FWD touring cars and understeer

[Sodemo]

Hello,

Just a general question really. How do FWD cars limit or reduce power understeer? I am speaking both with current TCR / NGTC regulations and things like S2000 or SuperTouring?

I know with SuperTouring that they had some pretty elaborate diffs, Rob Huff said that when driving the 1998 Nissan he said that being on the power actually helped steer/pull the car through the corners. Can anyone offer an opinion or elaborate on that?

From my own research, I have read that front drive tourers (supertourers) have approximately a 67% front aero bias which undoubtedly helps, this came from an article on the 1998 Alfa 156. I know also that *some* cars had stiffer rear springs and had virtually zero rear squat (anti squat).

Thanks.

[Johno.UK]

NGTC cars are very different from TCR cars in that they have inboard shocks with rocker arms whereas TCR cars are very much like their road going equivalents. No idea what that means in terms of the question but I remember BTCC drivers posting on other forums that the setup of an NGTC car is "weird".

This article - https://www.roadandtrack.com/motorsp...s60-wtcc-test/ - seems to be the opposite of Huffs Nissan which I guess shows that there is a big difference between how each car handles it.

"The really important part of driving the car is the braking," Björk tells me. "You have to brake as late as possible, straight into the corner, and then just get the right speed, and really carry the brake into the corner. A lot of trail-braking to the apex. If you don't do that, the car will end up in a big understeer. It doesn't like to be pulled through the corner on the throttle. That's the key to being really fast.

[antnee]

Limited slip diffs make a huge difference - I had one on an Alfa 147 and if you planted the throttle mid-roundabout, it would pull in tighter. Quite a strange sensation but one I did not get bored of.

Also, 9" wide slicks help on race cars with TCR and NGTC being 350-400bhp, that isn't a great deal more than you can get on FWD road cars (Cupra Leon for example)

[V8 Fireworks]

The short answer is they have lots of mid-corner chassis oversteer dialled-in, and therefore adding throttle adds understeer to widen the line for a tidy corner exit.

The power understeer in a front wheel drive race car, is no worse than the power oversteer in a rear wheel drive car! Both can be managed by throttle technique and throttle steering, albeit obviously the throttle steer behaves oppositely.

Chassis oversteer (i.e., soft front, stiff rear) and then adding understeer with throttle in the front wheel drive, versus chassis understeer (i.e., stiff front, soft rear) and then adding oversteer with throttle in the rear wheel drive. Logically, you want softer suspension on the driven end of the car for maximum traction, being the front on a FWD and the rear on a RWD. Of course, with the FWDs a lack of rear tyre temperature paired with the stiff rear suspension can result in massive slides in cold conditions!

[Sodemo]

Some of the setup data which I have seen would seem to tally with that.

For example, a lot of the supertourers ran about -5 camber, some ran -6 (Mondeo - Prodive), however some didnt run that extreme camber at all, some ran only about -3.5 at the rear (the Volvo S40), but ran a softer spring, equal to the front end. Virtually all cars ran less front camber. The one thing that is common across most cars is that they ran softer front springs than the rear. I think the Nissan's ran about 100nm at the front and about 160nm at the rear.

The Nissans ran about -4 front, -5 rear. Volvo -3.5 front, -3.5 rear. Hondas -4 front, -5.5 rear. I was never really sure why they ran so much rear camber, I thought initially it was to get rear temps up, but I am not that sure to be honest.

The ARBs I am unsure as often on the setup sheet they just state if its stiff or soft or have a colour code, so there isn't a figure to quote on those, but the Vectra data I saw did have a number and it was 103-370Nm/DEG front, 80-843 Nm/DEG rear, so I think the rear ARB was quite a bit stiffer than the front.

[GregUK]

Originally Posted by Sodemo

The one thing that is common across most cars is that they ran softer front springs than the rear. I think the Nissan's ran about 100nm at the front and about 160nm at the rear.

Spring rate doesn't mean so much per se. When comparing one car against another, what's more important is the resultant wheel rate (which is affected by spring locations/angles etc etc)

[br21]

Yes, exactly, you have different motion ratio on front and rear, different suspension design front and rear so you can't compare springs rates directly. Rears are quite light in TCR cars also, and biggest reason for big rear camber is to generate some heat in the tires.

[Trikes]

I Track / Hillclimb / Time Attack and Super Sprint a 04 Honda Integra Type R. Bought it with a decent pedigree from Interstate (here in Australia). It had some U/S traits which I wasn't happy about and I wasn't happy with the Lap Times. Whilst I did measure Wheel Rates and a few other things (just to bring me up to speed with the the car) the obvious thing to me being from racing 'other' FWDs - namely a Proton Satria GTi which ran rings around the Honda in any corner but hit the straight and it's all over for the GTi. Anyway I settled the U/S thing down by installing stiffer Rear Springs in (16's to 20') (Fronts are 16's). Lowered the R/C. Set the Front Toe Out at 2.0 and the Camber at 2.7. Rear has Toe In (just a little) with the wheels pretty much vertical. F/R ARB are the same size. Did just one thing at a time and the Results were a much improved car. I did have a chat with my tyre Supplier and I run M (255) up front with GS (Softs) (235) on the rear. Diff is a 1.5. I have full grip at both ends of the car about 80metres from the Start Line in most Weather. I have the car a little O/S on Turn In with the back end controlled with left foot on the brake pedal. Power is then added and once I spot the Apex the right foot is mashed to pull the car straight. It's that simple. I recently had a leading Mini Driver jump in the Honda and after two drives he said the car was 'sharp, very sharp in the steering'. To add something else I can outsmart myself and waste a lot of time by trying to work out everything but I've always used mind picturing of 'how can I go flat out through that corner'? Then I get out there and try some thing's. In a nutshell I fixed the U/S by making the back end come around sooner and in a controlled manor. It's now a case of 'What Understeer'? Honda went from being 2.5+ seconds outside the Lap Record to lowering them by 1.8 seconds plus in one season. It's regular Class winner and is always in the top few Outright. Any questions??? Fire away......