downshifts

[Jarrod]

we are running a manual shift, having trouble convincing our guy to use a clutch on downshifts, anyone got opinions, stories to relate, suggestions etc.?

[clausen]

Hi,

With a dog-box, which is what all motorbike gearboxes are, clutchless shifts are fine as long as they are done properly (match revs, etc).

Regards

Paul Clausen
Uni of Adelaide

[Moeye]

Have to rev match a little on the downshifts, or it's a rough corner entry with the back end skidding about.

[Jason Hickman]

In the 5+ years I had of driving formula
SAE cars, I never used the clutch for downshifts... We never had any transmission related problems.

With the relatively low engine braking associated with these cars, a properly executed clutchless downshift, does little to upset the chassis.

Plus it frees up your driver's left foot to experiment with and learn left foot braking, which I have always felt was the fast way to go in these cars.

Downshifting method:



full braking

blip throttle while still on brake (about 30 to 40% in our cars)

Grab downshift

the blip and downshift should almost be simultaneous.

Good luck!!

Jason
Univ. of Florida Alumni

[Jarrod]

compression locking the rear wheels was the big concern, but since we run a hand operated clutch anyway (left foot braking is the only way to go), hook up up the clutch and gear shift on a single mechanism, or separate but linked, (think UTA butterfly shifter) can eliminate the issue of rev matching with inexperienced drivers. Testing time is an issue here in OZ as Im sure many can attest.

[Angry Joe]

If a new guy is abusing your transmission, I suggest beating him repeatedly with a quickjack until he learns. We don't tolerate abuse from newbies.

If that doesn't seem like a diplomatic option, make sure he fixes that transmission when he busts it, and pays for the new parts.

Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Denny Trimble]

Yeah, we break in the newbies on courses with no shifting. Then, when they keep sticking around and showing promise, we let them shift. Setting up a 2nd & 3rd gear only course has worked well for us, because 1-2 is the easiest shift to get wrong. Still, we usually have to replace 2nd gear when we rebuild one of our motors.

University of Washington Formula SAE ('98, '99, '03)

[Big Bird]

We were clutchless shifting last year, (CBR motor), some drivers more aggressive with it than others. Put out of the final endurance event with a locked gearbox. Apparently due to a bolt holding the gear selector coming loose, but still I think all those load spikes transferred through the gearbox couldn't have helped.

It's a big risk assuming that your drivers can manage to learn clutchless shifting properly, and manage it successfully on race day and under race day pressure. Our drivers this year will all be using clutch at risk of them being beaten with very big stick if they don't. Or a quick jack, (thanks for the good idea Angry Joe).

Cheers,

Geoff Pearson
RMIT FSAE 2003

Design it. Build it. Break it.

[Sam Zimmerman]

I still don't like the clutch less downshifts not only because it is hard on the transmission, but I do not think that you get as efficient an entry into the corner, most likely because my skills are at the level where I would like them to be.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Carl Lopez from Going Faster!
A lot of inexperienced drivers rush into trying to shift without a clutch, mostly to be like the big guys...leave it up to the individual to decide when they, (and their transmission maintenance budget), are ready to move on to clutch less shifting.
Keep in mind that in downshifting there is no lap time advantage in shifting without the clutch...Getting the car into the lower gear a tenth of a second faster than the competition doesn't necessarily mean that the braking process is going to take a tenth of a second less.<HR></BLOCKQUOTE>

I keep in mind that while the "big guys" may not use the clutch, there are a lot of guys better than I who use their clutches religiously.

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[D Mack - CMT]

Hey Geoff,
You always resort to the big pipe over the head tactick. I remember that about you. hehe.
So does that mean you guys are going to use all the gears in your arsenal? I kind of reckon you will mostly be using 2 gears, 3 at most. Am I drunk for thinking this way?

[Gareth]

How do you rev match w/o clutching on a sequential gearbox?

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Sam Zimmerman:
...most likely because my skills are at the level where I would like them to be.
<HR></BLOCKQUOTE>

Sorry, I just saw a typo. The above should read, "most likely because my skills are not at the level where I would like them to be." That one little word made a big difference. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[Jason Hickman]

I am still against clutched shifts... As I said before, we never broke a transmission, but we did spin a clutch (due to drivers trying to be "smooth"). A properly executed clutchless downshift does not upset a FSAE chassis (or shouldn't for that matter).

The only time you should use the clutch is the start. This is where clutch abuse really comes in,I dont mean drop the clutch at 10,000 rpm, I mean slipping the clutch (trying to maintain a constant rpm, near torque peak, while controlling power to the rear wheels with the clutch), this has and always will be the quickest way to get off the line.

That said, spend your time teaching your drivers to drive smooth, without the clutch. You will find that it will be easier for them to concentrate on the turning, braking, and throttle application, if they dont have to try to modulate the clutch for a "smooth" downshift.

Anyway, thats just my $.02.

Jason
Univ. of Florida Alumni

[shiny side up!]

I agree with Mr. Hickman on most counts but the 'throttle blip' under braking. That certainly isn't necessary (and is counter productive, methinks...).

As for the Carl Lopez quote above, I doubt he was talking about driving with the same type of transmission that FSAE cars are using.

If a driver is more comfortable with using the clutch and has no real racing or motorcycling experience, then using the clutch is the way to go. But once you are getting into the intermediate range of FSAE drivers, it is probably time to ditch the clutch. Not that you absolutely have to clutchless shift to be fast, but it does allow you to left-foot brake, which will, in the end, get you that last few tenths/hundredths. There is a reason that 95% of CART and F1 drivers left-foot brake...

This year, lets put the engine back up front where it belongs!!