The Speeder seems pretty slow. Turning with the brakes on is VERY SLOW! I have found it best to just let 'er go. In other words, when circling the AT-ATs or turning to chase TIES, do so at regular or thrust speed--the brakes make it too slow.
I only use the brakes on 4 occasions on this level:
1. To knock out the probe droids in one pass at the beginning.
2. To slow down to get the bonus.
3. & 4. To blast away at the AT-ATs for boosted accuracy before roping them up.
"I am the Alpha and the Omega," says the Lord God, "who is and who was and who is to come, the Almighty." (Rev. 1:8)