Is the 3.70 diff just too much?

[I12XLR8]

I have been running the 3.70 GXP differential for just over a year now and I'm wondering if it's just too much gear for my needs. I mainly run the car as a DD and any off road performance driving is on the road track instead of the drag strip. The road track allows me to pick whatever gear suits me best so the rear gearing is somewhat irrelevant until I hit the high speeds and I'm assuming it holds me back.

I have been thinking of switching back to stock or maybe a 3.27 for just a little kick. The trouble is that the 3.70's feel incredible in almost all situations and as an added bonus they keep me out of the dreaded drone-zone on the highway. This car is going to feel like a Silverado once I change back, I just know it.

Here's my question...do I gain anything under 150mph by going with lower gearing? Assume I only care about top end and nothing about fuel economy...does it make sense to lower the gearing?

[ULTRA Z]

I want a 3.70 or 3.73 gear so bad when funds are better I will probably go to the 3.73 gear for my camaro rear

[I12XLR8]

I may not have phrased this properly. I would like to know if on the road track straights will I gain speed at my top end if I am not pushing the limits of 6th gear? Or in other words, if I ALWAYS have a few thousand RPM left in 6th would dropping back down to a taller gear gain me anything?

[Doug Hilliard]

I don't think it would gain you anything if you've still got revs to burn on the top end in 6th. It would improve your gas mileage though!

[Eidolon]

Can you define what you mean by "top end" here?

If you mean top speed, your gearing determines top speed by max vehicle speed at highest gear and max RPM. Dropping your final drive will obviously increase your theoretical max top speed, BUT because it reduces the mechanical advantage of your driveline, it also increases the time that it takes you to get there and also increases the chance that you won't have the power to overcome wind and tire resistance and driveline loss.

So theoretical max is up, but achievable may be down. It's the difference between 150 MPH in 1 mile versus 170 MPH in 2 miles when you've only got 1 mile to work with.

The one case I can see where switching back to a lower gear might come in handy is that the higher 3.70 gearing will reduce the amount of time you can actually spend in each gear, so you'll spend more time shifting. If you feel you're spending less time right in the power band and more time shifting back and forth hunting for the sweet spot with your gears, then dropping to a lower final drive might help.

As an example, if you go to hit the gas coming out of a corner and find you have to shift pretty much immediately, dropping down to a lower final drive may help because, while acceleration generally will be more sluggish, your lap time may still drop because you save time by staying in the power band coming out of the corners and not interrupting the power delivery by shifting.

[I12XLR8]

I do mean top speed. I'm currently running Calabogie (link in sig) mainly in 4th and 5th, with a short bump into 6th on the back straight. Shifting hasn't been an issue and is made even easier with the paddle shifting.

My 'concern' is with faster tracks like Mosport (also in sig) where I have a long back straight but have only been able to hit around 140mph. I still have room left in 6th before I have to shut it down but it's not still pulling hard then, although it is still pulling. However, I have been told that better tires will get me onto the straight at a higher speed and allow me to get closer to the exit turn before having to let off which will help a lot.

The car feels really strong in 4th and 5th and I don't want to lose that but with the 2.92's I could just run most of the courses in 3rd and 4th and likely retain it. I just don't want to switch back and feel that the car is slower then regret it. It's a tough one...

[SpeedRacerX]

I do mean top speed. I'm currently running Calabogie (link in sig) mainly in 4th and 5th, with a short bump into 6th on the back straight. Shifting hasn't been an issue and is made even easier with the paddle shifting.

My 'concern' is with faster tracks like Mosport (also in sig) where I have a long back straight but have only been able to hit around 140mph. I still have room left in 6th before I have to shut it down but it's not still pulling hard then, although it is still pulling. However, I have been told that better tires will get me onto the straight at a higher speed and allow me to get closer to the exit turn before having to let off which will help a lot.

The car feels really strong in 4th and 5th and I don't want to lose that but with the 2.92's I could just run most of the courses in 3rd and 4th and likely retain it. I just don't want to switch back and feel that the car is slower then regret it. It's a tough one...

