Suspension Theory

[losiXXXman]

Hope fully this topic will inspire good discussion without getting too cerebral, and you won't need a PhD in physics.

When the RC10 was in it's biggest heydey, all of these great aftermarket parts were produced in order to tweak the most out of its performance. Its interesting now, that as collectors, so many here are building many different 10's to display all the various incarnations. Anyway...

I remember a lot of articles BITD discussing the pros and cons of various setups. Since a lot of you here have multiple versions with different suspensions/trannys etc... I'd love to hear everyone give their opinions of different options.

Example: I think I had read that Trailing arm suspensions were particularly suited to rougher, bumpier tracks over the stock suspension. I also remember constantly reading about "tire scrub" and how longer armed suspensions had less of this, which was a "good" thing. (Tire scrub was defined as lateral movement of the tire across the track through the range of travel due to the arm moving through a smaller arc(longer arm) for a given travel displacement) OK, that does sound cerebral. Still later I read that longer arm suspensions are slower to react to terrain, which in my mind makes them suitable for smooth tracks, and leads me to believe shorter arms would be good for bumpier, rougher, less groomed tracks.

How do you feel your current runner compares to the totally stock RC10 (wide track front end of course!) ?

[Bugle]

I would have thought that the semi trailing arms would be worse for rough tracks due to the toe changes as the arm moves, effectively bump steering at the rear.

The reaction of the suspension is going to be based on where the shock is attached to the arm and how stiff the shock is set up. Surely a longer arm is better for a rough track, the more the suspension has to move the more you're going to notice the car wandering due to tyre scrub.

The RC10 front end isn't too great, it bump steers alot due to the steering linkages being longer than the arms, the B2 was a huge improvement.

[Charlie don't surf]

IMO trailing arms are only "better" on a rough track because of the rate of deflection as the arm goes through it's vertical movement ie-as the rear suspension contacted a change in terrain, lets say a bump in the track, the suspension moved back and away as the rear tire compressed, then forward and up as it traveled through it's arc of motion. This movement resulted in very little resistance through the motion because the vehicle was traveling in the same direction as the movement of the suspension--no vertical binding other than the damper, whereas the "standard" upper/lower control arm has resistance to this motion because of the upper camber links moving first outward as the suspension compresses, then inward as it completes it's upstroke--BUT it's moving in a different direction ( inward/outward) as the car which is moving forward over the bump.

Now the stock rear end of an RC10 was very rarely set up to take roll center into account--don't know why most never took this into consideration, but they seemed to not fully understand it at all, because you can change both the camber gain and speed of the horizontal transition of the entire rear end through the rear bulkhead positions--and just to make it even more ridiculous the tire carcass shape also came into play to how to tune for your roll center--flat tires like the Proline 8086 only worked well with a very neutral roll center ( also one of the reasons the 93' WC had only upper and long inner bulkhead positions molded into the bulkhead) long camber link that gave a slower reaction to camber changes in its movement and more positive camber in the outside rear tire through the corner--whereas the Proline 8080 had a similar tread, but a round profile it worked best with a shorter link and a lower bulkhead position that would keep the tire more perpendicular with the ground, allowing the center of the tire to stay in contact with the track instead of the outside of the tire as mentioned above.

As a rule, a car with shorter arms, lets say a stock RC10--on a good bite track, will be faster in the corners than say a RPM 91' worlds modified car. But, that's only in the corners, and only because the car is quicker to react to steering input (because of the arms percentage of the cars overall width, and the distance from centerline to inner pivot). But the RPM modded car will have an overall faster time because of it's smooth handling and slower reaction to changes in surface allowing for an easier driving car that doesn't get "thrown around" as much.

Lastly bump steer--this was IMO one of the great advantages to the RC10's geometry, also very rarely set up correctly ( almost as much as ackerman setup) you could change the car to bump in or out on compression, depending not on the length of the link--but the height of the link in relation to the arm on both the inside ( by way of shims under the bellcranks to raise the inside height) or by mounting the ball stud with or without shims, and on top or bottom of the steering knuckle also effecting the bump reaction. Hell, you could even change the ackerman AND toe in/out during initial/mid/end upstroke with bump steer effecting the other geometry . So you could have say a RC10 team car have 3 deg toe out while the car was at full throttle at a corner entrance ( allowing the car to turn agressively) then during the mid upstroke the car would negate the toe out and the fronts would become parallel to each other giving good mid corner speed, then when you burried the throttle again and unloaded the front end it went back to toe out and keep the car from pushing off the corner.

All the B2 and B3 did was remove these overlooked tuning parameters, and make a car that was akin to "picking your nose with mittens on" feel--very neutral--very fuzzy and for the general
public, very simple to tune--

This might be a little more that my 2 cents

[markt311]

I'm not going to go into all that detail that CDS did because I just don't know all the specifics of suspension like he does. I can give you a dumbed down version though

I race weekly with my stock RC10 Team Car and a fellow racer runs his 91 Worlds car every week. I've driven both quite a bit.

