Dr. Wack "P21S" P21S "POWER GEL" Wheel Cleaner 750ml

The P21S wheel cleaner swaps the brush for three minutes of dwell time

What is the P21S POWER GEL wheel cleaner? An acid-free cleaning gel from Dr. Wack that chemically binds iron-bearing brake dust and turns red-violet while it does it. Approved for painted, anodised, mirror-polished and chrome wheels. Not a paint cleaner, not a sealant, and nothing for a warm wheel straight off a drive.

P21S POWER GEL wheel cleaner is an acid-free cleaning gel from Dr. Wack for painted, anodised, mirror-polished and chrome wheels in alloy and steel. Its active ingredient, sodium mercaptoacetate, thioglycolate in the trade, locks the iron compounds out of brake dust into a water-soluble cage. Day-to-day that means the black deposit runs off with the rinse water instead of spreading across the spokes under a brush.

The gel consistency is not thickener for show. A thin cleaner slides down a vertical wheel face in seconds and takes its reaction time with it. The POWER GEL stays where the spray puts it: on the hub, down in the spoke roots, on the rim flange. It is that cling time that turns three minutes of dwell into three minutes of contact.

• Three minutes is enough, below ten degrees it is not. Dr. Wack gives 3 to 5 minutes of dwell time. If the temperature drops below 10 °C or the wheel is heavily caked, the manufacturer itself stretches that to at least 10 minutes. Work in February on summer timing and you rinse the reaction away before it has finished.
• The colour is a readout, not a bonus effect. The gel goes onto the wheel pink, so you see straight away every spot the spray missed. Wherever iron-bearing dust is sitting, the colour pulls through to a dark red-violet. After 3 minutes you know whether a second pass is needed before you even touch the hose.
• Four container sizes, one formula. 750 millilitres with a trigger gun, 2 and 5 litres as canisters, 25 litres as a refill station. Between the small bottle and the big containers the price per litre drops by around a third without a thing changing in the mix. What you lose is the spray head.

Detailing1's tip from the shop: We get a lot of questions about a whitish film left on the wheel after rinsing. That is usually not residue from the gel but limescale out of the rinse water, drying onto the warm wheel while you are standing at the next one. So work through wheel by wheel: spray, wait 3 to 5 minutes, rinse, wipe down with the drying towel, and only then the next one. Spraying all four at once looks like a time saver and costs you the second pass.

Below ten degrees the POWER GEL needs ten minutes

Spray onto the cold, dry wheel, wait 3 to 5 minutes, rinse off with a strong jet of water. Below ten degrees or with heavy brake dust, Dr. Wack stretches that to at least 10 minutes.

Cold means: a quarter of an hour after the last hard braking, and not in direct sun. A wheel that has just come off the motorway still carries the residual heat of the brake disc in its face. The gel dries on there before the reaction is through, and afterwards you are scrubbing dried cleaner instead of brake dust.

Dry is the second half of the condition. Hose the wheel down first and you dilute the gel at the moment you lay it on, weakening exactly the property you bought it for. Spray from the bottom up so gel running down always meets untreated surface, and take in the hub, the spoke roots and the edge against the tyre on purpose. Loose grit on the wheel is no problem, it comes off with it.

On quantity: generous, but not twice over. The gel works through contact, not through layer thickness, and a second coat onto a first one that is still wet buys you nothing but consumption. In the MOTORRAD hands-on test it was exactly this cling that explained the low usage: whatever stays up there needs no topping up. On a deep-dish wheel with narrow spokes a short second burst into the spoke roots still pays, because that is where the least gel arrives.

Rinsing then runs top down, until no pink haze comes off any more. Wheels come before the paint in the wash order, otherwise you carry the dissolved iron dust over the doors afterwards. If a residue is left after rinsing, a second short pass is the right answer, not a longer dwell. Users agree across the board that an hour of contact gets you no more than ten minutes does.

The colour change flags the brake dust, the dwell time is what dissolved it

The colour change is an indicator, not a cleaning step. It tells you where iron-bearing dust is sitting. The work was done by the minutes before it, not by the colour.

That is more than splitting hairs, because two wrong expectations hang off it. First: a wheel where almost nothing changes colour is no proof of a weak product, it is usually a wheel with little iron on it. Second: a deep violet wheel is not clean yet, it is marked. It only gets clean once the bound dust is in the rinse water.

Two hard limits go with that. The POWER GEL cleans, it does not protect. After rinsing, the wheel surface is bare and open, and the next lot of brake dust keys in just as fast. If you want to stretch the cleaning intervals, you lay a wheel sealant on afterwards, otherwise you start from zero every two weeks. And on wheels that have seen a whole winter season through, one pass is rarely enough. Two goes of three minutes beat one of twenty.