Are you competing against yourself (improving your time for personal reward) or other cars (either all together on the track or individually running)??

Next question: if competing against other cars, where are these races won/lost - on the straights or on the twisties??

What percentage of potential time or positioning gain can be attributed to making improvements in the straights versus making improvements in the twisties??

To me, race = purpose-built. Wreckwriter's car could probably start in the corner at 0 mph and blow by you at the middle or end of the straight even with your head of steam coming out of the corner BUT in the corners, not so much.

See where I'm going with this?

[I12XLR8]

I am on the track for 100% personal reward. I have not even bothered to time my laps except through my videos, and that is only to find a place for myself amongst the record holders :-)

As for what happens on the track, I have no issues on the straights as not much on the track can keep up with me there. This is just lapping so there are not many true performance vehicles out there (with the occasional exception that puts me in my place). I feel that I do well in the corners but so far have only been running the stock RS-A's so now that I have real rubber I will do much better. Coming out of the tight corners feels strong and I am not left wanting.

So, what is the problem then if everything seems fine? I really think that for ALL of the different driving I do that the short gears might be overkill. I am just try to gauge how changing the gearing will affect the events where I most enjoy driving the car...

[SpeedRacerX]

OK, some salient thoughts...

- Could the LSD itself be holding you back in turns? I hear that some roadcourse folks like the idea of a True Track or some other diff that more effectively locks and gets more power to the ground.

- You're just touching 6th now, which is an overdrive gear. On the longer track, you'll get farther into 6th with the 3.70. You will get even farther into 6th with less gear. Do you really want that? Aside from extra heat on the transmission, it's doubtful you'll reach the car's top speed but at least with the 3.70, you're getting near it, quicker.

- Today, you have to look at where the car shifts coming into the turn and out of the turn, where the RPMs are, etc to decide if the gear ratio is proper for the track you are on OR for the overall experience you like. If not and it bothers you, I would address it.

Overall, I think you are asking a question that is very difficult to answer. Unless there is something glaring holding you back, every road course track would require different gearing.

If you feel that you're not doing unnecessary shifting in turns, are in the right power band in the twisties, that you can utilize the power the car can deliver, and you aren't banging against the rev limiter on the straights, I would leave it alone.

I would also not make a decision until the new tires are on. That should make a big difference too.

[Eidolon]

I feel that I do well in the corners but so far have only been running the stock RS-A's so now that I have real rubber I will do much better. Coming out of the tight corners feels strong and I am not left wanting.

So, what is the problem then if everything seems fine? I really think that for ALL of the different driving I do that the short gears might be overkill. I am just try to gauge how changing the gearing will affect the events where I most enjoy driving the car...
I think I have to agree with SpeedRacer below...


I would also not make a decision until the new tires are on. That should make a big difference too.
This. I'd stick to one thing at a time. Change too much and you lose the sense for what the changes do for you. So I'd get a feel for the new tires and how they do for you before you swap up gears.

[Semperfire]

How are the BC's set up on the track days?

[I12XLR8]

Thanks, guys! I knew I needed to wait to run the new tires but lost sight of that. I'm good now ;-)

Semperfire - In the summer I have the car lowered about 1" and when at the track I put the BC's at 5 shy of full firm, front and back. With the sway bars removing most of the understeer and the bushings keeping everything tight the car feels pretty good. Once I stop sliding around as the suspension starts to push up against the new tires I'll be able to see where I have to upgrade next for my driving style.

Can't wait!

[WhatNext]

You are running RSAs on road courses!? Do let us know how things improve with new tires. BTW what are the replacements?

Another little thing to help figure out your gearing - On the long back straight where you feel you might be running out of rpms, compare that to your peak HP rpm (from a dyno curve). This would be a way to see how far beyond the peak HP you are and then see what specific gear changes would do to get you closer to the peak.

But since you mentioned that you were still pulling (with 3.70 gears at that), there probably isn't much to gain.

