In looking at a lot of build threads, and looking at a number of 4runners and tacos in person as well, it seems that many people run heavier shocks in the front than in the rear. The most common examples being 2.5's in front and 2.0's in the rear, or the 6112/5160 combo.

Now obviously, the engine sits in the front-and that's a lot of weight, so at first glance that seems reasonable. Thinking further though, rear bumper and tire carrier is in the back, drawers+fridge+cargo is in the back. Roofrack and everything on it is more over the rear than the front, so probably a 60/40 rear/front split or so. This would make me think that an even pairing would be better.

So my question is, how much does it matter whether the rear shocks are smaller? What is the real world effect? Obviously it would be nice to have all 2.5s around, but there's a real world cost that I'd rather avoid if something else will be 'good enough'.

People are going higher in the front to reduce the rake- THe front starts off mush lower than the rear so we are trying to level it out.

Am I missing the question?

Can you replace only the front? sure

You adjust the height with coils, 2.5 vs 2.0 has no impact on height.

I'm aware that you can replace just front or back, the question is are you likely to have increased roll, or have issues if your rear fades before the front, also, when going up trails, isn't there a lot more impact on the rear (see this clip of my wife with my 4runner for example).

My question is given all of that, why do so many people run larger diameter in front than in back.

The reason why so many people have them on the front is performance shock manufacturers only make the 2.5" front coilovers, 2.0 front performance coilovers don't really exist, I'm guessing because they don't hold up as well or the performance just isn't there.

Manufactures have obviously found 2.0" rear shocks have enough performance for the average truck and are cost-effective. When you start adding weight to the rear, need the added cooling capacity of more oil, or stronger shock shafts is when you want to move up to a 2.5" rear shock.

Fair enough. So how does one determine the cutoff from 2.0 to 2.5 for the rear? Is there a set weight point or use case scenario that determines that? I know I need more than the 5100s I'm running now, between fade and the occasional bottoming out that is obvious. I could run 2.0s for a while and see, but that's really not ideal if they have to be replaced again.

It doesn't matter. It won't effect any drive-ability.
2.5s are designed to give a smoother ride. The coils are what hold extra weight, not the shocks.

Funny thing, when I talk to Down South Motor Sports or FIlthy Motor Sports, or Accutune Offroad they all tell me that I really should have the 2.5s in rear.

Are they only saying that to bump up their sales? I doubt it, but here is everyone trying to tell me it doesn't matter.

Def a selling point.

This is basically the case I imagine. I have a Radflo 2.5" Front & Rear set-up (my kit was purchased through OLW when they were contracting Radflo for custom set-ups with custom valving for our vehicles) that came as a package.

My friend owns an FJ and has the same suspension kit, save for his shocks are 2.0" (this is after OLW closed their doors and let Radflo use their valving specs for their kits). So Radflo decided that 2.5" all around wasn't worth the effort I guess?

It's possibly a sales tactic, but it comes down to what you talked to them about. In my case I had an option to go with 650lbs springs in the front because OLW was out of 700lbs springs when I placed my order years ago. But talking with Andre (one of the owners) at the time and explaining I planned on full front & rear bumpers, full skids, ect. He said he'll call Eibach and get a set of 700's on rush order because the 650's won't cut my planned build.

So if you talked with them and detailed exactly what you want to do with the vehicle and how you're going to use it, they may be right in saying you'd be better off with 2.5's in the rear. But we weren't there so it's hard to say one way or the other. Most people just lift their 4Runners and throw bigger tires on them and don't really abuse them that much, so 2.0's in the rear are probably fine for the majority.

Hmm. I'm looking at 700s in the front also. I've actually got a pair of Fox 2.5s with king 700s that just need to be rebuilt and have DSC added before I toss them on the front. I've got front/rear bumper, armor, roofrack, arb drawers, fridge, RTT (occasionally), etc.

I've also got a pair of 2.0's for the rear (was a package purchase along with the 2.5s), but I don't want to go through the effort of mounting those if I'm just going to replace them down the road. Every shop I've talked to has said that 2.5s would be better, but then the forum goes and says there's no real difference.

I don't wheel too hard (see here for one of the more difficult things done in the 4runner in the last few months https://www.youtube.com/watch?v=UnUah93QxyA-my wife is driving here-great balls on her, but occasionally mixes up forward/reverse). I rarely go over 50mph offroad-most of the time it's just 30-40mph (where possible). I know I can't do the MetalTech long travel with as much weight as I have, so I figure I just want the best travel and smoothest ride I can get without paying an exorbitant amount. If that means getting the 2.0s rebuilt and valved for me I can do that. If it means getting the fox 883-26-004 I can do that. If it means getting a 10" bypass shock and a custom mount (like LTDSC) I would look into it, and probably run the 2.0s in the interim while I save my pennies.

It's interesting how variable this 'hobby' is. In so many other things there are technical specs or benchmarks that mean that you can know what you need and whether the product will work for your needs or not.

Anyways, thanks for your post.

Is there a set amount of weight that one would consider for that move from 2.0 to 2.5? I know I'm fairly heavy (front/rear bumper, armor, roof rack, drawers, fridge, etc), but no idea where that line is.

The extra oil capacity will make a big difference to handling over rough roads. Keeping in mind that the valving is based significantly on the spring rates, which is determined by the weight of the vehicle, suspension configuration, and other voodoo... and thus, the valving rates on the rear shocks, which really is what determines the "ride" of a shock, on a 4Runner, is going to have more to do with the spring rate of the chosen spring.

From what I came to understand is there's a reasonably narrow selection of spring rates available for the 4th gen, in two catagories: Stock weight and heavy duty. Which of course makes the same two classifications of shocks. Generally speaking, OEM Spring + OEM shock makes nice, ditto for HD.

Having said that, pound for pound, 2.0" vs 2.5" shock with the same spring... the 2.5" diameter shock will always give better sustained performance during heavy cycling. Further, I would estimate that the 2.5" shock may also provide more precise control for high speed / low speed dampening as that there's more volume of oil to move per inch of travel upwards, allowing the valving to more accurately dampen travel... Small potatoes I'm sure, on the highway, but a driver may notice this on a washboard road; but the extra oil capacity to keep the shock cooler, longer, will probably have a larger effect on performance.

If the radflo shocks are rebuild-able, the 2.5 is a better spend. It certainly won't have negative effects on road manners to have the larger shocks; as that I would surmise they were designed with similar spring rates in mind. However, with more weight to sling around, oscillation of the rear end down rough roads, it'll take alot of force to keep the rear axle under control... which makes alot of heat, making that extra oil real handy.

^ This. I went 2.0s w/ the remote reservoirs because I wanted the extra oil capacity and I couldn't afford the 2.5s w/ rr at the time. I'm running the 2.5 coilover in the front without the reservoirs because I didn't think I'd need that extra oil in the front and they allow for adding them later on if I decide I'm getting too much shock fade. My rears are due for a rebuild, but even on some of the worst roads I've never had an issue with them. Buddy of mine was told he would be fine with 2.0 non reservoir in the rear unless he was trophy truck racing for hours at a time.