Garage Project: Is Your Clutch Pedal Slowing You Down?

Photography Credit: Kevin Adolf

Want lower lap times? Right now, you can spend a few minutes dialing in the action of your clutch pedal. It’s an easy garage project.

When trying to trim down lap times, explains James Clay, president of BimmerWorld, properly timing the clutch engagement is very important. 

And to do that,” he continues, “it is critical to put the stop just slightly below the release of the pedal. Too high and you wear out your clutch or, worse, your transmission synchros. Too low and there is no way you can get your pedal timing right, and the long travel will take too much time–plus, you also beat up your clutch and driveline because of shock caused by poor timing.”

The data backs up those claims. An accomplished driver can shift gears in half a second, Clay says. “A driver that is good and focused on shifting quickly takes 0.4 seconds,” he adds. “Our gold standard for a pro-level driver with some lighter-weight equipment–clutch and flywheel–is about 0.25 seconds.”

So, about those faster lap times: The BimmerWorld team has found that those quicker shifts can raise straightaway speeds by up to 3 or 4 mph. 

Here’s the data to back up those claims. These graphs compare two drivers on VIR’s back straight. 


Click on either graph to open in a new window.

From the top, the data cells show speed on track, throttle pedal position, engine speed, and total time gained/lost. The lower chart is just a zoomed-in version of the top one. “The zoom better shows the resolution of the throttle trace and rpm spike in that shift,” Clay explains. 

Before the first shift on the back straight–third to fourth–both drivers are approximately the same speed,” he explains. “After the first shift, the blue driver is 2 mph faster than the red immediately.”

Clay dives deeper into the data: “In this shift, red comes off throttle at 1:19.766, back on at 1:20.269–almost exactly 0.5 seconds. Blue comes off throttle at 1:19.928, back on at 1:20.269–about 0.3 seconds.”

Note that clutch pressure would be an interesting data point also,” he continues, “and the blue driver shows the negative effects of shifting too fast: trying to jam all the actions of the sequence in. 

The ‘shift tail’ in the rpm graph shows that the driver overlapped pedals–a big no-no. The clutch pedal was already going down before the throttle pedal was fully released, although you can see in the graph that it was more of an issue of inertia than late throttle release. 

Nevertheless, this is one of the ways that shifting fast can damage the engine, clutch, or driveline–although adjustment of a proper clutch stop does make this much easier to time.

Over the duration of the full back straight, and with no other factors in these runs, faster shifting and the increased terminal mph achieved has made the blue driver, who came onto the straight slower, a total of 0.3 seconds faster in this straight alone.  

Add the front straight and the shorter middle straight and you just put at least half a second in your pocket through proper equipment adjustment and perfecting technique.”

To help dial in that clutch action, BimmerWorld has developed its “Junior Puck” Clutch Stop. It replaces the stock, tiny clutch stop–about the size of a quarter–with a meaty one based on a 2.5-inch-diameter junior hockey puck. Retail price is just $19.95, and it simply threads into place, replacing the factory stop. 

Why go wider in the first place? The heat of battle plus worn pedal bushings make it possible to miss the tiny stock stop and simply press the clutch pedal too far. The BimmerWorld stop is also longer than stock, as it’s designed to accommodate aftermarket equipment. 

There is a tremendous art to shifting a manual car properly and fast, and from years of selling these parts and coaching drivers, I see a wide range of talent and prowess,” Clay adds. “The clutch stop is a small but critical piece in setting up even a stock clutch system that is fast and functional.”


Photography Credit: Kevin Adolf

Wait, you might be saying, I don’t have a BMW but I’d still like to get in on this action. If you can add the appropriate threaded bung, you can add this clutch stop. (And really, could you make one this nice for less money? BimmerWorld already picked out a stop that’s the right size and hardness.)

If adding your own mount, we suggest strengthening that part of the floor with some extra sheet metal or at least some fender washers. 

We fit the BimmerWorld to our BMW 318is project car–a super-simple job–and we have made our own for other cars over the years. It’s one of those little details that add up to a dialed-in machine.

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Comments
View comments on the GRM forums
_
_ Dork
4/1/20 4:06 p.m.

This was cool. And informative. 

David S. Wallens
David S. Wallens Editorial Director
4/1/20 4:15 p.m.

In reply to _ :

Thank you, thank you. James knows a lot about stuff. 

Matt B
Matt B UltraDork
4/2/20 11:07 a.m.

Yeah I thought this was going to be about how "automatics are faster now blah blah blah".

I was happy to be wrong.  Good stuff.

