Bigger is Better.
Yup... this is pretty much how a lot of people pick their offsets and rim widths too... hence why I have this thread.
Why do we go for the wrong rear wheel/tire combo?
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Yup... this is pretty much how a lot of people pick their offsets and rim widths too... hence why I have this thread.
nsxtasy said:
Its a messy world
Most tire specs yield unmounted height/width/section width as primary unit of measure. Measured rim specifications I largely ignore and view as an overall indication of sidewall deflection characteristics.TURBO2GO said:
Never thought of this, and I've never heard this mentioned anywhere. Excellent point!
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I know I new here guy's so don't mind me jumping into the middle of a good conversation. I'm looking to acquire my first NSX this weekend!
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The suspension has been constructed for the offset and wheel size and vice versa. If the car takes a turn the front suspension geometry changes quite much in the NSX, with wider tires or lower offset the forces take place at points where it has not been constructed for.
Why did Honda never change the offset of the front wheels over three diffent dimensions over all these years? They've only changed it for 02+ in the rear, 56 versus 60 mm.
Or even more: why didn't Honda went to 18 with 02+ as they were already wide-spread ten years ago?
Regarding tire weight: tire-rack is +-1 pound from what I've measured on a few tires.
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I keep having to delete a post to make a post because 10K has to be special... LOL...
I'm surprised of this comment coming from you because you have attention to detail. The fact is, it matters a lot more than people think. Honda didn't shave the OEM wheel to save a pound because it was splitting hairs. They didn't forge the wheels because it was splitting hairs. I didn't take 200 pounds out of my car and stop at each part lightened or removed, and say "oh, this is just splitting hairs". Everything is a hair-split until you add it all up. This is an NSX, Why not do it right? 20mm going the wrong way in an offset *IS* a big deal. If you make a change, do it right I say.
You made me delete one of my post too, you cheater! LOL
I use a track set and a street set of wheels. My track set is one of the lightest around (same as Doc's) but in different sizes which are 17x7 and 18x9. My street set is 17x8 and 18x10 simply because I like the look better. I run two wheels because I want to run R-comps or NT-01s but not for the streets/canyons. If you want a one set for all conditions then are you prepared to compromise on your tires to do so? Either way you go.. You can't really use NT-01s for the street and you can't really make the best use of your brakes and fancy suspension with StarSpecs. Let's not even mention snow conditions (I love Socal hehehe).
The biggest impact of wheel offset, width, and diameter is how it affects the availability of tires. For example, if you can get those supersticky "extreme performance" tires in sizes for one set of wheels but not another, they will give you much better performance.
If you're doing this for the racetrack, tire width is probably more important than offset. But even tire width is much, much less important than differences between types of tires.
I don't mean to gloss over your question, but offset alone is just not all that important. It's important when it comes to whether the wheels/tires rub (which may or may not matter, such as for track use), and it may be important to some folks who care about looks (although most people would never notice differences in offset/"flushness").
One other thing to keep in mind regarding offset, and that is how offset works with wheel width. People often quote offset specs as such-and-such mm, which becomes important with respect to how it interacts with the wheel width. Offset has to do with how the wheel is positioned with respect to the wheel mounting surface, but the wheel width has to do with how far the wheel extends out from the centerline. So offset should really be quoted along with width, since both determine clearances, looks, etc. The diagram below, from the Tire Rack website, may be helpful.
That's generally a bad idea, for all kinds of reasons (rubbing, makes the car accelerate slower, etc). If you're concerned about reducing the gap in the wheel wells, just do it by lowering the suspension, not by using oversized tires.
While this is all true, keep in mind that the TCS unit part numbers do not follow the tire/wheel combos you listed.
The strangest part is that the 1994 NSX uses same TCS unit that's in the 1991-1993 despite the changes in wheel/tire sizes between those years. This leads me to believe that the 1991-'94 TCS unit has a larger (or less strict) operating range that other years..
Part numbers for Traction Control Units are as follows:
39900-SL0-023 - For the '91-'94 NSX
39900-SL0-033 - For the '95-'96 NSX
39900-SL0-043 - For the '97-'01 NSX
39900-SL0-053 - For the '02-'05 NSX
Part number source:
http://www.acuraoemparts.com
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+1 YES!!! I keep trying to explain this to people but nobody seems to get it..
This video is good at explaining the importance of Offset and the effect on the Scrub Radius it has at a top level.
<iframe width="420" height="315" src="http://www.youtube.com/embed/JAnIa5wcn4E" frameborder="0" allowfullscreen></iframe>
And a detailed article explaining it from H&R
http://www.hrsprings.com/technical/scrub_radius
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That sounds to me like an error in the parts catalog. I'm pretty sure the TCS units installed at the factory were different between '93 and '94.
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There's even a better video on there which explains what the front wheels are doing during cornering based on the OEM geometry. If you change that with ultra-wide wheels and small offset the cornering of the vehicle will be degraded.
To me it explains why the OEM wheels (without spacers) were working so good compared to bigger is better-combos. This also explains why Honda never changed the offset over the years.
OT: never saw this before: http://www.youtube.com/watch?v=lADVUgJpZXA
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I think that you're better off picking up a high-grippy tire to raise the grip-level than increasing the track via lower offset values. As it has been mentioned in this thread: some people only care about looks. Ultra-widebody, ultralow with ultra-wide track can't be driven fast or can't be driven at all.
Actually I found a 1991 TCS unit that has the original part number as 39900-SL0-013
But all publications & available websites seem to list 39900-SL0-023 as the replacement for it (and as a replacement for the 1991-1994).
39900-SL0-981, 39900-SL0-982, and 39900-SL0-983 seem to be the TCS unit for the Automatics..
Yup. I know the importance of the tire.
