The Carpet season is almost upon us, and with the hope for more mini's on the rug this year, comes the need for proper setup info.
Enter: Mark Brown and his M-chassis expertise. This write-up is from 2010, but still relevant now.
Have a look, and take notes. You just might have a chance at staying on the same lap as Mark this winter.
-Jesse
M_
Tamiya Mini Carpet Techniques
1
December 2010
Introduction
This short document summarizes
techniques for making an M03 or M05 Tamiya Mini perform well on carpet.
Setup Items
Here are the aspects of setup that differ significantly
between an outdoor and an indoor setup, in approximate priority order.
Tires and Inserts
Tires and inserts are the most
important part of setting up your Mini. It can be a lot of work to achieve the
‘perfect’ setup, but getting close is usually easy.
Fronts
Carpet generates a lot of side grip.
Running a really grippy front tire, like a Type A slick, on high-grip carpet will
give you too much side traction. Your car will traction roll.
You can prevent traction rolling by
applying super glue to the outer edge of the front tire, as explained in more
detail below. But if you use this technique with slicks, the most likely result
is a car that spends a lot of time on two wheels in the turns! That’s not the
quickest way around the track.
The usual front tire on high-grip carpet
is the M-Grip radial tire (TAM 50684). It gives more grip than the kit tire,
but less than the S-Grip radial (TAM 53254) and a lot less than the Type A slick (TAM 53340). On a carpet track with
less grip you can go faster running a grippier front tire.
The insert for an M-Grip or S-Grip
on the front should be something that does not alter the flat contact patch of
the tire. A harder tire like the M-Grip does not need a highly supportive
insert to work; the kit foam insert (TAM 53204) can work fine. S-Grips seem to
like a small air gap between the tire and insert; this results in a tire that
is slightly concave when unloaded, but gives a larger contact patch when
loaded. If you have one of the old 55D shaped inserts (TAM 53223), use it;
otherwise cut and glue a Tamiya TC insert to make the correct diameter, then
fill the gap between the wheel and this insert with a Tamiya foam insert, cut
as needed.
Rears
Rears are all about balancing the
car, given your car’s setup and especially the fronts.
Most people seem to like Type A
slicks in the rear. Most of the time I don’t; they usually nail down the rear of
my car too much, and when I get the rear free enough it becomes inconsistent
and does not carry good speed.
I generally end up with S-Grips on
the rear. No glue on them, unlike the fronts. And a fuller insert than in
front; I want something that makes the contact patch a little bit convex, so
the grooves in the tire will generate side-bite. Double-stuffing with a
cut/glued TC insert on the inside and soft Tamiya foam (TAM 50686) on the
outside is one combination that works for me.
Glue
To glue the outside edges of your front
tires, first clean the area you’ll be gluing with isopropyl alcohol or motor
spray. Use a good quality glue like Losi or ProLine that accepts a micro tube.
Cut about 15mm of tube and insert it partway into the opening of the glue
bottle. The micro tube will let you put the glue exactly where you want it,
which is: from the groove on the sidewall of the tire, up over the edge, and
covering the outer ½ of the outermost tread block. I’ll apply glue to about 1/6th
of the tire, then take a toothpick and run it over the glue to be sure it
covers the entire area and gets down into the cracks. If I don’t have the
micro-tube, I’ll drip glue onto the end of the toothpick and use the toothpick
to apply the glue to the tire. This is slow but it ensures that I don’t put
glue where it doesn’t belong.
Be sure to let the glue dry
completely before running the tires!
Keep an eye on the glue because it
does wear down. You’ll probably need to renew it every 3-4 race days.
Sauce
I rarely sauce the full tire on
high-traction carpet. On the front I might sauce the inner 2/5 of the tire (two
ribs out of five), while on the rear I’m saucing the inner 3/5. Small adjustments
in sauce are a great way to achieve the exact handling balance you are looking
for.
I like to clean rubber tires with
WD-40 between runs. However I only clean the area that I’m saucing that day. If
I clean the whole tire then the whole tire will pick up traction with each run,
and that can lead to disaster, especially if the front picks up more than the
rear. If I decide I want to reduce the amount of tire I’m saucing during the
day, I’ll clean the “abandoned” area of the tire with motor spray to reduce its
grip. When the race day is done I clean the entire tire with WD-40.
Diff
On carpet you want to run a diff
with a lot of internal resistance; this is called a “closed” diff. With an
“open” diff, when your Mini is leaned into a turn and unweights the inside
wheel, you’ll lose drive from the outside wheel and your car will push. I see a
lot of cars on the track that suffer from this.
There is a trade-off: The more closed
the diff, the less off-power steering you will have. But on a typical track the
Mini spends a lot more time turning on-power than off-power.
I never run a fully locked diff. With
a locked diff, if you crash the car and one of the drive wheels stops suddenly,
you are likely to break a tooth off of one of the internal gears: game over. It
only takes a little diff action to eliminate this problem.
Here’s a way to build the Mini’s
gear diff that works well for me on carpet:
- Get two
containers of Tamiya Anti-Wear grease (TAM 53439). Also get two extra
Tamiya 9mm washers (TAM 2300010), in addition to the two that come with
the gear diff in your Mini kit.
- Glue the
two 9mm washers that come with the diff to inside of the plastic case of
the diff, where the washers go when the diff is assembled. One washer is
glued inside the drive gear portion of the diff case, the other inside the
screw-on side portion of the diff case. Let the glue dry to full strength
before assembling the diff.
