Tech & Tool – IFS vs. Straight Axles

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Tech & Tool IFS vs. Straight Axles – with 30Pack Matt

 

E37 Tech and ToolsC: One of the common statements we hear around King of the Hammers is IFS and straight axle. I asked you to help folks that may not understand the difference dig into the basics and talk through the ins and out, and maybe the pros and cons, of each. Let’s start with the basics. What is an IFS and straight axle car?

M: Basically they are just going to be price differences when it comes to building the car and maintaining it. That’s one thing, the other is that the IFS or even the full independent (front and rear) is going to be a lot more comfortable for the driver in a race like the Hammers where you get pounded through the desert, then have to be able to think and navigate up a rock trail. In that case your comfort is something that is definitely worth a lot. IFS is great for going fast, and now it’s come along enough to rock crawl also. Yet, at the same time there are some straight axle cars that can hang right there with them.

C: So a Jeep that comes stock has a straight axle?

M: Yes, a Jeep would be a straight axle. Any F150, Chevy, or 4WD truck is going to be Independent Front Suspension (IFS). 1-ton Ford and Dodges are still a straight axle in the front. The benefit of the IFS is definitely ride quality, which is why a lot of the factory vehicles are going to it. There was a rumor going around that Jeep was going to switch to an IFS, but I think as far as up to the 2017 model they are going to be straight axles still, so they’re holding onto their roots.

C: One day maybe. That would be cool to have Jeeps come straight out of the factory as an IFS. What does the IFS do to our geometry when you look at the front suspension?

M: A lot of it has to do with leverage ratios. As the wheel moves 18-inches or 20-inches, the shock is going to move 14. When you slow that shock speed down when you are hitting the bumps, the shocks don’t get as hot and the ride control can be tuned finer.

The same idea goes for a trailing arm on a solid axle where you move the shock up the control arm, making a leveraging arm and changing the leverage ratio. It really changes how the car handles. It’s kind of the same idea working in both scenarios, but with arm and all the geometry changes there is a lot more fine tuning that you can do. IFS is like a ball-ping hammer, and straight axle is like a sledge hammer, sometimes you just have to hit it.

C: That’s a good way to put it.

M: Well we are talking about King of the Hammers here (laughs).

C: So on a straight axle we take your 18-inches of travel and 14-inches of suspension into consideration, as far as that example goes, you have that much suspension. With the IFS you still have the 18-inches of travel, but your suspension is having to work less?

M: You can build any car to kind of do the same thing, as far as everything moving the same amount. Independent suspension has always been limited by the outside CV or the outside axle joint. At full droop, full steer you have to think that you’re compounding the angles. Where the inside CV might only be 20 degrees, the outside might be 20 with the droop and another 20 or 30 degrees with your steering. Everything has to be taken into consideration. With a straight axle you can set up the steering and the steering doesn’t change as suspension cycles.

C: I understand the steering components, that makes a ton of sense. What are some other pieces of the IFS vs. straight axle that we should take into consideration when choosing one over the other?

M: One of the biggest things for high speed travel over rocky terrain is unsprung weight, which is weight that isn’t being held by the shocks like your axle, tires, and wheels. You can built pretty light straight axles, but an independent suspension is always going to have less unsprung weight. It’s going to be a lot lighter, and allow the shocks to move more freely, as well as allow the tire to travel with the ground and improve your control. Where a straight axle kind of skips across the top of the terrain, an independent axle will follow the terrain and give you more control because braking is important along with acceleration and steering. If you are coming into a really rough section and your tires are following the ground, that’s a good thing when you go to hit the brakes.

C: That’s a great point as well. In the beginning you brought up price, that was actually the very first thing that you mentioned when we talked about IFS. It’s been really interesting as I’ve been talking to builders along the way on the show who are building IFS cars as racecars, and one of the questions I keep bringing up is, when is this going to become something that the average wheeler can afford or really want? How do you see that playing into the everyday game of building cars or building the next level of Jeep?

M: I don’t think it will ever come into play as part of the mass market because the parts are so expensive and precise. I don’t think that you can bring the price down far enough on suspension like this and be able to keep the quality needed for the harshness the axle goes through.

Everyone was in an outrage when Jeep was talking about making the Wrangler IFS because then enthusiasts would have to cut all that off and put a solid axle in it to be able to wheel hard. There are pros and cons but I don’t ever think it will necessarily be affordable.

C: There’s also been an argument pretty much since the beginning of the IFS as to which is better at the hammers, IFS or straight axle. Is there any truth to an IFS being better or worse at the desert vs the rocks or a straight axle?

M: The IFS car is going to shine in the desert. The solid axle car used to shine in the rocks, but now all the weaknesses have been addressed on the IFS so they aren’t weak anymore. They are strong and you can rock crawl with them now without them doing goofy things. There’s been enough research and trial and error that all the bugs have been worked out. Solid axles are still really competitive, but the IFS and it’s technology is definitely better. It will be interesting to see how it turns out this year.

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