"yitznewton" (yitznewton)
10/01/2015 at 22:22 • Filed to: handling, front wheel drive
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"yitznewton" (yitznewton)
10/01/2015 at 22:22 • Filed to: handling, front wheel drive | 0
| 8 |
I’ve had my Mk4 Jetta for nine months now, and my only real gripe with the car is its tendency to understeer mid-corner. It’s typical for front-drive cars, and I gather that the VW A4 platform is actually known for being a step down from the earlier Golfs in that department.
After scoring Grassroots Motorsports’s !!!error: Indecipherable SUB-paragraph formatting!!! , I’ve been making my way through, and found a short article on exactly this topic. (Unfortunately I’ve lost track of which issue it was in... I will update this post if I re-discover it.) In terms of chassis tuning, the overall strategy is to stiffen the back end, which results in reduced grip in the back, allowing the rear to slide more, in relation to what the front is doing. Although community consensus is that a rear sway bar is the best upgrade for this, I’ve been resisting the idea of buying one, because I have this yearning to switch the Jetta out for an S2000 or another light RWD car, upon which the question would go away. So, how to make the best of what I have without investing more in the car?
There were two less invasive tactics mentioned in the article. One is better tires. I’m running performance Yokohama all-seasons, and the suggestion was that proper tires help the car’s balance. If I keep the Jetta past my current tires, I’ll look into getting legit summer performance tires.
Another idea was reducing rear grip via the rear tire pressure: either under-inflating or over-inflating, both of which reduce grip in different ways.
I had been running 38 psi front, 36 rear, but the article gave me the idea of going much lower in the rear. I decided to head to my local track-like section of road and try 40 psi front, 32 rear, measured cold since there’s no convenient “pit” area there.
I absolutely noticed a difference with the new pressures. I would say it moves the balance “more toward neutral,” still understeering, but not in nearly such a crippling way as before. The Jetta was much more willing to follow the curve after turn-in.
I also discovered a trick of quickly jabbing the throttle and then lifting off, just as the rear gets crotchety, basically forcing an enhanced lift-off effect on the chassis. I only happened to try it once reflexively, and of course it takes a lot longer than a straight lift-off. I’m not sure quite how effective it actually is, but I got the impression I was faster through the corner than just lifting off.
What are your budget FWD handling tricks?
bob and john
> yitznewton
10/01/2015 at 22:26 |
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you can try getting a wider tire up front / thiner tire out back
DrJohannVegas
> yitznewton
10/01/2015 at 22:34 |
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Don’t lower it at all. If anything, a bit more ride height will improve roll center, which is an important aspect of weight transfer in cornering. You aren’t going to fix the “front wheels do everything” problem, but you certainly can avoid hurting matters. Read Dick Shine’s stuff on Vortex.
See: http://forums.vwvortex.com/showthread.php…
Übel
> DrJohannVegas
10/01/2015 at 23:10 |
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Man, one of my long time dreams is to get some Shine suspension for my GTI, but I don’t believe it’s made anymore and nobody else offers a stock-ride-height option for the MkIV that I know of.
wafflesnfalafel
> yitznewton
10/01/2015 at 23:26 |
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I like the tire pressure difference front to back as well on my Mazda 3 - more personal preference I suppose - I don’t track it. But I like how it tucks into the corner at throttle lift better and the steering is generally sharper and livelier with 38ish front, 34ish rear running Michelin Pilot Sports
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DrJohannVegas
> Übel
10/01/2015 at 23:50 |
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KermaTDI still sells it. Don’t know what happened with his other distributors (I know he was reputed to be a difficult person to deal with at times), but:
http://www.kermatdi.com/koni-fsd-shine…
If the goods aren’t available, at least you can find the right rates and get the lengths from this info: http://forums.vwvortex.com/showthread.php…
Uug
> yitznewton
10/01/2015 at 23:59 |
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Wider tires up front and narrower in the rear helps. The front may feel more floaty depending on how zealous you get with tire widths but the narrower rears will allow the car to rotate more freely.
I’m not sure if this has been mentioned, but a stiffer/beefier anti-roll bar in the rear will also help the car to rotate better. Too much stiffness will cause snap oversteer
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Übel
> DrJohannVegas
10/02/2015 at 00:06 |
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I had heard the shop was no longer producing the parts, so I just assumed the KermaTDI page was out of date. Those spring rates however, are great to have, thanks!
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yitznewton
> yitznewton
10/02/2015 at 16:20 |
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I found the Grassroots article: Aug 2008, p. 164