Hyperblade's KP61 Racecar "KP61R" Discussion

[Hyperblade]

53 minutes ago, Rhyscar said:

Good find with the ackerman. I've seen FC Rx7 hubs and steering rack used on a starlet when converted to a front-rack. 

Is there any advantage to the FC RX7 hubs over the Ae86?

Just the two options are for my current setup:

AE86

• Design and replace steering arms
• New tie rods.

FC RX7

• Make shocks fit?
• Refit big brake kit (if it does)
• Some how mount to lower arm (assuming can just chaning taper)
• New tie rods

 

I don't mind doing more work if there are other advantages to be had with switching to something like the RX7.

Advantages there might be?

• Bolt on shocks
• Maybe bigger bearings?
• Better overall design?

Disadvantages might be

• How to deal with Roll center adjustment?
• Heavier?
• Less aftermarket options then? 

I have no knowledge of the RX7 stuff so open to any feedback.

[Rhyscar]

I can't remember the specifics, but it involved changing the leg. They have bigger bearings and more options for brake upgrades. I think the balljoint is same/similar/can be adapted. 

 

Someone with more recent knowledge could answer better (mine's over 10yrs old at this point). Or better yet, get in touch with Tony and have a chat about engine swapped Starlets... https://www.facebook.com/tomac.engineering/ 

[Hyperblade]

1 hour ago, Hyperblade said:

Is there any advantage to the FC RX7 hubs over the Ae86?

Just the two options are for my current setup:

AE86

• Design and replace steering arms
• New tie rods.

FC RX7

• Make shocks fit?
• Refit big brake kit (if it does)
• Some how mount to lower arm (assuming can just chaning taper)
• New tie rods

 

I don't mind doing more work if there are other advantages to be had with switching to something like the RX7.

Advantages there might be?

• Bolt on shocks
• Maybe bigger bearings?
• Better overall design?

Disadvantages might be

• How to deal with Roll center adjustment?
• Heavier?
• Less aftermarket options then? 

I have no knowledge of the RX7 stuff so open to any feedback.

I talked to someone in the know about this.

Aluminum so light for the strength, would be stronger and with bigger bearings.

Downsides getting the 4 stud version challenging in NZ as imported cars were mainly turbo which is 5 stud (America were mainly na thought).

Can't easily get the bearing races our of them without some hackery, Mazda only sell the full spindle, wont sell bearing kit (but don't need to change them often).

And getting harder to find these days.

So overall for me not worth the hassle to swap. If you were doing new suspension from the get go, you might consider it.

[Roman]

Another option is that the steering rack doesnt need to be low for any reason. Can put it and the steering arm higher if it helps packaging. Like on a dc5 or what they did with Binky

[cletus]

On 12/01/2026 at 16:50, Hyperblade said:

 

So overall for me not worth the hassle to swap. If you were doing new suspension from the get go, you might consider it.

this.

 

 

also

one advantage of making your own steering arms is you can heat and bend them to get the pivot points where you need them, which you cant do with a cast/forged part

 

[Hyperblade]

4 hours ago, Roman said:

Another option is that the steering rack doesnt need to be low for any reason. Can put it and the steering arm higher if it helps packaging. Like on a dc5 or what they did with Binky

My understanding is you want it parallel to the bottom arm.

I've heard that DC5/EP3 are not great from a suspension point of view. 

But clearance would be an issue with where the engine cross member is.

3 hours ago, cletus said:

this.

 

 

also

one advantage of making your own steering arms is you can heat and bend them to get the pivot points where you need them, which you cant do with a cast/forged part

 

Yeah, I'm thinking get it all into CAD and maybe pay for an expert to help advise on where things need to be, it's an opportunity to dial things in a bit better (if it needs it).

These guys can make me a new arm, they did the ball joint on my bottom arms.

https://www.hbiengineering.com/projects/2018/5/23/project-name

Or could get 3d printed out of China (pros/cons to that one for such an important part...)

Or CNCed so a few options I could take.

I need to see what's going to be required and will fit to then work out how to make it.

[NickJ]

26 minutes ago, Hyperblade said:

My understanding is you want it parallel to the bottom arm.

I've heard that DC5/EP3 are not great from a suspension point of view. 

But clearance would be an issue with where the engine cross member is.

Yeah, I'm thinking get it all into CAD and maybe pay for an expert to help advise on where things need to be, it's an opportunity to dial things in a bit better (if it needs it).

These guys can make me a new arm, they did the ball joint on my bottom arms.

https://www.hbiengineering.com/projects/2018/5/23/project-name

Or could get 3d printed out of China (pros/cons to that one for such an important part...)

Or CNCed so a few options I could take.

I need to see what's going to be required and will fit to then work out how to make it.

3d printing and fatigue life don't usually hang out together, machined from steel is a good contender for "better option" in this case

[Hyperblade]

1 hour ago, NickJ said:

3d printing and fatigue life don't usually hang out together, machined from steel is a good contender for "better option" in this case

That was my natural inclination too (but thought I would see what reaction I would get ), there's some things I'm willing to roll the dice on, but steering is one of those I really don't want breaking.

[NickJ]

1 minute ago, Hyperblade said:

That was my natural inclination too (but thought I would see what reaction I would get ), there's some things I'm willing to roll the dice on, but steering is one of those I really don't want breaking.

you gots me!

