tire ?

[tomsws6]

ok, when i bought my car it had 18in C6Z wheels on it with 285/35/18 on thye rear with 3.73 gears. I have since installed 305/35/18 MT DR. Iv done some calculating and it seems that my gear ratio has gone done from 373 to 3.65. Will this cause any issues with the speedo, performance? I cant get into 6th gear until 70ish now that iv got these tires on. Iv also installed LT's too. I just wonder with my small amount of mods(mild 355, P/P heads intake and lt4 hotcam and 373) if the motor isnt running right because of the gear ratio change? before the LT and MT i could go into 6th around 50ish with no issues.

[MavsFORMULA]

Here's the deal... The new ones are taller tires. Them making your gears relatively higher shows that. This is also gonna throw your speedo off by the same percentage. Probly around 3% or so in your case... Which really isn't much. I just went from a 26" 27*35-18 Pirelli to a 29" 305-45-18 Nitto DR(wh/ was way too big), and now back down to 26" 275-35-18 BFG CompT/A DRs.... This often why you see drag racers with tall tires, running gears that seem way too low for 1/4 mi(around the 5:1 mark sometimes)..

But it should never make your engine "not run right", You wont have as much power to the ground b/c they weigh more and you have also effectively "raised"(3.73 to 3.65) the final drive ratio so you won't be geared as well for low end acceleration... At the same time, you have more tire on the road and are obviously gonna grip better.. esp goin from street tire to a MT ET street radial.

Good Luck..
PM me if ya have another ?

Nick

[Transamman25]

Hey Tom,

You say the vehicle wont shift INTO 6TH until 70 miles an hour .... I take it your car is an Automatic? If it's the stock transmission, it will only have 4 gears, and by 6th, you are referring to OverDrive. If it is the case you DO have an automatic car and few mods you can easily get away with something like a Hypertech programmer, which will allow you to compensate for the tire change, returning your shift to it's original mph!

[tomsws6]

Hey Tom,

You say the vehicle wont shift INTO 6TH until 70 miles an hour .... I take it your car is an Automatic? If it's the stock transmission, it will only have 4 gears, and by 6th, you are referring to OverDrive. If it is the case you DO have an automatic car and few mods you can easily get away with something like a Hypertech programmer, which will allow you to compensate for the tire change, returning your shift to it's original mph!


na its a manual. I can shift it into 6th at a lower mph but it start shakin pretty bad.

[Jperran]

Youre speedo will be off, but there isnt any reason for it to make your engine run wrong. What is the engine doing? Just generally not running as strong as it was before? You said you did longtubes, maybe they have burned a wire or the spark plug wires are arcing? Just throwing out common problems