Suspension tuning - dampers, spring rates, etc.

[Xian]

And here’s some more discussion about the rear of the car:

https://honda-tech.com/forums/road-raci ... us-606414/

And here’s some details on the bumpsteer at the front of the car:

https://honda-tech.com/forums/road-raci ... a-2639712/

Assuming the Soooooper Genius is accurate in his measurements, we’re talking about 1/10” single wheel toe in during the corner entry phase. That’s something like 20% of the 0.5° “critical toe” number tossed around earlier. Yes, I’ve ignored the additive toe change of bump+compression because, if we’re honest here, how much does a slight amount of toe out on the unloaded, inside tire matter? Especially when the toe change under droop is even less than the toe change under compression.

This sorta leads us to conclusion #2; if the toe change under droop is roughly half that of the toe change under compression, what does that indicate? Yep, that out car is “too low” relative to the ride height that the engineers designed everything around. Does that mean we should raise the car out of the weeds so that we can get to a more neutral area of the toe curve? Or maybe it’s a case that lower is better because of the CG/camber curve/aero improvements? Only way to know is to test, test, test... and even then it’ll be tough to get apples to apples bracketing done where the driver and conditions don’t influence the results.

All this being said, I go back to my original feedback on fixing the front end bumpsteer: yes, you can fix it. No, it’s not something remotely on my radar as the impact is pretty inconsequential.

[aklackner]

In the process of over thinking here but have looked around and I see lots of info on rear bars but little on rates for the front.

Tried running some rough (as if it were a straight bar) dimensions through a calculator and came up with ~300lbs/in but that is probably at least +/- 50%, then of course there’s the bushings.

Anyone have a better number for the OEM front bar?

[Xian]

Short answer is “not really”. Longer answer is that some folks have tried to measure it and come up with some data points. IMO, given the limited bar options at the front of the car, I’d just try swapping out different rates and tuning around them. I’ve been happy with the stock or smaller bars on the front of the DC/EG chassis. I certainly wouldn’t shop the the larger (wasn’t there a 26mm one) option.

PS
Just remembered that Scott Rinde worked up a splined front bar option on his ITR. I seem to recall that he had a thread or 2 over on Hondatech.com and that may have been where I saw some basic rate information. His user name is RR98ITR.

[aklackner]

Thanks.

This is probably better suited for my rebuild thread but might apply some to others trying to keep an R on the street as well so....

I’m working on a shell that I want ultimately to see mostly street (LA area) with some hpde days.

I really don’t have any business playing at engineering but have been trying to do some modeling. (Because it’s easier than getting out and making real progress on cleaning up my shell, and it’s an excuse to spend some more money right :s )

I like the idea of being able to get some fine tuning done at some point and for some reason I’m also attached to the idea of running square spring rates (because it mirrors OEM?) but again want it to be street-able.

So all this amounts to I’m being silly and trying to convince myself I can beat the street/track tuning compromise better than Honda already had.

Here’s some of what I have in mind:
Koni sport
Koni coilover kit
Karcepts spherical mount
HyperCo 12” 175/350 spring
FCM bump stops 36mm front 76mm rear
Preload ~350lbs front ~175 rear
Bars OEM ITR front, OEM GSR Rear
Just thinking out of the box, I also have the 24mm ASR but I’m pretty sure I don’t have the talent for that

Just realized the legend is incorrect on the first model, should be reversed blue is rear.

[coolhandluke]

In the process of over thinking here but have looked around and I see lots of info on rear bars but little on rates for the front.

Tried running some rough (as if it were a straight bar) dimensions through a calculator and came up with ~300lbs/in but that is probably at least +/- 50%, then of course there’s the bushings.

Anyone have a better number for the OEM front bar?

Thanks to our Expo sponsor Eibach, they feel the FSB number is approximately 100lbs.

[coolhandluke]

Short answer is “not really”. Longer answer is that some folks have tried to measure it and come up with some data points. IMO, given the limited bar options at the front of the car, I’d just try swapping out different rates and tuning around them. I’ve been happy with the stock or smaller bars on the front of the DC/EG chassis. I certainly wouldn’t shop the the larger (wasn’t there a 26mm one) option...

