Forums » Grassroots Motorsports » Picking up front tire in turns? 1 2 3

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  June 1, 2011 9:50 a.m. crazyb New Reader

  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?

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  June 1, 2011 9:59 a.m. jstein77 Dork

  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.

  Jerry in Melbourne

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  June 1, 2011 10:04 a.m. Giant Purple Snorklewacker SuperDork

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

  Lord of drivel and harbinger of Floundering

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  June 1, 2011 10:12 a.m. jstein77 Dork

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

  Jerry in Melbourne

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  June 1, 2011 10:20 a.m. Giant Purple Snorklewacker SuperDork

  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.

  Lord of drivel and harbinger of Floundering

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  June 1, 2011 10:24 a.m. dogbreath Reader

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

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  June 1, 2011 10:30 a.m. Giant Purple Snorklewacker SuperDork

  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.

  Lord of drivel and harbinger of Floundering

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  June 1, 2011 10:35 a.m. ProDarwin Dork

  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.

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  June 1, 2011 10:35 a.m. fast_eddie_72 Dork

  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.

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  June 1, 2011 10:37 a.m. nervousdog HalfDork

  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.

  That was me that done that.

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  June 1, 2011 10:47 a.m. 93EXCivic SuperDork

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

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  June 1, 2011 10:59 a.m. HStockSolo New Reader

  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. :)

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  June 1, 2011 11:04 a.m. mad_machine SuperDork

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

  Be careful of your words, for someone will agree with them. Be careful of your conduct, for someone will imitate it. -Leih Tsu

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  June 1, 2011 11:22 a.m. Klayfish Reader

  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.

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  June 1, 2011 11:23 a.m. mad_machine SuperDork

  it would pick the rear up, right?

  Be careful of your words, for someone will agree with them. Be careful of your conduct, for someone will imitate it. -Leih Tsu

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  June 1, 2011 11:25 a.m. 92CelicaHalfTrac SuperDork

  

  SCAVENGE THE SEA FLOOR FOR NUTRIENTS

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  June 1, 2011 11:33 a.m. motomoron HalfDork

  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.

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  June 1, 2011 11:34 a.m. mad_machine SuperDork

  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

  Be careful of your words, for someone will agree with them. Be careful of your conduct, for someone will imitate it. -Leih Tsu

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  June 1, 2011 11:59 a.m. Duke SuperDork

  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.

  Junior Brown is my hero.

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  June 1, 2011 12:02 p.m. Klayfish Reader

  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.

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  June 1, 2011 12:02 p.m. 93EXCivic SuperDork

  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.

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  June 1, 2011 12:06 p.m. ransom Reader

  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?

  "In theory, there is no difference between theory and practice. But, in practice, there is." - Jan L.A. van de Snepscheut

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  June 1, 2011 12:31 p.m. mike Reader

  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.

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  June 1, 2011 12:36 p.m. T.J. SuperDork

  

  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.

  "During times of universal deceit, telling the truth becomes a revolutionary act." George Orwell

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  June 1, 2011 12:50 p.m. fast_eddie_72 Dork

  

  That looks fast...

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