mid mount wheelbase and weight % questions

[fastinfastout]

Hi, I had an x6 a long long time ago, and back then it was noted that a 35/65 was ideal.

I am toying of another idea for a mid mount, not sure which to buy. But I would prefer from the get go that it is the longest wheelbase available. Vega RB5 long maybe? but don't know how long it is....

besides the dex210 and losi 22, can someone give me some details of their mid mounts with their weight distribution figures, as well as their wheelbase please?

[fredswain]

I have been doing lots of research on how to make mid motor run well on American tracks with low grip. I started by studying the rear motor 2wd cars. I've measured about a half dozen of them so far and 5 of the 6 had 69% of the weight on the rear wheels with 1 car at 68% on the rear wheels. Close enough.

My CR2 had 63% on the rear wheels when I started. The problem it has is that it loses rear traction and can't accelerate out of corners as fast as the rear cars. I think many people view mid motor in the wrong way. Everyone I meet or talk to over here views the advantage of mid motor to be shifting the weight forward. I think that's the wrong way to look at things. I feel that the advantage in mid motor is the reduced yaw induced polar moment of inertia due to a more favorable weight placement within the wheelbase. A mid motor car should be more forgiving. The problem is that weight is shifted farther forward taking traction off of the drive wheels. That's how you need to think of them. Don't think of them as rear wheels but rather drive wheels.

The CR2 is a very short car. I feel too short. By lengthening the chassis on the front of the car, there is a slight weight bias shift rearward. This helps get some weight back to the rear. I am currently working on a new chassis for my car that will take the wheelbase to 11". While some may say you lose cornering ability, I point out that a good mid car increases it anyways. The long wheelbase gives more stability in the air and at speed. Our tracks here are very fast with long jumps.

I am custom making a plate for the rear of the car that goes under the motor. I have to hand build it since it is a cast part. It is a weight but the material combination I've chosen makes brass look light. By retaining the saddle packs, the longer wheelbase, and my weight, the rear bias should be right at 69%. I am also running no antisquat. I am hopeful that this will help make the car seem a bit more like a rear motor car but one that is more forgiving. That's an improvement over them.

Another area that I'm working on is the front end. I feel the rake is too high. A rear motor 2wd buggy that has so much weight so far back needs to be able to transfer some of that weight forward under braking so the front tires get some grip for cornering. Most cars today run 25 degrees. The 22 has the ability to run between 20 and 30 degrees and the original RC10 had 30. No 2wd car's front tires contribute to stopping the car.

On a 4wd car, the front wheels do contribute to slowing the car down so weight doesn't need to shift forward as hard. Those cars typically run only 7-10 degrees of front end rake. My best guess so far is to try 15 degrees. I know I'll need more than a 4wd but not as much as a rear motor since our weight may be located rear bias but is placed much further forward in the car rather than some out behind it. As of yet I have not seen a mid motor car company address this issue.

Anyways, these are the things I'm trying on my car. I think it's the direction that mid motor cars need to go to be competitive with rear motor cars on slippery tracks. The first step is the get the rear weight bias correct. The second is to transfer the correct amount forwards when slowing down.

[fastinfastout]

I'm thinking 67% should be good enough.

I have had my b4 and CR at 67% at good results.

However I'm not agreeing with your 0 anti-squat. More antisquat equals more forward bite, regardless of what the setup bible says.

[fredswain]

It's a bit of a paradox but I've had good results with getting the rear weight bias on rear motor cars more forward as well. The location of their weight helps rear traction but suffers from a greater yaw induced polar moment. Conversely I'm thinking that a mid motor car may actually need a percent or 2 more weight bias on the rear tires. However the location of the weight within the wheelbase should still mean it is more forgiving.

I want weight to transfer rearward on acceleration. Antisquat reduces that. I don't go by what others say. I go by what I feel should work. Sometimes I'm right and sometimes I'm wrong. I haven't had any luck with any amount of antisquat in mid motor on looser tracks.

[hloland]

My RB5 vega, DEX 210 with M4 and losi 22 are all 37% front 63% rear.

[fastinfastout]

bump to an old thread, with all the newer cars out now, I'm sure we can get some more numbers.

I've heard good things about the b5m and some have had them 34/66

I have an rb6 that I was thinking of converting to mid mount, however it seems for it to be competitive on clay, alot of $ needs to be spent, so may as well get a b5m.

any numbers on yok's or serpent's?