Sanity check...When do y'all shift? Gearing calculations...

[Tremelune]

I'm building a car that will be driven up mountains and down canyons and through twisty forests...It will spend as little time as possible stuck in traffic going from light to light. I expect it will spend most of its life between 3-6k rpm, revving up and down between turns...like a road race car, but with a slow racer at seven-tenths with the stereo on...

This seems to be unusual. When I tell people I'm going with 4.11 rear gears (with 26" tires) and a TKX, they seem to think I'm in stump-pulling territory, but my charts indicate otherwise...Like, I don't think I want 2nd gear going to 70mph just to go from 2500 rpm to 2200 rpm at 75mph in 5th...I don't think I'd ever hit redline in 3rd!

Red is the close-ratio gears with 4.11 rears, pink is wide-ratio gears with 4.11 rears, and orange is close-ratio gears with 3.54 rears (which is what is commonly recommended).

Is there something I'm missing? I'm benchmarking against other sportscars I've had whose gearing I liked, and 4.11s with the close-ratio TKX seems closest.

https://ensaster.com/pics/vehicles/cobra/transmission/tkx-gearing.png

[Gordon Levy]

gearing depends on your engine, where you make power and the weight of your car. The Roadster is 2300lbs, in no universe do you want or need 4:11 gears.

[rich grsc]

Get the 4:11's, put a really strong hitch on the rear, then you can plow the neighbors gardens. :p:rolleyes:

[Mastertech5]

You'll have so much torque with 4.11 gears that the tires are going to break loose whenever you get on it. Like Gorden says 2300 lbs. and go slip sliding away. A little Paul Simon there.

[Its Bruce]

The Roadster is 2300lbs, in no universe do you want or need 4:11 gears.

He didn't specify which planet he'd be driving up mountains and down canyons and through twisty forests...

[GoDadGo]

I'm running 3.73's and I love them; however, I've got a 6-Speed in my car.
(.75-5th & .50-6th)
With a TKX 5-Speed most folks, myself included, would suggest going with 3.55's

[scrubs]

I have a whopping 28 miles on my car and I seem to usually shift ~3-4k rpm.

[Jeff Kleiner]

Do the math.

TKX can be had with a 3.27 first gear or a 2.87. Fifth can be .68, .72 or .81

In my experience after having built and driven a bunch of these cars something in the range of 2.95-2.87 first coupled with a 3.55 rear is ideal, resulting in an overall reduction of ~10.2-10.4:1 On the other end I like around .7:1 fifth which results in ~2.4-2.5:1 overall.

For a first gear comparison:
3.27x4.11=13.4 overall
2.87x4.11=11.8 overall

For fifth:
.81x4.11=3.32 overall
.72x4.11=2.95 overall
.68x4.11=2.79 overall

Curious what the "benchmark" sports cars are that you're using for comparison.

My opinion; even with a 2.87 first and 4.11s you'll often find yourself looking for second about the time you get across the intersection. But you do you ;)

Jeff

[john42]

When do I shift? hold it to the wall, 6500rpm every time, every shift!

Just kidden :-)

[Al_C]

My 2 cents: if you haven't purchased or installed the rear end yet, go with 3.55s. With that gearing, I bet you can do all the twisty, hilly stuff in 3rd gear. It would be like driving an automatic, only better. 4.11s, you'll probably do everything in 4th gear. Just a guess. As to when I shift, it is rare that I look at the tach. Most of the time, I shift by sound or feel. I guess that's because I grew up with manuals and I'm old. Whatever.

[GoDadGo]

On curvy flat back roads (No Hills Cuz It's Flat Down Here) I'm typically in 3rd, 4th and 5th. 1st is just used for stop signs and stop lights, 2nd is used to embarrass folks playing the stop light game, while 6th is only for the Interstate Speeds of 70 MPH or higher. The sweet spot for my engine is between 2,500 & 6,000 RPM.

3.73 Rear Gears & 26" Tall Tires
Trans Ratios - 1st-2.68, 2nd-1.80, 3rd-1.29, 4th-1.0, 5th-0.75, 6th-0.50, Reverse-2.50

Hope this helps and sorry if it doesn't.

