twobone Posted August 16, 2012 Share Posted August 16, 2012 Everyone has a different set of variables from tire size to rear axle and gear box. I think I'm geared very low with my 185/60/13 tires and 4 speed box At 60mph, what are your RPMs? Mine is about 3,800 Link to comment Share on other sites More sharing options...
bsimon Posted August 16, 2012 Share Posted August 16, 2012 For comparison... 3350@60MPH in Direct. 2900@60MPH in Over. 225/50/16 3.92 axle I drive on the expressway in Direct unless I'm going faster than 80. Overdrive is just too friggin' noisy to be comfortable. Link to comment Share on other sites More sharing options...
dvl Posted August 16, 2012 Share Posted August 16, 2012 I'm predicting an engine speed of 3748 RPM for my car at 60mph (I'll verify when it's finally finished), with a 4 speed, 185/60/13 tires, and a 3.90 to 1 rear final drive ratio. I hope this helps, Dave Link to comment Share on other sites More sharing options...
Ian7 Posted August 16, 2012 Share Posted August 16, 2012 Everyone has a different set of variables from tire size to rear axle and gear box. I think I'm geared very low with my 185/60/13 tires and 4 speed box At 60mph, what are your RPMs? Mine is about 3,800 Very typical for a 4-speed Kent. Your engine isnt happy down low anyway, its not a modern fuel-injected torque producer, and FormulaFord guys run them between 6000 and 7200. Link to comment Share on other sites More sharing options...
Kitcat Posted August 16, 2012 Share Posted August 16, 2012 TwoBone, at 3800 rpm my X-flow Cat w/5sp on 15" wheels was doing abt 75 mph. Fifth was a nice cruising gear. Link to comment Share on other sites More sharing options...
twobone Posted August 16, 2012 Author Share Posted August 16, 2012 I wish I was going 75! I thought I heard the top gear of a 4 speed and a 5 speed T9 were pretty much the same. Maybe I need a different rear axle ratio Link to comment Share on other sites More sharing options...
Kitcat Posted August 16, 2012 Share Posted August 16, 2012 Your 4th is same as my 4th, so my 5th is overdrive. Moving to bigger diameter wheels and or tires mite be simplest solution, tho you wld lose some acceleration. The rear tires on my Birkin are abt an 1/2 inch taller than the fronts (Toyos vs Avons)and handling is still excellent. Link to comment Share on other sites More sharing options...
bsimon Posted August 16, 2012 Share Posted August 16, 2012 I heard the top gear of a 4 speed and a 5 speed T9 were pretty much the same Top gear in the T9 is an overdrive ratio. 4th is direct. Top gear in a Rocket box is direct. Link to comment Share on other sites More sharing options...
11Budlite Posted August 16, 2012 Share Posted August 16, 2012 My Birkin with 205/50-15 tires, 3.9 rear end, and .84 T9 5th gear is turning 2875 rpm at 60 mph. Here's a couple good gearing calculators, one from member JohnCh. [/url]http://www.throttle-steer.com/downloads.html http://www.our-nest.co.uk/Caterham/html_files/Files.htm Link to comment Share on other sites More sharing options...
locost7018 Posted August 16, 2012 Share Posted August 16, 2012 My 4 speed 1300cc xflow with 205/15 50 tires and a 3.90 diff turns 4200 @ 70mph. It really sings!!!! Would love to have a 5 speed. Russ Link to comment Share on other sites More sharing options...
sequential7 Posted August 17, 2012 Share Posted August 17, 2012 3450 @ 60MPH, but that still leaves me with another 6,750 RPM to play with :drool: Link to comment Share on other sites More sharing options...
ihckb2 Posted August 17, 2012 Share Posted August 17, 2012 How many of you have an accurate speedo? Chances are most are out at least 5 miles an hour. Do a 10 mile run with a GPS unit to check. Link to comment Share on other sites More sharing options...
twobone Posted August 17, 2012 Author Share Posted August 17, 2012 My 60mph reads at about 77mph. Of course that also means my odometer is spinning too fast to! Link to comment Share on other sites More sharing options...
JohnCh Posted August 17, 2012 Share Posted August 17, 2012 About 2650rpm at 60mph. My speedo is programmable based on tire circumference, and dead accurate up to 45mph according to our local radar signs. Doubt it gets into any significant error over the next 15-25 mph. -John Link to comment Share on other sites More sharing options...
The Stig Posted August 17, 2012 Share Posted August 17, 2012 I added a cycle speedo to my previous car (actually the only one that worked) and it can be calibrated perfectly. Cheap too but wireless ones dont work as well. Link to comment Share on other sites More sharing options...
lancylad Posted August 17, 2012 Share Posted August 17, 2012 Has anyone ever used the gps speedometers? Link to comment Share on other sites More sharing options...
HOTTTCAR Posted August 17, 2012 Share Posted August 17, 2012 That's all I use on the RV. It also warns me if I am speeding , as if that were possible. Link to comment Share on other sites More sharing options...
lancylad Posted August 18, 2012 Share Posted August 18, 2012 My mechanical speedo has been acting up so I have been relying on the one on my tom tom gps. I am seriously thinking of buying an actual gps speedometer. Any suggestions would be welcome. Link to comment Share on other sites More sharing options...
HankMauel Posted August 20, 2012 Share Posted August 20, 2012 I've used the "friendly, advisory" radar on a dead straight section of road out of Sacramento. I got a calculated 18.5 mph per 1000 rpms. I have "vintage" sized tires...from the days when the tires were skinny and the drivers were fat .... 155 x 13 (80 section) tires with a 3.90 rear end. The BMC A 1275 with .010 over and a mild cam makes about 90 hp. In my Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now