Gearing

[mwizard]

We finished up the season of the American Autocross series this wkend. Yesterdays course was fast and hi speed. Competition was high both days, but I am happy to have been within about 1 sec of DM, EM and some well prepped XP cars. I was in 3rd for the 2nd half of the course, but Mike wood in his 88 Van Diemen was in 4th for part of the course(and about 0.6 sec faster than I was). This got me thinking, my top speed in 2nd is about 60.5 mph, 80 in 3rd. I am thinking of re gearing to 55 in 2nd and 70 in 3rd and planning on a bit more slow speed punch and a bit more shifting 2nd to 3rd. I know there have been some posts about this topic, but I wanted to bring it up again here in the off season to get an idea what others are running and opinions on the topic.
And I need a 16/30 LD200 gear set to make it work, so if anyone is willing to part with one, let me know.
Mark

[mwood]

Mark, I was 3-4/4-3 twice yesterday, once today on the backwards course. The Hewland allows such quick upshifts, I've become a believer in the 4 gear set up.

I ended up 33.25 yesterday, 32.50 today...given the old tires I'm on, I felt it was an ok showing. What did you and Chris get down to today? I told Chris I expected 31's, no problem, with your fresh tires and the temps coming down from the RG2 peak.

[mwizard]

Chris got 32.5xx and I got 33.134, so the new tires did not make the difference. Neither of us made 3rd gear today.
Mark

[Barry Ott]

I run the following:
1st - 13/37 - 46.1
2nd - 16/35 - 60.0
3rd - 16/29 - 72.3
4th - 18/28 - 84.3

note that my engine doesn't rev quite as high as yours ( I used 6750 for my calcs.)

I like the gearing, it pulls well after shifts and 2nd and 3rd both work well for those "in between" speeds where hard accel isn't needed. i.e. I tend to carry 3rd once I shift, until I really need to downshift.

Barry

[mwizard]

I run the following:
1st - 13/37 - 46.1
2nd - 16/35 - 60.0
3rd - 16/29 - 72.3
4th - 18/28 - 84.3

note that my engine doesn't rev quite as high as yours ( I used 6750 for my calcs.)

I like the gearing, it pulls well after shifts and 2nd and 3rd both work well for those "in between" speeds where hard accel isn't needed. i.e. I tend to carry 3rd once I shift, until I really need to downshift.

Barry

Barry,
Thanks for the info. I just ordered the 16/30 from Pegasus, but I like the 16/29 ratio better as I prefer a little more room to work with in 3rd, so I will call them tomorrow and change it. I look forward to sorting out the 2nd 3rd shifting for faster driving.
Mark

[mwood]

Chris got 32.5xx and I got 33.134, so the new tires did not make the difference. Neither of us made 3rd gear today.
Mark

You guys never got into 3rd? Wow. I grabbed 4th on one run, which ended up being my fastest. But, it wasn't like I was hitting the rev limiter in 3rd, just felt doing it...

If you're limited to 60mph in 2nd and didn't need 3rd, you guys must not having been getting a good run into the acceleration zone coming back from the first turnaround/sweeper...that may have been where that 31 was hiding

Hey, maybe it makes sense to plan your gear purchases to ultimately be able to run a 4 gear, just to have more options to play with? Who knows, you may get addicted to rowing the Hewland..I'm finding it to be pretty fun. Also, Chris and I both were commenting on the amount of lateral play in your linkage. Given you're going to be shifting 2X, you might think about going through the heim joints and other articulated joints in the linkage and see if you can find anything. All my heims are pretty new, so the shifter feels tight, but I do need to change the rear universal, as it has too much play. Even so, I had to go through all the angles of the heims to get my shifter to feel right.

[mwizard]

Mike,
You must have a really low 3rd and 4th. I am going to play with the 2 to 3 shifts up and back before I include 4th. I think a lower 2nd will help on some of the courses we get with pin turns. Isn't it fun to be able to just pop open a trani and change the gearing?
Mark

[Dave SanF 50]

What tire circumference do you guys use for the R25B when you are doing your speed calculations?

[Barry Ott]

good question, just checked. I *was* using 22.5, but the hoosier specs say 22.6, so I guess my numbers go up a couple tenths.

Barry

[mwood]

22.44" on my copy of the spreadsheet.

