1 2 3
crazyb
crazyb New Reader
6/1/11 9:50 a.m.

Is it a bad thing. According to a few people my car seems to be picking up the inside front tire in some turns. I have not been able to really feel it yet. Only photo i have is apparently right before the tire came up. But I was wondering if this is a bad suspension characteristic and something I should work on tuning out?

jstein77
jstein77 Dork
6/1/11 9:59 a.m.

It means that you have more front roll stiffness than rear. It could mean understeer at the limit, but if it's well balanced otherwise there's no real harm in this behavior.

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
6/1/11 10:04 a.m.

Adding a little more rear bar or spring... or both will help keep it planted on an E30.

jstein77
jstein77 Dork
6/1/11 10:12 a.m.

That's assuming that you have a limited slip. With an open differential, more rear roll stiffness will increase wheelspin.

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
6/1/11 10:20 a.m.
jstein77 wrote: That's assuming that you have a limited slip. With an open differential, more rear roll stiffness will increase wheelspin.

If you are lifting the inside front tire of an E30 on the throttle exiting a corner you probably already have an LSD but regardless - if the rears stay planted to the road they won't spin, LSD or no. Adding too much rear bar, spring or both would certainly cause that but adding the "right" amount will help either case.

dogbreath
dogbreath Reader
6/1/11 10:24 a.m.

A lot of the fastest E30/E36 autocross and race cars I've seen would lift the front-inside on tight corners.

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
6/1/11 10:30 a.m.
dogbreath wrote: A lot of the fastest E30/E36 autocross and race cars I've seen would lift the front-inside on tight corners.

It is typical to set the E36 up with a lot of front bar because it lets the rear suspension put power down much earlier but 4 wheels on the road is always better than 3 so finding the balance is worth it for road racing where those tiny slices of time add up lap after lap. I can't speak for the auto-x crowd but it seems like the same logic would apply but might not be worth the $ and time for a few tics in 30 secs.

ProDarwin
ProDarwin Dork
6/1/11 10:35 a.m.
dogbreath wrote: A lot of the fastest E30/E36 autocross and race cars I've seen would lift the front-inside on tight corners.

This. Watch the DSP cars at national level events. Or the (former) BSP M3s. They spend a lot of time on 3 wheels. If there were a way to keep both fronts down and be faster, they would be doing it.

fast_eddie_72
fast_eddie_72 Dork
6/1/11 10:35 a.m.

It depends on the class you're building for too. My E Stock MR2 lifts an inside front, but it's the best compromise given the limitations of the rules. Having said that, I know some pretty darn fast street prepared cars that lift the inside front like crazy.

nervousdog
nervousdog HalfDork
6/1/11 10:37 a.m.

I knew the car in question would be a BMW when I saw the thread title. Other rear drive cars seem to keep both front wheels down except for Mustang convertibles (probably just body flex on those).

If its not understeering I wouldn't worry about it. There is a local E36 M3 that lifts the inside front wheel quite often and it doesn't seem to slow him down. He is consistently in the running for FTD against karts and a Porsche GT3.

93EXCivic
93EXCivic SuperDork
6/1/11 10:47 a.m.

The front inside tire will be producing very little to no grip.

HStockSolo
HStockSolo New Reader
6/1/11 10:59 a.m.
nervousdog wrote: I knew the car in question would be a BMW when I saw the thread title. Other rear drive cars seem to keep both front wheels down...

I've seen lots of RWD prepped autocross cars lifting front wheels. I've seen plenty of Porsches lift them quite high. E36 BMWs are known for lifting both inside wheels, and E30s for flipping over.

Generally 3 wheels is faster than 4. The inside tires have negligible grip, so if the suspension isn't maximizing the traction for the demands of the most stressed outer wheel, you are giving up time. Also pinewood derby cars are much faster riding on 3 wheels than on 4. :)

mad_machine
mad_machine SuperDork
6/1/11 11:04 a.m.

yes.. I have seen the porsches raise them up enough that it looks like you could replace the tyre while it is up there.

