Thursday, December 21, 2023

Brooks Glycerin 21 Multi Tester Review: 9 Comparisons

Article by Renee Krusemark, Peter Stuart, and Jeff Beck

Brooks Glycerin 21 ($160)


Renee: Brooks was generous enough to provide Peter and I samples of the Glycerin Stealthfit 21 during The Running Event. Glycerin is Brooks' most maximal high drop (10mm) trainer and comes in 4 different varieties: two different upper types (Stealth Fit knit and regular) with or without GTS (Go-to-Support) Guide Rails. I tested the non GTS Stealthfit and Peter the regular knit upper.  

The shoe  continues nitrogen-infused DNA LOFT v3 cushioning adding  2mm more stack height and also gets a new RoadTack rubber outsole and an updated flat knit upper. 


Extremely comfortable: Renee, Peter, Jeff

Fairly lightweight for the cushion: Renee, Peter, Jeff

Deluxe plush materials and a very well padded tongue: Peter, Jeff

Improved shape of midsole platform holds the foot better : Jeff

20g drop in weight from last year: Jeff


Slow to turnover: Renee

Toe-box is a little claustrophobic: Peter 

Not the lightest shoe: Peter

No heel pull tab: Jeff

Please find testers run bios at the end of the article after Comparisons.


Sample Weights: men’s regular upper 10.96  oz / 310.9 g (US11) 

women's Stealthfit upper 7.85oz / 222 g (US8)

Full Stack Height: 36mm heel / 26mm forefoot, 10mm drop

Midsole Stack Height:  28mm heel / 18mm forefoot

$160.  Available now.

First Impressions, Fit and Upper

Renee: Brooks labels the Glycerin Stealthfit 21 as having “premium cushioning and a stylish silhouette.” I agree. I wore the shoe during the last day of The Running Event and while traveling back home. I continued to wear it as a all day shoe for the next few days. The shoe is super comfortable in terms of its upper and underfoot feel. This is the first Glycerin I have worn, so I can’t compare it to previous versions. 

The flat knit upper fits my foot well. I have average width feet that are somewhat low volume. Some sock/bootie uppers have too much material for my foot and I have bunching or overlap across the midfoot. Not the case with this bootie sock type upper and the flat knit here. I do wonder if high volume feet might find the toebox shallow, but the knit stretches is meant to be compressing. 

Peter: The Glycerin 21 is a highly cushioned daily trainer. The geometry feels pretty traditional and step in is very comfortable. Overall there’s a lot of shoe, heavily padded ankle collar, heavily padded tongue. 

That said, it’s a comfortable shoe and easy to run in. The toe-box feels a little claustrophobic to me. 

It almost feels like I could size up ½ size and be totally good with it. There’s a little irritation on the outside of my pinky toe, but it doesn’t make the shoe un-runnable for me. 

Initial road-feel is on the firm-side of highly cushioned. It’s an efficient feeling shoe. I agree with Renee that turnover isn’t very quick, but it’s a recovery and easy day shoe for me, so that doesn’t bother me. 

Jeff: I go way back with the Glycerin in reviews and regular use - I've been running in the various Glycerin models for more than a decade (starting with the Glycerin 8!), and the Glycerin 16 was my first review for RoadTrailRun - and the last few models have been a substantial improvement. Last year's Glycerin 20 brought DNA Loft v3 material into the midsole, giving it a little bit of bounce while still solidifying itself as a solid daily trainer/easy day shoe, depending on your preferences. 

Left: Glycerin 20 Right: Glycerin 21

The 21 and 20 colorways, or at least the ones I have, are nearly identical, making it almost hard to tell the two shoes apart, and the similarities run much deeper than the color scheme. We've still got a very breathable mesh upper, solid rubber coverage on the outsole, and a wide and stable platform - even for the non-stability version. 

The fit is a dialed in from last year, and part of that the forefoot platform is just a touch (~3mm) narrower than last year. 

Left: Glycerin 20 Right: Glycerin 21

If you are familiar with last year's review, it was possibly the first time I listed a wide platform as a con, because it was ultimately too wide, and really needed some thick socks to get remotely good foot lockdown. No longer the case with the 21, between a slightly tighter weave mesh and slightly more narrow platform, the fit is much improved this time around. I've got no complaints about the toebox width either, there's enough to be spacious without being ponderous. 

The tighter weave mesh gives the shoe a little more premium feel as well, and last year's shoe didn't feel cheap. Lengthwise I'd stick true-to-size for a roughly thumb's width in front of the toe. Really my only gripe about the upper is the lack of a pull tab on the heel. Not a huge deal, doesn't make the shoe unrunnable by any stretch, but it'd be a nice inclusion.

Midsole & Platform

Renee: The nitrogen-infused DNA LOFT v3 is meant to be super-soft. I didn’t find it overly squishy, just incredibly comfortable. I like it best for daily wear and walking. The turnover is not the fastest despite the shoe being lightweight for all of the cushion it offers. 

The 10mm drop feels more like 8mm, which I found to be a positive when running on hilly gravel. 

