Lowering your NSX: rake and how to do properly

[TURBO2GO]

I searched and bumped and old thread with some questions but it seems to not have received any attention because of the old title so I am making a new thread.

What is the proper way to lower an NSX? The factory has a certain rake. People of the forum say that this rake is approximately 1/2" measured at the jack points. However, this seems to not be the proper way to measure car height. The service manual states that measured from these points they specify on the frame, there is an actual 1.5" rake. I don't know what that translates to at the jack points but they do not recommend using that method which almost all do. The rake changes both the balance and aerodynamics of the car.

Here is the PDF from the service manual:

http://www.nsxprime.com/forum/attachment.php?attachmentid=62692&d=1257333066

Measured from center of lower control arm bolt front and toe control arm bolt rear.

The confusing part is my mechanic says that measured at jack points he has 13mm, measured at these points he also has 13mm difference front to rear. But measured at this point, it should be 1.5" or roughly 38mm... Which is waaaay different than his measured 13.

Does my front need to go almost an inch lower??

Does this measurement on the service manual just not apply when a car is lowered? It seems like keeping the factory rake is not a bad thing to do instead of some arbitrary "looks good there".

 

[Honcho]

Dave, you'll notice the measuring points in the graphic above are not in the same plane. The rear point sits higher in the chassis than the front. So, the measure points can tell you how high the front suspension is or how high the rear is, but not how high they are relative to each other. In order to measure rake, you would need a rear point in the same plane to know how much higher the rear is relative to the front. Basically draw a level line from the front point and whatever it intersects in the rear would be your measure point. If you have a laser you could probably do this.

By way of example, my car is set to the NSX-R height, which is 156 mm front and 202 mm rear on 2002+ tire sizes. Because the R lowers the height more in the front than rear, rake should increase. But, if you use the jack point measure method, my rear points are 4.25" and front are 4.5". So, if you just measured using the jack points, you would think the rake is totally messed up. But, because we measured the actual suspension, we know it is right.

 

[TURBO2GO]

Paul, I am not quite sure I am understanding. If the ride height stock front is 6.7, and rear 8.2 (according to the numbers in the service manual), the rake is 1.5" (8.2 minus 6.7). So if I lower the car, don't I still want a 1.5" Difference? What difference does it make if they are in the same plane or not?

So if I drop the front an inch, and the rear an inch, the difference should still be 1.5 measured at these points. Right? What's wrong with my logic?

 

[RYU]

Make your life easy Dave. Don't use the OEM mounting points to measure ride height. It's commonly accepted that the front/rear jack points is the easier way to measure rake. If the variance of the distance of the two is 0" then you have even rake. If the rake is higher in the rear by 1/4" then you have 1/4" of rake in the rear.

I've talked to more NSX track guys where this is the universal measurement. No one remembers what the hell the OEM rake measurements are.

 

[LJSB]

Dave you are correct. The way to measure suspension height is by measuring as the manual suggests. The jack points, the wheel wells etc., are not correct.
Alignment is suspension geometry not body geometry. Please do not use the body.

The jack points on this car, the ones at the rocker, not to be confused with the lift point, are, IMO, too close to each other to give a useful reference of F/R rake.

Your logic is again correct in maintaining that F/R perspective of approximately 1.5" regardless of vehicle being raised or lowered. How that translates to the height of the body points ie., jack point, wheel well, eyt,. I don't know and frankly don't think you should worry about it. Neither are structural control points.

I'd be willing to bet your tech will be using metric units and not inches, but of course both will work.


Get it done right because this car really shows it stuff when set up correctly. I've aligned many NSX's. So many have come to me with their cars so out of whack. When aligned properly the remarks I get from the customers is usually one of surprise and joy because they didn't know how the car was supposed to, and could feel like. So, if done right, and it seems you're on the right track, I'm sure you'll be happy with the results. If you need any help just call.

Good luck.

 

[docjohn]

you so nice Joe.......enima.....

 

[TURBO2GO]

Joe that was my suspicion. Thanks for the advice. I'm going to stay with the guy tomorrow and make sure he does this right. Before he has his evening beer and decides 22mm= 1 inch.

