Rear Spring ?

[RACR_73s]

I have a couple of questions on the effects of rear spring changes. 2005 GRT....I currently run a 225 RR and 250LR in a 1/4 mi with medium to high banks. 1- What would going up #25 across the rear do to the car? 2- Keeping the #225 RR...what would going to a #275 LR do for the car (looking for more than loosen entry/tighten exit)? Not looking for engineering answers that I can't understand...just KISS answers on why or why not to do these changes. Your opinions, good or bad, are appreciated. ~Thanks~

[Matt49]

I have a couple of questions on the effects of rear spring changes. 2005 GRT....I currently run a 225 RR and 250LR in a 1/4 mi with medium to high banks. 1- What would going up #25 across the rear do to the car? 2- Keeping the #225 RR...what would going to a #275 LR do for the car (looking for more than loosen entry/tighten exit)? Not looking for engineering answers that I can't understand...just KISS answers on why or why not to do these changes. Your opinions, good or bad, are appreciated. ~Thanks~

I don't know how to give you a better answer than to describe the handling effects without being accused of sounding like an engineer...but I'll try.
Stiffer right rear spring will tighten entry assuming you are off the gas on entry. Stiffer right rear spring will also loosen corner exit assuming you are on the gas exiting the corner.
On LR, I'll make the assumption that your spring is behind the birdcage.
That being said, LR spring effect can be drastic to unnoticeable depending on driver. If your driver is very good at keeping the car on the bars via trail braking, they wouldn't care if you had a 100 pound spring or a 400 pound spring on the LR.
If your driver let's the car come down going into the corner and is "re-hiking" it coming off the corner, then a softer LR will generally make the car feel all around tighter and a stiffer LR will generally make the car feel all around looser.

[MasterSbilt_Racer]

I have a couple of questions on the effects of rear spring changes. 2005 GRT....I currently run a 225 RR and 250LR in a 1/4 mi with medium to high banks. 1- What would going up #25 across the rear do to the car? 2- Keeping the #225 RR...what would going to a #275 LR do for the car (looking for more than loosen entry/tighten exit)? Not looking for engineering answers that I can't understand...just KISS answers on why or why not to do these changes. Your opinions, good or bad, are appreciated. ~Thanks~

Generally, if you increase the roll resistance of one end (increase both spring rates), that end loses grip first. So, increasing rear spring rate should make the car looser.

[RACR_73s]

Matt - You did a good job explaining it. I don't mean to accuse people of sounding like an engineer, it is me that can't understand a lot of the answers on here. I am more on the side of letting the car come down off the bars but I have recently gone to a LRF shock that keeps it on the bars more and has helped with turning the car. My car used to be extremely tight going in and this (LRF shock) has helped me get the car turning without sacrificing the fact that I like to feel that the car is "under me" and not all hung "tail out" just to make it turn. ~Thanks~

MBR - That is the simple answer I was looking for. That is not what I want to happen so I will avoid that change. ~Thanks~

[keeks]

I don't mean to hijack the thread. As another tool to help loosen up a LLM I could change rear spring rates to achieve this?

[RCJ]

While i agree in theory with what these guys are saying.Changing the r/r spring is not an effective adjustment.We had to go up in rate so much to effect the middle that it was making a bigger effect on entry.It has to do with spring base and motion ratios.Where in the corner the car is tight is very important.Tight on entry, l/f spring rate,toe out,shocks will help .Tight in the middle, r/r bars,rear steer,stagger, softer front.

[Matt49]

To me, RR spring rate comes down to a bit of a compromise between roll rate and ride rate. Changing the spring rate itself has some opposing effects because decreasing roll rate tightens entry but decreasing ride rate loosens entry. Spring angle then becomes something to consider, now doesn't it? Food for thought I guess but I think this is the reason most folks just put a 225 on there and race...opting for other adjustments that are easier to predict how the car will respond.

[SS Motorsports]

It's an 05 GRT, all it needs is hard tires.

[grt74]

run 80-100lbs bite,stacked lr 400 over a 300 with lock nut just touching at ride height,it will do what you want it too,leave the 225 on the rr,if you go to a super slick place put the 250 on,the lr shock will need a fair amount of compression