[Neil_Roberts]

These aren't R25Bs, but the mold is probably the same:

http://www.apexspeed.com/forums/show...01&postcount=5

[Dave SanF 50]

I tried using the "mark a spot on the sidewall/tread interface and then roll the tire one rev" technique. I then tried ten revs. Because of the tire growth with speed, this method proved inaccurate.

I found the best estimate was to get the "know and accepted" length of a given race track and compare that to what my data logger stated was the length. I then modified my tire circumference in the logger to give the known track length. Making the assumptions that 1) the measurement of the track was in the center of the track and 2) that I spend an equal amount of time/distance inside and outside the center line of the track.

I found the circumference stated in the tire brochure was a couple of inches less that what I calculated based on my track length method. That's a lot of growth.

In an AutoX environment with attaining only about half of road race speeds, I would not expect anywhere near that amount of growth (increased circumference).

Your thoughts?

[Dick R.]

Hoosier specs indicate 22.6 inch diameter, 71.0 approximate circumference for the current tires.

Or, roughly 892 revolutions per mile for our approximate speed in gear calculations.

FYI the Taylor gearing charts use 22.5 inch diameter.

I will be adding wheel speed sensors for both rear wheels to my DL1 inputs this winter in order to record wheel spin and/or lockup. Also a throttle position sensor.

Regarding tire growth in autocross I suspect "not an issue". I've never seen any data where gps speed exceeded calculated speed based on rpm, tire diameter, gearing. In fact in rapid acceleration segments gps speed tends to lag rpm based speed even with a 20Hz DL1. I'm guessing wheel spin and maybe some inherent aspects of gps speed calculations.

Dick
CM 85

[Dave SanF 50]

I have also seen guys use one rear and one front wheel for speed sensor locations (LR,RF).

The throttle position sensor: also known as the lie detector as in "I took that turn without lifting" so the sensor must be wrong. LOL

[mwizard]

Back to gearing. I was planning on using 15/36 for 2nd. It turns out my 15/36 is a fixed first gear, and the only other low 2nd option is a 14/36 which would produce a max speed in 2nd of 51, only 5 higher than my first. This seems too low and not worth paying $237 to give it a try. Is anyone else running 14/36 2nd(of course I am asking the autocrossers)?
According to the Hewland site, http://www.hewland.com/svga/ld.htm, the 15/36 fixed is not an available item. Is there another source for gears?
Mark

[Dick R.]

The throttle position sensor: also known as the lie detector as in "I took that turn without lifting" so the sensor must be wrong. LOL

Yep! I get some indication from longitudinal g's actual throttle position is probably more accurate/direct.

My reason for both rears is relative rear wheel rpm is what I think I "need". I don't expect both rears "spinning" very often after they hook up after a hard launch. At some point I may add a front wheel sensor since the DL1 has 4 frequency channels available.

Dick

[rrobb]

Taylor Race.
Not a bunch of fixed firsts available for the ld200 though.

[Neil_Roberts]

...speed in 2nd of 51, only 5 higher than my first.

That's way too close for the 1-2 drop. This may not be worth anything, but here is the speed for each gear that I use:

49 59 69 79 mph typical courses
49 59 79 99 mph with monster straights

[Dick R.]

That's way too close for the 1-2 drop. This may not be worth anything, but here is the speed for each gear that I use:

49 59 69 79 mph typical courses
49 59 79 99 mph with monster straights

Neil and Barry (or anyone),

When using a 59/60 or so mph gear on fresh 25B's have you monitored wheel spin with D/A or otherwise? Also, Barry since you tend to "stay" in your 72 mph gear have you monitored the typical "out of the corner rev range" and whether there is any wheel spin in the corners where you don't go back to the 60 mph gear?

Thanks,

Dick

[Neil_Roberts]

When using a 59/60 or so mph gear on fresh 25B's have you monitored wheel spin with D/A or otherwise?

Wheelspin? Oh my yes, but I've only run on used R35As so far. The RPM vs mph plot looks like a bowl of spaghetti instead of the clear, straight lines that you get on a road course or a gear chart. It doesn't settle down while braking either, since there is considerable slip then as well. Not even an autox 4th gear shows a clear line on the graph.

