inspired in part by some of DavidM's comments back in the day, as well as Nick's posts about bump steering (and my own somewhat nightmarish experiences in this area) - i decided to do a non-scientific experiment to determine what effect tire pressure has on bump steering (especially rear bump steering).

there is a section of road near here that is a perfect testing ground for this purpose.

i started by taking this section of corners (over the bumps and broken pavement) at 34/34. i then altered tire pressure and noted my experience of the driving.

and the results:

31/31 - *severe* rear bump steer and noticable front bump steer as well.
32/32 - bad rear bump steer and noticable front bump steer.
32/33 - rear bump steer somewhat decreased but front bump steer oddly seems worse.
32/33 - similar to 32/33
32/34 - similar to 32/33 but front bump steer is pretty severe seeming now.
33/33 - bump steer noticable front and back, but managable.
33/34 - much the same as above.
33/35 - worse than 33/33 as front bump steer seems "jarring"
34/34 - bump steer noticable, but only at high speeds.
34/35 - very similar to above, perhaps improved.
35/35 - bump steer (front and back) only noticable when approaching the limit and even then managable.
35/36 - rear bump steer worse than above.

i know this is not scientific and there are many combinations that i did not try out. it's *purely* experiental. none the less, it's reinforced my belief that 35/35 is the optimal setup for me (and that this car is *really* sensitive to tire pressure).

 

Just like to say that on a hunch I ran 35 all around at sears point the other day, and it was GREAT. In particular, my drifting on slightly uneven surfaces was a LOT more predictable, and made it fun instead of scary. Although I'm running Kumho R compounds instead of S02's this further goes to show how much the bump steering is related to the suspension..

 

road and tire temps have a lot to do with the bump steer as well.

 

Was there a cool-down period between your runs? I'm wondering because, as the tires warm up, the pressure increases. Did you find yourself DECREASING gauge pressures after making runs at what were originally lower pressures than the ones you were setting up for the next run? (That sounds a little convoluted--hope you get what I mean.)

cal

 

totally understand.
and yes - there was a cool down *and* a pre-testing warm up run as well as regular rechecking of pressures all around.

hardly scientific, i know - but perhaps this can provide a tiny bit of additional data as we seek *solutions* to the bump steering issues.

 

32/33.....similar to 32/33

Very, very interesting....I never would have thought that would be the case?

LOL (J/K)

Utah

 

Totally agree with your 35/35psi finding. Seems like the 'sweet spot' for the S2000 .... I went by 'feel' as well and the pressures around 35/35 were the onces that felt the best to me (thouh I was looking for grip as well). I'm running 37/35psi (and have been so for good 3 months) as I found I needed even less flex in the front to suit my driving style.

Though, I had my car recently alligned and had some toe-IN dialled at the back. This stabilized the car even more at the limit. Makes the back even more stuck to the ground. It's much more of an effort to get the back out while before the allignemnet I could easizy provoke 'passive' overstear.

ps. Some of the local Honda dealers are setting all the S2000 with 35/35psi after their service. They say that they found that this pressure setting 'improves' the handling characteristics.

 

Thanks for the info. However, IMHO increasing front and lowering rear pressure a bit (to around 36/34) makes the car feel better when just driving around. Did you notice this, as well?

 

I have higher pressure at the front (37psi). I'm running that because even with 35psi at the front, I found myseft getting too much tyre flex under really hard cornering. It almost felt like the car was tripping over itself. Though this was pretty rare and I had to be pushing very hard. 37psi seems to eliminate this flex and I've been running that for a while .... I'm happy with the way the car feels.

Though, 35/35 is what I'd recoment to must people, and only if they find too much front-tyre-flex I would say try something higher.