I've been using P21 for over 15 years and it's the best wheel cleaner I've used to date that does not damage wheels. There may be other brands or flavors that work better but I haven't found any yet even though I have tried Griots, OE BMW and some others.
When Phil at Detailer's Domain posted up some pics of the Sonax brand wheel cleaner in action last week I was impressed and decided to do a comparison for my on edification. My results are my results and your's could vary for any number of reasons including the brake pad material and other crud that gets on your wheels.
Disclaimer: I have no association with any of the products tested or businesses mentioned in this test. I purchased the Sonax and P21 just like any consumer would do.
We start with two very dirty wheels that have baked on brake dust that have been sitting for at least 4 months. Even though these wheels were cleaned on the inside last Summer, a lot of the baked on brake dust would not come off even with a lot of P21 and other cleaners and a lot of brushing with a nylon bristle parts washing brush. Thus as a reference point some of the brake dust has been on these wheels for close to a year.
For all of these photos the Sonax wheel cleaner is used on the left and the P21 cleaner on the right. The P21 is the spray, not the gel. The Sonax is kind of a light gel or heavy foam consistency.
Both wheels were placed in the shade and sprayed with a liberal coat of wheel cleaner and allowed to sit for about 7 minutes.
Because these wheels were so filthy and the brake dust was caked on there was no point in just hosing them off as this crude was going to require some heavy elbow grease to get the worst of the grime off. For normal brake dust on the outside of the wheel a light wipe or brushing should be all that is necessary based on past experience.
This is a close-up to show how really bad the crud was on the wheels.
After considerable brushing and a good rinse we have the two wheels side by side for comparison.
The wheel on the left with the Sonax cleaner has considerably less crude left than the wheel on the right cleaned with the P21. Equal brushing effort was used as best as possible. The spoke area is where it's easiest to see the left over crud.
This is the Sonax wheel up close.
This is the P21 wheel up close.
After more cleaner and brushing the wheels started to look close to what I wanted - clean.
The only thing left on the painted surfaces now is some small tar spots to be removed. I like this look much better but it did require considerable work - as you would expect of baked on brake dust.
So here are my conclusions based on my experience with the Sonax and P21 wheel cleaners:
1. The Sonax definitely cleaned the heavy baked on brake dust best
2. For light brake dust either cleaner will probably work fine
3. The Sonax has a strong acrid odor compared to the sweet P21 odor -
Always use these types of cleaners outside with good ventilator for safety reasons
4. The Sonax removed baked on brake dust that the P21 would not remove regardless of how much I scrubbed
5. I did not detect any dulling of the clearcoat with either cleaner -
YMMV as there are many different wheel finishes
6. The Sonax is more expensive based on bottle size but when you need the best cleaning the Sonax is better than the P21 in my limited testing
7. When my current supply of P21 is exhausted I will switch to 100% Sonax wheel cleaner as it removes all the brake dust in my experience which is important on spoked wheels
Keep in mind that your experience may be different than mine. I still like P21 and think it's fine for lighter brake dust. For the heavy stuff or with certain brake pad compounds the Sonax looks to be better at removing the crud in my experience. It may also be easier to remove the heavy crud with the Sonax and a power washer. I didn't test that aspect. I have done that in the past with the P21 and it still did not remove the baked on crud.
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