[mwizard]

That's way too close for the 1-2 drop. This may not be worth anything, but here is the speed for each gear that I use:

49 59 69 79 mph typical courses
49 59 79 99 mph with monster straights

Neil, Looks like you use all 4 gears. My new set up will be 46 60 73 88 as the gearing I wanted to make 2nd a bit lower is not ava. and I have the new 4th. I will try this and can change to a lower 4th later.
Getting a set of 25b's on your car should help with the wheel spin.
Mark

[chrisw52]

All this talk on gears and I am now questioning my "optimal" gear setup.

I have enough gears to handle a 47, 55, 65, 82 setup or 47, 59, 74, 98 (4th gear is almost irrelevant in this setup)

The problem is for the "short" gear setup, I need to use a 15/36 2nd gear which is really small... smaller than the 14/36 non-fixed first gear I have in my pile..

Is that 15/36 going to be strong enough to handle the torque in 2nd gear? FWIW, this will be in a LD200

[Barry Ott]

Neil and Barry (or anyone),

When using a 59/60 or so mph gear on fresh 25B's have you monitored wheel spin with D/A or otherwise? Also, Barry since you tend to "stay" in your 72 mph gear have you monitored the typical "out of the corner rev range" and whether there is any wheel spin in the corners where you don't go back to the 60 mph gear?

Thanks,

Dick

Honestly, My setup isn't close enough to where I want for me to comment. Specifically, I'm still trying to minimize wheelspin to get it to drive like the Reynard used to. i.e. Miata, digital throttle

[mwizard]

All this talk on gears and I am now questioning my "optimal" gear setup.

I have enough gears to handle a 47, 55, 65, 82 setup or 47, 59, 74, 98 (4th gear is almost irrelevant in this setup)

The problem is for the "short" gear setup, I need to use a 15/36 2nd gear which is really small... smaller than the 14/36 non-fixed first gear I have in my pile..

Is that 15/36 going to be strong enough to handle the torque in 2nd gear? FWIW, this will be in a LD200

Chris, I was planning to use a 15/36 I had in stock but it turned out to be a fixed 1st and there is no 2-4 gear 15/36 set listed. There is a 15/30 listed so I would think it would be strong enough. How do you get 55mph in 2nd? That would be my first choice to handle the "funky" course elements we sometimes see.
Mark

[chrisw52]

Chris, I was planning to use a 15/36 I had in stock but it turned out to be a fixed 1st and there is no 2-4 gear 15/36 set listed. There is a 15/30 listed so I would think it would be strong enough. How do you get 55mph in 2nd? That would be my first choice to handle the "funky" course elements we sometimes see.
Mark

for one of the two the gear selector spread sheets you emailed me, I am using a 22.4" tire diameter. Then for my estimated shift points, I am using 6600 rpm as a hypothetical max rpm.

[Dick R.]

Honestly, My setup isn't close enough to where I want for me to comment. Specifically, I'm still trying to minimize wheelspin to get it to drive like the Reynard used to. i.e. Miata, digital throttle

Interesting. I assume you couldn't just "floor it" out of all cornering situations without wheel spin . . . right?

Of course if you and Neil cannot dial out wheel spin with fresh 25B's it "must be" all that Honda torque.

Dick

[mwizard]

Live and learn, I guess. I took my car trani apart this afternoon with help from a local FF road racer, Dave Jalen. I was expecting to put in 16/29 for 3rd and a 18/27 for 4th. What I found in my trani was a 16/30 for 3rd and a 17/28 for 4th. I can not remember how I came up with my idea of what my gear set was but this one is lower geared than I was going to change to, so I left all the existing gears. I have 46.2 mph max in 1st, 60.3 in 2nd, 70.3 in 3rd and 80.0 for 4th. I am going to try more shifts with this setup and have fun.
Mark

[DanW]

Live and learn, I guess. I took my car trani apart this afternoon with help from a local FF road racer, Dave Jalen. I was expecting to put in 16/29 for 3rd and a 18/27 for 4th. What I found in my trani was a 16/30 for 3rd and a 17/28 for 4th. I can not remember how I came up with my idea of what my gear set was but this one is lower geared than I was going to change to, so I left all the existing gears. I have 46.2 mph max in 1st, 60.3 in 2nd, 70.3 in 3rd and 80.0 for 4th. I am going to try more shifts with this setup and have fun.
Mark

Mark,

Its always helpful to have someone like Dave to go through a gear change with you for the first time. Now you know what you have. Write it down on your setup sheet so you will know for next time.