[Fot] VDCA, SVRA, VRG, VSCCA Tire Rules

Thu Oct 8 08:16:25 MDT 2026

Mike,

Thanks and appreciate the additional feedback.  I have a  R888s on another
set  of wheels, but have not driven with them yet.  I would be interested
in the results of your head to head comparison.  I think the R888s are
harder tires from what I understand, but similar temp ranges.

After more research, I have decided to stick with the Hoosier TDRs.  Just
feels the right thing to do even with the technical differences.

For those that might be interested, the Hoosier R8s will require a front
camber of (2.0) to (3.5) and a rear camber of about (2.0), which would be
difficult to achieve with the TR6, without radically changing the front
suspension.  I would rather stay vintage than make those kind of changes.
While at it, curiosity lead me to compare the Speedster to the TDR.  I
found the Speedster, being a radial, also requires a higher camber as
well.  Otherwise, with a camber of less than (2.0), it would wear the
outside of the tire more, and grip would be less.

Most of the FOT may already be aware of these differences, but some of this
is still new to me.  I learned that the HOTD-R tires use the same compound
as the Hoosier R7s (the Hoosier chart below confirms this).  The Speedster
uses a different compound, but has similar temperature ranges and hardness
(S9).

Thanks again for the response and hope the below helps those that might be
interested in looking at different tires.

Regards,

Mark Cook

*Hoosier Speedster Overview*

The Speedster is a modern DOT-approved racing radial disguised with a
period-correct vintage tread pattern.

• Setup Requirements: Because it is a radial, it demands significantly more
negative camber *(often -2.5 to -3.5 degrees total) *to keep the tread flat
under heavy cornering loads. It also relies on lower cold inflation
pressures compared to bias tires to achieve its optimal hot footprint.

• Performance Profile: It yields high absolute peak cornering speeds and
sharp steering response. However, the limit of adhesion can be more abrupt
than a traditional bias tire.

*Hoosier HOTD-R Overview*

The HOTD-R (Historic Old Timer Design - Radial/Race designation variant)
represents Hoosier's flagship bias-ply evolution for strict vintage rules.

• Setup Requirements: It functions exceptionally well on traditional
vintage suspension setups with modest negative camber *(e.g., -1.5
degrees).* It uses stiffer sidewalls that preserve fender clearance under
load without requiring heavy static lean angles.

• Performance Profile: The HOTD-R allows drivers to lean aggressively on
the tire, sliding the car predictably through corners. It handles heat
cycles gracefully and functions at a broader slip angle, matching the
classic driving style expected in historic motorsport classes.

*Hoosier Speedster Camber Profile*

• Target Front Camber: -2.5° to -3.5° of negative camber is required.

• Target Rear Camber: -1.5° to -2.0° of negative camber.

• Mechanical Necessity: As a radial tire, the sidewall is designed to flex
dynamically under lateral load. Without aggressive negative camber, the
tire will roll onto its outer shoulder, causing rapid outer tread wear, a
severe drop-off in grip, and potential center-rib blistering. Achieving
these specs on vintage suspension often requires modified upper control
arms, slotted pivots, or offset bushings.

*Hoosier HOTD-R Camber Profile*

• Target Front Camber: -1.0° to -1.5° of negative camber is ideal.

• Target Rear Camber: -0.5° to -1.0° of negative camber.

• Mechanical Necessity: The HOTD-R utilizes a stiff bias-ply construction.
The tire carcass is structurally rigid and resists rolling under cornering
force, meaning the tread stays flat relative to the wheel. If you run
excessive negative camber (over -2.0°) on a HOTD-R, you will ride strictly
on the inner edge of the tire in a straight line, overheating the inner
carcass and reducing braking efficiency.

The differences in carcass construction between the Hoosier Speedster and
the Hoosier HOTD-R dictate two entirely distinct driving styles on track.
Driving a radial requires high precision and managing a sharp edge, while
driving a bias-ply style tire requires managing weight transfer and driving
with the throttle through a slide.

1. Slip Angle Management

• Hoosier Speedster: Requires low slip angles. You must keep the car
tracking cleanly along the optimal geometric line. The tire delivers its
peak grip with very little slip (typically 4 to 7 degrees). If you
over-drive the tire and force the car into a slide, the grip drops off
abruptly, causing the car to snap or scrub off significant corner speed.