Yes, Agreed.
I can't imagine that increasing track in the rear by 60mm and the front by 40mm is not that important. It certainly puts more pressure on wheel bearings and some suspension components. Whether they stress and fail is dependent on many things but there is a reason why the stock track is what it is, right? designed as a whole with the suspension. Also if we are just talking about speed, and in that area you are saying "it's not that important", people do do a whole lot of even less important things don't you agree? certain aero and supposed engine mods. So "important" is relative to the person but getting away from this, it is good to understand the facts, that is what I am trying to do.
Yes, I fully get this relationship, but again my question is somethig else.
Lets take everything else out of this. Looks, flush fit, rubbing, wheel/offset combinations, etc. Lets assume it looks good, theres no rubbing, the wheels are exactly the same and only offsets are different, and tires are the same.
Here is what I want to know:
1) How is handling affected by increasing track width
2) How important is the ratio of track width front to rear and what role does that play in handling.
I hope I don't sound crazy for asking this over and over. I mean Ryu says it is splitting hairs, and GoldNSX says he feels a big difference. Some put 19/20 on their cars and they say they can't tell a difference. These are all subjective things. I am trying to distill the facts, so I can get a solid understanding. If this is waaaaay more complicated than any of us know, because of the relationship of track width/offset/suspension geometry, then I want to know that too. "Not knowing", will make me tend to stick closer to OEM. I am not trying to be a pain, this is a very common thing everyone changes on their NSX. Seems to me like it should be better understood.
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I admire your thirst for knowledge on this subject. From what I can tell based on the track photos of fully raced and tracked out NSXs like the FXD, Realtime, and others, it would appear that the most important aspect is widest track, and largest contact patch. You generally don't see track prepped competition NSXs running wheels with factory offsets.
Scrub radius seems to take a back seat to getting the largest contact patch and widest track.
EDIT.. Actually this appears to be an exception..:tongue:
Scrub radius seems to take a back seat to getting the largest contact patch and widest track.
EDIT.. Actually this appears to be an exception..:tongue:
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well it seems to take a back seat to the wider (not largest) contact patch, but we don't know if the wider track is a side effect of trying to fit the wider patch or not. It may be that there was just no other choice, and that performance in various areas may have actually been better with the factory scrub radius. After all, the entire suspension was designed with that in mind not with the center of the two patches sitting 6" further apart.
We do know that it is a side effect. The reason is because you can't fit a wider wheel/tire with the factory offsets in there without running into problems of the wheel or tire hitting the inside suspension components, namely the shock body. In order to get around that, you need to lower the offset.
Check out this thread where mcano wore out the inside of his tire because it rubbed against the strut body. His solution was to run H&R 25mm spacers.
http://nsxprime.com/forum/showthread.php?t=128958
So basically the benefits of pushing the wheel outward (lowering the overall offset) are:
1) The ability to run wider rims and tires which allow for increased lateral grip
2) Wider track
3) The extra clearance to run larger brakes rotors
4) Better looks
The downsides are:
1) A change in scrub radius which apparently affects steering feel & braking stability (when one side brakes harder than the other).
I should have stated "unintended side effect". Clearly we know that it has to happen to clear wider tires. That is what I meant by side effect. But we don't know for sure what that effect is on suspension geometry. We are trying to get to the bottom of weather it is beneficial to increase track or to keep it the same. There are plenty of times when you can increase the width of the contact patch without increasing track. As the suspension compresses, a wheel that is a few inches further out is not going to travel at the same angle as one that is further in on a double wishbone suspension. Also if we change the ratio of track width front to rear, I am not clear as to what those effects are either. I can assume that you increase understeer as you increase rear track compared to the front and vice versa but again I'm not really sure what happens and I doubt very many people here are. Spacers and offsets are just picked based on looks and clearance. Right now I need a minimum 15mm to clear my BBK. In the rear I have 20 or 25mm. But that's not necessary, I would have been ok with 15. I did it based on advice here. How steering feel is affected is a whole other question. And an important one IMO.
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That's your dilemma. You have to use a spacer to clear the brakes but I would choose the lowerest one. Or you could buy new wheels which offer more ET but don't scratch due to their design.
I can't proof if it has really to do with the geometry but I stronly guess it has to because I had the same tires sizes but mounted on different rims to compare to and the difference was quite noticable like 215/40/17 mounted on a 8/17 ET 43 and 7.5/17 ET 50.
Wait, so you're already running 15mm more in the front and 20/25mm in the rear?
If that's the case, can't you answer your own questions? How did the spacers affect the steering & braking? Does the steering feel numb?
It's very difficult for me to say because I also changed my suspension at the same time, went to new alignment settings, added the spacers, put in a BBK All at once. Feels like a different car but I don't know what to attribute to what. I feel like I am quite sensitive to changes, I can easily drive someone else's car and feel if a particular tire is low on air. Or if camber or toe is off. I am really tuned into chassis strength or flex, while most people next to me or the car owners say "I don't feel a thing". I am astounded, with the way my car handles righ now. It is 10X better. But I just went from 240 pound springs or whatever stock is to 1000. Went from el cheapo damper to a $10k one. The drawback is now I feel more chassis flex. Before, with the top on, I felt almost none. Now top on or off, I feel it. I feel it in the steering... I feel it in transitions. It's not terrible, but it's there. It's like the more I tighten up the car's muscles, the weaker the skeleton gets in trying to deal with it. Anyway this is off subject.
I will probably get a set of Advan RSII's, and I have quite a few choices for offset. 48, 35, 25, etc. more than one will fit and not rub. I am not super low and I have a VRH. So in trying to investigate what is best, I started trying to find out what the effects of offset are on steering and handling. Still far from clear but I will continue investigating it. Thanks for your input.
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