Laydown chassis

[Roger Nelson]

I would like to get peoples opinions on just how important is the frame work of a chassis, compared to having all the numbers right.......ala, caster, camber, weight, etc. I know this is a wide open question, but I am trying to figure out if the tube part of the frame is just a platform to mount the steering and rear axle on or (remembering this is a laydown) if it really doesn't matter that much. I have done this on and off for a long time and never have I seen a chassis take someone from the back to the front, all things being equal...........Thanks for your replies, I am not here to argue with chassis builders or others that will say this chassis is better then that one, I am looking for information.

[Greg Lindahl]

One way to answer your question for yourself is to calculate the percent of time you spend cornering during the navigation of a lap of your favorite roadrace course. You'll find that it is a significant percentage. Therefore, speed through and exiting corners is very important to overall lap times.
Lap time data indicates that castor/camber/toe/Ackerman/weight-distribution/chassis-flex and left/right balance all work together to determine corner and exit speed.
The low CG of laydown karts generates much less weight transfer in all directions than sprint karts, which all agree require correct chassis geometry and weight balance to work well. Between the low CG and aero-generated straightline speed, handling may be overlooked by competitors.

[Mike Sampson]

Good question Roger. No. There has been a lot of good chassis builders over the years. As you know, Hartman , Emmick, Margay, CKS, IKS, Dap, Hornet, Bug, Coyote, etc. etc. I've road raced almost 40 years....and the guys that run well are the best drivers and tuners.

[Roger Nelson]

The chassis I am modifying--building, will have the adjustabilty of camber, castor, toe, and weight-jacking to a point, the ackerman will be set up and somewhat adjustable, so I guess I am wondering what chassis flex will give me or not give me?? I wonder if a stiff chassis will allow me to run less castor, which would help in not scrubbing off speed, but what would the negative be for a stiff chassis?? I have to get that opposite rear tire to release going through a turn. It looks like a more flexable frame would make me have to run more castor to get the release??

[Peter Zambos]

In laydown karts of either the short or long wheelbase variety, typically the less caster you can run, the better. This is because the less caster you can run, the less bind, and therefore less RPM drop, will be experienced in sweeping turns. Having a chassis that has less flex, can, in theory, run less caster. This is one of reasons why you'll see some laydown chassis with multiple added gussets welded throughout.
At least this is my take on it.

Don't sell the chassis' contribution short, even in a laydown. Though long time and successful enduro pilots such as Grenier and Fulks surely don't have motors that are slugs, they put ample attention into their chassis. Many karters, even those that have been around the block a few times, often mistake chassis short-comings for engine issues.

[Roger Nelson]

I agree with you 100% Peter......although I never dismiss the ability of drivers, it is my opinion, thus my quest, that the chassis is where the speed is most often overlooked. The two people you mention always run up front. I am running an Animal which is down on power compared to most 2 strokes so I am looking for all I can tweek out of the frame. Weight is not an issue for me, as I have to weigh 410 and I have to load it with weight, so if that is the case I would rather put it(weight) in things that will help make it handle.

[Steve O'Hara]

Roger,
Road racing is all about reducing drag, both aero and mechanical.
The formula is very simple... you want the chassis as stiff and as narrow as the driver can handle. The stiffer and narrower you set your chassis up the more twitchy it will handle. The good drivers can handle knife edge chassis, most can't.
I won all my Duffys on Hartman chassis with the front wheels covering the kingpins to minimize front end scrub and always ran at least 35 psi in the tires. The Hartman chassis were very stiff and had mild front end geometry and many drivers hated them because they were not forgiving to the sloppy driver but they were fast and consistent if driven properly.
Steve O'Hara

[Greg Lindahl]

Really helps to have front brakes and good rear brake modulation with a stiff narrow chassis. I found most instability under braking, but cornering was good if you keep your right foot down hard to set/stabillize the kart.

[Roger Nelson]

Steve.........I have been trying to stuff all of the hardware I can, as far as I can, into the 6" rim, with front brakes............like trying to stuff 10lbs of stuff in a 5lb can, can't get to zero scrub with front brakes unless I want to make every piece including the wheel. The steering arm coming off the front spindle is what gives me the most problem, getting to the correct ackerman with trying to clear the brake hub in a challenge. I am also trying to get the engine as low in the frame as possible, so I am having to build an unconventional engine mount to do that.

[Steve O'Hara]

Roger,

Agreed, almost impossible to get the scrub radius down when using front brakes. On my Hartman chassis I used their front brake spindle but cut off the caliper mount and ran without the front brakes. The design of the front brake spindle had the steering arm moved inboard compared to their no front brake version.
When I built my GPX200 twin I built integral front hub and drum brakes so they could be tucked way inside the wheel. They didn't provide the kind of stopping power that the big disk brakes offered but we didn't need much front brakes for the kind of tracks we had to race on back then.
Good luck with your project, sounds like you are on the right path.
Steve O'Hara

[Roger Nelson]

Can we post pictures on here??

[Bill Martin]

[Roger Nelson]

MG]]

[Roger Nelson]

Only one picture showed up...........I'll get better at it

[Roger Nelson]

Here is the pedal set up..........http://i1320.photobucket.com/albums/u536/huntr61/IMAG0972_zpsb4bd4d5b.jpg