Its not impossible and there are ways to address it, but you'd be up and running faster with steel

[cletus]

https://lvvta.org.nz/documents/infosheets/LVVTA_Info_05-2010_Bump-steer_Swing-check_Procedure.pdf

 

https://lvvta.org.nz/documents/infosheets/LVVTA_Info_04-2010_Bump-steer_Measurement_Background_Information.pdf

 

These have good information on bump steer geometry

It would be interesting to check it before you change anything to see where it's at now 

 

[cletus]

This one has info on rod ends for steering 

I assume you don't have to worry about being road legal but it has info about good engineering practice for steering stuff if nothing else

 

https://lvvta.org.nz/documents/infosheets/LVVTA_Info_04-2020_Spherical_Bearing_Rod_End_Conversion.pdf

[Hyperblade]

13 hours ago, cletus said:

https://lvvta.org.nz/documents/infosheets/LVVTA_Info_05-2010_Bump-steer_Swing-check_Procedure.pdf

 

https://lvvta.org.nz/documents/infosheets/LVVTA_Info_04-2010_Bump-steer_Measurement_Background_Information.pdf

 

These have good information on bump steer geometry

It would be interesting to check it before you change anything to see where it's at now 

 

Thanks for those, they are awesome resources to start with! Really appreciate it.

Yep I want to measure what it's doing now, I can also work out what it was like with steering rack at rear, then can try and work out ideal, then see how close i can get.

12 hours ago, cletus said:

This one has info on rod ends for steering 

I assume you don't have to worry about being road legal but it has info about good engineering practice for steering stuff if nothing else

 

https://lvvta.org.nz/documents/infosheets/LVVTA_Info_04-2020_Spherical_Bearing_Rod_End_Conversion.pdf

Rego is actually on hold, but I don't have any plans to put back on road as it's probably an a fair bit of work.

However it's definitely worth knowing best practise, especially considering I load everything up higher then what you would see on a road car.

[mjrstar]

On 05/01/2026 at 14:17, Hyperblade said:

Won't this affect tyre scrub? and the way it behaves when you turn? 

Yeah, potentially for the better if you are running more offset wheels.

If you shoot a centre line from the top strut bearing through the bottom balljoint then see how that compares to the tyre contact patch centreline.

I pushed the bottom balljoint forwards and outboard on my honda when I went to wider wheels with less offset.

 

The caveman in me would be carving some primitive but strong steering arms from some suitable flat bar. Then spacing the steering balljoint to dial out bump steer.

[Hyperblade]

2 minutes ago, mjrstar said:

Yeah, potentially for the better if you are running more offset wheels.

If you shoot a centre line from the top strut bearing through the bottom balljoint then see how that compares to the tyre contact patch centreline.

I pushed the bottom balljoint forwards and outboard on my honda when I went to wider wheels with less offset.

Currently running zero offset 13x8 front and rear.

And have to be careful with clearance from brake calipers to spokes, very little room left there due to the size of the rotor/caliper.

Definitely something else to consider with all the other stuff though.

Some days I do wish i could just bolt a standard package on and move on to more fun things...

[mjrstar]

Actually I forgot you don't move the bottom balljoint, so your initial thoughts are bang on, you'd push the wheel out without shifting the bottom pivot.

[GARDRB]

MX5 is front rack...  Time for a double wishbone conversion

[Truenotch]

What's your scrub radius like at the moment? The cheapest and easiest thing to try would be adding a negative camber RCA to give you room to have the ackerman set up in the opposite direction.

It'll make the steering a bit heavier and the tyres will scrub over a bigger radius, but it'll be way less engineering than anything else suggested here so far.

 

You could actually make custom RCAs that only pivot one of the bolt holes if you wanted to - that way you get ackerman adjustment and don't move the balljoint as far as you would otherwise. 

[Hyperblade]

18 minutes ago, Truenotch said:

What's your scrub radius like at the moment? The cheapest and easiest thing to try would be adding a negative camber RCA to give you room to have the ackerman set up in the opposite direction.

It'll make the steering a bit heavier and the tyres will scrub over a bigger radius, but it'll be way less engineering than anything else suggested here so far.

 

You could actually make custom RCAs that only pivot one of the bolt holes if you wanted to - that way you get ackerman adjustment and don't move the balljoint as far as you would otherwise. 

I run 0 offset wheels so it's fairly good right now.

Interesting suggestion, something I hadn't considered, and your right would be easier to make!

Is available off the shelf from T3 store. https://technotoytuning.com/toyota/ae86/evolved-roll-center-adjusters-ae86-corolla

Just to confirm I'm not an idiot...

• Current setup has 2 long bolts that go through Steering Arm through the RCA and into the Stub Axle.
• With that setup I assume you must bolt the Steering Arm to the RCA then separately bolt the RCA to the Stub axle to allow you to offset it? Can't see any other way for it to work?

Your right in that adding negative camber should give more space for bottom join.

Need to finish the gearbox shifter relocation, then i'm going to get into this fully and get something under way.

[Truenotch]

1 hour ago, Hyperblade said:

• Current setup has 2 long bolts that go through Steering Arm through the RCA and into the Stub Axle.
• With that setup I assume you must bolt the Steering Arm to the RCA then separately bolt the RCA to the Stub axle to allow you to offset it? Can't see any other way for it to work?

Correct. The basic NCRCA has a set of through holes and a set of threaded holes to offset the balljoint and steering arm by your chosen offset.

With the "Evolved" ones, you can use either the through holes, the threaded holes, or a combination of the two to cancel out the factory ackerman: 

I reckon you could design a custom version of the evolved style with extra offset, then make a new steering arm (or swap the arms from side to side?) to account for the rest of the difference you need.