 

[stuntman]

Dave you are correct. The way to measure suspension height is by measuring as the manual suggests. The jack points, the wheel wells etc., are not correct.
Alignment is suspension geometry not body geometry. Please do not use the body.

Your logic is again correct in maintaining that F/R perspective of approximately 1.5" regardless of vehicle being raised or lowered. How that translates to the height of the body points ie., jack point, wheel well, eyt,. I don't know and frankly don't think you should worry about it. Neither are structural control points.

I'd be willing to bet your tech will be using metric units and not inches, but of course both will work.


Get it done right because this car really shows it stuff when set up correctly. I've aligned many NSX's. So many have come to me with their cars so out of whack. When aligned properly the remarks I get from the customers is usually one of surprise and joy because they didn't know how the car was supposed to, and could feel like. So, if done right, and it seems you're on the right track, I'm sure you'll be happy with the results. If you need any help just call.

Good luck.

The frame rail is not part of the bodywork of the car and is a reliable location not likely to change (such as fender heights). There is no "one way" that is right for measuring rake. You can measure it from numerous places on the car (subframes are good locations too). The main thing is to use the same immoveable location each time or when comparing car to car.

Measuring a car at 0 rake on the frame rails (which =1.5" at the stock location) is fine as long as you verify the difference.

IMO the frame rails are the quickest and most outboard part if the car that you can measure at and is what has been commonly adopted. It is not "wrong" by any means.

Turbo: also have your guy measure the frame rail jacking point heights and have that # on hand.


Billy

 

[TURBO2GO]

Billy so do you recommend keeping the stock rake?

 

[LJSB]

The frame rail is not part of the bodywork of the car and is a reliable location not likely to change (such as fender heights). There is no "one way" that is right for measuring rake. You can measure it from numerous places on the car (subframes are good locations too). The main thing is to use the same immoveable location each time or when comparing car to car.

Measuring a car at 0 rake on the frame rails (which =1.5" at the stock location) is fine as long as you verify the difference.

IMO the frame rails are the quickest and most outboard part if the car that you can measure at and is what has been commonly adopted. It is not "wrong" by any means.

Turbo: also have your guy measure the frame rail jacking point heights and have that # on hand.


Billy

Bill I know you are a very fine driver and have a keen awareness of how alignment feels and impacts how well you can get your car around the track.

I have no, or know of any reliable ride height measurements provided by the manufacturer(Honda) or a third party to reliably reference off the side members of the NSX to the datum of a level alignment rack and am not aware of a known manufacturer control point with which to use that will provide thus. The manual does not show or provide this either. Do you have them? I know you raced NSX'S so I wouldn't be surprised if you guys had your own. If so I wouldn't mind having a copy.

FYI the jack tabs are not located with fine enough precision to qualify as a control point and that's why even the manufacture doesn't use them to reference for chassis or suspension geometry.

If the tech is going under the car to do an alignment, using known control points that involve the assemblies where he is doing his adjustments anyway IMO make the most sense. After all, he's right there. :wink:

Again, I suggest you keep the stock rake.

 

[TURBO2GO]

Joe I believe there are many NSX's running around with unintentionally incorrect rake.

 

[LJSB]

Joe I believe there are many NSX's running around with unintentionally incorrect rake.

There are some that are intentional too! Some folks don't like the look of a raked car. They want low and wide. Dey be cruz'n!

 

[stuntman]

Bill I know you are a very fine driver and have a keen awareness of how alignment feels and impacts how well you can get your car around the track.

I have no, or know of any reliable ride height measurements provided by the manufacturer(Honda) or a third party to reliably reference off the side members of the NSX to the datum of a level alignment rack and am not aware of a known manufacturer control point with which to use that will provide thus. The manual does not show or provide this either. Do you have them? I know you raced NSX'S so I wouldn't be surprised if you guys had your own. If so I wouldn't mind having a copy.

FYI the jack tabs are not located with fine enough precision to qualify as a control point and that's why even the manufacture doesn't use them to reference for chassis or suspension geometry.

