Top speeds, laptimes and lot of this site runs off the data published in videos and spreadsheets produced by broughy1322.

Broughy1322 on YouTube
Broughy's Spreadsheets

Broughy spends countless hours testing each and every car so we don't risk wasting our hard ground money without knowing better. If you find his videos useful, please consider becoming a patron.

Broughy1322 on Patreon

If you'd like to know more about Broughy's tests, please visit these links.

How Top Speed Values Are Calculated Accurately

Lap Time Testing Videos Full Description

Top speed information is gathered from data published in videos by SD1ONE.

SD1ONE on YouTube

Some of the information and images come from GTA WIKI.

gta.wikia.com

RockStar Games GTA Newswire

RockStar Social Club

Cutting Coroners GP (PS4)

Handling.meta (forums.gta5-mods.com))

Handling.meta Wiki (gtamods.com))

A History of GTA Online DLCs & GTA 5 Updates