[I12XLR8]

I know, I know. Before I even got to the track I was told to run street tires so I don't push the car too hard. The RS-A's are noisy in the bends and let go AFTER they start screaming which is exactly what a rookie needs.

Now that I have a little experience with the car and my home track I'm going to start using Pirelli p-zeros (a set of wet, and a set of dry slicks). I'll slowly push my comfort zone until I find the cars limit. I'm in no rush to drive in the dirt ;-)

As for my top end I don't think that will be a concern at Calabogie but I will pay close attention to what is happening at Mosport and decide on gearing then.

[Semperfire]

Semperfire - In the summer I have the car lowered about 1" and when at the track I put the BC's at 5 shy of full firm, front and back. With the sway bars removing most of the understeer and the bushings keeping everything tight the car feels pretty good. Once I stop sliding around as the suspension starts to push up against the new tires I'll be able to see where I have to upgrade next for my driving style.

Can't wait!

Sounds good what bushings do you have? Curious how you have the sways as well?

[WhatNext]

Hey, that's the smart thing to do, dial in your car one step at a time. I do understand your starting with the RSAs, they protest just pushing them on curvy roads. But let you know when getting to their limits.

I enjoy following all the road racers on the boards. That's the best info on what works and what doesn't.

[I12XLR8]

Sounds good what bushings do you have? Curious how you have the sways as well?

Rear cradle bushings and differential bushings. I have the sways set a full stiff in the front and in the middle in the rear. As far as I can tell this is the best setting to 'cure' the built in factory under-steer. The car handles sooooo much better through a corner when set up like this. Just be careful though, the front end cuts tighter which I would imagine could cause the ass end to slide out if you're hitting it too hard.

[Semperfire]

Thanks for the feedback I am always curious about what works like whatnext said roadcoarse guys are generally set up different than go fast 1320 guys

[I12XLR8]

Hey, that's the smart thing to do, dial in your car one step at a time.

It is the smart thing to do but it doesn't scratch the itch that I always have ;-(

[Eidolon]

I have the sways set a full stiff in the front and in the middle in the rear. As far as I can tell this is the best setting to 'cure' the built in factory under-steer. The car handles sooooo much better through a corner when set up like this.
Huh. I've actually ended up with mine fully soft up front and fully stiff out back. With that setup, the car's initial response to too-aggressive throttle tip-in mid-corner causes the front to start to push, but just a bit more and the tail will get busy. Then again, that was with the Eibachs. I haven't tried setting anything up with the coilovers yet.

I'd initially tried fully soft front, middle setting on the rear, but that resulted in howls of pain from the front tires through every corner. It's been a year and a half since that outing, but as I recall, it just didn't have the front-end grip I wanted. With the current setup, it's actually hard to get a squawk, ever. I think my last instructor thought I wasn't pushing the car because the tires didn't make noise. Then again, I guess it's possible my front end grip is actually reduced because less roll resistance is transferred onto the front wheels.

You settled on where you're at now after a good bit of hunting, I'm guessing.

[I12XLR8]

Huh. I've actually ended up with mine fully soft up front and fully stiff out back. With that setup, the car's initial response to too-aggressive throttle tip-in mid-corner causes the front to start to push, but just a bit more and the tail will get busy. Then again, that was with the Eibachs. I haven't tried setting anything up with the coilovers yet.

I'd initially tried fully soft front, middle setting on the rear, but that resulted in howls of pain from the front tires through every corner. It's been a year and a half since that outing, but as I recall, it just didn't have the front-end grip I wanted. With the current setup, it's actually hard to get a squawk, ever. I think my last instructor thought I wasn't pushing the car because the tires didn't make noise. Then again, I guess it's possible my front end grip is actually reduced because less roll resistance is transferred onto the front wheels.

You settled on where you're at now after a good bit of hunting, I'm guessing.

Damn it, Kevin! As soon as I think I've read all there is to read, then put it into practice with success, you go ahead and shake things up! ;-P

I will try your set-up this spring and see what it feels like. I'd like to say that my decision was based on many track hours on different settings but that couldn't be further from the truth. I just knew that it felt way better than both at full firm or full soft.