If the tech is going under the car to do an alignment, using known control points that involve the assemblies where he is doing his adjustments anyway IMO make the most sense. After all, he's right there. :wink:

Again, I suggest you keep the stock rake.

Where is your alignment rack's datum point?

Many race teams use a flat surface plate to determine their reference point (even NASCAR teams use fender heights -which are for quick reference when they know what that # means relative to a more difficult to measure part of the car). You can use fender heights for a reference but since fenders can be tweaked, they aren't the best point to use unless you can baseline the numbers on a flat surface plate.

When on a properly leveled scale pad, you can use a 360* laser to create a horizontal plane and measure from a given point (including the jacking points) to find your base number. There are numerous ways to measure your ride height and rake, but often it's an arbitrary measurement that is helpful for A-B comparisons.

Since most people measure from the ground to the jacking points (which are good reliable places to measure from because the framerail on the NSX is so strong and consistent), this is probably the best way to compare your setup to what other people are running.

Now:

When you corner balance a car, you won't always (or might not want) the car to be even right to left. If you have a track with primarily left hand corners and you want the car to not understeer as much for left hand corners, having your crossweights closer to 48-49% might be advantageous over a 50% cross. Doing so will make all 4 of your ride height measurements at the jack points uneven.

Rake will vary on what's "Ideal". This is dictated by many things ranging from: Tire width, weight distribution, spring rate, ride height, center of gravity, anti/pro squat/dive, etc... Rake can affect the handling of the car by changing instantaneous centers, center of gravity, roll centers, etc... At the end of the day, 0-0.5" of rake is in the ballpark of normal measured at the jacking points.


Billy

 

[liftnot]

I remember Shad said sometime ago using the jacking points to measure your ride height.

 

[Hrant]

I remember Shad said sometime ago using the jacking points to measure your ride height.

He still does. It's a good easy way especially if you don't have the flexibility of the alternative.

 

[LJSB]

I understand how cars are aligned as I've been doing it over 40 years.

I also have a very thorough knowledge and understanding of measuring vehicles. I started with strings, moved to center line gauges, to tram gauges onto mechanical point to point, and then laser which is now old school and very difficult to use for 3D monitoring of multiple control points simultaneously. Now we're beyond that and use equipment to measure and record multiple control points referenced from absolute perfect center giving L/W/H of each point to a one mm degree of accuracy of each. I digress. Sigh...

Like many threads this one started out fairly simple with a simple clear question that has been answered and now we're into something else. This is why I will stop posting here on Prime "help" threads because it seems it does not serve to help the car owner solve a particular problem but instead gets blurred into something else that I don't usually want to be part of.

I find reciting pedigrees silly and something I generally loath to do. Mine is considerable and believe if I am reciting or even thinking of doing so, as I have above, it signals to me that I am well past my time to stop giving advice.

If anyone needs help with anything on their NSX and wants my input, pick up the phone because I'm done doing it here on NSXPrime.

 

[docjohn]

I will spend the rest of my days cajoling you back .....If you leave me now you'll take away the biggest part of me.....oooooooooooo Joey please don't go.....oooooooooooooo I just want you to stay.......:redface:

 

[Hrant]

Joe, I think the issue in here is perfection vs. practicality. No one is questioning your expertise and the more scientific approach. But for some, after an initial "good" alignment, tinkering with the rake at the jack points for on/off track scenarios is the practical option - we are not talking F1, just weekend boy racer stuff so 90% accuracy is good enough for most.

 

[TURBO2GO]

Joe, I think the issue in here is perfection vs. practicality. No one is questioning your expertise and the more scientific approach. But for some, after an initial "good" alignment, tinkering with the rake at the jack points for on/off track scenarios is the practical option - we are not talking F1, just weekend boy racer stuff so 90% accuracy is good enough for most.

Key phrase "after an initial good alignment"..... Yes, I get that. But that first one should probably just be done correctly as joe is suggesting. Then you can take your measurements, and if you need to make quick changes you have a reference point. With no reference point, trying to align properly using a less precise method is a little hack to me. It was Joe's original post several years ago on this that make me post this thread.