Brooks calls the transition “smooth” and “stable.” I agree the shoe is stable, and the transitions are smooth in a comfortable way, but not in a responsive  or quick way. For these reasons the Glycerin 21 works best at slow to easy paces for me. 

Peter: While the DNA LOFT V3 may be “super soft” on its own, I suspect that the fairly thick (by outsole standards) RoadTack outsole serves to firm up the ride pretty well. I find the shoe to be neither too soft nor too firm. It’s a nice mix of protective amount of foam with some stability and a very smooth transition. I agree that it’s an easy-day shoe, but a darn good one. 

Jeff: The second Glycerin to feature DNA Loft v3, this iteration of the versatile midsole isn't all that bouncy or soft. Other versions of the same material have been super bouncy, borderline uncontrollable, while this shoe has a hint of bounce, I'd agree with Peter's assessment that it's not too soft nor too firm. The refined shape of the midsole doesn't make it narrow by any stretch, it just isn't too wide anymore, a nice change of just a few millimeters.


Renee: The outsole is a new RoadTack made with rubber and recycled silica. I like the generous outsole coverage for gravel running. I think it helps with a stable landing given the soft nature of the midsole. The outsole might contribute to why I think the shoe runs on the “slow” side, but it compliments the shoe’s overall purpose and construction. The thickness and generous coverage might make the shoe feel slow to me, but it does help the shoe from “bottoming out” given the soft midsole.

Peter: RoadTack is excellent in wet and slippery conditions. I agree that the significant amount or rubber firms the foam up nicely. Grip is excellent and it would seem that the durability will be excellent. 


Jeff: Last year's shoe had a lot more rubber coverage, one large slab covered most of the shoe while a second one took care of the lateral heel, while this year's model is much more segmented - and the 21 is also much thicker as both Renee and Peter brought up. 

I'd imagine the thick rubber definitely plays into the shoe stability. It also has solid all season grip, and thus far durability is top notch. If this is Brooks' new road shoe rubber, it's a nice improvement, almost in the same league as Puma's PumaGrip branded rubber.

Ride, Conclusions and Recommendations

Renee: The Glycerin Steathfit 21 is a comfortable shoe that I could, and did, wear all day. At less than 8 ounces in my women’s size 8, it is relatively lightweight given its slotting in the cushioned/plush trainer category.  

For my preferences and gait I do feel the shoe runs slow and it works best and only for me for truly easy to slow runs. I enjoyed it the most running on hilly gravel and as a casual walking/daily shoe. 

The ride is stable and protective, and I thought it seemed more like an 8mm drop than 10mm when running on uneven and clumped gravel. While I probably won’t run in the shoe after review, I will continue to wear it casually. 

Renee’s score 9.0/10 (-.50 slow transition, -.50 best for slow/easy miles only)



The “classic fit” Glycerin 21 is a fairly traditional feeling daily trainer. Even though it has some high tech midsole foam, it feels like a good, solid old-school running shoe. I’d consider sizing up ½ size due to a somewhat confining toe-box. 

The ride is easy, comfortable and not punishing. For me, the Glycerin is a good recovery or easy day shoe. It doesn’t inspire me to run fast, but that’s not really what it’s here for. I like the 10mm drop too!  

If you’re in the market for a pretty traditional feeling shoe with a good new foam that should last forever, the Glycerin 21 is a solid choice. 

Peter’s Score 9.0 A solid if not wildly inspiring shoe. If the sizing/toebox were a little more generous it would be a no-brainer for me noting it is also available in 2E wide

😊😊😊😊 (I’d go  with 3.5 smiles if I knew how to do that! ). 

Jeff: Another year, another Glycerin model that works well, if not necessarily the most exciting shoe on the market. It's a great shoe for day-in, day-out training if you prefer more cushioning, or just the easier days if you aren't as much a fan of midsole stack as I am. 

Don't be convinced that DNA Loft v3 means soft and bouncy, like it does in the Aurora-BL, the thick rubber outsole does a great job taming the ride. 

The platform shrank just a bit in width, but it became even more stable by dialing in the fit, while the mesh got an even tighter weave and feels like a nice premium upgrade from last year, while also acting like a functional upgrade. 

Fans of plush and comfortable shoes, that aren't going to break the scale, will appreciate the changes they made to the 21.

Jeff's Score 9.3/10

Ride (50%): 9 Fit(30%): 10 Value(15%): 9 Style(5%): 9

9 Comparisons

Index to all RTR reviews: HERE

Brooks Glycerin 20 (RTR Review)

Jeff: The 20 was a solid update bringing DNA Loft v3 to the Glycerin line, but the 21 improves even more with a tighter weave mesh that feels more quality and holds the foot better, a slightly better sculpted midsole platform that doesn't feel ponderous, and an improved outsole with thicker rubber. The dialed in shape (along with less outsole coverage)  is likely the biggest reason the shoe dropped nearly 20 grams in my US10.5. Regardless, a solid well-cushioned shoe got even better.

