dunno

I don't know what the Xbrace does to help with the car structure but the OEM lower rear bar on mine was sort of bend closer to the end that the fuel thing was on. I got both the lower front and rear Neuspeed bars and the upper strut from Comptech. It looks good. Usually when I back out of the garage, i would heard cracking sound but not any more.

dbarnes

elviscos,

It is possible to measure the "flex" of the subframe relative to the frame, however, this would be a very expensive endeavor. Because the load is generated by a lateral acceleration it would be very difficult to setup a simple test to measure the relative deformation between the two pieces of structure. The best way to measure the effect of the X-brace is to perform what is called a modal survey - place a large number of accelerometers on the vehicle, input a known force (usually random white noise), measure the acceleration response and generate the transfer function for the vehicle (acceleration per input force reported in the frequency domain). During the development of the S2K Honda would have performed a modal survey of the car and correlated the data with its structural math (finite element) model. The results would show the frequency of each mode as well as the shape of the mode. To quantify the effect of the X-brace, two modal surveys would be done, one without the brace and the other with the brace.

To measure the loads carried by the X-brace, a series of strain gages could be bonded onto the brace. A minimum of four gages per leg would be required to measure the axial load and bending moments being passed thru the brace. If the transverse shear load is important, then a strain gage rosette would need to be added to measure the shear strain.

Ivs2k,

You are correct. Design allowables are usually significantly higher than anticipated design limit loads. Once the design limit loads are determined, a factor of safety (probably between 3-5) is applied to the limit loads and then a margin of safety (aerospace industry - I don't think the automotive industry uses margins of safety) is written for each structural component. Because a car is subjected to cyclic loadings, fatigue of a component is a major concern. Most likely each component is designed to have an infinite fatigue life. This is refered to as a fail safe design. Because of this, the design allowables are reduced to account for the degraded material properties at an "infinite" number of cycles. So although the design loads are much smaller than the design allowables, the structure is not loaded any where near its full static strength allowable. This type of a design is usually strength driven, and generally results in a stiffer structure.

-Donnie

The Reverend

I haven't really been following this discussion too much, but someone asked how to measure the flex in the chassis. Well, I don't know THE answer, but one fairly simple (albeit very time consuming) way would be to take a piece of thread and tie it between two points on the chassis where you think it stretches. Leave just enough slack for the amount of stretch you think is allowable. Then drive it. This isn't very scientific, but it's cheap if you've got the time.

The Reverend

on second thought, you can save a lot of time if you tie several threads of different colors (so you can tell them apart) with different amounts of slack. The one with the most slack that still breaks is the one for how much flex you have. Again, this isn't the most accurate or most scientific way, but you can't beat the cost.

Or on third though, you could just drive the car and not worry about it