Gearing - Yet another post on the topic

[Craig Henry]

Gearing:

Back when I purchased new gears for my RF92 few, if any, were running a car with a LD200. As most know, LD200 gear options for autocross are not great compared to the MK9. Also, I re-read all the gear posts and I know gearing can be a controversial and/or personal choice. I liked Jim Garry’s data on minimizing shifting due to time loss. Back when I ran the S2’s I could use a tall 2^nd, because of the higher torque and rpm limit, and 90% of the time leave it there. With the FF, I’m likely going to have to shift a bit more and I would like to minimize this.

Questions:

• Kent engine: What is the maximum RPM you are willing to hit (abuse?) to enable you to “stretch” a gear to prevent a shift? I’m guessing 7000?
• What is the maximum speed obtained on a “fast” Lincoln course in recent memory?

What I purchased: (I’ve never run the car…)

1st: 13:37 46.4 mph @6800
2^nd: 16/35 60.4 mpg @6800
3^rd: 17/33 68.1 mph @6800
4^th: 17/30 74.9 mph @6800

I’m concerned I didn’t gear 3^nd and 4^th tall enough (4^th likely never being used.)

Thanks in advance for the help.

Craig

[chrisw52]

your gearing is largely dependent upon the ring and pinion you are running.

With the 10:31you are pretty much restricted to the 13:17 and the 16:35 for a 1st and 2nd gears. If you have a 9:31 R&P, you have more options.

[lowside67]

There are two schools of thought for autocross gearing - either gear to have a single 1-2 shift and remain in second, or plan to shift 1-2-3-2-3-2-3 etc.

In general, autocross is heavily dominated by the former - just gear for second gear - but mod cars are somewhat the exception to the rule given how easily and fast we can shift.

Our Van Diemen was geared for approximately a 72mph 3rd which was perfect. Dropping down to second we would get a worthwhile bump in acceleration out of tight corners and better throttle steering than if we had only been geared to 72.

In my opinion, your 1-2 are fine and you need a taller 3rd. In a pinch you could move your 4th to 3rd, but ideally it would be more in the 72 range. It's unusual to need more than that at nationals I believe but we touched rev limit plenty of times with our 3rd gear.

Hope that helps,
Mark

[Jim Garry]

Hi Craig! I agree with Mark.

Are you going to be autocrossing again?

[-pru-]

In my opinion, your 1-2 are fine and you need a taller 3rd. In a pinch you could move your 4th to 3rd, but ideally it would be more in the 72 range. It's unusual to need more than that at nationals I believe but we touched rev limit plenty of times with our 3rd gear.

In line with what Mark has noted, I like using all the gears in the box with my speed @ 6800 rpm as follows:

1 - 45 (mph)
2 - 60
3 - 75
4 - 90

That is, a 15 mph spread between gears. With this gearing, I find myself in 3rd between most elements shifting down to 2nd upon entering an element. I use 4th for a few courses a year, but not as often as in years past (i.e. course design has been "reigned in" so to speak).

Another school of thought is using a smaller spread between gears with top speed in the low to mid 80's (i.e. a fair amount of shifting):

1 - 45 (mph)
2 - 57
3 - 69
4 - 81

From what I have observed in CM, there seems to be a fairly even distribution of across the three gearing options (i.e. long: 1-2, medium: 1-2-3, and short 1-2-3-4). Really depends on how much shifting you're willing to tolerate.

[Craig Henry]

Thanks everyone,

My gut told me 3^rd and 4^th were a tad low (what was I thinking 13 years ago?) Also, my notes tell me I have a 9:31 R&P and all my gear spreadsheets were created based on this, but I still need to verify it. I’ll try to keep it to 6800 but I’ve been known to push engines at times to keep from needing to do a quick up and down shift. I never liked the 3^rd to 2^nd downshift in the MK 9 but I’ve heard rumors the LD200 box is much better?

