Correcting speedo with larger tires, possible?

camry90

Member
hi, ST185 have too thin tire for my taste. 23.4 in outter diameter with 215/50R15. i would like to fit larger tires from the ST205 which have 1 inch more. it will also be easier for me to find rally tires in the 24 inch than the 23 inch.
my question is, is it possible to take the plastic speedo gear from the 205 and put it in my 185 tanny? or is it more complicated than that?
 

db

Active member
Going from a 23.4 inch diameter tire to a 24 inch diameter tire will not affect your speedometer enough to even make such a modification worth while.

Edited to add: You'll only be going about 1.7% faster than what the speedometer shows. 60 mph on the speedometer will actually be 61 mph. And that's assuming your speedometer is 100% accurate in the first place.
 

camry90

Member
the reason why i want something as acurate as possible is because i do navigational rallies and even miss a turn by 100 meters is alot especialy in the woods or going 110km/h trying to catch up on a straight. so i just want to see if there's a way to use ST205 speedo gears....
 

Simba

New member
camry90":12ruc9cp said:
the reason why i want something as acurate as possible is because i do navigational rallies

Then get a GPS or rally computer. If you're going to be plotting based on the stock speedo, you're going to end up in the shrubs regardless of what size tires/wheels you run. It's nowhere near accurate enough.
 

camry90

Member
i will use terratrip on top of that, i thought maybe there's a way to adjust the speedo gear. i am concern because jumping from 23.4 inch to 24.4 inch is quite a bite, isn't it?
if it's not, then i guess i can constanly use 24.4 inch tires....
 

fhalperformance

New member
Yeah you really cant rely on the stock speedo. I got pulled over this summer and my speedo was off over 25mph... I couldnt believe it so I got my father get it verified by his state trooper friends. Its like these cars hate me.
 

jlspec

New member
I'm not sure about alltrac/toyota having a bad speedo reading because my reads fine. I've tested it a couple of times with a CRX, Integra, S2000 and all our readings are pretty much the same. I tested by having my friend drive and seting their curise control to 70 while I set my at 70 by them and we just roll along together perfectly. I guess you might want to check tire size, axels, etc.
 
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