
We must be of the same certain age - it gets worse as the clock ticks on!
We must be of the same certain age - it gets worse as the clock ticks on!
Laughing into my senility,
Scottrik