Tyler H (Forum Supporter)
Tyler H (Forum Supporter) UberDork
4/2/20 11:39 a.m.

Great article!

BMW clutches definitely have a unique feel, especially coming from Japanese stuff.  The initial breakaway is a little stiff and then very light, with a long pedal throw.  I put these clutch stops in both my E46 and E36 and it made a world of difference.  

One of the biggest advantages to the wide stop is that the OE stop is so flimsy, if you put any lateral force on the pedal while its on the stop, it will slip past the stop and stick to the floor.  Never fun to have to reach down and pull the pedal back up in the heat of things.  Had that happen with both the E46 and E36 before adding a meaty stop.  

Truly one of the best $20 upgrades you can do to any BMW.  

Greg Smith
Greg Smith Dork
4/2/20 1:55 p.m.

I too expected this to be a pro-auto trans piece. Neat stuff!

Cactus
Cactus Reader
4/2/20 3:22 p.m.

I can think of a simpler solution, if your clutch is allowing slowing you down, quit using it altogether. Get a dogbox, quit wasting valuable time either being gentle with your synchros or rebuilding a gearbox with them because you're not gentle. An auto-manual/dual clutch can speed you up incrementally from there, but a dogbox is the ultimate for purist cred.

buzzboy
buzzboy Dork
4/2/20 4:17 p.m.

My e36 came with one of these installed. First modification I made to the car was removing it. It couldn't be adjusted far enough to let the clutch fully disengage. I still have to tell people, "clutch bites at the floor" and that's without the clutch stop.

ShinnyGroove
ShinnyGroove Reader
4/2/20 6:22 p.m.

Headed to the garage to investigate the clutch stop on my Miata.  Great article, thanks for posting.

David S. Wallens
David S. Wallens Editorial Director
4/2/20 8:09 p.m.
Matt B said:

Yeah I thought this was going to be about how "automatics are faster now blah blah blah".

I was happy to be wrong.  Good stuff.

Ha, didn't even think about that when writing the title. Glad you're all digging the piece. Major props to James for the help. This piece actually started out as something very different, but what we all wound up with is way better. 

Durty
Durty Reader
4/3/20 8:45 a.m.
buzzboy said:

My e36.... I still have to tell people, "clutch bites at the floor" and that's without the clutch stop.

Would that be improved with a new throwout fork or something? Biting at the floor seems like a problem that I have experienced in other e36 as well. 

Tim Suddard
Tim Suddard Publisher
4/3/20 9:44 a.m.

In reply to Durty :

Sounds lke there was something wrong with buzzboy's clutch. I have made this great, cheap mod to many of my project cars.

 

APEowner
APEowner Dork
4/3/20 10:07 a.m.

I would not have guessed that shift speed would make that big of a difference.  It makes perfect sense and I have no trouble believing the data.  I guess I heard, or read somewhere that shift speed isn't very important in road racing and accepted that at face value.

I'm going to bump fixing the soft 5th\reverse gate detent on the Miata up on my to do list.  I've adopted a slow, shift with my wrist, technique on my 2-3 shifts to avoid 2-5 shifts.  If that gate detent was firmer I could speed up my shift time significantly. 

I don't think I'm pushing the clutch pedal beyond the disengagement point but I'm going to take a close look at the data to see what my shift times are in the other gears. Perhaps I could benefit from a clutch stop.

frenchyd
frenchyd PowerDork
4/3/20 11:20 a.m.

In reply to David S. Wallens :

Or you can skip using the clutch pedal completely  except to get rolling. 
Use dog ring gears.  ( non syncro )  

Your  shifts become massively faster.  Basically  you just slam the lever either up or down. ( more detail in a bit) 

For decades race cars have used these.  
 

No you can't use this on the street unless you intend to drive like a jerk  If you try using dog rings while using the clutch pedal plan on replacing gears very frequently.  
A normal transmission has syncros. They are tapered brass ( usually)  cones that speed up a gear to match revolutions and allow the gears to slide together.  ( without the crunch you hear when the syncro is worn out) 

dog rings are straight cut gears with a notch on the side that catches the next gear to match speed and then lock in.  If you shift it as slow as you shift a syncro gear the notches bounce off each other and won't engage.  Persist and you'll round out the notch Possibly enough so it won't stay in that gear and spread a lot of metal through the gear box. It's worse if you have the clutch disengaged. 
 It works best at full throttle, say shifting from 2 nd to 3rd  you slightly hesitate for a nano second. As you slam the gear lever forward. The faster and more brutal you do it the better the gears look after  the race. No clutch 
Downshifting  is a little different,  when you are ready to shift for that same Nano second  you floor the throttle and jam the lever down a gear. No clutch  

Actually  on downshifts  if you know the transmission there is a certain revolution you can jam the lever down a gear and it snicks together so sweet  you'll want to pat yourself on the back. Still don't use the clutch 

One other advantage to a lot of dog rings. Like a quick change rear end you can just take the back end off. Slide the whole stack of gears out, mix and match them and slightly change ratios very quickly.  Let's say you come out below the power curve in one corner. You change change it to be exactly where power is best. 
 

