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Hello Again, Put a tach in and when doing 60 mph it is turning 4000 rpms. According to specs 4000rpm should be close to 70 mph. Checked readings with 2 tach and dwell meters and rpms are correct. How can this be? Thanks Again, Dennis P
http://www.advanced-ev.com/Calculators/TireSize/
Use compressed tire size…the flat bottom to the top
Bill Ascheman
Fiberfab Ford
Modified 5.0, 5sp., 4:11
Autocross & Hillclimb
"Drive Happy"I assume that you are using a GPS for the speed? If so, then you are correct that you should be going faster than 60 unless you are running very small tires or have a transaxle taken from a Kubelwagen or a Thing.
Dannie,
You have a VW? VW with stock size tires shoudl be approx 3000 rpm @ 60mph.
My guess is the same as Bill’s.
What size tires are you running?
Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica RoadsterIf you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)
Running 165/80/15 Kumho Power Stars. Reading re mph comes from stock VW speedo, 2 speedos gave same reading.
Shift into 4th gear.:-)
I run 60mph at 3000 with the same size tires 20# in front 25# in rear.
Check your speed with a GPS, the speedos could be wrong.mrlmd2013-06-22 12:09:54
4000 rpm in Bridget is 85 mph. Just checked this morning (Cobra in the rear view).:-)
165 80r 15s, Nankangs, I think.edsnova2013-06-22 20:50:06
FYI, 165/80-15s are 25.39 in diameter. If you know your gear ratio, you should be able to calculate RPM to MPH not considering tire slip. If your gear ratio were 1:1, then that would be 75.5 MPH per 1000 RPM. Take 75.51 and divide by your real gear ratio and that would yield MPH per 1000 RPM. For example, if you ratio is 3:1, then you would have 25.17 MPH per 1000 RPM.
The whole formula is
Tire Diameter*3.14*60minutes*RPM/12inches/5280feet/Gear Ratio=MPHOnce an engineer, always, hopelessly, an engineer.
bgtrn, a lot of us will be interested in what you found. (Are you sure that you did not have the tachs set on 6 cyl?)
Right!
clutch slipping–you’d smell that, I hope.Bad speedo?–two bad speedos bad in the same way? not likely. But a bad speedo cable with a rounded off square key at the hub? That might read equally screwy on two gauges.Here are your gear ratios in handy chart form. a final drive ratio of 3.67 to 1 is your most likely setup. Looks like it would take something like an old Kombi transaxle to put you at 4000 RPM at 60 MPH.Hi, tachs set correctly, the ones I use on my 4cyl MG and it matches the reading on the mgb’s tach. This may be a transporter gearing, according to the specs listed in chilton. It may explain why I can cruise up the mountains in 4th and actually accelerate. Problem is it is living at 4 grand on the roads or I’d get run over by all the trucks, suvs and basically crazy drivers in New york state, these days. Engine is fresh and does not seem to protest at a steady 4 grand. May have to correct it if I ever get to go on tours and hit highways. It is a swing axle,could it come from a truck or were gears swapped? Can’t go through the expense right now and I’d hate to do it and find it still has the same problem. I know with rear drive, one turns a wheel and counts the turns on drive shaft to determine gearing, anythig like this with Bug???????? Dennis P
I think it just may be that you’re using an older transmission than the IRS that most folks here have…
Swing-axle cars had a lower (higher numerically) gear ratio). They were used primarily when the engine HP was much lower (36, 40, etc.). The ’66 bug had a 50 HP 1300cc, updated to 53HP 1500 cc in 1967 and 68… the last of the swing-axles.To use a bug tranny in a split-window bus or Thing that used reduction gearboxes on the end of the swing axles to lower the final drive ratio even more, you had to flip the ring gear over in the transaxle. This reversed the direction that the axles turned, then the reduction gearboxes on the ends of the axles converted this back to “normal” rotation.Early FF TDr on 69 VW pan
Slowly coming back from the ashes...She is a swing axle 67. May just stick to beautiful, Blue Highways, until I find a bag of fifties. Thanks again.
Rear is supposed to be 4.125 ;1, allowing aprroximately 68-70 mph at 4,oo0 rpm, 60 mph at approx. 300o rpm, according to Samba threads. <aybe if I just search for atach that gives me the right reading[and watch my engine blow!]. Thanks again all
Yep. 85 mph@4000 rmp. Sure ticks off the t bucket boys when they get passed by Victoria. Leaving Yellowstone with my son on a road trip we did just that and he replied by roaring by at such high speed that Vicky twiched sideways. Bill Cosby is right . . . VWs are afraid of trucks.
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