STU: Understeer Understeer!! can you help ?
I set up the dealership I work for ex-world challenge bmw for scca road racing and the techniques I use for my auto-x cars are the same.
I find an empty parking lot, set up a skid pad and a slalom 1) Do tire temp and pressure baseline 2) camber curving 3) set up balance/feel with skidpad an a g meter 4) redo temp and pressure. The only thing I leave for the track is alignment fine tuning and wing blade height and angle.
I find an empty parking lot, set up a skid pad and a slalom 1) Do tire temp and pressure baseline 2) camber curving 3) set up balance/feel with skidpad an a g meter 4) redo temp and pressure. The only thing I leave for the track is alignment fine tuning and wing blade height and angle.
yeah a little (10 years of racing)
hehe all except with the mr2 I had the reverse weight bias and a better tire section to weight ratio and zero body roll. Not that the mr2 was a better car just more purpose built
My evo is a DD weekend warrior.
hehe all except with the mr2 I had the reverse weight bias and a better tire section to weight ratio and zero body roll. Not that the mr2 was a better car just more purpose built
My evo is a DD weekend warrior.
This is a good thread.
Even though I haven't always driven an evo, I have always driven AWD (its too practical in CO not to) and I have picke dup my own oppinions about how to make the cars feel right. Before all the track's closed down out here, I was a huge proponent of running a big rear swaybar and pretty stiff springs all around. But I had never auto-x'd before.
what I think about the swaybar issue, is both a front bar or a rear bar can be considered when trying to get more grip up front. It can be looked at like this:
Bigrear bar, hang the rear wheel a bit in the air because of the bar. You are basically using the rear to make the front gain grip, which is the end of the car that needs it more. the decrease in rear grip is not so detrimental to a FWD car however, but is in AWD. With this setup, you are trying to make the front roll less, because you will ultimately have more grip up front.
Typical tire behaviour is such that the total lateral grip for two tires is highest when they are loaded (vertically) equally. More weight on one and less weight on the other with the same total offers less lateral grip.
BUT if you run a front bar, you can do the same thing, to a certain extent. by running the right combo of spring rate and swaybar, you should be able to keep the front end flat and happy. and in turn, the rear will stay reletively flatter compared to above, so you will have more rear grip to work with (rear grip may not be much more during steady state cornering due to the behavior of typical tires, but the benefit here is you have the tires on the ground, and you can accelerate far earlier.) The catch 22 is if you run too much front bar, you will transfer too much weight in the front, and that makes the tires unhappy.
Then, if you add in the types of suspensions you are dealing with, you have to decide the ri ght balance of braking vs turning. with McPhearson struts, you lose camber under suspension compression, so a bigger front bar is favorable up front for good braking vs cornering balance. Double wishbone cars gain camber under comression, so that begs for stiffer front springs to aid in stopping suspension compression under braking.
So, for the evo, to ahve a well balanced car for any type of motorsports, I would run both a front and rear uprated bar. Or stick to stock bars. this way, you can use d ifferent spring rates to fine tune the car's balance, or other things such as shock compression/rebound, alignment, ect.
Keep in mind, thats only my oppinion, I dont have the money to try out that theory yet. haha
Even though I haven't always driven an evo, I have always driven AWD (its too practical in CO not to) and I have picke dup my own oppinions about how to make the cars feel right. Before all the track's closed down out here, I was a huge proponent of running a big rear swaybar and pretty stiff springs all around. But I had never auto-x'd before.
what I think about the swaybar issue, is both a front bar or a rear bar can be considered when trying to get more grip up front. It can be looked at like this:
Bigrear bar, hang the rear wheel a bit in the air because of the bar. You are basically using the rear to make the front gain grip, which is the end of the car that needs it more. the decrease in rear grip is not so detrimental to a FWD car however, but is in AWD. With this setup, you are trying to make the front roll less, because you will ultimately have more grip up front.
Typical tire behaviour is such that the total lateral grip for two tires is highest when they are loaded (vertically) equally. More weight on one and less weight on the other with the same total offers less lateral grip.
BUT if you run a front bar, you can do the same thing, to a certain extent. by running the right combo of spring rate and swaybar, you should be able to keep the front end flat and happy. and in turn, the rear will stay reletively flatter compared to above, so you will have more rear grip to work with (rear grip may not be much more during steady state cornering due to the behavior of typical tires, but the benefit here is you have the tires on the ground, and you can accelerate far earlier.) The catch 22 is if you run too much front bar, you will transfer too much weight in the front, and that makes the tires unhappy.
