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Changing from 11r 24.5 to 11r 22.5

I have a 1999 500 Detroit 60 series.

10 speed tranny, not sure about the rear ends.

I am doing 1425 rpms at 65 mph.

I run 11r 24.5 rubber.

I like to run at 65 mph, so would it hurt or help me to go to 11r 22.5.

What would the rpms go up to.

Thanks for any help.

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from the top of my head i seems your running with a 3.90 rear end ..if you drop to a 24.5 lp or 22.5 tall its going to hurt you.. if it was me i'd find some 3.55's then 9th gear gets longer legs 10th will be at 1275 rpm at 65 then change over to 22.5 wb tires... rpm will jump to 1340 ish

look for a 9speed and put a OD box on it that makes it a 13 OD but not a DBL OD.

if you are just running flat land you'll be okay with the 10spd.

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I have 11r22.5 on right now, and if I put 11r24.5 on do you know how much my speedometer will be off?


The convertible 9 spd transmissions are overdrive transmissions, meaning 8 gear is direct and 9th gear is overdrive. When you convert to a 13spd it gives you a double overdrive. 12 and 13 are overdrive gears anc converting to a 13 spd doesent change your final ratio. the final ratio in 9th gear is the same as the final ratio in 13th because its the same gear.


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If it was me I'd switch to low pro 22.5 tires and find the tire with the lowest rolling resistance. this will increase your rpm just about 150 RPMs at the same speed but with the better fuel mileage tire you shouldn't see a drop in fuel mileage, maybe even a gain. Run this set up for a while and then you can convert you rears to something like 3:55 if you want to. A 1999 series 60 detroit with 3:90 rears, low profile 22.5 tires and at 58 mph is killer fuel mileage. Typically with this same setup at 65mph 3:55 work best.

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