Gearing combos...

Just curious as to what ring & pinion/top gear/tire size combo people are running in their cars? What cruising speed range-mph at 3000-4000 rpms (in top gear), motor size (and specs if you don't mind) and observations; is your cruising speed enough? do you think your motor size and power is enough for said cruising speed range? Any other comments you feel add to the discussion?
Thanks in advance. Al

A 0.89 fourth and 3.88 ring & pinion is a common combo, along with 185/65-15 tires (24.5" diameter).
This combo will give you the following:
60 mph = 2857 rpm
70 mph = 3333 rpm

My car is an anomaly. I have the 185/65-15 tires and .89/3.88 combo, but my tach reads 3700 at 70 mph. I think my tach is out, but I just had it re calibrated, so I'm not sure what's going on.

If I had it to do again I would have gone with the 3.44 ring and pinion. Mind you, I have a big engine with plenty of torque.
Ron

Ron,
You had your tach calibrated but did you have your speedometer calibrated. At 3,700 RPM's, your speed is 77 MPH.

My speedo is off. I used my GPS. At 3800 rpm my speedo shows 75 mph, but my GPS shows 69 mph.
Ron

Something isn't right, Use this gear calculator link and it will give you speed and RPM's based on your tire size and gearing

http://www.scirocco.org/gears/

Yeah, I'd check with a different GPS unit. Your gearing, tach, and speedo are all in agreement.

No, my speedo is wrong. I've used two GPSs and the results have been the same. My next step is to hook my laptop up to my fuel injection computer and go for a drive. One of the gauges shown in the fuel injection profile has a rpm reading, which should be very accurate. I'll compare it to my dash tach.

Thanks for the info Ron. As you say, it's a common combo. I have a Berg 5 with a 3.88 r&p,1.58 3rd, 1.21 4th and the choice of either the .89 or .82 for 5th. According to the gear calculator I'm using, the  useable range of the 1.21 is 43-62mph (2800-4000 rpm). With the .82, 2800rpm doesn't happen until 64mph. I consider 2800rpm the "minimum constant engine speed" for highway cruising (much lower and the fan isn't turning fast enough for proper cooling), so 60mph in 5th would be about 2600rpm, and 62=almost 2700rpm; still doable, I suppose. But I am wondering if the gap isn't a little too big? As Ron knows, 100kmh (62mph) is the posted speed on a lot of highways in southwestern BC; that would be 4000rpm in 4th. I do have a .89 I could throw in there, but speed at 3500 would drop from 80 to 74mph (which, for my licence and wallet, might not be a bad thing...).

 

I do have a 1.48 3rd and 1.14 4th I could put in, but I don't like what that does to the 2-3 spacing with the 2.25 2nd. The 3.44 r&p with the .89 would work well as well, but the $350 cost and then sending it to Berg's to be lengthened...

 

Anybody with 2100 cc's and above: what do you think of your gearing? Any one using a .82 as top gear? I think I have to plot out the stock 3-4 gear spacing...stay tuned...