Best air bags or Timbren for lifted 2017 Toyota 4Runner rear coils  

Question:

Expert Reply:

Hi Paul, great question!

For your 2017 4Runner for an in-coil kit I recommend the Firestone Coil-Rite part # F4135. The Firestone kit is a solid option to help level things out and reduce sag. With your 3 inch lift though, I want to make sure we match it up properly before calling it a guaranteed fit. These kits are designed to install inside factory-style rear coil springs, so if your lift is using the original coils or coils that are very close to stock size, then you’re typically in good shape and they’ll work well.

Where I want to be careful is that not all lifts are done the same way. Some use spacers with the factory springs, while others use taller aftermarket springs that can change how much the suspension extends. Since the air bag sits inside that spring, if the spring is longer or allows more droop, it can stretch the bag more than intended. That’s why I’d want to confirm what rear coil springs you have before giving you a hard yes, just to make sure you don’t run into any issues down the road.

If it turns out you’ve got longer travel springs, a rear bump stop style upgrade like Timbren Rear Suspension Enhancement system part # TTORSEQ and spacer part # A25723-90AH00 can sometimes be a better and more reliable option for support instead of air bags.

With Timbren, the goal is to have the rubber spring sit close to the axle under load without riding on it all the time when unloaded. To see which spacer you would need, you would measure from the bottom of the frame at the bump stop location down to the axle. You’re aiming for about a 1 inch gap when unloaded. If you measure, for example, a 3 inch gap, you would want to add about 2 inches of spacers to bring it closer to that 1 inch working range so it performs the way it should.

If you’re not sure what’s back there, a quick photo or the brand of your lift kit will usually tell us everything we need to know.

What do you usually carry in the back of your 4Runner, camp gear, bikes, or more work-related stuff?

expert reply by: Heather A

0

Zane

4/23/2026

I did the Firestone airbags for a 2017 TRD off-road from etrailer.com I used the hoses supplied and mounted the Schrader valves on the rear bumper. Not too much of a problem for me. Inserting the bags into the interior of the spring was the toughest. You just got to work. I used some grease that got the job done. Then ran my hoses. I located my Schrader's separately on the plastic bumper just under the back hatch in the corners. Been running great with this hybrid system. I pull a 3,500 lb trailer with 10% tongue weight. Had a saggy back of the 4Runner. But not anymore. I use about 20 psi for trips. When not trailering I bring the air down to about 5 PSI. 2 years old going strong.

Heather A.

4/23/2026

@Zane That’s awesome feedback, Zane, really appreciate you taking the time to share that. Sounds like you did a clean install, and you’re spot on about getting those bags into the springs, that’s usually the toughest part of the whole job. What kind of trailer are you pulling?

Zane

4/24/2026

@Heather A. I have an Aluma 6'x16' V-nose all aluminum cargo trailer with a single axle and converted it camper. Total weight 3400# Zane

Heather A.

4/24/2026

@Zane Very Nice! We would love to see photos of your conversion if you ever want to send any.

Joe

4/23/2026

I have a 2020 TRD Pro 4runner with factory suspension. We haul a 2019 OffGrid trailer when we go camping in Colorado every year. We had the trailer sag also so we bought the Firestone airbags and as Zane mentioned above no more sag, installation was pretty straight forward with valves under the back hatch tucked away. When towing 20 psi, when not usually about 5 psi. They work great, had them for 4 yrs now and no problems. Not sure how they would work with a 3" lift though.