Using that approach you can over cam your engine to gain peak power but over a narrower power band.  
 The result is faster lap times. 
Most 5& 6 speed transmissions have 5 & 6 th gear as over drives not useful gears on the race track. Without losing the time syncro's cost you on a shift  you can shift so fast it's a continuous surge of speed.  

CrashingTiger
CrashingTiger New Reader
4/3/20 12:14 p.m.

In reply to buzzboy :

I still have to tell people, "clutch bites at the floor" and that's without the clutch stop.

Yeah, that's a  problem with your clutch somewhere. It shouldn't be doing that. 

buzzboy
buzzboy Dork
4/3/20 2:49 p.m.

It bites just off the carpet and has for 50k miles since I've owned it. I don't want to mess with it.

sir_mike
sir_mike New Reader
4/7/20 7:57 a.m.

I've done this to both my MK2 Cortina's.Mainly because on the one the original carpet padding has gone away and that made the pedal go in to far and the other because there is no carpet.It's a fix that really did work for my cars.And being hydraulic clutches the pistons cab go in to far and bottom out.A stop sets things right.

snailmont5oh
snailmont5oh Dork
4/7/20 11:48 a.m.
frenchyd said:

In reply to David S. Wallens :

Or you can skip using the clutch pedal completely  except to get rolling. 
Use dog ring gears.  ( non syncro )  

Your  shifts become massively faster.  Basically  you just slam the lever either up or down. ( more detail in a bit) 

For decades race cars have used these.  
 

No you can't use this on the street unless you intend to drive like a jerk  If you try using dog rings while using the clutch pedal plan on replacing gears very frequently.  
A normal transmission has syncros. They are tapered brass ( usually)  cones that speed up a gear to match revolutions and allow the gears to slide together.  ( without the crunch you hear when the syncro is worn out) 

dog rings are straight cut gears with a notch on the side that catches the next gear to match speed and then lock in.  If you shift it as slow as you shift a syncro gear the notches bounce off each other and won't engage.  Persist and you'll round out the notch Possibly enough so it won't stay in that gear and spread a lot of metal through the gear box. It's worse if you have the clutch disengaged. 
 It works best at full throttle, say shifting from 2 nd to 3rd  you slightly hesitate for a nano second. As you slam the gear lever forward. The faster and more brutal you do it the better the gears look after  the race. No clutch 
Downshifting  is a little different,  when you are ready to shift for that same Nano second  you floor the throttle and jam the lever down a gear. No clutch  

Actually  on downshifts  if you know the transmission there is a certain revolution you can jam the lever down a gear and it snicks together so sweet  you'll want to pat yourself on the back. Still don't use the clutch 

One other advantage to a lot of dog rings. Like a quick change rear end you can just take the back end off. Slide the whole stack of gears out, mix and match them and slightly change ratios very quickly.  Let's say you come out below the power curve in one corner. You change change it to be exactly where power is best. 
 

Using that approach you can over cam your engine to gain peak power but over a narrower power band.  
 The result is faster lap times. 
Most 5& 6 speed transmissions have 5 & 6 th gear as over drives not useful gears on the race track. Without losing the time syncro's cost you on a shift  you can shift so fast it's a continuous surge of speed.  

My dog box is based on a T-5, and the builder told me specifically not to shift fast without the clutch. There is no intermediate bearing, that the forces involved would cause problems. 
 

That said, my Fairmont has a cable clutch, so it has no "free play" the engagement distance is set completely by the condition/material of the clutch disk, and the distance off the floor is set by adjusting the length of the cable. 
 

Shifting quickly involves putting a little preload on the shift handle, then moving the clutch until the shifter moves (usually about half way through its travel). As soon as the shifter starts to move, MOVE IT NOW to the next gear. "Snick!"  The clutch is already on the way back out. 
 

Watch the first two seconds of this video for one of my early attempts at shifting fast. It *can* happen faster, if everything goes right. 
 

 

David S. Wallens
David S. Wallens Editorial Director
5/2/20 11:28 a.m.