Then, if you add in the types of suspensions you are dealing with, you have to decide the ri ght balance of braking vs turning. with McPhearson struts, you lose camber under suspension compression, so a bigger front bar is favorable up front for good braking vs cornering balance. Double wishbone cars gain camber under comression, so that begs for stiffer front springs to aid in stopping suspension compression under braking.
So, for the evo, to ahve a well balanced car for any type of motorsports, I would run both a front and rear uprated bar. Or stick to stock bars. this way, you can use d ifferent spring rates to fine tune the car's balance, or other things such as shock compression/rebound, alignment, ect.
Keep in mind, thats only my oppinion, I dont have the money to try out that theory yet. haha
This is a good thread.
Even though I haven't always driven an evo, I have always driven AWD (its too practical in CO not to) and I have picke dup my own oppinions about how to make the cars feel right. Before all the track's closed down out here, I was a huge proponent of running a big rear swaybar and pretty stiff springs all around. But I had never auto-x'd before.
what I think about the swaybar issue, is both a front bar or a rear bar can be considered when trying to get more grip up front. It can be looked at like this:
Bigrear bar, hang the rear wheel a bit in the air because of the bar. You are basically using the rear to make the front gain grip, which is the end of the car that needs it more. the decrease in rear grip is not so detrimental to a FWD car however, but is in AWD. With this setup, you are trying to make the front roll less, because you will ultimately have more grip up front.
Typical tire behaviour is such that the total lateral grip for two tires is highest when they are loaded (vertically) equally. More weight on one and less weight on the other with the same total offers less lateral grip.
BUT if you run a front bar, you can do the same thing, to a certain extent. by running the right combo of spring rate and swaybar, you should be able to keep the front end flat and happy. and in turn, the rear will stay reletively flatter compared to above, so you will have more rear grip to work with (rear grip may not be much more during steady state cornering due to the behavior of typical tires, but the benefit here is you have the tires on the ground, and you can accelerate far earlier.) The catch 22 is if you run too much front bar, you will transfer too much weight in the front, and that makes the tires unhappy.
Then, if you add in the types of suspensions you are dealing with, you have to decide the ri ght balance of braking vs turning. with McPhearson struts, you lose camber under suspension compression, so a bigger front bar is favorable up front for good braking vs cornering balance. Double wishbone cars gain camber under comression, so that begs for stiffer front springs to aid in stopping suspension compression under braking.
So, for the evo, to ahve a well balanced car for any type of motorsports, I would run both a front and rear uprated bar. Or stick to stock bars. this way, you can use d ifferent spring rates to fine tune the car's balance, or other things such as shock compression/rebound, alignment, ect.
Keep in mind, thats only my oppinion, I dont have the money to try out that theory yet. haha
Even though I haven't always driven an evo, I have always driven AWD (its too practical in CO not to) and I have picke dup my own oppinions about how to make the cars feel right. Before all the track's closed down out here, I was a huge proponent of running a big rear swaybar and pretty stiff springs all around. But I had never auto-x'd before.
what I think about the swaybar issue, is both a front bar or a rear bar can be considered when trying to get more grip up front. It can be looked at like this:
Bigrear bar, hang the rear wheel a bit in the air because of the bar. You are basically using the rear to make the front gain grip, which is the end of the car that needs it more. the decrease in rear grip is not so detrimental to a FWD car however, but is in AWD. With this setup, you are trying to make the front roll less, because you will ultimately have more grip up front.
Typical tire behaviour is such that the total lateral grip for two tires is highest when they are loaded (vertically) equally. More weight on one and less weight on the other with the same total offers less lateral grip.
BUT if you run a front bar, you can do the same thing, to a certain extent. by running the right combo of spring rate and swaybar, you should be able to keep the front end flat and happy. and in turn, the rear will stay reletively flatter compared to above, so you will have more rear grip to work with (rear grip may not be much more during steady state cornering due to the behavior of typical tires, but the benefit here is you have the tires on the ground, and you can accelerate far earlier.) The catch 22 is if you run too much front bar, you will transfer too much weight in the front, and that makes the tires unhappy.
Then, if you add in the types of suspensions you are dealing with, you have to decide the ri ght balance of braking vs turning. with McPhearson struts, you lose camber under suspension compression, so a bigger front bar is favorable up front for good braking vs cornering balance. Double wishbone cars gain camber under comression, so that begs for stiffer front springs to aid in stopping suspension compression under braking.
