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I'm thinking the handling still needs work (video included)


Tom1200

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The video (link below) is from a race two weeks ago; I'm in the red coupe just ahead of the camera car. You'll notice a ton of oil dry, in the group before us a Devin SS lined the course.

 

Ignore the wayward handling in turn one as I'm half in the marble and sawing at the wheel like a fiend. At the top of the hill everyone lined up like lemmings and braked early so I popped out and went for it, you can seem me get off the brakes and then back on them.

 

The driver of camera car (510) said he nearly went off when he out braked me.

 

The handling is nowhere near as unruly as the last video I posted but Mmm yeah it needs work. For my part as the loose nut behind the wheel it the car handles excellent (it actually does) but I know I'm way more comfortable with oversteer than most people.

 

Sadly my race ended on lap 3 as the motor went kablamo but for a car sporting 50-90 less horsepower than the cars I'm dicing with it does alright.

 

 

https://m.youtube.com/watch?v=FsApTh6m2Xw

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Rad video!  A buddy of mine ran a 1200 with an A series.  He called them the A-bomb later switched to a NA SR with a mega restrictor because the A series engines were just to much work to keep together.  Then switched to running a Nissan Sentra in more stock class.  I want to race something like that!  Love the 1200's! 

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Tom,

As a guy who also likes oversteer, I'd say you have a little too much based on the video. It appears to be two things happening,  oversteer and some suspension movement that is “steering” the car over crests and in compression sections. You can see the car moving around under you at these vertical transition points.

 

One thing that might help your general oversteer condition is more roll stiffness at the front, either a stiffer sway bar or stiffer springs. Or less roll stiffness in the rear, softer springs and/or less bar.

 

Another thing is the rear ride height looks like it could come down some. If you can lower the rear center of gravity, this may help as well. 

 

You mention that the car has a panhard rod. If it is height adjustable, it can also be used to adjust the car's handling balance by changing the rear roll center height. If you lower the panhard rod, it lowers the rear roll center. This increases the roll center to center of gravity moment arm length. By doing this it effectively reduces the rear roll stiffness and will help reduce oversteer. 

 

Leaf rear springs can also steer the rear of the car. As the spring arch flattens out under compression, it will lengthen the wheelbase of the car. In a corner one side will compress more than the other causing the axle to move further rearward on the loaded side, turning the axle so it is no longer at 90 degrees to the chassis. This will usually induce oversteer into the car by the axle driving the rear of the car into a larger corner arc. To limit this, use springs that are virtually flat (no arch) and limit the body roll as much as you can.

 

Another factor with rear leaf springs is how the axle moves relative to the chassis. The rear axle in side view pivots around the forward leaf spring mount. If the rear spring eye is higher than the front, the axle will move forward as it is loaded in a bump condition. To reduce this you will need to have eyes of the spring, front and rear, at the same height off the road. By using a flat spring and having the leaf eyes at the same height off the ground it will reduce the amount of fore/aft axle movement during suspension travel.

 

If the rear leaf eye is higher than the front you will need to have long rear shackles and thick lowering blocks to make the change. It may look strange, but it will help stabilize the fore/aft rear axle movement during suspension travel.

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@icehouse the A15 in my car was on it's 5th season and probably had 50 hours on a motor that never goes below 5500, spends most of its time above 6000 and revs to 8200 in a few places. The fact that it broke wasn't a shock. The had also overheated in a it way on a previous occasion, so it popping the head gasket wasn't surprising. A full race A-series has about a 6-10 hour service interval.

 

A good comparison on motors is Dave's fully built A15 made 156 whp whereas mine made 99whp; difference being my unwillingness to spend the cash needed for that extra 50hp and the fact that I'm lazy and don't want to deal with the shorter service intervals.

 

Dave the rear suspension has the traction arms and is set up per the competition suspension manual. The springs are flat and the spring eyes are at the same height. I believe the springs are 160 inch pounds. Also there is no panhard bar on it at the moment. As for the ride height yes it could be lower but I needed to raise it due to installing the H190 when I put the A15 in. The solution would be to cut and weld in a hump so the car can be lowered with out risk of the diff hitting the underside of the car. There is clearly some kind of rear steer going on. The frequency of the oscillation is not as rapid as it was but it's still there and can't be helping the lap times. While I don't think it's costing 4 seconds a lap willing to bet it's costing between 3 - 5 tenths. I initially thought I had a dead rear shock but the car weaves in both right and left handers. I also noticed the car dancing around over the bumps at the top of the hill after turn 2.

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Have you checked the droop at the rear? If the shocks are limiting droop it will create some really bad over crest issues.

 

My 1200 has a panhard rod and is quite stable. It might be something to consider. 

 

Also try to reduce some of the oversteer. Having a stable car will make it more comfortable to drive and that in itself generally reduces lap times. 

 

You can't hit the apex of a turn on every lap if the car is twitching all over the track. The more stable a car feels the more repeatable you can drive it. When you can repeat the proper line thru a turn every time, the faster you will drive the car. 

 

Most of the fast drivers are very smooth. If the car is stable, you can work on being smooth. It's hard to be smooth when you are always sawing at the steering wheel to keep the rear end from passing you.

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https://m.youtube.com/watch?v=CwTlvqOtRa8

 

Dave if you go to minute 24 of the video link above you'll the car is not near as unruly. I can't remember if this was just before or just after I installed the A15 but the car was significantly slower so I'm thinking the A12 was still in there. As for oversteer keep in mind that I started road racing on motorcycles first, to make matters worse most of my racing was on 125cc GP bikes which need to be ridden like an animal to get any speed out of them.

 

If you look at the original video; at the spot just before the 510 passes me note that while the back end is wiggling back and forth the front wheels are dead striaght. The oscillation occurs even when I'm holding the wheel in one position; I'm a steer with the pedals driver. Also my lap times when not dealing with traffic are within tenths of each other. Regardless the wayward wiggle needs to go. I'm not laboring under the impression that it's going to gain me 5 seconds a lap but it's surely worth 3-5 tenths.

 

As for suspension itself the rear shocks are the Koni classics listed in the motorsports catalog and they have more droop travel that the springs do. I'll be taking the car over to a buddies shop and seeing about the panhard bar. The video leaves no doubt there is some sort of rear steer going on.

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https://www.youtube.com/watch?time_continue=1015&v=9AWpI1dOp5E

 

OK one more, most of it is desperately dull; the camera angle sucks, go to minute 17 for the start. You can see what I'm doing via the reflection in the upper left of the windshield. Jump ahead to minute 27:50 and see the Formula Vee I was trying to hold off make an amazing pass. Also note you can kinda of hear the brake chatter, I missed the apex of the right hander at the top of the hill multiple times as the rotors were toast (high spot / pick up) and the pedal was starting to strobe. 

 

As you can see the car doesn't look nearly as unruly as it does from the outside.

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