Sorta related, but today I'm expecting a box from Dublin, Virginia. 

frenchyd
frenchyd PowerDork
5/2/20 12:28 p.m.
snailmont5oh said:
frenchyd said:

In reply to David S. Wallens :

Or you can skip using the clutch pedal completely  except to get rolling. 
Use dog ring gears.  ( non syncro )  

Your  shifts become massively faster.  Basically  you just slam the lever either up or down. ( more detail in a bit) 

For decades race cars have used these.  
 

No you can't use this on the street unless you intend to drive like a jerk  If you try using dog rings while using the clutch pedal plan on replacing gears very frequently.  
A normal transmission has syncros. They are tapered brass ( usually)  cones that speed up a gear to match revolutions and allow the gears to slide together.  ( without the crunch you hear when the syncro is worn out) 

dog rings are straight cut gears with a notch on the side that catches the next gear to match speed and then lock in.  If you shift it as slow as you shift a syncro gear the notches bounce off each other and won't engage.  Persist and you'll round out the notch Possibly enough so it won't stay in that gear and spread a lot of metal through the gear box. It's worse if you have the clutch disengaged. 
 It works best at full throttle, say shifting from 2 nd to 3rd  you slightly hesitate for a nano second. As you slam the gear lever forward. The faster and more brutal you do it the better the gears look after  the race. No clutch 
Downshifting  is a little different,  when you are ready to shift for that same Nano second  you floor the throttle and jam the lever down a gear. No clutch  

Actually  on downshifts  if you know the transmission there is a certain revolution you can jam the lever down a gear and it snicks together so sweet  you'll want to pat yourself on the back. Still don't use the clutch 

One other advantage to a lot of dog rings. Like a quick change rear end you can just take the back end off. Slide the whole stack of gears out, mix and match them and slightly change ratios very quickly.  Let's say you come out below the power curve in one corner. You change change it to be exactly where power is best. 
 

Using that approach you can over cam your engine to gain peak power but over a narrower power band.  
 The result is faster lap times. 
Most 5& 6 speed transmissions have 5 & 6 th gear as over drives not useful gears on the race track. Without losing the time syncro's cost you on a shift  you can shift so fast it's a continuous surge of speed.  

My dog box is based on a T-5, and the builder told me specifically not to shift fast without the clutch. There is no intermediate bearing, that the forces involved would cause problems. 
 

That said, my Fairmont has a cable clutch, so it has no "free play" the engagement distance is set completely by the condition/material of the clutch disk, and the distance off the floor is set by adjusting the length of the cable. 
 

Shifting quickly involves putting a little preload on the shift handle, then moving the clutch until the shifter moves (usually about half way through its travel). As soon as the shifter starts to move, MOVE IT NOW to the next gear. "Snick!"  The clutch is already on the way back out. 
 

Watch the first two seconds of this video for one of my early attempts at shifting fast. It *can* happen faster, if everything goes right. 
 

 

A. T5 gearbox still has the syncro cones. What has been done  is the old hot rodders trick of grinding out every other tooth in the  slider.  It's not a true dog ring. 
Seinz and Hewland are two dog ring gear boxes. And at least Seinz tells you not to slow shift .  ( I haven't called anybody at Hewland ) 

I had to replace gears after every track session when the original owner  insisted on using the clutch to shift. luckily with a Seinz you can do it like a quick change rear end,  take the back off slide the gears out clean out the metal shavings etc and slide in a fresh set of gears.  Laying on the grass in the pits it's about a 15-20 minute job. On the bench it's about 5 minutes. 
Look at the engagement method.  Basically there are open "boxes" where the gear slides over and catches the next gear. The sides of the "boxes" are back cut at an angle to hold the gear in. Lifting the throttle like you do with a normal syncro has the effect of speeding up one gear relative to the other making engagement more difficult. down shift you "floor it" to speed up the lower gear in the micro second the dogs are apart. 

Once he gave up and gave me his old box I had One fresh set of gears  in the box. And a few spare gears. Instead of  replacing the gears every session I raced using that gear box for decades. Still shifts very crisp and stays in gear. On the original set of gears. 
One other advantage to a true dog ring gear box is you only ever use the clutch to get rolling. I have a triple disk 7&1/2 inch Tilton clutch it's been used for more than a decade at somewhere around 40 races without replacement. I'm tempted to reuse it. In my next race car. While there is some wear about 1/2 of the friction material is still there and the floater disks still look usable 

snailmont5oh
snailmont5oh Dork
5/2/20 2:33 p.m.

In reply to frenchyd :

Here's a pic of the inside of my G-force T-5. It's a true dog box.

