I just ran in this Puma carbon plate racer that breaks all the rules — and it's one of the strangest shoes I've ever tried

The best carbon plate running shoes now have to abide by a set of rules set by World Athletics, which were put in place in response to world records tumbling since the introduction of the original Nike Vaporfly 4% in 2017.

These rules include a limit of 40mm for the midsole stack height of the shoe and a maximum of one carbon plate in the midsole. These are the two main constraints that Puma has deliberately flouted with the Puma Fast-RB Nitro Elite LD, with the aim of seeing exactly what could be achieved in a shoe if you ignored the rules.

The result is a monster of a running shoe that stands 58mm tall at the heel and 46mm tall at the forefoot, with three carbon plates crammed into the midsole as well to add more propulsion to the ride. The LD version of the shoe has laces, in contrast to the original Puma Fast-RB Nitro Elite, which had a laceless upper.

Even other rule-breaking shoes like the Adidas Prime X2 Strung have very tame designs compared to the Puma Fast-RB Nitro Elite LD, so how does it actually feel to run in such a radical shoe? I took it to the track to find out.

Puma Fast-RB Nitro Elite LD: price and availability

The Puma Fast-RB Nitro Elite LD launched in January 2025 and only 1,000 pairs were available to buy at that time. It costs $350 in the U.S. and £300 in the U.K., making it more expensive than most legal carbon plate racing shoes.

The ride is unbelievably bouncy at all paces

With three chunks of Puma’s springy Nitro Elite foam in the midsole, plus three carbon plates, you expect a lot of spring from the midsole of the Fast-RB and that’s exactly what you get when running at easy or faster paces.

I did a 5 x 800m session in the shoe, running the reps in around 2:40 with 200m of recovery done in around 50 seconds, and I ended up running 5K in 17:17 during the workout. I landed on the section of foam at the heel that then pushes you onto the three plates under the forefoot, which created a rockered, highly bouncy and enjoyable ride.

It’s more stable at speed than I expected

When I tested the Fast-RB laceless shoe I did worry about its stability around corners during my run, which I did at a mostly easy pace. Stability is still a worry with the laced version of the shoe on corners, but when I was running at faster speeds it did seem quite controlled for such a high-stack shoe.

The wide base under the forefoot certainly helps with this, as does the two-pronged heel design that helps to almost create a tripod with the forefoot that makes the shoe more stable than it has any right to be. The reliable traction from the PumaGrip outsole also helps to create a more secure feeling underfoot.

The laces are an improvement

I didn’t experience any heel slip or other major problems with the laceless Fast-RB but having laces means you can get a more secure lockdown fit with the shoe, and ensure you have no lateral movement of your foot, which does help to make the ride feel more stable.

It’s a heavy shoe

All the tech in the midsole of the Puma Fast-RB along with its high stack height means that its a very heavy shoe, weighing 12.8oz in my US men’s size 10 at a time when most of my carbon racing shoes weigh around 7-7.5oz in the same size.

This weight is mainly positioned in the forefoot and is very noticeable on the run, and despite being bouncy the shoe doesn’t feel that fast because of the hefty design. It might break the rules, but even if it was allowed in a race, the Fast-RB would be unlikely to break any records.

I’d rather race in Puma’s other shoes

I’m not an elite runner so I could race in the Fast-RB Nitro Elite LD without much fear of being disqualified, but it wouldn’t be the shoe I’d pick from Puma’s range if I was planning to try and run a PR at any distance, mostly because of its weight.

The Puma Deviate Nitro Elite 3 is an outstanding racing shoe that weighs 7.5oz and costs $230 (and is actually available), and would certainly be my pick ahead of the Fast-RB on race day. It might not be as bouncy as the Fast-RB, but it’s lighter and more responsive.

Verdict

The Puma Fast-RB is fun to run in and I'm all for brands experimenting with shoes like this. It will also be interesting to see if the tech and design features of the shoe start to trickle down into Puma's legal racing shoes, which have already been improving year on year.

For now, however, the high price of the Fast-RB and the limited amount of pairs that have been made available mean that it's more a collector's item than a shoe I'd recommend to lots of runners.

More from Tom's Guide

• The best carbon plate running shoes 2024
• I ran 40 miles in the Puma Deviate Nitro Elite 3 carbon racing shoe — here’s my verdict
• I raced 10K in the Nike Vaporfly 4% to see how the original carbon shoe compares to today’s racers — here’s what I learned