Turn, darn it, turn.

I am looking for some guidance on the most effective way to eliminate the understeer I currently have during steady state cornering.

Current set-up: 2009 Porsche Boxster base model with 6 speed MT, stock suspension (springs, struts, sways) with addition of adjustable camber plates. Camber -2.0 front, -1.8 rear, rear,  toe .05 deg, front toe .00 deg

Wheels 18x9 front with 245 40 18 and 18x10 rear with 275 35 18, Kumho 730 set 30 psi hot all around (no tire temps, sorry).

I promised my wife to not “ruin” this car as I made my NC Miata ride more harsh setting it up for autocross and HPDE. I do throw the stock 17” wheels on between events which improves ride quality significantly for the Boxster.

In my mind this means the knobs I can adjust are alignment, tire pressure, and sway bar replacement. My standard approach would be a bigger rear bar (likely adjustable as well). Are there other things I should consider first or instead? My NC Miata was set up just a tiny bit loose in steady state cornering and I was very comfortable with that.

Thank you.

I had good luck removing the front sway bar from my toyota MR2 spyder.  Not exactly the same car, but similar.  Might be worth a try.

Rear sway bar changes go a long way on these cars. Not sure what the options are for 987s but definitely get one that's adjustable if possible.

A bit more front camber would probably help too.

In reply to dps214 :

I would love to dial in a bit more front camber...with the factory slots I could only get -.6 degrees. With the adjustable plates I am now maxed out at the -2.0 degrees. To get more I would have to start modifying  the adjustable plates which I am reluctant to do.  Thank you.

Can you add caster?  It's like free camber that only appears when cornering.  Also, you said it happens during steady state cornering.  I assume that means it turns in well.

If it's NOT turning in well, add 1/8 inch toe out in the front.

Can you swap the wheels and tires front to back and see what it does?  It might look silly, but it's worth an experiment.

In reply to fusion66 :

Carroll Smith always said fix the end that isn't working; basically you want to make the back slide sooner to fix the front.

Is there an adjustable front bar? Can you go to slightly wider front tires?

Realistically you need to get tire temps as for all you know the front camber is good but I suspect it needs a touch more camber for track work. From memory I seem to recall most of the PCA track Boxsters around -2.5 front camber.

The final question is the understeer slowing the car down or is it just annoying to you? 

In reply to wvumtnbkr :

No free caster adjustments. Can be done with adjustable lower control arms which would also allow more camber. 

It does turn in well. Mostly a steady state issue that I think can/should be improved upon. Front to rear tire rotation is not an option due to fitment.

Put two bags of concrete mix in the frunk?

In reply to fusion66 :

Look at the tire pressure sticker on the door tag.  You need higher rear pressure than front.  You have too much rear grip and this will help a lot!  Start with recommended tire pressure as a baseline.  

In reply to Tom1200 :

No adjustment on the current factory sway bars.

I would need to roll the fenders and get a wider wheel to increase the front tire which is currently not appealing as the set-up is nearly new and shot the budget for a while. 

I agree that I really need temps so I will focus on getting data at the next event and using that to make a better informed decision. 

I feel the understeer  is slowing me down (and also annoying me) and hope to achieve a more neutral car with some minor adjustments in the future.  Thank you.

In reply to 914Driver :

In reply to AnthonyGS (Forum Supporter) :

Very sorry to say I did not look at this to begin with. Will do!

Will it still fully apply with the current 245/275 tires versus the stock 205/235 tires? I would think so at least directionally and then adjust as needed(?)

Thank you.

Tire pressure is definitely a tuning tool. A bit more of a setup compromise than the swaybar, but definitely a good tool to see if it's a change in the right direction before spending money.

Honestly I wouldn't worry about tire temps. 2* camber probably isn't enough, but you already know that and if you don't want to go spending money on more parts to add camber (which will also make tire fitment a bit more difficult) that's totally fine.

I've run a few different 245/275s on a couple of different 981s and have always ended up with at least a couple psi more rear pressure than front, fwiw.

Another note, 255s on 9" wheels is a totally fine fitment to get a bit more front grip without needing to buy wheels. No idea if that would fit in the fenders though.

