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Wheel offsets effect on handling

Joined
10 November 2000
Messages
246
Location
Northern California
I went from OEM wheels and OEM Yokohama tires to 17"/18" Volk GTC combo with 41 and 42 offsets - which are very different from OEM. The wheels look great but the handling suffered. I had not taken the car over 120 since I installed the new wheels - I did yesterday and it scared me. The solid feeling at speed is gone, replaced by a floating/wandering feel that it's just scary - nothing besides the wheels and tires is different and my car (a '99) only has 22K miles. My RL has the same tires (Pirelli PZero Neros) and aftermaket 18" wheels with correct factory offsets and it feels just as solid as it used to at 120 mph, so I'm sure it is the offsets that make the difference.

I think I will be going back to stock soon when my current tires wear out. My recommendation to those of you thinking of going to different wheels is: don't do it unless looks to you is more important than handling. Have any of you experienced the same with aftermarket wheels with the common 41/42 offsets? Have any of you replaced your wheels with bigger sizes but kept the factory offsets? I love the look of my wheels and I would keep them if I knew that factory offsets would fit and preserve the superb original handling.
 
This sounds like an alignment issue. Did you have the alignment checked when you changed your tires/wheels?
 
I'm not convinced its the difference in offsets that is the problem.
What's the tread width and aspect ratio?, tire pressure? new wheels? slightly bent rim? I went from 16/15 oem to 17/16 Forgelines on my '92 without problems (speeds up to 130, on the racetrack of course). I believe the offsets were within 5 mm of factory. Also switched my Accord's wheels from 55 mm offset stock to 40 mm offset ( same size: 225/50/17 ) without problems so far.
 
What are the front tire air pressures?

If they are above 35psi then take out 5 lbs of air, drive the car a short distance, and not at high speeds but pay close attention to the feel of the tires, then put the 5 lbs back in and do the same driving exercise. If you notice a huge difference in handling you may be running to much air, and caussing the tire to crown leaving the front contact patch very narrow, and when you hit a bump and reduce front end weight even for a second the front will feel darty. If you have a pyro tire temperature gauge that is the best way to set you presures to ensure even contact with the road surface. Many people run their tires at max pressure ratings and this is not the recommended tire pressure, our cars are very light in the front and can run lower tire pressures up front. Try it, and report back. Aftermarket wheels with different offsets and widths will give you a different feel from OEM, al least mine did, but nothing scarry.

Dave
 
GT-C owners please?

Can we hear from some GT-C owners on this please. Off the top of my head, Tan is the only one I know of who has GT-C's. Who else has them?
 
Arata said:
Do the wheels and tire also weight the same as the stockers, could this also be a factor?

They weigh more but not a whole lot more, I doubt that this is a factor.
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This sounds like an alignment issue. Did you have the alignment checked when you changed your tires/wheels?

Yes, the alignment was checked and it had not changed. Car is not lowered and shocks and springs are OEM.

What's the tread width and aspect ratio?, tire pressure? new wheels? slightly bent rim? I went from 16/15 oem to 17/16 Forgelines on my '92 without problems (speeds up to 130, on the racetrack of course). I believe the offsets were within 5 mm of factory. Also switched my Accord's wheels from 55 mm offset stock to 40 mm offset ( same size: 225/50/17 ) without problems so far.

215/40 in front 255/35 in rear/ 33 psi front, 37 psi rear/ new wheels are Volk Racing GTC-Face 1 with 3K miles on them in pristine shape.

DDozier

I will try lowering the air but I don't think that's it.
 
Is it possible that the tires are still brand new, so the mold release compound is making them slippery? Or have you driven a few hundred miles on them by now?
 
nsxtasy said:
Is it possible that the tires are still brand new, so the mold release compound is making them slippery? Or have you driven a few hundred miles on them by now?

The tires have 3K miles on them right now and they stick to curves just fine. The only thing I can think of besides the different wheel offset which positions the wheel in a different place with respect to the rest of the suspension, is the fact that I did not lower the car and it sits slightly higher. This would allow extra air to get under the car and produce a minor lift that was not there before - maybe.

With the OEM tires the car at speed felt to me like it was being sucked to the ground by a giant sucking machine underneath - rock solid without a hint of floatiness. At normal street speeds on public roads the car is just perfect with the new wheel/tire combo, the lower aspect ratio of the tires has even improved on the steering feel and turn-in response - the ride is also softer with the Pirellis. I still have my OEM wheels on which I'll install a new set of original Yokohamas and perhaps that is what I will use next time I decide to take the car over 120 mph.
 
I don't believe it is the offests. There are two people that come to mind that have almost an identical setup except 43 offset in the rear vs. your 42 offset. Neither one of these folks have complained at all. One of them I know drives his car fairly hard and absolutely loves this setup. Perhaps they will chime in.