- Now
assemble the diff as usual, using the two extra Tamiya 9mm washers to
replace the two washers your glued to the diff case, resulting in two
washers on each side (one glued and one free). As you assemble the diff, cover
all internal parts with Tamiya Anti-Wear grease and fill all cavities with
Tamiya Anti-Wear grease. The diff will hold more than two full containers
of grease, but two gets close enough.
- With the
diff fully assembled and the case screwed together, seal the seam in the
case using a small amount of Shoe-Goo. Let the goo dry fully before
running the diff.
Here’s what assembling the diff
this way accomplishes:
·
Gluing the washers to the inside of the diff
case prevents the washers from rubbing on the diff case and wearing through it.
This makes the diff last longer and work more consistently.
·
Running two washers on each side of the diff,
instead of one, helps reduce grease leakage through the “thrust bearings” of
the diff, and also adds friction to the diff action.
·
Filling the diff case with grease prevents the
grease from being thrown off the gears, and thereby maintains a high level of
friction in the diff action.
·
Sealing the diff case seam with Shoe-Goo
eliminates grease leakage through this seam.
The result of building the diff
this way will be a diff that is almost locked at first. The first couple of
times you run the car the diff will open up a little as the grease migrates
around inside the case, then it should stabilize and stay consistent without
any maintenance.
I’ve tried filling Mini diffs with
heavy silicone fluid (500K cSt) as used in the diffs of gas buggies. The
silicone fluid gives a nice heavy diff action, but it leaks more than grease,
so I prefer grease.
Ride Height (Camber)
Ride height is a very important
adjustment on the M03, because you adjust camber with ride height. Lower ride
height gives more camber and vice-versa. Adjustable camber links are now
available for the rear of the M03, and for both ends of the M05, but still I
adjust camber at both ends with ride height.
I like my M03 to have lots of
steering so I run the front end fairly low and the rear end fairly high. You
should experiment with ride height and see how the handling of your car
changes.
Beware running the car too low in
the rear. On the M03 with the plastic rear uprights, running low in the rear
can take away too much up-travel and make the rear end break away suddenly in
the turns. On the M05 with the receiver and ESC mounted on shelves outside the
main chassis, running low in the rear can cause the shelves to drag on the
track, taking away grip and possibly causing the rear of the car to hop. You
should be able to make the rear end of your car stable without running below
5mm in the rear. Perhaps you are running the wrong rear tires?
Shock Length
Shock length controls droop on the
Mini. Running less droop makes the car more responsive and less prone to
traction-roll. Running more droop makes the car drive better over bumps and
generally more predictable.
On high-grip carpet you want the
shocks fairly short. On a lower-grip surface you lengthen the shocks.
TRF TC shocks are long for a Mini
and will prevent you from running really small amounts of droop. Even so it is
possible to have a good setup with these longer shocks. The shorter TRF M-Chassis
shocks (TAM 54000) were not available back in 2003 when I built my M03, and so
I still run TRF TC shocks. My car’s shock length on high-grip carpet is about
54.25 mm end-to-end.
Springs
I run stiffer springs on carpet than I run outdoors. Springs
are not a major tuning point on the Mini but going stiffer in high-traction
conditions generally seems to work better, even if it does accentuate the car’s
tendency to traction-roll.
Sample Setups
M03
This is my base carpet setup.
Front tire: 60D Super Grip Radial
(53254). Half of outer tread block covered with CA.
Front insert: 55D shaped insert (53223)
Rear tire: 60D Super Grip Radial (53254)
Rear insert: Inner: hard TC insert (53435), cut/glued to fit Mini wheel. Outer:
soft sponge (50686)
Front ride height: 6mm (measured at
front of chassis)
Rear ride height: 6.5mm (measured at rear of chassis)
Front toe: 0.5 degrees out
Rear toe: 2 degrees in (53345)
Front shock: TRF TC damper (49198)
with 3-hole piston, 60wt Associated oil. Length 54.25mm.
Front spring: blue (53632)
Rear shock: Same as front except 40wt Associated oil
Rear spring: yellow (63631)
Wheelbase: Long (BMW Mini Cooper)
Diff: gear diff filled with AW
grease (53439)
M05
Troy Crabtree posted this setup on rctech. He ran it
successfully at Hangar 30 in Seattle.
Front tire: 60D M-Grip Radial (50684)
Front insert: 55D shaped insert (53223)
Rear tire: 60D Super Grip Radial (53254)
Rear insert: Inner: hard sponge (53255)
Front ride height: 4.5mm (to
achieve camber specified below)
Rear ride height: 5mm (to achieve camber specified below)
Front camber link: upper hole (2
degrees camber, fixed link)
Rear camber link: lower hole, (2 degrees camber, adjustable link)
Front toe: 2-3 degrees out. Outboard steering rod end in forward hole of
knuckle, shimmed to make steering rods near-level at ride height.
Rear toe: not specified; probably 1.5 degrees
Front shock: TRF M-Chassis damper (54000)
with 2-hole piston, 40wt oil, no foam above the bladder, one o-ring under the
piston to shorten the shock length.
Front spring: white (53633)
Rear shock: Same as front.
Rear spring: yellow (63631)
Wheelbase: Mid (Suzuki Swift)
Diff: gear diff filled with AW
grease (53439)
Conclusion
None of the techniques described
here is especially difficult, so give them all a try and you’ll probably end up
with a Mini that works really well on carpet. Have fun!
Revision history
1 December 2010. Initial version.
