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38/12.5/16 speed on speedo

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mentalmoshio sophs V8i:
235/70/16 to 750r16 is 10 percent increase

so every 2 inches is 10 percent increase speed

30inch to 38 inch is 40 percent

so 100mph on speedo is 140mph actual speed put simply

i cant change the speedo cause runs on 235/70/16 for road use

redhand:
Don't think so as a 33" tire will only give you a 14% increase in speed.
Oh and 235/70/16 = 29" diameter.

mobi:
when i put 31/1050/15 (30.3ish) on the speedo was spot on (the road tyres 235/70/16 was under) and now with 255/85/16 (33") i'm 5 mph over, so 30 on the speedo is 35mph

clbarclay:

--- Quote from: "steveo4v8i" ---235/70/16 to 750r16 is 10 percent increase

so every 2 inches is 10 percent increase speed

30inch to 38 inch is 40 percent

so 100mph on speedo is 140mph actual speed put simply

i cant change the speedo cause runs on 235/70/16 for road use
--- End quote ---



Hmm, how long since you did O levels or GCSEs?

A 10% increase (not necisserily 2") in size gives a 10% increse in speed.

Also a 235/70R16 is only 29" high so its a 3" increase to a 7.50R16.


Anyway back to the point, 38/29*100=131% increase. Therefore when driving at 70mph your speedo will actually read 53mph or when speedo reads 70mph your actual speed will be 92 mph


One option is to get a digital bike speedo which can be easily calibrated and run of a front output of the transpherebox. You can then have this speedo displaying the correct speed whilst on bigger tyres and use the factory speedo whilst on standard size tyres.

mentalmoshio sophs V8i:
the 10 percent was to be always under the speed limit . how many of u have got speeding tickets for being over by just 3 mph its easy done .
if a wanted a true reading i  would just us a road angel for a true reading but im not buying one.

i thought 255/65/16 had the same speedo reading if u had 30/9.5/15 or the following sizes

6oor16

650r16

215/80/16

205r16

225/75/16

235/70/16

with different amouts of tread that varies it a bit as well. your see what i mean by standing

a 235/85/16 road tyre next to a 235/85/16 bronco grizzly claw it will show u what i mean.

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