[Hoooper]

I just put 3.90s on mine with close ratio TR6060 trans, gears are 2.66/1.82/1.30/1.00/0.76/0.50, R888R tires. Redline shifting 7800, cruising shifting about 3000 or less. I like it, and it is a great match in my opinion for my engine and build setup with 600hp/500lbft. An engine with more low end torque wouldnt be as good of a match, my peak torque isnt until almost 5500 rpm although it does make over 350 lbft starting at about 2000 rpm. Some answers you will get come from 427s which might be making 50% more than that at 1500 rpm, so knowing what you are working with is important.

If you run some all season tire or even just a regular high performance summer tire you probably will find traction an issue in 1st and 2nd, maybe even 3rd, but that also will heavily depend on engine choice, tire temp, etc. I am not sure where you are sizing up 26" tires but my 315/40 R18 R888Rs installed and weighted work out to about 24.5". If you are planning on very rarely or never using the freeway your setup will be fine. If you do cruise the freeway much I think the fairly high 2500 RPM or so freeway cruise will be annoying.

One thing to keep in mind, builds vary DRAMATICALLY on here and you will be getting answers from people with completely different builds from yours. We need to know your engine choice, tire choice and size, suspension choice, and more about how you plan to drive it when not on the backroads to be able to give an answer that is actually useful

[Tremelune]

All fair. When I read about gearing, I see a lot of posts of people cruising around town in 4th at 40mph/1500rpm and then racing gearing discussion...without much in between.

I'm building a narrow-body, so the tires are around 205/70-15. The drop from 26.3" to 24.5" is 7%, and the drop from 4.11 to 3.73 is 9%. Fairly comparable.

I learned that the Jaguar IRS carrier changes above 3.73, so I think pegging that as my tallest makes sense instead of 4.11. This is my first rodeo, so I'm trying to walk well-worn paths.

The engine I'm building should have peak torque somewhere around 4500-5000rpm, and peak power at a redline of 6000rpm.

High RPM and frequent shifting is where the fun is for me. I'm alone on a windy road, listening to the machine sing the song of my people.

The green line is an E-Type jag with like 260-280hp...The slope aligns with 3.54 gears, but the shift points at speed align more with the 4.11 gears due to the lower redline of 5500rpm.

https://ensaster.com/pics/vehicles/cobra/transmission/jag-gearing.png

[GoDadGo]

Treme,

What are your proposed specs?

Displacement
Camshaft Specs
Intake Style
Compression
Head Specs
Headers vs J-Pipes
Induction Method (Carb vs Fuel Injection) Etc.

I don't drive around near the peak torque RPM which keeps me out of the ditches.

Steve

[edwardb]

...This is my first rodeo, so I'm trying to walk well-worn paths...

If that's the case, then you need to use 3.55 or 3.73 max. You've gotten responses from builders/drivers (Gordon and Jeff for starters) who have been at this for years with hundreds of builds and certainly well-worn paths. I've done builds with 3.27, 3.55, and 3.73. I personally agree 3.55 is the sweet spot for these builds. Which is why it's the most popular. 4.11 is too low.

[AA-ron]

I have a Ford Racing 302 (@360hp) and running a T-5 and 355’s. The bulk of my driving is on hilly back roads including mountain road driving through the Whites in NH and I can’t imagine a better set up. In truth, even with my somewhat mild motor, I only shift when I want to and not because I need to. By that I mean the car is so light and I have enough torque to muscle through most hills in just about any gear. However when I get on it and tach it up, it’s beyond fun.

[gbranham]

You're overthinking this. Your car will weigh 2300 pounds, give or take. Nearly any popular gear ratio will work fine. While I applaud you for jumping all in on the project, I think you're stuck in Analysis Paralysis on this.

[Mbufford]

He didn't specify which planet he'd be driving up mountains and down canyons and through twisty forests...

With the gravity on Mars, 4.11 could be perfect.

[CraigS]

I am assuming you have driven other cars on these roads. So what speeds did you usually attain and in which gears? I found w/ both 351 and 408 I liked using 3rd gear the most. And speeds on twisties might get to 80 in a few cases so that worked out fine. But I will say my engines were more TQ than HP and never ran >6000. And my country roads still have houses etc on them here and there so I liked running up to 80 when I could but preferred to do that relatively quietly so I could be doing 80 but no one noticed.