On mirror-polished and anodised surfaces Dr. Wack recommends a compatibility test on a hidden spot before the first use. And the smell: thioglycolate compounds have a sharp odour, the formula now carries fragrance on top, and that does not make it odour-free. In an enclosed space you notice it clearly, outdoors barely at all.

That leaves the line on the label. "Repeat test winner" holds for the range, not automatically for this bottle: in the AUTO BILD comparison in issue 22/2021 with eleven wheel cleaners, it was the P21S HIGH END wheel cleaner that stood top with 183 out of 200 points, not the POWER GEL. That is not a mark against it, it is a question of who entered: the POWER GEL was not in that field.

The test figure you can pin on this bottle comes from the MOTORRAD hands-on test, which landed on 4 out of 5 stars. It praised the cling and the material compatibility on paint and chrome, and criticised a spray head that worked itself loose in use. If you want the formula that went through the comparison test, take the HIGH END. If you need gel cling, a colour readout and big containers, you are in the right place here.

Dr. Wack builds the POWER GEL as a refill system, not as a one-way bottle

The POWER GEL comes in four container sizes from 750 millilitres to 25 litres. The big canisters carry no spray head, they are meant for refilling and not for direct use.

For one car that comes round every two to three weeks, the 750 millilitre bottle with the trigger gun is the right size. It is ready to go, it stands on the shelf without decanting, and it is the only version Dr. Wack ships with a trigger gun. From the second car in the household, with winter and summer wheels running in parallel, or with a driving style that makes the dust to match, the maths tips towards the 2 or 5 litre canister.

The 25 litre refill station is no clearance lot from a different batch. It is the same mix that runs into the 750 millilitre bottle in Baar-Ebenhausen, just without a trigger gun in the box. Dr. Wack has carried the product since 1976, and the spread of container sizes follows from that: hold a formula stable for half a century and you can fill it into the same bottle and the same drum for everyone from the home driveway to the tyre fitter.

Who the product is not built for belongs in the picture just as much. If you wash your car twice a year and let the wheels run in between, this is no one-shot rescue for baked-on deposits, it is a product that plays its advantage with regular use. On a painted winter wheel that has taken a season of chippings and road grit, the first pass takes the brake dust off and leaves the rest standing; only the second one makes it even.

And if you are only after shine, a wheel wax serves you better than a cleaner. The POWER GEL takes away, it lays nothing on.

One detail no manufacturer text mentions and that regularly causes grief with the big container: the 25 litre refill station comes without a tap. Order the drum with no tap and no pressure sprayer in the house and you are standing there with 27 kilos of gel you cannot get at. Two minutes of thought before you order save you a week of waiting with a full canister and an empty spray bottle.

Using the P21S "POWER GEL" wheel cleaner

From cooling down to a dry wheel

Wait at least a quarter of an hour after driving before you spray. The wheel has to be cold and dry: cold, because the gel dries on a warm wheel face before the reaction is through, and dry, because water dilutes the gel at the moment you lay it on. You do not work in direct sun at all, you put the car in the shade first.

Open the spray head and mist the wheel generously from the bottom up. Take in the hub, the spoke roots and the edge against the tyre on purpose, because that is where most of the dust sits and where the water jet reaches worst when you rinse. The gel stays put on the vertical face, so you do not need to top it up.

Let it dwell 3 to 5 minutes. At temperatures below 10 °C or on heavily caked wheels Dr. Wack calls for at least 10 minutes. In that time the pink gel goes red-violet wherever iron-bearing dust is sitting. That colour change is the readout, not the result.

Rinse off with a strong jet of water, top down, until no pink haze runs off, and wipe the wheel straight down with a drying towel. Work through wheel by wheel, not all four in parallel. If a residue is still visible, a second short pass follows, not a longer dwell time.

From the 2, 5 or 25 litre container you decant into a spray bottle or into the P21S pressure sprayer. The big containers come with no spray head, and the 25 litre refill station with no tap either.

Notes: The POWER GEL dissolves iron-bearing brake dust, it is no substitute for a sealant — after rinsing the wheel is bare and picks up the next lot of dust just as fast. On mirror-polished and anodised surfaces, check compatibility on a hidden spot first. The gel is approved for tyre pressure monitoring systems, which acid-based alternatives are not necessarily. The smell is noticeable despite the fragrance, so ventilate in enclosed spaces. Store frost-free and closed, away from food, out of the reach of children.