So, for the evo, to ahve a well balanced car for any type of motorsports, I would run both a front and rear uprated bar. Or stick to stock bars. this way, you can use d ifferent spring rates to fine tune the car's balance, or other things such as shock compression/rebound, alignment, ect.
Keep in mind, thats only my oppinion, I dont have the money to try out that theory yet. haha
the reason the car is so much better in the rain is because the inside rear wheel stays on the ground and the rear diff works like it's supposed to. when you lift the rear wheel in the dry and the stock (probably worn out) rear diff gives up all the driving torque goes to the front axle. the car then magically drives just like a FWD car and it sucks.
the only way to fix the suckiness is to prevent the car from going into 'FWD mode'. to many that means driving slow in fast out, to others that means stiff front bar and toe out in the rear. To me it says fix the rear diff. If you want to stay in STU then go to the dealer and buy a bunch of diff friction plates and rebuild the diff religously. if you don't want to rebuild the diff all the time then buy one that doesn't need lots of rebuilding like the John's TRE diff or a cusco and run in BSP.
once the rear diff is figured out, evo's rock.
Does anyone other than HKS make an adjustable front swaybar?
l8r)
With 10 years of racing under his belt I'm sure the OP already knew this ...
The EVO is so front heavy during braking and corner entry the front tires easily get overloaded and thus you get all that understeer during corner entry. Thus the extra need for slow in fast out ...
The car usually tripods during corner entry as you said, there many fixes to keep the inside rear on the ground eg: Front swaybar, stiffer front springs and something most people don't discuss, more droop in the rear shocks. Ofcourse each have their own positived and negatives ... it the end it's all about total balance.
I could play devil's advocate to what Drew said earlier but I better not or else he'll yank my sponsorship in a heartbeat
Last edited by DaWorstPlaya; May 8, 2008 at 06:04 PM.
I really do agree with almost everything that's been said, just some small differences here and there. I'm not trying to say rear swaybars are the ultimate suspension modification, just that they have some positives and negatives, and with the right set-up can work out very well.
- andrew
Last edited by GTWORX.com; May 8, 2008 at 05:30 PM.
Well I have some new updates. I very much doubt my rear diff is gone with only 6K miles on the car.
During the week I discovered that one of the rear sway bar end link nuts had walked almost all the way off. Fixing that I still decided to go to the hardest setting.
I dropped my pressures on the re01's to 32-34F/36R. The rears actually started to heat, gaining about 1.5 PSI over the 4 runs on a very brisk day. Again on sealed asphalt. I think next time I am going to run 33F/36R just a precaution.
There were alot of sweepers where applying gas was still not able to put the car into a minor drift. But the tire grinding understeer seams to be lessened.
A bystander commented that I had noticebly more body roll than the STI's. He said I looked very loose compared to them. I never felt like I had a lot of traction. The tires were protesting almost a constant symphony but I was able to turn, not super precisely but better.
I tried slowing down my entrances and 'skated around the sweepers' barely hanging on at near zero throttle. I am thinking my new enemy is body roll.
I could put the UCP's on to reduce the remants of understeer. But I think I am going to go with the front bar to try get this body roll controlled. There is alot of wasted energy as my chasis wallows form side to side. How much of a ***** is this bar to change ?
Thanks
During the week I discovered that one of the rear sway bar end link nuts had walked almost all the way off. Fixing that I still decided to go to the hardest setting.
I dropped my pressures on the re01's to 32-34F/36R. The rears actually started to heat, gaining about 1.5 PSI over the 4 runs on a very brisk day. Again on sealed asphalt. I think next time I am going to run 33F/36R just a precaution.
There were alot of sweepers where applying gas was still not able to put the car into a minor drift. But the tire grinding understeer seams to be lessened.
A bystander commented that I had noticebly more body roll than the STI's. He said I looked very loose compared to them. I never felt like I had a lot of traction. The tires were protesting almost a constant symphony but I was able to turn, not super precisely but better.
I tried slowing down my entrances and 'skated around the sweepers' barely hanging on at near zero throttle. I am thinking my new enemy is body roll.
I could put the UCP's on to reduce the remants of understeer. But I think I am going to go with the front bar to try get this body roll controlled. There is alot of wasted energy as my chasis wallows form side to side. How much of a ***** is this bar to change ?
Thanks