[Papa]

I have lots of time in my car in Colorado's mountains and 3:55 gears. Most of the mountain driving is at 40-50 miles/hour with exception of the hairpin turns where you're coming down to 15-20 miles per hour. Almost all of that is in 2nd or 3rd gear unless things level out and I go into 4th. I rev pretty high in 5th gear at 75+, and wouldn't be able to drive on the highway for long at all at those speeds with 4:11s.


https://youtu.be/LHrVKurPujw

[GFX2043mtu]

3:55 or 3:31 is what you want with any old style v8. As I said the exception is if you are using a voodoo or high reving +7k rpm motor of low displacement that needs to rev out to make torque. Otherwise all you will do with a 6k rpm 427 CI or similar motor is shifting and break tires loose.

[J R Jones]

I see video examples (including here) of people driving (and shifting) for the sake of shifting, not as required.

In high school my buddy's parents bought him a 66 Mustang 289 manual. He wanted to put loud mufflers on it and his father said "No, you will pound it just to hear the exhaust". He was right.
That era of muscle cars led me to road racing and really pounding the car until I learned that just pounding did not lead to winning, preservation of consumables is required, and smoothness delivers results.

Despite the OP description of use, I predict the majority of operation is in high or higher gears. Lower gears, especially 1st is of little consequence.
Later in life I evolved from muscle cars to small cars, small engines, and 5/6 speed manuals which delivered performance better than automatic transmissions. I found to match or exceed traffic acceleration, I launched in 1st gear with moderate throttle, shifting to 2cd and 3rd with WOT to reach my intended speed, then shift to 5th or 6th. Downshifting is avoided as long a I can maintain speed with engine torque.

There is a lesson observing automatic transmission function. Downshifts occur when power alone is not adequate to meet the throttle demand. However, with my thirsty 494ci 18,000lb RV, the cruise control will demand a downshift when a little patience and throttle modulation will hold speed adequately without adding 1100RPM frenzy with third gear. So much for cruise control artificial intelligence.
jim

[Bart Carter]

The 427 Cobra first tested by Car and Driver did 69 MPH in 1st gear. Just saying...

[Hoooper]

The 427 Cobra first tested by Car and Driver did 69 MPH in 1st gear. Just saying...

It was also a 4 speed and had a curb weight over 2500 lbs. CURB WEIGHT. Skinny low traction tires compared to modern tires, a rather lengthy 4.3s 0-60, etc. Some things about the original are OK to stay in the past

[BRRT]

The OP mentions using a Jaguar IRS carrier. What car is he building?

[Bart Carter]

It was also a 4 speed and had a curb weight over 2500 lbs. CURB WEIGHT. Skinny low traction tires compared to modern tires, a rather lengthy 4.3s 0-60, etc. Some things about the original are OK to stay in the past

My comment was meant to get people to think about not having too low a first gear. With the power to weight ratio of these cars, you should have a tall first gear. The first gear in my Ford GT (550 HP and 3495 lbs curb weight) goes to 60 MPH with no downside.

[hineas]

I did the same thing and played with a ton of different gear ratios. I thoroughly enjoyed it. I don't think you are over analyzing, but just considering all your options!

I made a similar spread sheet that does the same thing as your graph but just a different display. I made a copy in my Google drive and made it public access if you're interested.

https://docs.google.com/spreadsheets/d/1uAEJZBHfPHrFAgwpApmMPO-Iuxg1ypuEuLdD12qY7rM/edit?usp=drivesdk

Here is my take, and I have only built one of these cars and have 7,000 miles on it, so take it for what it's worth.

First off, I haven't researched that tire size. Will it fit? I know clearances are tight, so I just wanted to make sure. But I think the tire size you can get from FFR with the kit is slightly taller (26.6) so it should work.

I put your expected tire size in my calculator and assumed you get the 0.68 5th gear. Where I live the interstate is 80 mph. Cruising at 80 mph with 4.11 will have an rpm of 2858. Cruising at 65 mph will give you an rpm of 2322. If you get the 0.81 5th great 80mph is 3,404 rpm and 65mph is 2,766 rpm.

