[MrFlippant]

It's not purely a function of length, but also one of thickness.

For example, which may apply to your case, the Carrera guides are very long, but also very thick. BRM sells replacement blades, part number S-126, which are similar in length to the original, but quite a bit thinner, closer to the thickness of a Scalextric guide. These replacements will navigate the inside slot of a Scalextric R1 turn with ease, and no additional modifications needed.

Whenever we run Carrera cars on Sport track, we replace the original removable guide blade with the BRM product.