Klayfish
Klayfish Reader
6/1/11 11:22 a.m.

It's been a while since I ran autox, but when I was running nearly every weekend, there was a guy with a really old VW Scirocco. It was completely set up for racing, often setting FTD. It was on 3 wheels more than it was on 4.

mad_machine
mad_machine SuperDork
6/1/11 11:23 a.m.

it would pick the rear up, right?

92CelicaHalfTrac
92CelicaHalfTrac SuperDork
6/1/11 11:25 a.m.

motomoron
motomoron HalfDork
6/1/11 11:33 a.m.
ProDarwin wrote:
dogbreath wrote: A lot of the fastest E30/E36 autocross and race cars I've seen would lift the front-inside on tight corners.

This. Watch the DSP cars at national level events. Or the (former) BSP M3s. They spend a lot of time on 3 wheels. If there were a way to keep both fronts down and be faster, they would be doing it.

Exactly. When I was trying to do STU in my '98 M3 - ultimately an exercise in futility - It was all about the compromise of getting the thing to turn and getting power down. I ended up w/ the thinnest UUC rear bar and the biggest H&R front plus a lot of rear toe-in. The car would stick at WOT in most situations, but steady state hard cornering had lots of daylight under the inside front. It does it on track at well, particularly in a couple places @ Shenandoah.

mad_machine
mad_machine SuperDork
6/1/11 11:34 a.m.

those kinds of corners.. that inside wheel is not carrying much weight anyway.. so in the air or on the tarmac, it is not going to make much of a difference

Duke
Duke SuperDork
6/1/11 11:59 a.m.

There was an extremely fast DSP E36 328i at the first event I ran this season. It would do the RWD version of the Neon Shuffle all through the fast slaloms. Easily 2"-3" of air under the inside front. Sure didn't seem to slow him down any.

Klayfish
Klayfish Reader
6/1/11 12:02 p.m.
mad_machine wrote: it would pick the rear up, right?

Actually, now that I think about it, you're right. It was the back tire it was picking up, not the front. Like I said, it's been a while... And it would pick that wheel up nice and high, like a dog at a fire hydrant.

93EXCivic
93EXCivic SuperDork
6/1/11 12:02 p.m.
mad_machine wrote: those kinds of corners.. that inside wheel is not carrying much weight anyway.. so in the air or on the tarmac, it is not going to make much of a difference

This. Don't worry about it if the balance is good.

ransom
ransom Reader
6/1/11 12:06 p.m.

Arg... There was an article in Racecar Engineering a while back (not really a direct competitor to GRM, are they? Am I tempting a smiting?) which talked about this.

IIRC, there was an item to consider with respect to the transition from least-weighted tire on the ground (continued roll has effect with respect to F/R roll stiffness distribution, I think) to tire off the ground (nonlinear, suddenly additional roll has no effect on relative distribution of roll resistance, so all you get is camber loss and travel usage?).

I don't have time to dig it up or google for similar right now, but does the idea ring any bells?

mike
mike Reader
6/1/11 12:31 p.m.

My Alfa GTV racecar picked up a front wheel in many turns. With that car it was all about roll centers and c.g. The car had a higher cg than I would have liked, along with a forward weight bias. And as a lowered car with A-arms up front and a live axle out back, the front roll center was quite low while the rear roll center was high. Without a big front bar, the front of the car rolled like mad, tipping the wheels due to the poor camber gain built into the geometry. With a big bar, it worked better but picked up the inside front. I never did have strong enough springs on that car.

T.J.
T.J. SuperDork
6/1/11 12:36 p.m.

3 wheels = fun 2 wheels = scary (don't have any pics of that)

I've seen DSP BMWs that looked like they could step the front wheel right over a cone during autox runs.

fast_eddie_72
fast_eddie_72 Dork
6/1/11 12:50 p.m.

That looks fast...

1 2 3
Our Preferred Partners
nI48zNZvn2CLIPlHVkexF8eMb7U2J3iV