Racing setup/ car feedback

[icehouse]

After 10 hours of behind the wheel racing I have a few questions you guys may be able to answer. Usually I just bug Keith but I'd like everyone's input. I notice this mostly under yellow flag laps driving 70% (or more if I'm trying to sneakily catch some cars) That on and off throttle I can feel the rear toe in and out. I did play with the rear tow settings. I had miles of rear toe like Keith but it our car is like maybe 110WHP and it was killing our straight away speed. So we adjusted it out slowly until it felt bad and then towed it back in. Is this just normal? Is it the trailing arm bushings? I notice with other 510's I have that cheap tires with flexy sidewalls feel similar. Maybe it's just the slip angle? I just drive around it but it would be cool to make the rear feel more stable. The X-member has solid aluminum bushings.

[Pista_510]

Trailing arm bushes will have an influence. Are you using rubber / urethane or metal (ie. spherical) in the pivot points?

[icehouse]

Trailing arm bushes will have an influence. Are you using rubber / urethane or metal (ie. spherical) in the pivot points?

They are the stock rubber bushings. could there be that much flex?

[Pista_510]

The stock rubber bushing has some flex and, while its contribution to toe change is significantly less than that caused by the Datsun semi-trailing arm geometry, every small amount of movement that is eliminated, so as to not get amplified at the tire, is an incremental improvement.
Unfortunately, the inherent limitations (from a toe change perspective on roll due to cornering forces and / or throttle input) of the semi-trailing arm in a 510 (and other vehicles) mean that the we're faced with the limited options of dialing in a lot of static toe in (as you've done), make the suspension (super) stiff to limit movement and somewhat have to accept the compromises.

[bertvorgon]

What he said......

There is also the factor that when we are hard on it, any gooofyness is kinda lost in the heat of combat.

I used to hate the feel of my car when I ran real race tires at slow speeds, car hunted like is was looking for rabbits in the hedge.

Mushy tire side wall does not help either...another reason I hated the R888's, especially on the rear.

You are experiencing the weight transfer at on/off throttle subtlety. When you are hard on it, in theory, the weight to the rear stays kind of static for lack of a better word, then on the brakes, back on the throttle.

[icehouse]

Yeah I know the limitations of our rear suspension. But this felt beyond that. A few Ratsun guys made some good guesses. On was low tire pressure on one side. Which I checked at the beginning of each race. That race we did have a blow out. I wonder if it was slowly going down. Another guy said a worn out LSD which is also right. Are diff has been getting worse and worse. It will do 1 tire fire pretty easy if you push it. So I'm going to shim it over the winter.

[bertvorgon]

HA...soft tire...mushy sidewall.....

[Pista_510]

HA...soft tire...mushy sidewall.....

Literally my next questions....

[icehouse]

I guess I didn't even think about tires because it's a spec series so we have to run Hankook RS-4's but I never noticed the feeling before.

[bertvorgon]

Tires and tire pressure can make a tremendous difference to how the car "feels". It is the link to the road and seat of the pants feel.

That is why on the Specialty road race cars they have tire Relief Blow offs, to keep the tire pressure at the "magic" number depending on the track.

[icehouse]

Tires and tire pressure can make a tremendous difference to how the car "feels". It is the link to the road and seat of the pants feel.

That is why on the Specialty road race cars they have tire Relief Blow offs, to keep the tire pressure at the "magic" number depending on the track.

Do you notice a best grip pressure vs. a best feel pressure? Our car likes a low pressure for grip but it feels better at a higher pressure. I need to get a data system and do better testing.

[bertvorgon]

Absolutely!

I found that even with the cantilever GoodYear race slicks and of course the street tires

My 048's work best at about 26 to 28 PSI...but.....they "feel" best at 30 PSI cold.

Norm really experienced that too.

In watching the Specialty Team, they of course go for best grip as that is the fastest...given they are very good drivers.

On the street, I like to really feel the tire right away on TOSS IN, as there is no luxury of leeway in terms of having to stay in my lane.

All that being said, driver confidence is the most important, as you will not be fast if you do not trust the car.

[funwithmonkeys]

I know on my tires I usually take the better feeling pressure over the better gripping. Driving on the street with little room for error feeling confident in the car is more important than maximum grip in my opinion. I can push it harder for longer if it feels better. Some of the tires I tried a 1lb difference would make a huge difference in how the car felt. The tires would warm up while driving and then cool back off 10 min later and the car did not feel consistent. My current tires feel consistent over a 7lb range. Makes for easy set up and confidence in the car over a wide range of tire temps.

[datzenmike]

Tires and tire pressure can make a tremendous difference to how the car "feels". It is the link to the road and seat of the pants feel.

That is why on the Specialty road race cars they have tire Relief Blow offs, to keep the tire pressure at the "magic" number depending on the track.

Do you notice a best grip pressure vs. a best feel pressure? Our car likes a low pressure for grip but it feels better at a higher pressure. I need to get a data system and do better testing.

You probably do this, but keeping a log of tire type, weather and temperature as well as track temperature and any changes, tire pressure range used and lap times can point the way to what works and what doesn't..

[bertvorgon]

That is a given for any one serious about how their car handles...log book(s)!

This is especially important when you are running the same track all the time, then you can look at back to back setups, of course changing only one thing at a time...ha..ha...

I/we did this during the Solo Drivers Association races at Boundary Bay, same course every third Sunday, This sure helped with car setup, at least for me.