Mugen had a 26mm FSB, but I wouldn't recommend it without a RSB in similar/greater rates.

PS
Just remembered that Scott Rinde worked up a splined front bar option on his ITR. I seem to recall that he had a thread or 2 over on Hondatech.com and that may have been where I saw some basic rate information. His user name is RR98ITR.

Scott quickly makes me mind :explode: with his knowledge.

[Xian]

In the process of over thinking here but have looked around and I see lots of info on rear bars but little on rates for the front.

Tried running some rough (as if it were a straight bar) dimensions through a calculator and came up with ~300lbs/in but that is probably at least +/- 50%, then of course there’s the bushings.

Anyone have a better number for the OEM front bar?

Thanks to our Expo sponsor Eibach, they feel the FSB number is approximately 100lbs.

If that’s per side, I’d buy it (so ~200 in roll). IIRC, Hollis did some testing on the smaller EF front bars and said they were in the 125# range (in roll).

I think I tried a larger front bar on one of my ITR’s but I may be wrong... actually, I’m pretty sure I did. It was an experiment of running more front bar and less front spring. I got the roll rate about right but then had problems unloading the inside front more than normal and the Torsen diff not having enough lockup for it. Wouldn’t be an issue with a better diff but I still wouldn’t chase the big front bar setup too far; it’s way easier to toss some spring at it.

Regarding a GSR rear bar, there’s literally nothing that could convince me to run that small a rear bar. You can run square rates with a decent size rear bar without any issues. I’m not a huge fan of super high rear rates on anything outside of a wheel to wheel car.

[aklackner]

I think I get where you’re coming from on the rear bar, here’s my rational:
I picked the dual rate springs specifically for roll control. The front sits too deep for this to work there but the rear sits in the transition at static. In roll the outside will see the 350in/lbs, however the inside will only see 175in/lbs. This means there’s already a built in 175in/lbs differential if I only get another 75in/lbs (*movement from each side) that seems like it will knock out roll pretty well. At least that’s my theory.

I picked up a GSR bar for $60 shipped so at least it’s a cheap experiment and I can always try to sort out the 24mm ASR if after some experience I think I can manage it on the track.

I’d love any thoughts on these ideas.

Also Not sure if any one has tried but I’ve modified bmw rear shock mount gaskets to help dampen the noise from the spherical uppers. Minimal modification is required and it should help any water from getting up there too.

[Xian]

I think I get where you’re coming from on the rear bar, here’s my rational:
I picked the dual rate springs specifically for roll control. The front sits too deep for this to work there but the rear sits in the transition at static. In roll the outside will see the 350in/lbs, however the inside will only see 175in/lbs. This means there’s already a built in 175in/lbs differential if I only get another 75in/lbs (*movement from each side) that seems like it will knock out roll pretty well. At least that’s my theory.

I picked up a GSR bar for $60 shipped so at least it’s a cheap experiment and I can always try to sort out the 24mm ASR if after some experience I think I can manage it on the track.

I’d love any thoughts on these ideas.

Also Not sure if any one has tried but I’ve modified bmw rear shock mount gaskets to help dampen the noise from the spherical uppers. Minimal modification is required and it should help any water from getting up there too.

I see where you’re going (the idea that the inside will be “pushing down” less than the outside) but is that taking into account the effect of the sway bar? As the car rolls and the outside rear is compressed, the swaybar will also move “up” and push upward against the inside rear (which will be in the 350# portion of travel). Assuming the bar is at least 175#/inch, the inside corner will never move into the lower rate portion of the progressive spring rate.

Certainly give it a try but I think you’ll find more rear bar is what you want... and more spring. If I were setting another ITR up, I’d start in the 750F/500R, stock front bar, and at least a stock rear bar (preferably the 24mm or thin wall splined bar).

[coolhandluke]

...Certainly give it a try but I think you’ll find more rear bar is what you want... and more spring. If I were setting another ITR up, I’d start in the 750F/500R, stock front bar, and at least a stock rear bar (preferably the 24mm or thin wall splined bar).

I always value your input Xian.