I doubt it is the wheels. I would suspect a tire issue, either bad batch of tires or air pressure problem. You may want to get a second opinion on the alignment as well.
 
I suspect a combination of things, offset not being one of them. First off keep in mind that stock alignment means toe-out in front. That’s great for crisp turn-in but very rare on street cars because it causes directional stability problems at speed. The reason you don’t have that with the OEM tires is that they are designed to scrub/pull inward, giving back some of the directional stability. The rears are similar in the opposite direction. That’s the only real “magic” of the OEM tires and why they are corner specific.

So, if you put normal tires on the car and retain the toe-out up front you will lose some of the directional stability. A little extra caster can help, but the NSX already uses a lot of that, for the same reason.

Of course many of us use non-OEM tires and the symptoms are not as sever as you describe, which is why I think there is another factor already mentioned by someone. Check the front to rear ride height. Although this has been debated here before, I contend that even a very subtle amount of negative rake (nose up) will adversely affect aerodynamics and cause the already light front end get lighter, exacerbating the directional stability problem.

Edit: BTW, before assuming that the wheel/tire change did not impact front/rear height balance because the standard formulas (or tire specs) say your sizes retain the correct stagger, make sure you account for rim width. You probably increased rear wheel width more than front which stretches the tire and gives a slightly smaller diameter. There may be other issues contributing to front lift such as rear springs sagging or a missing front chin spoiler allowing more air under the front.
 
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Another possibility is a bad tire, perhaps with the tread partially separated from the carcass causing the wandering.

Or it might just be the incorrect offset you are using. Honda specified those unusual offsets for a reason and changing them changes the steering geometry. That will account for some, although perhaps not all, of your handling problems.

sjs said:
The ... OEM tires .... are designed to scrub/pull inward, giving back some of the directional stability. The rears are similar in the opposite direction. That’s the only real “magic” of the OEM tires and why they are corner specific.
Actually, it is just the opposite. The fronts are built to scrub/pull outward and the rears to scrub/pull inward.
 
NSX Maven said:
...Actually, it is just the opposite. The fronts are built to scrub/pull outward and the rears to scrub/pull inward.

I believe not, unless we are debating a matter of perspective somehow. The suspension alignment is toe-out in front. That causes the car to wander when pointed straight, which is why most street cars have toe-in. The way they offset that is to design the tire to pull/track in the opposite direction of toe, inward towards each other. The rears of course are the opposite.
 
No I don't think we are talking from a different perspective.

The front suspension is, as you state, set up with toe out, which is unusual. But this does not cause the car to wander because (if properly aligned) each side will pull in the opposite direction and by the same amount thereby cancelling the opposing sideways forces and making the car run straight and true. What the toe out setting does do is to pre-tension the steering and the tires, so there is no delay in turn in. When the wheel is turned the NSX turns in - and turns in right now!

The ply steer which is built into NSX tires does not cancel out the toe out suspension setting. What would be the point? One could get the same effect by simply eliminating the toe out and specifying tires without ply steer. Instead the ply steer also serves to enhance the turn in and control through the corner.

At the rear the opposite happens. The purpose of that is to reduce the oversteer which is inherent in the NSX's design.

You gotta love Honda. The design is brilliant and is why the NSX was and still is a benchmark for supercar handling!
 
sjs said:
before assuming that the wheel/tire change did not impact front/rear height balance because the standard formulas (or tire specs) say your sizes retain the correct stagger, make sure you account for rim width. You probably increased rear wheel width more than front which stretches the tire and gives a slightly smaller diameter.
Stock '99 tire sizes and outer diameter (without taking deflection into account):
215/45-16 23.62 inches
245/40-17 24.72 inches

His tire sizes and outer diameter:
215/40-17 23.77 inches
255/35-18 25.03 inches

Thus the nominal increase in ride height is 0.08 inch front and 0.16 rear. Other factors can change the ride height - you mention the wheel width but my guess is that this is similarly tiny (compared, for example, with tread depth, which can account for variations of up to 0.25 inch at either end). All in all, I doubt that ride height is a factor here... but feel free to check it according to the procedure in the service manual to make sure.
 
I did the opposite and went from an aftermarket 16/17 combo to oem 16/17. I used 3 different tires on the aftermarket 16/17 combo and the car always understeered badly. I suspect part was due to the lower offset in the rear rims (increased rear track width). BTW, I typically run 32/40 psi front/rear. With the oem 16/17 wheels with oem tires, the car feels wonderful. It still understeers but quite a bit less. I just acquired an oem 15/16 combo and am anxious to see how they feel.
 
