Lowering your wheel offset at the front (+55 -> +45, for example) increases your scrub radius, that is the lateral distance on the ground between your steering axis and the center of the tire contact patch. This means equal longitudinal loads (brake loads, for example) at one wheel create different moments about the steering axis causing different forces at your hand (more force for the lower offset case).

Under braking on flat surfaces, there will be no difference in feel as the two moments cancel each other out. But braking on a rough or uneven surface can cause loads into the steering wheel due to the variation in normal force and thus braking force at each wheel. The lower the offset, the more pronounced this is. Also, the electronic steering on the s2000 was tuned for a +55 offset. I have found it intervening when it shouldn't when I use a different offset wheel, probably because of these higher or different loads. Maybe resetting the steering system could make it learn, but I am not sure.

This increase in scrub radius also increases the lever arm for lateral loads (cornering) so thus the cornering loads feel different at the steering wheel.

Also, lower offset wheels may make it seem like there is more "feel" in the steering wheel at all times, but this is again due to the increase in scrub radius as you are actually "lifting" the car as you steer (also a function of kingpin angle, I believe).

Putting +65 rear wheels on the front of the s2000 causes the scrub radius to decrease and I have found a loss in steering feel in some situations due to this.

ZDan, thanks for the monologue...good info.

az3ar, usually tire width is not taken in to account when determining track width, only the wheels offset. What offset wheels are you using with your 255 tires?

 

^I am using +45 all around

 

I'm curious about the possibility of some numbers missing in the calculations shown here.

Track is the center of the wheel to the center of the opposite wheel on the front and back of the car. The calculations should take into account not just the offset difference but the wheel width increase as well.

If you look at offset only and use a wheel of any width and an offset of say +47 you will have only increased the track of the car form the offset:

Front
8mm per side or 16mm total or .63"
Rear
18mm per side or 36mm total or 1.42"

If you are still using the stock F 7" and R 8.5" wheel the above numbers will be the only difference in track and also rubber on the road outside to outside difference.

If you are using 12" wheels, just to illustrate a point. The track difference from offset would be the same but the increase in rubber on the road width, outside to outside, after including the wheel and tire width difference would be:

Front
Offset .63" + Wheel Width increase to the outside or track ^, 5" = 5.63" = 143mm

Rear
Offset 1.42" + 3.5" = 4.92" = 124.9mm

** For a 17X9 +47 the track width increase would be:

Front
Offset .63 + 2.5 = 3.13"

3.13"/57.9"(oem track width) = 5.41%

Rear
Offset 1.42 + 1 = 2.42"

2.42/59.5 (oem track width) = 4.1%

I'm interested to know how this would change the calculations made in the previous comments or am I incorrect in thinking this was unaccounted for.

 

Right.
Think about it, this statement is at odds with your previous statement. Whether you have 17x7 +45 or 17x9 +45 wheels, the track is the same. Wheel width doesn't factor into track width. If the offset is the same, the center of the wheel is in the same place, and the width from the center of the left wheel to the center of the right wheel is unchanged.

[QUOTE]If you are using 12" wheels, just to illustrate a point. The track difference from offset would be the same but the track increase including the wheel width difference would be:

Front
Offset .63" + Wheel Width increase to the outside or track ^,

 

Yes I get that the track width will not change unless the offset is changed.

My statement was poorly written.

In writing this:
"The track difference from offset would be the same but the track increase including the wheel width difference would be"

What I meant to say was:
The track difference from offset would be the same but the increase in rubber on the road width, outside to outside, after including the wheel and tire width difference would be:

I have edited the statement in my post above to correct this.

I would still like to know if that increase in rubber on the road width difference, which seems quite substantial would change the calculations.

Or are the calcs that you guys are using only effected by the offset and not by a 2.5" increase to the overall width of the outward edge of rubber side to side as noted on the front in my example with the 9.5" +47 wheels.

If that's the case then there must be some way of taking that into consideration also. Seems like that would account for a significant difference in handling characteristics.

thanks

 

subscribed... so far what I know about track increase has either been about spacer or wheel offset.

 

call me a simpleton... but all this armchair racing stuff, however fascinating (as i love crunching numbers myself), doesn't always manifest itself in reality

jon, was cool getting to watch you roaming around SOW this weekend. you passed me going up the 14N in the morning heading to the track day with the black 3 series behind ya.

anyway, back on topic, here're my experiences with different track widths. all relative to stock ap1:

265/35 on 10.5 +22 (stretch ) = car's steering was much more stiff, not nearly as nimble as it was stock (205s on +55). car would also tramline much more; never got to try on the track with that setup

255/35 on 10.5 +22 (stretched) = steering feel was restored to a point, less tramlining, steering became a bit more sensitive (in a good way). didn't feel as if i had to coax the car to go in one direction as much as with the 265s

255/35 on 9.5 +38 = nearly stock feel (great!) very easy on the hands... sorry not too many technical terms here

255/35 on 9.5 +13 = tramlines again to a point that i'd say falls right under the 255s on the 10.5 +22s. easily tolerable, but still quite a noticeable difference.

hope to see you again (and actually meet you) at the track next time



btw, long story short... to answer your original post:
^^ my own experiences with my S
and any offset change above +40 makes you feel a difference imo.

 

so are u saying, with the +22 offset u actually felt like handling was negatively affected?

 

of course there were other factors to consider, stretched tires mainly... but when i had less stretch with the 265s on there, the steering was less responsive than when i had more stretch with the 255s. felt like i was bogging the steering system a bit. but even with the 255s on there, the steering was harder and had more resistance than when i had 255s with the +38s

handling i cant say for sure, since i never tracked that setup, but fwiw, the steering was definitely worse. not tremendously worse, but noticeably sluggish

edit: i'll have a new track set up soon, 17x9 +10 already on order so im hoping the steering factors and handling are more dependent on the size of the tire/wheel than the offset

 

[QUOTE=edspecR,Aug 3 2010, 01:27 AM] jon, was cool getting to watch you roaming around SOW this weekend.