The stock team car has a little more offpower steering for the reasons CDS stated, but on power going through sweeing corners it pushes badly. I have to feather the gas and slow down a lot to hold a tight line. Through the infield it runs just as good as the 91 worlds car.

The 91 worlds car feels more stable when it hits ruts or holes, where my team car just wants to hop or kick the rear end out a little. The worlds car feels much more precise, although I think it has a little too much up travel in the front end. It also pulls around the sweepers with the front tires, instead of feeling like the rear tires are pushing it and trying to make the car go straight. Off power the team car has a little more steering (again like Charlie said a short arm car will have).

Overall we turn similar lap times, my fast lap was a 12.8 and his was a 12.4 ( he's also a much better driver than me). They both do some things well that the other car doesn't do so good. It's just a different approach at the same car.

As far as trailing arms go, I have no idea, I've never driven a trailing arm car.

[Brandon G]

Mark,
I tried the square rib fronts (off of my B4) the other day, and the track likes these better than the rounded ribs. Gave me more steering all around. The front holeshots I put on the day we raced for the main was a BIG mistake. They make the B4 turn like mad, while on the 91 worlds, it just made me mad.

What surprises me the most about the RC10 is how 2 similar cars, team cars running the same setup for the most part, can feel so very different on the track. I drove Mark's car and also Dave's (another fellow vintage enthusiast in Nashville) and they had very few similarities as far as track manners goes. Motor plays a big part in the tuning of the RC10. I ran a 13.5 in mine last weekend, and loved how it ran. You can see the difference in the lap times. The B4's with the 10.5 weren't smoking me down the straights anymore. In fact, the only place I could see a difference was on the entry to the sweeper (on power push) They could simply hold a tighter line and put the power down earlier. In an 8 minute main, the top 3 were on the same lap. (me being 3rd) And considering who I was racing against and the cars they were driving, I was highly satisfied.

I have noticed with the 91 worlds setup, how very forgiving the balance of the car is. In the turns where you might have to apply some brake to help the chassis rotate more quickly, I rarely had to worry about looping out. Yes the car has noticable understeer, but with my B4, add a little too much brake and the thing would swap out easily. The B4 also would want to loop out if you give it a little too much power out of a turn. Not so with the 91. In the hands of a smooth driver with good throttle control, the B4 will egde out on top everytime however. As it should.

The Team cars, as Mark pointed out, have a little more turn in grip, but seem to have more on power push. The 91 car seemed to have a pretty good balance between the two.

[Charlie don't surf]

Have you tried any different bump steer settings in the front?

[markt311]

I've been too busy blowing up brushed motors to try any tuning yet lol

I'm going to play around with front toe and bump steer spacers next time I get to race which might be a few weeks. I have .062 (2x.031 washers) under the outer ball end now. My car doesn't have any bump steer as it is now, do you think taking one washer out and getting a little bump steer would make the car feel a little more aggresive?

[Charlie don't surf]

It can help, I remember seeing you guys mention part of the offroad course goes through part of a dirt oval? if the DO corners are where you are having the most trouble the bump steer will def. help, but you may want to try less castor--the B4's that are killing you in the sweeper have a 25deg K/U and a -5, 0 & +5 ( 20,25 & 30 deg) castor blocks. They might just be getting more contact with the surface in that corner

[markt311]

Our offroad course uses 3/4 of the dirt oval, everything but the back straightaway. I'll try to find some 20 or 25 degree caster blocks, I haven't had any luck finding any so far . I might have to try fitting B4 blocks and spindles if I can't find any.

Thanks for the help

[Charlie don't surf]

I'll dig through the box, I should have quite a few, ( we always used less than 30 deg in DO) it seems to make a big difference for me.

[markt311]

Thanks, please wrap them up in Hanes boxerbriefs, they offer more support for the cargo, and send them to me. I'll need more than one set cause JSR is probably gonna hit me up for a set if he finds out I have some.

Just send me a PM

Thanks Reg

Mark

[Greenie]

This is a good thread. I may have to read it again and again, but I'm getting lots of good suspension info out of this. Please be patient if I interject later on with some typical noob questions. I've been into RCing for 20yrs but I've never understood to this level before.

I was always just a neighborhood kid who said "Wheels look good and straight, let's run 'er."

[jsrracing]

mark i went to o rear hubs /short the rpm were 1.5 and long only


yep i will let you know if i find some 20 and 25 im thinking the stock sc10 are 25


you think front bump steer

the new tires make the car real (to much on power push)(tends to over rotate low speed on/ off power) i was thinking anti-squat adding some.

[Charlie don't surf]

20's are easy, the 25's were not found in my stash, the b4/t4/sc10 numbers are based off of a 25deg K/U though, so you would need the t4 20deg, then drill them out to 1/8" for both pins-and then you got 25deg blocks in your car- and I can post some setup Bump steer pics if you like-

anti squat might help, but it also may make the rear very loose on accel, by not allowing enough rear weight transfer

[jsrracing]

pic are always good . you prob hit it, bump steer is a biggie when you get right .