NSX Maven said:
No I don't think we are talking from a different perspective...

I'm quite aware of the benefits of front-toe out and why it is used, but I think you are wrong about it causing a tendency to wander. Yes of course it puts equal tension on each side, but because they point out, away from the direction of travel, it produces a vague feel when going straight. That is why it is so uncommon. Toe-in points both sides to the center line of the direction of travel and gives a better sense of directional stability. Try it both ways on any "normal" car and you will see what I mean.

The NSX suspension is a-typical in many ways and may be inherently less prone to the negative aspects of toe-out, plus it uses a great deal of caster which gives a solid on-center feel. And even the negative camber helps to make it feel planted.

But back to your point about the scrub, you may very well be correct. It has been well over a decade since I first read the details of the design and didn't think more about it until I bought one a few years ago, so my memory could be faulty. However, I don't think your reasoning that the design as I describe is pointless. Just because the tire carcass is built to scrub inward would not necessarily cancel the positive benefits of toe-out during turn-in. The actual effects of toe and scrub are surely different or they wouldn't need both, which is why it seems plausible that the latter is intended to cancel only the negative aspects of the former. At least that's what I've believed and said for quite some time now. If there is a technical paper explaining the opposite then I would like to read it so as to learn the truth and stop spreading falsehoods.
 
sjs said:
So, if you put normal tires on the car and retain the toe-out up front you will lose some of the directional stability.
So how much toe-out should we target for with aftermarket wheels and tires? What are the alignment specs of your cars?
 
KGP said:
So how much toe-out should we target for with aftermarket wheels and tires? What are the alignment specs of your cars?

I stick with the stock specs give or take. The steering is less razor sharp and the directional stability suffers a bit, but I'm more interested in actual performance than in the perception of performance provided by the OEM rubber and I think some of the newer tires offer that.
 
NSX Maven said:
The front suspension is, as you state, set up with toe out, which is unusual. But this does not cause the car to wander because (if properly aligned) each side will pull in the opposite direction and by the same amount thereby cancelling the opposing sideways forces and making the car run straight and true. What the toe out setting does do is to pre-tension the steering and the tires, so there is no delay in turn in. When the wheel is turned the NSX turns in - and turns in right now!...
Another thought on this point while I continue to chew on the direction of ply steer/scrub/conicity. The pre-tension to steering and tires does serve to tighten the steering response but, as you say, either type of toe accomplishes that. Front toe-out is preferred because it not only pre-tensions but also gets the front to point in the desired direction more quickly (rather than fighting against it), at least for that first instant. And that leads me to my point. That tendency to make the steering seemingly quicker on initial turn in is exactly why toe-out makes it feel “nervous” at high speeds in a straight line. If toe-out makes a car turn in quicker than it would with toe in, then it will naturally be more difficult to keep straight because the slightest movement of the wheel will cause a greater change in direction. (wander, nervous, call it what you want.) You can’t have it both ways, expecially in real-world conditions where pavement is not billiard table flat and smooth. That is, unless you come up with a clever way to keep the benefits of toe-out while “masking” the negatives, which has always been my take on the special tire design. But I’ll admit that the jury is still out on that topic.
 
Good thread,I wonder,are those pirellis directional?if so make sure they are rotating in the correct direction.I also think that a toe out front aids turn in but hurts straight line stability,and the oem tire scrub does not aid in turn in but does give better straight line steering feel.The other item that I have noticed which affects totol driving feel and sense of stability is the wght of the aftermarket setup.I subjectivly feel the car is less stable and responsive when I go from lighter wheels to bigger heavier wheels/tires.You also get more wandering of the larger tires over crowned and irregular pavement.If the bling dos'nt make up for the untidy ride quality then go for a set of after market wheels in 17/17 size to allow the newer oem tires.
 
On the toe-out effect on directional stability, my experience is the opposite, i.e. more toe-out increases directional stability. I don't know what the physics involved are but this is my seat of the pants impression.

My car had way too much toe-out from the factory when it was new, it was like -7mm, which made the front tires wear out in less than 7K miles (very unusual for a new '99). During this time the directional stability was phenomenal; if anything, I felt a resistance to changing directions when going into a curve, with the steering very heavy. When I realigned with new tires to a more conservative -1mm of toe out in front and less toe-in in the back too (I believe I left 2mm toe-in) - directional stability was not as solid but still very good. The new tire/wheel combo is just twitchy and floaty at high speeds.

The tires are not unidirectional but they do have a side out and they are correctly installed. I also feel now that I should edit my reference from "scary" to "a definite deterioration of the straight line stability with a wandering and floaty feeling", perhaps scary was an exaggeration, it is not like it's going to leave the road at any second but a definite "pay attention to the road because it just might do something funny"
 
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