You definitely, definitely need more rear air pressure. I ran my 986 S at 32/34 for my codriver and 32/36 for me. At 32/36 it would absolutely *rotate* as soon as you wanted it to. If you set same pressure f/r it is going to plow no matter what you do.

In reply to fusion66 :

Like you I prefer a car a bit loose, so yes understeer is annoying. 

I'd work on the front. Do one more event and get the tire temps...........I'm going with it needs 1/2 degree more. 

I'm running a 2011 base Cayman. I'm in the same boat as you. I didn't want to ruin the street ride/handling so the only mod I made was to go with front adjustable LCAs.  I have -2.5/-1.8 camber, zero toe F and -.05 total toe R. I'm running Goodyear Supercar 3 (245/275) at 32/33 psi. The tire temps are very even and the car is very neutral.  I'd bet that your tire pressures are too low. I would try adding 1-2 psi front and 3-4psi rear (32/34 hot) and see how you like that. Then try playing with the pressure stagger F/R to match your taste.

In reply to CAinCA :

Thanks for that feedback - I will definitely be increasing and then playing with tire pressure to see if I can find the balance I am looking for.

30psi hot is low overall, even more so for a mid-engined car that will understeer naturally. 

I like to start high and square on pressures and then work my way down. I'd probably start at 38/38, and take pressure out 1psi at a time, starting with the fronts. Somewhere around 34/36 front and 38 rear, you'll probably find a twitchy point. At that point, switch to the rears and dial out 1 psi at a time until twitchy becomes rotatety.  

If this were me, I'd just go to the mall parking lot and do some long figure 8s while playing with the pressures. 

The goal is to maximize the grip on each corner and then move the grip around (bars, springs) to get the characteristics you want.  
 

Simply reducing the grip on the grippy end, while potentially giving you a neutral or loose car, results in less overall grip. 
 

With zeeeero boxter experience, I'd think smaller front bar and/or larger rear would be a good place to start, especially considering your goals (street driven, wife likes it, less-expensive changes, etc.)

DocRob said:

30psi hot is low overall, even more so for a mid-engined car that will understeer naturally. 

I like to start high and square on pressures and then work my way down. I'd probably start at 38/38, and take pressure out 1psi at a time, starting with the fronts. Somewhere around 34/36 front and 38 rear, you'll probably find a twitchy point. At that point, switch to the rears and dial out 1 psi at a time until twitchy becomes rotatety.  

If this were me, I'd just go to the mall parking lot and do some long figure 8s while playing with the pressures.

Yeah but you're forgetting that the front end is also light. 38psi in those front tires and the outer tread block won't be touching the ground. Pressure depends on a lot of things including the tire model, but 30psi in the front is about right.

I feel like this is a known behavior with this chassis.  As suggested above, you can probably get some improvements by adjusting tire pressures, which will basically reduce rear grip and thus reduce overall grip but improve balance.  The known behavior has a known solution, which is more front camber.  Some GT3 LCA's and 2.5-2.8 degrees of front camber are probably the definitive answer to your question.  If it were me I'd get a pyrometer and an accurate tire pressure gauge and start with some measurements.  If you don't know where you're going, any road can get you there.

Porsche recommends 30/32 cold for street use. That winds up being 34/37 -36/39 during "lively" driving. These cars don't like square pressures. That's a sure fire way to get understeer.

Cheapest option would be to swap the 275s to the front :-)

Personally I think that amount of tire stagger wouldn't suit a fantastic 50/50 weight distributed lowish powered momentum car. I would run a square setup to give me some tire rotation capabilities and ability to run finer tweaks to the car through suspension tweaks.

You are inducing a good amount of understeer with your tire setup then having to tweak the car so it handles neutral to the lower grip axle.

Olemiss540 said:

Personally I think that amount of tire stagger wouldn't suit a 50/50 weight distributed car

Good thing that's not what's being discussed here. More like 45/55.

Yeah...more front tire would be nice. But until he's ready to chop the fenders off he's not getting more than maybe 255s on the front.

It's light enough that a 245 square setup would probably be enough tire to go quite quickly. 

What's the reasoning for the larger rear tires?