 

frenchyd
frenchyd PowerDork
5/2/20 3:33 p.m.

In reply to snailmont5oh :

Yes it is. Didn't know anyone was doing that. 

noddaz
noddaz UltraDork
5/2/20 7:10 p.m.

 

 

 

 

snailmont5oh
snailmont5oh Dork
5/2/20 7:32 p.m.
noddaz said:

 

 

 

 

I think every single one of us understands scope creep. 
 

David S. Wallens
David S. Wallens Editorial Director
5/2/20 7:57 p.m.

BimmerWorld order has landed. smiley

msterbeau
msterbeau New Reader
5/3/20 9:05 a.m.

How does one adjust the stop correctly? 

I would put the car up on jack stands, get it close to where I think it should be and then use an assistant outside the car telling me when the drive wheels start turning (Obviously the car is running) to dial it in. Something like that?  Is there an easier way?

wspohn
wspohn Dork
5/3/20 10:56 a.m.
msterbeau said:

How does one adjust the stop correctly? 

I would put the car up on jack stands, get it close to where I think it should be and then use an assistant outside the car telling me when the drive wheels start turning (Obviously the car is running) to dial it in. Something like that?  Is there an easier way?

Park on a slight hill in first gear with engine off. Put a block a couple of inches behind the back tire or in front of you are nose down (and a handy assistant as a failsafe if you like).

Install the stop in the car. Push down the clutch pedal. Keep adjusting the stop inward until the car rolls against the block when you push the pedal in.  Done.

Vigo (Forum Supporter)
Vigo (Forum Supporter) MegaDork
5/3/20 10:45 p.m.

Most cars have unsynchronized reverse so it's pretty easy to tell the clutch engagement point in most cars by just holding the shifter in a specific spot where reverse is not engaged but the gears are touching. When the clutch starts to engage you'll feel it through the shifter as the moving gear starts to clash against the stationary one.

weedburner
weedburner Reader
5/4/20 11:13 a.m.
David S. Wallens said:


Click on either graph to open in a new window.

From the top, the data cells show speed on track, throttle pedal position, engine speed, and total time gained/lost. The lower chart is just a zoomed-in version of the top one. “The zoom better shows the resolution of the throttle trace and rpm spike in that shift,” Clay explains. 

“Before the first shift on the back straight–third to fourth–both drivers are approximately the same speed,” he explains. “After the first shift, the blue driver is 2 mph faster than the red immediately.”

Clay dives deeper into the data: “In this shift, red comes off throttle at 1:19.766, back on at 1:20.269–almost exactly 0.5 seconds. Blue comes off throttle at 1:19.928, back on at 1:20.269–about 0.3 seconds.”

“Note that clutch pressure would be an interesting data point also,” he continues, “and the blue driver shows the negative effects of shifting too fast: trying to jam all the actions of the sequence in. 

“The ‘shift tail’ in the rpm graph shows that the driver overlapped pedals–a big no-no. The clutch pedal was already going down before the throttle pedal was fully released, although you can see in the graph that it was more of an issue of inertia than late throttle release. 

“Nevertheless, this is one of the ways that shifting fast can damage the engine, clutch, or driveline–although adjustment of a proper clutch stop does make this much easier to time.

“Over the duration of the full back straight, and with no other factors in these runs, faster shifting and the increased terminal mph achieved has made the blue driver, who came onto the straight slower, a total of 0.3 seconds faster in this straight alone.  

“Add the front straight and the shorter middle straight and you just put at least half a second in your pocket through proper equipment adjustment and perfecting technique.”

 

The most telling thing I see in graphs is the engine rpm traces. It's obvious that the quicker driver made more power thru the shift, evidence of that is in the rpm flare. The engine's rotating assy absorbed energy during the shift which is what caused the flare, then the car was able to transfer that added flare energy to the track without spinning the tires. The result was more power applied to the track over the same time period. Pedal stop adjustment may have had a hand in changing the driver's timing to create the flare, but harnessing that rpm flare without breaking traction is what made him faster.

I actually have clutch pressure data on my car, and also have a way to adjust the rate that the clutch actually engages. The main benefit of being able to adjust clutch engagement rate is the ability to reduce the intensity of energy transfer between the rotating assy and chassis, to a level that doesn't cause the tires to break traction. Most customers are using my ClutchTamer and Hitmaster clutch control devices in a drag racing setting, but some road and rally guys are also using them as more efficient alternatives to the Tilton Flow Control Valve

Grant

 

 

msterbeau
msterbeau New Reader
5/6/20 2:21 p.m.

In reply to wspohn :

Nice.  Thanks.  

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