Question: Is the LD200 capable of putting a tall 2^nd gear where 4^th is? I recall doing this in an old BM formula car that had a MK 9. Once you got to 3^rd it made any needed 3 – 2 – 3 shifts an easy straight shot. I think we had to grind the fork a bit to make it work.

I recall some VERY open “road” courses in Salina (back when pru was in a Vega) so it’s nice to hear that might be a thing of the past.

Jim, I’m trying to get the car back together. I’ve likely purchased $25K (don’t tell Susan) in new parts over the past 14 years. It has been Christmas every day unboxing all the new stuff I forgot I purchased… several duplicates too. Retirement has been great! I haven’t missed a single day of boarding a plane Sunday morning at 6:00 am and getting home past midnight on Friday 40+ weeks a year. Based on some recent posts, I get the impression you might be rejoining the CM group?

If I’m DFL too much the plan is to purchase a nice Piper Lance or M20J I’ve wanted for decades. My airplane fund went to Syracuse University Law school several years back... early on I balked but I did the math and it clearly showed the tuition was significantly cheaper than a divorce in the long run.

Thanks again.

Craig

[Jim Garry]

Glad you and I will be back in the class together!

[lowside67]

I never liked the 3^rd to 2^nd downshift in the MK 9 but I’ve heard rumors the LD200 box is much better?

Honestly it really is a non-event doing the 3-2 shift, even loaded up or in a busy autocross. I was quite worried about it but it took no time at all to get used to it.

-Mark

[Lynn]

My set up book is at the shop which is 20 minutes away, so I don't have the exact gear ratios which are in my Reynard. But it is geared for 1-2.

[CM/FFdriver]

I felt that the 1 - 2 shifting points would work well on these car because the Ford engine pulls so hard coming out of turns.

Back 5 years ago I tried the 1-2-3-4 shifting because some of the Autocross events at Crow's would be above 70mph and found hitting the rev limiter in 3rd is not fast.

I have tried the 1-2-3 shifting, with 3rd going to 75 mph and with Crow's landing event being 70mph it worked out great of late.

From MHO it really depends on the events you go to if you never get above 55 mph no point going to 3rd, learn to drive the car and your set up for black top payment and concrete, but you could learn to shift with out a clutch and use all 3 gears to become fast and efficient.

You could look on YouTube and watch some incar of the National's in the CM class and see different shifting points

Ben

[t walgamuth]

I just found this thread thanks to Clemens. It is great!

I thought I saw somewhere that a sequential shifter is legal in autocross....is this true? If so anybody with experience with them?

[Lynn]

Mechanical linkage only. No paddle shifters. Add 25 pounds to minimum weight.

[t walgamuth]

Mechanical linkage only. No paddle shifters. Add 25 pounds to minimum weight.

Ahah! 25# is a lot.

[CM/FFdriver]

Wait, CM can use a paddle shifter ?

Ben

[Jim Garry]

No.

[t walgamuth]

Wait, CM can use a paddle shifter ?

Ben

sequential shifter.

[JoeE]

I went a different route since my car is dedicated Autocross only and I am classed as AM just for fun but, didnt buy new letters yet. I have type1 VW out to 94x78 and VW transaxle. I had the trans built to have two (2) 2nd gears, normal 1-2 shift then across the gate I have 2nd gear ratio in 3rds position and a 3rd gear ration in 4ths position. Yes it took some doing on my builders part to pull it off. This works on small courses in stock 2nd gear and we also run it Pocono and there you need 70+ mph in a few sections. Right now I top out at 65ish in my current 3rd ratio.

Its working well but, I have a lot of power unused so I am upping my ring and pinion from 3.88 to 3.40 this offseason to get well into the 70's. To be able to shift between 2nd and 3rd without the gate crossing is golden. I just short shift across the gate from 1st once rolling from start.

[jrh3]

?nice to see the Banshee running. Lots of work and looking good.