Honda S2000 Rear Subframe Modifications

I’ve been autocrossing the S2000 for something like three years now. The last year was the first season where I did all the events that our local club (The Motorsport Club of Ottawa) had put on plus a few events that were put on by the Club Auto-sport Des Laurentides. I’ve made pretty decent strides in my driving during this time and I had a bit of a break through last year. I am starting to catch up to some of the guys in the club that have been doing it a while. I also feel like I know what I am doing behind the wheel, at least for the most part.

The last event we did last year was put on by the CADL. It was held on the large skid pad at the PMG Technologies in Blainville, Québec. We had a good bit of rain at this event and to suggest that my car was a handful is an understatement. The way the skid pad was paved and contoured for rain drainage meant that on the fastest part of the course we were driving across a few meter wide flowing water rivers every five or so meters. At least that is how I remember it; maybe I have the scale wrong. At this part of the course I was shifting from second to third gear at just over 100 km/h and then would be hard on the brakes at around 110 km/h. This part of the course also had some intentional slight chicanes added to it to force us to either slow down or at least change direction slightly. Both myself and my buddy Steve Fong were driving my car. Both of us had some big scary spins at high speed where we skipped across the aforementioned rivulets.

The S2000, especially my car’s vintage, has a reputation for being a bit of a handful at the limit. I have found this to be the case. Not stupid, sudden scary behaviours though; the car is docile to the limit and the limit is quite high. But, at this limit the car can get away from you quite easily. I liken it to balancing a pencil vertically on the end of your finger. It’s fun for a while but then you get tired and the pencil falls off your finger. If you aren’t in the mood for pencil balancing it can be quite tiresome.

When I first got the car and mentioned this behaviour some people suggested that it was a “grow into the car” thing or that I should learn to drive better. Funny thing is that when I drove later year S2000s I didn’t have any pencil balancing problems. In fact, I was faster in the other, later cars. At the rainy PMG event I tried out Naresh’s Mazdaspeed Miata (second generation Miata with a factory turbo setup that had been mildly tweaked). In Naresh’s car I was something like 3-4 seconds faster AND I could play Initial-D drift king in the car. I could hang the tail out at any angle I wanted at will in spite of not fitting in the car and being clumsy with the pedals. It was a revelation of sorts. I don’t want to have to put up with the way my car drives!

So, what to do? There are aftermarket rear suspension pieces that replace the rear toe links. The theory behind the S2000′s twitchiness is that the toe change curve with suspension cycle is not controlled in a manner such that the car is docile at the limit. The transitions in toe are fast and this catches drivers out. I have no doubt that the way it is delivered the car could be very fast in the correct hands. Just take a look at this video on Youtube of Motoharu Kurosawa driving the S2000 at the Nurburgring:

I’m not Gan San!

I wasn’t keen on doing the aftermarket links because they replace the factory style joints with Heim joints. Heim joints are great on a dedicated race car or rock buggy but in my opinion they have no place on my road cars or trucks. The other issue was that the more developed versions weren’t available any more. The company that made them stopped. There was a “knock off” version out there by another company but I had heard a few things about the quality of those pieces. I also didn’t want to be stuck with parts in the future that had no recourse for spares. I’ve seen and done that before.

The other option was to do the factory changes that Honda had started doing with the 2004 model year S2000. The rear suspension and driveline of an S2000 is all contained within a subframe structure. This subframe structure is interchangeable between the early and late cars.

I am uncertain whether this subframe has a different geometry from the earlier cars of if the geometry change is all done in the suspension peices that bolt to the subframe. Internet lore says that it is a combination of the subframe with the vertical upright and one of the A-arms or it is just the A-arm or it is just the toe link. Confusing and not definitive. At any rate, in order to get the parts to make changes the best value is to purchase the entire subframe with all the parts still on it. I managed to find one for sale in Toronto and drove down to bring it home. There are pictures of the subframe and it’s addtional pieces on the page Honda S2000 Rear Suspension Subframe.

Once I got the subframe home I stripped it and checked its condition. There are a few obvious things I didn’t like about how it was constructed. The front lower A-arm mount is a pressed steel affair that does not appear to be very stiff. Additionally the rear transverse crossmember seemed to be incomplete. The bottom was open or unboxed. It did not seem to be a very stiff structure. The way this crossmember attached to the round longitudinal members was somewhat light as well.

One of the interesting things about the subframe is that it was hand welded. The shape of the welds leads one to think it was MIG welded and there are various start and stop marks on some of the welds. Surprising. I like “perfect” robot TIG welds personally. There was nothing wrong with the welds on the subframe, I just was not expecting to see indicators of it being hand made.

Steve suggested I look to the Japanese tuners to see what they had done to subframes over the years. JUN, Opera and Spoon have made modified subframes. I took some of their ideas and came up with this series of templates and tubes to add structure and stiffness to the subframe.

In the end I did not bother with the tube work. It would have been very fiddly work and it would be a pain to deal with if I ever had to remove the rear differential bushings. After I finished welding the braces for the strnegthening the transverse crossmember I was happy with how the piece looked and felt: solid.

The additions I made were to box the control arm mounts, stiffen the rear transverse crossmember, and to stiffen the front lower control arm mounts. I think these are adequate changes that give good value for the effort and amount of metal added to the subframe. I thought I had more images of the build up of the subframe before paint but I guess not.

The next two articles on this topic will be the actual install into the car and then an article on what if any changes it made to the handling of the car at the limit at the track. I’m not expecting the car to be as docile as a Miata but I hope it will be a little more controllable for us mere mortals.

This entry was posted on May 30, 2010 at 9:24 pm and is filed under S2000 (AP1), Tech. You can follow any responses to this entry through the RSS 2.0 feed.