On my car I have the 3.55s with a 0.64 5th gear and 25.7" tires. I am at 2379 rpm at 80 mph. At 65 mph I'm at 1933 rpms, which I love. To be frank, for cruising at 80 mph, I wish my rpms were lower, but my rpms are perfect for cruising at 65. I personally wouldn't want higher rpms in 5th grear.

Would you be fine with 4.11s? Absolutely, but only if you are going with the bigger tires and won't be spending a lot of time above 65.

However, your initial question was about shifting. I accelerate moderately quickly but stop at the speed limit. When I'm pulling onto a 55 mph road, I shift from 1st into 2nd around 40 mph, then I shift from 2nd to 5th at 55-60 mph. I skip 3rd and 4th.

This is a little less fun because I skip all the gears, but I wouldn't change my gearing because I would loose comfort cruising at 65-80 mph. Also, shifting more would slow down my 0-60 times since I only have to shift one time from 0-60.


On the otherhand, because the car is so light I cruise in 4th gear on 25 mph roads and 5th gear on 35 mph roads each at about 1000 rpms. Even then I can still go uphill without shifting because the car is so light compared to the engine power, and I only have the 347.

Lastly, if you go with the 3.73s like you are thinking and the 0.68 5th gear, you will be at 2107 rpms at 65mph and 2593 rpms at 80 mph. Much better in my opinion. Me personally, I would prefer the 3.55s, but only you can choose what you want. I do think you would be happy with either.

Sorry for the rambling post, it is 1:00 am... I hope it made sense!

[Hoooper]

My comment was meant to get people to think about not having too low a first gear. With the power to weight ratio of these cars, you should have a tall first gear. The first gear in my Ford GT (550 HP and 3495 lbs curb weight) goes to 60 MPH with no downside.

Ford set it up so that the magazines wouldn't have to shift before 60 when getting their 0-60 times. That was pretty common when all the performance cars were manual since obviously shifting during the run when your competition didn't have to it's a big time penalty. If 0-60 is your goal a long 1st gear is definitely the way to go, or if you're using 1960s tech tires and transmissions. If not, it makes more sense to focus on the driving experience as a whole. If he is canyon driving he's likely to spend almost none of that time in 1st.

[Tremelune]

The first gear in my Ford GT (550 HP and 3495 lbs curb weight) goes to 60 MPH with no downside.

Not having to shift until highway speeds is itself a downside...Half of the fun on a windy road is rowing through the gears!

I have a car that hits 70mph in 2nd, and I find those gears to be noticeably too long. It's more fun to drive my older car with less power that hits redline in 2nd at 60mph.

It seems I would rather have less power and shorter gearing than the opposite. There's only so much internet rumination one can do, though...I'm just gonna choose something reasonable, see how it feels, and go from there.

The roads matter a lot, too, and that's hard to translate from one person to the next.

[hineas]

Not having to shift until highway speeds is itself a downside...Half of the fun on a windy road is rowing through the gears!

I have a car that hits 70mph in 2nd, and I find those gears to be noticeably too long. It's more fun to drive my older car with less power that hits redline in 2nd at 60mph.

It seems I would rather have less power and shorter gearing than the opposite. There's only so much internet rumination one can do, though...I'm just gonna choose something reasonable, see how it feels, and go from there.

The roads matter a lot, too, and that's hard to translate from one person to the next.

I think this is perfect. Only you know how you are going to drive it. Each of us builds the car we want for how we will drive it, not the car someone else wants.

Luckily, in the grand scheme of things, it is feasible to change gearing if you don't like what you choose.

[Bart Carter]

...I have a car that hits 70mph in 2nd, and I find those gears to be noticeably too long. It's more fun to drive my older car with less power that hits redline in 2nd at 60mph...

If you tell me what transmission you will be using, or at least the gear ratios in it, I can give you the speed in each gear at at max torque and HP with different rear ratios.

For instance, based on your given tire diameter of 26.4, your 6,000 RPM red line and a T5 2.95 1st gear set, your speeds with a 3.55 rear would be:
1st 45
2nd 68
3rd 99
4th 132
5th 210 (theoretical)

Your RPM drops from 6,000 RPM would be:
1st to 2nd, 4,000 RPM
2nd to 3rd, 4,100 RPM
3rd to 4th, 4, 500 RPM
4th to 5th, 3,800 RPM

Simply a matter of putting in the data and calculating.