OCRC
 

At OCRC, the majority of us 17.5 stock racers run 3-gear. For mod, its a mix and personal preferrence between the 2 gear-boxes.

Its an inexpensive investment and worth testing both out. Look at your 5/10/15 average lap times and let the numbers decipher which works better overall.

Good luck!

I am planning on switching my b5m to a 3 gear tranny. I run 17.5 class and maybe 13.5.
what do I need to buy to make the change?
91607 3 gear box
91603 motor plate
91604 3 gear cover

I already have the MIP 14195 topshaft. Will this work or do I need to but the Associated 91606 topshaft and 91560 bearings?

Also, I want to put in cut gears. CB design is out of stock. Who else makes good cut gears that will work?

I am also assuming that my stock B5M chassis will work and I don't need the b5m Lite chassis. Is this a correct assumption?

thanks,
tim

Don't fret it. We all have been there and most of us will share the information we have.

You should use whatever works best for you.

I got a b5m lite recently because of all the upgrades it comes with but should I switch the lite chassis for the standard b5m chassis for mod or will it not make much of a difference?

^ been curious about this as well as I've been pondering picking up one or the other, but would mainly be running mod.

It will be just fine in modified. The lite chassis may be lighter, but we were changing chassis' to get more flex, the lack of weight was just an added bonus.

Does anyone have any real world testing experience on a loose track to indicate if there is an actual benefit to 4 gear over 3 gear? Just wish there was a factory "heavy mod" version of the b5m because I'd rather have the thicker chassis and 4 gear for running outdoor in loser conditions with large wind catching jumps with abrasive landings in mod. For me, all the light options such as a 3 gear transmission and thinner chassis are going the wrong direction for running 2wd competitively outdoors.

The milled chassis adds flex which might benefit outdoors. Aside from that, the brass items help many people that run outdoors to get the weight where they need it. Socket who posted above was using a square backs and I think the rear brass C block for outdoor racing. Adding weight is pretty easy.

I've been using the lite chassis for every outdoor race this year. The flex it has is similar to cutting the waterfall! I added the brass c block which pretty much gets the milled weight back. I also have only run 4 gear because our tracks typically do not produce enough grip and I'm almost positive the 3 gear would be at a disadvantage. I'm still using a shorty pack btw. So far the cars been phenomenal!

Many outdoor tracks here in Michigan are more old school, topsoil surfaces. I've done lots of testing on them with my two mid motor cars and the 4 gear is better for my driving style in mod. It definitely gives you more rear bite while accelerating and also really helps when pitching the car around mid air after rough jumps that don't always launch you cleanly. That being said, it makes it harder to use the brakes as it pitches more weight forward, but I tend to just scrub speed by throwing the car sideways.

However, it is a smaller difference than I expected going between the two gearboxes (both AE). The biggest difference was getting the car around 1550-1580 with a 68-70% rear weight bias. Also, more flex helped a lot more than the gearbox swap by doing the waterfall mod and/or using a more flexible chassis. I've currently settled on the infinity chassis with weights/brass exactly where I want it and the 4 gear transmission in mod and the an aluminum chassis I've milled myself with the 3 gear transmission in stock. Both cars run shorties at the weight mentioned above so I can play with the bias more easily track to track.

I have yet to play with the lite chassis, but my guess is that its increased flex over the stock one is more ideal and then adding some brass in the rear to change the bias/overall weight would be than the way to go.

Let me congratulate you on a well written and helpful post.
Thank you.

Well, honestly I really hate tuning with flex. I'd rather have a super rigid car and find another solution if more grip is needed--such as more droop or roll or softer springs, but I digress. Good info on the 4 gear, that's what I was looking for.

So the light chassis is milled out, not thinner? I'm not going to NOT use it because it flexes more, you just won't see me cutting parts and removing screws to find flex--I'll just run it because it comes with the car if it doesn't wear out faster on an abrasive surface.

In the past i would have agreed with you 100% on chassis flex.
However in off road there are so many variables it is hard to run a car as soft as you want to get grip while still maintaining a platform that can handle the jumps and landings. Not saying it can't be done but it will take longer to get there.

What is the waterfall mod?