is it a difficult/expensive task to have a mechanic recalibrate my speedometer after i get bigger rims and tires? they're going to be 18s with 255/40 or 45. not sure which. also not sure if this is the right column. thanks

 

It depends you need just to change the driven gear (easy) or the drive gear (tougher, must remove the tail off the tranny and disconnect the driveshaft).

The best alternative, would be to change your tires to a combination of rim, tire width and aspect ratio that results in nearly the same overall diameter as your current tire. Sometimes this is easy if there is plenty of selection and sometimes you are limited in selection.

The problem with changing the speedo gears is that the specific combo of drive/driven gears may not be available for your transmission.

So what are your normal tires? If you tell me, I can tell you the aspect ratio of the tire in 18" with your desired width that will come close to your existing setup. Whether that specific aspect ratio is available is something you'll have to check.

 

i have a 91 Z with stock 16'' rims and 245/50 tires on it right now. i would like 18'' chrome irocs but if i get them to match in total diameter the sidewall will be small enough that the rim could get dented from pot holes and such. so i was questioning the speedometer changes to compensate for all around larger tires. i might just have to settle for 17s instead.

 

Bigger wheels Give you a higher top speed anyhow

Just get good ad judgeing speed from your Tach, Like on Mine at 5500 RPm in OD Im doing 160 mph... Hmm...

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85 Z28 - Daily Driver
60 Ranchero - Project ( Money Hole )