Brooks Ghost Max (RTR Review)

Jeff: Brooks' biggest daily trainer is a generation behind the Glycerin in midsole, it has the DNA Loft v2, which isn't nearly as soft or responsive as the v3, even the tamed down execution of it in the Glycerin 21. While all three of us felt like the Glycerin 21 was a relatively straightforward daily trainer, when up against the Ghost Max it feels more like a carbon plated racer. The Glycerin upper also feels more premium and it tips the scales about a half ounce lighter. The Ghost Max is a solid super-cushioned trainer, but the Glycerin 21 effectively outclasses it in the same category.

ASICS GEL-Nimbus 26 (RTR Review)

Jeff: ASICS answer to the Glycerin got a big upgrade with last year's Nimbus 25, and the 26 is a nice refinement and subtle upgrade - sound familiar? The Glycerin and Nimbus line up very well with each other, with the Nimbus heavier, more plush, and noticeably softer, while the Glycerin is lighter and a little more responsive. Both great daily trainers, just a matter of preference.

New Balance 1080v13 (RTR Review)

Jeff: New Balance's big daily trainer follows the same formula as the Glycerin. It's a little softer than the Glycerin, while also weighing just a little bit less, and has a slightly lower stack height. Its platform isn't quite as wide, and it isn't quite as stable as the Glycerin, but you won't confuse it with the Novablast 4.

Saucony Triumph 21 (RTR Review)

Jeff: Saucony's iteration of the well-cushioned daily trainer archetype, the Triumph 21 is a few grams lighter than the Glycerin, with a higher stack, and is slightly firmer - especially under the heel. The Triumph has a knit upper that holds the foot even better than the Glycerin, and is a little more responsive, I'd slot in in between the Novablast 4 and Glycerin 21.

Adidas Supernova Rise (RTR Review)

Peter: Both of these are old-school daily trainers, full of new-school materials. The Supernova Rise turns over a little faster. Both provide a really smooth ride and can go all-day. 


On Cloudeclipse (RTR Review)

Peter: The On Cloudeclipse is my favorite daily trainer of the year. Where the ride of the Glycerin is smooth, the On feels smoother. Where the ride of the Glycerin is easy, the ride of the ON is easier. They’re in a similar category, but the ON is a much better daily trainer for me. The upper fits me better and the ride is more fun.

Jeff: I'd agree with Peter again, though I'd even say it also adds a nice bounce to it too. ON really outdid themselves with the Cloudeclipse.

Asics Novablast 4 (RTR Review) 

Peter: The Asics NOVABLAST 4 is a really fun new-school trainer. It feels and is higher up and has a little more pizazz than the Glycerin, while the Glycerin feels a little more stable and smooth on the road. 

Jeff: Completely agree with Peter. While it's also a well cushioned daily trainer , it's a very different execution favoring bouncy and responsive instead of soft and smooth. Both do their thing well, just a matter of how you prefer your daily trainer executed.

Saucony Ride 17 (RTR Review)

Renee: The Ride 17 is similar in that it is a high stack shoe. Despite being almost an ounce heavier in my size, the Ride 17 is a faster shoe with a more dynamic ride and midsole. For training, I prefer the Ride 17. For all-day comfort, and a softer midsole, the Glycerin 21 is better. Sizing is comparable. 

The Brooks Glycerin 21 is available now at our partners below

Men's & Women's SHOP HERE

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Tester Profiles

Renee is a former U.S.Marine journalist, which is when her enjoyment of running and writing started. She isn’t that awesome of a runner, but she tries really hard. Most of her weekly 50-60 miles take place on rural country roads in Nebraska, meaning mud, gravel, dirt, hills, and the occasional field. She has PR’s of 1:30:59 for the half marathon and 3:26:45 for the marathon.

Peter lives in Austin, Texas and has been a sub 3 hour marathoner as well as a 1:21 half marathoner in recent years.

Jeff Beck is the token slow runner of the RTR lineup, and as such his viewpoints on shoe and gear can differ from those who routinely finish marathons in three hours or less. Jeff runs 20 miles per week on roads and trails around Denver, CO (and sometimes on the treadmill when the weather gets too much for a Phoenix native). Jeff only got into running in his 30s, as a result his career PR's are 4:07 for the marathon and 5K at 23:39. Jeff has finished several ultra marathons, from 50K up to 50 miles, and is still debating if he wants to go down that road again.

Samples were provided at no charge for review purposes. RoadTrail Run has affiliate partnerships and may earn commission on products purchased via shopping links in this article. These partnerships do not influence our editorial content. The opinions herein are entirely the authors'.

Comments and Questions Welcome Below! Please let us know mileage, paces, race distances, and current preferred shoes

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Anonymous said...

"Full stack" is considered midsole, outsole, and the insole. Correct?

Sam Winebaum said...

Hi Anonymous, Full Stack includes outsole, midsole, board and sockliner
Sam, Editor

Anonymous said...

What shoe is this again? Brooks correct? I’m so sorry 😢 I’ve been feeling under the weather.