Advice needed for Autocross tires and tire configuration.

[Jeff Berk]

I've tried Auto-X three times but my car broke down due to vapor lock once and a damaged battery cable another time. I made it home eventually under my own power. 

This past weekend I got a successful 8 runs in at Dragway 42 near Cleveland, OH. The event took place in their parking lot which is a lawn area crisscrossed by pavement. This was their last event of the year so I'm making plans for my 260z's hibernation upgrades.

One issue I'd like to address is rear tire grip. I've tried lowering my air pressure to 28.5 psi in the tires all around but my rear tires could still use a little more grip.  I'm currently using Kumho Ecsta AST KU25 All-Season 225/50R15 91H which are performing well on roadways. I started looking at a track tire alternatives that I can switch to for auto-X and came across some 225/50R15 Hoosier R7 with 3/4 thread remaining on usedracingtires.com at $100 each (plus shipping). I am likely only able to haul two extra wheels in my '74 Z so unless I want to risk driving with these slicks on the public streets, I would be limited to switching out only one axel at the auto-X event. 

Now the questions:

1) Are there any issues with using my Kumho tires in the front and these Hoosier slicks in the rear?

2) Has anyone had experience with usedracingtires.com?

3) Since I'll be purchasing a pair of steel wheels to go with the track tires, should I stick with 15 inch wheels? I'm not sure what width and setback are needed for stock fenders and lowering springs, factory drum brakes in the rear.

Thanks for reading

Jeff

Edited November 7, 2023 by Jeff Berk
added picture

[Patcon]

I think I would consider adding a trailer hitch and a small enclosed utility trailer. Haul the tires, a floor jack, spare fluids a few tools in the trailer.

I can't help with the tires.

Do you have a limited slip differential?

[Jeff Berk]

No LSD. Just an R200 installed in the early '80s by a previous owner.

[Patcon]

LSD is probably the biggest thing to help with traction

[heyitsrama]

+1 on the LSD, I've heard good things about MFactory LSDs, there was also an "OBX" LSD that was a more "affordable" option, if you go the OBX route, it required modifications to the hardware. There are threads on HybridZ...

How are the gear ratio of the rear end treating you? Do you plan to make changes to the brake system?

 

1. IDK, test it out and see what happens. 🙂 Report back....

2. Check Craigslist too 🙂

[crayZlair]

20 hours ago, Jeff Berk said:

 

This past weekend I got a successful 8 runs in at Dragway 42 near Cleveland, OH.

Now the questions:

1) Are there any issues with using my Kumho tires in the front and these Hoosier slicks in the rear?

2) Has anyone had experience with usedracingtires.com?

3) Since I'll be purchasing a pair of steel wheels to go with the track tires, should I stick with 15 inch wheels? I'm not sure what width and setback are needed for stock fenders and lowering springs, factory drum brakes in the rear.

 

 

Been to 42 a few times with my '73 FP car. Fast and fun.

Q1. It's probably best to use the same tires front and rear. You want the car to be as "neutral" as possible. Too much front traction can induce oversteer, to much rear traction can induce understeer.

Q2. No

Q3. I see that you are running HCS. The rules only allow for an 8" rim width. When I drove my '76 car in BSP, I went with a 16x7 rim with a 225-50-16 tire. I tried 16x8 rims, but they rubbed a little. You should probably stay away from steel rims. They are less expensive than alloy, but much heavier. Un-sprung weight is your friend.

I have a Gleason Torsen carrier in my R200, but I got it back in the 80's. Probably hard to find anymore. Quaiffe makes a similar unit, but they are expensive.

Come on over to Toledo Express Airport next season!

 

 

[Jeff Berk]

It looks like my best option to control my car around the sharp Auto-X turns would be to install an LSD. I'm tabling my tire upgrade for now but if I go back to it, I can always buy a full set of 4 and car-top two of them.

Documentation from the owner back in the early 1980's listed the front brakes as FIA Nissan Racing Calipers (4-pistons). I don't know how to differentiate this unit from a Toyota 4-piston so I'm assuming it is still the current unit. 

I'd like to keep my costs to around $500 +/- so if I go with an LSD it looks like it might have to be the OBX unit. I started looking at videos on its installation. I have access to some uber-gear-heads in my area for support if I get stuck (R&R Restoration & Repair in Kent, OH and Case Western Reserve University's [ThinkBox] machine shop, Cleveland, OH).

I've been avoiding the Toledo auto-X because of its distance and my concern over the reliability of my car (see my initial post about break downs). I think I have issues sufficiently under control now and my daughter's family live 5 miles from the Toledo airport and could come to my aid if I get into trouble so I might risk it next season and see you there grazyZlair.

 

[Zed Head]

On 11/7/2023 at 10:46 AM, Jeff Berk said:

rear tire grip.

Is one tire breaking loose or both?

Looks like you still have room to lower the car.  That will make a big difference.  And anti-roll bars.  

[Jeff Berk]

Perhaps breaking loose is the wrong words. I get tire screeching and oversteer both right and left. I understand that oversteer is inevitable when the car is pushed beyond its limits. I want is to expand the car's limits. I thought sticky tires was my most cost effective way to do this but now it sounds that an LSD might be the way to go.

My suspension configuration is as follows (italics indicates early 1983 owner upgrade based on documents that came with the car.):

1)      Technics front/rear anti-sway bars (links and bushings replaced 2018)

2)      Quick steering knuckles (I have no idea what this is)

3)      FIA Nissan Racing Calipers (4-pistons)

4)      KYB front/rear struts (2018)

5)      1-1/2 inch lowering Eibach Performance Spring Kit (2017)

6)      Front strut tower bar

Edited November 9, 2023 by Jeff Berk

[Patcon]

Quick steering knuckles are shorter steering arms on the bottom of the front struts. They connect to the tie rods on the steering rack. The shorter length means steering inputs cause more tire movement for the same input versus stock knuckles

[Patcon]

Another thought is front castor and camber setups. This might be a challenge for a street driven car but I would expect alignment settings would help with the oversteer

[Jeff Berk]

6 hours ago, Patcon said:

Another thought is front castor and camber setups. This might be a challenge for a street driven car but I would expect alignment settings would help with the oversteer

I've never touched the castor and camber, just the toe in using a tape measure and two aluminum plates. I'll need to read up on the other two adjustments.