posted on April 20, 2010 16:09
Project Nissan Sentra Spec-V part 5; Lessons in Geometry
By Mike Kojima
Although Nissan hyped up the Sentra Spec-V as a performance sedan in its marketing campaign, in truth the car was a little more than a piece of basic transportation with a few performance enhancing bells and whistles. The car was cursed with a crude beam axle rear suspension and a McPherson strut front suspension whose geometry was designed around efficient packaging and relentless understeer rather than performance. Because of this, the Sentra is at a significant disadvantage in the handling department when compared to its FWD rivals, mainly Hondas, the Scion TC and even the Infiniti G20. Despite of all this, we at MotoIQ are always up to an engineering challenge and we set about to rework the SE-R's suspension to attempt to make it a little more competitive.
To read more about Project Spec-V click here!
The stock Sentra suspension is plagued by a bunch of soft squishy rubber suspension bushings. Soft rubber is good for a smooth quiet ride but it hurts performance by making the alignment of the suspension inaccurate under load which makes it harder to keep the rubber on the ground. Soft rubber also makes the car slower to respond to steering inputs and dulls the driver’s feel of the car.
Global performance Products came to our rescue by providing us with a set of hard 90 durometer polyurethane bushings for our front lower control arms.
Global Performance Products also provided hard urethane rear trailing arm bushings.
A neat feature of the Global bushings is that they have an optional bushing with an offset hole that can be used to get additional positive caster in the suspension geometry. This is good because positive caster causes the tire to lean into the turns when the wheel is turned helping traction. Positive caster also helps stability.
The stock rear trailing arm bushings are huge gushy doughnuts of rubber with cutouts that allows the rear suspension to move around over 1” under side load and braking. That is not good. The solid hard polyurethane cuts this down to very small fraction of an inch.
We are going to run a 235/40-17 NT01 tire on this car and the best wheel for this tire size is a 17x8” wheel. We have also determined by measurement that an offset of 38-40mm is going to be needed to fit inside our wheelwells. The trouble is that we were unable to find such a wheel in the lightweight forged construction that we require in the 4x114.3 bolt pattern that the Sentra uses.
However there are many quality wheels made in the 5 lug 5x114.3 bolt pattern that cars such as the EVO, STi, 350Z, RSX Type S and other cars use. So the choice was simple, be stuck using ultra expensive custom wheels or to convert our car to 5 lug.
Our front hubs were easy to modify. We used ARP extended racing studs from a Spec Miata application, buying them from Summit Racing. We simply drilled our hubs to the new bolt pattern using a turret vice on a drill press and pressed the new studs into the hubs with a hydraulic press.