• Hoosier HOTD-R: Thrives on high slip angles. This tire is designed for
traditional vintage four-wheel drifts. Peak adhesion occurs at a much wider
slip angle (8 to 12+ degrees). The breakaway characteristic is incredibly
progressive, allowing you to deliberately slide the rear end to help rotate
the car without losing momentum or risking a sudden spin.

2. Steering Inputs & Precision

• Hoosier Speedster: Demands smooth, minimal, and precise inputs. Because
the modern radial construction provides a sharp, immediate steering
response, aggressive hand movements will overload the front contact patch.
You must feed the steering in gently and catch slides instantly before they
exceed the tire's narrow peak grip window.

• Hoosier HOTD-R: Requires proactive, deliberate, and busier steering. The
stiff carcass design responds beautifully to aggressive initial turn-in to
set the platform. Once the car is balanced in the corner, you will find
yourself constantly modulating the steering wheel and balancing the car's
attitude using fine adjustments of the throttle.

3. Braking and Corner Transitions

• Hoosier Speedster: Favors straight-line threshold braking. Radials
maximize their longitudinal grip when flat. You want to get the heavy
braking done while the wheels are pointed straight, then transition
smoothly off the brake pedal as you initiate turn-in (trail braking must be
managed carefully to avoid overloading the front outer tire shoulder).

• Hoosier HOTD-R: Excels at aggressive trail braking and pitch management.
Because the tire carcass remains stable under compression, you can carry
the brakes deep into the apex to pin the nose and break the rear traction
loose intentionally. The tire is highly forgiving during rapid weight
transitions, allowing you to manipulate the car's balance mid-corner using
the chassis' natural roll.

On Thu, Oct 8, 2026 at 9:36 AM Mike Harmuth <ofracer at gmail.com> wrote:

> Hi Mark. I've been using the Hoosier TDRs for years on my Spit and all
> groups accept them. This year, I had, what turned out to be a mounting
> problem, with a fresh set of TDRs and I needed tires ASAP after the K Cup
> so I bought a set of Toyo Proxies R888R (full width tread tires). Again,
> these are allowed with every racing group. They have a smaller diameter
> than the TDRs which helped me in the boot at the Glen but not so much on
> the straights. I've sorted out the mounting problems with the TDRs so I
> plan on a back to back comparison next weekend at Thompson to see what
> works best there (slower track, probably the Toyos).
>
> Our racing group, HRG, allows the R7s and similar tires at every event
> except our joint weekend at the Glen with VRG. That's the one VRG event
> (out of 3 last year) where HRG tire rules were not allowed.
>
> mike h
>
> On Tue, Oct 6, 2026 at 12:34 PM Mark Cook <mecook635 at gmail.com> wrote:
>
>> Just following up on my earlier email to see if anyone has thought about
>> the tire rules and my question below.
>>
>> Thanks,
>>
>> Mark Cook
>>
>> On Sun, Oct 4, 2026 at 8:21 AM Mark Cook <mecook635 at gmail.com> wrote:
>>
>>> All,
>>>
>>> So, I it is time to replace my Hoosier TDRs on my TR6.  This TR6 was
>>> previously run in SCCA with Hoosier R7 SM7.5 (Spec Miata).   When I
>>> purchased the TR6 In 2024, then current VDCA/SVRA tire rules did not allow
>>> these tires and I switched to the TDRs.
>>>
>>> In 2026 SVRA and VDCA changed the rules for Group 8/CP to allow
>>> the Hoosier R7/R8, as well as the Toyo Proxes RR.  It appears that VRG and
>>> VSCCA continue to require fully treaded tires in CP/DP classes, like the
>>> Hoosier Speedster and TDR.  Though, VRG is deferring to other organizations
>>> tire rules in joint events (VIR / Summit Point with VDCA as example).
>>>
>>> I think most of you run in VDCA Group 3, but has anyone running in Group
>>> 8 CP/DP changed or considering changing to Hoosier R8s or Toyo Proxes RR?
>>>
>>> Thanks,
>>>
>>> Mark Cook
>>>
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