Esprit1 said:
With all the recent talks of wheel spacers, wheel offset, and monster wide tires/wheels, I did a search on NSX Prime but didn't find any conclusive threads on this subject. (Please kindly direct me to these threads if they were written.) There were some brief but general and sometime heated debate on the effect of wheel spacers, but none really touch on the truly technical aspects of wide track NSX. For those who are technically inclined or experienced, please kindly share some of your thoughts.
A few questions immediately came to mind and I'm sure there may be many more:
1. Effects of wide track on suspension settings.
2. Excessive high negative camber especially on lowered cars with wide wheels/tires.
3. Toe in recommendation front and rear on wide track.
4. Sway bar and general setting recommendations.
5. Effects of over/under steer and recommended counter-measures.
6. Wheel bearing load and possible roll resistance issues.
I'm sure many of you are also interested in learning more on these issues. Please educate us......... :smile:
Best Regards
Paul
1. Effects of wide track on suspension settings.
Having a wider track on a car essentially lowers its center of gravity and better stabilizes the car. There is a great book called Tuning to Win that I recommend you read, that goes over this topic. It all actually makes a lot of down to earth sense with diagrams. Fundamentally, you want the wheels/tires towards the extreme ends of the vehicle but their are other variables that often come into play as well.
Actually, I had a very in-depth discussion on this topic with the
Racers Group the other day. I like to defer to their opinion as far as speed shops go, as they do have 14 consecutive podiums so far.
Per their opinion, on most production sports cars, widening the track by up to about 1/2" or so is entirely acceptable for handling on an otherwise OE vehicle with say just adjustable suspension and an performance alignment. Moving to lower offset wheels to keep the center line in check and have other supporting modifications, then you can push that out even further for added benefit. They run really wide low offset center lock wheels on Riley hubs / Scott spindles on their wide body race prepped Porsche's.
What is really relevant which they mentioned and I agree with 100% is to 1) Stop bench racing theory with guys on forums and to quantify any changes with lap times and 2) make bigger changes so the results are more easily observed. You can always regress later. A lot of a race car is feel, and you just have to try it and see if it works and thus results in a lower lap time for your vehicle on a given track. The principles only take you so far, and then you need to start maintaining accurate data and taking things further with your own R&D. If in doubt, just try it and measure the effects.
2. Excessive high negative camber especially on lowered cars with wide wheels/tires.
When setting camber you need to be thinking of not only the wheels placement to the ground but also to the wheels relation to the suspension geometry as it moves. Having extreme amounts of negative camber is beneficial for off-road only road course cars whereas the life cycle of the tire is mostly spent deformed under hard cornering. By adding the negative camber, it essentially causes the tire to be optimized and stay planted under hard loads. On road going cars which are not being driven hard, for the most part excessive negative camber will manifest itself as having the inner edges of the tire worn out prematurely and a very expensive tire bill. The lowering and the expensive wide tires will simply exaggerate the effects. Alignments are all about compromise.
3. Toe in recommendation front and rear on wide track.
The Toe settings is not directly linked to the wider track. Just because you increase the track and displace the original location of the wheel does not directly equate to the tow needing to be changed to accomodate anything.
However, it may be necessary to change the Toe settings for a specific target alignment, or even a specific road course or specific driver even to change the directional stability of the vehicle and accomplish something specific. Toe-out encourages the initiation of a turn, while toe-in discourages it. Racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. Road going street cars are typically set up with toe-in, while race cars are often set up with toe-out. It also is a little dynamic, but that is another topic entirely. There is a good write-up on it here-
http://www.advancedracing.com/chassissetup.php
4. Sway bar and general setting recommendations.
5. Effects of over/under steer and recommended counter-measures.
These two are really related. Small adjustments can be used to both increase/decrease under steer and over steer. There is a half way decent guide that can be found here from the SER guys:
http://www.se-r.net/car_info/suspension_tuning.html
As you make a change in spring rates, sway settings, tire pressures, alignment, etc.. you will either reduce or induce under steer or over steer conditions. The goal is obviously to set the car to neutral in most instances.
6. Wheel bearing load and possible roll resistance issues.
Wheel bearing loads in your hub will obviously increase as the weight of the wheel/tire combination increases. As the weight increases stresses will go up. All in all, it is important as you start adding more wheel/tire to the vehicle to be aware of the effect it is having on corner weights. It is a compromise among strength, rigidity, etc...
As you start increasing the width of the tire, and using sticker compounds the rolling resistance will increase significantly. Take off the crappy H rated tires, and put a new biggie sized set of Yokohama A048's on a bone stock Honda civic DX and drive around town for a few weeks and you'll quickly know what I mean. The car friction circle has obviously increased, but the 4 cylinder's ability to accelerate the vehicle has also noticably been now compromised as a result.
Race cars, like in JGTC use full Bridgestone racing slicks on huge wheels in sizes up to 18X14.5 so obviously there is a lot of rolling resistance as a consequence for that much tire. However, it doesn't really matter because it gives them tons of lateral grip and significantly increases the potential of their friction circle, and they have twice the HP in order to over come it.
