GSR Autosport Global Time Attack M4

[bluekn8286]

Originally Posted by GSR Autosport

Having more seat time now in the M4 I think the answer is somewhat yes and no. If you really want to put down some good times you really need to move to a performance oriented damper.

We tried the lowering springs mainly because we were looking to get more front negative camber (we were able to get -1.8), which is not ideal but something... again trying to deal with the understeer issues. With a lower CG the weight transfer of the car was a bit better but because of the reduced operating range of the damper and the fact that the H&R 435 springs we were using were not heavy enough to support the compression weight under load, high speed cornering composure was less than ideal.

Willow Springs was not a good track for the lowering springs because it is a fast, flowing track with bumps in critical braking areas (Turn 1) and corners (Turn 8). There aren't too many technical sections where you need to aggressively transition the car. I would expect the stock spring setup might be better at this track.

Now Buttonwillow is a much more technical track so transitioning the weight of the car is much more critical. It's also very smooth as it was just recently paved. I think the lowering springs could actually help at this type of track.

If you are just doing a track days for fun, every once in awhile I think the lowering springs are fine just note there limitations and be cognizant of the potential behavior changes in the car when you load up the suspension.

-Nick

This is a great way to explain how modifying the stock suspension with "high performance" springs aren't going to always net you the best results on the track. The stock springs on an M car were designed and tested for the chassis they support and changing that will only lead to inconsistent results. I am definitely in support of coil-overs because the high level of adjustability allows you to properly dial in the car for any application you choose.

[GSR Technik]

swifty asked about comparison of OE M springs and lowering springs so we thought we would take a look at two somewhat similar corners from our tests at Buttonwillow (with stock springs) and Willow Springs (with lowering springs).

We took a look the right-hand "Riverside" turn from Buttonwillow and the right-hand "Turn 8" from Willow Springs. Both are grip limited corners but Turn 8 is about 30 mph faster and a lot bumpier.

Below is the G-force trace data from the Riverside corner at Buttonwillow:


The lateral G loads look about .2 G's less in Riverside as compared to Turn 8. There is also about .2 longitudinal/acceleration G's which is putting more load on the rear.



Below is the G-force trace data from the Turn 8 corner at Willow Wprings:


The lateral G loads are maximized laterally - almost no longitudinal loads which makes sense as the corner is pretty much taken at maintenance throttle. I guess the biggest difference is we have much more weight on the front left spring in this corner - compared to Riverside.

We experienced pretty harsh suspension behaviors in Turn 8 in the bumps. Looking at the data this could have been coming from the front as each time the car hit a bump the car would bounce to the left a foot or so.

Although it's interesting to take a look at this data I don't think we can really determine a material difference between the two springs unless we test the OE springs at Willow Springs. It's tough to say that the OE springs would handle the loads in Turn 8 any better than the lowering springs.

If you are at SEMA come check out the GSR Autosport BMW M4 Global Time Attack car in the Achilles Tires booth.

-Nick